Nutrient cycling in dairy systems under different levels of intensification¹

ABSTRACT

The objective was to evaluate the effect of intensifying dairy systems on the uptake and return of nutrients in pastures. The experiment was conducted using four milk production systems on Mombasa grass pastures in the humid tropics, during the rainy season in 2009. This was a 2 x 2 factorial (two nitrogen fertilization levels and concentrate supplement or not for grazing animals) completely randomized design with four replications (paddocks). Nitrogen levels corresponded to 400 and 800 kg. ha^-1.year^-1, and supplementation was given to only two out of four groups of animals with milk yield above 11 L. day^-1. Pastures fertilized with the highest nitrogen level had higher contents of macronutrients in plant tissues and the litter but resulted in lower concentrations of N and Ca in feces. The uptake of macronutrients per grazing cycle was also higher in these pastures. The supplementation caused a decreasing effect on the content of N in dead pasture material, P in litter, and Ca, Mg, and P in feces. Decomposing litter represents the main source of nutrient return to the pasture, especially calcium, phosphorus, and nitrogen.

Key words:
Litter; Mombasa Grass; Nitrogen; Supplementation; Pastures