Research was conducted with sweet corn (Zea mays L.) to evaluate the p
re-sidedress soil NO3 test (PSNT) originally developed for use on fiel
d corn on a wide range of New Jersey soils. Soil NO3-N concentrations
reflected differences in N availability due to manure or preplant N ap
plication. The relationship between soil NO3-N concentration and relat
ive yield of marketable ears was examined using Cate-Nelson analysis t
o define the PSNT critical level. Soil NO3-N concentrations > 25 mg .
kg(-1) were associated with relative yields at greater than or equal t
o 92%. The success rate for the PSNT critical level was 85% for predic
ting whether sidedress N was needed. Including NH4-N in the soil analy
sis did not improve the accuracy of the soil test for predicting wheth
er sidedress N was needed. Although the PSNT is quite accurate in iden
tifying N-sufficient sites, it appears to offer only limited guidance
in making N-fertilizer rate predictions. The PSNT is most useful on ma
nured soils, which frequently have sufficient N. The test likely will
help decrease the practice of applying ''insurance'' fertilizer N and
the ensuing potential for NO3 pollution of the environment.