Characterization of corn Nitrogen status with a greenness index under different availability of Sulfur
Several methodologies measure leaf greenness intensity and relate it to crop N status. There is no evidence, however, of the utility of this variable to detect N deficiencies in corn (Zea mays L.) under S deficiency. The objective of this work was to evaluate the potential of two indexes based on leaf greenness intensity to detect N deficiencies in corn under different levels of S. Two experiments at Balcarce, Argentina (Bce I and Bce II), and one at 9 de Julio, Argentina (9dJ), were conducted during the 2005–2006 and 2006–2007 seasons with different levels of N and S. Weekly measurements of greenness index (GI) were performed, and whole-plant samples were taken at four developmental stages to determine crop N and S accumulation. No N x S interaction was found in any measured variable. Nitrogen increased dry matter N and S accumulation, grain yield, and GI. Sulfur fertilization resulted in increased S accumulation in all experiments, and grain yield at Bce II and 9dJ. This nutrient also increased GI during several crop stages in all experiments. A nitrogen sufficiency index (NSI) was related to its relative yield (R2: 0.67, 0.63, 0.43, 0.67 for stages V5–V8, V9–V11, V13–V14, and V15–V18, respectively) under different S levels. On the other hand, a new index called relative greenness index (RGI), proposed for situations that could present S deficiencies, was also related to its relative yield (R2: 0.67, 0.81, 0.63, 0.82 for stages V5–V8, V9–V11, V13–V14, and V15–V18, respectively) under different S levels. The regression lines of both indexes were coincident for all sample dates. It was concluded that crop N status can be characterized under different levels of S through the NSI. Future research, however, should test these results under a wider range of S levels.