DON’T LET

As for crop availability, the authors explained that N is primarily in the organic form in poultry litter, up to 80%. Organic N needs to mineralize before becoming available to crops. Studies have shown that approximately 45% to 55% of the total N becomes available to the plant the first year of application. Reduction of N availability may occur when the litter is aged or has gone through some level of composting. Ammonium volatilization is usually higher on warm, windy days, but incorporation can reduce this loss and potential runoff losses.

On the flip side, a large fraction of manure P is available immediately after application, between 50% and 100%. Similarly, nearly 100% of K is available with proper application. Moisture content and nutrient concentration can be highly variable, depending on production conditions, storage, and handling methods. The authors reminded farmers that laboratory analysis is the best way to determine the level of nutrients in the litter.

Unlike commercial fertilizers that can be mixed to achieve a desired nutrient content, manure comes with fixed nutrient ratios. These ratios often don’t align perfectly with the needs of field, and this can lead to over or under application of certain nutrients, including nitrogen and phosphorus.

In a University of Minnesota Extension Crop News article, extension educator Chryseis Modderman posed the question, “Should you apply manure based on nitrogen needs or phosphorus needs?” The answer, she wrote, depends on the soil and the manure test results.

If a field is already high in phosphorus, a farmer may decide to apply manure on a phosphorus-based rate to avoid further build up. If phosphorus levels are low, a nitrogen-based rate would work well as long as it won’t elevate phosphorus levels too high.

Even though phosphorus is less mobile than nitrogen, Modderman explained there is still a risk of loss through runoff and erosion. To avoid phosphorus build up, she shared two strategies. One is to apply the nutrient at a phosphorus-based rate. An alternative method is to apply manure at the nitrogen-based rate, but then not apply any more manure to that field until the excess phosphorus has been utilized.