Submitted to: Proceedings of Great Plains Soil Fertility Conference
Publication Type: Proceedings
Publication Acceptance Date: January 15, 2000
Publication Date: January 15, 2000
Citation: WIENHOLD, B.J., HALVORSON, A.D. NITROGEN MINERALIZATION RATES ACROSS A MANAGEMENT INTENSITY GRADIENT IN NORTHERN GREAT PLAINS. PROCEEDINGS OF GREAT PLAINS SOIL FERTILITY CONFERENCE, 8:135-140. 2000. Interpretive Summary: Integrated livestock-crop systems are common throughout the Northern Great Plains. These integrated systems require a variety of management practices that impact soil fertility. This study compared the nitrogen supplying ability of soils from fields under a range of cropping and grazing practices. The nitrogen supplying ability of the soil was greater from annually cropped fields and fertilized crested wheatgrass pasture than fro crop-fallow fields and grazed native pasture. The low nitrogen supplying ability of the native pastures relates to the perennial vegetation and internal cycling of nitrogen in these soil-plant systems. These results suggest that annual cropping and fertilized crested wheatgrass pasture improve soil fertility when compared to crop-fallow and are viable management practices for this region.
Technical Abstract: Integrated livestock-crop systems in the Northern Great Plains require that numerous management practices, varying in input intensity, be utilized. A long-term grazing study (established in 1916) and a cropping system study (established in 1984), both located near Mandan ND and having similar soils, were used to compare N-mineralization rates across a range of management practices. Harvest index and root:shoot ratios were used to estimate total dry matter production for the cropping system study. Root:shoot ratios and root turnover rates were used to estimate annual dry matter inputs from forage production data in the grazing study. Soil samples were collected from the 0 to 2 and 2 to 6 inch depths of all fields. Nitrogen content was determined by dry combustion and N- mineralization rate was determined using a laboratory incubation method. Nitrogen mineralization rate was correlated with N content in the 0 to 2, 2 2to 6, and 0 to 6 inch depths. Nitrogen mineralization rates in the 0 to 2 and 0 to 6 inch depths were well correlated with dry matter production on cropped soil and fertilized pasture soil but not on grazed native pasture soil. Nitrogen mineralization rates in the 2 to 6 inch depth were well correlated with dry matter production in all soils. Results suggest that N-mineralization rates increase as dry matter inputs increase along the gradient from crop-fallow, annual cropping, to fertilized improved forage. Dry matter inputs in native range are of poor quality and N-mineralization rates are low in these systems.