Scientists in the College of Agriculture and Life Sciences have been working to help agricultural producers meet a revised federal nutrient management standard that requires an assessment of phosphorus losses from farmland.

College researchers have developed and tested the phosphorus loss assessment tool (PLAT). The PLAT is an index that helps researchers determine total phosphorus losses more accurately by accounting separately for different loss sources and other factors. It measures the loss due to such considerations as the chemical’s binding to sediment, soil runoff, leaching and applications by producers.

Why the concern about phosphorus? Farmers apply fertilizers containing essential nutrients such as phosphorus, nitrogen and potassium to increase crop yields. Although the nutrients are necessary, in excess, they overstimulate organisms in lakes and streams, reducing water quality.

Current regulations base the amount of nutrients producers can apply to a field on a crop’s nitrogen needs, said Steven Hodges, former Soil Science Department extension leader. But organic nitrogen sources also contain significant phosphorus. Plants require much less phosphorus than nitrogen, so phosphorus can accumulate in field soils. “Over time, soil phosphorus builds to very high levels, eventually moving from fields into surface and groundwater,” Hodges said.

The revised U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS) phosphorus regulations could seriously impact producers, he said.

The regulations, effective since April in North Carolina, could mean that some agricultural operations that produce animal wastes might need to increase their land base.

Here’s why: Under the regulations, a field’s assessed phosphorus loss potential — low, medium, high or very high — determines if its nutrient management plan can be based on the crop’s nitrogen needs. If the field shows high phosphorus loss potential, it can’t receive more phosphorus than is removed in the harvested crop. If the assessment is very high, only pre-plant phosphorus is allowed. And some land may not be allowed to receive any phosphorus at all, so no manure would be allowed.

“The critical issue for animal producers is that they may have to expand acreage to handle the manure they produce,” Hodges said.
To comply with the regulations, producers might need up to 20 acres of land for each acre they now use under a nitrogen-based plan, said Hodges.

Producers don’t have to submit new nutrient management plans immediately, but phosphorus-loss-potential assessments are mandated for any new site within nutrient-sensitive watersheds that receive organic byproducts: manure or any nutrient source, including fertilizers. Assessments also will be required when current animal waste-management permits are reissued, if a waste-management plan changes, or if a producer receives new state cost-share funds.

“We have approximately 5,000 existing nutrient management plans in North Carolina based on the previous nitrogen-based standard,” he said. “Since North Carolina regulations simply adopt the latest NRCS standard rather than writing our own, we needed to ensure that we had a science-based assessment process.”

The PLAT was developed to help remove guesswork from the planning process. The tool also includes input about waste application and accounts for good crop management by considering stream buffer lengths and widths, water control structure use and pond and sediment basin use.

Before implementing the PLAT and making it part of the North Carolina standards, researchers rigorously tested its effects on producers.

Deanna Osmond, N.C. Cooperative Extension soil science specialist and PLAT development committee member, coordinated a study that randomly sampled about 1,400 farm fields across the state to run through the PLAT.

Said Hodges, “We want regulators and the farm community to understand the potential economic and environmental impact of this regulation.”

—Art Latham