SPATIAL VARIABILITY OF SOIL PHOSPHOROUS LEVELS BEFORE AND AFTER POULTRY LITTER APPLICATION

Accurate assessment of environmental research on small plots requires knowledge of the spatial variability in soil properties at small spatial scales. Management practices, such as manure application, can affect this variability, which should be accounted for in small plot studies. The goal of this research was to evaluate the spatial variability of soil extractable P (EP) on eight large plots before and after poultry manure application in 2003 and 2004. Soils were collected on an approximate 10-m random grid in all plots. Spatial variability was assessed through semivariance analysis, and the ratio of nugget/total semivariance was used to classify spatial dependence. In general, spatial structure was only found in the larger plots. Spatial dependence was moderate to strong after application in 2003, with nugget/total semivariance ratios ranging between 0.09 and 0.4. This can likely be attributed to four significant rainfall events that redistributed soil EPon the landscape. The lack of spatial variability in 2004 postapplication EP reflects the inherent random variability that arises from manure application, as no major rainfall event occurred between application and soil sampling. The range over which soil EP varied was less than 25 m in all plots for which spatial variability could be detected, suggesting that it should be accounted for in small plot studies.