A Decision Aid for Fallow Replacement Crop Selections Based On Soil Water At Planting In the Central Great Plains.

Better soil conservation, precipitation use efficiency (PUE), and economic returns from introduction of summer fallow replacement crops into the dryland winter wheat-summer fallow (WF) cropping system have been reported in the semiarid Central Great Plains of USA. However, due to the highly variable precipitation, selection of a fallow replacement crop with assured net returns for the system is a challenge. We evaluated the potential of several crops to be used as fallow replacement crops in relation to soil water available at planting.  We simulated long-term yields and calculated net returns for three grain crops [corn (Zea mays L.), canola (Brassica napus), and proso millet (Panicum miliaceum L.)] and two forage crops [foxtail millet (Setaria italica L. Beauv.) and spring triticale (X Triticosecale rimpaui Wittm.)] at various levels of plant available water (PAW) at planting at Akron, CO and Sidney, NE. Long-term weather data at Akron and Sidney and crop modules in the RZWQM2 model were used. Yield responses of the crops to 25, 50, 75 and 100% PAW at planting in the whole soil profile (180 cm) (WP) or only in the top 45 cm soil profile (TP) were simulated. All crops showed significant (p<0.01) yield increase to increasing initial PAW levels in both the WP and TP, but the yield responses of corn and canola to increasing PAW in TP were of little practical significance.  The two forage crops gave greater net returns than the three grain crops for all initial PAW levels investigated at both Akron and Sidney.  Among the grain crops, proso millet was the most profitable crop at Akron, while canola was the most profitable crop at Sidney. The data and figures generated in this study can guide the selection of a spring- or summer-planted crop in a WF system if a measure or estimate of PAW at planting is available.