-‘——"-v fl, .r—v "v --v—..,.._....... THE EFFECT OF NITROGEN AND PHOSPHORUS ON THE GROWTH OF APPLE AND PEACH TREES IN SAND CULTURE ' l > , . v Thad: far the Degrob of PM D. MICHIGAN STATE COLLEGE C S Waltmm ' ~ 1941 “flyw. THE EFFECT OF NITROGEN AND PHOSPHORUS ON THE GROWTH OF APPLE AND PEACH TREES IN SAND CULTURE U \ >J’qu“ '. C Si Waltman A THESIS Submitted to the Graduate School of Michigan State College of Agriculture and Applied Science in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture l 9 4 1 W £97 /4} ./7’// //f M wESMS 140111- gym: or CONTENTS Introduction ------------------------ Eerie! of literature .................... Response to nitrogen --------------- Response to phosphorus .............. Nitrogen deficiency --------------- Phosphorus deficiency -------------- Experilental procedure ------------------ Composition of the nutrient solutions ------ Growth measurements --------------- Chemical analyses ---------------- HethOds of analysi s ............... Results -------------------------- Growth --------------------- Chemical analyses ............... Reaction oi the nutrient solution ------- Deficiency symptoms -------------- Nitrogen deficiency symptoms ------- Phosphorus deficiency symptoms ------ Summary ------------------------- Literature cited -------------------- Appendix (Tables and graphs) -------------- NNH 10 13 15 17 {3 32 32 8'5 52 53 67 THE EFFECT OF NITROGEN ANDIPHOSPHDRUS ON THE GROWTH OF APPLE ANDIPEACH TREES IN SAND CULTURE by C. S. WALTMAN Introduction Much investigational work has been done with fruit and vege- table plants of various kinds to determine the influence of nitrogen and.phosphorus on growth and fruiting ability. Certain rather definite relationships have been found to exist between the available nitrogen supply and vegetative growth and likewise between vegetative growth and fruit production. In the same way. phosphorus has been shown to in- fluence these conditions in certain respects and to have a rather marked influence on the root deveIOpment of plants and on certain other char- acteristics that are associated with growth and fruit bearing. During comparatively recent years many research workers have turned.their attention to a study of plants grown in artificial media in which nutrient materials of various kinds could be supplied in the amounts desired and observations and determinations made to show the characteristic symptoms and conditions which deve10p in the absence or overabundance of certain elements. In short. the plants have been grown under controlled conditions where the worker has found it much easier to diagnose the cause of certain physiological disorders and then to use this information for the correction of similar troubles found under field con- ditions. . As stated in the work of Alexander, Morris and Young (1), the growth of plants in water culture and other media is an old practice. "In 1679 Edde Mariette grew plants in water and found that they required earthly salts. nitre, and ammonia, and John Woodward in 1692 published the first definite account of growing plants without soil. Dunhamel. in 1758 was the first to grow plants to maturity in water culture. However, it was not until after the discovery of nitrogen, hydrOgen and oxygen in 1785 that definite steps in the nutrition of plants were made.I Much information can be found in recent literature as to the ef- fect of various nutrient elements on growth and composition of different plant parts and many reports have been written regarding the symptoms of malnutrition. The purpose of this investigation was to determine the influ- ence of nitrogen and phosphorus in varying amounts on the growth of apple and peach trees in sand culture and to study the characteristic symptoms which deve10p when these materials are omitted from the nutrient solutions or when they are used in quantities considered excessive. In a previous publication (88). the seasonal course of soluble nitrogen and.phosphate phosphorus in apple and peach shoots of orchard trees under several cultur- al practices and different fertilizer treatments was reported. The investi- gation herein reported was done as supplementary to the previous work. Review of Literature Response to N trogen. The general effect of nitrogen is to pro- mote vegetative vigor, increase leaf area, produce a deve10pment of deep green color in the foliage. cause leaves to be retained longer on the trees in a season and benefit the set of fruit. It is the nutrient element that is most likely to be found in insufficient quantities under average condi- tions and in many cases proves to be a limiting factor to successful pro- duction. Gardner, Bradford and Hooker (32), Chandler (l2). CooPer (17). Armstrong (2), Hooker (N2). Murneek (57). and others have pointed out that nitrogen fertilizer used with both apple and peach trees has resulted in increased vegetative activity. greater leaf area and an increase in the amount of bearing surface. Trees growing under conditions where the supply of available nitrogen is abundant deve10p darker colored foliage than under conditions where the available supply is limited. Proebsting (61), work- ing in California, has found that nitrogen influences the amount of shoot growth, the abundance of foliage, the color of leaves. the time of leaf fall and the time of fruit maturity. Reports have also been given which show that trees which have made poor growth because of an insufficient sup- ply of nitrogen are more subject to the attacks of some insect pests and are also less able to survive conditions of severe winter cold. Heinicke (36) has shown that the nitrogen requirement of a large apple tree producing 25 bushels of fruit is 3.9 pounds per tree, and Magness (52) has calculated a necessary nitrogen intake of 1.5 to 1.75 pounds per tree per year. According to Magness, part of this intake may be returned to the soil in the form of blossoms. leaves, fruits. etc.. but approxi- mately one pound per tree per year is permanently removed from the soil. Magness emphasizes that these figures refer to nitrogen intake and not fertilizer applications and that the intake under certain soil conditions and with certain cultural practices may be much less than the amount ap- plied in the form of fertilizer. -h- Hewlett (MS) found that the sodium-nitrate equivalent of the total nitrogen withdrawal up to full bloom by the total number of flowers on twenty- to thirty-year-old trees would range from .5 to 1.20 pounds and that this represents only a part of the nitrogen necessary for growth of the tree and deve10pment of the fruits to maturity. In his work he found but little withdrawal of nitrogen by flowers during the period of full bloom. Lagasse (#5) studied the nitrogen-carbohydrate ratios in apple trees and found in general that trees which received three pounds of ni- trate of soda in the spring. alone or in combination with acid phosphate and muriate of potash, were much deeper green and made better terminal and spur growth than where no nitrate was used. He also found yields to be noticeably increased by the treatment. VanSlyke (8h) reported as early as 1905 on the total quantity of nitrogen required by some apple varieties and estimated that for heavy- bearing Baldwin trees l.h13 pounds per tree would be needed and for Rhode Island Greening 1.527 pounds per tree per year would be used. Williams (92) made nitrogen determinations of apple trees which had been fertilized with nitrogen and found an increased amount of total nitrogen in shoots as a result of the fertilizer application. The amount of the increase was determined largely by the time of the fertilizer ap- plication. Three pounds applied in March definitely increased the per- cent of total nitrogen in the tree early in the season and when three pounds were applied after harvest it gave a high nitrogen concentration in the shoots which was maintained during the remainder of the season. Sullivan and Cullinan (71). Sullivan and Baker (72). and Baker (M). have made extensive studies of the response of apple trees to nitro- gen fertilizer and found terminal and trunk growth to be correlated with the nitrogen content of the trees. They found that cultivated trees with a cover crep, without organic fertilizer. made greater growth and con— tained more nitrogen than trees in bluegrass sod that received a nitrogen fertilizer. In their tests they found that trees in bluegrass made slow- er growth and came into bearing later but eventually surpassed the culti- vated plot in growth. yield and nitrogen content. Sullivan (71) reported on the analysis of shoots from Grimes Golden trees and recorded.the great- est total nitrogen content in trees that received tillage and a cover crop. He found these trees to have a greater total nitrogen content during the growing season than trees in sod or in alfalfa. The trees in sod showed the lowest amount of total nitrogen in spite of the fact that they were the only trees that received inorganic nitrogen fertilizer and the leaves on these trees were light green and terminal shoot growth was short. Sullivan found.that the difference in total nitrogen between different plots was much greater during the active growing season than during the dormant season. Under average conditions trees that are well supplied with nitro- gen will make good growth and.produce leaves that are synthetically active unless some adverse conditions such as poor drainage, shading. etc.. pre- vents it. Thus Kraus and.Kraybill (uh) have pointed out in their out- standing study of the nitrogen-carbohydrate relationships in the tomato, that even the an abundance of amino acids and other forms of soluble ni- trogen is present. which may not necessarily include nitrate, yet without an available supply of carbohydrates there may be decomposition of protein. Vegetation is then weakened and the plants are not fruitful. Remy (63) has pointed out that if the nitrogen is below a certain level fruit bud differ- entiation is hindered. I In studies somewhat similar to those of Kraus and Kraybill. Laurent (N6) and Godlewski (3h) found that nitrate could be assimilated in darkness to amide compounds but not to protein and that protein synthesis could occur only in the presence of light. Nightingale (58), working with several different kinds of plants. found.that nitrate is not necessarily associated with the growth response of plants and.that tomatoes with no nitrate in the nutrient culture or tis- sues of leaves. stems or roots grew rapidly when the carbohydrate supply was increased.by subjecting the plants to short-day conditions or to total darkness. This investigator was of the Opinion that nitrate in these plants may have been formed from the decomposition of protein or some other nitro- gen compound. With regard to the use of nitrogen fertilizer applied in the fall to fruit trees. most investigators are of the Opinion that such applica- tions do not tend to increase the percent of nitrOgen found in the shoots during the dormant season. In fact, Roberts (66) points out that the ab~ sorption of large quantities of nitrogen late in the season might cause chemical changes in the tissues that would reduce resistance to winter cold. Roberts' findings seemed to indicate that as nitrOgen was taken up there was a change in the carbohydrates even before these materials could be used in growth. In some fall—fertilized Elberta peach trees at Lexington (89) only those fertilized with sulfate of ammonia showed an increase in soluble nitrogen during the dormant season. over the check trees. In fact. trees treated with cyanamid and sodium nitrate showed a decrease in their perb centage of soluble nitrogen in comparison with the untreated checks. There was a downward trend during the winter in soluble nitrogen in peach twigs of all trees regardless of fertilizer treatment. The average for 2“ weeks during fall and winter was lower than the percentages found in the same groups of trees before they were fertilized with nitrogen in the fall. Several investigators have determined the nitrogen content of leaves. stems and roots of young trees during the latter part Of the grow- ing season and Combes (16) found that leaves undergoing senescence on the tree lost much Of their nitrogen. while those yellowing Off the tree lost very little even the attached to a piece of the branch toward which nitro- gen would normally move. He found that part of the nitrogen which passes back from the leaves accumulates in the branch near the point where the leaves were attached. He also concluded that nitrogen migrates in the fall from the leaves to the stems and then to the roots and he even venp tured the suggestion that under certain conditions the roots may excrete nitrogenous substances into the soil. Both Combes (16) and.Le Clerc (M7) are Of the Opinion that the problem of what becomes of the nitrOgen com- pounds at the time leaves are yellowing can only be solved by making an analysis of the branches and preferably the whole tree or plant. In the first part Of this work. during which the seasonal course of soluble nitro- gen was determined in shoot growth of Winesap apple and Elberta peach (88). it was found that soluble nitrogen averaged considerably lower during the winter. in both apple and peach. than during the active growing season. The nitrogen was considerably'higher in peach shoots during the winter than in apple and the content Of apple shoots was maintained at a relatively con- stant low level during the winter. At least. between the apple and the peach. there appears to be a close relationship between the soluble nitro- gen content Of winter shoots and the ability of the plants to resist winter cold. Ripple (6M) made studies Of the transfer of nitrogen from the _ leaves and found that the nitrogen compounds which are translocated from the leaves are largely proteins. especially those forming the chlorOplasts. He found the highest content of nitrogen in leaves in June and the lowest at the time Of chlorOphyll degeneration. Under conditions where nitrogen was deficient he found leaves beginning to yellow early in the season with the oldest leaves yellowing first. He indicated that the younger leaves may absorb nitrOgen from the Older. weaker ones. Similar determinations were made by Murneek and Logan (56) and they concluded that nitrogen migrates from the leaves into the spurs and branches where it may be laid down temporarily in the form Of reserve pro- tein and that the removal of nitrogen from the leaves is due primarily to a decrease in the water-insoluble fraction. They found that eventually the nitrogen is translocated to the older wood and possibly to the root system. Murneek found that the amount of nitrOgen translocated from the leaves to other parts Of the tree may amount to as much as 22 to “0 percent. Weather conditions. according to their Opinion. greatly influence the translocation Of nitrogen. particularly its initiation and speed Of move- ment. They found.that cool weather appeared to hasten it but a killing frost destroyed the process. Loomis (51) in his investigational work found large quantities Of protein nitrogen stored in the bark and wood of trees whence it was digested.and used in early Spring growth. He considered the success of fall nitrOgen applications and the cumulative effects Of nitrogen ferti- lization with ammonia as probably related to this storage. He found.that nitrogenous salts appeared to be synthesized to organic compounds in the roots of apple and other trees and as a result of this synthesis. to be readily translocated only in the phloem tissue. He found. that as a re- sult Of this. ringing stOps the upward flow Of nitrogen as well as the downward movement of carbohydrates. Studies of similar nature have been conducted by Curtis (19) (20) and Murneek and Logan (56). Thomas (73) thinks that the nitrogen content of leaves of the apple begins to decline as soon as active growth ceases. He found the most rapid decrease to occur during yellowing and that it continued until de— foliation was complete. His findings seem to indicate that storage is mainly in one- and two-year-Old wood. In another study Thomas (75) found that nitrogen accumulated in one- and two-year twigs of the apple during the late dormant season and.as growth started this nitrogen moved into the new shoots and leaves. depleting the tissues of the twigs. Similar results were found by Waltman (88) for apple and peach and by Piney (59) who studied the new growth of beech. Results similar to those Just mentioned were obtained by Traub (82) who found that the nitrOgen maximum is reached in March or April Just preceding rapid growth extension. After the marked decline in ni- trogen with rapid growth extension the nitrogen content is relatively con- stant during the summer. It was also practically constant during the dor- -10- mant season. He found that the dormant-season content Of nitrogen is largely non-amino or protein nitrOgen and decreases as the active growing season approaches and reaches a minimum usually in June. Childers and Cowart (1N) and several other investigators have shown that the photosynthetic activity of leaves is considerably influenc- ed by their chlorOphyll content and this in turn is affected by the avail- able nitrogen supply. Iron also plays an important part in chlorOphyll formation and altho it is not a part of the chlorOphyll molecule an avail- able supply is necessary because it serves as a catalyst. In a similar way. nitrogen is an essential element in the develOpment of chlorOphyll and also a component part Of the chlorOphyll molecule. Plants which are well supplied with nitrogen make more vigorous growth because of their greater ability to synthesize more food. Resoonse to Phosphorus; In general. the response made by plants to applications of phosphorus fertilizer is less pronounced than to nitro- gen altho certain well-defined symptoms characterize plants growing under conditions where the phosphorus supply is deficient. Russell (67) states that the most obvious effects of phosphorus are on the root system and the production of seeds Plants well supplied with this element have a much greater root develOpment and produce seeds in a satisfactory way. Russell points out that phosphates are the most important phosphorus nutrients and that they tend to hasten the ripening process. Phosphorus appears to be essential to mitotic cell division. probably because it is a constituent Of the nucleus and is necessary also for the normal transformation Of starch. Apparently starch may form in the absence of phosphorus but does not change to sugar. Russell states -11- further that phosphorus appears to increase the develOpment of meristematic tissue and the efficiency Of the chlorOplast mechanism.. It is suggested by Gardner. Bradford.and Hooker (32) that the elaboration and assimilation of phosphorus. like nitrogen. appears to take place in the leaves. for the most part. The amount Of phosphorus assimi- lated is stated to be closely related to the amount of illumination the plant receives and appears to be connected.with photosynthetic activity. They point out that the elaborated.phosphate compounds occur in nucleic acids. nucleins and nucleo-proteins. substances always present in the cell nucleus and considered to be associated.with various enzymes in all plant tissues. They state that most tissues contain approximately six times as much nitrogen as phOSphorus. There is a suggestion that both nitrogen and phosphorus may be combined in the same molecule, altho phosphorus apparently does not play the same part as nitrogen in plant metabolism. These authors quote the work of Harris who says "It has been shown by several investiga- tors that the content Of phosphorus is generally low in acid soils and largely unavailable for use by'plantsJl This condition is further explain- ed by Stoddart who says that acid soils convert any calcium phosphate that may be present into soluble compounds which are either washed out or are fixed in an insoluble form by the formation of iron and aluminum phOSphates. Several investigators. including Blake. Nightingale and Davidson (10). have found that a deficient supply of phosphorus to young apple trees resulted in a high accumulation of carbohydrates in both tOps and roots. These workers found. however. that the trees eventually became low in starch and proteins and high in sugars. Lilleland (H8) grew peaches in soils in California that were ex- -12- ceptionally low in phosphorus. He found that treated trees retained their leaves longer in the fall than the untreated check trees: however. the phos- phorus fertilizer did not affect the time of bloom. time Of ripening or the amount Of shoot growth. He found.a yellowing of the foliage which appear- ed to be due to a depression Of nitrogen absorption caused by the addition of phosphorus. Proof was added tO this assumption by the analysis Of leaves. which showed a lower nitrogen content in phosphorus-treated trees. Results somewhat similar to these were Obtained by Thomas (7h) (75) who found lower'P/N ratios in apple trees in tanks where nitrogen had been added. He also found a greater amount of phosphorus absorbed by these trees. Further work by Lilleland (N9) in California. on soils low in phosphorus. gave striking results in increased shoot and root growth from phosphoric applications on several species Of fruit. Shoot growth Of apples was increased by 79 percent. apricots 66. prunes 89. and peaches 105 per- cent. Apple root growth was increased 37 percent. apricots an. prunes (apricot roots) M2. and peaches 80 percent. He found the tOp-tO-root ratio to be increased on apples by the phosphorus application but Obtained no sigh nificant difference on the other species. Scott (69) found that in a sandy soil in South Carolina the omis- sion Of phosphorus to peaches did not show striking differences from the fertilized trees. However. the trees which received no phosphorus yielded significantly less. grew more slowly and showed.poorer fruit-bud develOp— ment. In this experiment an unsatisfactory growth Of rye cover crOp re- sulted on the plots where phosphorus was not used. Similar comments on cover cr0p growth under conditions where the phosphorus supply is limited are Offered by Chandler (l2) and others. -13- Nitrogen Deficiency: Deficiency in the nitrogen supply usually results in poor. weak growth. small. yellowed leaves and generally poor fruit develOpment. Childers and Cowart (in) state that "Any nutrient which directly or indirectly influences leaf color. stomata or other characteris- tics of foliage would be expected to influence the leaf activity." Thus, they found that leaves deficient in nitrOgen assimilated about one-third as much carbon dioxide and transpired about 70 percent as much water as did the full-nutrient leaves. Their trees were grown in washed sand in a green- house and the ones which received no nitrogen develOped the most striking symptoms. The leaves were small and light green; none of the shoots grew more than twelve inches in length and all formed their terminal buds early. Similar results were Obtained by Blake. Nightingale and Davidson (10) (11) with one—year-Old Blaxtayman root-grafted apple trees grown in sand cul- tures in six different nutrient treatments. The lack Of an external supply of nitrogen was associated with an early appearance of yellowish—green leaf blades and.a reddening of veins Of lower leaves. The upper leaves later exhibited this condition and all leaves assumed.an upright position with the petioles. forming narrow angles with the stems. The angles formed by the leaf petioles with the main stem became more and more acute as growth continued. These investigators noted similar results in their study of growth Of Delicious apple trees under field conditions (9) also the leaves became more brittle as they develOped the yellowish—green color. The cambial activity Of these trees was very limited.and ceased early in the season. resulting in short shoots of small diameter. The carbohydrate ac- cumulation was high and root growth extensive. woody and abnormally slender. In the second season new growth was very slow and. weak and finally the tree -1h- produced.a few small. spindly branches 2 to 6 inches long. The new growth develOped from the original tree base rather than from the previous seasons growth. The new leaves were thin. narrow and definitely yellow from the time of their first appearance. with peach trees grown in sand. Davidson and Blake (21) obtained results similar to those with apples. Shoot growth was restricted in length and diameter and the older leaves first yellowed and later the young leaves lost much of their green color. Typical purplish-red spots develOped on the foliage and the cell walls were abnormally thiCk. Carbohydrates accumulated rapidly in the tape and roots were yellowish. slender but fairly extensive. Davidson and Blake (22) point out in another publication that the develOpment of a nutrient-deficiency symptom is dependent primarily on two factors: "(a) the rate of growth of the trees and (b) a failure of the root media to supply the limiting nutrients in amounts and proportions ade- quate for that rate of growth.“ The results found by Blake and his co-wonkers were obtained also by Veinberger'and Cullinan (91) Fisher (31) Wallace (85)and.Hoagland.and Chandler (39). Weinberger and Cullinan emphasized that there were no com- plete descriptions of the symptoms produced.in peaches by lack of mineral elements. except phosphorus and.potassium. With their trees which received no nitrogen a large number of fibrous roots were formed. They found rela- tively three times as much fibrous root growth by weight in prOportion to tap as for trees in complete nutrient solution. Part of the work by Fisher (31) was with tomato plants which were given a culture containing excess nitrOgen. This treatment stimulated vege- tative growth at the expense of flowers and fruit. Terminal shoot growth of these plants was depressed but lateral branches were numerous and but few -15- fruits were set. The leaves were spotted with dead.areas. curled. roughly pimpled and yellowed interveinously. The time of maturity was greatly de- layed.and resistance to disease and inseCts reduced. Root growth was light brown with few branches. Under certain conditions it appears that the continued use of cer- tain nitrogen fertilizers may produce physiological disorders. Rawl (62) reports on a case of this nature in a sandy soil in South Carolina where sulfate of ammonia alone had been used continuously over a period of years. and certain characteristic symptoms develOped. The trees grew poorly. did not form fruit buds prOperly and produced low yields of small peaches. The leaves first changed to a yellowish light green. later to a very pale yellow. followed by burning or scorching of the tips and leaf margins. Tests of pH on the soils indicated that the continued use of sulfate of ammonia had re- sulted in high soil acidity. Complete fertilizers applied to these trees produced good growth and good yields of marketable fruit. The eXperiment was not arranged to show whether phosphorus or potassium gave the greatest benefit in affecting the recovery of the trees. ' Phosphorus Deficiencygg The general effect upon plants of an insufficient supply of phosphorus is less pronounced and probably in some respects less serious than for nitrogen. The fact that fruit trees frequently fail to show ready response to phosphorus applications under conditions where grain crepe make noticeable gains. can probably be ac- counted for in one of three ways: (1) tree roots penetrate deep. if soil conditions permit. and in that way probably obtain part of their phosphorus supply from lower soil levels: (2) trees may actually use con- siderably less phosphorus than the shallow, fibrous-rooted grain crOps; -16- (3) trees may be able to use their phOSphorus in a different form from that required by plants of the grass family. In any event. there are conditions under which fruit trees develOp symptoms of phosphorus starva— tion and considerable work has been done in recent years by means of arti- ficial media which emphasize theSe characteristic symptoms so that they may be more readily recognized under field conditions. The work of Blake. Nightingale and Davidson (10) (11) (21) . Weinberger and Cullinan (91). Wallace (85). Hoagland and Chandler (39) and others. shows that phosphorus deficiency symptoms. in the early stages. are very similar to those of nitrogen starvation. except that decided yellowing of the foliage is not common. The upper leaves usually remained dark green with the mid-ribs. veins and petioles definitely tinged with purplish-red. Shoot growth was generally very slender and.young leaves thin. small. dark green and tinged with purple. The green color of leaves where phosphorus was deficient was lacking in the luster characteristic of the foliage on plants making vigorous growth. Fibrous root growth.was restricted by a deficiency of phosphorus and roots that formed were slender and contained an abundance of nitrate. Carbohydrate. largely sugar. ac- cumulated in both tOps and roots and was found in greatest amount near the tips of new growth. Ihwidson (23) found that under some of the soil conditions of New Jersey. peach trees may develOp deficiency symptoms of phosphorus and a base at the same time. In sand cultures. his studies indicated that phosphorus deficiency in peach trees develOps independently of. or may coexist with. deficiencies of calcium. potassium or magnesium. Omission of phosphorus resulted in an increase in pigmentation and in the formation of -17- narrowt dark ochre-green leaves. almost regardless of whether or not the treatment was also deficient in a base. Leaves that are deficient in phOSphoruB are affected much less in their photosynthetic activity and transpiration rate than those defi- cient in nitrogen. This was shown by Childers and Cowart (1h) who con- cluded that nitrogen plays a much more important role in photosynthesis and transpiration of apple leaves than phosphorus or potassium. alone or combined. Procedure Two varieties of apple and one of peach were used in this ex- periment. The apples were one-year-old grafted trees of the Staymared and.Paducah varieties and the peaches were one-year-old Elberta trees. The trees were selected for uniformity from nursery stock of our own prepagation and were taken directly from the nursery rows. They were treated uniformly as to tap and root pruning and placed in the culture Jars containing a high grade of washed. sharp sand. The trees were selected in March after having grown one season in the nursery and were washed free of all soil and the root system pruned so that all fibrous roots were removed and only moderate-sized roots left. The apple tOps were cut back to a height of approximately fifteen inches and the later- al growth on the teps of the peach trees was reduced to stubs about an inch in length and these were thinned so that there was an Opportunity for about five buds to start from each tree trunk. The cultures consisted of seven different nutrient solutions with variations in the content of nitrogen and phosphorus and were applied -13- in such a way that one tree of each of the apple varieties and two peach trees received the same nutrient treatment. The nutrient elements other than nitrogen and phosphorus were supplied to all trees in equal amounts. Three-gallon stone Jars provided with a drainage hole in the bottom were ‘used and lh.500 grams of sand were placed in each Jar. A cork stOpper containing’a small glass tube was placed in the drainage hole so that a quantity of the solution from the sand could be collected for pH determina- tion when fresh solution was added to the Jars. . The Jars were arranged out-of-doors. on a framework supported by small sawhorses. To provide a satisfactory cover for the Jars. two pieces of board were used for each Jar. cut in a semicircular form somewhat larger than the diameter of the Jar. The straight edges were then beveled and small nails driven at the lower circular edge of each board to hold the halves in position. In this way the beveled edges were held together and the boards were held by the nails against the inside edge of the jar so that they provided a s10ping cover for each container. A.notch was made in each half of the cover. for the tree. After the board covers were in position. a piece of heavy mulch paper was placed over each one and fastened to the boards by means of thumb tacks. To further prevent water entering the jar at the center of the cover where the tree trunk emerged. a pad of cotton was pushed into the hole be- tween the tree and the board. Trouble was experienced in this connection by sparrows pulling the cotton from around the trees. so a one-hole rubber stepper split Open on one side. was set around each tree on tap of the cover and over the cotton. On several occasions during the course of the experi- ment. weighings were made before and following heavy rains and at no time did water enter the Jars. The sand used was a moderately fine grade of white glass sand ob- tained from West Virginia. It was thoroly washed with tap water and then with distilled water. and dried. It was found by chemical tests to contain no nitrOgen or phosphorus. The analysis of the sand"I showed it to run 99.58 percent silica with very small percentages of iron and aluminum oxides. In a previous experiment with strawberries (86) this medium was found to be en- tirely satisfactory for plant growth. For an experiment of this nature sand appears to be the most satisfactory medium and has been recommended and used successfully by many investigators (ll) (13) (25) (5M) (65) (70). Composition of the Nutrient Solutions Many different kinds of nutrient solutions have been suggested by investigators who have found them suited to their particular types of work. It appears probable that a solution containing all the necessary nutrient elements in prOper proportions for general plant growth may not give equal results with different species of plants. For example. in the assimilation of nitrogen. it has been shown by Pirschle (60) and by TiedJens and.Robbins (77) that many cr0p plants can assimilate ammonium and nitrate provided the hydrogen-ion concentration of the nutrient solu- tion is suitable to the form of nitrogen used. It appears further that the necessary pH value may be specific for each species. TiedJens and Blake (79) state that it appears that pH values below 6 generally favor nitrate assimilation and values of 6 or above favor ammonium assimilation. * Supplied by the firm in West Virginia from which the sand was obtained. A test here at this Station showed 99.85 percent insoluble in hydrochloric acid. -20- Studies which have indicated similar results regarding nitrate assimilation have been made by Baudisch (7) (8). TiedJens and Blake (79) found that apple trees absorbed and assi- milated.ammonium nitrogen without oxidation to nitrate and that the hydro- gen~ion concentration of the culture medium limited. directly or indirectly. the assimilation of both ammonium and nitrate. Their studies indicated that in soils where the pH value was comparatively low ammonium was appar- ently oxidized to nitrate before assimilation of nitrogen occurred. ‘Under conditions where the pH of the culture medium was favorable for ammonium and nitrate. respectively. ammonium produced a more rapid growth response than nitrate. In a study of the effect of different nitrogen carriers on the performance of apple trees, BatJer and Sudds (6) found that trees made greater root growth where nitrate of soda was used in place of sulfate of ammonia. In their eXperiment. root growth on nitrated trees was often more than twice as much as on sulfated trees. They found also that the soil was much more acid where sulfate of ammonia had been used. Studies similar to those of BatJer and Sudds were made by Clark and Shive (15) with tomato plants. Their findings showed that the concen- tration of ammonium nitrogen in the roots varied with the pH of the ex- ternal medium. Higher concentrations of ammonium nitrogen were present in the roots of plants grown in solutions of high pH than in those grown in solutions of low pH. High concentrations of ammonium in the roots ac- companied high rates of absorption of ammonium from the solutions. The work of TiedJens (78) indicated that the nitrate ion was assimilated most satisfactorily by tomato and apple when absorbed from an acid nutrient solution of approximately pH ”.00. The ammonium ion was assimilated most satisfactorily when absorbed from a nutrient solution having a constant pH value of 5.0 to 6.5. varying somewhat with the variety. He found that ammonium ions were immediately absorbed by plants without further change and were assimilated directly and more rapidly than the nitrate ion. and that the volume of growth obtained from nitrate and ammonium depended on the concentration of the nitrogenous salt in the nu- trient solution and the available carbohydrates. Under conditions where a large amount of carbohydrate was available. ammonium was assimilated more rapidly than where the supply of available carbohydrate was small. In an experiment with strawberries in sand culture (86) in which ammonium nitrate was used to furnish the nitrogen. the plants grew best at a reaction of pH 5.3 to 5.5. The nitrOgen content of this solution was 292 ppm. Work by Emmert (30) at the Kentucky Station. with tomatoes and lettuce grown in treated soil. gave variable results as to the best pH for plant growth and yield. With tomatoes. the heaviest yields were pro- duced by the use of sodium carbonate added to the soil to maintain a pH of 8.3 to 8.”. The second heaviest yield resulted from the use of the same material where the pH was maintained at 7.3 to 8.0. The heaviest lettuce yields also were produced where sodium carbonate was applied to maintain a pH of about 7.5. It seems probable that some other effect than on pH value may have occurred from the use of sodium carbonate on ,this soil. The results obtained by Hoagland (38) were similar to those of TiedJens and Blake (79). He found that the reaction of a culture solu- tion has an important bearing on the absorption of ions. He observed that the absorption of the N03 ion was favored by an acid reaction and that nitrate penetrated far more rapidly into the cell sap of some plants from an acid than from an alkaline solution. He further emphasized that the hydrogen-ion concentration may be one of the chief variables governing the colloidal behavior of the protoplasm of the cell. This view is further strengthened by Chandler (12) who points out that in winter-injured tissue there is an increase in hydrogen—ion concentration of the cell sap, accom— panied by a disruption of the colloidal stability of the protOplasm. The maintenance of a reaction that is most suitable to the growth of plants is difficult under soil conditions largely because of the buffer action of the soil. In artificial cultures of either sand or solutions a definite. stable pH is maintained more easily. altho several things have an influence on it. Trealease and Trealease (81) state that "the solution constituents that have the most pronounced influence upon reaction changes are the nitrates or ammonium salts employed as sources of nitrogen for the plants". Working with wheat plants in solution cultures, they obtained best growth at an approximately stable pH value of 5.1. Their cultures were arranged at pH values of “.3. 5.1 and 6.0 and were maintained at these values by varying the ratio of NOg/NHh in the solutions. The NOg/NHh ionic ratios of 50/50. 80/20 and 90/10 were used to obtain the initial pH values indicated above. The salts employed were KN03 and (NHh)250n. With the lower NOg/NHu ratio the pH value of the solution decreased rapidly under influence of the plants and approached in extreme cases a pH value of 3.0. With the higher ratio, the pH value increased rapidly, tending to reach a limiting value of 6.5. -23- They state that "The anions of the nitrates. together with H ions derived from the solution. are absorbed by the plant more rapidly than the cations. thus tending to decrease the hydrOgen-ion concentration. On the other hand. the ammonium salts have the Opposite effect; their cations enter the plant more rapidly than their anions. and the hydrogen-ion con- centration is thereby increased, regardless of whether the actual absorp- tion of the cations occurs in company with CH ions derived from the solu- tion or whether NHQ, resulting from a decomposition of(NHu0H, is absorbed by the plant." They found that young plants seem to remove NH” ions more rapidly than N03 ions. Scofield (68) calls attention to the point that plants do not absorb water and dissolved substances from the soil solution in the same prOportions that these constituents occur together in that solution. This evidently has a direct bearing on the absorption of different salts by plants growing in either sand or solution cultures. Blake. Nightingale and Davidson (11) adjusted to pH 1+.2 the nutrient solution to be used for apple trees in sand culture, and found that between the times when additional solution was added. the solution in the sand tended to become less acid. about pH 5.0 to 5.2. They found in previous work (79) with young apple trees. that the pH range indicated above was excellent for growth with the nutrient solution which they employed. Suggestions for balancing nutrient solutions. their adjustment to a suitable reaction and the preparation of special equipment for use in growing plants in sand and solution cultures are offered by Turner and 21'enry (83), Davis and Hoagland (2h). Hill and Grant (37), Hoagland and -gh- Arnon (1+1). McCall (55). and Shive and Robbins (70). In the preparation of the nutrient solutions used in this ex- periment it was desired to have variations only in the content of nitro- gen and phosphorus. With this point in mind the solutions were arranged as follows: 1. Basal (complete). 2. No nitrogen. 3. Low nitrogen. l/M as much as No. 1. M. Excess nitrogen, twice as much as N . l. 5. No phosphorus. 6. Low phosphorus. l/M as much as No. 1. 7. Excess phosphorus, twice as much as No. 1. A modification of the solution used by Blake, Nightingale and Davidson (11) was employed.and iron was supplied to all solutions by the use of ferric citrate. One cc of a 0.5 percent solution of this material was used for each liter of solution at the time they were made up. This procedure has been found satisfactory by Marsh and Shive (53) and by Weinberger and Cullinan (91). At the beginning of this experiment and continuing for a period of ten days after the trezifzet in the jars. only distilled water was added. This gave a chance for the reserve ma— terials within the trees to be used before any nutrient solutions were supplied. After the trees had started to grow, the nutrient solutions were supplied at the rate of approximately 500 cc every other day during- the first few weeks of the experiment. This amount of solution added to the jars resulted in the leaching of 50 to 100 cc which was collected each time for pH determination. As the season prOgressed and the trees grew, -25- fresh solution was added to each Jar each day and the amounts gradually increased. One tree of each of the apple varieties and two peach trees received the same nutrient treatment. Table 1 gives the chemical compounds used. in grams per liter, and table 2 the concentration of the elements in each of the nutrient so- lutions used. in parts per million. -26- emdwo H. coauomuapom cm are acneuoaa mowsdwosm. u: woman pow Hanan. gig in l 2. mg- 5a. was l. was. Haas- was”- mmmmo: 0.3mm 0.8mm ohmmm 0.83. In 0.25 0.83 onopm.mmmo o.mzmm o.m:mm o.m:wm o.m:mm o.m:mm o.m:mm o.mzmm ammo:.~mmo o.mm~m o.mm~m o.mmmm o.mm~m o.mm~u o.mm~m o.mm~m amazon o.m:oo -u- o.pmoo H.mmoo 0.:mmm o.mu:u 0.:mmm azou .u. u.. --- --- o.mmm: o.~mmm --- Azmrv ammo: -u- --- --- -u- --- --- o.mmmu ”nopm.:mmo o.o~mo o.owmo o.ono o.o~mo o.oumo 0.0Hmo o.o~mo mason o.owmp o.o-p o.o-~ o.oH- o.o-~ o.o-~ o.onH emommmo~.ummo o.oomo o.oomo o.oomo o.oomo o.oomo o.oomo o.oomo -27- deH. No zcanpnun ewoaeuno He «no uowuawouw. Ha pone. won IHHHHon. aH.aon« 0 mpan an eHsuo: H\: a»- l m a»- so eeo.: H\: ens-u m neon: m «as «women nachos muons. crows. muons. soapnana “my mm mm mm mm mm mm mm onHOHna Anny HHm Ham Ham HHm HHm HHm HHm anmnnans many mm mm mm mm mm mm mm annmwnnno Anna m m m m m w m Haas Hana H H H H H H H mnnaeaons. Amy mm mm mm on u HH Ham sznomne Hay mm: nu mm Ham Ham mom Hmu onHoeHn. AOHV aHm uHm «Ha «Ha aHm «Hm «Hm manun Amy Hm mm mm Hm Hm mm mm mason “av a a a a a a a -23- The concentration of elements in these solutions varies some- what from those employed by Blake. Nightingale and Davidson (11). par— ticularly in the content of nitrogen and chlorine and in the absence of sodium. Under field conditions. where sodium nitrate is commonly used as a fertilizer. there is undoubtedly an accumulation of sodium in the soil which tends to cause an increase in the pH value. In the humid sec- tions of the country the sodium is not likely to prove a detriment to plant growth. However. Hoagland and Snyder (M0). working with strawberries. found that some varieties were highly susceptible to injury from sodium salts even tho the sodium was present only in moderate concentration in the solution. The symptom was a marginal burning which sometimes spread.until the whole leaf was killed. Considerable diversity of opinion exists among investigators in regard to the most satisfactory concentration of elements for the best growth of plants. Cullinan and others (18). working with peach trees in sand cultures. found increases in growth of taps and roots when the nitrogen concentration of the nutrient solution was increased. up to 60 ppm. With phosphorus. however. they obtained no increased growth with concentrations above h ppm. It now appears from the work of Cullinan and.athers that the concentration of phosphorus used in the work herein reported was considerably greater than necessary. Nevertheless. the ar- rangement of cultures gave an Opportunity for studying the effects of both deficiencies and excesses. in apples and peaches. Further evidence in this connection was obtained by BatJer and Degman (5) who found that growth in their phosphorus series was approximately uniform in all series which received M ppm or more of phosphorus. They found that phosphorus deficiency symptoms occurred only when the phosphorus was completely lacking. In their nitrogen studies with apple trees. they found somewhat less linear growth with the nitrogen concentration at 60 ppm than at 168 'ppm. Reduction in the nitrogen supply below 60 ppm reduced the amount of growth almost quantitatively. Growth Measurements. To determine the growth reaponse of the trees for the different nutrient treatments. measurements of diameter and linear growth were made at weekly intervals thruout the summer. The dia- meter of the tree trunk was measured at the point where it came thru the cover of the Jar and also one foot above the cover. The diameter of the new growth was calipered at a point approximately one inch from the older wood. The leaf and new-growth characteristics were observed frequently and measurements were made to determine the effect of the nutrient treat- ments on the angle formed between the leaf petioles and the shoots on which they were growing.' At the end of the season the trees were removed from the Jars. weighed and photographed and the effect of the treatments on root growth was studied. The results of these measurements together with several of the photographs are shown and described in the following pages. Chemical Analyses. For the determinations of soluble nitrOgen and phosphate phosphorus in this study. the first samples were taken from the tOp third of the twigs which were cut off each tree at the time of potting. Later. the tap third of a shoot on each tree was analyzed. All determinations were made colorimetrically from samples taken in duplicate. Methods of Analysis; In the previous work (88) chemical analy- ses of twigs were made at weekly intervals to determine the seasonal course of soluble nitrogen and phosphate phosphorus in Winesap apple and -30- Elberta peach trees in the orchardt under various treatments of culture and fertilization. The methods used for the analysis are briefly described in the bulletin Just cited and in a Journal article (87). They are modifica— tions of the procedures develOped by Emmert (26) (27) (28) (29) for his studies with vegetable plants. The determinations of both nitrogen and phosphorus were made upon duplicate samples. In 1926 it was suggested by Loomis (50) that colorimetric procedures for many types of determinations might eventually be found most suitable and he emphasized that any sample worth taking was worth duplicating. Loomis offered suggestions on methods of sampling, preservation of material and certain procedures for chemical determinations. He further stated that in the bulk of physiological analy- ses the statement of chemical results as percent of the green weight of the tissue appeared to be of the greatest significance. various other methods have been develOped for rapid chemical tests of plants and soil as a means for determining fertilizer needs. and suggestions on their use are offered by Gilbert and Hardin (33) and by Thornton. Connor and.Frazer (76). Further proof in regard to certain procedures that were followed in this work and the conclusions that were drawn has been given by Traub (82) who found that the greatest nitrogen content in twigs occurred in the spring Just before growth began. Similar results were obtained in the pre- vious study (88) in apple and peach trees in the orchard. {Also in agreement with the work of Traub was the fact that nitrogen was relatively constant and at a low level during the dormant season. Similar results were obtain- ed by Thomas (75) and.Piney (59). In this study and in the previous work, the outer third of twigs .31- was used for analysis because preliminary tests (87) had shown that some- what higher concentrations of soluble nitrogen occurred in this region than in the median and basal sections. From the results obtained it was thought that the portion of the twig showing the highest analysis of solu- ble nitrOgen would present the most accurate picture of the amount avail- able for metabolic processes. Harvey (35) has pointed out that substances which tend normally to decrease thruout the growing season, like nitrogen, are always most abundant in the tips of shoots and least abundant in the basal portions and are associated generally with good growth conditions. It was found in the previous study (88) that. in tissues where no injury had resulted from freezing, an increase in the amount of phos- occurred phate phosphorus/slightly in advance of the time that new growth began but the amount in twig tissue was soon reduced when leaves had been formed in sufficient number to utilize the phosphorus. In twigs where severe winter injury had occurred (90) the amount of phosphate phosphorus continued to increase notwithstanding the fact that the injury was so severe that no new growth was formed. It has been pointed out by Gardner, Bradford and Hooker (82) that phosphorus is at a maximum in nearly all tissues when buds are swelling and that the chief difference between phosphorus and nitrogen in this respect is that phosphorus reaches a minimum in most tissues in April or May when trees are in bloom while the minimum for ni- trogen is not reached.until midsummer when active growth has been com- plated. Fresh tissue was used for these analyses. A similar procedure has been suggested by Loomis (50). Tottingham (80) has pointed out that .32- both freezing and desiccation modify the nitrogenous constituents in such a manner as to make impossible the true separation of the nitrogenous fractions. Other investigators have verified these results. It would appear from the conclusions reached by these different workers that a pro- cednre of freezing or drying would change the amount of nitrogen from any one type of nitrogen determination and the amount would differ from that resulting from extraction of fresh tissue. Results Erowth. After the trees had been set in the jars and new growth had started. the excess buds were removed so that only two shoots were allowed to grow. In practically all cases the most vigorous shoots developed near the distal end of the trunk. The two most vigorous shoots were permitted to grow in order that one of these might be used for chemi- cal analysis after the trees had been growing for several weeks. leekly records were kept from the beginning. on amount of new growth, trunk dia- meter increase and characteristics of leaf and petiole development. The results of these measurements are shown in the graphs and tables in the appendix. Tables :3. 5 and 7 and figures 1. 2. 3. u. 9. 10. 11 and 12 give the growth measurements for apples. Tables 11. 6 and 8 and figures 5.5, 7. s. 13. 1h. 15 and 16 give the growth measurements for peaches. 'lhe measurements given for each date in the tables are averages of three weeks. while those shown in the figures are individual weekly measurements. -33- The results shown in tables 3. 5 and 7 for the growth of the apple trees indicate rather clearly that the reaponse of the Paducah variety under the conditions of this eXperiment was better. in most cases. than that of Staymared. The exceptions to this statement were the Paducah tree growing in the no-phosphorus culture and the one which received the basal nutrient treatment. Measured by trunk diameter increase. either at the jar cover or one foot above. the no-phosphorus tree failed to respond satisfactorily. altho in percentage green weight gain it exceeded the Staymared. In the basal nutrient treatment. the Paducah tree made less linear growth and also showed.a lower percentage green weight gain than the Staymared. In total linear shoot growth. the trees of the two varie- ties were nearly identical where phosphorus was omitted from the nutrient solution. In comparison with this. the Paducah tree showed a percentage gain in linear growth of 105 percent where the phosphorus was doubled over the amount used in the basal solution. while the Staymared tree show- ed a percentage gain of only 7.3 for the same treatment. This striking difference is at least suggestive of the phosphorus utilization of these two varieties and.would indicate that Paducah trees should respond ex- cellently in soil where the phosphorus content is high. In fact. such a response has occurred.with Paducah trees in bluegrass soils where the phos- phorus content is unusually high. No explanation can be offered for some of the other differences in growth response of these two varieties in sand culture except to state that under field conditions trees of the Paducah variety grow more rapid- ly and come into bearing at a relatively earlier age than Staymared. Pos- -Bu. sibly some further explanation can be found in the natural growth reaponse of these two kinds under field conditions. The Paducah is a variety of Kentucky origdn and is considered to be a seedling of Home Beauty. It possesses the habit of starting into growth relatively late in the spring and ceases growth fairly early in the summer. It grows vigorously. how- ever. and bears heavily and regularly. The Paducah may be classed dis- tinctly as a fall apple and the Staymared as a winter sort and this may account in some degree for the difference in growth of the two kinds in sand culture. In every case except in the basal solution. the response in growth as measured by total linear increase was greater for Paducah than for Staymared. Likewise the percentage increase in weight of this variety was appreciably greater in all cases except the basal nutrient and no- phosphorus Cultures. The same relationship between the two varieties also held true for the gains in trunk diameter. whether the measurements were made at a point near the crown or one foot above that point. When the diameter measurements of the current growth were compared. however. the greatest gains were not always shown by the Paducah. The stem diameter measurements for peaches showed quite consis- tent increases for all nutrient treatments except the ones where nitrogen was omitted. In this case. relatively small gains were made in either the old or current stem and likewise there were but small amounts of new linear growth. In comparing the linear growth and percentage increases in weight 4'5- of trees of apple and peach. the fact stands out rather clearly that the peach is more sensitive than the apple to a deficiency in the phosphorus supply. In the apple cultures where phosphorus was omitted the average gain in weight of the two trees was 9% percent while the peaches which re- ceived the same treatment gained only 15 percent. The symptoms of phos- phorus deficiency. however. were more noticeable on the apple than on the peach trees with the possible exception of the change in the color of the foliage. In comparison with the peaches. which showed small percentage gains in weight in the absence of a phosphorus supply. the apples grew fairly well. while in the cultures where the phosphorus supply was doubled over the amount used in the basal solution. the apple trees gained con- siderably more than the peach. Under field conditions in most soils of Kentucky. the con- tent of water soluble phosphorus is 10w. averaging considerably less than one part per million. This is true in the areas where the principal com- mercial orchards of apples and peaches are grown. In the bluegrass sec— tion of Central Kentucky. the soils are outstandingly high in their phos- phorus content but even under these conditions the water soluble fraction probably would not run more than one part per million. The bluegrass area is not a commercial fruit growing section and it appears doubtful if trees grown there thrive any better or even as well as in other parts of the state where the phosphorus content is known to be low. In general. the cultures which contained no nitrogen appeared more detrimental to the peach trees than to the apples and the effect of this treatment on the peaches was most obvious in the lack of new growth. the yellowish green color of the leaves and the red discoloration of the bark. .86- In fertilisation experiments with.peaches under orchard condi- tions.Ashley'(3) found.that the gains made by trees were in direct pro- portion to the amount of nitrogen which they received. The results ob- tained in the experiment herein reported do not agree with the findings of.Lsh1ey. For the quantities of nitrogen used in these cultures. there were only slight increases in green weight gain when the nitrogen was in- creased.from 56 to 22h parts per million and even a slightly smaller gain when the nitrogen content of the solution culture was increased to ”RS parts per million. It seems quite probable. however. that under field conditiOns and.particularly on light soil with smaller quantities of nitro- gen than were employed.in these tests. gains made by trees would be in di- rect proportion to the quantities of nitrogen which they received. The relative quantities of nitrogen used in the first four cultures in this experiment were 0. 1. u and.8 while the respective green weight gains for these trees were 0. 1. 1.3 and 1.26. Hearly the same relationship was found.for linear growth increases for the trees which received these four treatments with results of O. 1. 1.1 and 1.1. It appears that nitrogen. when used in excess of 60 parts per million in solution cultures for peaches cannot be expected to give greatly increased results in linear growth increase or in green weight gains. In fact. Cullinan. Scott and laugh (18) found that when nitrogen was used on peach trees at quantities of 120 and 168 parts per million the gains were not significantly greater than when it was used.at 60 parts per million. lhen the same comparison is made with the apple trees as is shown above for the peaches. it is found that the heavier nitrogen applica- tions are even less effective in inducing vegetative growth. Comparing the green weight increases in the different nitrogen cultures. the respective .37- gains were 0. 1. .19 and .68. for the relative quantities of nitrogen of O. 1. h and 8. while the linear growth increases for the same trees were 0.1. .63 and .72. It appears that the heavier applications of nitrogen were detrimental to the growth of the apple trees in sand culture. A point of particular interest with respect to vegetative elongation and the diameter increase of current growth is the fact that shoot growth con- tinued over a considerably longer period on the apples than on the peaches and that the diameter of the current growth continued to increase on the apple trees until late summer. On the peach trees. however. very little increase in shoot diameter occurred after August 3. The shoot growth on peach trees was rapid at first but was practica11y completed within a month or six weeks after the trees were potted. On the apple trees. shoot growth was moderately rapid but continuous until about the first of Sep- tember. This comparative condition of growth. at least the elongation of shoots. is quite different from that of normal tree growth under field conditions.. In general. with trees of moderate vigor. the apple completes; its shoot growth in a season several weeks in advance of the time that shoot growth on peaches is terminated. As stated previously. the roots of all trees were pruned uni- formly at the time they were set in the Jars. All the fibrous roots were removed and only roots of moderate size were left on the trees. At the end of the experiment the roots were examined and photographed. the re- sults of the examination are recorded in tables 9 and 10. Table 9. sand culture. -38- Growth of Staymared and Paducah apple tree roots in Nutrient Tree Characteristics of the root growth treatment number ‘ l. Fairly good. Laterals slender and quite numerous. Fibrous growth dense. Basal 8. Moderately good. Few slender laterals. Fairly good fibrous growth. 2. Very little growth. Tree died in the 7th week. No nitrogen . 9. Extensive root system. Laterals numerous. slender and long. Fibrous growth heavy. 3. Moderately heavy growth of laterals and fibrous roots. l/h nitrogen 10. Many long. slender roots but comparatively few new fibrous roots. In general fairly good. h. Good. Laterals long. Fibrous develOpment good but not extensive. 2 nitrogen . ll. Moderately good but neither lateral nor fibrous roots numerous. 5. Several long. slender laterals. Very little fibrous develOpment. No phosphorus 12. Laterals long. slender and not numerous. Fibrous de- velOpment poor. 6. Rather poor. Not many laterals. Fibrous growth weak. l/u phosphorus 13. Fairly good. Laterals not numerous. Fibrous growth moderately dense. 7. Very good. Laterals numerous. Fibrous growth heavy. 2 phosphorus 1M. Good. Laterals fairly large and long. Fibrous growth moderately heavy. ’ The first tree in each pair is Staymared: the second. Paducah. .39- Table 10. Growth of Elberta peach tree roots in sand culture. Nutrient Tree Characteristics of the root growth treatment number 15. Good. Good develOpment of laterals. Many fibrous roots. Basal l6. Rather poor. Not many laterals. Fibrous growth weak. 1?. Moderately good but not heavy. ,Many slender laterals. No nitrogen Fibrous develOpment quite dense. 18. Moderately good. Lateral growth fairly extensive. Fibrous growth only fair. ~ 19. Very extensive root system. Laterals long and numer- ous. Fibrous growth especially good. l/h nitrogen 20. Boots rather short but numerous. Lateral and fibrous growth good. 21. Very poor. Both lateral and fibrous develOpment Smalle 2 nitrogen 22. Poor. Laterals few and short. Fibrous growth very limited. 23. Rather poor. Laterals limited in size and number. Fibrous growth week. No phosphorus 2M. Weak and stunted. Not many laterals. Only a few weak fibrous roots. 25. Good. Laterals long and numerous. Fibrous develOp- ment gOOd. l/h phosphorus 26. Fairly good. Laterals numerous but bunched together. Fibrous growth extensive. ' 27. Good. Laterals long'and numerous. Fibrous develOp- ment moderately heavy. 2 pho sphorus 28. Good. Laterals quite long. Fibrous growth moderate- ly heavy. .140- The growth of roots in general. on both apples and peaches. was enhanced in the cultures in which the nitrogen supply was either lacking or limited. These results are in agreement with the findings of Blake. Nightingale and Davidson (11). Weinberger and Cullinan (91) and others. Weinberger and Cullinan found relatively three times as much root growth by weight in preportion to tOp on trees growing in a solution where no nitrogen was supplied as on trees growing in a complete nutrient solution. The response of trees under these conditions appears to be due to a cessa- tion or marked retardation of cambial activity. In this work. lateral ex? tension in growth of roots was apparently quite rapid but increase in die- meter very limited when the nitrogen supply was low. Careful examination of the roots in the cultures where nitrogen was omitted disClosed that much of the cortex had died and sloughed off. In this respect. the roots of these plants differed considerably from those which had grown in the basal nutrient solution. In the latter. the diameter of the roots was larger and the cortical tissue was alive and white. Similar results were reported by Blake. Nightingale. and Davidson (11). With apple or peach trees which received no nitrogen. the effect of this’treatment appeared to be much more serious upon tap growth than upon root growth. There was considerable evidence. particularly in the peach trees. that when the nitrogen supply was double the amount used in the basal so- lution. root growth was seriously retarded. This same condition has been noted.on numerous occasions with plants under field conditions when the soil was extremely rich or when excess quantities of nitrOgen—carrying fertilizers had been used. The effect of these conditions on root growth -hl- is generally exactly Opposite to their effect on vegetative vigor of the parts above ground. The trees growing in the cultures in which no phOSphorus was supplied. formed only fairly good root systems and the treatment appear- ed more detrimental to the peach than to the apple. Particularly in the apple. the laterals were long and slender and.in both kinds of trees the develOpment of fibrous roots was poor. Russell(67) has pointed out that phosphorus is necessary for mitotic cell division and it appeared from the type of growth of roots in these cultures that cambial activity ceased relatively early where the external supply of phosphorus was lacking. Wallace (85) found that phosphorus starvation caused stunting of fruit tree roots and the cause for this appears to be lack of starch transfor- mation. The starch forms satisfactorily in the absence of phosphorus but is not changed to sugars. It was pointed out earlier in this discussion that the vegeta- tive growth of peach trees was evidently seriously affected by the lack of an adequate phosphorus supply and now it appears from the studies of root growth in peach trees that this portion of the plant is likewise seriously checked when phosphorus becomes limited. The effect of this treatment on both tOp and root growth was more detrimental to the peach than to the apple. When the phosphorus supply was doubled. the roots of all trees made good growth but it seems likely that the amount of phosphorus used in these solutions was more than was actually necessary for adequate and perhaps even for maximum growth. 442- PhotOgraphs of the root systems of all trees are shown in later pages. The tissues of all trees were analyzed for soluble nitrogen and phosphate phosphorus at the time they were set in the Jars and again in late summer. The first analyses were made from a portion cut from the t0p of each shoot which was growth of the previous year. Later in the summer. the upper third of one of the main sheets at the tap of each tree was analyzed in the same way. The procedure used for the determina- tions is described in another publication (87). The results are given in table 11. m BWUHQ HHe remand :. om spews man woman «Home meomwnm we mean ocwdcnoa mowsdwo sweeomoo wen promenade prompwouse an «no mamas. renew Hm. mun evooam. venom eon auwwpos ow «we amour «peace. l eeomn3m5« _ womww n 20 owaeommm H\: awesome: W m muauOMoo m 20 evomwnowdm H\: peomcnoufim mm evompwoufla use. ow some wseeae mesa. weeeam J1.»sm. sense _ sen. m_>eeae l eem. 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