Introduction
Dairy manure can be successfully applied to alfalfa both prior to planting and after establishment. Manure provides a source of major nutrients and micronutrients. Added benefits may result from improved soil physical properties and increased biological activity. However, inappropriate application may burn leaves reducing yield and forage quality. Heavy application equipment may compact soil and damage alfalfa crowns thereby lowering yield and shortening stand life. In weakened alfalfa stands, nitrogen (N) in manure may stimulate the growth of grasses and weeds, further diminishing the proportion of alfalfa in the sward.
Other crops such as corn and grass hay should be the preferred crops for manure application by dairy farmers. Cornfields closest to the barn often receive manure at rates above crop requirements, resulting in N imbalances and over application of P and K. Alfalfa and other forage legumes will use applied N from manure. These crops do not require supplemental N due to their ability to fix atmospheric N. Manure applications to alfalfa may be necessary on dairy farms with herds that produce more manure than can be used on available cropland. Manure application to alfalfa would increase the total land area available for spreading, and thus would decrease the amount spread on any one field, improving the N balance, lessening the potential for nitrate leaching. Research shows manure application to alfalfa could decrease symbiotic N2 fixation.
Recommendations
Pre-plant Manure Applications
Use information from manure analysis of N, P, and K concentrations to set rates adequate to supply needed nutrients according to soil test recommendations.
Avoid applying manure at nutrient rates greater than the alfalfa crop can use and ensure adequate incorporation so alfalfa seed is not planted in areas of excessive manure concentration. These may result in poor alfalfa stands and increased weed growth. Apply manure P and K only to balance the crop need for the entire crop rotation.
Spread manure when soils are firm so wheel traffic by the manure spreader will not cause excessive soil compaction and future stand problems.
Manure Applications to Established Alfalfa Stand
Apply manure to the forage fields containing the highest proportions of grass since these fields will benefit most from the manure N. Usually these fields will be the oldest stands, although application to established pure young alfalfa stands is possible without detriment where N utilization is the objective. Watch soil test levels of P and K.
Liquid or solid dairy manure can be applied. Excessive rates may contribute to salinity problems and cause salt burn (or scald with dairy pond water) to the alfalfa leaves or suffocate plants. An increase in nitrate leaching can be expected if plant nutrients exceed crop requirements.
Manure should be applied immediately (within one or two days) after removing a cutting. This reduces the risk of salt burn and forage palatability problems.
Spread manure only when soils are firm, to reduce soil compaction, prevent field rutting, and minimize damage to the plant crowns.
The most efficient use of the nutrients in manure would occur when manure is applied to the alfalfa at the P utilization rate, or to the rate that would maintain the soil test level P for the entire crop rotation (corn, small grain and alfalfa).
Solid manure spreaders should be adjusted to break up large manure clumps that might smother regrowth.
Weeds
One of the major farmer concerns for application of manure on alfalfa is weed intrusion. Presence of weed seeds in manure varies and depends on type of farm operation, feeds, and manure management.
Research shows proper application of manure at the optimum rate does not increase weed problems and does not significantly alter stand purity.
Residual effects
Application of manure to alfalfa will benefit succeeding crops both from residual N and other essential plant nutrients like P and K.
Research shows corn planted after manured alfalfa in the rotation may not need any extra N and P fertilizers. Additional N fertilizer application should be based on preplant or the pre-sidedress soil N test in applicable regions. Application of N fertilizer to corn following manured alfalfa may result in overfertilization and thereby increase nitrate leaching potential.
Application of manure to alfalfa at the N requirement rate will over-supply P and K to the subsequent crops and build up soil test levels of these nutrients to environmentally hazardous levels.
Bibliography
Daliparthy, J., S. J. Herbert, L. J. Moffitt, and P. L. M. Venman. 1995. Herbage production, weed occurrence, and economic risk from dairy manure application to alfalfa. J. Prod. Agric. 8:495-501.
Daliparthy, J., S. J. Herbert, and P. L. M. Veneman. 1995. Excess dairy manure management: Impact on groundwater quality. pp 343-354. In K. Steele (ed.), Animal Manures and the Land-Water Interface Conference. Lewis Publishers. Boca Raton, Florida.
Daliparthy, J., S. J. Herbert, and P. L. M. Veneman. 1994. Dairy manure applications to alfalfa: crop response, soil nitrate, and nitrates in soil water. Agron. J. 86(6):927-933.
Herbert, S.J., J. Daliparthy and P.L.M. Veneman. 1993. Application of dairy manure on alfalfa. Proceedings XVII Int. Grassland Congress: 830-831.
Peterson, T. A., and M. P. Russelle. 1991. Alfalfa and the nitrogen cycle in the corn belt. J. Soil Water Conserv. 46:229-235.
Schmitt, M. A., C. C. Sheaffer, and G. W. Randall. 1991. Utilization of liquid manure in alfalfa production. p. 30-37. In Proc. 21st Natl. Alfalfa Symp. Rochester, MN. 14-16 Feb. Certified Alfalfa Seed Council, Davis, CA.
Schmitt, M. A., C. C. Sheaffer, and G. W. Randall. 1993. Preplant manure and commercial P and K fertilizer effects on alfalfa production. J. Prod. Agric. 6:385-390.