Conservation Tillage and Irrigation Effects on Corn Root Development

The effects of conservation-tillage practices on the root environment of corn (Zea mays L.) may differ with varying amounts of irrigation. Dryland, 50% irrigation, and 100% irrigation treatments were applied in combination with disc, no-tillage, and a postemergence chisel treatment designed to allow rapid infiltration of irrigation water. The study was conducted during the 1980 growing season at the Nebraska Agricultural Experiment Station near Mead, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls). Root samples were taken to 1.50 m in 0.15-m increments. Sampling was done at 60 (V8), 77 (V14), and 90 (R2) days after planting. Root length per soil volume as a function of depth from the soil surface was characterized using hybrid B73 X Mo17. Root length exhibited linear and often quadratic distribution over sampling depths at all sampling dates. The 100% irrigation treatment exhibited greatest total profile (0to 1.5-m) and surface (0to 0.15-111) root length at R2. Dryland and 50% irrigation treatments were associated with relatively greater root length proliferation deep in the soil profile. Differences in root length distribution were not as pronounced at stages V8 and V14. Chisel and no-tillage treatments, with crop residues at the soil surface, resulted in greater surface (0to 0.15-m) and total profile root length than discing. Corn roots tended to explore the lower profile to a greater extent under water stress conditions. This phenomenon, in conjunction with soil water conservation by no-tillage methods, may allow irrigators to increase water-use efficiency by better use of stored soil moisture. Additional index words: No tillage, Reduced tillage, Water regime, Water stress, Root distribution, Zea mays L. I RRIGATED corn (Zea mays L.) comprises a significant portion of total U.S. corn production. It is estimated that future additions in imgated acreage will be with center-pivot systems (Gilley and Mielke, 1980). Recent concerns about irrigation energy requirements have led to widespread use of low-pressure center-pivot systems. These low-pressure systems may induce runoff and soil erosion due to their high water application rates unless conservation practices are employed. Surface residues have also been shown to reduce evaporative water loss from the soil surface (Hill and Blevins, 1973) and were associated with reduced runoff (Van Doren and Triplett, 1969). Soil water and temperature regimes and other soil physical factors can affect corn root growth. These soilrelated factors often differ among various tillage systems. Crop residues often associated with conservation-tillage practices have been shown to reduce soil surface temperature (Griffith et al., 1973), which can affect the direction of root growth (Chaudhary and Prihar, 1974). Chaudhary and Prihar (1 974) also found that conventional tillage encouraged earlier and deeper penetration of corn roots into the soil profile than did no-tillage, but no-tillage corn had more roots in the top 0.20 m of soil during early growth stages. It is clear that tillage systems alter the soil environment, thus providing a potential for affecting corn root distribution within the soil. Irrigation has been shown to affect total corn root weight and distribution. Irrigated corn produced more total root mass than dryland corn in one Kansas study (Mayaki et al., 1976), but dryland corn had a greater proportion of its total root mass below 0.30 m in the soil. Robertson et al. (1980) found both irrigation frequency and total water application affected root distribution and total root length. Moderate water stress imposed by light, infrequent irrigations was associated with the greatest total root length for corn. The objective of the present study was to characterize corn root length distribution within the soil profile as af. fected by irrigation and tillage. MATERIALS AND METHODS