Effect of Mandatory Nutrient Management Planning on Soil Phosphorus Status.

Since 2002 Maryland farmers have been required to follow phosphorus (P) based nutrient management plans, using soil test recommendations and Maryland’s P Site Index to guide P applications. Our objective was to better understand how these regulations affected P concentrations and saturation in Maryland agricultural soils. Between 1994 and 1995 researchers collected soil samples from 50 fields located across Maryland and analyzed them for Mehlich-3 P (M3P) and ammonium oxalate-Fe (OxFe) and -Al (OxAl). In 2012, we visited the same 50 fields, sampled them, and conducted the same soil analyses. These field sites were distributed across the state of Maryland, were under varied management practices, and were sampled at 0-20 cm depth. Field sites showed a general increase in M3P and P saturation across the state post-mandatory nutrient management planning. Notably, no fields remained in the “low” agronomic soil test P category by 2012. This could potentially be explained by the requirement for soil testing and increased focus on nutrient management education. The nutrient management regulations were designed to slow soil P concentration increases in soils with the highest P status and redistribute manure P applications to fields with lower P loss potential. Therefore, it is not surprising that soil P concentrations continued to increase after implementation of nutrient management laws.