COSTA, Patrícia da Silva.
Résumé:
Forage cactus is adapted to semi-arid climate regions, making up an important food source for the herds and animals during the dry season, especially in the Northeast of Brazil. Besides being a plant which is adapted to the climate and soils of the region, research proves its massive increase of productivity when exposed to adequate water and nutritional availability. However, not a lot is known about the effect of productivity gains on the quality of production. The objective of this study was to evaluate the bromatological composition of forage cactus varieties fertilized with nitrogen rates in the semi-arid region of Brazil. The experiment was conducted in the open field, at the Poço Redondo farm, in Santa Luzia, PB. The experimental project was a randomized complete block design with a 3x5 factorial scheme, consisting of three varieties of forage cactus (V1 = Baiana; V2 = Miúda and V3 = Orelha de Elefante Mexicana) and five nitrogen rates (N0= 0, N1= 150, N2= 300, N3= 450 and N4 = 600 kg ha-1 of N), with three replicates. The chemical composition was expressed as dry matter, mineral matter, crude protein, ethereal extract, neutral detergent fiber, acid detergent fiber, total and non-fibrous carbohydrates. The data were submitted to analysis of variance, polynomial regression and test of comparison of means. There was a significant effect of nitrogen rates and difference between varieties, as well as interaction between these factors, except for neutral detergent fiber and ethereal extract. The averages of the variables had a quadratic adjustment, with the exception of crude protein and total carbohydrate contents that were adjusted to the linear model. The levels of dry matter, neutral detergent fiber, acid detergent fiber, crude protein and ethereal extract were increased with the augmentation of the nitrogen mulching supply, reaching maximum values, followed by reduction in the higher rates, except for the protein contents which had linear increase. There were reductions of non-fibrous carbohydrates and total carbohydrates as the nitrogen rates were increased in the irrigation water, except for the Miúda variety, which after reaching critical values of these carbohydrates expressed an increase in these levels. Among the varieties, Baiana had higher levels of dry matter, neutral and acid detergent fibers, total and non - fibrous carbohydrates. Miúda had a higher mineral content. It should be emphasized that the performance of these varieties, for the variables considered, depends on the nitrogen rate. The bromatological composition of forage cactus varieties is positively influenced by fertirrigation with nitrogen rates in the Brazilian semiarid region. The practice of nitrogen fertilization can be recommended for forage cactus cultivation in the region, observing the optimum nitrogen rates for each bromatological component.
