It used to be that the only time farmers spread manure on alfalfa ground was before they plowed the stand under in preparation for planting corn.
Times are changing. It”s not uncommon for livestock producers to spread manure prior to seeding alfalfa or topdressing an established alfalfa stand.
There are some good reasons for these new approaches and some reasons to avoid the traditional plowdown strategy. But like most crop management matters, the best approach depends on many factors – things like the quality of the stand, soil test levels, when you apply and what kind of animal made the manure.
To help sort out the pros and cons, a group of crop scientists from across the Midwest teamed up to address the topic. Their conclusions are contained in a new publication, “Applying Manure to Alfalfa: Pros, cons and recommendations for three application strategies.”
Authors Keith Kelling of the University of Wisconsin-Madison and Michael Schmitt of the University of Minnesota base their conclusions on research results from a number of states.
They discuss each of the three strategies in turn – preplant, topdress and plowdown – and explain how various factors affect the chances of improved yields, crop injury and nutrient loss in each case.
They note that one reason for the increased interest in spreading manure on alfalfa is regulatory pressure. Faced with concerns about nutrient runoff and leaching from row crops, producers are searching for other places to spread manure. Also, many producers simply don”t have enough corn ground to accommodate all of the manure their animals produce.
Applying to manure has its advantages, the authors note. One is scheduling flexibility: If you spread on alfalfa, you have substantial cropland available for spreading during summer months. There are also crop nutrition benefits. Manure provides secondary nutrients and micronutrients as well as nitrogen, phosphorus and potassium. And alfalfa does an excellent job of recycling nitrogen from the soil. Given the choice, an alfalfa plant will extract nitrogen from the soil before fixing it from the air. And alfalfa”s deep roots can extract mobile nutrients from greater depths than corn roots can.
The potential pitfalls fall into two categories: Crop injury and leaching or runoff of excess nutrients. Whether you capture the benefits and avoid the pitfalls has a lot to do with your timing and application strategy, the authors point out.
Although each strategy has its own risks and benefits, from an environmental standpoint, the riskiest method may well be the most common one: plowing down manure before rotating to corn.
“When you add up the nitrogen contributed by the alfalfa and the manure, and then add in the nitrogen from any fertilizer applied, the total amount of available nitrogen may exceed recommendations,” the authors say.
“Research in several states has found little, if any, response to additional nitrogen following alfalfa. It may turn out that the environmental costs of this management strategy are simply too high,” they add.
Copies of the publication cost $1.25. They can be ordered from Soils Extension Office, UW-Madison, 1525 Observatory Dr., Madison, WI. The publication can also be downloaded at no charge here. For more information call (608) 265-0648.