MANURE AND FERTILIZER EFFECTS ON ALFALFA PLANT NITROGEN AND SOIL-NITROGEN

Applying manure to alfalfa (Medicago sativa L.) poses a potential risk for overloading the soil system with N. The objective of this study w as to evaluate the effect of preplant nutrient treatments on alfalfa h erbage and crown root N and soil nitrate-N. The effects of three prepl ant manure rates (3 000, 6 000, and 12 000 gal/acre) and three equival ent P and K fertilizer rates were investigated at Rosemount and Waseca , MN, on a Waukegan silt loam (fine-silty over sandy or sandy skeletal , mixed mesic Typic Hapludolls) and on a Nicollet clay loam (fine-loam y, mixed, mesic Aquic Hapludolls), respectively. Alfalfa herbage N rem oval was highly correlated to herbage dry matter yield. Herbage N remo val in the establishment year was greater for the manure treatments th an the P and K fertilizer treatments at the Rosemount sites. The avera ge herbage N removal in the seeding year was 229 lb N/acre for Rosemou nt-North and in the production year was 278, 341, and 233 lb N/acre fo r Rosemount-South, Rosemount-North, and Waseca, respectively. Measured soil nitrate-N in plots receiving manure peaked 30 to 50 d after manu re application, averaging 328 lb/acre, and decreased throughout the gr owing season. Peak nitrate-N amounts were proportional to the amount o f manure applied. After the second alfalfa growing season, soil nitrat e-N amounts were not significantly different among treatments. This st udy's data indicate that preplant manure applications do not result in consistently more N in the soil or in the plant after 2 yr of alfalfa .