Nitrogen fertilization in a psammophilous grassland of San Luis, Argentina

Three treatments were conducted to assess and compare in psammophilous grasslands the effect of different urea doses on the DM production, as well as to determine and compare the efficiency of utilization of the nitrogen applied in an area closed to the water supply. The three treatments were implemented in spring: N0 = natural grassland burnt without fertilizer, N140 = natural grassland burnt and fertilized with 140 kg of urea ha-1 and N240 = natural grassland burnt and fertilized with 240 kg of urea ha-1. Split plot design in blocks was applied (two repetitions). Cuts were performed in January and March. In each sampling unit, the dry matter production was quantified and the forage species were differentiated from the non-forages. The efficiency of nitrogen utilization emerged from the difference between the fertilized and the non-fertilized material, compared with the nitrogen applied. Factorial ANOVA was used. The factors fertilization, forage aptitude, and cut time affected the DM production (P < 0.05). The grassland had very low production of forage species (N0: 38.33 g DM m-2). The N application provoked increment in them (N140: 83.13 g MS m2 and N240: 83.33 P < 0.05), as well as in the non-forages (N0: 85.67 vs. N140: 133.83 g MS m2; P < 0.05). In March, the forage species reached the maximum production, with 240 kg of urea ha-1 (174 g DM m-2) and they surpassed the non-forages (116.33 g DM m-2). The highest efficiency in the utilization of the applied nitrogen was shown in the group of non-forage species, with 140 kg urea ha-1 (13.54 kg of DM kg of N applied-1). The fertilization with high doses of urea improved the productive condition and the receptivity of the degraded grasslands, being possible to use the forage and biomass accumulation in seasons of pasture shortage. Key words: natural grassland, degraded areas, burning, N efficiency, production.