Leaf attributes are more efficient than soil mineral N to evaluate the availability of this nutrient to maize

In Southern Brazil, N availability to maize is evaluated based on soil organic matter, without considering N content in the soil or in the leaves. This work aimed to evaluate the efficiency of soil (NO3--N and NH4+-N levels) and plant (total N tissue, chlorophyll content and chlorophyll relative index) parameters as indicators of N availability during maize ontogeny. Maize was submitted to different nitrogen rates and side-dress application times. The study was carried out in Lages, Santa Catarina State, Brazil, during the 2008/2009 growing season. The experiment was set in a randomized block split plot design. In the main plot four N rates were evaluated: 0, 50, 100 and 200 kg ha-1. Two timings of N side-dress application were assessed in the split plots: all N applied when maize had four or eight expanded leaves and half rate applied when maize had four and the other half when it presented eight expanded leaves. Evaluations were performed between the growth stages of six expanded leaves and silking. The soil N content did not correlate with grain yield or any other plant characteristics regardless of growth stage. Therefore, they were not adequate to predict N availability to maize. Grain yield was not related to the chlorophyll relative index or total N level in leaves during early stages of crop development, but it was correlated with them when the evaluations were made from the 9th expanded leaf onwards. Plant characteristics were more suitable than soil parameters to predict N availability to maize and the crop grain yield.

nitrate; chlorophyll relative index; leaf total nitrogen; Zea mays (L.)

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