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.