Small ruminant impacts on rangelands of semiarid highlands of Mexico and the reconverting by grazing systems

The north-central semiarid region of Mexico has been exposed to systematic grazing since colonial times. The grazing impact on rangelands has degraded soils and reduced diversity and productivity. The most common and detrimental cause of soil degradation is soil erosion which destroys chemical, physical and biological properties. To determine the effect of grazing systems on rangelands, several studies were performed. Such studies included a description of soil profiles to categorize degradation and the evaluation of water erosion changes due to further degradation processes under grazing systems (rotational, RG and continuous, CG). The study was carried out on a rangeland of the ejido Pánuco, Zacatecas, from 2002 to 2005. Soil degradation was classified by identifying 6 groups with similar soil profiles (GSSP) which were described as: (1) low degradation soil; (2) medium degradation soil with A horizon lost; (3) high degradation soil without A and B horizons lost; (4) high degradation soil with in situ development; (5) high degradation soil with calcareous material; and (6) high degradation soil without development, which is a very shallow soil above the parental material. Further degradation was determined by soil erosion measurements performed in the study area and the surroundings. With respect to soil losses their values were systematically less for the RG system under the native vegetation conditions studied (P < 0.01). Changes in the production systems may imply a reconversion of the system. Some changes include a modification in the intensity of use of rangelands, starting with a new grazing system, as well as changes in technology which may be simulated by GIS.