FARM NUTRIENT MANAGEMENT PRACTICES IN TWO GEOGRAPHICALLY DIVERSE WATERSHEDS IN THE COTTONWOOD RIVER WATERSHED OF MINNESOTA, USA

摘要

The characteristics of a river are shaped by the quality of the tributaries that flow into it and each of the tributaries in turn reflects the management practices that occur on the soils and landscapes in their drainage areas. In the Cottonwood River of Minnesota, USA and many of its tributaries, nutrient enrichment [primarily nitrogen (N) and phosphorus (P)] and suspended sediments contribute to nonpoint source pollution. Our objective was to assess farm characteristics and nutrient management practices among producer/operators in two southwestern Minnesota watersheds, and relate these characteristics to soil and landscape differences as reflected by agroecoregions. Producer/operators were interviewed in a face-to-face interview during summer 2002 about agricultural production management practices in two tributaries of the Cottonwood River. The Sleepy Eye Creek watershed (SECW) is located in gently rolling to flat soils formed in glacial till. The Highwater-Dutch Charley Creek watershed (HDCCW) is located in moderately steep, 2-6% slope, soils formed in glacial moraine. Nitrogen and P rates applied to corn were significantly greater in the SECW than the HDCCW, and more of the N was applied in the fall in the SECW than in the HDCCW, where more was applied in spring. More farmers tested soil for plant available P in the SECW than in the HDCCW. Results from both watershed indicated that forty-seven (29%) fields with soil test phosphorus records exceeded 25 ppm (Bray 1) or 20 ppm (Olsen). Nineteen (7.4%) fields received applications of both manure and N fertilizer, and 13 (5.1%) fields received applications of both manure and phosphate (P) fertilizer. Nitrogen and P application rates ranged from 234 to 315 kg N ha~(-1) and 134 to 168 kg P_2O_5 ha~(-1) for fields receiving both manure and fertilizer. Strategies for improving nutrient management practices in these two watershed areas should take into consideration soil and landscape differences that influence which nutrient management practices are most risky and which are most likely to improve water quality.