Phosphorus Dynamics in Tennessee Soils Receiving Various Long-term Manure Applications

Manure application is an age-old process used by agriculturalists to fertilize the soil. In the past, manure application has been loosely based on the N need of the crop. However, this can lead to the potential over-fertilization of P. Long-term manure application has been shown to increase total soil P concentrations as much as eight fold. This study was conducted in order to determine the effects of long-term manure application on P characteristics of Tennessee soils. A total of 10 farms located in the various physiographic regions of Tennessee were sampled. Four of the farms received swine, three dairy, and three poultry for time periods ranging from 10-50 years. There were three main objectives for this study to (1) evaluate the chemical and microbial characteristics of the selected long-term manured fields, (2) compare various extraction techniques for determining bioavailable P in long-term manured fields, and (3) evaluate the use of a P-index for predicting site vulnerability to P movement. We found that manure application significantly increased the majority of the soil P fractions measured. However, manure application did not have a significant affect on the microbial characteristics measured. The extractable P concentrations of the sampled fields varied depending on the extraction procedure used, manure application, and depth of sampling. Both versions of the P index studied predicted sites that were vulnerable to P movement, however additional research is necessary to better evaluate the P indexing system and how it correlates to actual P movement off-site.