DAIRY MANURE APPLICATIONS TO ALFALFA - CROP RESPONSE, SOIL NITRATE, AND NITRATE IN SOIL-WATER

Many dairy farmers apply manure predominately to land cropped to corn (Zea mays L.), often in excess of crop N requirements, resulting in potential groundwater contamination. Our research objective was to study the impact of dairy manure applications to established alfalfa (Medicago sativa L.) on crop response and on soil and sail water NO3--N concentrations. Field experiments were initiated in 1990 on an Occum fine sandy loam variant soil (coarse-loamy, mixed, mesic Fluventic Dystrochrepts) at South Deerfield and on an Agawam fine sandy loam soil (coarse-loamy over sandy or sandy-skeletal, mixed, mesic Typic Dystrochrepts) at Sunderland in western Massachusetts. Treatments consisted of zero N, low manure N (112 kg N ha(-1) yr(-1)), high manure N (336 kg N ha(-1) yr(-1)), low N fertilizer (112 kg N ha(-1) yr(-1) from NH4 NO3), and high N fertilizer (336 kg N ha(-1) yr(-1) from NH4NO3). Liquid dairy manure or NH4NO3 was spread on the surface immediately after the first cutting in June 1990 and again in June 1991. Porous ceramic cup suction samplers were placed at the 30-, 60-, 90-, and 120-cm depths. Soil water was monitored throughout the year except in winter, when the topsoil was frozen. Movement of NO3--N was observed to be more rapid in the sandier Agawam soil than the Occum soil. Nitrate-N concentrations in water collected under alfalfa during summer and fall were significantly higher than in the spring. High concentrations of NO3--N coupled with increased soil saturation during the fall make this period critical for monitoring NO3--N movement. High manure application to alfalfa resulted in high soil water NO3--N levels in the fall of 1991 on the Occum soil at the South Deerfield site. Application of N fertilizer at the high rate resulted in significantly increased NO3--N concentrations. Low manure application to alfalfa did not increase NO3--N concentrations in soil water compared with alfalfa receiving no N fertilization. Application of manure to alfalfa at the low rate had no significant effect on dry matter (DM) yields, N accumulation in herbage, and soil NO3--N at the 0- to 25-cm, 25- to 50-cm, and 50- to 100-cm depths. Dry matter yields were significantly lower at the South Deerfield site in 1991-1992 than in 1990-1991 for the high manure application. At the Sunderland site, no significant difference in yield was observed. Dairy manure can be applied to established alfalfa at the low rate of 112 kg N ha(-1) without any adverse impact on herbage production or nitrates in soil water.