Replacing Fallow with Continuous Cropping Reduces Crop Water Productivity of Semiarid Wheat

By Robert M. Aiken, D. M. O'Brien, B. Olson, L. Murray. 2013

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Water supply frequently limits crop yield in semiarid cropping systems; water defi cits can restrict yields in drought-aff ected subhumid regions. In semiarid wheat (Triticum aestivum L.)-based cropping systems, replacing an uncropped fallow period with a crop can increase precipitation use effi ciency but reduce wheat productivity. Our objective was to analyze crop sequence and environmental eff ects on water use, components of water productivity, and net returns of winter wheat (WW) in a semiarid region. A fi eld study was established to evaluate eight 3-yr crop sequences, including a wheat phase followed by a feed grain phase (corn (Zea mays L.) or grain sorghum (Sorghum bicolor (L.) Moench)) and an oilseed phase (OS; spring canola (Brassica napus L.), soybean (Glycine max (L.) Merr.), sunfl ower (Helianthus annuus L.), or none (fallow)). Standard measurements included crop water use (WU), canopy leaf area index at anthesis, biomass, grain yield, and yield components. Net return (NR) was calculated as the diff erence between crop revenue and total operating costs. Replacing an uncropped fallow period with an OS crop reduced water productivity responses of WW (biomass, grain yield, and NR) by 18, 31, and 56%, respectively, relative to that of WW grown aft er fallow. Th ese responses to continuous cropping corresponded to reductions in all components of a water-limiting yield production function. Th e modest water productivity observed (0.28-0.62 kg m -3 ), relative to a reported global range of 0.6 to 1.7 kg m -3 , indicates opportunity to improve wheat water productivity through management and genetic gain.

Subfields: Ecology, Evolution, Behavior and Systematics, Global and Planetary Change, Soil Science

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