CHANGES IN SOIL PROPERTIES IN A CENTRAL PLAINS RANGELAND SOIL AFTER 3, 20, AND 60 YEARS OF CULTIVATION

Cultivation of native rangeland generally leads to a reduction in its organic C and N. However, most studies comparing duration of cultivation to organic matter changes are usually confounded by differences in soil type and/or management practices or are restricted to comparisons of a single long-term cultivation period with an adjacent rangeland site. Our study was conducted to determine short- and long-term changes in soil properties due to cultivation where major influences from soil type and management were minimal. Four contiguous sites where cultivation had occurred for 0, 3, 20, or 60 years were sampled. Soil samples were analyzed for total and labile organic C, N, and P concentrations and for selected physical and chemical properties. Increasing years of cultivation resulted in decreasing silt content of the soil surface and a decrease in depth of lime. After 60 years of cultivation, total soil organic C, N, and P had declined by 55-63% in the surface 15 cm, but about half of this loss occurred during the first 3 years of cultivation. In comparison, the labile fractions of the organic C and N declined by 67-72% after 60 years, but over 80% of labile C loss and more than 60% of the labile N loss occurred during the first 3 years of cultivation. Although half of the total decline in P came from the organic P pool, this decline represented about a 60% decrease in the organic P level in the first 3 years. The proportion of organic C in labile form declined after 3 years of cultivation but thereafter increased to a proportion comparable to the adjacent rangeland condition. The proportion of organic N in labile form was not significantly affected by cultivation. The data indicate that this sandy soil is highly susceptible to organic matter decomposition with cultivation.