Enhancing Cool-Season Legumes Production and Contribution to Soil Nitrogen.

Efficient cool-season legume production can expand the window of forage production, improve forage nutritive value, and improve soil nitrogen (N) status for subsequent cropping. It is well documented that legumes, in symbiotic association with rhizobium bacteria, fix atmospheric N₂ to plant available forms in the soil, and may not require N fertilization. However, in soils with poor native fertility, starter N fertilization could enhance legume growth and development, and subsequently, boost their N fixation capability. In a field study, we evaluated the impacts of starter nitrogen fertilizer application on several cool-season legume species, and assessed contribution of legumes to N status of the soil. Sixteen cool-season legume species were grown in North-Central Florida on soils with poor native fertility. The legumes were either supplied with a modest starter N application at 30 kg N ha^-1 or without starter N application. After the growing season, soil samples were collected from randomly selected treatments to monitor changes in N content of the soil. Across all legume species, the starter N fertilizer application significantly increased DM yield of the legume forages by at least 40% (40% to 160% increase). Consistent with several studies, the legume production generally improved the N status of the soil, relative to N background levels. The greatest N contribution occurred in the treatments that received the initial starter N application. Thus, in soils with poor native N status, a modest starter N could be applied to cool-season legume crops to increase productivity, and further improve the soil N status for subsequent forage production.