The Spatial Variability of Soil Nitrogen and Carbon in a Pasture System.

The Spatial Variability of Soil Nitrogen and Carbon in a Pasture System  

J. Van Noy, M.S. Coyne and O. Wendroth

Department of Plant and Soil Sciences, University of Kentucky

The spatial variability of soil total nitrogen (TN) and soil total carbon (TC) levels play an important role in agriculture and the environment. Extensive laboratory procedures show the relationship that soil TN and TC have and how they can govern microbial transformations in a soil environment. However more extensive mapping of this relationship in a field setting needs to be done. This preliminary study used geostatistical modeling to explore the spatial patterns of soil TN and TC across a sinkhole in Woodford County KY prior to renovation with added forage legumes. In 2012 samples were taken from the top 30 cm at depths of 0-10cm, 10-20cm, and 20-30cm. Samples were taken in a four row grid at 10 m intervals along 180 m transects across the sinkhole. Samples were analyzed for TN, TC, pH and other soil mineral properties. TN by depth was 0.25-0.33% at 0-10cm, 0.13-0.20% at 10-20cm, and 0.09-0.20 at 20-30.  TC by depth was 2.4-3.7% at 0-10cm, 1.0-1.8% at 10-20cm, and 0.9-1.5% at 20-30cm. Geostatistical models were used to show spatial variation of TN and TC. Auto Correlation models showed that soil TN and TC had a spatial relationship over a short distance and no relationship at greater distances. Cross correlation analysis revealed that TN and TC were spatially correlated. TN of a previous position at higher topography tended to lead TC at a lower elevation. This trend suggest that addition of legumes to the pasture could lead to increase in TN and TC. Understanding the spatial relationship of TN and TC in agriculture and environmental fields is important for making management decisions. Effective management can lead to more available nitrogen for plant utilization and potentially lead to increased carbon sequestration.