Fertilização nitrogenada do algodoeiro prescrita por sensor óptico no oeste da Bahia

Abstract

Proper nutrition nitrogen in cotton directly affects obtain high productivity of the crop. Decision making based on the use of sensors is an alternative to increase the efficiency of fertilization with this nutrient, however, the accuracy of the sensors and the vegetative stages most suitable for the realization of the readings are not well defined. In this context the present study had the following objectives: I - Evaluate the effectiveness of an optical sensor to estimate the nutritional status of cotton crop under different N rates; II- Which phenological stages the optical sensor has higher efficiency. III - Establish response curve in the cotton productivity in relation to nitrogen and estimate reference values to use the optical sensor on the prescription variable rate fertilizer. The experiment was conducted in the agricultural year 2012/13 on a Oxisol in the western state of Bahia. The experiment was conducted at three sites and experimental design was a randomized block design with seven treatments and three replications. Treatments consisted of the following N rates: 0, 45, 90, 130, 150, 180 and 220 kg ha-1 applied at 43 days after sowing (DAS) in area 1 and 32 DAS in areas 2 and 3. Readings vegetation index (IV) were carried out in three seasons, corresponding to 63, 75 and 97 DAS in area 1 and 45, 57 and 80 DAS in areas 2 and 3, using the optical sensor N-Sensor ALS® (YARA) . Adjacent stages and the read points IV, samplings to determine dry matter (DM) were taken, and measurement of the absorbed nitrogen and plant height, furthermore, the determination of the yield of cotton was carried out. The sensor reading and the other factors evaluated were subjected to regression analysis by the statistical program Sigma Plot 11. The N fertilizer applied significantly altered the vegetative attributes evaluated. Reading the IV optical sensor showed high correlation with crop nutritional status determined by N does in the three areas evaluated for the different stages of evaluation. Reading the vegetation index obtained by the sensor also showed high correlation with the 8 parameters plant height, DM and N absorbed. The productivity of cotton crop showed a quadratic fit with the N levels in all experiments. The preliminary calibration value suggesting that the critical IV would be equal to 60 for the stage F1 in the middle of the three areas studied.