Resposta técnico-econômicas da cana-de-açúcar a níveis de irrigação e adubação nitrogenada.

Abstract

The knowledge of water-soil-plant-atmosphere relations and sugarcane responses to irrigation and nitrogen fertilization are key to improving yields agribusinesses of this agricultural culture in the Brazilian Northeast. Therefore, with the objective of To evaluate sugarcane responses to irrigation slides (L) and nitrogen doses (N) was an experiment was installed in the region of Rio Largo - AL The irrigation slides were determined on the basis of reference evapotranspiration (ETo) 0,0 ETo, 0,25 ETo, 0,50 ETo, 0.75 ETo, 1.00 ETo, 1.25 ETo and 1.50 ETo and the N doses were: zero, 50, 100, 150 and 200 kg N per hectare. The air temperature during the survey ranged from 21.3 to 29.2 ° C, mean of 25.2 ° C. In the sugarcane cycle it rained 2,137 mm and the crop evapotranspiration (ETc) it was 1,642 mm, in the cane it rained 1,976 mm and the ETc totaled 1,628 mm. Even so, there was a water deficit of 606 and 461 mm and a water excess of 1,100 and 809 mm in the first and second production cycles respectively. The average agricultural productivity of sugarcane it was 160 t ha "1 and the sugarcane cane 130 t ha" 1. The most economical efficiency blades (with the kg of total recoverable sugars (ATR) worth R $ 0.3985 and the millimeter of water applied R $ 3.20) were 610 mm in cane and 213 mm in cane, while the doses of N most economically viable were 126 and 100 kg of N ha "1, in the sugarcane and sugarcane cycle, respectively. The average quantities of ATR per ton of sugarcane were 145.7 in sugarcane and 147.8 cane; industrial yield in tonnes of sugar per hectare in sugarcane ranged from 17.1 to 26.01 ha ', in the irrigation slides and from 21.7 to 23.71 ha "1 in the nitrogen doses; in sugarcane were 16.3 to 20.8 t ha "1 compared to L and 18.5 to 19.8 t ha "1 compared to N. Production growth rate ranged from 9.3 to 14.4 tonnes sugarcane per month (t month "1) and from 9,3 to 11,9 t month" 1, in the first and second cultivation cycles, respectively. The amount of N extracted per ton of sugarcane produced was from 0.32 to 1.22 kg in cane and from 0.39 to 1.51 kg in cane. Regarding the amount of sugarcane produced per kg of N applied in the first production cycle, ranged from 58.0 to 122.0 kg of N sugarcane and in the second cycle it was 35.5 to 82.0 kg of sugarcane. Irrigated sugar cane in both cultivation cycles, with 150% of ETo produced on average 51.0 t ha "1 more than sugarcane cultivated without irrigation and in relation to nitrogen fertilization, the fertilized treatment with 50 kg N produced 8.5 t ha "1 on average more than nitrogen-free fertilizer. irrigation equivalent to 190% and 165% of ETo and N rates of 167 and 157 kg N ha "1 maximized agricultural productivity in the first and second cycle of cultivation respectively. And the most efficient irrigation blade and N dose plant sugarcane were 610 mm 126 kg N ha "1 and in sugarcane 213 mm kg of N ha "1. The final agro-industrial yield per hectare is more dependent on agricultural productivity than the amount of ATR. Root-type regression curves and the second polynomial response surface of sugarcane agricultural productivity with irrigation slides and nitrogen rates. The marginal rate of water replacement by nitrogen and the combinations of these factors that result in the lowest cost of production varied according to the irrigation blade, the dose nitrogen production and the desired agricultural productivity. The rational sugarcane production region in relation to irrigation slides and nitrogen doses and quite wide and provides a wide range of options for combining these factors for said agricultural crop.