Relationship between soil nitrate accumulation and in-season corn N nutrition indicators

Ziadi, N., Bélanger, G. and Claessens, A. 2012. Relationship between soil nitrate accumulation and in-season corn N nutrition indicators. Can. J. Plant Sci. 92: 331–339. Nitrogen management tools are required to optimize crop growth and yield while minimizing the likelihood of N losses to the environment. We previously determined that non-limiting N conditions for near maximum corn (Zea mays L.) grain yield are reached with the following threshold values for three in-season plant-based indicators of corn N nutrition determined at approximately the V12 stage of development: N nutrition index (NNI) = 0.88, leaf N (NL) concentration = 32.7 mg N g⁻¹ leaf DM, and relative chlorophyll meter (RCM) values = 0.95. Our objective was to study the relationship between these plant-based indicators and soil NO₃-N content in an effort to develop tools to reduce the likelihood of soil NO₃-N accumulation without affecting grain yield. This study at 5 site-years in Québec consisted of six N fertilizer rates (20–250 kg N ha⁻¹). The NNI, NL concentrations, RCM values, and soil (0–0.15 m) NO₃-N content were measured weekly from July to early August, while soil NO₃-N content to a 0.90-m depth was measured in late August and October. During the growing season from July to early August, the proportion of data points above the average soil NO₃-N content was greater under non-limiting N conditions (NNI ≥ 0.88, NL concentrations ≥ 32.7 mg N g⁻¹ leaf DM, or RCM values ≥ 0.95) than under limiting N conditions. Furthermore, the mean soil NO₃-N content of the data points above the general average was much higher under non limiting than limiting N conditions in late August (167 vs. 78 kg NO₃-N ha⁻¹ for NNI and RCM; 166 vs. 112 kg NO₃-N ha⁻¹ for NL concentration) and October (68 vs. 49 kg NO₃-N ha⁻¹). High soil NO₃-N accumulation during the season and at harvest occurs only when in-season plant-based N indicators are greater than their threshold values.