Farmer adoption of efficient inorganic nitrogen fertilizer management practices in South Dakota

Nitrogen (N) fertilizer use has led to reductions in air and water quality but is essential for increasing crop production. Following the 4Rs of nutrient management (right: source, rate, timing, and placement), specifically following university N rate guidelines, proper urea fertilizer management, use of enhanced efficiency fertilizers, and splitting up inorganic fertilizer-N applications can minimize potential negative environmental effects. Data from a 2019 probability sample survey of 465 South Dakota farmers were used to examine how local and operational characteristics (geographic location, tillage practice, and farm size) are related to the adoption of these four Rs of nutrient management practices. Factors included in inorganic N rate decisions from most to least were use of preplant soil test N (74%), yield potential (68%), previous crop credit (48%), manure credit (25%), and tillage type (16%). Of all the factors used to make fertilizer-N rate decisions, only the use of previous crop and manure credit factors were influenced by farm location and tillage method but not farm size. Of all respondents, 30% used urease inhibitors to minimize ammonia (NH3) loss and 31% applied urea before predicted precipitation. However, farms in drier, central South Dakota and no-till farms used urease inhibitors and applied before predicted precipitation more often than farms in wetter, eastern South Dakota and conventional-and reduced-tillage farms, who were more likely to use tillage to incorporate urea. To minimize leaching and denitrification loss, farms in eastern South Dakota where normal rainfall is greater used nitrification inhibitors or slow-release fertilizers and split-N applications (48% and 53%, respectively), while fewer farms in central South Dakota where normal rainfall is less used these technologies (34% and 36%, respectively). Larger farms more frequently used urease and nitrification inhibitors, and/ or slow-release fertilizer technologies to minimize N loss. These results indicate that local and operational characteristics including geographic location, tillage, and farm size influence on-farm decisions concerning the adoption of these 4R management practices and should be considered when investigating and promoting 4R practices.