CHANGES IN CEC AND PARTICLE SIZE DISTRIBUTION OF SOILS ASSOCIATED WITH LONG-TERM ANNUAL APPLICATIONS OF CATTLE FEEDLOT MANURE1

Soil cation exchange capacity (CEC) is important in plant nutrient uptake and ion movement and is highly correlated with organic carbon content and clay content of soil. However, there is no quantitative information about changes in soil CEC caused by changes in soil organic matter content as a result of long-term manuring practices. The changes in soil CEC associated with long-term annual applications of cattle feedlot manure (1973-1991), at up to three times the recommended rates, on characteristics of an irrigated and a nonirrigated Dark Brown Chernozemic clay loam were studied. For this study, manure came from a site with a lower sand content soil than that of the site where the manure was applied. The changes in soil particle distribution were also examined. After 18 annual applications of manure, the sand content at the 0 to 15-cm depth of soil in nonirrigated plots and at the 0 to 15 and 15 to 30-cm depths of soil in irrigated plots had decreased significantly. The soil CEC, total organic carbon content (TOC), and total nitrogen content (TN) at the 0 to 15 and 15 to 30-cm depths increased with increasing rates of manure, except for the CEC at the 15 to 30-cm depth under nonirrigated conditions. There was no significant effect of long-term application of manure on inorganic carbon content. The increases in CEC were attributed mainly to the increases in TOC. Increases in soil CEC caused by increases in TOC through manuring were smaller than those caused by increases in an equivalent amount of TOC through natural soil formation processes.