Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2006
Publication Date: 7/8/2007
Citation: Mackown, C.T., Heitholt, J.J., Rao, S.C. 2007. Agronomic feasibility of a continuous double crop of winter wheat and soybean grown solely for forage in the Southern Great Plains. Crop Science. 47:1652-1660. Interpretive Summary: Small grain, forage, and stocker cattle production are major agricultural enterprises in the Southern Great Plains. While winter wheat is often grown for both grain and forage, this leaves gaps in available forage and creates a lack of alternative forage because wheat fields are traditionally till-fallowed during the summer. Double cropping winter wheat with soybean could provide a high quality source of forage that compliments summer grass pastures, reduces erosion from fallowed wheat fields, and offers N benefits to the following wheat crop. Delays in planting soybean in wheat fields harvested for grain or used for season long grazing would shift the growth of soybean to the driest and hottest part of the summer. We evaluated the option of harvesting wheat for hay at the heading stage so soybean planting would occur earlier and growth conditions would be more favorable. Soybean forage production following wheat cut for hay ranged from only 1200 to 1700 lb/acre at beginning seed fill. Cattle readily consumed soybean leaves but left stems and pods. Because of low soybean productivity, 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 dry-land double crop forage system for the southern Great Plains is limited. This information will be useful to researchers, consultants, and producers wishing to use soybeans as an alternative source of forage following wheat in a dry-land cropping system.
Technical Abstract: In the Southern Great Plains winter wheat is grown for grain-crop and used extensively for forage. During summer, wheat fields are normally fallow and summer forage is mostly native and improved warm-season perennial grass that decline in quality as they mature. Dry-land double cropping soybean behind winter wheat could provide a source of high 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 behind 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 treatments combinations of two wheat fertilizer N levels (0 and 112 kg N/ha) 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 when soybean grazing and harvest occurred at beginning seed fill, and crude protein ranged from 129 to 220 g/kg resulting in a 3 yr average N uptake of 44 kg/ha. 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 dry-land double crop forage system for the southern Great Plains is limited.