Soil Water and Water Use in Long‐Term Dryland Crop Rotations

Dryland crop rotation systems are sustainable only if there is sufficient water available for profitable crop production. The objective of our study was to identify potential crop rotation systems for the central Great Plains and similar semiarid areas that increase soil water, fallow water accumulation, fallow efficiency, and water productivity of major crops. The study was conducted from 2000 through 2017 near Tribune, KS. Four summer crops [corn (Zea mays L.) (CR), grain sorghum (Sorghum bicolor L.) (GS), soybean (Glycine max L.) (SB), and sunflower (Helianthus annuus L.) (SF)] along with winter wheat (Triticum aestivum L.) (W) were grown in 1‐, 2‐, 3‐, and 4‐yr rotations, with most rotations including a fallow (F) phase. Rotations were W–CR–SB–F, W–F, W–CR–SF–F, W–GS–F, W–SF–F, and W–CR–GS–F from 2000 through 2006 and W–CR–F, continuous GS, W–F, W–GS–CR–F, W–GS–F, and W–CR–GS–F from 2008 through 2017. Results showed that available soil water (ASW) at corn planting was in the order W–CR–GS–F = W–CR–SB–F > W–CR–SF–F for 2000–2006 period and ASW and water productivity were in the order W–CR–GS–F = W–CR–F > W–GS–CR–F for the 2008–2017 period. The ASW in the 30–150 cm profile depth at sorghum planting and crop water productivity were in the order W–GS–F > W–CR–GS–F for the 2000–2006 period and in the order W–GS–CR–F = W–GS–F > W–CR–GS–F = GS–GS for the 2008–2017 period. ASW at wheat planting and crop water productivity were greater in W–F and W–GS–F in the wheat‐based rotations. Results consistently showed that with summer crop planting there was greater soil water following wheat than another summer crop. Core Ideas Soil water at planting of summer crop, prior off‐season soil water accumulation, water use, and crop water productivity were greater following wheat than following another summer crop. The longer fallow period between wheat harvest and grain sorghum planting and yield potential of grain sorghum compared with corn, sunflower, and soybean justifies wide adoption of winter wheat–grain sorghum–fallow in semi‐arid regions Soil water at wheat planting, fallow accumulation, water use of wheat, fallow efficiency, and crop water productivity were greater in winter wheat–fallow and winter wheat–grain sorghum–fallow of the wheat‐based rotations.