Função de produção e pegada hídrica da palma forrageira sob lâminas de irrigação e adubação nitrogenada.

Abstract

Economic analysis and water footprint are important for understanding the amount of inputs used in crops, and thus, to determine the optimal economic amount with a view to increasing revenue and reducing environmental impacts. The objective of this study was to determine the production function and water footprint of the forage palm under irrigation depths and nitrogen fertilization. The experiment was carried out under field conditions in the municipality of Santa Luzia - PB. The experimental design was in randomized blocks and a 5 x 5 factorial scheme, with five irrigation levels - LI (25, 50, 75, 100 and 125% of ET0), five levels of nitrogen - NN (0, 150, 300, 450 and 600 kg ha-1 of N) and three replications. This design was used for three cultivars of forage palm (Elephant Ear, Baiana and Miúda. It was evaluated: thickness, area and number of cladodes; green mass and water productivity; efficient use of nitrogen; production function, blade that maximizes production, maximum productivity, economic analysis and water footprint of the studied cultivars. The LI of 125% of ET0 had the greatest influence on the variables analyzed for the cultivars Orelha and Baiana. NN greater than 300 kg ha-1 provided maximum performance of the forage palm in growth and yield. The productivity of Elephant ear (680.0 t ha-1) and Baiana (647.7 t ha-1) were higher in the harvest than 12 MAP; for Miúda the highest productivity (254.0 t ha-1) was obtained at harvest at 18 MAP. The increased availability of water and nitrogen in the soil favored the growth and productivity of the forage palm. The production of irrigated and fertilized forage palm in the semiarid region is a promising and economically viable activity. The tools used to define the viability of the cultivation of forage palm make it possible to verify the viability of the investment, as they present positive net present value and internal rate of return. The total water layer that maximizes productivity (779.0 mm) associated with a higher dose of nitrogen (600 kg ha-1) resulted in greater productivity, obtaining greater net revenue and better cost benefit ratio in the cultivar Orelha de Elefante. The lowest consumption was blue water (13.3 m3 t -1), followed by green water (24.2 m3t-1), with the highest consumption of gray water (31.1 m3t-1). The increase in applied NN reduced the green, blue and gray water footprint of forage palm cultivars. The increase in LI decreased the green and gray water footprint and increased the blue one. The cultivar Orelha de Elefante provided the smallest green, blue and gray water footprint. The water footprint of the irrigated and fertilized forage palm is the smallest found in the literature, showing the great potential of this forage for regions with little water availability.