112 PRESIDEDRESS SOIL NITRATE TEST FOR SWEET CORN

Abstract

The presidedress soil nitrate test (PSNT) is an in-season soil test that evaluates the N supplying capacity of soil before side dressing to adjust N application rates. Increasing acceptance of this soil test among field corn growers in New Jersey has shown it to be an effective practice. Nitrogen application rates were reduced by an average of 45 kg-1 ha without loss of crop yield. Field calibration research to extend use of the PSNT to sweet corn has the potential to improve N fertilizer recommendations for this crop. A critical concentration of 25 mg kg-1 NO3-N in the surface 30 cm of soil is generally considered adequate for field corn. Certain crop features of sweet corn (earlier harvest, smaller plant size and population) suggested that the critical NO2-N level might be lower than for field corn while market quality suggested that it might be a higher value. Results from 40 sweet corn field calibration sites in New Jersey indicate that the PSNT critical soil NO3-N concentration may be greater for sweet corn than field corn. A preliminary critical level of 30 mg kg-1 NO3-N in the surface 30 cm of soil is suggested for use of the PSNT on sweet corn. Further research is being conducted to improve sidedress N recommendations based on the PSNT.