INFLUENCE OF MACROCLIMATE, LANDSCAPE POSITION, AND MANAGEMENT ON SOIL ORGANIC-MATTER IN AGROECOSYSTEMS

We investigated patterns of soil organic matter, microbial biomass, and potential C and N mineralization in soils across landscape, regional, and management treatments in eastern Colorado. Total soil C, N, and P, microbial biomass, and C and N mineralization were highest at a northern site and on toeslope landscape positions. No-tillage and perennial grass treatments had significantly higher microbial biomass and C mineralization rates than conventional tillage treatments after only 5 yr of treatment, but only at the sites and landscape positions with high production and organic matter contents. Potential N mineralization was not different among management treatments. We suggest that a simple relationship between total soil organic matter and nutrient supply rates holds for relatively static systems represented by spatial gradients, but that transient systems undergoing losses or gains in soil organic matter may have a lag in nutrient supply responses due to immobilization dynamics.