Of the numerous factors affecting crop yield, the major factor for corn and soybean in the southeastern Coastal Plain appears to be available soil water Inadequate rainfall and soil compaction, which limits root exploration of stored soil water exacerbate this problem. Potential solutions, though costly and energy intensive, include irrigation and annual deep tillage. Sometimes, doing both provides additive yield increases for corn. The objectives of this study were: (1) to prove a site-specific irrigation system, and (2) to test the separate and combined effects of irrigation, tillage, N-fertilizer and crop rotation on corn and soybean yield. A center-pivot irrigation system that had been modified to allow variable-rate water and nutrient applications to 100-m{sup}2 plots within the system was used to manage an experiment with corn-soybean rotation, irrigation, deep tillage, and N-fertilizer treatments during 1995-1998. The modified center-pivot system satisfactorily applied water and N fertilizer to the treatment areas, and reliability of the control system improved during this experiment. Irrigation increased corn yield all years (8 to 135) and soybean yield three of four years (26 to 31). Deep tillage increased yield in only two years, for corn (4 to 6). For these soil and weather conditions, irrigation increased corn and soybean yields more consistently than deep tillage. The site-specific irrigation facility performed as expected and should provide the research infrastructure to answer many long-standing questions about irrigated cropping systems in the southeastern Coastal Plain.
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