PRONÓSTICO DEL CAMBIO EN ALGUNAS PROPIEDADES DE LOS SUELOS AGRÍCOLAS AL MODIFICARSE LAS CONDICIONES MICROCLIMÁTICAS PREDICTION OF SOME AGRICULTURAL SOIL PROPERTIES CHANGE DUE TO MODIFICATION OF MICROCLIMATIC CONDITIONS

Agricultural activities produce changes in chemical and physical properties of soils. Two kinds of change in soil properties can be considered: direct change, as a result of plant, soil and water management, and indirect change, caused by modification of microclimatic conditions. The prediction of indirect change of agricultural soils was realized in this study by means of a new method based on the relationship between some chemical and physical properties of Mexican soils not used in agriculture, and located in flat areas at altitudes up to 2500 m above sea level, and the local hydrothermal index (radiative index of dryness) IHT=R/(L Pr), where R and Pr are mean annual values of net radiation and precipitation, respectively, and L is latent heat of evaporation. The change of vegetation (in comparison with the one existing before agricultural use of soil) causes albedo change and the corresponding change of net radiation from R to R1. The irrigation with an annual amount Lr increases accumulated annual water infiltration into the soil from Pr to Pr+Lr and changes the index from IHT to IHT1=R1/(L(Pr+Lr)). The gradual indirect soil property changes were evaluated for the conditions of irrigation and rain fed agriculture calculating the indexes IHT and IHT1, as well as the established relationship between IHT and regional soil properties. The results show that the soils with natural vegetation are most fertile in the climatic zones with values of IHT inside the interval (1.0, 1.4). This means that agricultural practices should attempt to maintain the index IHT1 in that interval managing (within the possible levels) the values of R1 in rain fed lands or of R1 and Pr+Lr under irrigation. Such approach could support soil conservation and contribute to the attainment of a sustainable agriculture.