Replacing fallow with warm-season annual crops in dryland wheat systems

Rotating wheat (Triticum spp.) with fallow is a popular practice in the North American Great Plains, in spite of environmental degradation and economic inefficiencies. Two-year crop sequences were established in four fields in central Montana to determine if grain yield could be maintained when wheat followed warm-season annual crops compared with fallow in shallow (soil depth ≤650 mm) dryland soils. More than 15 warm-season species along with three crop mixtures were managed as cover, forage, and grain or seed crops in the 1st year. Differences were not detected in volumetric soil water content (VWC) following fallow and warm-season crops (P > .8). Wheat yield following fallow averaged 2.1 Mg ha–1 and was comparable following warm-season broadleaf crops and grass-broadleaf crop mixtures (2.0 Mg ha–1, P > .50), while trending downward slightly following grasses (1.9 Mg ha–1, P = .08). Previous crop management (cover, forage, and grain or seed crop) did not affect subsequent wheat yield (P = .98), but did affect wheat grain protein (P < .01). Wheat grain protein concentration was higher following fallow (124 g kg–1) than warm-season grass and broadleaf crops, as well as mixtures (116 g kg–1), but was below the 132 g kg–1 threshold indicating N deficiency, regardless of previous-year treatment. These results indicate that grain yield of wheat can be maintained following warm-season annual crops compared with fallow in central Montana and similar semi-arid environments with shallow soils, though soil N supplementation is needed to optimize grain yield and quality.

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