WI‘IW'I 1 l I l (W IWIII‘IHI 144 943 THS WM. ERR "53 IuETH ZS F1231: a. ”571:: 4:“; ~ ‘1'!” 5"” 1?: d“; autos \NIJ‘IT5£EY 11:; 1} .. " i-.- .4 its» 52 2:. man. WATERING METHODS FOR CERTAIN ORNAMENTAL PLANTS By JOHN S. HARMAN A THESIS Submitted to the School of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1956 ABSTRACT This investigation was designed to compare surface irrigation and subirrigation of container-grown nursery stock out of doors over a period of eleven months. Comparisons were made of plant growth, time required to irrigate, and amount of water used. At the same time four types of pots were tested to determine their efficiency under'irrigation a'nd prevailing weather conditions. Pinus mugo Mgghus, Euonymus fortunei Vegetus, Taxus media Hicksi, Philadelphus coronarius Aurea, Clethra alnifolia, and Rosa hybrida cv. Else Poulsen because of their variety were selected for the irrigation trials. The containers tested were constructed of tar paper, tin, plastic, and heavy waxed paper. Plastic pots gave the best results, closely followed by the nursery cans. After three months the tar paper containers deteriorated rapidly and were not as permanent as the other types. The waxed Lily cups were of little value as plant containers after only four weeks. Wooden beds for surface irrigation and concrete beds for subirrigation were constructed to contain the potted plants. ii it. 1 ll "all. The amount of water used in subirrigation was 1.98 times greater than that used for surface irrigation. Surface-irrigated plots required almost twice as much time to water as did the subirrigated plots. Use of subirrigation repre- sented a large saving in labor. Maintenance for both plots was equal in amount of time consumed. Differences in plant growth between irrigation trials were small, unable to be observed visually, and not considered to be suf- ficiently different to be of great importance. The mortality rate of plants under subirrigation was higher than under surface irrigation. It was not believed that there was sufficient cause to preclude recommending the use of subirrigation for growing potted ornamental plants. Accompanied by two black and white figures and eleven tables. _M?.wafia\. iii [[[I’lllllll'l ACKNOWLEDGMENTS The author wishes to express his appreciation to Professor Donald P. Watson for his guidance and assistance. To Wenonah C. Harman for her encouragement and understanding; and to my sons, J. Craig and D. Kirk Harman, without whose absence this thesis could not have been written. iv TABLE OF CONTENTS PROCEDURE ................................. RESULTS ................................... Irrigation and Rainfall ........................ Evaluation of Four Types of Pots ................ Time Study ................................ Growth of Irrigated Plants ..................... DISCUSSION .................................. SUMMARY ................................... BIBLIOG RAPHY ............................... 16 16 18 22 22 29 31 33 LIST OF FIGURES Figure . Page I. Plan: Surface-Irrigation Bed ................ 10 II. Plan: Subirrigation Bed and Water Meter Installation ............................. ll TABLE LIST OF TABLES Amount of Water Supplied to Subirrigated and Surface-Irrigated Plots ................ Amount of Water and Time of Application to the Subirrigation and Surface-Irrigation Plots ............................... Inches of Rainfall Recorded at the Site of the Experiment and at the East Lansing Weather Station ......................... Time Required for Irrigation and Main- tenance ............................... Volume of Growth in Milliliters of Pinus mtigo Muhgus as Influenced by Surface Irrigation and Subirrigation, and Type of Container ............................. Volume of Growth in Milliliters of Euonymus fortunei Vegetus as Influenced by Surface Irrigation and Subirrigation, and Type of Container ............................. Volume of Growth in Milliliters of Taxus media Hicksi as Influenced by Surface Irrigation and Subirrigation, and Type of Container ............................. Volume of Growth in Milliliters of Philadelphus coronarius Aurea as Influenced by Surface Irrigation and Subirrigation, and Type of Container . . . . . . . ..................... vii Page 16 17 19 22 23 24 24 25 TABLE 10. 11. Page Volume of Growth in Milliliters of Clethra alnifolia as Influenced by Surface Irrigation and Subirrigation, and Type of Container . . ...... 26 Volume of Growth in Milliliters of All Living Plants in Surface-Irrigated and Subirrigated Plots ........ . .............. 27 Volume of Growth in Milliliters of Rosa hybrida cv. Else Poulsen as Influence by Surface Irrigation, Subirrigation, and Waxed Lily Cup Containers ................. 28 viii INTRODUCTION It has been observed that ineffective watering and faulty irri- gation represent a tremendous financial loss to the grower and re- tailer of healthy, vigorous plant materials. Skilled labor, required to prOperly maintain and water potted ornamental plants, is expensive and difficult to obtain. Consequently, nurserymen are searching for new methods which will decrease the amount of skilled labor required, and at the same time produce high quality plants. Production of various greenhouse crops using subirrigation has been successful (Ray and Kiplinger, 1944; Seeley and Post, 1950). It was theorized, therefore, that subirrigation could be ap- plied to the production of container-grown nursery cr0ps. The present investigation was designed to supply information relative to the feasibility of subirrigation as a commercially ac- cepted practice for potted nursery stock--to provide water utilization data for surface-irrigated and subirrigated plots of pot-grown orna- mental plants . REVIEW OF LITERATURE Clements (1934) pointed out that, since terrestrial plants deve10ped, they have been influenced by transpiration. They are dependent upon it to keep them in proper nutritional balance, after they become adapted to a given environment. When transpiration becomes too intense it may cause the death of the plant if nothing is done‘to the external factors which influence it. Transeau (1926) very clearly showed the magnitude of tran- spiration in his experiments with maize. He estimated that during the growing season 276 kg. of water were evaporated for every kilogram of dry weight produced. This is equal to sufficient water to cover an acre to a depth of fifteen inches. Variations in soil moisture have been shown to have a direct effect on tranSpiration (Yuncker, 1916). Using Zea Mays Hogues Yellow Dent, he found that the water requirement was decreased for plants growing in dry soils and increased for plants in moist soils. The growth rate of plants, on the moist soils was very rapid, with a high transpiration rate accounting for a greater water requirement. These findings were supported by Heinicke and Childers (1935) on Malus Sp. 3 Briggs and Shantz (1916) observed wind, radiation, and water to be interrelated in their effects on transPiration rate of plants. Over a ten-day period it was found that some of the small grains lost twelve to sixteen times their dry weight through transpiration. Some annual crops, during this same period, transpired one-fourth of all the water lost through the entire growing season. Finnell (1928) found that Tagetes Sp. plants, when exposed to wind over a period of sixty days, doubled their water requirements. Prevailing weather conditions and their effects on water requirements played an important role in the use of supplementary irrigation. Soil .moisture has been shown to be directly related to plant growth and deve10pment. Furr and Magness (1930) concluded that Malus sp. can function at near the maximum rate as long as the moisture content of the entire root zone is appreciably above the wilting percentage. A restricted root zone gave a more pronounced reaction to reduced moisture supply. Veihmyer (1927) and Veihmeyer and Hendrickson (1927), using orchard crops, agreed with the fore- going observations. Veihmeyer (1927) pointed out that as long as soil moisture was maintained above the wilting point there would be little increase in production by addition of water and bringing the soil to field capacity. 4 He concluded that capillary movement of water laterally was slow and not effective in distributing water evenly throughout the soil. He suggested, therefore, that in order to reach the desired moisture content the entire area must be irrigated. Working with dwarf PLrus communis, Barss (1930) observed that an abundance of water was accompanied by increase in all types of vegetative growth and in the length of the growing season, with emphasis being placed on the relationship of the physical condition of the soil and the supply of available nutrients to water require- ments. Khankoje (1914) demonstrated some of the factors which influ- ence water requirements of plants. Using various small grains, legumes, and vegetables, he found that type of cr0p, soil fertility, age of plants, and the amount of moisture in the soil were directly related to water requirement. Briggs and Shantz (1914) reported that light intensity, temperature, and wind also influenced water requirements of plants. Their work indicated that varieties within a given crop varied widely in water requirements; that strains could be developed to make more efficient use of water in dry regions. Soil type and water requirements of a plant must be consid- ered in determining irrigation procedures. Powers (1920) found that coarser soils required more water, had a low water-holding lllll! . I! . :ul‘ .... Ill-Ill" capacity, and a comparatively low amount of surface area, pore Space, and organic matter. Therefore, more frequent irrigation was required. Timing of irrigation was important, and when the soil mois- ture reached a given point, irrigation substantially increased yields. High soil fertility decreased water requirements of the plants, and over a twelve-year period saved much water in irrigation. Subirrigation, a specialized system of supplying water to plants from beneath, has been used in greenhouse culture and to a lesser extent for field irrigation. Renfro (1955) found that sub- irrigation of field crops by raising the water table increased the concentration of salts in the soil surface. When adequate under- drainage was maintained, however, rains tended to wash much of the surface accumulation downward. Stephan and Kiplinger (1944) supported this point with plants grown under glass. Occasional surface watering overcame salt accumulation. Van Loan (1950) grew Dianthus Sp. under surface irrigation, automatic injection, and constant -level subirrigation. Both subirri- gation plots produced greater total plant growth and better quality blossoms. Surface watering tended to destroy soil aggregation faster than subirrigati on. Seeley and Post (1950), comparing surface and subirrigation methods, found no significant difference in Rosa Sp. production. Stem length was good in plots watered by both systems. Houston and Chadwick (1947) rooted cuttings of Rosa hybrida Better Times and Taxus cuspidata under overhead irrigation, hand, and constant-level subirrigation. Rosa hybrida Better Times rooted best under the overhead irrigation, while there appeared to be little difference in the rooting of Taxus cuspidata in all of the plots. Sub- irrigation by hand appeared to be most favorable of the subirrigation treatments. Kofranek and Fischer (1949) revealed no significant difference between surface irrigation, automatic injection, and constant-level subirrigation in bottom break production of Rosa sp. in benches. Withrow and Biebel (1936) prOposed a method of supplying nutrient solutions to plants by means of subirrigation. It consisted, in principle, of pumping nutrients from a submerged reservoir into the bottom of a shallow bed of fine gravel or cinders with a centrifu- gal pump. Once the bench was flooded the solution was allowed to flow back into the reservoir. This system had the advantage of frequent and complete flushing of the roots with air and nutrient solution, economy of nutrients, and completely automatic Operation over a long period of time. Seed plots of Aster sp. and Apium Sp. were subirrigated by Jones (1943). Less frequent watering, uniformly moist soil, and better germination resulted. The seeds did not wash or move around in the flats, and could be fertilized without injuring the newly germi- nated seedlings. Stephens and Volz (1948), subirrigating Mathiola Sp. and Callistephus chinensis, pointed out that soils high in organic mat- ter content indirectly accounted for better areation and counteracted extreme wetness by beneficially affecting porosity and structure of the soil. Soil studies with subirrigation in the greenhouse by Ray and Kiplinger (1944) demonstrated some interesting relationships with reSpect to soil drying. They found that a light soil dried more rapidly on the dark days of winter. This type of soil did not com- pact, and any accumulation of salts at the soil surface was readily corrected by means of overhead watering. Cook _e_t_a_l_. (1953) emphasized some of the factors which affect constant-level subirrigation. Two soils, Oshtemo sandy loam and well-aggregated Brookston clay loam, were used to grow Anti:- rhinum Sp. Plants produced the highest quality blooms when grown in sandy loam twenty-one inches deep or nine inches of clay loam. It was concluded that the water in sandy loam rose so rapidly that 8 a more shallow soil would have an excessively high water-air ratio. The capillary rise in the clay loam was slower, which permitted a ,more shallow soil depth. More extensive experiments on subirrigation as a commercial practice have been carried out to more fully evaluate its possibilities, because of reduced labor. Post (1939) concluded that it was much more economical to subirrigate in a commercial greenhouse. Uniform drying of the soil balls, practically no root growth through the holes in the pots, and a decrease in frequency of watering of the subirrigated plots pointed toward a sound commercial practice. Further experiments by Post (1940) resulted in the following advantages of subirrigation: soil did not compact and decrease areation, foliage was not wet after watering, fertilizer was not lost in the drainage water, mechanical injury to foliage was eliminated, and subirrigation aided in preventing spread of leaf diseases. The work of Jones (1943) and Van Loan and Cook (1950) concur with Post and lend further support to subirrigation as a commercial practice. .i ‘7} l' 1!! Mal-.1 E III. 1" i PROCEDURE Because of labor requirements, high cost of operation, and desire for good quality of plant growth, a project was designed to compare two systems of irrigation: hand watering on the surface of the soil in pots (surface irrigation), and automatic watering of plants from beneath (subirrigation). The experiment began July 30, 1955, and was discontinued June 30, 1956. All procedures were handled according to accepted nursery practices. For comparison of the two methods of watering, the amount of plant growth and the amount of labor required for main- taining the experimental plots were recorded. Two surface irrigation beds were constructed of 2 x 4 and 2 x 8 inch lumber bolted together. The completed beds measured 6-1/2 feet by 9 feet by 8 inches (Figure I). Two subirrigation beds, measuring 6-1/2 feet by 9 feet by 3-1/2 inches (Figure 11) were constructed of concrete. A one-inch depth of pea gravel was placed on the bottom of each bed to allow for drainage of both irrigation and rain water. Each subirrigation bed was equipped with a drain which facili- tated rapid removal of water after the soil in the pots was sufficiently -—PEA 10 2X8 LUMBER g/ZX 4 LUMBER GRAVEL PERSPECTIVE FIGLRE I PLAN: SURFACE IRRIGATION BED n- 3%“ —' PEA GRAVEL CONCRETE 9‘ 3" - r" DRAIN L I / ' .L 6%" ‘— METER OUTLET WATER gm: LIL T 'l 11-— PERSPECTIVE Q FIGURE]! PLAN: SUBIRRIGATION BED AND WATER RETER INSALLATION ll 12 moist. These drains remained open at all times, except when the plants were being irrigated, eliminating the hazard of water stand- ing beneath the pots. A water meter which registered 0.10 gallon was set up at the water outlet to record the amount of water used on the plants (Figure II). During the winter months the meter was stored, and prior to its reinstallation in the spring it was calibrated to insure maximum accuracy. The meter was designed so that variations in water pressure did not affect its efficiency. Rainfall at the experimental site was recorded by a standard rain gauge. This was compared to the rainfall recorded by the East Lansing weather station and a record was obtained of the amount of water received by the plants through both irrigation and rainfall. Four types of pots, 8 inches in diameter, were used during the experiment: tar paper, tin, plastic, and heavy waxed paper. The waxed paper pots were used for one month; other pots were placed in the plots and subjected to the prevailing outdoor conditions for the entire eleven months. The pots were examined weekly and observations relating to their durability, water-holding capacity, and physical appearance were listed. 13 The following plants, because of their variety, were selected for the irrigation trials: Pinus migro Mughus, Euonymus fortunei _ Y_e_g§tus, Taxus media Hicksi, Philadelphus coronarius Aurea, Clethra alnifolia, and Rosa hybrida cv. Else Poulsen. All plants were potted using the standard Michigan State soil mix. The soil components were: “two parts soil [Clay loam], one part sharp sand, and one part German Peat. The fertilizer components were two parts ‘Hoof and Horn,‘ two parts Super Phos- phate, and one part Potassium Sulphate, Widmoyer (1955)." The soil was partially mixed by hand, and then put through a soil shred- der to insure uniformity. Fertilizer was added as the soil was placed in the shredder using two pounds of fertilizer in four bushels of soil mix. Potted plants to be irrigated were placed in the beds and spaced according to size and spread of the branches. As plant size increased, the pots were rearranged to give maximum benefit from sun and rainfall. A heavy mulch of leaf mold was employed during the winter months for protection from the frost and wind. Labor required to maintain and water each plot was recorded and used for further comparison of surface irrigation and subirrigation. In order to measure labor requirements, maintenance and watering were recorded separately. The watering consisted of only those 14 operations pertaining to the actual placing of water on the plants. Maintenance involved weeding, arranging of plants, mulching, fertil- izing, and minor repairs. A stainless steel coffee urn was fitted by firmly cementing a glass titration tube with waterproof putty in place of the glass water gauge. This tube was graduated in 0.10 mls. to indicate the level of the liquid in the urn. The urn was rinsed thoroughly to remove all foreign materials and partially filled with clean tap water, to which was added one-half teaSponfull of detergent per gallon, in order to reduce the surface tension and eliminate the accumulation of air bubbles on the plant surfaces. The level of the solution in the urn was adjusted to accom- modate the plant. To measure the volume of the plants, each plant was marked with an oil base paint on the stem, inverted, and im- mersed in the water to this mark. It was necessary to keep the plants from coming in contact with the sides or bottom of the urn. The level of the water in the titration tube was recorded before the plants were dipped. After the plants were submerged the read- ing on the tube was recorded. Following this second reading the plant was removed and the original reading rechecked before sub- merging the next plant, because some water remained on the plant surfaces and altered the original water level in the urn. 15 During the entire process of measuring, it was found to be important to keep the water completely free of any foreign material. Debris tended to decrease accuracy of the determinations, and blocked the pipe between the urn and the meter. One person was required to dip the plant and a second per- son to take the readings, especially when measuring large plants which were bulky and difficult to handle. All plants were measured at the beginning and at the close of the experiment. A period of eleven months separated the initial and final measurements. Through the use of the water displacement method, increases or decreases in growth were obtained for each plant in the experiment. RESULTS Irrigation and Rainfall The total gallons of water received by the surface-irrigated and subirrigated plots over the eleven-month period is shown in Table 1. Water applied to the subirrigated beds exceeded that used on the surface-irrigated beds by 888 gallons. TABLE 1 AMOUNT OF WATER SUPPLIED TO SUBIRRIGATED AND SURFACE-IRRIGATED PLOTS (gallons for each plot of ninety plants: eleven months) H20 Rainfalla Total Type of Irrigation (gallons) (gallons) (gallons) Subirrigation . . . .’ ........... 1,793 207.90 2,000.90 Surface-irrigation plot ......... 905 207.90 1 ,112.90 a Estimated gallons based on 10.60 inches at the site. The amount of irrigation water received by both plots is presented in Table 2. Variations in quantity of water applied to the surface-irrigated plots resulted from selective watering. The plants were examined individually, and those which appeared to be dry were 16 AMOUNT OF WATER AND TIME OF APPLICATION TO THE TABLE 2 SUBIRRIGATION AND SURFACE-IRRIGATION PLOTS l7 T Surface Irrigation Subirrigation Date Gallons Date Gallons 7-11-55 59 7-11-55 94 7-17-55 51 7-13-55 126 7-22-55 34 7-17-55 136 7-29-55 7 7-22-55 113 8- 1-55 38 7-31-55 153 8- 3—55 41 8- 3-55 118 8- 4-55 43 8- 9—55 135 8- 9-55 49 8-19-55 109 8-19-55 37 8-26-55 74 8-23-55 21 9- 2-55 66 8-25-55 30 9- 8-55 61 9- 1-55 33 9-18-55 107 9- 5-55 34 9-22-55 64 9- 8-55 33 5-28-56 70 9-11-55 36 6- 3-56 116 9-18-55 43 6-10-56 96 9-22-55 39 6-13-56 70 5-28-56 48 6-22-56 85 6- 3-56 37 6-10-56 39 6-13-56 41 6-17-56 38 6-22-56 34 6-30-56 40 Total 905 Total 1 ,793 18 watered. Soil in the subirrigated pots dried more uniformly and at a slower rate than did those which were surface-irrigated, de- creasing the frequency of watering. Variations in the amount of water applied to the subirrigated plots resulted from the practice of filling the irrigation beds to different depths. There appeared to be no difference in the rate of water uptake by the soil as a result of different water depths in the irrigation bed. Rainfall at. the experimental site and the East Lansing weather station (Table 3) revealed minor differences. Evaluation of Four Types of Pots New tar paper pots were satisfactory as plant containers, under both types of irrigation, during the first three months of this investigation. Following this period, however, the effects of water became apparent. The bottoms of some pots began to break apart, causing the soil to be released into the irrigation beds. The heavy- duty staples used in their construction tended to work loose, per- mitting the sides to separate. The tar paper developed a water- soaked appearance and remained damp for long periods after an application of water. Once the tar paper pots became weakened they were difficult to handle without breaking apart. During the experiment some of the containers had to be replaced. Illi'll TABLE 3 INCHES OF RAINFALL RECORDED AT THE SITE OF THE EXPERIMENT AND AT THE EAST LANSING WEATHER STATION Site of East Lansing Date 1 Experiment Weather Station (inches) (inches) 7- 1-55 0.45 0.44 7- 2-55 0.13 0.15 7- 4-55 0.03 0.07 7- 8-55 0.05 0.08 7- 9-55 0.41 0.41 7-15-55 2.40 2.23 7-16-55 0.11 0.13 7-27-55 0.48 0.48 8- 3-55 0.22 0.42 8-14-55 0.59 0.50 8-23-55 0.35 0.44 8-27-55 0.30 0.18 8-29-55 0.31 0.31 8-30-55 1.03 1.23 9-10-55 1.07 0.04 9-23-55 1.00 0.92 9-27-55 0.25 0.15 10- 6-55 1.30 1.00 10- 7-55 0.72 0.66 5-20-56 0.02 0.01 5-22-56 0.25 0.10 5-26-56 0.13 0.13 5-27-56 0.02 0.01 5-29-56 0.03 0.03 Total 10.60 10.12 20 Moisture retention by the soil in the tar paper pots was comparable to that of the other types of containers until the pots began to deteriorate. Under surface irrigation these pots allowed water to leak out before a sufficient amount was taken up by the soil. As a result, the soil dried out rapidly and required more frequent irrigation. Those plants under subirrigation remained moist longer because the water standing in the beds was taken directly into the soil through the holes in the weakened containers. Rooting through the tar paper in the surface-irrigated beds was profuse, and increased as they weakened. The amount of root growth in the subirrigated trials was small, with the exception of those pots where the bottoms had broken open. When the tar paper pots were mulched during the winter, mice knawed holes through the tar paper and chewed the roots of the plants. Rodent injury was so extensive that it resulted in the death of 16.66 percent of all the plants in tar paper containers. Nursery cans showed only slight effects from exposure to prevailing weather conditions and irrigation water, but loose joints appeared in 25 percent of all the cans used in this experiment. Repeated moving of the cans caused the joints at the sides of the pots to loosen, allowing some of the surface irrigation water to drain out before it was taken up by the soil. Under subirrigation, 1 I1 ll. I‘IIIV 11.1 Ill 1! I] II" I". .II III. All]! all 21 water uptake was not altered by the loose joints since the water was taken directly into the soil through perforations in the con- tainers. The nursery cans were in good condition after eleven months. No rodent damage was found; special handling was not required. Roots grew through the perforations at the base of the cans under surface irrigation, but this condition was confined to only two cans in the subirrigation trials. Plastic pots were the most satisfactory of the plant containers used, and at the end of the eleven-month period were in excellent condition. Constant moving had no effect on them; rodent damage was not present. The soil in these pots appeared to retain moisture for longer periods. Slight rooting through the drainage holes in the pots was found in the surface-irrigated plots, but none appeared in the subirrigation plots. Waxed Lily cups containing Rosa Sp. plants were placed in the irrigation trials for the final four weeks of the investigation. These cups, constructed of heavy wax-coated paper, were in very poor condition after the four-week period. They had become badly water soaked, resulting in torn or split containers. A large number of roots grew through the bottoms of the cups in the surface- irrigated beds, while only a few were found: in the subirrigated trials. lilvilll 1'! ill. III-"I'll. III Juli l I 22 Time Study The total amount of time required for watering and maintain- ing the irrigation plots is contained in Table 4. Watering time of the subirrigated plots was substantially less than that of the surface- irrigated plots. Time spent in maintenance of both plots was equal. TABLE 4 TIME REQUIRED FOR IRRIGATION AND MAINTENANCE (ninety plants per treatment; four months) f a . Watering Maintenance Total T ype 0f Irrigation (hours) (hours) (hours Subi rrigation .......... 3 .2 3 5.08 8 . 31 Surface irrigation ....... 6.1 6 5.08 1 1 .24 4 IL 8‘Weeding, fertilizing, and Spraying. Growth of Irrigated Plants The growth of Pinus mpgo Muhgus in both subirrigated and surface-irrigated plots (Table 5) was variable. Plants grown in tar paper and plastic pots in the subirrigated plots showed a de- crease in growth, while those plants grown in nursery cans increased in size. The decrease in growth was directly attributed to serious rodent damage which occurred during the winter months. 23 TABLE 5 VOLUME OF GROWTH IN MILLILITERS OF PINUS MUGO MUHGUS AS INFLUENCED BY SURFACE IRRIGATION AND SUBIRRIGATION, AND TYPE OF CONTAINER J l. Subirrigation Surface Irrigation Type of Pot Original Final Original Final Tar paper . . ......... 0.750 0.367 0.530 0.530 Nursery cans ......... 0.423 0.567 0.480 0.700 Plastic ............. 1.10 1.00 0.642 0.750 Note: All figures expressed as average milliliters displace- ment for six plants. Plants of Pinus mugo Muhgus in nursery cans and plastic pots under surface irrigation increased in size, while the growth of those in tar paper pots remained constant. Minor damage by rodents was found on the plants potted in the tar paper containers. Euonymus fortunei V_egetus, as Shown in Table 6, increased in size with no great difference between treatment or type of pot. Increase in size of Taxus media Hicksi (Table 7) showed a Slight variation throughout all treatments. The growth of the surface- irrigated plants was somewhat less than those under subirrigation. IIIIII‘IIIIIIIIIIIIIIII liil‘l II IIIIIIII.‘ El 24 TABLE 6 VOLUME OF GROWTH IN MILLILITERS OF EUONYMUS FORTUNEI VEGETUS AS INFLUENCED BY SURFACE IRRIGATION AND SUBIRRIGATION, AND TYPE OF CONTAINER Subirrigation Surface Irrigation Type of Pot Original Final Original Final Tar paper ........... 0.070 0.170 0.080 0.130 Nursery cans ......... 0.050 0.137 0.062 0.112 Plastic ............. 0.060 0.170 0.050 0.116 -—: Note: All figures expressed as average milliliters diSplace- ment for six plants. TABLE 7 VOLUME OF GROWTH IN MILLILITERS OF TAXUS MEDIA HICKSI AS INFLUENCED BY SURFACE IRRIGATION AND SUB- IRRIGATION, AND TYPE OF CONTAINER 1 Subirrigation Surface Irrigation Type of Pot Original Final Original Final Tar paper ........... 0.100 0.283 0.241 0.308 Nursery cans ......... 0.162 0.225 0.200 0.275 Plastic ............. 0.150 0.283 0.083 0.250 —__ 1 Note: All figures expressed as average milliliters diSplace- ment for six plants. 25 Volume of growth of Philadelphus coronarius Aurea, as shown in Table 8, increased in both the subirrigated and surface- irrigated plots, with no obvious difference between treatments. TABLE 8 VOLUME OF GROWTH IN MILLILITERS OF PHILADELPHUS CORONARIUS AUREA AS INFLUENCED BY SURFACE IRRIGATION AND SUBIRRIGATION, AND - TYPE OF CONTAINER Subirrigation Surface Irrigation Type of Pot Original Final Original Final Tar paper ........... 0.125 0.250 0.062 0.187 Nursery cans ......... 0.066 0.400 0.058 0.325 Plastic ............. 0.062 0.150 0.070 0.200 Note: All figures expressed as average milliliters displace- ment for six plants. Subirrigated and surface-irrigated plants of Clethra alnifolia (Table 9) increased in size, but there was slight difference between plots. Three inches of all terminals of these plants winter killed, causing a decrease in the total amount of growth. The slight differences in growth between treatments for all Six species tested (Table 10) was minimized because of the high mortality rate among plants grown in the subirrigated trials, as 26 TABLE 9 VOLUME OF GROWTH IN MILLILITERS OF CLETHRA ALNIFOLIA AS INFLUENCED BY SURFACE IRRIGATION AND SUB- IRRIGATION, AND TYPE OF CONTAINER T fi Subirrigation Surface Irrigation Type of Pot Original Final Original Final Tar paper ........... 0.050 0.134 0.050 0.133 Nursery cans ......... 0.050 0.150 0.050 0.170 Plastic ............. 0.050 0.116 0.050 0.166 Note: All figures expressed as average milliliters diSplace- ment for six plants. compared to those under surface irrigation, with the exception of Euonymus fortunei Vegetus. Damage from mice and rabbits appeared on all dead plants except for five Pinus mugo Muhpgpp. Growth of Rosa hybrida cv. Else Poulsen (Table 11) devel- oped uniformly with little variation between irrigation plots. These plants were not subjected to winter conditions and therefore a valid comparison cannot be made. TABLE 1 0 27 VOLUME OF GROWTH IN NIILLILITERS OF ALL LIVING PLANTS IN SURFACE-IRRIGATED AND SUBIRRIGATED PLOTS (eleven months) I Subirri ation Surface No. Of a g Irrigation Plants Lost Varieties Sur- Ori Or' Sub- fa , 3' Final , 13' Final irri- °,e lnal lnal , rri- gatlon , gation Pinus mugp Mughus ....... 0.660 0.543 0.550 0.660 11 3 Euonymus fortunei Vegetus ....... 0.060 0.160 0.058 0.116 4 6 Taxus media Hicksi ........ 0.134 0.268 0.175 0.277 2 0 Philadelphus coronarius Aurea ........ 0.086 0.254 0.063 0.260 7 3 Clethra alnifolia . . . 0.050 0.132 0.050 0.153 8 1 -—1 r F ’— aThose plants which died as a result of irrigation procedure and those damaged or killed by rodents. Note: All figures expressed as average milliliters diSplace- ment for from seven to eighteen plants. 28 TABLE 11 VOLUME OF GROWTH IN MILLILITERS OF ROSA HYBRIDA CV. ELSE POULSEN AS INFLUENCED BY SURFACE IRRIGATION, SUBIRRIGATION. AND WAXED LILY CUP CONTAINERS Subirrigation Surface Irrigation No. of Plants Lost Sub- Surface Original Final Original Final _ , , , , 1 rrl gation Irrigation 0.072 0.192 0.075 0.204 1 0 DISCUSSION The subirrigated plots received a total of 1.98 times as much water as the surface-irrigated plots. Some of this water was drained away from the subirrigation beds after the soil in the pots had been sufficiently moistened. In commercial practice this water could be drained into a reservoir and used for future irrigation. Withrow and Biebel (1946) describe a reservoir for this purpose. There is no way to reuse water placed on surface-irrigated beds. There was no apparent difference between plant growth of the subirrigated and surface-irrigated plots. This conclusion agrees with the work of Seeley and Post (1950), and Kofranek and Fischer (1949). Subirrigation decreased watering time by almost half that of ‘ surface irrigation, and frequency of watering was less. These findings agree with the work of Post (1940), Ray and Kiplinger (1944), Jones (1943), and Post (1939). The need for skilled labor in watering potted nursery stock might be eliminated by the use of subirriga- tion. At the sametime the plots are being filled, weeding, spacing, fertilizing, and spraying can be accomplished. It is necessary to Z9 30 treat the maintenance and watering operations of surface-irrigated plots as separate tasks. Although tar paper and waxed paper pots proved least satis- factory over an eleven-month period, they were adequate for periods up to three months under either type of irrigation. Plants might be held in nursery cans for an extended period of time as water and changing weather conditions had little effect on them. This container could be recommended for use in surface or subirrigation beds. The plastic pot was excellent for both types of outdoor irriga- tion trials; the pots were attractive and easily removed. The subirrigated plants in this experiment seemed to be more susceptible to rodent injury than those under surface irrigation. A protective program against these pests would overcome this source of damage. SUMMARY This investigation was designed to compare surface irrigation and subirrigation of container-grown nursery stock, out of doors, over a period of eleven months. Comparisons were made of plant growth, time required to irrigate, and amount of water used. At the same'time, four pots were tested to determine their efficiency under irrigation and prevailing weather conditions. Pinus muigo Mughus, Euonymus fortunei Vpgptus, Taxus media Hicksi, Philadelphus coronarius Aurea, Clethra alnifolia, and Rosa hybrida cv. Else Poulsen because of their variety were selected for the irrigation trials. The containers tested were constructed of tar paper, tin, plastic, and heavy waxed paper. Plastic pots gave the best results, closely followed by the nursery cans. After three months, the tar paper containers deteriorated rapidly and were not as permanent as the other types. The waxed Lily cups were of little value as plant containers after only four weeks. Wooden beds for surface irrigation and concrete beds for subirrigation were constructed to contain the potted plants. 31 32 The amount of water used in the subirrigation was 1.98 times greater than that used for surface irrigation. Surface-irrigated plots required almost twice as much time to water as did the subirrigated plots. Use of subirrigation repre- sented a large saving in labor. Maintenance for both plots was equal in amount of time consumed. Differences in plant growth between irrigation trials were small, unable to be observed visually, and not considered to be sufficiently different to be of great importance. The mortality rate of plants under subirrigation was higher than under surface irrigation. It was not believed that there was sufficient cause to preclude recommending the use of subirrigation for growing potted ornamental plants. BIBLIOG RAPHY Barss, Alden F. 1930. Effect of moisture supply on develOpment of gyms communis. Bot. Gaz. 90: 151-177. Briggs, Lyman J., and H. L. Shantz. 1914. Relative water require- ment of plants. Jour. Agr. Res. 3: 1-65. 1916. Daily transpiration during the normal growth period and its correlation with the weather. Jour. Agr. Res. 7: 155-213. Clements, Harry F. 1934. Significance of transpiration. Plant Physiol. 9: 165-172. Cook, R. L., A. E. Erickson, and P. R. Krone. 1953. Soil factors affecting constant water level sub-irrigation. Proc. Amer. Soc. Hort. Sci. 62:491-496. Finnell, H. H. 1928. Effect of wind on plant growth. Jour. Amer. Doc. Agron. 20: 1206-1210. Furr, J. R., and J. R. Magness. 1930. 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