The Effect of the Grazing System on Nitrogen Losses, Production and Quality of a Mixture of Pasture in Southern Chile.
Rolando Demanet, Carlos Canseco, Pedro Núñez, and María de la Luz Mora. Univ de La Frontera, Av. Francisco Salazar 01145, Temuco, Chile
Chile is a country of a great variety of soils and environmental conditions, which permit the development of different production systems of beef and dairy cattle. During the last years, these systems have been intensified, and the increase of N-fertilizers application has created a high environmental impact through leaching of nitrates (NO3-) to water (Mora et al., 2004). On the other hand, the quality of pastures is diminished due to losses of nutrients and the alteration of the biogeochemical cycles of C, N, S and P. The pasture management improves the growth, persistence, diversity of the species and the fertility of soils. Furthermore, the frequency and the intensity of the grazing modify the quantity of accumulating biomass and the quality of the pasture (Kennedy et al., 2005). The objective of this study was to evaluate the effect of the frequency and intensity of spring grazing on the N-losses by leaching and on the yield and quality of a permanent pasture on an Andisol of Southern Chile. The experiment was carried out during the 2004/2005 season on paddocks of 165 m2. A mixture of pasture of Lolium perenne, Festuca arundinacea, Dactylis glomerata and Trifolium repens was established on an Andisol of Southern Chile (38°50¢ S, 72°42¢ W, 70 m above sea level). The chemical analysis of soil indicated 18 mg kg-1 of P Olsen, 33 mg kg-1 of N, pH of 5.53, 120 g kg-1 of organic matter, and 2.3% Al saturation. Fertilizer applied at sowing was 230 kg P2O5 ha-1 and a total of 138 kg N ha-1 was applied in three splits. Four criteria of grazing were evaluated: frequent-heavy (T1), frequent-light (T2), infrequent-heavy (T3) and infrequent-light (T4), each with three replicates, and a experimental design of random blocks were used. In each paddock, a lysimeter of PVC (7.5 cm diameter and 55 cm deep) was installed to measure the leaching of N as NO3--N and NH4+-N. The leached N was analyzed by Kjeldahl digestion. The availability of Dry Matter (DM) in pre- and post-grazing was determined with the Rising Plate Meter. Furthermore, total phytomass, apparent consumption (AC), botanical composition, coverage, Crude Protein (CP), Metabolizable Energy (ME) and Neutral Detergent Fiber (NDF) were measured. Data were analyzed using an Analysis of Variance (ANOVA) and significant difference means were separated with the Tukey multiple test (P≤ 0.05). The results showed that NO3--N was lost in lesser extent in the treatment T1 (3.55 mg L-1). In the other treatments the losses were 8.8 (T2), 7.93 (T3) and 6.88 mg L-1 (T4). For all the treatments, the NO3--N leaching was lower than the maximum level permissible in USA (10 mg L-1) and European Union (11.3 mg L-1). Furthermore, the losses of NH4+-N ranged between 2.52 and 3.83 mg L-1, and the leaching of NH4+-N was smaller than those from NO3--N in all treatments. On the other hand, the availability of DM (kg ha-1) of the input and output were 2231 and 1182 (T1); 2267 and 1642 (T2); 2718 and 1189 (T3) and 2736 and 1591 (T4), respectively. The AC presented differences during the spring season. Thus, the AC was higher in T3 and T4 treatments compared with T1 and T2 treatments. The highest yield was obtained in T3 (5.7 t DW ha-1). The greatest coverage was obtained in the treatments that were managed under light grazing (T2 and T4). In the treatment T4, both the lowest contribution of Lolium perenne (17.3%) to the botanical composition and the highest content of senescent material (47.5%) were observed. Additionally, T4 presented the lowest contents of CP (12.9%), ME (2.28 mcal kg-1 DW) and NDF (53.9%). Acknowledments: FONDECYT-1020934 and Project FIA (FIA-PI-C-2003-1). References: 1) Kennedy, E., O'Donovan, M., Murphy, J., Delaby, L. and O'Mara, F. 2005. The effect of early and delayed spring grazing on the milk production, grazing management and grass intake of dairy cows. Proceedings of a satellite workshop of the XXth International Grassland Congress: 152. 2) Mora, M. L., Ordoñez, C., Cartes, P., Vistoso, E., Pino, J., Jara, A. y Demanet ,R. (2004). Reciclaje de nitrógeno proveniente de purines en una pastura de Lolium perenne L. Simposio: Residuos orgánicos y su uso en sistemas agroforestales. Sociedad Chilena de la Ciencia del Suelo. Temuco, Chile. Universidad de La Frontera 20, 243-256.