Alternative practices for sediment and nutrient loss control on livestock farms in northeast Iowa

Abstract

A number of structural and managerial practices were evaluated to determine their environmental and economic effectiveness on animal feeding operations in the upper Maquoketa river watershed in northeast Iowa. Economic and environmental model simulations were performed over a 30-year time horizon for each of these practices using extensive data collected from the study area. Results from model simulations indicate that while most of the practices (including terraces, no till farming, contouring, and in-field contour buffers) would reduce sediment and sediment-bound nutrient losses significantly, they have very little benefit on soluble nitrogen and phosphorus losses. This is primarily because the increased infiltration rates resulting from those practices leads to greater losses of subsurface and return flow in the heavily tile-drained watershed. Nonetheless, when these practices are combined with judicious commercial fertilizer use, appreciable reductions in soluble nutrient losses are also indicated, and improvements in sediment loss are maintained. Terraces are indicated to provide the greatest sediment loss reduction (over 60% reduction) at the watershed level, relative to the status quo. Accordingly, installed terraces also lead to the highest simulated reductions in organic nitrogen and organic phosphorus (over 70%). Predicted reductions in sediment for most of the other practices ranged from almost 30% to about 45%. Corresponding reductions in simulated organic nitrogen and organic phosphorus losses range from about 35% to almost 50%. Economic model simulations also show varied impacts. In general, costs of sediment reducing practices range from about $6 per hectare of implemented area with contouring to almost $65 per hectare when terraces are installed on high-slope cropland. Terraces also indicated the greatest sediment loss reduction. On the other hand, judicious commercial fertilizer use is indicated to offset these costs by as much as roughly $50 per hectare. The study indicates that programs that offer producers some flexibility in choosing practice combinations may lead to the best outcomes.