|Evett, Steven - Steve|
Submitted to: Proceedings of the Annual Precision Ag Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/16/2000
Publication Date: N/A
Interpretive Summary: The way in which precision agriculture methods are employed depends on the scale at which soil properties change. The effectiveness and expense of such methods may vary with scale also. The present study involves soil properties that affect plant growth, such as water content, pH (acidity), salinity, and organic matter content; and it shows that these properties vary across a field differently depending on whether the field is tilled o left as rangeland. Soil acidity varied much more in tilled land than in rangeland, probably due to both erosion on upslope areas decreasing the depth to caliche (a calcium carbonate layer) and tillage mixing the soil. Salinity and organic matter showed more variation across the rangeland than across the tilled field, due both to the nonuniform distribution of cattle dung and urine in the rangeland and to soil mixing during tillage. Soil water content varied more in the tilled field, probably due to runoff from upland areas to lower areas. Runoff on rangeland was probably less due to grass and shrub cover. Long term tillage will likely increase the variation in soil water content and acidity across fields, requiring additional effort and expense to maintain uniform crop production.
Technical Abstract: Many recent studies have investigated soil spatial variability in cultivated lands. Less research has been conducted on native range variability. This study examines the spatial variability of pH, electrical conductivity (EC), soil organic carbon (SOC) at three depths (0-5 cm, 5-15 cm, and 15-25 cm), and soil water content at 0-15 cm in 200 x 350 m plots on adjacent cropland and rangeland. Descriptive statistics were used to quantify soil variability, and geostatistics were used to determine the degree and range of spatial dependence. EC exhibited the greatest variability, followed by SOC, soil water content, and pH. Cropland exhibited greater variability of water content at both times of sampling, pH and EC at first depth, and less variability of SOC than rangeland at all three depths. For pH, cropland had strong spatial dependence at the first two depths, and moderate spatial dependence at the third depth. Rangeland had no spatial dependence at the first depth, and weak spatial dependence at the second and third depths. For EC and SOC, cropland had either moderate or weak spatial dependence at all depths. Rangeland EC had no spatial dependence at the first depth, while EC at the other depths and SOC at all depths had moderate spatial dependence. Soil water content exhibited strong spatial dependence on cropland, but moderate spatial dependence on rangeland. Cropland pH likely is controlled by depth to free carbonates, while EC and SOC are affected by tillage and farming practices. All measured parameters on rangeland are affected by the non-uniform distribution of dung and urine from grazing cattle.