Eficiência bioeconômica da adubação de pastagem natural no sul do Brasil

Abstract

This research was aimed at evaluating the plant and animal production and the economic response of a native pasture submitted to the application of N-P-K and nitrogen levels during the 1998/99 growing season. The experiment was conducted at Estação Experimental Agronômica of the Universidade Federal do Rio Grande do Sul (EEA - UFRGS). The pasture was fertilized in 1996 using 3000kg ha-1 of lime and 500kg ha -1 of 5-20-20. The one third of these amounts was considered as that concerning the 1998/99 growing season, in the economic analysis. The treatments were nitrogen (N) levels (zero, 100 and 200kg ha-1 of N) as urea, in a randomized block design with two plots by treatment. The experimental animals were beef heifers with initial age of 1,5 year-old and average live weight of 160kg. The forage mass, dry matter accumulation rate, green dry matter total production and the N transformation efficiency in primary production were enhanced by the N level applied (P< 0.1). The treatments 100 and 200kg ha-1 of N increased the costs in 104.1 and 208.2%, respectively. The treatment 200kg ha-1 of N presented the greater area live weight gain, the gross margin and the N conversion efficiency in animal product. The greater net financial return was reached when only lime and N-P-K fertilization were applied. The native pasture showed a positive response to the fertilizer application, within the amplitude of amount of the input applied in this experiment.