Adubação fosfatada e nitrogenada em sistema de partejo rotacionado de capim Massai com ovinos em Neossolo Quartzarênico Órtico

Abstract

The goal of this paper was to evaluate the interaction of phosphorus and nitrogen fertilization, as well as availability and its performance in productivity of Panicum maximum cv. Massai, availability in the soil, nutritional aspects, and ruminal degradability, voluntary intake and tracking available phosphorus applied through fertilization, animal mineralization and P cycling system in Quartzipsamment soil. The experiment was conducted at EMVZ - UFT, in a randomized block, 2x2 factorial, using P (50 and 200 kg ha-¹ of P2O5) and N (100 and 400 kg ha-¹ N) and control unfertilized with four repetitions. The study area consisted of 32 paddocks each (301 m²), with already established Panicum maximum cv. Massai pasture. The experimental area was managed under intermittent stocking with variable stocking rate. It was used 28 mixed breed sheep for grazing management. Evaluations were made before and after grazing regarding the agronomic and structural characteristics and productivity of Massai grass, and soil chemical characteristics. Moreover, it was evaluated the nutritional value of the forage including bromatological parameters, degradability and intake, using titanium dioxide as an external indicator of consumption, and how much it was able to modify animal biometrics. It was also evaluated the P balance in the system which was estimated based on existing fractions in the soil, plant and animal, and additions resulting from fertilization, mineralization by animals and P cycling in the system. Both fertilizations temporarily modify the chemical characteristics of the soil, increasing pH, Mg, P, V%. The layers from 0 to 10 cm achieved the highest values of the base. Fertilization of P and N increase forage production and consequently provide an increase in stocking rate. However, it is necessary to establish a fine adjustment between the quality and quantity of forage produced and provided to sheep in order to obtain the highest gain per area. Fertilization alters the nutritional quality of Panicum maximum cv. Massai grass especially in high concentrations of P. Among the nutritional parameters evaluated, fertilizations influence the NDF, grass digestibility and voluntary intake by animals. Soluble phosphorus sources added have little residual effect on Quartzipsamment soil. The destination and the possible mobility and consequent loss of phosphorus in the soil-plant-animal system in Quartzipsamment soil should be better studied in order to increase production efficiency. An installment possibility of soluble phosphate fertilizer levels above 50 kg P2O5 ha-¹ is an alternative to avoid P fertilization inefficiency in Quartzipsamment soil.