Effect of tillage systems on runoff losses of nutrients, a rainfall simulation study

ABSTRACT THE objective of this study was to evaluate the effects of different tillage practices on the loss of N and P in runoff and sediment from experimental plots using simulated rainfall. Twelve plots on each of three different Iowa soils were planted to corn and six tillage practices were used. Sim-ulated rainfall was applied to the plots and surface run-off samples were collected. The water fraction of the runoff was analyzed for N03-N, NH4-N and P04-P; the sediment was analyzed for total nitrogen and avail-able phosphorus. At all sites, the available P content of the eroded soil increased with residue cover; however, decreased soil loss with increased residue cover offset the higher avail-able P content of the eroded soil. Loss of total N with sediment was inversely related to the percentage of soil covered with residue. Losses of N03-N, NH4-N, and PO4-P with water were small as compared with N and P losses with sediment. Soluble nutrient concentrations were positively correlated with the amounts of soil sur-face covered with residue. Conservation tillage practices were ineffective in reducing the loss of water soluble nutrients; however, they did reduce total nutrient loss by controlling erosion.).