o cl c-oflv!‘.’\'”o,.. II‘

RESIDUAL AND CUMULATIVE EFFECTS, : _;  '   -_ -_ : - .

0F

mmsm APPLéED m ASANDY LOAMQSOIL . :i -' 4 ~ ‘

Thesis for the Degree of. M. 8?. *
MICHIGAN STATE UNIVERSETY'
.EAMESL STARR
1§70

m:-
1Hs-‘sm ' \

LIBRARY
Michigan State

1 University (4

 

 

ABSTRACT

RESIDUAL AND CUMULATIVE EFFECTS
OF
NITROGEN APPLIED TO A.SANDY LOAN SOIL

By
James L. Starr

Residual and cumulative effects of three nitrogen
carriers. at three rates of application were studied on a
sandy loam soil while growing corn (£32 E§l§)- The nitrogen
carriers urea. NHQNOB. and NH3 were applied at zero, 8“, 168.
and 252 kg/ha with one to four annual applications.

Yield benefits from one annual application were
observed for three years. These residual benefits were
increasingly significant with the two higher rates of
application.

Upon repeated annual applications of nitrogen fertilizers.
a distinct portion of the total response could be identified
with each year of application. Cumulative residual benefits
increased with rate of application and with carriers in the
order urea <NH4N03 <NH3. As much as 78 percent of the

current year's nitrogen response could be ascribed to the

previous two or three years of repeated nitrogen treatments
with NH3 and 50 percent with the other two carriers. The
greater response to NH3 was attributed primarily to decreased
nitrogen loss with injection vs. surface application of the
other two carriers. The residual effects of the highest
application rate of NHuNO3 was to decrease corn yields. This
result was apparently due to increased inhibitory factors
associated with decreasing soil pH.

Cumulative residual soil acidification increased with
the rate of nitrogen application and with the carriers in
the order NfluNO3> urea>N113. Repeated annual additions of
nitrogen at the higher rates of all three carriers resulted
in soil pH values below 5.5 for portions of the growing
season.

Maximum retention of nitrogen in the soil after three
annual nitrogen applications occurred at the 84 kg/ha rate.
Maximum retention of carbon occurred at the 168 kg/ha rate.
The net effect of increasing carbon retention was a widen-
ing of soil CPN ratio from 12.5:1 in control plots to 15:1
for the 168 kg/ha rate.

After three annual applications of 252 kg/ha. both soil
carbon and soil nitrogen were reduced below the level in the
controls. The C:N ratio declined abruptly to 13.531.

These results were taken as evidence that fertilizer
nitrogen inputs in excess of crop removal were promoting

net mineralization and depletion of soil organic nitrogen.

A highly significant quadratic relationship between
soil carbon and nitrogen was obtained over the 160 plots
in the experiment. This relationship was taken as evidence
for effects of treatment on the active organic fraction,
i.e. on organic materials most recently added to the soil.
The first derivative of this function indicated that carbon
and nitrogen were being immobilized in a ratio of 30:1 in
control plots and 15:1 in plots receiving the highest
nitrogen rates.

At the highest NHuNO rate, nitrogen applied in excess

3
of calculated crop removal could not be accounted for to a
depth of five feet and was assumed lost by leaching or
denitrification. VOlatilization losses from surface applied
urea were probably responsible for smaller yield responses

to residual and current applications of this carrier as

compared with NHB'

RESIDUAL.AND CUMULATIVE EFFECTS
OF
NITROGEN APPLIED TO A SANDY LOAN SOIL

B!

James Li'Starr

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirement
for the degree of

MASTER OF SCIENCE

Department of Crop and Soil Sciences

1970

- —‘

3
f.

._ N
E)

9n c?
6 C. p
k. \1

{3(2)

ACKNOWLEDGMENTS

The author is grateful to Dr. A. R. Holcott for his
continued availability and the giving of encouragement,
instruction and advise through all phases of the production
of this thesis. This has been an invaluable learning
experience that would not have been possible except for
the time-consuming interaction between Dr. Wolcott and
myself. -

This experiment was initiated by Drs. H. D. Foth and
J. F. Davis with financial support from the Michigan
Agricultural Ammonia Association.

Use of the Michigan State University computing

facilities was made possible through support. in part,
from the National Science Foundation.

11

TABLE OF CONTENTS

Page
INTRODUC.TION O O O O O O O O O O O O O 0 O O O O O O 1
LITEMT URE REVI E w = O 0 O O O O O O O 0 O O O O O O O O 3

The Effect of Inorganic Nitrogen Application
on the Uptake of Soil Nitrogen . . . 7
The Effect of Inorganic Nitrogen Application

on 8011 1111111118 0 o o o o o o o c o o o o o o 8
Greenhouse Studies . . . . . . . . . . . . . 11
Nitrogen Losses From the Soil . . . . . . . . . 13
Soil Nitrogen and Corn Growth . . . . . . . . . 21

EXPERIMENTAL PROCEDURES AND METHODS OF ANALXSIS . . 22
Field Treatments 0 O O O O O O O O O O O O O O 22
$011 sapling o o o o o o o o o o o o o o o o o 23
8°11 TeSting O O O O O O O O O O O O O O O O 25
Statistical Analysis . . . . . . . . . . . . . 26

RESULTS AND DISCUSSION 0 O O O O O O O O O O O O O O 28

Yield History . . . . . . . . . 28
Sources of variation in 1967 and. 1968. . . . 31
Residual Effects of Nitrogen on Corn Yields . . 34
Cumulative Effects on Corn . . . . . . . . . 36
Incrementation of Residual Response . . . . . . 40
Relative Efficiency of Carriers . . . . . . . . 45
Forms of Residual N in Soil . . . . . . . . . . 50
KJeldahl N in the soil . . . . . . . . . . 50
Crop residues . . . . . . . . . . . . . . . 59
Mineral nitrogen . . . . . . . . . . . . . 62
Other soil sources of N . . . . . . . . . . 70
Effects on Soil pH . . . . . . . . . . . . . 71
Effects on Soil Calcium and Magnesium Levels . 77
Effects on Soil Phosphorous and Potassium
Levels 0 O O O O O O O O O O O O O O O O O O 81

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . 85
BIBLIOGI‘UDPHY O 0 O O O O O O O O O O O O O O 0 O O O 92

APPENDIX 0 o o e o o c o o o o o o o '0 o o o o o 98

Table

1.
2.

9.
10.
11.
12.

13.
14.

150

LIST OF TABLES

Basal fertilizer and management . . . . . . . .

Corn yields over a four-year period in relation
to residual and cumulative effects of
fertilizer nitrogen . . . . . . . . . . . .

Monthly rainfall. average temperatures, and
deviations from the norm . . . . . . . . .

Approximate significance probabilities of F in
1967 for variance associated with experimen-
tal design categories . . . . . . . . . . .

Approximate significance probabilities of F in
1968 for variance associated with eXperimen-
tal design categories . . . . . . . . . . .

Absolute increases in yields of corn over
controls which received no nitrogen . . . .

Relative increases in yields of corn eXpressed
as percent of maximum for carrier or rate
of nitrogen . . . . . . . . . . . . . . . .

Relative yield responses incremented over years
of N application . . . . . . . . . . . . .

Soil nitrogen in November 1967 . . . . . . . .
Soil carbon in November 1967 . . . . . . . . .
Soil CxN ratios in November 1967 . . . . . . .

Soil carbon, nitrogen and C:N ratios in
relation to annual rates of N application .

Nitrate nitrogen in soil sampled August, 1968 .

Distribution of ammonium and nitrate with
depth on August 14, 1968 . . . . . . . . .

Effects of nitrogen carrier and rate of
application on soil pH . . . . . . . . . .

iv

Page

24

29

30

32

33

35

41

42
51
53
55

58
63

64

72

LIST OF TABLES (cont.)

Table Page

16. Extractable Ca and Mg in soil sampled
November. 1967 o o o o o o o o o o o o o o o 78

17. Effects of nitrogen carrier and rate of
application on the November 1967 lime
requirement . . . . . . . . . . . . . . . . 80

18. Extractable K in soil sampled November. 1967
and August. 1968 . . . . . . . . . . . . . . 82

19. Extractable P (Bray P ) in soil sampled
November, 1967 ana August. 1968 . . . . . . 83

LIST OF FIGURES

Figure Page

1. Cumulative effects of annual nitrogen
applications on relative yields of corn
in 1968 o o o o o e o o e o e o e o o o o c 37

2. Cumulative effects of annual nitrogen
applications on corn ear weights in 1968 . 38

3. Cumulative effects of annual nitrogen
applications on numbers of fertile stalks
in 1968 O O O O O O O O O O O O O O O O O O 39

#. Residual and cumulative effects of N rates
on 1968 yield increases over controls . . . 4h

5. Incremented responses of corn in 1968 to
residual and current inputs of nitrogen
from three fertilizer sources . . . . . . . #7

6. Immobilization ratios in relation to soil
carbon and nitrogen contents . . . . . . . 57

7. Soil carbon, nitrogen and CzN ratios in relation
to increasing rates of fertilizer N after
three annual applications . . . . . . . . . 57

8. Corn yields on residual plots in 1968 in
relation to soil N in November 1967 . . . . 60

vi

INTRODUCTION

Nitrogen efficiency and losses as related to plant
growth have been of concern in agronomic research since
1877 when lysimeter studies of nitrate began at the
Rothamstead Experimental Station (Russell and Richards,
1920). This problem is more than of academic interest.
As is pointed out by Boawn. Nelson. and Crawford (1963),
the efficiency with which the current crop utilizes
nitrogen and the extent of carry-over into subsequent
growing seasons is important for making good nitrogen
fertilizer recommendations.

Furthermore. as the price per pound of nitrogen goes
down and the rate of fertilizer application increases.
the potential for pollution of surface and ground waters
through leaching of nitrate and for adverse residual
effects on soil acidity are also becoming of increasing
concern.

There is a long history of attempts to identify
forms of nitrogen in soils and in plants which could be
used as a basis for controlling this nutrient for efficiency
in fertilizer practice. In technologically advanced

areas of the world. the objective of efficiency in

2

nitrogen use is now coupled with that of identifying
criteria and practices which may be used for controlling
-hazardous accumulations of nitrate in agricultural lands.

The objective of the research reported here was to
evaluate residual and cumulative effects of three nitrogen
materials at annual rates up to 252 kg N/ha (225 1b N/Acre).
.The experimental design permitted an estimate in the fourth
year of carryover effects from each of three preceding
annual applications. Major residual effects were expressed
on the response of corn to the current year's nitrogen
-input. Significant effects on soil pH and nitrate levels

were noted.

LITERATURE REVIEW

The literature here reviewed is related to the
residual characteristics of fertilizer nitrogen. A
detailed survey of the mechanisms by which nitrogen is'
lost from the soil is beyond the scope of this review.
except as it is brought out in the papers dealing
with nitrogen studies.

Residual nitrogen studies have been carried out in
a variety of ways. both in the field and in the greenhouse.
One of the procedures for estimating residual nitrogen as
reported by White (1957). Dumenil and Pesek (1958). and
White and Pesek (1959). involved the determination of the
rate of increase of nitrogen in cats with various rates of
nitrogen applied the previous year. With three medium
textured soils. 60. 120. and 180 pounds of nitrogen were
applied to corn. The residual response represented a
carryover of about seven percent of the nitrogen applied
to corn the previous year at the 60 lb. rate and about
49 percent at the 180 lb. rate. In soil which had received
the latter treatment. 88 pounds of residual nitrogen was
found mainly in the form of nitrate at a depth of six
to 21 inches. No appreciable quantities of residual

ammonium were found.

4

A mineralization test showed that the effect of the
residual nitrogen on nitrifiable forms of nitrogen in
these soils was negligible. There was also a high
correlation between effects of residual nitrogen and
plant uptake of soil nitrate. The small amounts of
nitrate in the surface layer. according to White (1957).
improved the root growth and thus facilitated the utili-
zation of residual nitrogen in the subsoil by the plants.

In an earlier study by Pesek and Dumenil (1956). under
Iowa conditions. the average residual carry-over from #0
to 60 pounds of nitrogen applied to corn. when measured
with oats the following year. was about 25 percent.
However. following wet seasons the residual effect was
usually equivalent to less than a 20 percent carry-over
of nitrogen. while following dry seasons it was in the
neighborhood of 30 percent. Pesek and Dumenil conclude
that the residual response in areas where the rainfall
is 30 to 35 inches per year is likely to be of little
importance past the second crop-year after application.

In an experiment by Broadbent and Nakashima (1968).
tagged nitrogen fertilizers were applied to pots in which
an attempt was made to eliminate leaching and denitrification
losses through a controlled watering system. When nitrogen
was applied on the soil surface as ammonium nitrate and
ammonium sulfate. the volatilization loss of ammonia ranged
from 24 to 39 percent. However. when these were banded at

a depth of 7.5 centimeters. volatile losses were negligible.

5

0f the various forms of nitrogen applied. the nitrate
sources were decidedly superior to other forms with respect
to efficiency of plant uptake by a sequence of sudan grass.
tomatoes. and corn over a 31k day period. A comparison of
plant uptake of tagged ammonium in ammonium nitrate versus
tagged nitrate in ammonium nitrate. showed differences
ranging from nine to 20 percent in favor of the nitrate.

Since leaching and denitrification were carefully
controlled. the extent of selectivity for nitrate over
ammonium by the plants grown was likely greater than it
would be under field conditions.

A study with corn in a fine sandy loam soil by Boawn
et al. (1963) showed an average residual response equivalent
to #4 percent of the original ammonium nitrate applied
during the first year of nitrogen removal. This percentage
was expressed in terms of the current season's nitrogen
application needed to produce the same amount of nitrogen
uptake as by the residual crop. Residual nitrogen reaponse
during the third year of plant growth was insignificant.

Vista (1960) tells of an experiment in which nitrogen
was applied at various rates to grass and to a sequence
of crops. All the nitrogen removed in the subsequent
crops was measured. without additional fertilization until
all residual nitrogen was removed. Erosion and leaching
losses were minimized by selection of experimental sites
and by careful irrigation. The results were quite variable

with seven to 50 percent total recovery on the fine textured

6
soils. One fine sandy loam yielded a total recovery of
nearly 80 percent. Viets suggests that denitrification
after rain or irrigation may have‘accounted for some of
the loss.

The effect of residual nitrogen is influenced by the
kind of crop grown. according to the findings of Widdowson
and Penny (1965). Their experiment employed an alternating
wheat-potato rotation on a clay loam soil. Zero. 50. and
100 pounds of nitrogen per acre were applied to wheat. and
zero. 75. and 150 pounds of nitrogen per acre were applied
to potatoes. Nitrogen applied to potatoes always increased
wheat yields the next year. The residue from 150 pounds
of nitrogen for potatoes had the same effect as applying
about 55 pounds of nitrogen to the following wheat crop.
There was less carry-over effect in the following wheat
crop when the wheat was topdressed with nitrogen.

Potato yields were little affected by the application
of nitrogen to the preceding wheat crop. The period of
residual benefit from nitrogen fertilizer was just one
year. in that there was no gain for either crop from
nitrogen applied two years before.

The findings of Clark (196“) agree with the findings
of these investigators in that he found very little
residual effect upon the yield of cotton from nitrogen
two years after application. With zero to #00 pounds of
nitrogen applied per acre. nitrogen uptake by the cotton

varied considerably over the three-year period.

7
Nitrogen uptake the first year increased from 80 to

110 pounds as the application of nitrogen was increased
from 100 to 300 pounds per acre. When the application
was increased to 400 pounds per acre. the current year's
nitrogen uptake decreased. Residual nitrogen taken up
during the second year increasedeith each successive
increase in the rate of application. until it equaled
that taken up the first year at the 300 pound rate. At
the 400 pound rate. the second year's residual uptake
exceeded the first year's direct uptake. By the third
year. uptake of nitrogen dropped to about 45 pounds per
acre regardless of the rate of application. Apparently
by the third year. the fertilizer nitrogen was lost

from the soil through crop removal. leaching. volatili-
zation or denitrification. or it had become a part of the
organic fraction of the soil through immobilization.

The Effect of Inorganic Nitrogen Application
on Uptake of Soil Nitrogen

The addition of fertilizer nitrogen will usually
increase the uptake of soil nitrogen by the crop. This
phenomenon has been noted in N15 studies by several
investigators. with a number of explanations being given.

Broadbent and Norman (1947) suggest that increased
uptake of soil nitrogen with increased nitrogen fertili-
zation may be due to a rise in the mineralization rate.
resulting from a stimulation of the microflora by added

mineral nitrogen. In sharp contrast with this explanation

8

is one given by Stewart. Johnson. and Porter (1963). who
say that increased uptake of soil nitrogen could be expected
if neither immobilization nor mineralization rates changed.
simply by fertilizer nitrogen replacing soil mineral
nitrogen in the immobilization pool. thus allowing more
soil nitrogen to be available for plant uptake.

According to Allison (1965). if crop growth is in-
creased as applied fertilizer nitrogen is increased.
there will be a corresponding increase in the size of
the root system. The net result is that more nitrogen
will be taken up by the plant. He notes that N15 studies
are conducted under conditions of maximum exploitation of
the available nitrogen supply. so higher recovery rates

can be expected than under normal field conditions.

The Effect of Inorganic Nitrogen Application
on Soil Rumus

The effect of added inorganic and organic nitrogen
materials upon soil humus has been the object of much
study. Allison (1955) summarizes some of the commonly
accepted views by saying that soil humus has a CxN ratio
of about 10 or 12 to 1. and that 25 to 35 percent of the
initial plant carbon will remain to form humus regardless
of whether inorganic nitrogen is applied or not. Thus
Allison concludes that added nitrogen will not affect the
soil humus very much. but will greatly affect crop growth.
High nitrogen applications will often result in higher car-

bon content. but this is due to the production of more

9

residues. not because inorganic nitrogen has resulted
in the retention of more crop residue carbon.

Since the nitrogen content of microbial protoplasm
is about 3 to 12 percent. the C:N ratio of the added
materials must be below 20 to 25. or about 1.5 percent
nitrogen or greater. for any appreciable net mineralization
of nitrogen (Harmsen and Kolenbrander. 1965). Jansson
(1958) warns against being misled by the I'priming effect"
of fresh additions of organic materials to the soil. These
, priming effects according to Jansson. may result when
an addition of energy-containing material. whether con-
taining nitrogen or not. to the soil may extend and speed
up cyclic transformations. This may result in a net
mineralization greater than that of the untreated check
and possibly. even in a net depletion of total soil
organic nitrogen.

Bingeman. Varner. and Martin (1953) in a study with
C3“+ tagged additions of alfalfa insolubles and complete
alfalfa. found that there was an initial increase in
mineralization of native soil carbon. The greatest in-
crease occured in the first two weeks. then a return to
near normal mineralization rate. This in itself says
nothing of the mineralization of soil nitrogen.

According to Harmsen and Kblenbrander (1965). when
starting with a high CzN ratio. the carbon is rapidly
liberated and lost as 002 while the nitrogen is mainly

retained in organic form until the energy per unit nitrogen

10
ratio has become sufficiently reduced to allow for an
accumulation of inorganic nitrogen. Only from that
moment onward is there a "net mineralization" of nitrogen.
During the foregoing stages. the nitrogen of the original
substrate may have been mineralized repeatedly. but there
was no accumulation of mineral nitrogen. Such temporary.
reversible mineralization can be designated as "primary
mineralization". whereas the accumulation of inorganic
nitrogen is the "net mineralization".

Thus the CzN ratio of the added materials must be
considered as well as the CzN ratio of the soil organic
matter in predicting the net mineralization of soil
nitrogen. Bartholomew. (1965) expresses both positive
and negative ideas concerning the value of the CzN ratio.
Positively. the C:N ratios reflect nitrogen immobilization
and mineralization. In decomposition of organic residues.
carbonaceous materials supply the major energy source for
microorganisms. The nitrogen is assimilated as protein
in microbial tissue as a function of the growth of the
organisms concerned.

Negatively. since the CxN ratio involves the normal
errors of determination of both the carbon and nitrogen.
it is often less reliable as an index of nitrogen immobili-
zation than is nitrogen percentage. Furthermore. inter-
pretations are frequently made which go beyond the under-
standing of the actual chemical and biological mechanisms

of immobilization in the decay process.

ll

Greenhouse Studies

The efficiency of utilization of fertilizer nitrogen
by plants in most greenhouse studies is about 85 to 90
percent in the first crop. The residual effect in terms
of percent of the initial application is therefore lower
than that usually reported under field conditions.

In a six-year greenhouse study with tagged nitrogen
on an infertile acid sandy loam soil. Jansson (1963)
found that eight to 14 percent nitrogen losses occurred
when part of the tagged inorganic nitrogen was still in
the soil. Jansson proposed that this loss occurred
through denitrification. He also found that once the
nitrogen had been organically immobilized it was liable
to a very slow net mineralization process. The plant
availability of the organic and clay fixed nitrogen
averaged about one percent of the fertilizer addition
per year.

When cats were harvested at maturity. nitrogen
losses were confined to the year of addition. When the
harvesting took place at early stages of growth. then
losses also occurred during the second year.

Broadbent and Nakashima (1965) have also shown that
once inorganic fertilizer nitrogen is incorporated into
the organic cycle in soil. it is remineralized only very
slowly. The presence of growing plants on the soil during

the period of nitrogen application resulted in more efficient

12
utilization of the fertilizer than where planting was
delayed several weeks. regardless of whether straw was
added or not.

In an experiment by van der Paauw (1963). over a
seven year period. the residual effect of nitrogen applied
in the previous year averaged 5.6 percent of the effect
of a corresponding fresh application. The residual effect
of nitrogen not taken up in the previous crop averaged
13.5 percent. The results were similar with different
crops and soils. The residual effect of nitrogen not
removed in the first crop was related to rainfall during
the intervening winter. As the November-toufebruary
rainfall decreased from 10 to seven inches. the residual
effect from nitrogen not accounted for in the first crop
increased from two percent to 17 percent.

legg and Allison (1967) conducted another greenhouse
study in which 50 to 200 ppm of nitrogen was applied for
cats. They investigated recovery of the nitrogen by the
oats and a following crop of sudan grass. The residual
nitrogen taken up by the first cutting of sudan grass. as
a percent of the tracer nitrogen which was not removed by
the previous crop. ranged from 10 to 41 percent and in-
creased with the rate of application. Availability of
residual nitrogen to a second cutting of sudan grass dropped

to 4.5 percent of the remaining tracer nitrogen.

13

Nitrogen Losses From the Soil

Nitrogen losses from the soil occur through erosion.
leaching. volatilization of ammonia from plants and soil
surfaces. microbial denitrification. and chemical re-
duction of nitrite.

In a brief review of nitrogen losses from the soil.
it soon becomes apparent that the form of nitrogen loss
that has been studied the most extensively is leaching.
Leaching losses have been studied by use of lysimeters
since 1877 (Russell and Richardson. 1920). Allison (1965)
states that a general study of the data from lysimeters
of the type commonly used. that is. shallow. filled-in
lysimeters. seems to justify the conclusion that they do
not serve as a satisfactory basis for judging the amount of
leaching losses of nitrogen under field conditions. How-
ever. he feels that they do bring out the importance of
the various factors that affect the magnitude of leaching
losses. These factors include the cropping system. soil
texture. infiltration rate. and ease of water movement
through a soil column.

Benson and Barnette (1939) performed a series of
leaching studies on four coarse-textured soils after
application of several nitrogen sources. Sufficient
quantities of water were applied to the test areas to
provide three inches of drainage water at intervals of

one. four. 10. and 21 days. They found that all the

14

nitrogen that was applied as nitrate was leached. while
only one-third of the ammonium applied as ammonium nitrate
was leached. The amount of urea leached as urea was
dependent upon the time of leaching. with 35 percent
removal one day after application and 16 percent when
the leaching occurred four days after application.
Ammonium nitrogen was retained efficiently until nitri-
fication began. then both ammonium and nitrate nitrogen
leached.

Utilizing isotopic nitrogen. Owens (1960) was unable
to account for an average of 33 percent of applied nitrogen
two years after 120 pounds per acre had been applied as
ammonium sulfate. This loss was assumed to have taken place
via denitrification since the soils were maintained at field
capacity. thus yielding anaerobic conditions in soil micro-
pores. The leaching losses varied from five percent at 12
inches of rainfall over a five-month period to 20 percent
at the 24-inch rainfall level. The amount of fertilizer
in the soil at the end of the two-year period was 38
percent and was unaffected by the soil moisture treatment.

Some guidelines as to the amount of leaching loss in
relation to rainfall have been given by Gardner (1965).
He notes that the distance which nitrate will move downward
depends not upon total rainfall but upon the amount of rain-
fall which actually passes through the soil. For this
reason. correlation of nitrate leaching losses with rain-

fall is not as direct as might be expected. This is

15
especially true under cropping conditions when plants are
continually extracting water from the soil. Gardner pro-
poses the use of excess rainfall over evapotranspiration
to estimate the probability of leaching losses.

Nelson and Uhland (1955) point out that the amount
of rainfall which passes through the soil is not the only
factor controlling the amount of leaching loss. Where
percolation occurs. the amount of nitrogen leached from
the root zone depends upon the amount of nitrate in the
soil. the fertilizer applied. and the rate of formation
of nitrate from ammonium. Among other things. this rate
is dependent upon temperature. According to Nelson and
Uhland. considerable nitrification can occur over a period
of time. even at temperatures of 45°F.

According to studies by Burns et al. (1965). nitrate
formation may take place at considerably lower temperatures
than 45°F. Their field data show that nitrification pro—
ceeds rapidly in the early fall and that complete thermal
inhibition does not occur until the soil temperatures
approach freezing. The rate of nitrification however.
declined rapidly below 50°F. in the fall. It commenced
again rather abruptly when this temperature was reached
in the Spring.

Another factor controlling the amount and rate of
nitrification is the availability of water. Fitts.
Bartholomew. and Reidel (1955) found that nitrate production
will take place over a fairly wide range of soil moisture

conditions. One hundred centimeters of tension. or just

16
less than field capacity. provided the optimum moisture
for the production of nitrate. Burns (1969) reports similar
findings on a loess-derived silt loam. In the soil moisture
tension range of zero to 15 bars. the maximum nitrate
accumulation rates occurred at 0.1 bar. which corresponds
to slightly more water than that held at field capacity.

The importance of factors which control leaching in
modifying the residual character of fertilizer nitrogen
is apparent in the work of Pearson et al. (1961) in the
Scutheastern United States. They report that fall-applied
nitrogen was only 49 percent as effective as spring-
applied nitrogen when measured by corn yields. In terms
of nitrogen recovery. the relative effectiveness of fall
vs. spring application was about 62 percent. Under
similar conditions where 200 pounds of nitrogen per
acre was applied to corn in the Spring. there was a large
residual benefit to two succeeding crops during the follow-
ing 16 months. Total recoveries of nitrogen amounted to
70 to 77 percent in three crops. Pearson et al. concluded
that recoveries can be good even in humid regions. if the
nitrogen is applied at a time when leaching is at a min-
imum and when a crop is present to assimilate it.

The amount of leaching that occurs in relation to
rainfall has been examined by Harmsen and Kolenbrander
(1965). They report that the vertical downward diaplace-
ment of nitrogen in sandy soils at field capacity is about
45 centimeters per 10 centimeters of rainfall entering the

soil. This figure drops to about 30 centimeters for soils

17
in which 20 to 40 percent of the particles are less than
20 microns in diameter. They conclude. that complete loss
of nitrogen from permeable sandy soils may occur in humid
climates even during normal winters. During the summer
growing season. nitrate is seldom carried downward beyond
the reach of plant roots except during unusually rainy
periods.

It may be assumed that any infiltration of water will
result in some downward movement of nitrate and that later
capillary movement will result in some upward movement
within the soil (Wetselaar. 1961). It becomes important
to ask how deep must nitrate move before "leaching" or
actual nitrogen loss occurs. Any answer must consider
rate and height of capillary rise and. thus. the texture
of the soil profile.

Wetselaar (1962) reported that the upward movement of
nitrate in a clay loam was restricted to the top 18 inches
of soil. This implies that any nitrate leached below this
depth. in this soil. cannot be returned to the topsoil by
capillary movement. If the root system of a given crop
extends below this depth. then nitrate below 18 inches is
not necessarily an economic loss. 0n the other hand. any
nitrate leached below this depth and below the root zone of
crops grown may be considered lost in terms of management
and control. This nitrate will. undoubtedly reach the

ground water and move to nearby lakes and streams.

18

Another important mechanism of nitrogen loss.
especially in humid regions. is denitrification. Allison
(1965) states that there are many opportunities for denitri-
fication to occur under field conditions if nitrate or
nitrite are present. In well-drained sandy soils. oppor-
tunities for loss of nitrogen by microbial reduction are
negligible. In fine textured soil. such losses may be
large since oxygen deficiencies. due to poor drainage and/or
rainfall in excess of infiltration. occur frequently for
periods of several days.

Allison (1963) discusses several mechanisms of chemical
denitrification. One such mechanism is by chemical decom-
position of nitrous acid. The nitrite ion (N02) is stable.
The undissociated acid (RN02) is formed below ph 7.0 and
is increasingly unstable with decreasing ph below 6.0.

The dismutation in dilute solution may be written:

3hN02 —-) 2N0+HN03+H20
At higher concentrations the following reaction may be
observed (Black. 1968):

2hN02——-) N0+N02+320
Black cites data from a Ph.D. thesis by D. W. Nelson in
which nitric oxide according to the above reactions.
appeared only when the atmosphere contained no oxygen.
When small amounts of oxygen were present. nitric oxide
was oxidized rapidly to nitrogen dioxide. Lack of oxygen

would normally occur in saturated conditions. however.

19
water would be available to form nitric acid:
2 N02 + H20 —-) ENOB + RN02
Thus no loss of nitrogen dioxide was observed. except
at extremely acid pH.

Another chemical reaction that may be more important
in terms of denitrification losses is the chemical reduction
of nitrous acid by organic matter. The reaction seems to
be related to the amount of lignin or of lignin-derived
structures in the soil organic fraction. Brenner (1957)
found that nitrous oxide was liberated upon treatment of
humic acid or lignin with nitrous acid in the Van Slyke
reaction. Black (1968) again reporting from Nelson's
thesis. says that extracted soil organic matter. prepared
lignins. and soils high in content of organic matter all
promoted decomposition of nitrite.

Clark and Beard (1960) in earlier experiments obtained
similar findings and concluded that since nitrite is an
intermediate in the microbial oxidation of ammonium to
nitrate and since denitrification of nitrite by soil
organic matter is a chemical reaction. then much of the
naturally occurring volatile loss of nitrogen from aerobic
soils occurs during the nitrification process.

These losses may be large. according to Allison (1965).
under conditions where considerable nitrogen as ammonia.
urea. or green manure is added to acid sandy soils and

ammonia oxidation is delayed at the nitrous acid stage.

20
The extent of nitrogen loss as a result of volatili-
zation of ammonia is commonly negligible from soils
having pH values less than neutral unless there is
enough free ammonia to raise the pH locally. These losses
increase with increasing pH and temperature and are greatest
in soils of low cation exchange capacity (Pesek and
Dumenil. 1956).

The greatest loss through volatilization of ammonia
occurs in most soils as anhydrous ammonia is being injected
in soil. According to Pesek (1964) these losses occur
when the soil is too wet or too dry. when the application
is too shallow. or when the rate of application per volume
of soil is too great. The latter may occur through the
use of application furrows which are too far apart.

Righ potential losses of nitrogen from urea fertilizers
may occur if the urea is not mixed well with the soil. or
if the surface becomes dry. Urea hydrolyzes rapidly in
soil and forms high local concentrations of ammonium
carbonate and high ph. The major inefficiencies of urea
nitrogen occur through losses of ammonia as a result of
surface soils drying out after hydrolysis has taken place
on moist soils. These potential losses are magnified.
according to Pesek (1964). by high pH. low base exchange

capacity. and by high temperatures.

21

Soil Nitrogen and Corn Growth

Predicting the soil's ability to supply nitrogen
for the growth of crops has been the concern of researchers
for a long time. A meaningful prediction cannot be made
without considering the needs of the plant concerned in
relation to its pattern of growth. Romaine (1965) cites
data from Ohio showing quite clearly that the time of
greatest nitrogen demand by the growing corn plant is
during the time that the ear is being formed. These data
show that 48 percent of the nitrogen uptake by corn occurs
during the third month. and nearly 60 percent during the
third and fourth months together.

0n the basis of field experience in Michigan. Lucas
(1969) has proposed that 40 pp2m of nitrate-nitrogen in
the plow soil represents a critical level for estimating
the adequacy of nitrogen available to corn during the
tasseling. silking and pollination period when its need

for nitrogen is greatest.

EXPERIMENTAL PROCEDURES AND METHODS 0? ANALYSIS

Field Treatments

In 1965 an experiment was initiated on the Soil
Science Experimental Farm at Michigan State University
to evaluate residual effects of three different nitrogen
carriers at three rates of application. The experiment
was designed to follow residual and cumulative effects
over a four-year period on continuous corn (Egg mayg).
Ten treatments. including the control. were replicated
four times in a randomized complete block design yielding
a total of 40 plots. Each plot was 14 by 100 feet (4.26
by 30.4 meters).

To introduce variation in residual and cumulative
effects of fertilizer nitrogen. these main plots were
subdivided as follows: The entire plot received the
nitrogen treatment the first year. Each succeeding year.
25 feet less of each plot received nitrogen until the
fourth year. when each 100 foot plot was subdivided into
four 25-foot sub-plots. These sub-unit treatments were
randomized within blocks. but not within nitrogen treat-
ments. The resulting systematic grid arrangement was

taken into consideration in the analysis of variance.

22

23

Four rows of corn were planted on each plot. with
the planter set to deliver 17.500 to 19.600 kernels per
acre (43.000 to 48.000 kernels per hectare). Michigan 400
hybrid seed was used each year.

Basal fertilizer and management were the same on all
plots (Table 1).

The nitrogen carriers were urea. ammonium nitrate.
and anhydrous ammonia. Each nitrogen carrier was side-
dressed on knee-high corn at the rate of 75. 150. and 225
pounds of nitrogen per acre (84. 168 and 252 kg/ha). The
anhydrous ammonia was knifed in between each two rows. The
urea and ammonium nitrate was spread byhand between each
two rows and then mixed with the soil by shallow cultivation.

The soil has been classified as a Hodunk Sandy Loam
which belongs to the subgroup Ochreptic Fragiudalf
(Schneider. Johnson. and Whiteside. 1967). See the Appendix
for the description.

Soil Sampling

In November of the third year. 1967. and in early
August of the fourth year. 1968. soil samples were taken.
The soil sample for each plot consisted of 20 cores taken
to a depth of 10 inches with a soil probe. The 20 cores
were taken randomly between the center two rows and
their fertilizer bands. They were passed through a
one-fourth inch screen in the field and thoroughly

mixed. Subsamples of the screened soil were spread

24

wwma “Aomnmmlov mmma

.Aonummuov $3 £8-95 $3 «Snummuoa
«Axlmuz w£\wxv aoao some Hoh.aoudaaphom Amman proa *

 

mumbapazo .moas cum m02.52
m

 

 

 

amendmedm . z pomficH n sash
me a m eoecmm oom omnomuo unmam m mam
. 30.3 S
”mono mom”
opmbdpaso
mansoo .moas mmmhfiodam m hash
nozemzmmmonemedm mm ones
32 pooncH am mass
m: a m ececmm om smusmnw weaned“ mom” .om sea
£306 dozoan . Asoa
ens ammoeeoam 0mm omuomuo Hash use nmuaaapnmc Hmmem coma.n%.>ozN m
. one o H
as >Hpaso masses
.soas one 02:32 mmoade Hm mm mafia
mmz poo 2H om «new
we a m emezmm oom omuomuo ocean .3oam .mo%mzmomfl
opra H30 oandod
.ons was oz m2 mmoaomoam 3N «nah
mmz poonna ma ones
we a m emeesm oom .ommouuo pcmag .3oam Hm seam m
a one o H
meson. oaom\na omaunommnz
maaommm paoaoosam ovum mmmmm o m a
doom *amuaadpamc Hemmm : as as 0 open

 

pnoaewdsaa use HoNAHthoh Hmmmm .H canoe

25
shallowly in five-pound paper bags laid on their sides on
the drying racks in the soils barn. After one week the
samples were ground to pass a two mm screen.
The 1967 samples were placed in one-pint icecream
cartons for storage while the 1968 samples were sealed

in plastic bags for storage.

Soil Testing

The Michigan State University soil testing lab
received approximately one-half of each sample for routine
analysis. Soil pH. lime requirement. P. K. Ca. and Mg
were determined on the November 1967 samples. The August
1968 samples were analysed only for pH. P. and K.

The November 1967 samples were ground to pass a
100-mesh screen in preparation for the total nitrogen and
total carbon analysis. A modified version of Bremner's
micro-Kjeldahl method (Bremner 1965) for total nitrogen
analysis was used to determine total nitrogen. A complete
description of the modified semi-micro-Kjeldahl method
may be found in the appendix.

A high induction furnace. model 750-100 Leco. was
employed for making the total carbon determination. A
sub-sample of soil ranging from 0.1 to 0.2 grams was com-
busted with about 1.0 gram of tin and 1.5 grams of iron
catalyst. In this instrument. the carbon is converted into

carbon dioxide which is then quantified by the change in

26
thermal conductivity which results when the carbon dioxide
is mixed with oxygen.

The August 1968 soil samples were exposed to ammonia
fumes while on the drying racks. thus the ammonium values
were all very high and quite meaningless. Nitrate deter-
minations were made on these samples. using the Brucine

technique by Greweling and Peech (1965).
Statistical Analysis

In the field. the nitrogen treatments were randomized
within each block while the year of nitrogen application was
systematically imposed across N treatments. The appropriate
analysis of variance is that for a split plot with sub-units
in strips (Cochran and Cox. 1957).

V An arbitrary decision was made to consider year
of application as the unit category and nitrogen treatment
as the sub-unit. This choice has no effect on the
analysis. since each main effect and treatment interaction
is tested by the corresponding interaction with blocks.

Two separate analyses were performed on each observed
variable: (1) main effects and interactions with years of
ten nitrogen treatments. including the control; and (2)
factorial main effects and interactions of carrier and
rate (nine treatments). and their first and second order

interactions with years.

The
examined
Use
Computer
from the

by Ruble

2?
factorial interactions with years were also
by multiple correlation analysis.
of facilities in the Michigan State University
Center was made possible by support.in part.
National Science Foundation. Programs developed

et al. (1969) were used.

RESULTS AND DISCUSSION

Yield History

Corn yields over the four-year period are given
in Table 2.

Year-to-year variation in yieldswas influenced by
weather. Non-significant responses to applied N in 1965
were due to critical shortages of moisture from early
spring through July (Table 3). There was some evidence
that the deeper placement of NH3' which was injected. may
have made more N available from this carrier at the higher
rates than from the_other two. which were mixed with the
surface soil by shallow cultivation.

Nitrogen not used in 1965 was used effectively in
1966. Residual N carried over from 1965 was adequate
for maximum yields and there were no significant differences
for residual vs. current applications of N in 1966. Yields
in 1966 were the highest for the four years of the experi-
ment. This reflects a combination of favorable soil
moisture. at planting time. more timely rains in June.

July and August and generally higher temperatures in July

and August in 1966 than in the other growing seasons.

28

29

00000\snv00.0 a 00\0n*

 

 

 

 

Am.00 «0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 mg 000.0000
0.00 0.00 0.00 0.50 5.00 0.00 0.05 0.000 0.000 0.05 000
0.00 0.00 0.00 0.00 0.50 0.50 0.50 0.000 0.000 0.55 000
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.500 0.000 0.00 00 002
0.00 5.00 0.00 0.00 0.00 0.05 0.00 0.000 0.00 5.00 000
0.00 5.50 0.00 0.00 0.00 0.00 0.00 0.000 0.50 5.00 000 0
0.50 0.00 0.00 0.00 0.00 0.00 5.00 0.000 0.00 0.00 00 02002
0.55 0.05 0.00 0.00 0.00 0.00 0.00 0.000 0.000 5.00 000
0.05 0.00 0.00 0.00 0.50 0.00 0.00 0.000 5.000 5.00 000
0.00 5.50 0.00 0.00 0.00 0.00 0.00 5.00 0.00 0.00 00 0000
0.00 0.00 0.00 5.00 0.00 0.00 0.00 0.05 0.00 0.50 0 0000000
-----unguuunuuuuuuuuunuuuuun-*00\0n u---uuuuuuuuuuuuuunnnnuunuuu
0000
5000 5000 5000 00\00
0000 0000 0000 0000 0000 0000
0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
000HQQ0
:o0000wwmmw,z no 0000» 2 0000000

 

000mlt

 

N000 00m0 w0m0
wimmmulmmmwmmm

 

 

:0wo0000 00N0H00000 no 0000000 ebdpdasaso
000 00000000 on 00000000 :0 UO000Q 0000u0so0 0 00>o 00H000 a0oo

.N OHDdB

30

:000dm 002000: 0:00:00 0:» 00 30o: 0:» com: 00000 000 50o: 0:0 ao00 0:O0000>0Q 0
0o00000 300050 0020003 mmm 0:00:00 000m 000 ao00 0000 0050000080» 000 00000000 *

 

 

 

 

 

 

 

50.0 00.0 00.0 00.0 00.0 00000000
50:00 .000 0-0 .000 50:00 0000 00-00 0000 00:00 00:
maO0000paooaoo 0000:00m .0000 .003054 on has
05.0 50.0 00.0 00.0 00.0- 00.0- 00.0 00.0 00.0- 05.0: 00.0- 00.0- .000
05.0 00. 0 00.0 00.0 .00.0 00.0 00.5 00.0 05.0 00.0 05.0. 00.0 0000
0.0- 0.0 0.0 0.0 0.0 0.0- 0.0- 0.0- 0.0 0.0 0.0- 0.0- .000
0.00 0.00 0.00 0.00 0.05 5.00 .0.00 0.00 0.00 0.00 5.00 0.00 .0000 0000
00.0 05. 0 00.0 00.0- 50.0- 00.0- 00.0 50.0- 00.0 00.0- 00.0- 00.0- .>00
00. 0 00. 0 00.0 00.0 00.0 00.0 00.0 00.0 05.0 05.0 00. 0 00.0 0000
0. 0 0. 0- 0.0- 0.0- 0.0. 0.0- 0.0 0.0- 0.0 0.0 0. 0- 0.0 .>00
0. 00 5. 00 5.00 0.00 0.00 5.00 0.00 0.00 0.50 0.00 0.00 0.00 .0000 5000
00. 0- 00.0 05.0- 50.0- 00.0 00.0- 00.0 05.0- 00.0 00.0 00.0- 00.0- .>00
00. 0 00. 0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00. 0 00.0 0000
0. 0- 0.0 0.0 5.0- 5.0: 0.0 0.0 0.0- 0.0: 0.0 0. 0 0.0- .>00
0.00 0.00 0.00 0.00 0.00 0.05 0.00 0.00 0.00 0.00 0. 00 0.00 .0000 0000
00.0 05. 0 00.0: 00.0 00.0 05.0- 00.0- 00.0- 00.0- 50.0- 00.0: 00.0 .>00
00. 0 50. 0 00.0 05.0 05.0 05.0 00.0 50.0 00.0 00.0 05.0 00.0 0000
5.0 0.0 0.0 0.0 0.0: 0.0- 0.0- 0.0 0.0. 5.0- 0.0: 0.0: .000
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.50 0.00 0.00 .0000 0000
.oom .>oz .000 .0000 .004 0050 0:50 002 .004 .00: .900 .000 000
000002 0
0*a0o0 on» ao0m 00o0000>00 000 .000500000500 0000000 .00000000 hanuno: .m 00900

31
Yields in 1967 and 1968 were limited by deficiencies
of moisture and by abnormally low temperatures during cri-
tical growth periods. Nevertheless. significant yield
responses were associated with both residual and current

year's inputs of fertilizer nitrogen.
Sources of variation in 1967 and i968

Probabilities in the first column of tables 0 and 5
show that highly significant components of yield variation
were associated with soil variation (replication). years of
N application. nitrogen treatment and year 1 treatment
interaction.

subdivision of treatment variance in the factorial
analysis indicates that treatment effects on yield in both
seasons were associated with both carrier and rate. In 1968.
a significant carrier 1 rate interaction also appeared.

the number of fertile stalks (harvested ears) per
hectare and the weight per car were strongly influenced by
replication. year of N'application and treatment. Treatment
effects on car weight included significant effects of both
carrier and rate and a significant carrier 1 rate interaction.

variance in total soil N in 1967 was not significantly
associated with any design category (Table 4). In the case
of soil c. variance approaching significance at five percent
was associated with replications and years of N application
in the plots which received the factorial N treatments. The
ratio of carbon to nitrogen varied significantly in association

32

 

 

 

 

 

 

 

 

00:. mmm. 000. 00:. 500. 000. mmo. mum. 000. 0mm. 0 H o N 0
000. 500. 000. 000. 500. 000. 005. :00. 00m. 000. 0 a 0
000. 000. m0m. mmm. mno. :mo. 0mm. ,0mm. 000. omo. o H N
5mo. 000. 005. 05m. 050. 05m. m5n. mom. m00. 00m. 0 N o
000. 000. 000. 050. 000. 500. 000. ~00. 00m. 000. 00000
05m. 000. 005. 000. 050. 00:. 00m. 00:. 5mm. moo. 00000000
050. 000. 050. 500. 500. 000. 000. 000. 000. 000. 00000
000. 0 000.v 0 000v 000. 000. 000. 000. 500. 000. 000. 0000000000000
000000000 0000 00000 000000000
N50. 00m. 000. 000. 5mo. moo. 00m. m0m. emu. nooow. a H 0
:00. 00m. :00. 00m. 50m. 000. 000. 000. :m:. mooko 0000000009
000.. 000. 000. 000. 000. :00. 000. 000. 000. 000. 00000
000. moooJV.0oo. 000. 0:0. 500. 000. 000. 000. moo. 000000000000
000000000 0000 00000
02 00 0 0 .0000 0 \ 0 z
.IIIAWIIIdmmMflIIII..00004 0000 m z o 000oa 00009 0
0000 000 000 0wwwo 00000000
nllmmmmmmmlmmmm
I[, 000000000 000000 00
0000000000 000000 000000000000 0003 00000co000
0000000> 0cm 0000 00 0 0o 0000000000000 000000000000 000500o0004 .0 00009

33

 

 

 

 

0000000000 0000

 

 

000000005 000000 00

 

I 0000000000 mo00

 

 

000. 000. 000. 000. 000. 000. 000. 0 0 0 0 0
000. 000. 000. 000. 000. 000. 000. 0 0 0
000. 000. 000. 000. 000. 000. 000. 0 0 0
000. 000. 000. 000. 000. 000. 000. 0 0 0
000. 000. 000. 000. 000. 000. 000. 00000
000. 000. 000. 000. 000. 000. 000. 00000000
000. 000. 000. 0000.v_ 000. 000. 0000.v 00000
000. 000. 000. 000.. 000. 000. 000. 000000000000
000000000 0000 00000 000000000
000. 000. 000. 000. 000. 000. 0000.v 0 0 0
000. 000. 000. 000. 0000.v 000. 0000.v 0000000000
000. 000. 000. 0000.v 000. 000. 0000.v 00000
000. 000. 000. 000. 000. 000. 000. 000000000000
. 000000000 0000 00000
0 00m; 00 2-002 .0: 00%
00000w0000mM 00m mmwn 00000 00000000

 

0000000000 000000 000000000000 0003 0000000000 00000000
00% @000 :0 h 00 0000000909000 000000000w00 00080000004 .n 00908

34
with the replications, years and the second order
interaction: years I carriers x rates.

Other soil tests in Tables # and 5 reflected prin-
cipally soil variation among replications. Residual effects
on soil ph tended to be additive as N applications were
repeated year after year. but a significant interaction
between year of application and carrier was expressed in the
November 1967 samples. A year I carrier interaction approach-
ing significance was indicated for lime requirement. also.

The level of available P in soils sampled during the
growing season in 1968 reflected a highly significant year

x rate interaction.

Residual Effects of Nitrogen on Corn Yields

Both in 1967 and in 1968. corn yields were increased
significantly by residual effects of nitrogen applied in
previous years (Table 6).

Residual benefit from the 1965 applications was still
apparent two years later in 1967 and three years later in
1968. Significant increases over the controls were asso-
ciated with the higher rates of anhydrous NH3.

Where a second annual application of nitrogen was
made in 1966. the level of residual response in the 1967
and 1968 harvest years was increased substantially. A
third annual application in 1967 resulted in additionally
increased yields on residual plots in 1968.

.Hoapsoo Hobo coaches“ pascamaswam a 902 a
.psooama n pd economnav no: one
Hoppoa mean on» an doasdasooom names .Amnma .saosdnv oosoamfiaswo mo mowsmm o...d

 

 

 

 

 

 

 

 

 

 

sa.m :a.m sa.m :a.m m~.: m~.: m~.s am
a ~.e¢ a m.nm a n.n~ a o.mH a o.m¢ a m.m¢ a :.md «mm
a m.ms one m.a~ n m.:fi and o.m a n.m¢ nu o.mm pm o.HH mofl m
pm a.m= 0 «.0H 9 o.mH Ham o.m a m.m: sane H.Hn and 0.: am 22
on H.Hm on m.mfi an :.a an 0.”: a o.on moon m.fi~ fine 3.“ «mm
o :.om one s.mm n fi.mfi and m.m a m.mm one H.nm Ham m.m mos
o a.om on H.o~ n a.Hfi and m.m a «.m: oeo m.mfl Ham N.m am mozsmz
one m.mm pm H.6m p s.~H an» 5.0 m m.mm eons «.mm Haw m.n mmm
one n.mm o m.mfi n H.0H «pm H.s m «.m: we «.mfl an n.o- mod
a H.NH Ha o.~ an H.a Haw m.a a m.m: o H.ma Ham «.5 am «on:
M» -uu-uu-u-u--u---unnnuuu-uuuuuuu-n a:\as n-uu:uuuuunuunuu-nuunnunuuuuu
mom”
mwma moma mood w2\wx
mom” moms coma coma coma
momfi mwmfi mood mom“ mom“ mead moma
coaaqao
soapooaa o 2 no made 2 aoanamo
mom” momm
Hue» awobadm

 

somonpd: o:
cobdeooa seas: maonpsoo Hobo shoe ho mvaouh ad mommonosd opsdomn< .w canoe

36
Cumulative Effects on Corn

The cumulative responses of corn in 1968 to residual
and current inputs of nitrogen are depicted graphically
in Figures 1. 2 and 3.

Actual control values. corresponding to 100 percent
on each graph. were “1.2 hl/ha (Fig. i). 128 g/ear (n3. 2)
and 22.000 ears/ha (Fig. 3).

The last value indicates that only one-half of the
planted population survived or obtained sufficient nutri-
ment to produce an ear of corn on the control plots. The
number of fertile stalks increased with annual increments
of residual nitrogen and with nitrogen applied in 1968
(F13. 3).

Something less than half of the increased yield in
Fig. 1 was due to the increase in number of ears harvested
(Fig. 3). The balance was due to a somewhat parallel
increase in weight per ear (Fig. 2). Partial correlation
coefficients significant at 1360005 were obtained for ear
numbers (ryn-w - .979) and for ear weight (ry..n c .98#)
in the following regression: '

E! - -55.5 4- .0022214 .3629w (32 «986)

where: E! :- estimated yield. nil/ha
N a number of ears/ha

W’u ear weight. g/ear

 

37

 
   

 

 

 

 
   

 

Carriers
2K)C)" [SFUFI3
CINH4NO3
f; '75- OUREA
2
g I50L
o
“5 I25~
‘5 1 1 I L
{3 I00
°’ 200 L
3 Rates
A252 Kglhc
3 I75- 0 I68 ..
E) o 84 "
>' I50~
E
o
C) |2£5" o””””,”’4y_
1 J l i
'00 I965 I965 I965 I965
I966 I966 I966
I967 I967
I968
Years of N Application
Figure 1. Relative increases in yields of corn in 1968 in

relation to residual and cumulative effects of

fertilizer nitrogen

38

Carriers
I50 " A NH3
0 NH4NO3

   
 
  
 
  

 

 

 

 

 

I40 - o UREA
g :30
C:
o
0 I20
1..—
o
E HO
8
h p ' l
8, IOO
" '50 L Rates
(D
-o— _. A252 Kglha
£3. '40 a |68 "
g I30- ° 84
8 I20
I I0
, L I 1
I00 I965 I965 I965 I965
I966 I966 I966
I967 I967
I968

Years of N Application

Figure 2. Cumulative effects of annual nitrogen
applications on corn ear weights in 1968

39

 

 

 

    

 

 

 

Carriers
|4()" 4§BH13
DNH4NO3
A '30 _ o UREA 3
15 L
z .
fig IZKDF- f; o
o 7)
o I l0 - "
'E
8 1* I L l
._ IOO
a)
3
'40 ' Rates
‘é’ A 25% Kg/ha
.. 0 l6 -
“u I13C) C) £94
8 .
:3 I53C>"
m
E
.o I I0 -
IE
1 L l L
'00 I965 I965 I965 I965
I966 I966 I966
I967 I967
I968

Years of N Application

Figure 3. Cumulative effects of annual nitrogen
applications on numbers of fertile stalks
in 1968

40

Although weight per ear was calculated from yields
and ear numbers. the two independent variables were not
highly intercorrelated (rn. - .227). The probabilities
in Table 5. indicate that variation in ear numbers was
associated.mainly with soil variation (replication) and
with the increasing differential in soil productivity
associated with successive annual applications of N.

Ear weights and yields. on the other hand. were influenced
strongly also by differences in carrier and rate of N
application.

Incrementation of Residual Response

In Table 7. main effects of carriers and of rates
are considered in.terms of relative yield responses in
1967 and i968. Yields increased with each successive
annual application. The rate at which these year-to-
year increases occurred also increased with the amount of
N applied and with carriers in the order urea (W03 (N213 .

It may be assumed that benefits from nitrogen applied
in previous years would have contributed similarly to the
yields on.plots which received.additional nitrogen in the
harvest year. On this assumption. the relative increases
in Table 7 have been incremented by year of N application
in Table 8.

In 1967. there was little difference in total relative
response to the three carriers. However. the extent to

which residual and current inputs of nitrogen contributed

Lu

Table 7. Relative increases in yields of corn expressed

as percent of maximum for carrier or rate of

 

 

 

nitrogen
_Igars of N application LSD(.05)
for
Carrier 1965 1955 1965 1965 years
1966 1966 1966 within
or 1967 1967 N
1968 treatments
rate of N
---------------- percent ---------------
1967 harvest year:
Urea 8.3 43.1 97.7 26.1
NHuNo3 13.6 51.6 98.7 26.1
LSD(.05) ns 16.7 ns
84(kg/ha) 9.7 43.8 92.4 24.3
168 13.6 59.7 99.8 24.3
252 20.3 66.6 100.0 24.3
LSD(.05) ns 13.0 ns
1968 harvest year:
Urea 11.0 21.3 34.8 61.3 18.
NE 17.4 39.9 52.6 100.0 18.4
LS%(.05) ns 14.0 14.0 14.0
84(kg/ha) 9.5 26.5 33.9 74.5 24.2
168 18.2 34.2 51.5 99.5 24.2
252 17.9 42.8 74.7 100.0 24.2
LSD(.05) ns ns 21.0 21.0

 

42

 

 

 

Table 8. Relative yield responses incremented over years
of N application
Relative yield increases
Carrier associated with Total
or year of N application relative
rate of N increase
1965 1966 1967 1968
-------------- percent --------------
1967 harvest year:
Urea 8.3 34.8 54.6 97-7
NH3 22.? 55.1 22.2 100.0
84 (kg/ha) 9.7 34.1 ’ 48.6 92.4
168 13.6 46.1 40.1 99.8
252 20.3 46.3 33.4 100.0
1968 harvest year:
Urea 11.0 10.3 13.5 26.5 61.3
NHuNO3 9.3 14.9 20.2 19.8 64.2
N83 17.4 22.5 12.7 47.4 100.0
84 (kg/ha) 9.5 17.0 7.4 40.6 74.5
168 18.2 16.0 17.3 48.0 99.5
252 17.9 24.9 31.9 25.3 100.0

 

. ..

.-

43
to the total response varied greatly. In the case of N33.
about 78 percent of the yield increase could be ascribed
to residual N from.1965 and 1966 and only 22 percent to the
N applied in 1967. With the other two carriers. approxi-
mately half of the response could be assigned to residual
sources and half to the current year's application.

In 1968. the response to NH3 was much greater than
to urea or NH4N03.. The difference was due principally to
more effective use of the current year's application of NR3.
Circumstances of weather in 1968 were responsible for this
difference and will be described in the next section.

Increments of residual response in.Table 8 increased
with rate of N addition. At the 252 kg rate. residual
accumulations accounted for about 67 percent of the total
yield response in 1967 and about 75 percent in 1968. The
25 percent relative increase which could be ascribed to the
1968 application.at this rate was equivalent to an actual‘
increase of about 10 hl/ha (Fig. 4). The resulting ratio
of 25 kg N per hl (19 lb N/bu) can hardly be considered
economic.

In previously reported studies of residual nitrogen
availability. no consideration has been given to the effect
of repeated annual applications. Residual incrementation.
as illustrated in Table 8 and Fig. 4. must be given increas-
ing attention as more growers use more N year after year

on the same acres.

44

mHoApsoo Hobo commenced odes» mood so cocoa

 

 

 

 

 

 

sowoauas no maeoumo o>aomassso use Hmsodmam .: oasmam
3&9: 2.82.4 8:34 2 w
New _ we. em 0 m
. . . w
0 let .m a
» II$WI. a . nv_ mm
.1 .m. 5
ON m

U

s 4 mumw “H.
Aw

I mom. 0 on I
< . mmm. .32 6 .mm M
$9.82 .89 a own.

8m. New. .82 .89 a 1 w.

20:40:83 2 co mm<w>

45
Relative Efficiency of Carriers

Evidence has been presented in Tables 2. 6. 7.
and 8 that residual benefits accumulated more rapidly
with N33 than with the other two carriers. Also. the

total response in 1968 to residual and current year's

applications of NHuNO and urea was only about 60 percent

3
of that for NH .

These difgerences. however. were expressed as
main effects. They lead to erroneous generalizations
unless circumstances of application and significant
interactions between the carriers and rates and years
of application are taken into account. These interactions
are not readily apparent in tabular data.

A number of mathematical models were examined for
their usefulness in describing these interactions in
the 1968 yield response data. The function finally
chosen made use of a quadratic on number of annual
applications to supply a unique constant term for the
quadratic on rate of N for each carrier within each
application year. The model chosen for the reSponse to
N within carrier within year of application had the
following form:

EX1.a+bA1.cnf.

'FM?

7 2
(d N + e N )
1 13 i 13 1

46

where: Eli a estimated yield increase for an
individual carrier

A1 a number of repeated annual applications
of the ith carrier

Ni 3 rate of application of the ith carrier

3 a rate of application. coded as 1.2 and 3

The coefficient of multiple determination (R2 a .658)
indicates that only 66 percent of the total variation in
yield response was accounted for. Nevertheless. the plotted
function in Fig. 5 provides a realistic picture of sig-
nificant interactions between carriers and rate on yield
response to successive annual applications of fertilizer
nitrogen.

The curves in Fig. 5 represent the response observed
on separate series of plots which received 1. 2. 3 and 4
annual applications of N. The area between the curves
is shaded to represent the incremental contribution from
each successive annual application. The assumption is
made that similar increments of available nitrogen would
have contributed to the total response on plots which
received all four annual applications.

The percentage points on the vertical axis are
relative to the maximum yield increase with N33 taken
as 100. p f

Three practically important differences among the

three carriers are reflected in Fig. 5.

 

 

 

 

 

75 UREA «
so: \\3\\>
25 '\\\\\\‘ Isé<%6\7\/\/:
O /' ///////////////,'9 95/1

 

84 I68 252
75 P NH4 N03
\\ \ x
50L I968\\

 

// \ \ \ ,19/6/
25 \ \\\\I96\6\
FMSBEW \\

84 I68 252

I00 ~NH3

[1/1<<\\

. .7 ll
2" :\\\<\\ V“ . 9.//

o {/////77////./ // /
84 I68 252

N APPLIED ANNUALLY (kg/ha)

Figure 5. Incremented responses of corn in 1968 to
residual and current inputs of nitrogen from
three fertilizer sources

 

 

 

 

CORN: I968 RELATIVE YIELD INCREASE (percent of NH3 maximum)

 

48

The most striking difference is in the response of
corn to the 1968 application of the carriers. At the
84 and 168 kg level. NH3 applied in 1968 was much more
effective than urea or NHQNOB. Referring to Table 2. a
similar differential response in favor of NH3 had been
expressed in 1965. but it did not appear in the case
of current year's applications in 1966 or 1967.

The 1965 differences were not statistically
significant. but they may have reflected a moisture
advantage in a dry year for deep placement (injection)
of NH3 (of. Table 3).

The uniquely greater effectiveness (observed in
Table 8 and Fig. 5) of N33 applied in 1968 is readily
explained by sequences of rainfall associated with the
times of application of the three carriers in 1968 (of.
Table 1). The three carriers were applied between two
periods of above average rainfall (Tables 1 and 3). The
soil remained near field capacity during this period. It
may be assumed that the 1.90 inches of rain from July 23-27
and the 1.34 inches of rain from August 5-8 resulted in
considerable percolation.

The relative inefficiency of urea and NHuNO3 applied
in 1968 can be ascribed to leaching of urea and/or volati-
lization of N33 released by its hydrolysis and to leaching
and/or denitrification of the N applied as nitrate in
the salt.

49

.A second feature of difference in Fig. 5 is the
evidence that. at the 84 kg level of N application. the
residual benefit from urea applied in previous years was
less than with the other two carriers. As noted in Table
1. both urea,and NHuNOB were sidedressed (broadcast by
hand) and mixed in by shallow cultivation. This is a
very inefficient placement for urea (Benson and Barnette.
1939. Pesek and Dumenil. 1956. Pesek. 1964).

In 1965. 1966. and 1967. sidedressings were followed
by periods of 9 to 16 days before precipitation occurred

which might have moved urea down to a safer depth or have
(promoted absorption of NH3 released by hydrolysis. Single
light rains five days after application in 1966 (.21 inches)
and the day after application in 1967 (.25 inches) would
have promoted hydrolysis but little movement. Hydrolysis
of urea and volatilization of NH3 would have been enhanced
. also by periods of high temperature after application
(5 to 14 consecutive days with maximums of 80 to 95°F).
volatilization losses due to inappropriate placement
of urea were not reflected in yield responses to the current
application of N in these earlier years (Table 2). Differ-
ences in residual response were. however. significant
(Tables 7 and 8).

‘A third difference among carriers in Fig. 5 relates to

residual behavior at the highest rate of N application. In

the case of urea and NH3. the residual contributions to 1968

yields increased with rate of N over the entire range of

50
treatment. With NRQNOB. however. residual benefits reached
a maximum and then declined at higher rates of application.

The declining residual benefit from NHuNO3 can be
explained if residual effects on soil acidity are taken
into consideration. At the 252 kg level of N addition.
soil pH in August 1968 was 5.3. 5.5 and 5.7 for NH#N03.urea
and NHS. respectively. These may be compared with pH 6.0
for control plots.

Effects on soil pH will be discussed in greater detail
in connection with Tables 11 and 12. It is apparent, however.
that unfavorably acid soil conditions had developed more
quickly with NH4NO3 and that these would have tended to
oppose beneficial residual effects at high rates of this

carrier.
Forms of Residual N in Soil

It may be assumed that residual benefits to corn were
due. mainly. to carryover of available nitrogen at depths
in the soil within reach of the roots of succeeding crops of
corn. Forms of nitrogen which.might have been carried over
include organic N in soil humus or in corn residues. nitrate
in the soil solution and ammonium.adsorbed on the exchange
complex or fixed reversibly by collapsible clay minerals.

eldahl N in the soil
Values for total N in Table 9 would have excluded
nitrate but would have included both organic N and ammonium.

51

 

 

 

ma owe. «me. sac. .z msdbaeoea muoaa sou Amamehvmnsem
as as as as no as Anc.vnmq
no see. awe. go. one
as omo. nmo. ooa. mow n
no mmo. nmo. mac. no «mo. moa. omo. am mm
on. mac. omo. wmo. «mm
as «we. coo. mmo. owe
e: “we. Re. :3. a: woo. use. see. 3 mesons
_ no «mo. «mo. ewe. «nu
ma omo. awe. new. new
no «mo. moo. mmo. on mac. moo. «mo. am memo
as omo. ”we. moo. o Hoausoo
maedaaso hem” announces» mom”
£3

a no aeaaamo
ovum

 

 

 

bwmd nonlbhoz ad flowchudfl Adam .m OHAIQ

52

Analytical and sampling errors in the determination of
total N and total C are high relative to variation which may
have practical significance in the field. For example. a
difference of .001 percent N in Table 9 is equivalent to
30 lb/acre to the 10-inch depth that was sampled. A.differ-
ence of .01 percent C in Table 10 is equal to 300 lb/acre.

None of the variation in percent N or C was related
to treatment or years of application with statistical
significance. However. significant year-to-year variations
in C:N ratio (Table 11) did reflect net removals of N and/or
net addition of C by the large crops of corn which were
harvested in 1966 (of. Table 2).

A.detailed examination of the relationships between
Gland N in these soils will help to evaluate the extent to
which N may have been immobilized and carried over in soil
organic matter from one year to the next. The relations
ships observed also illustrate a number of principles
which have been established in the extensive literature
on soil nitrogen (Allison. 1955: Bartholomew. 1965:
Harmsen.and Kolenbrander. 1965: Jansson. 1958).

The quantity of organic matter in the soil is
largely determined by the balance between annual inputs
of C in plant debris and annual losses of C by respiration.
The C:N ratio is an important consideration since it
influences the extent to which immobilization of mineral
N or mineralization of organic N will occur. A.critical

53

 

 

 

 

 

on em.” m~.H em.« .2 msubdoooa ocean Hon Amasehvmnsox
as as on as as Ame. Vang
as HH.H a~.a aw.“ «mm
as n~.a on.« an.“ mod n
as H~.H an.a mm.” on ma.« we.” o~.H em mz
on a~.a m~.« m~.H mnu
3 2; no; on; s: n
no em.“ mm; mm.” 3 8; on; 34 on ones:
as as.“ mo. H mm.“ «mm
as on.« em. « am.« we"
on 3.“ no.“ out“ no 34 on. a an.“ so 8.5
ms Na.u ~a.a n«.a o flamenco
masseuse mead announces» swam .
:33: on» 33 33 can»? 83 83 33
one case» mead mead mean case» “was woman nmma
Rosana 3343 “3.33 .33 zoo cognac
modes aeaaaso moses acemfiseaau ovum
mead wannabe: ca sconce Haom .oa canes

54
ratio for normal crop residues is C:N - 30 or 35 to 1.
which corresponds to an N content of about 1.5 percent.

The linear regression of C on N for the 120 plots
sampled in the fall of 1967 was highly significant
(r u .663) and indicated that there was. on the average.
a 600-lb/acre change in soil C for each 30-lb change in
soil N.

The ratio of change was 20:1. which is wider than
the C:N ratio of the soils themselves (Table 11). This
ratio reflects changes in the more active fractions of
soil organic matter -—those portions most recently
derived from decomposition of corn residues in which the
C:N ratio was of the order of 45:1 or higher.

The change in proportion of Cato N was not linear.

A highly significant (P s .007) quadratic term was expressed
in the polynomial of Fig. 6. The derivative of this
function

dN/dC . -.089 + .110 c
was used to calculate the ratios of C to N immobilized
in the active soil organic fraction at each level of soil C.

As seen in Fig. 6. this immobilization ratio. at the
lowest C and N contents. was about 30:1. This would have
been the situation in control plots where no inputs of
fertilizer N were made and where inputs of C were limited
by reason of low yields and restricted production of corn

residues (of. Table 2).

55

 

 

 

 

 

 

 

 

mo.o o.nu n.3H ¢.na .z mnahdoooa uuoam you Aun¢Ohvna¢ox
an a: an an a: an Amo.vnmq
a: «.nu 0.3“ o.m« «mm
as m.n« a.a« o.n« mod n
so.“ v.3 Ti «.3 3 mad 3: 3.3 an ma
an m.m« n.m~ n.n« «nm
3 3: m. a w...” 3:
a: 3: as: YE mm.” 3: or: v.2 3 mafia:
nu e.md s.nd s.ma «mm
mm.” a.¢a «.na M.NH we“
mo.a o.mfi ~.¢H s.m« mm.“ o.~a m.ma .m« an comb
mm.a ¢.NH o.¢u «.n« o Honunoo
uncanndo swag mane-ouch» uwma
can»? an» 33 33 was»: 3: 3m." 1&3
and name» “can mom” mvaa undo» nwma nwmfi home
3953 $933 n___o.a..».3__.._..nmm.¢_.a.”Icing z «a $238
|HmmdmmWMfldmmmu ymmMMHMJmmmmmmmmfllllllll. ovum
swan Hussite: nu weapon 3.0 Adam .«a oaaea

56

 

 

 

 

0'230" “JO E
~_—v Q)
.9 8
¢- a)
a? 25 _ 3
c:

.f._.> -09 g
E: 20- .8.
'5 '2
<3 2

E ~=.us-.asec+.055 c :5
g l5- L R3588 1s-.009 L 1 -.08 a,

m I.2 l.3 |.4

Sail Carbon (percent)

Figure 6. Immobilization ratios in relation to soil
carbon and nitrogen contents

4.5.4“. S“)lL.'V

Soul Carbon (percent)
00 CM
02
"’ t
C)
F:
C)
3
_ z
£3
a 5
00 (O
at 0
Soul Nitrogen (percent)

2!
(fl
l
CD
CD
CD

 

 

O
r

 

I
l2.5 I35 I45
Soil C:N Ratio

Figure 7. Soil carbon. nitrogen and C:N ratios in
relation to increasing rates of fertilizer
nitrogen after three annual applications
(No a control; N1.N2.N3 - 8“. 168. 252 ng/ha)

57
The immobilization ratio in Fig. 6 decreased with

increasing C and N contents. approaching the C:N ratio
of the soils themselves as a limit (of. Table 11).

When inputs of fertilizer N exceeded the capacity
of the crop to respond by producing an appropriate excess
of residual C. the balance in favor of immobilization
and increasing C and N contents was abruptly reversed
(Fig. 7).

In relation to theory. the 30:1 ratio at low N and
0 contents in Fig. 6 is in the critical range where an
increase in C would promote net immobilization of N. whereas
an increase in N would permit net mineralization.

Over the range of Fig. 6. increasing C was accompanied
by increasing retention of N. The increase in C. however.
was due to increased growth of corn in.response to fertilizer
N which also increased the size of the microbial population
and the annual rate of decomposition. This increase in
respiratory loss of C was responsible for the narrowing
immobilization ratio.

Maximum.quantities of N were retained in humified
soil organic matter when fertilizer N was used at the
8“ kg rate (Fig. 7. Tables 9 and 12). Additional increases
in C occurred at the 168 kg rate. The increased C pro-
duced by corn at this rate. however. was insufficient to
maintain a balance in favor of immobilization and retention
of N. At the 252 kg rate. residual levels of both N and C
declined sharply.

58

Table 12. Soil carbon. nitrogen.and C:N
ratios in relation to annual
rates of N application

 

 

Rate Year of N's licatian Average
of i 9 for
N 1966 1966 ~ rate of

1967 N
kg/ha Percent total N in soil
0' .087 .081 .090 .086

84 .092 .097 .091 .095
168 .099 .090 .088 .092
252 .093 .087 .085 .088

18D(.05) ns ns ns ns

Percent total C in soil

0 1.132 1.123 1.121 1.125
8“ 1.231 1.383 1.210 1.276
168 1.302 1.286 1.246 1.278
252 1.230 1.200 1.102 1.191

L8D(.05) ns ns ns f us

8011 C:N ratio
1 14.0 12.0 13.2
h 14.0 12.3 13.7
168 13.3 14.5 i .3 1 .0
It 10.0 13 5 13.6
L8D(.05) ns ns ns ns

 

59

The sharp reversal towards narrowing C:N ratios in.
Fig. 7 is evidence that the annual balance between inputs
of C and N at the 252 kg rate now favors netndneralization
and depletion of humified soil organic matter.

This depletive balance of C and N may be inferred
also from the relationship in Fig. 8 between kJeldahl N
in soil samples taken November 1967 and corn yields in
1968 for the 120 plots which received no N in 1968. Only
14 percent of the total yield variation was accounted for.
but the overall relationship was highly significant
(Pr(.0005) and the coefficient for the squared tern
approached significance (P 2.06). Maximum yields were
associated with the lower levels of residual N in the
plow soil.

It is clear that the higher rates of N which produced
maximum.yields of corn did not produce increases in resid-
ual organic or ammonium forms of N in the plow soil. as
determined by the kJeldahl procedure. Rather. the reverse
was true. ‘

The question remains. where did the N come from to
produce the residual responses observed at high rates of

urea or NH3 in Fig. 5 ?

Crop residues
The soil samples taken in the fall of 1967 did not

include surface residues from the 1967 corn crop. These

were avoided in sampling or were removed by screening.

6O

.umma acnae>oz ca somoapas Haom on
soupaaoa ca mom“ :a mooaa Hasuumoa so amass» saoo

2:853 5m. 5 2 am .338.

.m

 

8.. mac. omo. mmo.‘ .mo.

mw.mw_“umw swanmwdv_.nu wk
N2 8872 m6. . cents.

 

onsmam

N
ID
was

co <1-
to ID
(DU/N) 896| U! SPIGM

Q
In

61
No measurements of stover production or N content were
made.‘ A.tentative estimate of N that might have been
carried over in the stover can be calculated from the.
yields of grain.

Romaine (1965) notes that a 150-bushel corn crop
grown under optimum.fertility will contain.135 pounds of
N in the grain and cabs and 65 pounds in the stover(abput
1 percent N). On this basis. stover left on the control
plots in 1967 would have contained about 20 pounds of
N per acre (cf. Table 2). The carryover from plots which
produced 90 hl/ha or more (80 bu/acre) would.have been
about double this. if no allowance is made for the fact
that the stover on these plots probably would have conp
tained a higher percentage of N. If it is assumed that
N content of stover at the higher rates of N application
was 1.5 percent (Cook. 1962). the carryover would have
been about 60 pounds (67 kg/ha).

With their low N content. the stover from control
plats would be expected to immobilize additional N during
their decomposition whereas the high N residues would be
expected to release some N to the 1968 crop. A.re1ease
of 25 or 30 percent (15 to 20 pounds of N) would have
:nroduced the 12 to 13 bushels of corn which is represented
in Table 8 as a 31.9 percent incremental increase attri-
butable to carryover from the 1967 N application at the
252 kg rate.

62
These calculations are illustrative only. They do
indicate that significant residual benefits from fertilizer
N may be carried over in the form of increased quantities

of stover of increased N content.

Mineral nitrogen
Data in Table 13 show that nitrate in the plow soil

 

(0 to 10 inches) at the time of tassel appearance was
uniformly low in all plots except those which received
fertilizer N in 1968. Ammonium concentrations in these
same samples were unusually high. but there were reasons
to suspect that this was due to contamination from atmos-
pheric sources during storage in paper bags.

According to Lucas' (1969) proposed "critical nitrate-
nitrogen" level. all of the nitrate values in Table 13 are
in the positive response range except that for the highest
1968 application of N. Comparison with Table 7 shows that.
in fact. a significant increase in yield of corn was obtained
with the 168 kg application in 1968 but no further reSponse
was obtained with 252 kg.

The fact that corn yields should be related to the
capacity of the soil to maintain a moderately high level
of nitrate in the plow soil is surprising in view of the
quantities of nitrate and much larger quantities of
ammonium which were present in the root zone (surface 20

inches) of these soils (Table 10).

63

Table 13. Nitrate nitrogen in soil sampled August. 1968

 

Averages

Years of N a lication
Rate 1963 1953 1933 1933

 

Carrier of N 1966 1966 1966 Treatment Carrier
196? 1967
kg/ha 1968
-------------- pp2m --_—--—---—-----_
Control 0 17.0 17.0 16.0 16.5 16.6
Urea 84 17.3 15.3 18.8 32.5 21.2 22.9
168 18.8 18.8 21.3 3 .5 23.3
252 15.3 17.8 15.8 7.8 20.1
168 16.3 23.3 15.0 39.3 2 .h
252 18.8 18.8 19.5 01.8 2 .7
NH3 84 15.3 20.0 17.3 30.8 20.8 22.1
168 19.5 15.3 19.3 35.5 22.4
252 16. 17.5 19.3 39.5 23.2
LSD(.05) ns ns ns ns ns. ns

 

61+

«use madness A.c

 

 

 

 

“mm Amman am: new .z« oo on o nausea
mma Amov mes om .e« cm on smuaasoa
won me mum no“ .:a em on o ”Mecca
on an .aa am Aooumsc «.mna . man
as A*c was as Amsnenv «ma . n.am
as am an on Aemnsmv n.Hm u do
on as on on Asmtmav «e a n.om
ms es «mm mm” Amauo . n.om u 0
11111111111111: poomtoaom Ham 2 .AQ tuttttuttttntt
(Imozsmz ms mozemz as
2 msxms mnm Honscoo z an\ma «mm Hospeoo A.adv so
zropsnsaz zaasaeosas space Haom

 

moms .sa sasma< no ensue and: oneness ens addsoaaa so nonsenansuan .sa canes

65

Soil samples for Table 14 were stored in sealed glass
containers to avoid contamination by atmospheric NH . The
unusually high ammonium levels in the surface 12 inches
must. therefore. be taken seriously. They can be explained
in terms of effects of unusually wet soil conditions asso-
ciated with several periods of rainfall concentration in
1968 (Table 3).

The surface soils of this experiment are underlain by
a moderately impermeable sandy clay loam B horizon at about
16 to 25 inches (Appendix A). Theyvere periodically sat-
urated and remained near field capacity for periods up to
two weeks after each of the rainfall concentrations in May.
June. July and August. Higher than normal temperatures were
associated with each of these periods.

Nitrification is retarded by restricted aeration
under conditions of high moisture to a much greater extent
than are heterotrophic processes of organic matter decom-
position. A.maJor effect of restricted aeration on decom-
position is to reduce the extent to which N is immobilized
in thepresence of carbonaceous substrates (Bartholomew.
1965; Harmsen and Kolenbrander. 1965).

The residues from the 1967 corn crop would have
decomposed under conditions favoring rapid decomposition
with minimal immobilization and restricted nitrification
of released ammonium. Conditions favoring denitrification

would have occurred also from time to time.

66

The quantities of ammonium in the surface 12 inches
(Table 14) greatly exceeded the amount added as NH4N03
or the quantities that might have been carried over in
stover from the 1967 corn crap. This indicates that soil
humic N had been extensively ammonified. The normal
immobilizing effect of corn residues during early stages
of decomposition was not expressed with either treatment.
Instead. its rapid decomposition may have supplied energy
to support microbial attack on humified organic materials
which are not normally utilized because of their low energy
content. This is the phenomenon referred to in the liter-
ature as the "priming action" of fresh residues on decom-
position of soil organic matter (Bingeman. et al.. 1953;
Uinsor. 1958; Jansson. 1958).

Below the 12-inch depth. there was essentially no
difference in quantities of either ammonium or nitrate
in either profile. except for a marked.accumulation of
ammonium in the 36 to 48-inch layer under the NHuNOB
treatment. This indicates that considerable ammonium
had leached to this depth. It was detained by sorption
in the clay loam.B horizon and protected against nitri-
fication because this horizon remains saturated or near
saturation for much longer periods of time than upper
horizons after heavy rains or during seasons of low
evapotranspiration.

Except for the surface 0-12 inches. the two profiles

are analogous to two chromatographic columns with

6?
essentially similar capacities for retaining ammonium
or nitrate. Since they were not loaded the same. it must
be assumed that much more mineral nitrogen had.moved to
depths greater than five feet under the NHhNO3 treatment
than in the control plot. Major movement would have been
as nitrate. but ammonium has leached also as indicated
by the buildsup at 36 to 48 inches.

Total mineral N (NH: plus N03) in the control profile
was 374 pounds per acre to a depth of five feet. The
total for the NHuNOB plot was 722 pounds.

A.total of 900 pounds of N per acre had been applied
as NEuNOB over the 4-year period. A.calculated 200
pounds had been removed in the 25? bushels of grain and
cabs harvested over the previous three years. This plus
the 722-pounds found in the profile would account for all
of the fertilizer N that had been applied.

However. it must be assumed that additional mineral
N was released from.soil sources. This release from soil
sources would have been at least as great as in the control
plot since the analyses for kJeldahl N. which would have
included.ammonium. were similar (Table 9).

The estimate of soil release in the control plot must
take into account the 130 pounds of N in 168 bushels of corn
and cabs harvested over the first three years. This plus
374 pounds found in the control profile gives an estimate
of 504 pounds of N which must have been.mineralized from

soil sources. since no fertilizer N had been applied.

68

If a similar release from.soil sources had occurred
in the NHuNOB plot. then an equal quantity must have
been.lost by denitrification or by leaching to depths
greater than five feet.

On first thought. a loss of 500 pounds of N per acre
is staggering. On an annual basis. however. it is only
125 pounds per year. This is the difference between the
225 pound annual rate used on this plot and 100 pounds.
which is the maximum recommendation to farmers for corn
on soils of similar productivity without irrigation in
Michigan (CES Bul. E-550. 1966). Thus. 125 pounds more
N was applied each year than could be expected reasonably
to enter into the crop or into biological systems
involved in its decomposition.

The crop and biological systems associated with it
in the surface horizons appear to be the only mechanisms
for retaining N in the soil for any period of tune. Data
in Table 13 indicate that these systems are mainly oper-
ative in the surface 12 inches. Foth (1962) has shown
that this is where 80 to 90 percent of the corn root
system is to be found. It includes the plow soil (0 to
10 in.) where decomposition of surface residues takes
place after plowing.

It may be concluded that the plow soil dominates
the nutritional environment of the corn plant. In turn.
the crop and the microflora of the plow soil. which are
supported by the crop. dominate the N economy of the total

69
profile. Some recycling of mineral N from the 12 to
24-inch depth can be expected to occur by capillarity
and by root uptake. since eight to ten percent of the
corn root system is to be found.here. Recycling from
the 24 to 36-inch layer will be minor since corn roots
extend only randomly to this depth and.mass capillary
movements upward from this depth occur infrequently
(Netselaar. 1962).

Most of the mineral N below 24 inches has. therefore.
moved beyond.recovery. How much of the N above 24 inches
may yet be recovered will depend upon crop and climatic
factors affecting its uptake. conversion from one form to
another and its vertical movement. If 50 percent of it
were to carry over usefully to the 1969 season. as Pesek
(1964) suggests. a 60-bushel corn crop could be predicted
on the control plot. This is a reasonable expectation
(of. Table 2).

The predicted 1969 yield on the NRuNO3 plot would be
135 bu/acre. This exceeds the yield potential for this
soil without irrigation. Residual yields of 95 to 105
bu/acre were obtained at this level of N addition in the
favorable 1966 season.

Data in Table 14 indicate that mineral N in excess
of crop response will be quickly lost beyond recovery.
Only N which is retained in the upper 24 inches of the
soil by recycling through the crop and its associated
microflora can contribute significantly to residual

70
carryover for the benefit of succeeding crops. Under the
soil and climatic conditions of this experiment. beneficial
effects of fertilizer N were carried over by these systems
for three years. It appeared. however. that beneficial
residual effects of the 1965 applications would not have

been detected in a fourth season.

Other soil sources of N

The data and discussion in the previous section
suggest that as much as 500 pounds of mineral N were
released from soil sources. If this all came from organic
matter in the plow soil. it would represent a decrease in
organic N of.017 percent.

Changes this great were observed in plots which
received N treatments. if allowance is made for up to
.005 percent ammonium which have been included in the
kJeldahl N determinations of Table 9.

Since these samples were all taken at the same time.
there is no basis for inferring any trend over time in
the control plots. The data in Table 14. however. show
that extensive release of mineral N has occurred. The
release must be at a substantially high rate in order to
maintain nitrate concentrations in the soil solution
equal to those under NH4N03 through the entire profile
below 12 inches.

Mineralization of soil organic matter probably has

resulted in declines in soil organic nitrogen. The rate

71

of depletion has been less rapid at lower N rates than
the heavier N applications. This reflects more efficient
recycling and immobilization due to lower N content of
corn residues. The possibility exists. also. that non-
symbiotic fixation of atmospheric N may be supported by
these low N residues (Jensen. 1965).

another possible source of N in these soils may
have been ammonium previously fixed by clay minerals.
Preliminary analysis of surface soil from a control and
an NfluNOB plot indicated the presence of vermiculite to
the extent of five to 20 percent of the clay fraction.
Since the clay fraction represents only 18 percent of
the surface soil. fixed ammonium must be dismissed as

a significant source of N.
Effects on Soil pH

Probable sources of soil pH variation were noted in
connection with tables 4 and 5. Soil pH variation in
relation to N treatments for the November 1967 and the
August 1968 samplings is shown in table 15.

Increases up to 0.5 pH units occurred on most plots
between the November 1967 sampling and the following
August sampling. A decrease in soil pH during the summer
months has been observed by several investigators (van der
Paauw. 1962: Collins. Whiteside. and Cress. 1970).
Although reasons for seasonal and year-to-year changes
in soil pH are not well understood. there is agreement

on some of the fundamental processes involved.

72

 

 

mm m: m: as on m: as Ano.vmnq
om.m na.n nm.m no.8 mm. m «mm
me.m mm.“ mm.“ mo.m me. n mod n
om.m sm.m .oa.n mm.m mm.m mm. m em. mz
«o. m mm. m mo.m om.“ mm. m «mm
mm. m mm. m mo.e mm.n ma. m men n
Hm.m mm. n me. n oo.e no.0 .mm. m am ozssz
ma.“ me. n me. n ma.n ma.m ma. m «mm
ma.m mm. n me. n mm.m nm.m mm. m was
mm.n ma.m mm. n ma. n mm.n mm.m om. n :m sons
00.0 mm.n mm.m ma.o ma.e o Honssoo
moms smswsa
me me a: mm.o mn.o we Amo.vomq
en.n om.n oa.m mo.n mmm
me.m o~.n me.m ne.n men
mn.n so.“ an.“ on.n as.“ as mmz
mm.m ma.m mm.m mm.m «mm
as.m ma.n ma.m mo.n we” m
an.“ no.“ oe.m ne.m ma.“ as ozssz
es.m as.m mm.m mm.m n:.m «mm
m:.m me.m m:.m mm.n mm.n we”
mo.m mo.m mm.m mm.m mw.m mu.n :m sea:
ma.m mm.m ma.m ma.w o Honseoo
moms Honaoboz
z memm sexes
so when mom” 2
seem Hosanna sessssona coma coma mean no

 

comm acaaaao

 

newswoa< soaamoaa a 2 no mama»

 

ma Haom so soapmoaaaam mo cams and Hosanna camoupdn no muoemum .ma canoe

73

Initiating processes of soil acidification involve
differential accumulation of anions in excess of basic
cations in the soil. Plants tend to take up cations and
anions in approximately equivalent quantities. However.
nitrate and sulfate are reduced to amino and sulfhydryl
forms when they are assimilated by the plant. Protons
and anions are produced when they are released by decom-
position and are oxidized again to nitrate and sulfate.

Because of the great reactivity of the R ion. the
protons which appear initially with surplus anions in
solution quickly react with the exchange complex or with
soil minerals to release bases. A cation-anion balance
in the soil solution. and a buffered pH. are achieved
through this release of soil bases which accumulate as
residual free salts in the absence of leaching.

The decrease in soil pH with time during the
growing season is usually attributed. in part. to the
effect of these free salts. Thus in the absence of
leaching. soluble salts tend to accumulate through the
growing season. This increasing salt concentration shifts
cation exchange equilibria in the direction of increasing
h ion activity (the "salt effect"). For this reason. soil
ph determined in water tends to reach a minimum in temperate
climatic zones in the fall of the year. It tends to return
to a higher level. characteristic for the soil. in the
spring or early summer as surplus salts are removed by

leaching.

74

The leaching of residual free salts is the essential
process whereby soils are depleted of bases and made
residually more acid. The development of residual
acidity is expressed by an increase in buffer acidity
(lime requirement) and/or by the failure of soil pH
each year to return to the previous year's pH.

That seasonal soil pH variation is controlled by
mechanisms other than the "salt effect" has been shown
by Collins et al. (1970). Just what these other mechanisms
are is not clearly understood.

The normal acidification process is greatly affected
by nitrogen fertilization. The three N carriers used in
this experiment are considered to have essentially similar
residual acidifying effects. on soil pH (Nolcott. 1964).
however. the initial reactions of these carriers are not
the same. Urea and N83 have an initial basic effect
whereas the NH4N03 has an initial acidic effect. The
reactions by which these initial effects take place may[
be written as equations (1) to (3). The initial increase
in soil pH with urea and N33 is due to the formation of
the ammonium ion upon hydrolysis:

N83 3883 11341103 q-h NH; . 03" (1)

(NH2)200 —-> (NH#)2C03 iii-i N848003 + Na; . 011' (2)

NHhNOB. the salt of a weak base and a strong acid

upon hydrolysis results in an immediate decrease in ph:

NfluNOB .flQfla. NHuOH + 8* + N03 (3)

av.-

--..-.

75
The initial akalizing effect of urea and NH} is

reversed as the basic cation. N83. is oxidized by nitrifying
bacteria to nitrate. disengaging two protons in the process.
Under most humid soil conditions. nitrite is oxidized to
nitrate by Nitrobacter faster than ammonium is converted

to nitrite by Nitrosomonas. thus the complete reaction may
be written as:

N112; 4103—9 23" . N0} + 8011 (4)

Adams and Pearson (1967) point out that the ultimate
acidity that develops from fertilizer in a particular
horizon is realized only after the residual salts are
removed from that horizon by leaching. The comparison
of the August 1968 pH values in the current year's N
addition plots (Table 15) with the residual N treatment
plots supports this statement.

The most pronounced effect in terms of soil pH
variation occurred in the current year's N addition for
both the 1967 and 1968 samplings. The residual acidifying
effects of the N carriers may be seen in the plots
receiving N treatments in other than the year of sampling.

In addition to the N carrier. the rate of N application
is also an important factor in the potential acidification
of the soil. Increasing acidification with rate of
application is expected within each carrier as the rate
of application exceeds the ability of the crap to reSpond
in additional growth. and with the increasing production

_of h ions from reactions (3) and (4).

.--..--A4

76

Within the current year's N addition in 1967 and 1968.
ph was sharply depressed by high rates of urea and NfluNOB.
This was true for NH3 in 1967. but not in 1968. Due to
the weakly to moderately developed fragipan in the B-
horizon of this soil. water movement through the profile
is restricted. The upper profile was saturated during
abnormal rainfall concentrations in May and June of 1968
(Table 3). The soil remained unseasonably wet and was
periodically saturated above the B-horizon during the
more normal rainfall concentrations in July and August.
Thus. for two-thirds of the growing season the soil was
much wetter than normal. hence less well aerated. As a
result. the higher ph values for N33 in August 1968 are
likely due to the inhibition of nitrification of injected
NH} to a greater extent than in the case of surface applied
urea or ammonium in NH4NO3. It should be noted from
equation (N) that N from urea or N33 must be 50 percent
nitrified to neutralize alkalinity released when they
are hydrolyzed. equations (1) and (2).

In the non-current year's N addition plots. the
greatest acidifying effects were associated with the
highest rates of application. This buildup in residual
acidity was highest with N34N03 and the lowest with N33.
Annual increments of acidity which exceed the capacity of
more readily decomposed soil minerals to release bases will
accumulate in the soil in the form of aluminohexahydronium

and protonated hydroxy aluminum and iron (Coleman and

77

Thomas. 1967). This in effect increases the potential
acidity (lime requirement) of the soil. The rate of
annual accumulation of potential acidity is greatly
accelerated at pH levels below 5.5 and becomes a principle
buffering mechanism below pH 5.0 (Wolcott. et al.. 1965).

It is apparent in Table 15. that plots receiving the
higher rates of N in the form of any of these carriers
are experiencing pH's of 5.5 or less for at least portions
of the year. Accelerated increases in lime requirement can
be expected. even if pH is seasonally restored to higher
levels by leaching of surplus salts arising from nitrifi-
cation and mobilization of soil bases (Wolcott. et al..
1965; Coleman and Thomas. 1967; Schafer. 1968).

Soil pH's associated with current year's treatments
in Table 15 are in a range where toxicities of Mn or
other nutritional derangements can be expected to begin
showing up. Such effects on corn nutrition may have
contributed to the lower yield responses to NH4N03 than

to the other two carriers.
effects on Soil Calcium and Magnesium Levels

According to the F statistics in Table 4. the only
factor associated significantly with Ca and Mg levels was
soil variation (replications). A carrier x rate inter-
action approaching significance (P - .087) was eXpressed
for Mg. Some of the variations associated with treatments

in Table 16 are of interest.

78

Table 1.6. Extractable Ca and Hg in soil sampled

November. 1967

 

Years of N a lication
I963 1935 1933

 

Carrier Rate Treatment
of N 1966 1966 means
kglha _;2§7

------------— pp2m -------------
Calcium _
Control 0 920 1240 800 980
Urea 84 1120 1040 1120 1090
168 1280 1320 1280 1290
252 1000 1000 1000 1000
NH4N03 84 1360 1240 1200 1270
168 1360 1280 1240 1290
252 800 800 760 790
NH3 84 1120 920 1160 1070
168 1080 1000 960 1010
252 1200 1240 1040 1160
LSD(.05) . ns ns‘- ns‘ ns.
Magnesium
Control 0 89 106 83 93
urea 84 105 96 106 102
168 96 116 89 100
252 73 83 .71 75
N34N03 84 115 99 93 102
168 121 141 109 124
252 86 74 64 72
NH3 84 102 86 86 91
168 86 74 74 78

252 121 119 80 107
LSD(.05) ns ns ns ns

 

79

Irreversible declines in soil pH are due to base
depletion. Acidity produced by a process such as nitrifi-
cation results. not only in displacement of exchangeable
bases. but in release of bases by mineral decomposition.

In the absence of leaching. displaced and released bases
accumulate in the soil solution as free salts of surplus
anions. Ammonium acetate extraction as used in this study
makes no distinction between exchangeable bases and their
free salts.

It is not surprising. therefore. that extractable
Ca and Mg as determined here were frequently higher in
soils receiving N fertilizers than in the controls. This
increased level of extractable Ca and Mg also affected the
lime requirement (Table 17). resulting in a less pronounced
increase in potential acidity for many of the treatments
than might have been expected.

The accumulation of surplus free salts and their
subsequent removal by leaching is closely related to the
production of surplus nitrate and its removal from the soil
profile by leaching. It was estimated earlier (p. 68) for
the 252 kg/ha rate of NH4N03 addition that as much as 125
pounds of N per acre could not be accounted for. If it is
assumed that this was entirely lost by leaching of nitrate.
the equivalent associated annual leaching loss of Ca would
have been 180 pounds. or 98 pounds of Mg.

The low values for Ca and Hg in Table 16 at the

252 kg/ha rate of NH4N03 suggest that their annual rate

80

 

 

as me mfi.o am.o am.o an.o Ano.vamq
H~.~ ma.a mm.~ om.~ mmm
ma.m om.n on.m om.~ mod n
mn.m mm.m ma.~ na.~ em nz
so.m mo.m mm.m mo.m «mm
an.m oo.~ me.~ oo.m mos m :
om.~ om.a no.“ m~.m oo.~ am oz mz
on.~ mn.~ na.m mm.~ n~.~ «mm
os.m w~.~ oo.m mm.~ ma.m we“
om.~ n¢.~ an.~ om.~ mm.~ ma.~ em «on:
0H.~ oo.~ oo.~ on.m o Hoapeoo
2 co moms «sums
ovum Hosanna peoapeona mom” coma 2 co
$9.8m HOHHHmU

 

 

 

mommao>< sodwmoaa a Ziwm mama»

useseadswcn cswa mead nonaoboz
on» so soapmoaadmc we open and aoaaamo sowoaua: no mpocumm .ma canma

81
of loss with this treatment exceeded the rate at which
these bases are released by mineral decomposition.

The sum of exchangeable plus soluble bases extracted
with ammonium acetate represents a balance between removal
by crops or leaching and release by mineral decomposition.
The data in Table 16. therefore. do not reflect base
depletion as reliably as the evidence for irreversible
pH changes in residual plots discussed in connection with
Table 15. or the evidence for displacement of bases by
exchangeable Al in Table 17.

Effects on Soil Phosphorous and Potassium Levels

The effects of N treatment on extractable K and P
are shown in Tables 18 and 19. The primary factor related
to changes in soil K.and P was soil variation (replication)
according to the probabilities shown in Tables 4 and 5.
However. there was a high probability for a significant
year by rate interaction for P in 1968 (Table 5).

Due to the close relationship between soil pH and
the solubility of various Al. Fe. and Ca phosphate compounds
it would be expected that extractable P would be directly
related to soil pH. A comparison of Tables 15 and 19
shows this not to be the case. This lack of correlation
is likely due to the complications introduced by soil
variation and to the time lag for phosphate solubilities

to come to equilibrium with changing soil pH.

82

Table 18. Extractable K in soil sampled November. 1967
and August. 1968

 

ears of N a lication Averages
Rate 1933 1935 1965 1933

 

Carrier of N 1966 1966 01966 Treatment Carrier
1967 1967
kg/ha __;968 _
November 1967 ------------- PPZm --"---'-’--'----
Control 0 126 102 119 117
Urea 84 127 130 106 117 112
168 124 104 97 106
252 118 122 109 115
mum3 84 126 114 113 117 117
168 129 108 103 111
252 134 124 118 123
NH3 84 122 136 115 123 114
168 118 114 105 111
252 126 104 103 109
LSD(.05) ns ns ns ns ns
August 1968
Control 0 136 119 109 113 119
urea 84 127 130 121 126 126 119
168 127 111 113 121 118
252 128 102 113 111 114
NH4N03 84 132 111 108 113 116 115
168 134 109 104 102 112
252 132 128 104 106 117
NH3 84 117 123 115 121 119 115
168 123 113 96 100 108
252 126 148 95 106 118

LSD(.O5) ns ns ns ns ns ns

 

'\)§1}

83

Table 19. Extractable P (Bray P1) in soil sampled
November. 1967 and August. 1968

 

Years of N a ication Averages

 

 

 

 

Rate 9 5 9 19 f 1
Carrier of N 1966 1926 1926 Treatment Carrier
9 7 19 7
ks/ha $968
November 1967 * =- -=----- PPZm -=*—- ‘ —==- ——
Control 0 93 86 95 92
urea 84 92 90 92 91 89
168 90 78 85 84
252 97 94 90 90
NHuN03 34 71 78 79 77 79
168 82 72 7o 74
252 91 95 81 87
NH3 84 94 90 85 88 89
168 93 96 101 98
252 83 81 79 80
Lsn(.05) .ns ns ns 1‘18. ns
August 1968 .
Control 0 67 74 67 78 71
Urea 84 81 86 83 89 85 85
168 90 84 83 103 90
252 91 75 83 70 80
N84N03 84 7o 66 66 76 69 72
168 75 61 60 63 65
252 91 88 79 72 82
NH3 84 83 91 76 84 83 81
168 87 9o 95 89 90
252 79 73 70 56 69

LSD(.05) .ns ns ns ns ns ns

 

84
There is no evidence for depletion of K in Table 18.
The leaching equivalent of 125 pounds N per year would be
350 pounds K per acre. It must be assumed that K as well
as Mg and Ca accompanied nitrate into drainage. Fertilizer
inputs of 60 pounds per year plus release of K by decom—
position of soil minerals apparently offset leaching and

crop removal of exchangeable plus soluble K.

SUMMARY AND CONCLUSIONS

Information from earlier experimenters indicate that
in most years one can expect approximately 50 percent
residual benefit in the crop year following N additions
and no significant residual benefit thereafter. These
reported experiments have had one serious limitation.
though. in view of the common practice of monoculture.
That limitation is the lack of more than one year of
N application.

The field experiment used here was designed to
determine the effects of three N carriers at three rates
of application. with systematically incremented and
systematically deleted annual N additions over a four-
year period. Variation in yields of corn and soil tests
were noted in response to these treatments.

Residual benefits to corn were observed in these
experiments in each of the three years following Just one
annual application of N. These benefits were highly
significant with the two higher rates of application of
N83. with repeated annual N additions. residual yield
benefits were cumulative. A portion of total residual
response could be identified with each year of application

up to the fourth year.

85

86

Cumulative carryover benefits increased with the
carriers in the order urea<NHl+N03 (N83. In the 1967
harvest year about 78 percent of the yield could be
ascribed to residual benefits from NH3 and about 50
percent from the other two carriers.

In 1968. with four annual N applications. the reSponse
to Nh3 was nearly 40 percent greater than for the other
two carriers. This advantage for NH3 was ascribed to
deeper N placement and to less loss due to volatilization.
denitrification and/or leaching. It would be inappropriate
to conclude from this experiment alone that NH3 will give
the greatest efficiency in N uptake and the least N loss.
Esther. when evaluating N carriers. the circumstances of
weather and application methods must be given consideration.

Increments of residual response increased with the
rate of N addition. In the year of the fourth successive
N application. about 50 percent of the yield reSponse to
N at 84 kg/ha could be ascribed to carryover from the three
previous annual applications. About 75 percent of the
yield response in the fourth successive year of N appli-
cation could be ascribed to carryover from the three
previous annual applications at the 252 kg/ha rate.

Cumulative residual effects on corn yields were due
to incremented increases in ear number (fertile stalks)
and ear weight. However. as the productivety capacity of
the soil was approached. or as limitation of crop yields
was effected by declining soil pH. then the yields leveled
off or declined.

87

Incrementation of residual response to N is an
important consideration for N fertilization and management
whenever N is applied two or more years in succession.

Although variation in total N and C in the soil could
not be correlated significantly with treatment. the inter-
relationships between soil N and C were highly significant.

The C:N ratios of the soils ranged from 12.0 to 14.6.
The relationship between treatment and C:N ratios was not
readily apparent. however. a linear regression of C on N
indicated that C varied with N in a ratio of about 20:1.
This ratio of change represents effects of treatment upon
the active fraction of soil organic matter. A highly
significant quadratic term showed that the change in soil
N with change in soil C was not linear.

The derivative of this quadratic function was used
to calculate the ratios of C to N immobilized in the
active soil organic fraction at each level of soil C content.

The highest immobilization ratio of about 30:1 occurred
when no N was applied during the four years of the experi-
ment. resulting in limited production of corn residues.
Thus with low N fertilizer application and low C fixation
by corn. the C:N ratio of the active organic fraction was at
its highest. As the rate of applied N increased. the total
C and N increased and their ratio increased until the limit
of the soil's productive capacity was approached.

Maximum N was retained in the soil at the 84 kg/ha
rate of application. Total N decreased at higher rates of

application. Maximum C was retained at the 168 kg/ha rate.

88
At the 252 kg/ha rate. total C decreased abruptly and was
accompanied by an abrupt change from widening to narrowing
C:N ratio. Clearly. and in accordance with theory. net
retention of N was associated with widening C:N ratio.
and net mineralization of soil N was associated with
narrowing C:N ratio.

Calculations were made which illustrate that signifi-
cant residual benefits from fertilizer N would be carried
over in the form of increased amounts of plant residues of
increased N content. This could have amounted to an addit-
ional 40 pounds of residual N for the 252 kg/ha rate over
the control.

Nitrate-N in the plow soil at the time of tasseling
in 1968 was uniformly low in all plots except those which
received fertilizer N in 1968. Corn yields were related
to these nitrate—N levels.

Ammonium N in the plow soil at this time was high.
reflecting the abnormally wet season and retarded nitri-
fication of ammonium N applied in fertilizer or released
by mineralization from organic sources.

Relatively large quantities of mineral N were observed
from 12 to 60 inches in two profiles: a control and a plot

which received 1008 kg/ha N as NHuNO over the four-year

period. Sufficient leaching had taan place so that there
was a marked buildup of nitrate and ammonium at the three
to four foot depth.

It was estimated that 125 pounds per acre per year

were lost by denitrification and/or leaching to depths

89
greater than five feet on the 252 kg/ha NHQNO3 plots. This
is equal to the amount of N applied in excess of that
currently being recommended on this soil by the Crop and
Soil Sciences Department at Michigan State University.

Mineral N in excess of crop response will thus be
quickly lost beyond recovery. The economic loss of surplus
fertilizer N is of negligible concern relative to the
depletion of soil bases and the eutrophication of surface
waters which accompanies nitrate movement.

Soil N retained in the upper 24 inches of the soil
by recycling through crop residues and associated micro-
flora can contribute significantly to residual carryover
for the benefit of succeeding crops. Under the soil and
climatic conditions of this experiment. beneficial effects
of fertilizer N were carried over by these systems for
three years. Carryover of beneficial effects into the
fourth year appeared unlikely.

Soil pH was determined in November and August of the
third and fourth treatment years respectively. An increase
in soil pH. up to 0.5 pH units. was observed from November
to the following August in plots receiving N during the
sampling year. This "seasonal" pH variation was attributed
in part to the leaching of salts through the fall. winter.
spring and early summer. thereby reducing the "salt effect"
on the pH determination itself. The August determination.
therefore. reflected more realistically the characteristic
growing season acidity ascribable to N carriers when they

are applied annually on this soil.

9O

Inhibited nitrification in the fourth year was.
apparently. the cause of a significantly higher pH for
the current year's injection of anhydrous N83 as compared
with surface applied urea and NH4NO3' In November of the
previous year. acidity and free salts from nitrification
produced comparably low soil pH values with all three
carriers.

Net residual acidity from N carriers was best esti-
mated in residual plots which did not recieve N in the
current year. Residual acidifying effects for the three
carriers were in the order N113< urea<NHuN03.

The greatest acidifying effects were associated with
the highest rates of N application. This buildup in
residual acidity resulted in soil pH values of 5.5 or
less for all three N carriers for at least portions of the
year. The net effect of these low pH's is to accelerate
depletion of bases and increases in lime requirement and
to greatly increase the probabilities of toxicities of
Mn and Al.

The change in the base status was not readily apparent
from the tests for Ca. Mg and K extractable with N NHquc.
Ca and Mg levels remained at or above the controls for all
treatments excepting for the plots with the lowest pH (the
N84N03 plots receiving 252 kg/ha). Potassium levels did
not vary significantly from those for the controls. These
results were likely due to a continued release of bases

from primary and secondary minerals through action of

91
hydrogen ions released by nitrification. Released bases
would have accumulated partly on the exchange complex and
partly as free salts. mainly nitrates. Ammonium acetate
extraction as used here did not distinguish between
exchangeable bases and bases present as free salts. Thus
the soil tests for Ca. Mg and K did not give an indication
of the extent to which bases were removed from the soil.
Irreversible declines in soil pH and increases in lime
requirement do reflect the fact that basic cations are
being replaced by acidic Al on the exchange complex and
that base supplying minerals are being depleted.

There were no discernible effects of N treatment on
extractable P. There was a high probability for a signifi-
cant year by rate interaction for P in 1968. however.
interpretable relationships were not apparent in the data.
This may have been due to the complications introduced
by soil variation and to the time lag for phosphate
solubilities to come to equilibrium with the decreasing
soil pH.

BIBLIOGRAPHY

Adams. F.. and Pearson. R. w. 1967. Crop response to lime
in the southern United States and Puerto Rico. In
R. w. Pearson and F. Adams. (ed.) Soil Acidity and
liming. Agronomy 12:161-206.

Allison. F. E. 1955. Does nitrogen applied to crop residues
produce more humus? Soil Sci. Soc. Amer. Proc.
19:210-211.

Allison. F. E. 1963. Losses of gaseous nitrogen from soils
by chemical mechanisms involving nitrous acid and
nitrites. Soil Sci. 96:404-409.

Allison. F. E. 1965. Evaluation of incoming and outgoing
processes that affect soil nitrogen. In N. Bartholomew
and F. Clark. (ed.)Soil Nitrogen. Agronomy 10:573-606.

Alexander. M. 1965. Nitrification. In w. Bartholomew and
F. Clark (ed.) Soil Nitrogen. Agronomy 10:309-346.

Benson. N.. and Barnette. R. M. 1939. Leaching studies
with various sources of nitrogen. Agron. J. 31:44-54.

Bingeman. C. N.. Varner. J. E.. and Martin. w. P. 1953.
The effect of the addition of organic materials on
the decomposition of an organic soil. Soil Sci. Soc.
Amer. Proc. 17:34-48.

Black. C. A. 1968. Soil-Plant Relationships. 2nd. Ed..
John Wiley & Sons. Inc. New York.

Boawn. L. 0.. Nelson. J. L.. and Crawford. C. L. 1963.
Residual nitrogen from ammonium sulfate fertilizer
and from alfalfa plowed under. Agron. J. 55:231-235.

Bremner. J. M. 1965. Total nitrogen. In C. A. Black (ed.)
Methods of soil Analysis. II. Chemical and
Microbiological Properties. Agronomy 9:1149-1178.

Bremner. J. M. 1957. Studies on soil humic acids:
observations on the estimation of free amino groups:
reactions of humic acid and lignin preparations with
nitrous acid. J. Agr. Sci. 48:352-360.

92

93

Broadbent. F. E. 1965. Effect of fertilizer nitrogen on the
release of soil nitrogen. Soil Sci. Soc. Amer. Proc.
29 3 692-6960

Broadbent. F. E.. and Norman. A. G. 1947. Some factors
affecting the availability of the organic nitrogen
in soil - a preliminary report. Soil Sci. Soc. Amer.

Broadbent. F. E.. and Nakashima. T. 1965. Plant recovery of
immobilized nitrogen in greenhouse experiments. Soil
Sci. Soc. Amer. Proc. 29:55-60.

Broadbent. F. E.. and Nakashima. T. 1968. Plant uptake and
residual value of six tagged nitrogen fertilizers. Soil
Sci. Soc. Amer. Proc. 32:388-392.

Burns. R. S. 1969. Influence of soil moisture tension on
nitrate accumulation in soils. Soil Sci. Soc. Amer.
Proc. 0 33 3 263-2660

Burns. R. 8.. Bartholomew. W. V.. Shaw. R.. and Pesek. J.
1956. Influence of temperature on nitrification in soils.
Soil Sci. Soc. Amer. Proc. 20:357-360.

Clark. R. E. 1964. Direct and residual effects of two
mixtures of nitrogen and phosphorous upon the growth
of scale cotton in the Pecos valley. Agron. J. 56:18-20.

Clark. F. E.. and Beard. W. E. 1960. Influence of organic
matter on volatile loss of nitrogen from soil. Trans.

Intern. Congr.. Soil Sci. 7th Congr.. Madison 11:501-
508.

Cochran. W. G. and Cox. G. M. 1957. Experimental Designs.
2nd ed.. John Wiley & Sons. Inc.. New York.

Coleman. N. T.. and Thomas. G. W. 1967. The basic chemistry
of soil acidity. In R. W. Pearson and F. Adams. (ed.)
Soil Acidity and Liming. Agronomy 12:1-34.

Collins. J. B.. Whiteside. E. P.. and Cress. C. E. 1970.
Seasonal variability of pH and lime requirement in
several southern Michigan soils when measured in
different ways. Soil Sci. Soc. Amer. Proc. 34:56-61.

Cook. R. L. 1962. Soil Management for Conservation and
Production. John Wiley & Sons. Inc.. New York.

Duncan. D. B. 1955. Multiple range and multiple F tests.
Biometrics 11:1-42.

94

Fitts. J. W.. Bartholomew. W. V.. and Heidel. H. 1955.
Predicting nitrogen fertilizer needs of Iowa soils:
I. Evaluation and control factors in nitrate production
and analysis. Soil Sci. Soc. Amer. Proc. 19:69-73.

Foth. H. D. 1962. Root and top growth of corn Agron J.
54 3179-52 0

Gardner. W. R. 1965. Movement of nitrogen in soil. In
W. Bartholomew and F. Clark (ed.) Soil Nitrogen.
Agronomy 10:550-572.

Gerretsen. F. C.. and DeHoop. H. 1957. Nitrogen losses
during nitrification in solutions and in acid sandy
soils. Can. J. Microbiol. 3:359-380.

Grewling. T.. and Peech. M. 1965. Chemical soil tests.
Cornell Univ. Agric. Exp. Sta. Bul. 960.

Harmsen, G. W.. and Kolenbrander. G. J. 1965. Soil inorganic
nitrogen. In W. Bartholomew and F. Clark. (ed.) Soil
Nitrogen. Agronomy 10:43—92.

Jansson. S. L. 1958. Tracer studies on nitrogen transfor-
mations in soil with special attention to minerali-
zation-immobilization relationships. Kungl.
Lantbrukshhgskolans Ann. 24:101-361.

Jansson. S. L. 1963. Balance sheet and residual effects of
fertilizer nitrogen in a six-year study with N-15.
Soil Sci. 95:31-37.

Legg. J. 0.. and Allison. F. E. 1967. A tracer study of
nitrogen balance and residual nitrogen availability
with twelve soils. Soil Sci. Soc. Amer. Proc. 31:403-406.

Legg. J. 0.. and Stanford. G. 1967. Utilization of soil and
fertilizer nitrogen by plants in relation to the
available nitrogen status of soils. Soil Sci. Soc.
Amer. Proc. 313215-219.

Lucas. R. E. 1969. Cultural trials on irrigated corn.
Mich. Agr. Exp. Sta. Rep. 84.

Nelson. L. E.. and Uhland. R. E. 1955. Factors that influence
loss of fall-applied fertilizers and their probable
importance in different sections of the United States.
Soil Sci. Soc. Amer. Proc. 19:492-496.

Owens. L. D. 1960. Nitrogen movement and transformations in
soils as evaluated by a lysimeter study utilizing
isotopic nitrogen. Soil Sci. Soc. Amer. Proc. 24:372-

376.

95

Pearson. R. W.. Jordan. H. V.. Bennett. 0. L.. Scarsbrook.
C. E.. Adams. W. E.. and White. A. W. 1961. Residual
effects of fall and spring-applied nitrogen fertilizers
on crop yields in the southeastern United States.
U.S.D.A. Tech. Bul. 1254.

Pesek. J. T.. and Dumenil. L. 1956. An extra dividend from
fertilizer use. Plant Food Rev. 2(3):4—6;31-32.

Pesek. J. T. 1964. Comparing efficiency of nitrogen
fertilizers. In V. Sauchelli. (ed.) Fertilizer
Nitrogen. A.C.S. Monograph 161:365-391.

Romaine. J. D. 1965. When fertilizing consider plant food
content of your crops. Better Crops with Plant Food
May-Junezi-8.

11111318, We Le. K181, De Fe. and. Rafter. Me E0 1968. Mich.
Agr. Exp. Sta. Stat. Series Descriptions 5.14.16.

Russell. E. J.. and Richards. E. H. 1920. The washing out of
nitrates by drainage water from uncropped and unmanured
land. J. Agr. 301.. Part I. 10:22-43.

Scarsbroad. D. E. 1965. Nitrogen availability. In W.
Bartholomew and F. Clark. (ed.) Soil Nitrogen.
Agronomy 10:486-507.

Schafer. J. W. 1968. Nitrogen carrier induced changes in
chemical. mineralogical and microbial properties of
a sandy loam soil. Ph.D. Thesis. Mich. State Univ..
E. Lansing. Mich.

Schneider. I. F.. Johnson. R. W.. and Whiteside. E. P. 1967.
Tentative placements of Michigan soil series in the
new soil classification system. Soil Sci. Dept.. Mich.
State Univ.

Steward. F. A.. Johnson. D. D.. and Porter. L. K. 1963.
The availability of fertilizer nitrogen immobilized
during decomposition of straw. Soil Sci. Soc. Amer.
Free. 273656-659.

United States Dept. Commerce. Climatological Data. Mich.
Section. 1965-1968.

van der Paauw. F. 1963. Residual effect of nitrogen fertilizer
on succeeding crops in a moderate marine climate.
Plant and Soil. 19:324-331.

van der Paauw. E. 1962. Periodic fluctuations of soil
fertility. Plant and Soil 17:155-182.

96

Viets. F. G. 1960. Recovery of fertilizer nitrogen on
irrigated and dryland soils of the western United
States. Trans. Intern. Congr.. Soil Sci. 7th Congr..
Madison 11:486-493.

Wetselaar. R. 1961. Nitrate distribution in tropical soils.
II. Extent of capillary accumulation of nitrate during
a long dry period. Plant and Soil. 15:121-133.

Wetselaar. R. 1962. Nitrate distribution in tropical soils.
III. Downward movement and accumulation of nitrate in
the subsoil. Plant and Soil 16:19-31.

White. W. C. 1957. Nature and effects of residual soil
nitrogen. Iowa State Col. J. Sci. 32:286-288.

White. W. C.. Dumenil. L.. and Pesek. J. 1958. Evaluation
of residual nitrogen in soils. Agron. J. 50:255-259.

White. W. C.. and Pesek. J. 1959. Nature of residual
nitrogen in Iowa soils. Soil Sci. Soc. Amer. Proc.
23:39-42.

Widdowson. F. V.. and Penny. A. 1965. Experiments measuring
the residual effects of nitrogen fertilizers. In
Soils and Fertilizers 29:198.

Winsor. G. W.. and Pollard. A. G. 1956. Carbon-nitrogen
relationships in soil. I. The immobilization of
nitrogen in the presence of carbon compounds. J. Sci.
Food Agric.. 7:134-141.

Wolcott. A. R. 1964. The acidifying effects of nitrogen
carriers. Agr. Ammonia News July-Aug.:1-4.

Wolcott. A. R.. Foth. H. D.. Davis. J. F.. and Shickluna. J.
1965. Nitrogen Carriers: I. Soil effects. Soil Sci.
Soc. Amer. Proc. 29:405-410.

APP EN DI CES

APPENDIX A

HODUNK SERIES

The Hodunk series consists of moderately well drained

Gray-Brown Podzolic (Ochreptic Fragiudalf) soils with

fragipans which developed on calcareous sandy loam glacial

till. Hodunk soils are found in association with the well

drained Hillsdale and moderately well drained Elmdale series

which are also developed on calcareous sandy loam till.

8011 Profile:

AP 0-7"
A2 7-16"
Blm 16-25 ll

Hodunk sandy loam

Dark grayish brown (10YR 4/2) to very dark
grayish brown (10YR 3/2): sandy loam:
moderate fine. granular structure: friable
when moist and soft when dry: medium
content of organic matter: medium to
slightly acid: abrupt smooth boundary.

6 to 11 inches thick.

Yellowish brown (10YR 5/4): pale brown
(10YR 6/3) or light yellowish brown (10YR
6/4): sandy loam: weak. fine. granular to
subangular blocky structure: very friable
when moist and soft when dry: medium acid:
abrupt wavy boundary. 6 to 20 inches thick.

Brown (10YR 5/3) to pale brown (10YR 6/3):
sandy loam to light sandy clay loam:
massive to weak. thick. platy structure:
firm when moist and brittle when dry: weak
to moderately developed fragipan: few thin
clay flows: medium to strongly acid: clear
wavy boundary. 4 to 12 inches thick.

98

99

B2 25-46" Brown (10YR 5/3) to yellowish brown

3 QOYR 5/4) mottled with yellowish brown
(10YR 5/8) and dark brown (7.5YR 4/4).
mottles are common. medium. distinct: sandy
clay loam: few thin clay flows: weak.
medium. subangular block structure: firm
when moist. strongly to medium acid in
the upper part and slightly acid in the
lower part: abrupt irregular boundary.
15 to 30 inches thick.

CE 46+" Light yellowish brown (10YR 6/4) to
brown (10YR 5/3) mottled with yellowish
brown (10YR 5/6 - 5/8). mottles are common.
medium. distinct: sandy loam: massive to
very weak coarse. subangular block
structure: friable when moist and hard
when dry: calcareous.

Tonograpny: Gently to moderately sloping till plains and

moraines.

grainage and Permeability: Moderately well drained.

Surface runoff is slow to moderate. Permeability is

moderate to slow depending upon the degree of development

of the fragipan.

Natural Vegetation: Deciduous forest consisting of sugar

maple. beech. oaks. and hickories.

A.

B.

APPENDIX B

MODIFIED SEMIvMICRO KJELDAHL METHOD FOR SOILS

Reagents:

1. Concentrated H SO .

2. 10 Normal NaOH so ution.

a. Prepare from N-free flakes in deionized water
and allow to stand several days.

b. Equip with aspirator bulb and ascarite tube
to prevent absorption of C02.

3. Boric acid solution.

a. Heat 1800 ml of deionized water to boiling
to remove C0 .

b. Add 40 g. boéic acid. stopper. swirl to dissolve
and cool in cold water bath.

4. Potassium sulfate-catalyst mixture: mix by grinding
15 g. K2804: 1 g. Cusou°5H20: and .7 3. Se.

50 0.01 _N_ 1123040

6. 30% H 0 in brown bottle with glass stopper may be
needea go rinse soil particles down flask during
digestion.

7. Cigarette paper. _

8. Indicator: .1 g methylred «:- .1 g brom-cresol green in

250 ml methanol.

Procedure (excluding nitrate):

1. Grind soil sample to pass 32-40 mesh screen.

2. Weigh duplicate samples containing 0.5000 g. on
weighted cigarette paper. roll and drop into
KJeldahl flask.

3. Add 2 ml H20. swirl. allow to stand for 30 minutes.

4. Add 0.8 3. K 504 catalyst mixture.

5. Add 2 ml congentrated H280 . heat cautiously on
digestion stand until wateg is removed and frothing
stops.

6. Heat until digest clears.

7. Continue to boil gently for at least one hour.
regulating heat so that the H280 condenses about
1/3 way up the neck of the flask. Allow to cool.

8. Slowly. and with swirling. add 10 ml deionized water.
continue swirling until undissolved materials are
in suspension.

9. Flush out distillation apparatus for 5 minutes with
steam to clean and bring to temperature.

10. Add 3 ml of H B0 solution to a 25 ml erlenmeyer
flask which 18 marked at a volume of 15 ml.
11. Add one drop of indicator.

100

12.

13.

14.
15.

16.
17.
18.
19.
20.

101

Place erlenmeyer flask under the condenser of the
distillation apparatus so that the tip is about

4 cm above solution.

Add one ml of 10 N_NaOH to funnel at start. note
height in funnel. then add 10 ml more NaOH.

Insert KJeldahl flask into distillation apparatus.
Drop 10 ml of the 10 N NaOH into the flask. close
stop cock. open steam system. close steam by-pass.
Collect 15 ml of distillate in 3-5 minutes.

Remove erlenmeyer flask.

Flush system out.

Titrate to first pink color with the .01 N 82804.
Calculate percent nitrogen.

% N . (T-B)(N)(1400)
s

g ml sample nitrated

u-ml blank titrated

- normality of H sou used in titration
a sample weight n mg

03sz

 

\mnmsuuuum 1llilwALUlllflnlflHfllfllLHNIH

3