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FORAGE & GRAZINGLANDS

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

^a USDA-ARS Grazinglands Research Lab., 7207 W. Cheyenne St., El Reno, OK 73036
^b Texas Agricultural Experiment Station, 17360 Coit Rd., Dallas, TX 75252. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture or the Texas Agricultural Experiment Station

^* Corresponding author (Charles.MacKown{at}ars.usda.gov).

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.

Abbreviations: CT, conventional tillage • MG, maturity group • NT, no tillage