Produção e qualidade da forragem da cana-de-açúcar RB92579 em função da adubação fosfatada aplicada na quarta rebrota

Abstract

Sugar cane is a fodder widely used to feed ruminants on small, medium and large farms. The objective of the present study was to evaluate the nutritional status, yield and forage quality of sugarcane variety RB92579, as a function of phosphate fertilization applied in the fourth regrowth of sugarcane in a sandy soil. The research was conducted in a commercial field of a producer associated with Cooperativa Pindorama, located in Coruripe - Alagoas. Prior to the implantation, previous evaluations and samples were carried out for the choice of sugarcane plots, having chosen a field with soil without aluminum exchangeable in the 0 to 20 cm layer and with few failures in regrowth. The study consisted of five phosphorus doses (P): zero (control), 30; 45; 60 and 90 kg P per hectare, applied at the bottom of the open furrows between the rows of sugarcane. In the maximum growth phase of the fourth regrowth sugarcane, + 3 leaves were collected to evaluate the nutritional status of the plants. Leaf limb was analyzed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), copper (Cu), iron contents. (Fe), manganese (Mn) and zinc (Zn). Forage yield, industrialized stalks and sugars, the percentage of industrializable stalks in the aerial part biomass and the quality of the juice were analyzed. The obtained broth was analyzed for soluble solids (Brix), apparent sucrose (POL) and broth purity. Another subsample including industrializable stalks, pointers and dry leaves and green leaves was collected for determination of dry matter biomass of sugarcane and bromatological analysis. The average values of +3 leaf nutrient content, shoot biomass accumulation, industrializable stem production, soluble solids content and apparent sucrose content in the juice, juice purity, and recoverable sugars production, as well as the crude protein, phosphorus, sulfur, cellulose, hemicellulose and lignin contents in the RB92579 area biomass were submitted to analysis of variance. Regarding the nutritional status, the plants presented adequate leaf contents, except for the elements boron, copper and manganese. For broth quality, average values of 19.85% were obtained for soluble solids; 14.04% for apparent sucrose in the stems; 88.43% for broth purity; 13.70% for stalk fiber and 140.9 kg of recoverable sugars per ton of industrializable stalks. The average yield of industrializable stalks and total recoverable sugars was 71.2 t per hectare and 10.1 t per hectare, respectively. The average values of dry matter accumulation in sugarcane aerial biomass wererespectively 95.63 t per hectare and 30.35 t per hectare. For the variables related to bromatological quality of forage were obtained mean contents, in g per kg, 16.81 for crude protein; 0.70 for phosphorus; 229.5 for cellulose; 226.4 for hemicellulose and 37.4 for lignin. Thus, it was concluded that none of the analyzed variables was influenced by phosphate fertilization applied in open furrow between the fourth regrowth.

Key words: Livestock, ruminant feeding, phosphate nutrition and production system.