Se of greenness index to determine the optimal economic rate of nitrogen in maize

Abstract

In regions with water excess at the beginning of the growing season, the application of nitrogen (N) in early stages of corn is not the best strategy to maximize the use efficiency of this nutrient. The chlorophyll meter Minolta SPAD could be used to monitor the nitrogen status and estimate the deficit or excess of N with respect to the optimal economic dose (dOED) during the crop growing season. The utility of chlorophyllometer Minolta SPAD® 502 was evaluated to monitor the maize nitrogen status and define the dOED using three price ratios (18, 10 y 5 kg maize grain kg fertilizer). Fourteen no-till maize experiments of N fertilization were carried out in the southeastern Buenos Aires (SEB). The greenness index (IV) was determined at the stage of 6 and 10 leaves (V6 and V10) and the ISN (ratio between IV of a given treatment and that of the maximum N rate) was calculated. Nitrogen deficit or excess respect to OED (dOED) was calculated as the N rate minus OED. The ISN was associated with dOED in V6 and V10 but the r² was higher for V10 (0,44 to 0,59 vs. 0,71 to 0,73, respectively). In V10, a single model was adjusted for 10:1 and 5:1 price ratios (ISN = 0,98 + 5e-5xdDOE - 3,9e-6 xdDOE²; r²= 0,68), which differed from the adjusted for 18:1 ratio (ISN = 0,97 + 5,4e-4xdDOE - 3,7e-6*dDOE²; r²= 0,73). The ISN value for dOED= 0 was 0,98 and 0,97 for 10:1 and 18:1 price ratios, respectively. These results shown that ISN determined with SPAD 502 chlorophyllometer allows to determine dOED for maize across different production conditions, and make possible take in-season N dose decisions. This would help to minimize N losses, increase N use efficiency and reduce environmental impact of N fertilization in no-till maize.

Keywords

• Conopy sensors
• nitrogen nutrition