Resumo

MEDINA OROZCO, Lenin Ejecatl et al. Soil, water and nutrient losses in an acrisol under different agronomic systems in Michoacan, Mexico. Agric. Téc. Méx [online]. 2008, vol.34, n.2, pp.213-223. ISSN 0568-2517.

In the upper part of Cuitzeo Lake watershed, Michoacan, Mexico, farmers use a traditional short-fallow production system. With this system, land is sown one year, and left without cultivation from one to three years for grazing. This system is used mainly on Andisols and Acrisols, and it is supposed to be associated with soil degradation due to low nutrient recycling level and to excessive tillage during the cultivation year. The objective of this study was to measure soil, nutrient and runoff losses under the traditional short-fallow system (AV), and under two alternatives systems: organic (O), and improved traditional (TM) systems. Research was carried out on an Acrisol in the Cointzio sub-watershed, during three years under rainfed conditions on 1 000 m² runoff plots without replications. Results showed that soil losses under all systems were permissible (< 1.2 t ha^-1 year^-1), except in TM and O in 2002 when the plant coverage was less than 20%, with a significant increase of runoff and nutrient losses when land was left on fallow due to soil surface bulk density increase. This change did not occurred with the O and TM systems, perhaps due to soil tillage effect. Main nutrient losses in the three treatments were: N, Ca²⁺, Mg²⁺, Na⁺, and K⁺. Above mentioned results suggests that soil degrading effect, under the AV system, is more intense on soils when they are left on fallow than when those are cultivated. Best practice for reducing water, soil, and nutrient losses were: dense crops such as oats, and the use of crop residue cover (30% cover), the last one was also the best management for decrease evaporation. An analysis of soil losses to sub-basin level showed that erosion can be reduced significantly by using crop residues as mulch during crop production (TM).

Palavras-chave : degradation; nutrient loss; rehabilitation; sustainable.