Sweet corn crop nitrogen status evaluation by stalk testing

Abstract

Sweet corn (Zea mays L.) growers evaluating new practices for N management, such as the presidedress soil nitrate test (PSNT), are interested in relating observations about crop performance at time of harvest to their N fertility program. For this purpose, the concentration of nitrogen (N) in the lower portion of sweet corn stalks was examined on the day of harvest as a basis for evaluating the crop N status. Sweet corn stalk tissue was collected from N-rate experiments by cutting a stalk section at 15 and 35 cm aboveground and removing leaf material from the resulting 20-cm segment. Samples were dried and analyzed for total Kjeldahl N. Relationships between crop yield and stalk N concentration indicated that concentrations <11 g·kg-1 are N deficient and underfertilized; N concentrations between 11 and 16.5 g·kg-1 are marginally deficient; and between 16.5 and 21 g·kg-1 the N status is optimum. Concentrations of N >21 g·kg-1 are above optimum and indicate that sweet corn was overfertilized with N. When soil nitrate concentrations (PSNT >25 mg NO3-N per kilogram) indicated sufficient N at time of sidedressing, stalk N concentrations generally indicated N sufficiency at harvest.