IIIIIIIIIIII IIIIIII IIII IIIIII L. 32101 7734 LIBRARY Michigan State University This is to certify that the thesis entitled The effects of Soil Density on Prunus Root Systems. presented by Reginald Nhamodzavo Mandoga has been accepted towards fulfillment of the requirements for MS degree in HURT . 7753/ J". (:1; 'vi / Major professor Date //A Go 3 / / 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution ___~ _.._‘ ”Aw ""—"- — MSU LIBRARIES . RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. EFFECTS OF SOIL DENSITY ON PRUNUS ROOT SYSTEMS. BY Reginald Nhamodzavo Mandoga A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1987 ABSTRACT THE EFFECTS OF SOIL DENSITY ON PRUNUS ROOT SYSTEMS by Reginald Nhamodzavo Mandoga Four Prunus rootstocks g; mahaleb seedling, MxMZ (g; mahaleb x g; avium), GI 148-9 (3; avium x g; canescens and CF 677 (g; persica x’ g; amygdalus) were grown in containers at 3 soil density levels (1.0, 1.3 and 1.7g/cc). At the highest soil density level, GF 677 had the greatest total root length and root penetration ratio and MxMZ had the greatest propensity to form a shallow root system. Soil matrix ethylene increased with soil density. Mahaleb was associated with the highest concentration of soil matrix ethylene and GF 677 with the least. There was an inverse relationship between soil matrix ethylene and total root length. Root penetration ratio increased with increase in hydraulic conductivity. Soil compaction significantly reduced Montmorency scion performance and the degree of reduction in scion performance was greatly dependent on rootstock type. Montmorency/ Mazzard out performed Montmorency/Mahaleb. Dedicated to My Mother and Father whose support for my education over the years has created an atmosphere whereby acquisition of knowledge to me has become a desire rather than a task. 11 ACKNOWLEDGEMENTS I wish to express my appreciation to the members of my committee, Dr. R.L. Perry, Dr. J. Flore, Dr. J.A. Smucker and Dr. F. Pierce for their advice and support. I am also grateful to Mr. C. Edson for his technical help. Finally, I wish to express special thanks to my wife Jennifer and son Fadzi for their unfailing patience and encouragement. iii LIST OF TABLES . LIST OF FIGURES INTRODUCTION . . EFFECTS OF SOIL DENSITY TABLE OF CONTENTS SECTION ON ROOT GROWN PRUNUS ROOTSTOCKS . . . Abstract . . . Literature Review Materials and Methods Results . . . Discussion . . Literature Cited THE EFFECTS OF ABIOTIC AND BIOTIC ROOT SYSTEM AND SOIL MATRIX Abstract . . . Literature Review . Materials and Methods Results . . . . Discussion . . Literature Cited THE EFFECTS SOIL COMPACTION THE SCION . . . Abstract . . . Literature Review . Materials and Methods Results . . . Discussion . . Literture Cited 1 GROWTH OF SECTION II SECTION III vi SOIL FACTORS ON ETHYLENE PRODUCTION . . ROOTSTOCK CONTAINER TYPE ON Page .viii 18 19 20 23 27 34 37 MAHALEB 39 4O 41 43 47 53 56 58 59 60 61 66 76 79 SECTION IV THE EFFECTS OF ARTIFICIALLY COMPACTED SOIL AND NATURALLY DENSE SOIL ON MONTMORENCY/ P.MAHALEB. . Abstract . . . . . . . Literature Review . . Materials and Methods Results . . . . . . Discussion . . . . . . Literature Cited . . . 82 83 84 87 90 94 96 LIST OF TABLES Table Page SECTION I 1. Effect of soil density levels on 4 Prunus rootstocks grown in containers . . . . . . . . 29 2. Mean total root length of four container grown Prunus rootstocks grown under various levels of mechanical impedance . . . . . . . . . . . . 30 3. Mean RPR of four container grown Prunus rootstocks grown under various levels of mechanical impedance . . . . . . . . . . . . . 31 SECTION II 1. Analysis of variance . . . . . . . . . . . . . 49 2. Effect of soil density on root dry weight and rooting density of P; mahaleb rootstock . . 50 3. Effect of Pythium and Phytgphthora on rooting density of g; mahaleb rootstock . . 51 SECTION III 1. Average shoot ethylene production (ppm) per 1000 cc of space . . . . . . . . . . . . . . . . . . 68 2. Average soil tension (Kpa) before each watering O O O O O O I O O O O O O O O O O O 68 3. Analysis of variance . . . . . . . . . . . . . 69 4. Effect of soil density level on Montmorency sour cherry growth measurements . . . . . . . . 70 5. Effect of rootstock on Montmorency sour cherry growth measurements . . . . . . . . . . . . . 71 6. Mean root penetration ratio of two rootstocks under two levels of soil density . . . . . . . 72 7. Mean root count above and below the compacted zone 0 I O O O O O O O I I O O O O O I O O O O 73 SECTION IV 1. The effect of artificially compacted soil and naturally compated soil on RPR . . . . . . . . . 93 APPENDIX A1. Mean root count of 4 Prunus root system above and below soil layer compacted to 1.7 g/Cc BD 0 O O O O O O O O O O O O O O O O O O O 98 vii LIST OF FIGURES Figure SECTION I Experimental layered soil containers . . . Soil matrix ethylene levels for 4 Prunus rootstocks at 1.7g/cc BD . . . . . . . . . The relationship between soil matrix ethylene and total root length . . . . . . SECTION II Experimental layered soil container . . . . Cumulative soil matrix ethylene over a 10 week periOd O O O O O O O O I O O O O O O 0 SECTION III Experimental layered soil containers . . . Effect of soil bulk density and rootstock on leaf area and stem diameter of Montmorency sour cherry . . . . . . . . . . Effect of soil density and rootstock on shoot dry weight of Montmorency sour cherry . SECTION IV The relationship between root penetration ratio and hydraulic conductivty . . . . . . . . . . Comparison of hydraulic conductivity under field and controlled environment . . . . . . viii Page 24 32 33 45 52 64 74 75 91 92 INTRODUCTION Prunus root systems differ greatly in their tolerance to biotic and abiotic factors. Overall performance of a tree, that is vigor, productivity and longevity is heavily influenced by the innate level of tolerance to these factors. The root system of P; Mahaleb is highly sensitive to anaerobic and dense soil conditions, Phytophthora and Pythium root rots. Also many sweet cherry scion varieties are incompartible with P.Mahaleb. Trees on Mazzard are less productive and susceptible to crown gall (51). Studies under controlled environment have shown that Mazzard is slightly tolerant to anaerobic conditions than Mahaleb (10). In general among the Prunus species, plum root system has the greatest tolerance to wet, dense soil conditions. Peach has a low tolerance but better than Mazzard and hybrids between peach and almond have higher tolerance than peach (63). Trees on root systems that are sensitive to wet, dense soil conditions, do not perform well in soils which have any one of the following physical limitations; fragipan, compacted zone or perched water table. Any one or a combination of these conditions is common in many soils in Michigan. Consequently, variable tree health within an orchard site may be directly related to variable soil profile characteristics. Wet soil conditions are also thought to be conducive to Phytophthora and Pythium root rots diseases. As a result of these soil problems in some stone fruit growing areas in Michigan, research directed at elucidating the effects of soil physical limitations on Prunus root system is in progress and part of the. work done the last two years is reported in this thesis. LITERATURE REVIEW Plants require that water, nutrients, oxygen and space for roots to grow be available in the soil and that accumulation of toxic substances be avoided if maximum production is to be attained. The soil's physical suitability for crop production depends on the characteristics of its pore system. The pore system can be affected by the arrangement of particles or pedons. Soil pressed together resulting in high density is termed compacted (25). This concept includes not only the densification of soil but also the progressive decrease in permeability to gaseous exchange and water, additionally, soil thermal relations are altered and mechanical strength is increased. Plants growing in the soil must be able to overcome the physical resistance they encounter. In order to achieve this, they need adequate supply of plant nutrients and a proper chemical balance, an adequate exchange of oxygen and carbon dioxide, and an adequate supply of soil moisture. The ability of the plant to find space or force its way into the soil is often the most important factor limiting plant growth. In compacted soils, the roots are usually larger than soil pores through which they are supposed to grow. Roots must force their way into the soil and hence can only grow in soils that are compressible. They will rarely enter light textured soils if its bulk density (BD) exceeds 1.7-1.8g/cc or a heavy textured soil if BD exceeds 1.5—1.6 (9). Roots grow in the soil when new cells are formed and the turgor pressure inside these cells is sufficient to overcome the constraint of the cell walls (15) and any external constraint caused by surrounding soil matrix. The difference between turgor pressure and cell wall constraint is called root growth pressure (24 ). The root growth pressure must be greater than the impedance acting on the cross section of the root if it is to grow. As the degree of external impedance increases, the roots become shorter and much thicker (60). Many researchers have shown that roots are unable to reduce their diameter in order to enter pores narrower than their diameters (19,70,74); thus if they are to grow through compacted soil they must displace soil particles to widen the pores by exerting pressure greater than the soil's mechanical strength. Numerous studies have been conducted on the effects of mechanical strength (3,8 23,27,60). In one study where barley roots must overcome external imposed pressure of only .2x105N/m2 to enlarge pores; the rate of root elongation is reduced by 50% and if the pressure in the soil is increased to just .5x105N/m2 root extension is reduced by 80%. It is known that roots can exert pressure as great as 10x105N/m2 (24). This may explain the ability of some roots to eventually penetrate the compacted zones. At very high levels of soil compaction, roots fail to penetrate compacted zones and internal water drainage is restricted. Restricted internal water drainage leads to anaerobic conditions since water displaces oxygen from soil pores (6). This usually results in waterlogging conditions. At intermediate levels of soil compaction oxygen and compaction are both operative in determining root penetration (33,44,47 ). At optimum levels of either factor, root penetration ability is governed by the other factor. Root penetration in compacted soils is inhibited by the reduced pore spaces between soil particles and this often results in structural changes in the impeded root (33). Insufficient root anchorage frequently result from mechanical impedance (25). This may lead to lodging of a plant. Also, roots which encounter severe physical restraint frequently become flattened and grow in a zigzag manner. Elongation of these roots is less compared to that of roots growing in non compacted soil. Many researchers have reported that soil air space should be above 10% for normal plant growth and the permeability of the soil to water based on hydraulic conductivity should not be below 0.25cm/hr (20, 72). Excessive water and poor aeration result in a low prOportion of unsuberised roots surface area and hence lower absorptive capacity of the whole root system (59). Water can only enter suberised roots through lenticels, wounds and breaks around root branches ( 5, 43 ). Roots which develop in well aerated soil are long and light in color with numerous root hairs. Those that develop under low oxygen levels are thicker, shorter and dark in color with few root hairs and are differentiated near the root tip (15,54 ). Oxygen deficits are typically more serious than carbon dioxide excess (41,42) As long as oxygen levels are high enough, excess carbon dioxide can be tolerated (66). When about 90% of the interconnected soil pores become water-filled rather than air-filled, roots and aerobic soil micro-organisms begin to asphxiate ( 19 ). Gaseous products of their metabolism accumulate while the entry of atmospheric oxygen to replace that used in respiration is denied. Later when the reserves of oxygen dissolved in the soil water become exhausted, toxic substances such as ethanol, hydrogen cyanide and partially reduced intermediates of carbohydrate metabolism, accumulate. Intermediates in the anaerobic breakdown of carbohydrates are thought to be the substrate for soil matrix ethylene ( 26 ). Anaerobic bacteria may also be involved (67). Some microorganisms can degrade ethylene in the presence of oxygen ( 2, 21 ). Therefore, it may be reasonable to conclude that waterlogging conditions result in ethylene accumulation because firstly, microbial production is increased by anaerobiosis, secondly, vigorous microbial degradation is prevented by anaerobiosis and thirdly, the balance is entrapped by the presence of water in the interconnected pore space. All plant parts are capable of producing ethylene, although the production rate is normally low. Ethylene production plays an important role regulating plant processes ranging from germination to senescence (1,35). It is now established that methionine serves as the precursor of ethylene in higher plants (46). The conversion of methionine to ethylene requires oxygen. 8- adenosylmethionine,(SAM) is an intermediate in ethylene biosynthesis ( 4, 49 ). SAM is converted to 1- aminocyclopropanecarboxylic acid (ACC) and the ACC to ethylene (18,48,53) in the presence of oxygen. The enzyme involved in the conversion of ACC to ethylene is oxygen dependent (4). The formation of ACC is the rate limiting step in ethylene biosynthesis. Ethylene production is known to be regulated by a variety of developmental and environmental factors. As part of the normal life of the plant, ethylene production is induced during certain stages of growth such as germination, fruit ripening and senescence of flowers. However, ethylene can also be induced by a number of external factors such as wounding and various him-l. “!!sz V" r environmental stresses (1,46). Stress induced ethylene is associated with such factors as flooding, ( 16,17 ), mechanical wounding, (14, 32, 34, 37, 39, 55), water stress and fungal oxidates (67,69). In all cases both ACC and ethylene content are low before stress and increase following stress. Aminoethoxyvinyglycine (AVG) is a potent inhibitor of ACC synthase and its application to stressed plants effectively eliminates the increase in ACC formation and the production of ethylene. Stress induces the synthesis of ACC synthase (14,22,39,73) which in turn causes the rapid accumulation of ACC and the marked increase in the production of stress ethylene. Since ethylene is not produced by roots under complete anaerobic conditions and because of its gaseous nature it cannot be transported to the shoot in significant amounts, it has been suggested that a "signal" is synthesized in the anaerobic root and transported to the shoot where it causes ethylene evolution (17). Bradford and Yang 1980, have shown that waterlogging in tomato plants not only blocks aerobic conversion of ACC to ethylene in the root, but also causes increase in the synthesis of ACC which is subsequently transported through the xylem to the shoot where it is aerobically converted to ethylene. The difussion coefficient of ethylene is about 10,000 less in water than in air. As a result when a significant proportion cf the plant's surface is covered by water , the metabolically generated ethylene becomes trapped within the tissue. The amount will be some function of the rate at which ethylene is produced by the tissue and the depth of water covering it ( 31,36 ). Roots of different species elongate faster in well aerated conditions when exposed to lower concentrations of ethylene, but more slowly when these are increased above a certain level. Optimum levels differ between species and this may be related to the different rates of endogenous ethylene production (38). White mustard roots produce ethylene at a fast rate and consequently very little additional ethylene is required (.02-.05ppm) before root extension is retarded. However, rice roots produce much less ethylene and more exogenous ethylene (>1ppm) is needed to supplement this before adverse effects of ethylene can be realised. The effects of increased soil matrix ethylene include swelling of roots rendering them less efficient in water and mineral uptake, leaf senescence, leaf abscission and slow shoot growth (36,38,69). Prunus species and interspecific hybrids vary greatly in their tolerance to waterlogging conditions (7, 11, 12, 13, 28, 29, 30, 40, 50, 57, 61, 63, 64,). In general, . peach, apricot and almond rootstocks are among the least tolerant to wet, waterlogged soils (64). 10 Peach x almond hybrids have more tolerance than peach seedlings and plum has the greatest tolerance of all (63, 64) and peach root system is more tolerant than Mazzard which in turn is more tolerant than Mahaleb (51). Differences in resistance to waterlogging in Prunus have been found to be associated with the metabolism of a cyanogenic glucoside, prunasin. Under anaerobic conditions, prunasin is hydrolysed to hydrogen cyanide, which is autotoxic ( 63,64 ). The differential sensitivity of Prunus root systems to waterlogging conditions is closely related to the ability to hydrolyse prunasin. Secondary effects of anaerobic conditions resulting from soil compaction may play a role in waterlogging conditions. These effects include invasion of roots and stem pieces by soil fungi like Phytophthora and Pythium species which thrive in waterlogged soils (52 65, 71, 75). LITERATURE CITED 1. Abeles, F. B. 1973. Ethylene in plant Biology. New York Academic Press 2. Abeles, F. B., L. E. Cracker., L. E. Forrence., G.R. Leather. 1971. Fate of Air Pollutants: Removal of Ethylene, Sulfur Dioxide and Nitrogen Dioxide by Soil. Sci. 173: 914-5 3. Abdalla, A.M., D.R.P. Hetteriaratchi., A.R. Reece, 1969. The mechanism of root growth in granular media. g; Agr. Eng. Res. 14:236-248 4. Adams, D.O., S. F. Yang. 1977. Methionine in apple tissue: implication of S-adenosylmethionine as an intermediate in the conversion of methionine to ethylene. Plant Physiol. 60: 892-6 5. Addams, R.M., 1946. Entrance of water into suberised roots of trees. Plant Physiol. 21:109-111 6. Andersen, P.C. et.al. (1984). Leaf Conductance, Growth and Survival or Willow and Deciduous Fruit Tree Species under Flooded Soil Conditions. g; Amer.Soc. Hort.Sci. 109(2):132-138 7. Anonymous, 1978. Les porte-greffes du pecher, CTIFL- Documents No. 59 IVE 8. Barley, K.P. 1962. The effect of mechanical stress on growth of roots. g; Expt. Bot. 13:95-110 9. Barley. K.P., E.L. Graecen. 1967. Mechanical Resistance as a Soil Factor influencing the growth of roots and underground shoots. Adv. Agron. 19,1 10. Beckman, T. G., R.L. Perry. 1986. The effect of scion and graft on root growth potential of two seedling cherry rootstocks, Prunus mahaleb L. and g; avium L. (Mazzard). Fruit Var. 11. Bellini, E. 1982. "La colturo del pesco", In Prospecttive per L'agricoltura Collinare Fiorentina, Camera di commercio Industria, Artigianatoe agricolture di ferenze , pp 13-57 12. Bernhard, R., C. Grassely. 1959. Les pruniers 11 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 12 porte-greffes du percher,Jour, Fruit gt Maraich d'Avignon, 75-100 Bernhard, R.C., et al 1979. Orientations des travaux de selection des potre-greffes du percher a la station de recherches d'arboriculture fruitiere de Bordeaux. Proc Eurcapia Fruit sect. Symp. Tree Fruit Breed. Angers, France; Sept. 3-7 Boller, T., H. Kende. 1980. Regulation of wound ethylene synthesis in plants.Nature 286: 259-60 Boynton, D. 1939. Soil atmosphere and the production of new rootlets by apple tree root systems. Proc. Am. Hort. Sci. 37: 179-180. Bradford, K.J., S. F. Yang. 1980. Xylem transport of ACC in waterlogged tomato plants. Plant Pysiol. 6:322-6 Bradford, K. J., S. F. Yang. 1980. Stressed induced production in the ethylene requiring tomato mutant diageotropica. Plant Physiol. 65: 327-330 Cameron, A.C., et a1 1979. Increased production of ethylene by plant tissue treated with 1- aminocyclopropane-l-carboxylic acid. Hort Sci 14:178-80. Cannell, R.Q. 1977. Soil aeration and compaction in relation to to root growth and soil management Adv.Appl.Biol. 2,1-86. Childs, W.H. 1941. Photosynthesis, transpiration and growth of apple trees as influenced by various concentrations of oxygen and carbon dioxide in the soil atmosphere. Proc. Am. Soc. Hort. Sci. 38: 179-180. Cornforth, S. 1975. Pesistence of Ethylene in aerobic Soils. Plant and soil Sci 42: 85-96 Fuhrer, J. 1982. Ethlene Biosynthesis and cadmium toxicity in leaf tissue of beans. Plant Physiol 70:162-167 Gill, W.R., R.D. Miller. 1956. A method for study of the influences of mechanical impedance and aeration on growth of seedling roots. Soil Sci. Soc. Am. Proc. 20:154-157 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 13 Gill, R.W ., G.H. Bolt. 1955. Pfeffer‘s studies of the root growth pressures exerted by plants. Agron.J. 47:166-8 Gill, R. W. 1961. Mechanical impedance of plants by compact Soil. Transactions gf the ASAE. Goodlass, G., K. A. Smith. 1978. Effects of organic amendments on evolution of ethylene and other hydrocarbons from soil. Soil Biology and Biochemistry. 10:201-205 6055, M. J. 1970. Further studies on the effect of mechanical resistance on the growth of plant roots. Report Agr. Coun. Letcombe Lab. ARCRL 20: 43-45 Grasselly, C. 1981. Rootstock research programmes Past and Present. Rootstock variety interaction affecting fruit induction and growth Peach production Course III Clemson University, S. Calorina, 6pp. Grasselly, C., et al 1980. Les pruniers' porte- greffes du pecher: Vignt annees d' experience du comportement des principeaux types. Arboriculture Fruitiere 322: 47-52 ' Grasselly, C., P. Rogers. 1970. Compartement dans le sud-ouest des pruniers porte-greffes du pecher, Bull. Tech. Infor. No 254: 623-632 Heinicke, A. J. 1932. The effect of submerging the roots of apple trees at different seasons of the year. Proc. Am. J; Soc. Hort. 29: 205-207 Hoffman, N. E., S. F. Yang. 1982. Enhancement of wound-induced ethylene synthesis by ethylene in preclimacteric cantaloupe. Plant Physiol. 69:317-322 Hopkins, R. M., ‘ W. H. Patrick. 1969. Combined effect of oxygen content and soil compaction on root penentration. Soil SE; 108, no.4: 408-413 Hyodo, H., T. Nishino. 1981. Wound induced ethylene formation in albedo tissue of citrus. Plant Physiol. 67:421-423 Imaseki, H., A. Watanabe. 1978. Inhibition of ethylene production by osmotic shock. Further . Iii-Fa 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 14 evidence for membrane control of ethylene production. Plant Cell Physiol 19:345-48 Jackson, M. B., D. J. Campbell. 1976. Waterlogging petiole epinasty in tomato: the role of ethylene and low oxygen. New Phytol. 76:211-229 Kende, H., T. Boller. 1981. Wound ethylene and 1-amino-cyclopropane-l-carboxylate synthase in ripening tomato fruit. Planta 151:476-81 Konings, S. H., M. B. Jackson. 1979. A relationship between rates of ethylene production and the promoting or inhibitory effects and exogenous ethylene and water on root elongation. g; Plazenphyisologie 92: 385-397 Konze, J. R., G. M. K. Kwiatkowski. 1981. Rapidily induced ethylene formation after wounding is controlled by regulation of 1- aminocyclopropane-l-carboxylic acid synthesis Planta. 151: 327-330 Knight, R. L. 1969. Abstract Bibliography of Fruit breeding and genetics to 1965.Prunus Comm. Agr. Bur. Tech. Comm.No.31 Kramer, P. J. 1950. Soil aeration and tree growth. Proc. 26th. Inter. Shade Tree Conf. 51-58 Kramer, P. J. 1949. Plant and soil water relationships. Mc Graw-Hill, N.Y. Kramer, P. J., H. C. Bullock. 1966. Seasonal variation in the Promotion of suberised and unsuberised roots of trees in relation to the absorption of water. Am. Jour. Bot. 52:200-4 Lewis, L. J. 1984. Regulation of root development Ann. Rev. Plant Physiol. 35:223-242 Lieberman, M., L. M. Mapson. 1961. Genesis and biogenesis of ethylene. Nature 204:343-45 Lieberman, M. 1979. Biosynthesis and action of ethylene. Ann. Rev. Plant Physiol. 30:533-91 Loustalot, A. J. 1945. Influence of soil moisture 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 15 on apparent photosynthesis and transpiration of pecan leaves. g; Agr. Res. 71:(12)519-532 Lurssen, K., et a1 1979. 1-amino-cyclopropane-1- carboxylic acid an intermediate of ethylene biosynthesis in higher plants. 2; Pflanzenphysiol. 92:285-294 Murr, D.P., S.F. Yang. 19 . Inhibition of in vivo conversion of methionine to ethyleneby L- canaline and 2,4-dinitrophenol.Plannt Physiol. 55:79-82 Norton, R. A. et al 1963. Rootstocks for plums and prunes. Carf. Agr. Exp. Sta. Leaf No.158, 8pp Perry, R. L. 1984. Working with soil limitations for orchard crops. Proc. Ontario Hort. Conf. Ministry of Agr. and Food. 164-171 Quamme, H. A., C. Stushnoff. 1983. "Resistance to environmental stress" in Methods in fruit breeding. J.N. Moore and J. Janick, Eds., Purdue University Press, W. Lafayette In.,246-266 Rando, R. R. 1974. Chemistry and enzymology of K cal inhibitors. Science 185:320-24 Richard, S.C.A., C.H. Wadleigh. 1952. Soil Physical Conditions and Plant growth Academic Press, N.Y. 73-251 Riov, J., S. F. Yang. 1982. Autoinhibition of ethylene production in citrus peel discs. Supression of 1- aminocyclopropane 1- carboxylic acid synthesis. Plant hysiol. 69:687-90 Rom, R.C. 1984. The peach rootstock situation: An interaction pespective, Fruit Var. g; 37:(1), 3-14 Rom, R.C. 1984. A new generation of peach rootstocks. Proc. 43rd. Nat. Peach Coun. Ann. Convention pp.59-68 Rovia, A. D., E. L. Graecen. 1957. The effect of aggregate disruption on the activity of microorganisms in the soil. Aust. J; Agr.Res. 8: 659-673 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 16 Ruark, G. A., et a1 1982. The influence of soil compaction and aeration on the root growth and vigor of trees. A literature review. Russell, R. S., M.J. Goss. 1974. Physical aspects of soil fertility- the response of roots to mechanical impedance. Neth. g; Agr. Sci. 22: 305-318 Salesses, G., C. Juste. 1971. Recherches sur l'asphyxie radiculaire des arbres fruitieres a noyaull. Comportement des porte-greffes de types perche et prunier: Etude de leur teneur en amygdaline et des facteurs intervenant dans l'hydrolyse de celle-ci, Ann. Amerlior. Plantes 21(3) 265-280 Salesses, G., et a1 1970. L'aspyxie radiculaire chez les arbres fruitieres, Bull. Tech, Info. No. 251 pp403-415 Saunier, R. 1966. Method de determination de la resistance a l' asphyxie radiculaire de certains porte-greffes d'arbres fruitieres, Ann. Amelior. Plantes. 16(4) 367-384 Saunier, R. 1970. Resistance a' l'asphyxie radiculaire de quelques porte-greffes d'arbres fruitiere, CTIFL-Document No.26 Sharpe, R. 1974. Breeding peach rootstocks for southern USA, HortScience 9(4) 362-363 Slayter, R. O. 1967. Plant water relationships. Academic Press, N.Y. 73-251. Smith, A. M. 1976. Ethylene production by bacteria in reduced microsites in the soil and some implications to agriculture. Soil Biology and Biochemistry. 8:293-298 Smith, A.M. et al 1973. Sorption of gaseous atmospheric pollutants by soil.Soil Sci 116 :313-319 Smith, K.A., R.S. Russell. 1969. Occurence of ethylene and its significants in anaerobic soil. Nature 222:769-71 ‘ Taylor, D. W., R.R. Bruce. 1968. Effects of soil strength on root growth and crop yield in the 17 southern USA. Trans. Int. Congr. Soil Sci 9th 1:801-811 71. Traquair, J. 1984. Etiology and control orchard replant problems: A review, Can. g; 21; Path. 6:54-62. 72. Vomocil, J. A., W. J. Flocker. 1961. Effect of soil compaction and storage and movement of soil air and water. Trans. of the ASAE 73. Wang, C. Y., D. 0. Adams. 1982. Chilling induced ethylene production in cucumbers. Plant Physiol. 69:424-27 74. Weirsum, L.K. 1957. The relationship of the size and structural rigidity of pores to their penentration by roots. Plant Soil 9:75-85 75. Yadava, V. L., S.L. Doud. 1980. "The short life and replant problems of deciduous fruit trees", in Hort. Reviews, Vol. 2 J. Janick, Ed., Avi Publ. Co. Westport, C.T. pp1-116. 18 SECTION 1.: EFFECTS OF SOIL DENSITY ON ROOT GROWTH OF CONTAINER GROWN PRUNUS ROOTSTOCKS ABSTRACT. Four Prunus rootstocks MXM2 (g; mahaleb L.x P; avium L.), GI 149-8 (P.avium L. X g; canescens Bios.), g; mahaleb L. and CF 677 a cross between Prunus persica and Prunus amygdalus were grown in plastic cylinders with a mid-section 2.5cm thick of soil compacted to one of the three soil bulk density levels 1.0, 1.3 and 1.7g/cc. Total root length, and root penetration ratio were measured above and below the compacted zone 8 weeks after planting. GF 677 developed the greatest total length of root at all soil density levels among all rootstocks and GI 148-9 had the lowest. At soil density level of 1.7g/cc, GF 677 had the greatest RPR' that was significantly different to that Of other 3 stocks. MxM2 had the greatest propensity to form a shallow root at high level of soil compaction. Soil matrix ethylene was monitored at 2 weeks interval throughout the test period and was found to be highest for P mahaleb and least for GF 677. 19 LITERATURE REVIEW Restricted root growth limits nutrient and water availability even when these are present in adequate amounts in the soil. Soil mechanical stress is usually the cause of restricted root growth (5). Soil compaction usually leads to poor soil drainage and aeration. Under conditions of excessive soil moisture, water occupies the entire pore space which ordinarily contains about half water and half air. When there is little or no oxygen supply, the roots are not able to carry out the usual rate of respiration (6). After a long period of exposure of roots to high soil moisture, the roots loose their capacity to absorb and translocate sufficient water and minerals to the top for proper leaf functioning and good growth. Symptoms of excessive soil moisture on shoot include yellowish green leaves, small leaves that abscise early and reduced shoot elongation (6). Fruit tree root systems differ in their tolerance to supressed soil oxygen which occurs in flooded soil. Pecans are most tolerant, followed by quince, pear, apple, citrus, plum, cherry, apricot, peach, almond and olive ( 18). In general, peach root system is slightly more tolerant than mazzard which is slightly more tolerant than mahaleb to anaerobic conditions (17). It 20 21 has also been noted that peach x almond hybrids are more tolerant to wet, waterlogging conditions than peach root systems and that among Prunus root systems, the plum is the most tolerant (21). In highly compacted soil, oxygen is not only absent or more Often in short supply (10), but also the normal exchange of gases from the root to the soil is also frequently impeded (19). Under reduced partial pressures of oxygen, roots are straighter, shorter and there is an increase in the number of laterals per unit Of root (7,8,23). Root penetration and exploration of the soil horizons are essential if maximum crop yields are to be achieved (1). Soil compaction reduces both the size and abundance of soil pores through which plant root systems develop (4). Root systems stunted by compaction generally reduce plant vigor and crOp yield. A soil bulk density of 1.39/cc or less is usually ideal for most annual crops (1). In compact soils, root growth rates are typically reduced and roots often thicken (19,20) Branching patterns are modified greatly, with lateral roots often differentiating uncharacteristically close to the apex (11). In roots that bend after an encounter with an impenetratable layer of soil, the position of lateral root intiation shifts and the lateral roots predominate in the cOnvex side of the bent root (9). A role for ethylene in the development of 22 mechanically impeded roots has been suggested by several workers (13,20). Kays et. al. (13), have shown that when axial growth of broad bean (Vicia faba L.) roots was impeded, the rate of ethylene evolution increased by as much as six times the rate of unimpeded controls and that when the rooting barrier was removed, the rate of ethylene evolution decreased to nearly the rate of control roots. This Observation, coupled with the fact that applied ethylene can cause thickening and shortening of roots (2,13,22) suggests a role for ethylene in the response of roots to mechanical impedance. However, species differ in their rate of endogenous ethylene production (11). Under waterlogging conditions, ethylene is not able to escape freely to the atmosphere because its diffusion coefficient is 104 less in water than in air (3). The purpose Of this experiment is two fold: first, to evaluate the effect of soil density and rootstock type on root growth and secondly, to monitor the stress induced ethylene production in 4 different root systems. MATERIALS AND METHODS. Four Prunus rootstocks MXM2 (P.mahaleb L. x P; avium L.), GI 149-8 (E; avium L. x g; canescens L.), GF 677 a cross between Prunus persica L.and Prunus amygdalus and Mahaleb seedling were grown without scion in cylinders each made up of three sections. All the stocks except P; Mahaleb were rooted cuttings. Polyvinyl chloride cylinders with an internal diameter of 7.6cm and a wall thickness of 0.67cm were used to establish three layered soil containers Figure l. The bottom and top sections were 7.6cm high and contained uncompacted soil and the middle section was made up of a 2.5cm thick layer of soil uniformly compacted to any one of the following bulk densities (BD) 1.0, 1.3 and 1.7g/cc. BD of 1.0g/cc represents uncompacted soil and 1.7g/cc highly compacted soil in which very few roots if any grow (9) whilst BD Of 1.3g/cc represents an intermediate level of soil density in a heavy soil type (1,9). Loam soil (Ockley Loam) consisting of 20% clay, 50% sand and 30% silt , collected from a declining cherry orchard was sieved through number 10 and 60 screens to uniform granules ranging from 0.25 to 2.0mm. The soil aggregates were equilibrated to a constant gravimetric soil moisture content of about 16%. Sandy loam soil compacts well at this soil moisture content (1). The soil was compressed into 2.5cm high cylinders by a mechanical 23 24 <—-——ROOTSTOCK TOP SECTION <—CONTAI NING UNCOMPACTED SOIL MIDDLE SECTION <—CONTAINING COMPACTED SOIL BOTTOM SECTION <——CONTAINING UNCOMPACTED SOIL I VIII/U CHEESE CLOTH AND FILTER PAPER # I IVIII/I RUBBER BAND Figure 1. Experimental layered soil containers. 25 hydraulic piston of diameter slightly less than 7.6 cm (Carver type, model 20505-1). Soil bulk densities of 1.0, 1.3 and 1.7g/cc were achieved by packing a specific mass of oven dry soil in the middle cylinder. The three cylinders tOp, middle and bottom were assembled into a single cylinder by aid of plastic duct tape. A filter paper and then cheese cloth were placed at the base Of each bottom cylinder and were kept in position by a rubber band. Each soil container was saturated with water for 48 hrs, drained and then the rootstocks were planted. Plants were weighed after trimming the roots to a uniform length and number. The design of the experiment was a Complete Randomized Block design with 5 replications. Each experimental unit consisted of a unit cylinder made up of three sections and a plant and there were 12 factorial treatments ( 3 bulk density levels x 4 rootstock types). The plants were grown in the greenhouse at day temperature of 80°F and at night temperature of 70°F with 14 hr of light for 8 weeks. During the course of the test period, plants were treated the same. Equal amount of water (50ml) was applied to each plant whenever plants growing in non compacted soil required watering. The experiment was terminated 7 weeks after root intiation had ocurred. This was enough time to allow those roots that are capable of growing in all the three 26 soil layers to grow. Also, leaving the plants in the containers for a longer period could have resulted in other factors (mainly competition for space), masking the effects of soil density and rootstock type on root growth. At the end of the test period, total root length and and root penetration ratio (RPR) which is defined as the ratio of the number of roots that exit the compacted zone to the number of roots above the compacted zone was measured (1). Values for the RPR were only taken from the central 20.3 cm2 area of the middle cylinder. This avoided counting roots that grew towards the soil-container interface. The number of roots above and below the middle section of the container was determined by separating each container into its primary components and then physically counting the number of roots in each layer. Roots were washed from soil by the hydropneumatic elutriation method (1). Soil matrix ethylene was monitored below the compacted zone through a septum in the bottom section at 2 week intervals. The levels of soil ethylene were determined on a gas chromatograph on an alumina column. The total root length of each plant was estimated by the Newman's (16) line intersection method. RESULTS Effects 9f §Q_gg Root Growth. Increasing BD from 1.0 to 1.3g/cc and above significantly reduced both total root length and RPR which were both highest at BD of l.Og/cc and least at BD of 1.7g/cc, Table 1. Significant interaction between BD and rootstock type was detected for both parameters (RPR) and total root length). Effects 9: Rootstock and B2 23 Root Growth. GF 677 had the greatest length of roots at all soil bulk density levels. A soil bulk density of 1.7g/cc reduced total root length from a 1.3g/cc BD by only 18% for GE 677, 75% for mahaleb, 54% for GI 148 and 78% for MxM2, Table 2. The RPRS of the 4 rOOt systems were not significantly different from each other at the lowest BD l.Og/cc. At a BD of 1.3g/cc GF 677 root system had the highest RPR that was significantly different from the other 3. MxM2 had the lowest RPR at BD 1.7g/cc, Table 3. Changes in soil matrix ethylene When soil matrix ethylene was monitored below the compacted zone, it was found to increase with time for all stocks at BD 1.7g/cc. The highest levels of soil matrix ethylene were detected in soil in which mahaleb root system was growing and least in which GF 677 root system grew (Figure 2). There was an inverse relationship between total root length and soil 27 28 matrix ethylene for all rootstocks tested (Figure 3). At lower BD levels 1.0 and 1.3g/cc very little ethylene was detected. 29 Table 1. Effect of soil density levels on 4 Prunus rootstocks grown in containers. Mean Mean BD (g/cc) Root Length(cm) RPRz z 1.0 532.70a 0.99a 1.3 395.50b 0.59b 1.7 205.80c 0.29c 2 Values in the same column followed by the same letter are not significantly different at 5% level, by Duncan's Multiple Range test. 2 RPR: Root Penetration Ratio. = # Roots Exit Dense Layer # Roots Above Dense Layer 30 Table 2. Mean total root length (cm) of four container grown Prunus rootstocks grown under various levels of mechanical impedance. Bulk Density x w Rootstock l.Og/cc 1.39/cc % 1.7g/cc % 2 GF 677 870a 740a 15 610a 18 Mahaleb 650b 595b 8 145b 75 MXMZ 350C 200C 43 45bc 78 G1 148-9 280C 55d 80 25c 54 2 Values in the same column followed by the same letter are not significantly different at 5% level, by Duncan's Multiple Range test. x % root length decrease from 1.3 t0 1.7g/cc BD. w % root length decrease from 1.0 to 1.3g/cc BD. 31 X Table 3. Mean RPR of four container grown Prunus rootstocks grown under various levels of mechanical impedance. Bulk Density Rootstock l.Og/cc 1.3g/cc 1.7g/cc 2 GF 677 0.99a 0.68a 0.51a MXMZ 0.99a 0.56b 0.10b Mahaleb 0.99a 0.60b 0.23c GI 148-9 l.OOa 0.45C 0.31d 2 Values in the same column followed by the same letter are not significantly different at 5% level, by Duncan's Multiple Range test x RPR: Root Penetration Ratio. = # Roots Exit Dense Layer # Roots Above Dense Layer 32 .0m 0035. _. um 9.03309. uncan— ES «.95. 953:5 5me zom .N 9:9". om 02:24.3 mmhm< m>o Ono—ES 5sz =3 035.:an No.32... .E+ E+ . . n—n—+.._m.._.m JQ+Jw.._.m JQ+Jm..—.m E+£Q+Jw PM 4% Pm — n P p p ‘8 In 5 | I- - '5 s s \ ~ ~ ~ s s x 3.3.. H I I ~ I I I I I la: ss ” \ I/ x I x ll ~ I s X . a; N am mm. on. m5. 0; Nikki NI NOILVHLNEONOO 3N3'IAH13 DISCUSSION Many researchers have reported that Phytophthora megasperma and Pythium species are not very pathogenic to cherry rootsystems (6,13). This seems to be the case in this study where no plant was killed by these pathogens. Although it has been reported that the incidence Of Phytophthora causing root diseases increases with soil compaction (7), in this experiment the pathogen effect on RDW did not significantly increase with soil density but RD did. RD appears to be a more sensitive measure of root volume than RDW which is not only affected by quantity of roots but also by the size (3). BD alone had a significant effect on RDW. The higher the BD the lower was the RDW. This is not surprising because the severity of these pathogens Phytophthora in particular, is thought to be realized only when plants are periodically flooded (4) but flooding alone causes the same effects reported for Phytophthora disorders (5,14). Both BD and Pathogen factors had significant effect on RD. RD decreased significantly at higher BD. This confirms what has been reported in the literature. The lack of significant interaction between BD and Pathogen disagrees with research conducted on soybean, where pathogen effect increased with increase in BD (6). The significant effect of pathogen factor was mainly due to Phytophthora megasperma and not to Pythium irregulare. P; megasperma has been reported to cause root and crown root of Mahaleb 53 54 cherry seedlings that were grown in artificially infected potting medium and periodically flooded (4). In this study plants were not flooded but soil compacted to 1.7g/cc BD retained more moisture than soil at 1.0 and 1.3g/cc. NO root or crown rot was Observed and also no plant was killed by the pathogens. This Observation seem to indicate that infection by Pythium species is not a significant factor in the death and poor performance of Mahaleb seedlings. Among fungi, the production of ethylene has been convincingly demonstrated by 3 species, Pennicillium digitatum, Blastomyces dermatitidis and Agaricus campestricus bispprus. Production of ethylene by other Species is questionable (10). Phytophthora and Pythium species have not been reported as major producers of ethylene (10). This seems to be the case in this study where very little ethylene was produced by the fungi. At higher BD 1.7g/cc, the roots produced higher levels of ethylene than at lower BD both in presence and absence of fungi. The highest level of ethylene was attained by roots growing in absence of fungi at BD 1,7g/cc. The fact that plants when subjected to stress produce higher levels of ethylene (9) may explain the higher levels Of ethylene at higher BD than at lower BD. Further experimentation with an additional set of plants subjected to periodical flooding will be helpful in elucidating whether the reported deaths and poor 55 perfomance of Mahaleb seedlings grown in artificially infected medium is due to pathogen or anaerobic conditions. LITERATURE CITED 1. Abeles, F.B. 1985. Sources of ethylene Of horticultural significance. in Ethylene and Plant Development. Roberts, J.A. and G.A. Tucker eds. Butterworths. 2. Burg, S. P. 1962. The Physiology of Ethylene formation. Ann. Rev. Plant Physiol. 13:265-302 3. Bennie, A.T.P. and R. Du T. Burger. 1983. Root characteristics of different crops as affected by mechanical resistance in fine sandy soils. 10th National Congress 9; The Soil Science Society 9: Southern Africa S.Afr. Dep. Agric Fish. 29-32 4. Bielenin, A. and Jones, A.L. 1988. Pathogenicity of four species of PhytOphthora isolated from sour cherry trees in Michigan. PhytOpath 78 000:000 5. Day, H.L. 1953. Rootstocks for stone fruits. Calif. Agric. Exp. Stn. Bull. 736. 80p. 6. Devay, J.E. et al 1968. Poria root and crown rot of cherry trees. PhytOpath. 58:1239-1241 7. Gray, L.E. and R.A. Pope. 1982. Influence of soil compaction on the severity of Phytophthora root rot of soybeans. Phytopath. 72 (8) 1136 8. Hayes, J. E. and H. S. Aldwinckle. 1983. Phytophthora root and crown rot of cherry in New York state. PhytOpath. 73:366 9. Hogsett, W. E. et al 1981. Biosynthesis of stress ethylene in soybean seedlings: similarities to endogenous ethylene biosynthesis. Physiol. Plant 53:307-314 10. Ilag. L., and R. W. Curtis. 1968. Production Of ethylene by fungi. Sci. 159:1357-1358 11. Mircetich, S. M. and M. E. Matheron. 1976. PhytOphthora root and crown rot of cherry trees. Phytopath. 66:549-558 56 12. 13. 14. 15. 57 Silbernagel, M.J. and L.J. Mills. 1984. Effects of cultural practices on snap bean seed production in compacted root rot conducive soil Phytopath. 74: (9) 1141 Smith, R.E. and E. H. Smith. 1925. Further studies on pythiaceous infection of deciduous fruit trees in California. phytopath. 15: 389-404 Smith, R. E. 1941. Diseases of fruits and nuts. Calif. Agric. Ext. Serv. Circ. 120:167 Yang, S. F. and N.E. Hoffman. 1984. Ethylene Biosynthesis and its regulation in higher plants. Ann. Rev. Plant Physiol. 35:155-189 58 SECTION III THE EFFECTS OF SOIL COMPACTION AND ROOTSTOCK TYPE ON THE SCION ABSTRACT Scion performance was evaluated on "Montmorency" cherry scion cultivar budded to either Mazzard or Mahaleb rootstock and grown under two levels of soil compaction, 1.0g/cc and 1.7g/cc bulk density. Soil compaction had significant adverse effect on leaf area density number of leaves per shoot, trunk cross sectional area, final shoot height and shoot dry weight. Rootstock type had significant effect only on leaf area density, trunk cross sectional area and shoot dry weight. Soil density and Rootstock type also had a significant effect on leaf area density, trunk cross sectional area and shoot dry weight. Montmorency on Mazzard significantly out performed that on Mahaleb (in terms of leaf area density, trunk cross sectional area and shoot dry weight) under compacted soil conditions. Shoots on Mahaleb and grown in compacted soil produced more ethylene than those on Mazzard and under same soil conditions. 59 LITERATURE REVIEW Several researchers have reported that under conditions of extended waterlogging which is usually common in compacted soils, trees may be killed outright ( 7 ). After a long period of waterlogging, the roots loose their capacity to absorb and translocate sufficient water and nutrients to the top for proper leaf functioning and good shoot growth. Symptoms of poor drainage in compacted soils include yellowish green leaves which do not carry photosynthetic process efficiently, marginal and tip burning on leaves, smaller leaves that abscise prematurely, weak shoot growth and ceasation of shoot extension growth early in the season, bark with light green or yellowish cast, thin foliage both in thickness and number Of leaves, heavy blossom which is usually followed by light fruit set, small fruit that are small with somewhat high in color and which drop early in the season (7). Loustalot ( 16 ) in 1945, reported that photosynthesis was completely stopped if the roots of a pecan tree were flooded for 20 days. Transpiration decreased by about half the expected rates. When excessive water was drained, photosynthesis and transpiration rates increased. The ability of the plant to recover after being subjected to waterlogging conditions depends upon the intial vigor and character of 61 growth and the length of the flooding period. Flooding is also known to induce ethylene production by the stressed plants (3,5). Heinicke et al (13) showed that flooding which is common in compacted soils accentuates the deficiencies of nutrients in apple trees inspite of the fact that the elements may be in the soil. Soil compaction results in poor soil aeration and low oxygen supply to the roots. This in turn results in reduction Of root growth, leaf area and total weight of the plant ( 7 ). When a rootstock root sytem is subjected to compacted soil, scion performance is affected according to the rootstock type. Slowik (21), found that trees on M26 were more adversely affected by soil compaction than trees on M4. In peach scion vigor, budding success and trunk cross sectional area have been found to depend on rootstock type (15). Webster (23) showed that the abundance of apple roots was related to the total soil porosity. However, M12 was an exception to the rule. It had many roots in soil of poor porosity because of its tolerance to poor aeration. The effects of rootstock on scion are affected by such factors as rootstock seedling source, scion/rootstock interaction, soil and climatic conditions (17). In general, the order of scion vigor is as follows; F12/1 > Mazzard seedling > Mahaleb seedling (1,10,12,20). In good soil, sweet cherries on Mahaleb may 62 be larger than those on Mazzard at first but Mazzard rooted trees will usually overtake and surpass them (24). In gravelly soil of Utah (9) and Colorado (6), trees on Mahaleb are more vigorous than on Mazzard. Trees on Mahaleb can be more vigorous in drought conditions than on Mazzard. Conversely, trees on Mazzard are more vigorous in heavy wet soils. Many scientists have reported that the source of the seedling is as influential on the productivity and vigor of the scion as is the species of the rootstock (2,8,11,18,24,25). Comparatively, very few studies have dealt with the effect of rootstock type and soil compaction on scion performance. The objective of this study, is to determine the effects of Mahaleb and Mazzard rootstocks and soil compaction on growth of Montmorency cherry scion variety under controlled conditions. MATERIALS AND METHODS. Loamy sand soil (Miami Loam) collected from a declining cherry orchard was sieved through number 10 and 60 screens to uniform granules ranging from 0.25- 2.00mm. Young trees with montmorency buds still dormant were grown for 16 weeks in three layered containers of 25cm internal diameter. Each container consisted of three separate cylinders, the top, middle and bottom held together with duct tape. The top and the bottom cylinders were 15cm high and the middle was 11.25cm high. The top and the bottom cylinders contained Baccto professional planting mix composed of equal quantities of Sphagnum peat moss, vermiculite and perlite. The middle layer contained non compacted soil or soil compacted to 1.7g/cc BD. Compaction level was achieved by packing 10.68kg of soil for the control, l.Og/cc BD and 17.89kg to achieve 1.7g/cc BD. A 50.6kg hand compressor was used to compact the soil. The base Of the bottom cylinder was covered'with a double layer of cheesecloth and perforated aluminium foil held in place with a rubber band, Figure 1. This design was adapted from that of Zimmerman and Kardos, 1960. The roots of the trees were trimmed to ‘a uniform length 5cm and the trees were planted to the same depth. 63 64 I <——BUDDED CHERRY TREE TOP SECTION <—CONTAINING GREENHOUSE MIX MIDDLE SECTION <—CONTAI NING COM PACTED SOIL V—i VIII/U BOTTOM SECTION 4—CONTAINING GREENHOUSE MIX A CHEESE CLOTH # AND ALUMINIUM FOIL (I /\/\/I/\ RUBBER BAND Figure 1 . Experimental layered soil containers. 65 Before planting the trees in the three layered containers, the trees were grown in the planting mix for 5 days to see whether the budded montmorency buds had taken or not. The trees were either budded to Mahaleb or Mazzard rootstock. The design of the experiment was a Randomized Complete Block Design, 2 factor (BD and rootstock type ) factorial. Each treatment was replicated 3 times. During the course of the test period (16 weeeks), each plant was treated the same. Equal amount of water was applied to each plant whenever plants growing in non compacted soil required watering. The plants were grown into single shoot plants by nipping off all side shoots as they came up. A gas sample of ICC was drawn twice / week from a plastic bag covering 10cm length of shoot. An air tight environment within the shoot was achieved by use of plasticine. The gas sample was run over a gas chromatograph on an alumina column to determine ethylene concentration in ppm. Moisture relationships were determined in each container in Kilopascals (Kpa) of soil suction by a tensiometer just before each watering. Other parameters measured were leaf area density (14), leaf number per shoot, shoot dry weight, trunk cross sectional area (TCA) and extension shoot growth. RESULTS Soil compaction significantly affected all the parameters that were measured. Leaf area density, trunk cross sectional area, number of leaves per shoot, scion height and shoot dry weight decreased significantly when soil was compacted to a BD level of 1.7g/cc, (Table 1). Average ethylene production by a shoot of given length per given volume of air, was higher in shoots with roots growing in non compacted soils. Soil moisture tension was greater in the drier non compacted soil than in the wetter compacted soil (Table 2). The type of rootstock used had a significant effect on leaf area density scion diameter and shoot dry weight and had no significant effect on scion height and number of leaves per shoot. Montmorency on Mazzard root significantly out performed that on Mahaleb in terms of leaf area density, trunk cross sectional area and shoot dry weight, (Table 5). Bulk density x rootstock effect was significant on leaf area, scion diameter and shoot dry weight and had no significant effect on number of leaves per shoot and scion height. The performance (in terms of leaf area index, trunk cross sectional area and shoot dry weight) of scion budded to a rootstock growing in compacted soil was significantly greater in scion budded to Mazzard rootstock than to Mahaleb rootstock. In non compacted soil environment, no significant differences in scion 66 67 performance were observed between scion budded to Mazzard and Mahaleb rootstocks, (Figures 2 and 3). Mazzard root system above the compacted zone was more dense and fibrous than that of Mahaleb (Table 6). Also Mazzard root had a higher root penetration ratio in compacted soil than Mahaleb (Table 7). 68 Table 1. Average Shoot Ethylene Production (PPm) per 1000 cc of space. BD g/cc ROOTSTOCK MAHALEB MAZZARD 1.0 0.1 0.1 1.7 2.3 0.5 LSD (0.05) 0.3 0.3 Table 2. Average Soil Tension (Kpa) before each watering. BDg/cc ROOTSTOCK MAHALEB MAZ ZARD 1.0 1.2 1.5 1.7 0.2 0.3 LSD (0.05) NS NS 69 Table 3. Analysis of variance. X F VALUE Y VARIABLE Z SOURCE DF EMSDF 1 2 3 4 5 A 1 2 430.9** 36.0** 61.8** 651.0** 232.0** B l 4 72.9** 4.5 0.6 78.3** 25.6** AB 1 4 30.8** 1.2 0.4 23.4** 9.6* X Significant at 5% (*) or 1% (**) level, otherwise nonsignificant. Y Variable Description 2 1 = Leaf Area Density (cm ) 2 = Final Shoot Height (cm) 3 = # of leaves / shoot 2 4 = Trunck cross sectional area (mm ) 5 ? Shoot Dry Weight (9) Z Factor A = BD B = Rootstock AB= BD X Rootstock 70 Table 4. Effect Of Soil Density level on Montmorency Sour Cherry growth measurements. VARIABLEZ BD LAD FSH LF# TCA SDW 1.0 67.4 87.0 51.0 83.3 89.1 1.7 40.3 48.3 22.2 10.7 40.8 LSD (0.5) 3.7 15.7 8.9 0.3 7.7 Variable Description . 2 LAD= Leaf Area Density (cm ) FSH= Final Shoot Height (cm) LF#= Leaf # / Shoot 2 TCA= Trunck cross sectional area (mm ) SDW= Shoot Dry weight (g) 71 Table 5. Effect of Rootstock on Montmorency Sour Cherry growth measurements. VARIABLEZ ROOTSTOCK LAD FSH L# TCA SDW Mahaleb 48.3 60.8 35.1 26.4 55.4 Mazzard 59.4 74.5 38.0 51.5 74.4 LSD (0.5) 3.2 NS NS 0.3 7.7 Z Variable Description 2 LAD= Leaf Area Density (cm ) FSH= Final Shoot Height (cm) L# = Leaf # / Shoot 2 TCA= Trunck cross sectional area (mm ) SDW= Shoot Dry Weight (g) 72 Table 6. Mean Root Penetration Ratio of two rootstocks under two levels of Soil Density. Soil Density Rootstock l.Og/cc 1.7g/cc Mahaleb 0.99 0 Mazzard 0.99 0.12 LSD (0.05) NS 0.09 73 Table 7. Mean Root Count above and below the compacted zone. Rootstock Mahaleb Mazzard 2 Above 168a 379b Below 03 46b 2 Values within a row followed by the same letter are not significantly different at 5% level by Duncan's Multiple Range test. 74 E5. LoaoEmE Edam qqqqq Mazzard “*3 ‘ii:1 Mahaleb \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\o ........................................................................... .D ............................................................................. ................................................................................ ................................................................................. ................................................................................... u u d u \\\\\\\\\\\\\\\\\\\\\ . d d 4 ................................................................................. ................................................................................ .................................................................................... ............................................................................. ................................................................................. ............................................................................... .................................................................................. .........v...... .. ...... ...............nc............¢..>......-..u.-m.o......nP.->>NIFI .............................. ............................... .................................................. ................................................................................................ ......................................................................................................... ............................................................................................... .......................................................................................................... ...................................................................................................... ........................................................................................ ............................................................................... .............................................................................. ................................................................................. ........................................................................ ............................................................................................. Eu. no; .63 Bulk Density (Qlcc) ntly different Ignifica a variable are not 3' 3 Multiple Range Test. e letters within area and stem diameter of Montmorency sour Figure 2. Effect of soil bulk density and rootstock on leaf cherry. R\\\\\\\_\\\\\\\\i. Iff‘ffi Mahaleb §\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ . ................................................................................................ ................................................................................................ ................................................................................................. ............................................................................................... ............................................................................................... .................................................................................................. ............................................................................................ ........................................................................................... ...................................................................................... ...................................................................................... ............................................................................................... ..o.u........... ........................................................................................ ....-..-.......-..,. .................... ...................................................... ...............,.......... ...,....... .... ....... ,........ .....,...,.............. ........, ....,...........................-...... ......... 000000000 O 9 8 7 6 5 4 3 2 .0l 3. £225 to .85 CI Bulk Density (g/c at 5% love ntly different cherry. ncy sour Figure 3. Effect of soil density and rootstock on shoot dry weight of Montmore DISCUSSION Many authors working with plants grown in compacted soil have reported that soil compaction adversely affect plant growth and that the extent to which the plant is affected depends on nature of the root system (15,17,22). This appears to be the case in this study where soil compaction had significant effect on all parameters measured and where significant interaction between BD and rootstock was observed between some of the parameters measured. Leaf area density was significantly affected by soil compaction and rootstock type. Soil compaction significantly reduced leaf area density on Mazzard rooted trees growing in compacted soil had significantly larger leaf area density than Mahaleb rooted trees growing under similar conditions. This confirms what has been reported in the literature, (1,10,11). The reduced leaf area may imply a reduction in the potential amount of carbon fixed since the photosynthetic apparatus is reduced. This may affect the overall performance of the tree and hence, in compacted soil Mazzard rootstock may be a good preference to Mahaleb. Soil compaction alters physical arrangement of soil particles resulting in poor internal water drainage and gaseous exchange between _atmosphere and soil. Final shoot height and number of leaves per shoot were significantly affected by soil compaction. Rootstock 76 77 type had no significant effect on these two parameters. The non significant effect of rootstock type on leaf number and shoot height, may be due to compensatory shoot growth experienced by trees grown in compacted soil when the root growth is at its lowest ebb. The rate of shoot compensatory growth appears to be dependent on the extent to which root growth declines. The greater the decline in root growth, the greater may be the shoot compensatory growth. Although, field observations indicate that trees on mahaleb often are more vigorous early possibly due to greater drought tolerance (17), plants in this experiment did not experience drought stress. The significant effect of BD and rootstock type on (TCA) and shoot dry weight confirms what has been reported by other researchers (7,13). Trees grown in compacted soil had significantly thinner stems and the total dry weight of the shoots was significantly lower than that of control trees. In compacted soils, trees on Mazzard root are more vigorous than those on Mahaleb (17). This appears to be the case in this study in which Mazzard rooted trees grown in compacted soil out competed those on Mahaleb grown under similar soil conditions. The tendency of mazzard rootstock to produce a more fibrous rootsystem above the compacted zone may be a significant contributory factor to this observation. In non compacted soil, no significant differences in scion performance were observed between trees on Mazzard 78 and Mahaleb rootstocks. This does not agree with the report that trees on mahaleb do better than those on mazzard (5). The most likely explanation to this is differences in environments under which the plants were grown. Soil moisture tension was found to be very low in compacted soil than in non compacted. This implies that trees growing in non compacted soil required watering long before those growing in compacted soil and since watering frequence for all the plants was based on the requirements of plants growing in non compacted soil, plants in compacted soil experienced waterlogging conditions. Waterlogging conditions lead to anaerobic soil conditions which in turn lead to stress induced ethylene production (3,5). Soil compaction leads to poor internal water drainage which in turn leads to anaerobic conditions. Under total anaerobic soil conditions, a "signal" is thought to be produced in the root and transported to the shoot where it causes ethylene production (5). This may be the explanation for the increased ethylene production by shoots whose roots are subjected to mechanical impedance. Although there were no significant differences in ethylene production between shoots on Mahaleb and Mazzard, shoots on Mahaleb produced on average more ethylene than those on Mazzard. This area deserves more investigation before a firm conclusion can be drawn. 10. 11. 12. 13. LITERATURE CITED Anonymous. (1978). Annual Rept. Dept. of Agric. Tech. Serv. Rep. of S. Africa. 241pp. Anthony, R.D. et. al. (1938). Orchard tests of Mazzard and Mahaleb understocks. Proc. Amer. Soc. Hort. Sci., 415—418. Bradford, K.J. and S.F. Yang. (1980). Xylem transport of ACC in waterlogged tomato plants. Plant. Physiol. 6: 322-6 Beckman, T. G. (1985). Seasonal patterns of root growth potential of 2 containerized cherry rootstocks, P. Mahaleb L. and P. avium L. cv. Mazzard. MS Thesis. (1980). Stress induced ethylene production in ethylene requiring tomato mutant diageotropica. Plant Physiol. 65: 327-330 Byrant, L.R. (1940). Sour Cherry Rootstocks. Proc. Amer. Soc. Hort. Sci. 37:322-323 Childers, N.E. and D.G. White. (1950). Some Physiological effects of excess soil moisture on winesap apple tree. Ohio Agric. Expt. Stn. Res. Bull. 694 Clark, W.S and R.D. Anthony. (1946). An orchard test of mazzard and mahaleb cherry rootstocks. Amer. Soc. Hort. Sci., 48: 200-208 Coe, F. M. (1945).Cherry rootstocks. Utah Agr. Expt. Stn. Bull. 319 and review by Fruit Varieties and Hort. Digest. 1,18 Day, L. H. (1951). Cherry rootstocks in California. Calif. Agr. Expt. Stn. Bull. 725 Fogle, H. W. et. al. (1962). First year production records from a cherry rootstock study. Proc. Wash. State Hort. Assoc.y 58, 71-75 Gruppe, W. (1982). Characteristics of some dwarfing cherry hybrid rootstocks, Justus- Liebig Universitat, Giessen, FRG Res Rept., 2pp Heinicke, A.J. et. al. (1939). Cork experimentally produced on Northern Spy apples. Proc. Amer. 79 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 80 Soc. Hort. Sc. 37: 47-52 Kappes, E. M. and J. A. Flore. (1985). Unpublished. Layne, R.E.C. (1987). Peach Rootstocks. " In Root- stocks for Fruit CrOps". Eds. R.C. Rom and R.F. Carlson. N.Y. John Willey and Sons. 185- 216 Loustalot, A.J. (1945). Influence on soil moisture conditions on apparent photosynthesis and transpiration of pecan leaves. Jour. Agr. Res. 71:(12) 519-532 Perry, R.L. (1987). Cherry Rootstocks. “In root- stocks for Fruit CrOps". Eds. R. C. Rom and R.F. Carlson. N.Y. John Willey and Sons. 217- 264 Roberts, A.N. (1962). Cherry rootstocks., 54th. Ann. Rept. Oregon Hort. Soc. pp 95-98 Ruark, G.A. et. al. (1982). The influence of soil compaction and aeration on root growth and vigor of trees. A literature review. Part I. Arbor. Jour. 6: 251-265 Schmid, P.P.S. and Feucht. (1980). Isoelecric focusing of proteins and some enzymes from secondary phloem of cherry graft combinations I. Proteins in Winter, Sci. Hort. 12: 55—61 Slowik, K. (1970). Influence of machinery compaction on soil physical properties and apple tree growth. Prase Inst. Sadownictwa W; Skierniwcach Tom; Xiv 140 Van-Huyssteen, L. and Van Zly, (1983). Effects of soil compaction on subsoil root penetration and shoot growth of wine grapes. 10th. National Congress of soil Sci. Soc. of S. Afr. East London, S. Africa. 164 Webster, D.H. (1978). Soil conditions associated with absence or sparse development of apple roots. Can. J. Plant Sci. 58961-969. Westwood, M.N., and H.O. Bjornsted (1970). Cherry rootstock for Oregon. Oregon Hort. Soc. Ann. Rept. 61: 76-79. Westwood, M.N., et.al. (1976). Comparison of 81 mazzard, mahaleb and hybrid cherry rootstocks for "Montmorency” cherry Prunus cerasus L. g; Amer. Soc. Hort. Sci 100 (5), 536-541 25. Zimmerman, R.F. and L.T. Kardos. Effects of Bulk Density on Root Growth. Soil Sci. 91: 280-288 82 SECTION IV THE EFFECTS OF ARTIFICIALLY COMPACTED SOIL AND AND NATURALLY DENSE SOIL ON MONTMORENCY / E; mahaleb L ABSTRACT Hydraulic conductivity and soil bulk density were measured under controlled and field conditions and were related to root penetration ratio of Montmorency / P; mahaleb L seedling trees under field conditions. Values under controlled environment were related to those under field conditions and were found to be lower than those under field conditions by a factor of about 3. Root penetration ratio increased with increase in hydraulic conductivity. Under controlled conditions roots failed to go through compacted soil at 1.7g/cc BD but managed to pass through compacted soil under field conditions with approximately the same soil density level. 83 LITERATURE REVIEW When unimpeded, plants develOp a root distribution that' is characteristic of the species and perhaps the cultivar (5). Plant roots expand through the soil when the hydrostatic pressure within a cell arising from the osmotic potential of the vacuole overcomes cell wall pressure and resistance offered externally by the soil. Root growth is restricted in compacted soil irrespective of whether the compaction arise from cultural equipment or is genetic in origin. A penetrometer soil strength of 1.6 Kpa, measured at a volumetric water content of 16.9% (FC) was sufficient to lower plum root density to about 50% of that observed at a lower strength ( 7 ). In that study, trunk diameter was highly correlated with the average profile root density. Many devices have been used both in the field and laboratories to evaluate soil strength. Soil resistance to insertion of penetrometer is, like water infiltration a secondary indicator of soil compaction and is not a direct physical measurement of any specific soil condition (4,10). Also, like water infiltration it is affected by other factors besides soil compaction. The most important of these factors being soil moisture content which usually masks the influence of soil density differences. Penetrometer resistance is also influenced by soil texture. As a result the velocity permeameter, 84 85 a device whose readings are not influenced by the soil moisture content is prefered to the penetrometer (10). Also evaluation of penetrometers of varying sizes and shapes revealed that penetrometers do not simulate root penetration (6). The velocity permeameter is a useful and reliable device in determining soil density without influence of texture (12). It utilises changes in the falling column of water as input to a computer program which processes, the information to yield the hydraulic conductivity of the soil sample. The device measures saturated hydraulic conductivity (K) in the range 0.001-80 cm/hr or more (10,12). This range compares fairly well with that of saturated K in the laboratory (8). Laboratory determined, soil bulk density is a direct measurement of soil compaction and is very accurate. However its significance depends upon the soil type (4). In the field the soil has long unbroken tube-like passages that reach from the upper layers of soil down to the water table. These capillary tubes help to remove water from the upper layers of soil (3). When the soil is removed from the field to the pot, the long capillary tubes are destroyed. Thus, the soil does not function the same way it did in the field. Unless the soil is loosened or opened up by addition of sand, perlite, peat moss or other, it stays wet (3). Very little work has been reported on how soil and 86 perennial plant parameters measured under controlled environment relate to field conditions. The purpose of this study is to determine the relationship between bulk density and hydraulic conductivity measurements under controlled environment and field conditions and how they relate to root distribution of Montmorency/Mahaleb. MATERIAL AND METHODS Greenhouse Study. Loamy sand soil (Miami Loam) was collected from a cherry orchard. The soil was seived through screens to uniform granules (0.25-2mm). Young budded cherry trees on mahaleb with the buds still dormant were grown for 16 weeks in containers of 25 cm internal diameter. Each container consisted of 3 separate cylinders, top, middle and bottom held together with duct tape. The tOp and the bottom were 15 cm high and the middle was 11.25 cm high. The top and bottom cylinders consisted of planting mix composed of peat moss, perlite and vermiculite and the middle cylinder contained either uncompacted soil or soil compacted to 1.7g/cc bulk density. Compaction level was achieved by packing 17.89 kg of soil in the cylinder. A hand compressor (50.6kg) was used to compress the soil. Before planting the plants, the roots were trimmed to a uniform length (5cm) and the trees were planted to a same depth. During the course of the test period the plants were treated the same. Equal amounts of water were applied to each plant whenever plants growing in the non compacted soil required watering. The design of the experiment was a Randomized Complete Block design with 3 replicatiOns. 'At the end of the test period, (16 weeks) saturated hydraulic conductivity was measured in each container by the velocity permeameter. Root penetration 87 88 ratio (RPR) for each plant was calculated as the ratio of number of roots that exited the compacted zone to that of roots growing above the compacted zone. Field Study In the field (Loam Site), soil samples (cores) were taken randomly throughout the field. At each station, 20 samples (4 replications x 5 different depths 15cm apart) were taken. Each soil core was oven dried and soil bulk density was determined. Sites were randomly selected for hydraulic conductivity determination and at each site, 20 readings were determined (4 replictions x 5 depths). Root distribution of randomly selected, 3-year-old Montmorency cherry trees on mahaleb rootstock and planted at 1x3m was determined by the trench profile method. The trench profile method was chosen for root distribution studies because of its suitability for combining root distribution with soil profile characterization (1,2,9,11). A trench about 1.5m deep was excavated parallel to the tree row and 45cm from the tree. The soil profile face closest to the tree was used for root distribution study. The face was smoothed and levelled using a hand chisel and then washing the trench wall with a spray of water to expose the roots. A rectangular metal frame 120x240cm of galvanized pipe strung with white string provided a grid 10x30cm. The number, diameter and location of each root in each 10x30cm grid was recorded on grid paper. The data was 89 summarized on the basis of the total number of roots regardless of diameter and the number of small (<2mm), medium (2-5mm) and large (>5mm) roots. Greenhouse to Field Study comparison. The root distribution of each tree was related to bulk density and hydraulic conductivity reading of the sample site closest to the tree. Field velocity permeameter readings were related to those taken in artficially compacted soil. RPR of roots growing in the field was determined by calculating the ratio of number of roots growing below soil layer whose bulk density was 1.7g/cc or nearly close to 1.7g/cc, to that of roots growing above this layer. RPR under field conditions was related to that under controlled environment. RESULTS RPR increased with increase in hydraulic conductivity and there was a positive correlation between RPR and K with a correlation coefficient of 0.64, Figure 1. Hydraulic conductivity under controlled environment was about 3 times lower than in the field at approximately same bulk density. When K under controlled is trebled, a high correlation with a correlation coefficient of 0.9 was observed, Figure 2. At approximately, the same bulk density 1,7g/cc plants growing in artificially compacted soil had zero RPR whereas those growing under field conditions, had an average RPR of 0.27, (Table 1). 90 91 3.5 ,- 3.0 P a: 2.0 1.5 1.0 Hydraulic Conductivity (cm/hr) 0.5 o l 1 4 1 . 1 J 0.1 0.2 0.3 0.4 0.5 0.6 Root Penetration Ratio Figure 1. The relationship between Root Penetration Ratio and Hydraulic Conductivity. 92 P o I Hydraulic Conductivity (cm/hr) under field conditions '0 l 0 I l 1.0 2.0 Hydraulic Conductivity (cm/hr) under Controlled environment raised by a factor of 3 Figure 2. Comparison of Hydraulic Conductivity underfield and controlled environment. 93 Table 1. The effect of artificially compacted soil and naturally compacted soil on RPR. SOIL RPR Artificially compacted soil (BD 1.7g/cc) 0.00 Naturally compacted soil ( BD 1.7g/cc) 0.27 LSD (0.5) NS DISCUSSION Hydraulic Conductivity as related to RPR. RPR increased with increase in hydraulic conductivity and a positive correlation was observed between the two parameters with a correlation coefficient of 0.64. The increased RPR with increase in K confirms what has been reported in the literature where roots capability to explore soil horizons has been reported to decrease with increase in soil resistance (3,5). A lower K value implies high soil resistance. The correlation between the two parameters was not very high mainly because the values for the two parameters were not taken at exactly the same site. In many cases values had to be approximated. K under controlled environment and field conditions In the field where soil has not been disturbed water moves fast. When soil is collected from the field and placed in a container after being seived, the capillary tubes are destroyed and capillary action to pull‘ water from the soil is reduced (3). This appears to be the case in this study where K under artificially compacted soil was lower than in field at same bulk density. The differences in age between the one-year-old plants under controlled conditions and 3-year-old trees in the field, appears to have affected the K values also since thicker roots from older plants have a greater capability to open 94 95 soil than thinner ones associated with young plants. The more-the soil is opened up the greater the K values. Also natural fissures and gravel may have contributed to the high K values in the field. Under controlled conditions, K values were reduced by a factor of about 3. Based on this observation, one may conclude that if the K value under controlled environment is multiplied by 3, then a corresponding field K can be determined and this can be related to root distribution in the field, (Figure 1). This study deserves more research in order to establish a factor which can be used to relate K under controlled environment to field conditions. RPR under artificially compacted soil was zero and under field conditions was 0.27 at approximately 1.7g/cc. This is not surprising because soil in the field is very variable especially, soils of glacial till origin in Michigan. Within a very small area soil may be at different levels of bulk density. 10. 11. 12. LITERATURE CITED Beukes, D. J. 1984. Apple root distribution as affected by by irrigation and different soil water levels on two soil types. J; Amer. Hort. Sci. 109:723-728. Bohm, W. 1979. Methods of studying rootsystems. Ecological studies 33. Springer-Verlag, Berlin. Boodley, J. W. 1981. The Commercial Greenhouse. Delmar Publishers. New York. Chancellor, W.J. 1977. Compaction of Soil By Agricultural Equipment. Division of Agric. Sci. Unversity of California. Bull. 1881 Gerwitz, A., and E.R. Page 1974. An emperical mathematical model to describe plant rootsystems. J.Appl. Ecol. 11:733-781 Graecen, E.L., et. al. 1968. Soil resistance to metal metal probes and plants root.Soil Sci vol. 4:769-779 Grimes, D.W. et. al. 1982. Plum root growth in a variable - strength field soil. J; Amer. Hort Sci. 107(6) 990-992 Hillel, D. 1980. Fundamentals of soil physics. Academic Press. New York. Layne, R.E.C., C.S. Tan and R.L. Perry. Characterization of Peach Roots in Fox Sand as influenced by sprinkler irrigation and Tree Density. J;_Amer. Soc. Hort. Sci. 111 (S):670-677. Merva, G.E. Falling head permeameter for field investigation of hydraulic conductivity. ASAE Paper no. 79:2515 Oskamp, J. 1932. The rooting habit of deciduous fruit on different soils. Proc. Amer. Soc. Hort Sci. 29:213-219 Saavalainen, J., and S. Rintanen. 1986. A new method for measuring saturated hydraulic conductivity. Finnish g; Water Economy Hydraulic and Aric. Engineering. 27(3)31-34 96 SUMMARY In dense soil Mazzard performed better than Mahaleb. This data confirms field observations. Rootstocks that form a dense fibrous root system above a compacted zone (e.g. MxM2 and Mazzard) physically escape from anaerobic conditions. This observation is not revealed by flooding experiments and is typically of what happens in the field. This technique may be used to screen rootstocks for tolerance to soil density. Use of larger containers is preffered since this will facilitate measurement of more parameters. Montmorency/Mazzard perform better than Montmorency/ Mahaleb in dense soil. This confirms field observations. Measurements under controlled environment correlated very well with those under field conditions. 97 APPENDIX 98 Table A1. Mean root count of 4 Prunus root systems above and below soil layer compacted to 1.7g/cc BD. Rootstock GF677 MxM2 Mahaleb GIl48—9 2 Above 156a 205a 98a 90a Below 78b 20b 23b 30b Z Values within a column followed by the same letter are not significantly different from each other at 5% level, by Duncan's Multiple Range Test.