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Turn Brown Into Green -- Avoid Manure Nutrient Loss

October 18, 2013
By: Davis Michaelsen, Pro Farmer Inputs Monitor Editor

The University of Wisconsin Discovery Farm (UWDF) has taken a close look at nutrient runoff from manure in soils throughout the year to determine the best time to spread either liquid or dry manure. Timing can mean the difference between fertilizing the soil with manure, and fertilizing the creek.

In fact, UWDF estimates that 100 cows produce more than $8,500 per year of manure. This figure is based on fertilizer prices of $0.55/lb. for N, $0.45/lb. For phosphate and $0.45/lb. for potash. "We don't often think of manure as one of the more valuable products that animals provide us," Amber Radatz, program co-director told Bloomberg.

We are talking mostly about nitrogen as phosphate and potash runoff only as part of a sediment complex, and winter losses are generally minimal. The majority of N losses, however, are from frozen soils as soil temps dip below 50°F and conversion to nitrate is held up. The pause in the conversion process has N waiting around for the soil to warm up and it can easily be carried away in a soaking rain.

Late fall and early winter are the best times to spread manure with the least amount of risk for loss to runoff. Precipitation events following shortly after a manure application impact nutrient runoff more dramatically the sooner the precipitation falls after the application. In other words, if you spread manure in the morning and it rains all afternoon, the chances of keeping that nutrient in the soil are small. However, if precipitation holds off for a few days, or even a week, more nutrient will be saved than lost.

The table below is adapted from a UWDF publication and details how much runoff one can expect in each month of the year given average precipitation.

 
% of annual runoff
Runoff frequency
January
4%
50%
February
16%
58%
March
34%
100%
April
4%
54%
May
12%
38%
June
19%
42%
July
3%
42%
August
3%
19%
September
<1%
19%
October
3%
23%
November
<1%
15%
December
1%
35%

 

According to the research, most runoff occurs during the period between February and June which contributes roughly 80% of annual runoff. Right now is the best time to spread manure and I know a number of farmers in my area have taken the time to do just that in the few days between picking beans and harvesting corn.

One of the ideas brought up by UWDF was to save a few 'less risky' fields to spread manure when conditions are less than ideal. The fields with the least risk for runoff will have a gentle slope if any and are located far from natural surface water and bedrock. With the EPA asking states in the Mississippi Basin to reduce N&P runoff, manure management will be a part of compliance and while regulations are not in play presently, if officials do not deem the public voluntary effort as having an impact, regulations could rule the future.

The University of Wisconsin Discovery Farm offers a great resource here that will help growers avoid fertilizing the creek, and give crop nutrition a natural boost. Click here for more from UWDF...


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