Native forage quality, quantity, and profitability as affected by fertilization in northern Mexico.

Abstract

Fourteen treatments of nitrogen (N) and phosphorus (P) fertilizers were applied in an overgrazed eight rangeland in northern Mexico, during 1990 and 1991. Eight treatments were applied using ammonium nitrate as a source of N (60-0-0, 60-30-0, 60-60-0, 80-40-0, 120-30-0, 120-60-0, 120-90-0 and 180-60-0 kg ha-1), 2 treatments with ammonium sulfate (60-30-0 and 120-60-0 kg ha-1), 2 with urea (60-30-0 and 120-60-0 kg ha-1), only P (0-30-0 kg ha-1), and the control (0-0-0 kg ha-1). Triple superphosphate was applied as a source for P. The 80-40-0 treatment was included because it was the commonly recommended rate for the area. Fertilizers were applied at the beginning of the rainfall season (July) and forage was harvested in late October (1990) and mid-November (1991). Dry matter production, crude protein (CP) content, and in situ digestibility were determined. An economic analysis was used to obtain the best economic treatment for forage production. In 1990 with a precipitation of 377 mm, dry matter production was significantly affected for both source and rate of N. The maximum amount of dry matter was obtained with a rate of 120-90-0 kg ha-1 using ammonium nitrate. However, the best treatment in terms of economic return was 120-30-0 kg ha-1 as ammonium nitrate. Urea did not produce as well as other N source treatments. Crude protein was highest in treatments with the higher N, but no significant trend was evident. In situ digestibility was not affected by rate or source of N fertilizer. During 1991, precipitation was higher than in 1990. Significant differences were determined among N rates but not in N source. In fact, urea produced greater in dry matter production than other N sources at the same rate. The maximum amount of dry matter was obtained with the 180-60-0 treatment using ammonium nitrate with 4,190 kg ha-1, but the best economic treatments were the 120-30-0 and 60-0-0 with a marginal return rate of 377% and 355%, respectively. Results of CP and in situ digestibility were similar to those of 1990.