Continuous winter wheat ( Triticum aestivum L. em Thell.) is the foundation for most US Southern Great Plains (SGP) agriculture. Inorganic N fertilizers are important to wheat production, but increasing N prices have caused producers to reconsider growing legumes during summer fallow for green N. This study was conducted during 2008 to 2012 to determine the potential for using lablab [ Lablab purpureus (L.) Sweet cv. Rio Verde] to support wheat under conventional and no-till management compared with soybean [ Glycine max (L.) Merr. cv. Laredo] and three inorganic fertilizer treatments (none, 40, and 80 kg N ha -1). Legume seeds were inoculated and sown after wheat harvest each year, grown from June to August, and terminated in early September. Wheat was then sown with or without preplant tillage and grown to maturity. Grain yield, N concentration, and N accumulated in grain were analyzed to define N treatment, tillage system, and year effects. The amount and distribution of precipitation during 2008 to 2012 varied from 53 to 92% and 63 to 160% of the long-term averages for wheat (688 mm) and legume (162 mm) phases. Tillage effects were nonsignificant ( P<0.76), but N treatment * year interactions were significant for grain yield, N concentration, and N accumulated in grain ( P<0.01). The legumes resulted in some single-year increases in grain yield, but the overall yield response was inconsistent. The legume treatments reduced N concentration in wheat grain compared with the unfertilized control. These results show that neither legume was an effective short-term (?4-yr) N source for systems of continuous wheat production in the SGP.
