Adubação nitrogenada à taxa variada com o N-Sensor nas culturas do milho e trigo

Abstract

Most tropical and subtropical soils present insufficient availability of nitrogen (N) to meet the demand of maize and wheat in order to obtain high yields. The N in plants can be evaluated through the use of sensors of active optical spectrometry, on which stands the N-Sensor, equipment able to determine the N rate to be applied in coverage in real-time. The objective of this study was to evaluate the efficiency of variable-rate nitrogen fertilization with use of the N-Sensor and to correlate it with different parameters of the plant during the development of maize and wheat in Oxisols of the RS. The experiments were performed in Tio Hugo and Cruz Alta with corn and Victor Graeff and Cruz Alta with wheat. It was evaluated the effect of different doses of variable-rate and fixed-rate Nitrogen in plant parameters such as chlorophyll meter readings and dry weight, N content in dry weight and amount of N absorbed per unit area, correlating them with the Biomass Vigor Index (BVI), recommended dose from the N-Sensor and grain productivity. During the applications of nitrogen fertilizer it was collected an average between 235 and 345 records per hectare of BVI and recommended doses by the N-sensor. The yields of maize, for the variable-rate treatments, and although did not differed from the uniform-rate, were of 9273 kg ha-1 and 8571 kg ha-1 respectively for Tio Hugo and Cruz Alta, standing above the Southern average in the 2008/09 crop year (5570 kg ha-1). The experiments with wheat achieved an average productivity of 2520 kg ha-1 in Victor Graeff and 2858 kg ha-1 in Cruz Alta, above the average of the South region, which is around 2070 kg ha-1. The results showed that the chlorophyll measured by the SPAD was an early indicator for the recommendation of nitrogen fertilization for corn in the experiment conducted in Tio Hugo. At the stage of 8 fully expanded leaves, the critical value determined was 44.5 SPAD values. For wheat there was no correlation between the parameters evaluated and plant productivity. The critical content of SPAD at the flowering stage was 40.6. There was significant correlation between the dose indicated by the N-sensor and the productivity of wheat in the experiment in Victor Graeff, showing the efficiency of diagnosis with the sensor. The increase in grain yield with the application of variable-rate N by using the N-Sensor, compared with the fixed-rate N application, ranged from 8.05% in Cruz Alta and 3.6% in Tio Hugo for corn and 0.2% for wheat in Cruz Alta. Furthermore, there was a reduction of 4.35% in Victor Graeff for wheat and more studies should be conducted in order to adapt this new technology to the Brazilian crop.