Saturday, 15 July 2006

Soil Indicators for Determining the Impact of Management on the Stability of Grasslands in Cattle Exploitation.

Sandra Lok, Institute of Animal Science, Carretera Central Km 47 1/2, San JosÚ Las Lajas, La Habana, Cuba

The degradation of the grasslands is a phenomenon of global transcendence (Holzer and Krechbaun 2001) and it is reflected directly in the decrease of the soil fertility, which is one of the natural resources of slowest recuperation. The determination of indicators that allow detecting in an easy and trustworthy way their productive and ecological impact is a present challenge. Therefore, the objective of this work was to select indicators of the soil stability in grasslands in cattle exploitation. The study was performed in 2002, 2003 and 2004 in the Institute of Animal Science located in Havana, Cuba. Two grasslands were evaluated: a) silvopastoral system based on Leucaena leucocephala/Panicum maximum in hydrated red ferrallitic soil (Oxisol), b) mixture of creeping legumes in brown red fersialitic soil (Andisol). Seventy soil indicators were determined such as texture, structure, resistance to penetration, value n, humidity, pH, organic matter, content of nutrients, subterranean phytomass, mesofauna and macrofauna. The physical and chemical indicators were measured annually when the rainy season was stabilized, whereas the biological indicators were measured twice per climatic season. The analysis was made by the methodology of Torres et al. (2003). Those indicators with values of preponderance higher than ▒0.78 and that were located in the components that accounted for at least 65 % of the variance accumulated were selected. A linear analysis of variance was performed to those indicators and the range of confidence was calculated for the 95 % of probability. The indicators selected in the grasslands (table 1) had adequate values in correspondence with the type of soil (Alonso 1997) and manifested a significant improvement with the increase in time of the exploitation of each grassland. Thus, they showed that both are kept productively stable and their managements have had a positive ecological effect. The indicator distribution of aggregates in humidness and the subterranean phytomass coincided in both grasslands, regardless they are located in different soil types and with different plant cover. This showed that they may be important for the control of several grasslands. The performance and state of the soil stability could be characterized by a reduced group of indicators. These indicators showed that the management improved the grasslands productively and ecologically. Thus, they are recommended for their systematic control.

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