Conservation Tillage is essential in arid and semiarid areas, where carbon contents in soils are low and the water is the main limiting factor for crop development. This technique is part of what nowadays is called Conservation Agriculture. It is recommended to avoid soil erosion and water losses by evaporation and runoff due to residue cover from the preceding crop left at the surface. Conservation Agriculture also includes cover crops, crop rotation and integrated nutrient management. The studies of this PhD thesis have been performed in two different soils: a calcareous soil (Typic Xerofluvent) where the experimental plots were set up and an acid easily erodible soil (Leptosol Eutrico) located in a commercial agricultural farm. Two experiments were carried out in the experimental plots: a long-term experiment established in 1992, where traditional (soil inversion) and conservation tillage (reduced tillage) were compared and a short-term experiment established in 2004 where traditional tillage and no-tillage were compared. In the commercial agricultural farm the study consisted of the application of an occasional mouldboard ploughing (common practise to avoid potential soil compaction by continuous no-till) in an area where no-tillage had been applied in the last eight years. In both cases the studies were focused on the period 2007-2009, under a sunflower-pea-wheat rotation in the experimental plots and with wheat in the commercial agricultural farm. The results showed that the conservation tillage techniques had positive effects on soil quality, especially at surface, causing improvements in physical properties, decreasing CO2 emissions, and increasing different carbon fractions contents as well as different biochemical parameters (soil microbial biomass carbon and enzymatic activities). Moreover, conservation tillage techniques did not negatively affect crops and similar yields were obtained under different tillage systems (sometimes slightly higher under conservation tillage). From the results obtained in this study, we can conclude that conservation tillage is highly recommended for our experimental conditions (semiarid rainfed Mediterranean conditions), considering the improvement at surface (“the skin of the Earth”), where differences between treatments were higher than at deeper layers. We also demonstrated that traditional tillage system is not justified even occasionally in erodible soils, due to the important decrease of soil quality.

El presente trabajo ha sido realizado gracias a una beca predoctoral del Programa Nacional de Formación de Personal Investigador (FPI), del Ministerio de Educación y Ciencia, adscrita al Programa AGL2005-02423.

Peer reviewed

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