Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 8, 2006
Publication Date: November 15, 2006
Citation: Sadeghi, A.M., Graff, C.D., Starr, J.L., McCarty, G.W., Codling, E.E., Sefton, K.A. 2006. Spatial variability in phosphorus before and after poultry manure application in small plots. Soil Science. 171:850-857. Interpretive Summary: Accurate assessment of environmental research on small plots requires knowledge of variability in soil properties at small spatial scales. In precision agriculture studies, variability in the underlying process that control crop response and the environmental fate of nutrients can be studied in terms of the spatial variability in soil physical and chemical properties. While many field studies have been conducted to evaluate crop response to variability in soil nutrients at large scales, few studies investigate spatial variability within small plots. Because most agricultural research relies in part or entirely on small plot designs, understanding the variability of soils at small spatial scales is important for interpretation of results. This paper discusses the spatial variability of soil phosphorus within 8 small plots before and after the application of poultry manure. Results show that there is inherent variability before and even after poultry manure application. The strength of the spatial variability, however, can be liked to natural variability or management practices. Evaluation of this data reveals the need to appropriately account for spatial variability of soil phosphorus in small plots before and after manure applications, and the role field management plays in changing the variability.
Technical Abstract: Accurate assessment of environmental research on small plots requires knowledge of the spatial variability in soil properties at small spatial scales. The effect of management practices, such as manure application, can affect this variability and should be accounted for in small plot studies. The goal of this research was to evaluate the spatial variability of soil total phosphorus (TP) on 8 small plots before and after poultry manure application in 2003 and 2004. Soils were collected on an approximate 10 m grid in all plots. Spatial variability was assessed through semivariance analysis and the ratio of nugget to total semivariance was used to classify spatial dependence. Detection of spatial structure was dependent on the number of samples within each plot. Spatial dependence was moderate to strong after application in 2003 with nugget to total semivariance ratios ranging between 0.09 and 0.4. This can likely be attributed to 4 significant rainfall events that redistributed soil TP on the landscape. The lack of spatial variability in 2004 post application TP 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 TP 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.