Uso del índice de verdor para determinar la dosis optima económica de nitrógeno en maíz

Abstract

En regiones con excesos hídricos al comienzo de la estación de crecimiento, la aplicación de nitrógeno (N) en estadíos tempranos del maíz no es la mejor estrategia para maximizar la eficiencia de uso de dicho nutriente. El medidor de clorofila Minolta SPAD® 502 podría ser utilizado para monitorear el estatus nitrogenado y estimar el déficit o exceso de N respecto a la dosis óptima económica (dDOE) durante la estación de crecimiento del cultivo. Se evaluó la utilidad del clorofilómetro SPAD 502 para monitorear el estatus nitrogenado del maíz y definir la dDOE para tres relaciones insumo/producto (18:1; 10:1 y 5:1). Se realizaron 14 experimentos de fertilización nitrogenada en maíz bajo siembra directa en el sudeste bonaerense (SEB). Se determinó el índice de verdor (IV) al estadio de 6 y 10 hojas (V6 y V10) y se calculó el ISN (cociente entre IV de un determinado tratamiento y el de la máxima dosis). El dDOE se calculó como la dosis de N aplicada menos la DOE. El ISN se asoció con la dDOE en V6 y V10, siendo el r2 mayor para V10 (0,44 a 0,59 vs 0,71 a 0,73, respectivamente). En V10, se ajustó un único modelo para las relaciones de precios de 10:1 y 5:1 (ISN= 0,98 + 5e-5xdDOE – 3,9e-6 xdDOE2; r2= 0,68), el cual difirió del ajustado para la relación 18:1 (ISN= 0,97 + 5,4e-4xdDOE – 3,7e-6*dDOE2; r2= 0,73). El valor de ISN para una dDOE=0 fue de 0,97 y 0,98 para el primer y segundo modelo, respectivamente. Se concluye que el ISN determinado con el clorofilómetro permite calcular la dDOE en cultivos de maíz creciendo bajo diferentes escenarios productivos, facilitando la toma de la decisión de aplicar N durante la estación de crecimiento. Esto contribuiría a minimizar las pérdidas de N y el potencial impacto ambiental negativo de la fertilización

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-5xdOED – 3,9e-6xdOED2; r2= 0,68), which differed from the adjusted for 18:1 ratio (ISN = 0,97 + 5,4e-4xdDOE – 3.7e-6xdDOE2; 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.

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-5xdOED – 3,9e-6xdOED2; r2= 0,68), which differed from the adjusted for 18:1 ratio (ISN = 0,97 + 5,4e-4xdDOE – 3.7e-6xdDOE2; 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.