Soil Test p Status.

Phosphorus (P) enrichment of surface and ground water involves a combination of high STP levels and site and source factors that favor the transport of P by water flows overland and trough the soils. Long-term applications of manure have generally increased soil test P (STP) levels to a greater degree than has fertilizer application because most manure is applied to meet the nitrogen (N) needs of the crops. Preliminary research found that subwatersheds within the major poultry production counties in Mississippi have a high potential for soil and water degradation from manure P. A study was developed to increase the understanding of the potential effect of P in soils for the top 20 poultry production counties in Mississippi on water quality. Study goal and specific aims were addressed by performing a descriptive summary and an analysis of temporal dynamics of the STP results. A database of 15,057 soil tests performed by the Mississippi State University Extension Service Soil Testing Laboratory for 10 annual periods from 2002-2003 to 2011-2012 were the basis to perform the study.

The STP level ranges did not show important variations from the first (5 to 3780 lb ac^-1) to the last year (5 to 3980 lb ac^-1), but for peak STP values observed at the 2^nd (5990 lb ac^-1) and the 7^th year (4840 lb ac^-1) of the study. However, the mean STP level showed an increasing trend from the first (113 lb ac^-1) to the last year (302 lb ac^-1).

On the basis of soil fertility criteria, the 38% and 69% of the soils tested in the first and the last year, respectively, have STP levels above the high STP category, which are considered to exceed levels of P crops requirement. These soils should not receive additional external P source.