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.
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Iversen et al. (1985) studied this question.