Influence of Subsurface Irrigation and Organic Additions on Top and Root Growth of Field Corn '

Numerous attempts have been made to increase root proliferation by modifying soil profiles possessing undesirable chemical and physical properties. Field and laboratory studies were conducted over a 5-year period on an Evesboro loamy sand (mesic, coated Typic Quartzipsamments) soil from Delaware to determine the effect of organic additions and type of irrigation on corn (Zea mays L.) grain yield, root distribution, and on selected soil properties. The study also sought to determine if organic additions would increase the effectiveness of subsurface irrigation. Organic additions, made only in the 1st year of the study, consisted of 10 x 40 cm chisel (C) openings at 76 cm intervals which were filled with solid waste (SW) and/or poultry manure (PM) at 65 metric tons/ha. No attempt was made to superimpose corn rows directly above the chisel openings. Irrigation types were subsurface (SSI), and trickle irrigation (TI). Grain yields were significantly higher in C + SSI than in C + TI treatments. Chiseling + SSI increased the average 5-year corn yield 4,300 kglha over C alone which demonstrated the pronounced effect that SSI had on yield. Organic additions had no signifciant effect on grain yields, although yields for the C: + SW treatment were numerically higher than for the C + PM treatment each year of the study, and the former averaged 1,150 kg/ha higher over the 5-year period. The C + SW treatments also produced higher yields than the control (NC). Chiseling, without incorporation of organic materials (C) was no more effective than leaving the soil undisturbed (NC). Organic additions enhanced root growth more than yield of corn. The subsoil was essentially devoid of roots without chiseling or organic additions. The highest CEC and organic matter levels at the end of the 5-year study were found in the organic addition trench adjacent to the SSI lines. Corn roots proliferated in this region and in most cases enveloped the irrigation lines. Lateral as well as vertical movement of Ca, K, Mg, and P occurred with the lowest concentrations occurring in the plow layer. Movement of plant nutrients laterally from the organic addition trench into the surrounding subsoil probably contributed to root extension and could be significant in terms of nutrient utilization. Additional index words: Irrigation, Organic wastes, Atlantic Coastal Plain soils. ANY of the sandy-textured Ultisols of the SouthM eastern and Middle Atlantic States have a densely packed A2 horizon below the plow layer. The A2 horizon often restricts root penetration which reduces the storage capacity of plant available water and makes agricultural crops susceptible to drought (Reicosky et al., 1977). Numerous attempts have been made to increase root proliferation by modifying soil profiles possessing undesirable chemical and physical properties. Methods used include deep subsoiling, slip plowing, deep plowing, double digging, trenching, and backhoe mixing (Mech et al., 1967; Robertson et al., 1966; Eck and Davis, 1971; Kaddah, 1976; Bradford and Blanchar, 1977). Cassell(l980) attempted to alter the water retention characteristics in two soils by deep and medium plowing. The deep plowing operations in' Published with the approval of the director of the Delaware Agric. Exp. Stn. as miscellaneous paper no. 970. Contribution No. 14! of the Dep. of Plant Science. Received 27 Jan. 1982. Extension agronomist and professor of plant science and assistant professor of soil chemistry, respectively, Dep. of Plant Science, Univ. of Delaware, Newark, DE 19711. duced no direct increase in water-holding capacity in either soil. Deep plowing of a Norfolk lamy sand however, decreased the infiltration rate which increased run-off. Weatherly and Dane (1979) found that with conventional tillage, soil water movement and water uptake were less for non-subsoiled treatments than for other treatments. The two subsoiled treatments and the no-tillage-no-subsoiling treatment indicated root penetration and soil-water uptake below 50 cm. In-row subsoiling was shown by Bennett (1939) to encourage deeper rooting of cotton (Gossypiunz hirsutum L.) and soybeans (Glycine max L.) and yields were increased, especially during dry years. With plentiful soil moisture, soil strength decreased and root development was less inhibited by traffic and textural pans. Doty et al. (1975) grew millet (Sataria italica L.) and sweet corn (Zea mays L. var. Sacchareta) on a Varina sandy loam soil with a compact A2 horizon disrupted by chiseling to a depth of 38 cm. Chiseling increased millet dry matter and sweet corn yields significantly. The chiseled soil produced yields comparable with irrigated non-chiseled soil. More water was also available for plant use in the chiseled soil than in the non-chiseled soil. The authors also found that chiseling the soil to disrupt the compact A2 horizon will sustain millet and sweet corn production from 8 to 24 days longer under drought conditions than moldboard plowing or shallow disking and harrowing. Researchers have also attempted to mitigate the presence of pans by deep placement of lime, fertilizers, and organic materials (Bradford and Blatichar, 1977; Cassell, 1980). Cassell (1980) employed deep tillage, medium tillage, and conventional tillage techniques to add lime and P to some Atlantic Coastal Plain soils. With deep-tillage, soil pH and P levels were higher at the 38to 51-cm depth than with conventional or medium-tillage systems. Numerous researchers have sought to ameliorate undesirable soil chemical and physical properties by adding composts or by mulching. Hortenstine and Rothwell (1973) found that compost applications kept soil pH at the level of the control treatment; however, there was a drop in pH as the result of mineral fertilizer applications. Soil P was increased over the control with the two highest rates of compost. Soil K and Ca were increased with the 16-, 32-, and 64metric tons/ha rates of the compost and the mineral fertilizer. The compost significantly increased the CEC and organic matter content of the soil when applied at the highest rate of 64 metric tons/ha. Vitosh et al. (1973) found that organic matter and exchangeable Ca, K, and Mg increased with increasing rates of manure. Jackson et al. (1977) surface applied broiler litter at rates up to 134.4 metric tons/ha. They found that organic matter decreased from 1.7% in the check plots to 1.4% at the high rate of broiler litter. The net decrease in organic matter with increasing