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This study was designed to determine to what extent tillage and fall growth as affected by planting data influence profile soil water for spring growth and yield of monoculture winter wheat (Triticum aestivum L.). The study was conducted for 3 crop years (1982–1985) at Stillwater and Lahoma, OK. A randomized-block design with a split-plot arrangement was used where main units were tillage and subunits were 4 plantings spaced 1 month apart. Soil water was measured using the neutron-scattering method. The effects of tillage and amount of fall growth on profile soil water (PSW), total soil water in the 1.2-m soil profile, differed between the two locations. At Stillwater, neither tillage nor differences in fall growth affected soil water. During the third year at Lahoma, where precipitation was more limiting, a significant tillage effect on PSW developed at jointing. No-till (NT) was significantly greater than that of the conventional tillage (CT). This effect was observed consistently through the 1.2-m profile. The effect of fall growth on spring PSW was not consistent. The fall growth effect on grain yield was significant at both locations in all 3 years except for Stillwater in 1982–1983. However, there was no tillage by planting date interaction. The mid-September and October planting dates consistently had higher yields than the mid-August and November planting dates. The use of NT has a potential to increase spring profile soil water for the production of monoculture winter wheat in the South Central Great Plains. However, the potential to deplete this increase through increased fall growth by planting early exists and there is further need to evaluate the benefits of additional forage obtained with earlier planting vs. the depletion of stored soil water and the potential effect upon grain yields. |
