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The Relationships of Nitrate Concentrations in Young Corn Stalks to Soil Nitrogen Availability and Grain Yields¹

The importance of N in crop production makes accurate estimation of the available N in the soil desirable, especially with increasing costs of N fertilizers and concern for environmental hazards associated with excessive fertilization. Although several soil N availability indices have been developed, none of those tested has had wide success in Pennsylvania. A 2-yr study was conducted in central Pennsylvania to determine if nitrate (NO^–₃) analysis of young corn plants (Zea mays L.) was significantly related to soil N availability. The NO^–₃ contents of basal stalks were determined weekly for several weeks after emergence in two N fertilizer response experiments in 1982 and 1983. The soil in sites in 1982 and 1983 were Murrill silt loam, a Typic Hapludult, and Hagerstown silt loam, a Typic Hapludalf, respectively. Stalk NO^–₃ –N increased with increasing N fertilizer rates. The effect of plant age on stalk NO^–₃ concentration varied between the 2 yr, probably due to hail damage or available water differences. Differences in stalk NO^–₃ among N fertilizer treatments increased with time in both years. The optimum time for sampling appeared to be approximately 30 days after emergence (DAE). Correlations of stalk NO^–₃ at this time with relative grain yield and N uptake were significant (r>0.94) both years. Based on regression lines, at approximately 30 DAE, the critical concentration of stalk NO^–₃–N (for 95% of the plateau yield) was about 11 g NO^–₃ kg^–1 in 1982, and 16 g NO^–₃–-N kg^–1 in 1983. Combined data from both years had a significant but lower correlation (r=0.754) between stalk NO^–₃ and relative grain yield, with an apparent critical concentration of 15.7 g NO^–₃–N kg^–1. The potential for predicting soil N availability from NO^–₃ tissue testing appears possible if the environmental factors that affect tissue NO^–₃ accumulation can be identified and quantified.

Key Words: Plant analysis • Relative yield • Soil fertility • Zea mays L.

² Research assistant, professor, and senior research aide, respectively, The Pennsylvania State Univ., University Park, PA 16802.

Received for publication October 12, 1984.