Greenness index profile in maize canopy: Implications for crop N status diagnosis

Abstract

Context

The greenness index of the ear-leaf in maize (Zea mays L.) has been used to assess crop nitrogen (N) status, but it may not accurately predict yield responses to late N fertilization.

Objective

This study aimed to i) analyze differences in the greenness index and N sufficiency index (NSI) across maize canopy leaf positions and their relationship with soil N availability, N nutrition index (NNI), and grain yield, and ii) evaluate the accuracy of NSI determined in different leaf positions in predicting the grain yield response to N fertilization at silking.

Methods

The greenness index was measured across the maize canopy profile under varying N rates and application timings in five field experiments. Bell-shaped models described the greenness index distribution, and relationships among NSI, NNI, and relative grain yield (rGY) were analyzed.

Results

At silking, NSI differences were more pronounced in lower leaves, showing stronger associations with soil N availability (R² > 0.69) and NNI (R² > 0.58), compared to the ear-leaf (R² = 0.37 and 0.54, respectively). The NSI vs rGY relationship showed no differences among the three lower leaf positions. Measurements in upper leaves had weak associations with crop N status or yield responses. Only NSI from leaves in the lowest position below the ear-leaf predicted yield response to N fertilization at silking.

Conclusions

Measuring NSI in lower leaves provided a better assessment of crop N status, improving predictions of yield responses to late N applications, and supporting more precise N fertilization strategies for modern maize hybrids.