Wednesday, November 15, 2006

Evaluating Decision Rules for Dryland Crop Selection.

David C. Nielsen, Merle F. Vigil, and Joseph G. Benjamin. USDA-ARS, Central Great Plains Research Station, 40335 County Road GG, Akron, CO 80720

No-till dryland cropping systems in the central Great Plains have more water available for crop production than the traditional conventionally tilled winter wheat (Triticum aestium L.)-fallow systems because of greater precipitation storage efficiency. That water is used most efficiently when a crop is present to transpire the water, and crop yields respond positively to increases in available soil water. The objective of this study was to evaluate yield and precipitation use efficiency of cropping systems where crop choice was based on several crop selection rules incorporating a grass/broadleaf rotation scheme and crop responses to available soil water and expected growing season precipitation. Available soil water at planting was measured at several decision points each year and combined with three levels of expected growing season precipitation to provide input data for water use/yield production functions. The predicted yield from those production functions was compared against established yield thresholds, and crops were retained for further consideration if the threshold yield was exceeded. Crop choice was then narrowed by following a rule which rotated summer crops with winter crops and grasses with broadleaf crops. Yields, gross receipts, and economic precipitation use efficiency from the various opportunity cropping selection schemes were compared with yields, gross receipts, and economic precipitation use efficiency from four set rotations [wheat-fallow (conventional till), wheat-fallow (no-till), wheat-corn-fallow (no-till), wheat-millet (no-till)]. Two of the four opportunity cropping selection schemes resulted in higher gross receipts and economic precipitation use efficiency than the set rotations, with the other two selection schemes resulting in lower gross receipts and economic precipitation use efficiency than the set rotations. Cropping frequency can be effectively increased in dryland cropping systems by use of crop selection rules based on water use/yield production functions, measured available soil water, and expected precipitation.

Handout (.pdf format, 520.0 kb)