USA - Farmers using poultry litter need to avoid excess phosphorus on land

If farmers want to continue using poultry litter as fertilizer on their fields, they will need to avoid excess phosphorus going on the land. That is the advice of Dan Philbrick, Natural Resources Conservation Service district conservationist in Barry County, who talked at a meeting Feb. 11 in Neosho. Missouri has no regulations covering phosphorus applications. Current application regulations are based on nitrogen. Phosphorus is needed for plant growth and is not toxic to plants, livestock or humans, he said. University of Missouri soil-test recommendations are made to meet phosphorus needs for the coming crop and for amounts to build phosphorus in soils where the nutrient is needed. It normally takes 10 pounds of phosphorus per acre to increase the level in the soil by a pound, he said. Commercial fertilizer is quickly available to plants while no more than 70 percent of the nitrogen in litter is available to plants the first year. Nutrients in any poultry litter are not automatically balanced for any use. Generally, a ton of broiler litter will have 60 pounds nitrogen, 70 pounds phosphorus and 50 pounds potassium. The range of nutrient content per ton of litter can range from 45-81 pounds nitrogen, 50-79 pounds phosphate and 35-75 pounds potash. Often, phosphorus is the nutrient least needed by plants, he said. He recommended applying litter at levels to meet phosphate needs and commercial fertilizer for other nutrients. Fescue that will produce three forage per acre can need a fertilizer blend of 90-30-100. Grazing cattle will return 95 percent of the nutrients back to the land in manure and urine, he said. Corn to produce 150 bushels grain per acre needs 140-55-40 pounds of fertilizer. "Applying litter at the right time and in the right amount is the way to be most benefits from litter used as fertilizer," he said. John Lory, University of Missouri nutrient management specialist, said phosphorus can be lost when carried off the surface by water or by slowly leaching through the soil. Most litter pollution comes from phosphorus, he said. A small change in phosphorus levels quickly lowers water clarity. The critical time for phosphorus loss, regardless of its source, is the first two weeks are a surface application when rainfall can carry a lot off the land. Most benefits come from not applying litter on muddy or frozen ground or within a few days in advance of heavy rain forecasts, he said. Nutrient loss is greatly reduced when litter is immediately plowed into the soil, he said. "Timing of litter application on land is our biggest problem," Lory said.