Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/1996
Publication Date: N/A
Interpretive Summary: Marginal farmland on the Southern Plains is deficient in nitrogen. On such land we found little benefit to ensuing wheat hay crops from growing unfertilized or nitrogen fertilized grass. Following alfalfa, substantial wheat hay crops were grown for 5 years on a loamy soil, however, the benefit from alfalfa was considerably less on a deep sandy soil. This study provides criteria to evaluate residual effects of soil stabilizing forage crops and to make nitrogen fertilization recommendations on succeeding crops.
Technical Abstract: Increasing N fertilizer prices give rise to the question of N benefits from legumes in cropping systems on the Southern Great Plains. This study quantified wheat hay production and N uptake over 7 years following 6 years of alfalfa, cicer milkvetch, or grass (Old World bluestem) production in western Oklahoma. Precipitation over the 7 years averaged 550 mm yr-1. The major residual N effects were measured within the first 5 years. On a fine sandy loam soil, wheat hay yields averaged 3070 kg ha-1yr-1 over 5 years following alfalfa, 2580 kg ha-1yr-1 following milkvetch, and 950 kg ha-1yr-1 following grass; N uptake attributed to the residual effect from legumes (calculated by the difference method) averaged 34 kg N ha-1yr-1 from alfalfa and 25 kg-1 ha-1 yr from milkvetch. On a deep loamy sand soil, wheat hay yields averaged 1290 kg ha-1 yr-1 over 5 years following alfalfa and 710 kg ha-1yr-1 following grass; N uptake attributed to the residual effect from alfalfa averaged 8 kg N ha-1 yr-1. Thus, the residual N effect attributed to legumes was substantial on the fine sandy loam soil and relatively small on the deep loamy sand soil.