Application of Dairy Manure on Alfalfa

Applying dairy manure to alfalfa (Medicago sativa L.) as ,in alternative 10 excess application to· corn (Zea mays L.) may reduce nitrate pollution of groundwater. Field experiments were conducted at 2 sites in Massachusetts, USA, lo study the impact or dairy manure application to alfalfa on forage yield, weed infestation· and nitrate movement. Treatments were an unfertilized (no N) check.· plot, low and high manure (112 and 336 kg N/ha/year equivalerit), and low and high N fertiliser (112 and 336 kg N/ha/year from NH4NO3),'. Liquid dairy manure was applied 10 • alfalfa immediately· after 1st· cutting during spring of 1990 and 1991. Water samples were collected through porous cup suction water s.\mplets placed at JO; 60, 90 arid 120 cm depths. Treatment differences in mean NO3-N concentration · in leachate were significant at both experimental sites. Significant amounts of NO3'-N were observed in water samples ·collected during both years and covariance was high among treatments·, sampling depths and the sampling dates. There were no differences in mean NO3-N concentrations hi leachate from low (112 kg N/ha) manure and control plots, whereas' high (336 kg N/ha) fertiliser ·and high manure (2nd year only) showed significantly more NO3-N iii leachate than the control. Manure application to alfalfa neither reduced forage yield nor increased weeds. These preliminary results· suggest that farmers could apply excess dairy manure to alfalfa at lower rates equivalent to 112 kg N/ha depending upon soil texture with few adverse effects on ·groundwater quality.