SOIL NITRATE CONCENTRATIONS UNDER CORN AS AFFECTED BY TILLAGE, MANURE, AND FERTILIZER APPLICATIONS

A 3-yr study was conducted to examine combination effects of tillage (no-till, conventional-till), manure, and inorganic fertilizer (ammonium nitrate) on leaching of nitrates from the root zone of corn (Zea mays L.). Soil cores were collected every spring to a depth of 210 cm and analyzed for NO3-N. Leaching of NO3-N significantly increased as fertilizer N rates increased, especially when rates exceeded the crop's potential to assimilate N. The concentration of soil nitrate (averaged over depth and tillage) in Year 3 of the study under the unfertilized control plots was 2.5 mg NO3-N kg-1, whereas the concentration under plots fertilized with 260 kg N ha-1 was 8.7 mg NO3-N kg-1. Soil nitrate concentrations were consistently lower under no-tillage when compared with conventional-tillage. Tillage differences were greatest when high rates of N were added to soil. These results indicate that the use of no-tillage cultivation may reduce the leaching of nitrates beyond the crop root zone.