Agronomic Feasibility of a Continuous Double Crop of Winter Wheat and Soybean Forage in the Southern Great Plains

In the southern Great Plains, dryland double‐cropping soybean [Glycine max (L.) Merr.] after winter wheat (Triticum aestivum L.) could provide quality summer forage, partially offset mineral fertilizer N applied to winter wheat, and lessen soil erosion. Waiting for wheat grain to mature, however, delays soybean planting and subjects growth to dry and hot conditions. Planting soybean after a hay crop of wheat was investigated to determine the feasibility of the system as a source of livestock feeds and N uptake by both crops. Twelve treatment combinations of two wheat fertilizer N levels (0 and 112 kg N ha−1) and six summer management treatments (fallow: conventional and no‐till; soybean: grazed, cut for hay, green manure, and mulch) were arranged in strips across four replications. Soybean biomass ranged from 1.35 to 1.90 Mg ha−1 when soybean grazing and harvest occurred at seed fill, and crude protein ranged from 129 to 220 g kg−1 resulting in a 3‐yr average N uptake of 44 kg ha−1 Within each N fertilizer level, average wheat forage yields were not different, but yield increased 29% with N fertilizer and crude protein was inversely related to yield. Double‐cropped soybean failed to offer any yield‐enhancing N benefit to wheat or enhance soil N and C content after 3 yr, even when used as a green manure. Unless a producer is willing to accept the low productivity of soybean as a double crop with wheat, the feasibility of this dryland double‐crop forage system is limited.