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