Winter wheat and prose millet yield reduction due to sunflower in rotation

Producers wishing to diversify crop production systems from the traditional winter wheat (Triticum aestivum L.)-fallow system of the central Great Pla ins need information regarding the impact of sunflower (Helianthus annuus L .) on subsequent winter wheat end prose millet (Panicum miliaceum L.) yield s. This study was conducted to quantify winter wheat and prose millet yield reductions due to the lower available soil water that exists when sunflowe r is the prior crop in rotation. Eight crop rotations-including combination s of winter wheat (W), prose millet (M), corn (Zea mays L.) (C), sunflower (Sun), and fallow (F)-were established in 1990 and evaluated for yield, ava ilable soil water at planting, and crop water use in 1995, 1996, and 1997. The experiment was conducted at Akron, CO, on a Weld silt loam (fine, smect itic, mesic Aridic Paleustoll). Available soil water at wheat and millet pl anting was lower where sunflower had been the previous crop than where sunf lower was not the previous crop. In dry years, rotations with sunflower as the previous crop had lower wheat and millet water use than other rotations , but averaged over 3 yr, there was no effect of sunflower on wheat or mill et water use. Average wheat yield in a W-Sun-F rotation was about 30% lower than wheat yield from W-C-Sun-F, W-M-Sun-F, W-C-F, and W-F. Average millet yield in a M-Sun rotation was 43% lower than millet yield from M-W-C. Whea t yield declined by 178.5 lb/acre (3 bu/acre) for each inch decline in avai lable soil water at planting. Millet yield declined by 295.6 lb/acre for ea ch inch decline in available soil water at planting. In making the decision to include sunflower in crop rotations, producers will have to consider im pact on subsequent crop yields, as well as costs of production, market valu e of crop, impact on pest problems, and total productivity of all crops in the rotation.