Spatial variability of early season nitrogen availability indicators in corn

Abstract

The pre‐sidedress nitrate test (PSNT), a soil test used to refine sidedress fertilizer nitrogen (N) recommendations in corn (Zea mays L.), has shown great potential to reduce the excessive use of N fertilizer in corn production systems in the Northeast. The research reported in this paper evaluated the application of the PSNT to site‐specific management by investigating the spatial variability of several early season soil and plant indicators of N availability in a uniformly managed 16‐ha no‐till corn production field. The spatial variation in PSNT nitrate concentrations, total organic carbon (C) and N in the soil, and corn biomass yield and N content at the fifth leaf development stage were characterized from 189 samples taken during the 1994 growing season on a triangular grid with a 30 m minimum separation distance. There were no significant correlations found between any of the variables studied. All the variables studied were normally distributed with the exception of total organic C and biomass yield, both of which approximated a log‐normal distribution. Geostatistical analysis revealed significant spatial variation and spherical semivariogram models were developed for each variable. Results suggest that the average minimum grid size used in this study (30 m) may not have been adequate for an accurate estimation of nugget semivariance in total soil C and N and corn tissue N concentration. Plant indicators exhibited landscape features influencing biomass production and N uptake that were not revealed by the soil variables studied. These results illustrate the potential utility of integrating soil and plant productivity indicators to identify and address limitations to crop production using site‐specific management.