A gronomy J our n al • Volume 110 , I ssue 1 • 2 018 W ater availability at critical growth stages of crops is the major yield limiting factor in dryland crop production (Farahani et al., 1998;Allen, 2012). Dryland agriculture is a special case of rainfed agriculture practiced in arid and semiarid regions. In these regions when irrigation is not used, water conservation becomes the primary focus of management decisions because growing season precipitation is seldom suffi cient to fully meet evapotranspiration demand. Conditions of moderate to severe plant water stress occur during a substantial part of the year and storage of water during fallow for use by a subsequent crop is oft en practiced (Nielsen et al., 2016). Available soil water at planting and ISP are usually the only two sources of water for annual crops such as corn and grain sorghum grown in dryland systems. However, the singular contribution of ASWP for corn and grain sorghum yield was seldom studied.Th e impact of water availability on grain yields of corn and grain sorghum has been studied in depth through yield relationships with ISP or diff erent irrigation levels Payero et al., 2006;Klocke et al., 2011;Assefa et al., 2014;) and with crop water use (Nielsen and Vigil, 2017). Th e infl uence of cropping system on ASWP and on subsequent grain yield has been reported for wheat (Triticum aestivum L.) (Nielsen et al., 2002;Nielsen and Vigil, 2005) and results from these studies indicated that wheat yields were correlated with ASWP. Th e results from Nielsen and Vigil (2005) also suggest that the relationship between ASWP and wheat yield varied year-to-year depending on evaporative demand and ISP. Studies in water-yield relationships of proso millet (Panicum miliaceum L.), pea (Pisum sativum L.), triticale (Tritico secale rimpaui Wittm.), foxtail millet (Setaria italic L. Beauv.), corn, grain sorghum, bean (Phaseolus vulgaris L.), and sunfl ower (Helianthus annuus L.) (Lyon et al., 1995;Felter et al., 2006;Nielsen et al., 2009) suggest that the eff ect of ASWP was greater for short duration crops (bean, proso millet) compared with long duration crops (corn, grain sorghum, sunfl ower).Increase in ASWP due to changes in management practices was among the main factors that contributed to the greater portion of the 139% grain sorghum yield increase in the years 1939 to 1997 (Unger and Baumhardt, 1999
Core Ideas• Yield gains from available soil water at planting decreased as inseason precipitation increased.• Corn yield gain 27 to 33 kg ha -1 (mm available soil water at planting) -1 at in-season precipitation of 196 to 215 mm.• Corn yield gain 9 to 25 kg ha -1 (mm available soil water at planting) -1 as in-season precipitation increased to 288 to 354 mm.• Sorghum yield gain 12 to 22 kg ha -1 (mm available soil water at planting) -1 at in-season precipitation of 163 to 281 mm.• Sorghum yield gain 0 to 6 kg ha -1 (mm available soil water at planting) -1 at in-season precipitation of 315 to 382 mm.