Herbage Production, Weed Occurrence, and Economic Risk from Dairy Manure Applications to Alfalfa

Abstract

The spreading of dairy manure on forage legumes requires more information about the impact of manuring on yield, stand persistence, and weed incidence. The research objective was to evaluate the effect of dairy manure applications on herbage yield and weed infestation of established alfalfa (Medicago sativa L.) and to assess the economic risks of this management. Field experiments were initiated in 1990 on an Occum fine sandy loam variant soil (coarse-loamy, mixed, mesic Fluventic Dystrochrept) at Deerfield and on an Agawam fine sandy loam soil (coarse-loamy, mixed, mesic Typic Dystrochrept) at Sunderland in western Massachusetts. Treatments consisted of no N, low and high manure-N (100 and 300 lb N/acre from approximately 5000 and 15 000 gal liquid manure/acre per year, respectively), and low and high N fertilizer (100 and 300 lb N/acre per year from ammonium nitrate, respectively). Liquid dairy manure or ammonium nitrate was spread on the surface immediately after the first cutting in June 1990 and again in June 1991. Application of manure or ammonium nitrate at low or high rates to alfalfa increased total herbage yield compared with no N treatment at the Sunderland site but no response was observed at the Deerfield site over the 2 yr of study. Application of manure or ammonium nitrate to alfalfa at both the sites had no significant effect on overall weed incidence compared with unfertilized alfalfa. Manure applications to alfalfa followed by a dry period can influence weed growth more than in a normal year as it was noticed in the August 1991 cutting. The differences in alfalfa yield due to manuring and no N application were not of economic significance. This alternative practice of manure application to alfalfa does not involve a significant economic risk for dairy farmer. The results show that dairy manure can be applied to alfalfa without any adverse effects on herbage yield or weed incidence and with no economic risk on productivity. This alternative management strategy for surplus dairy manure can effectively reduce overapplications of manure on corn (Zea mays L.) fields and increase the total land area available for spreading.