Effects of irrigation and plastic mulch on soil properties on semiarid abandoned fields

The Guadalentin Basin in Spain is one of the driest areas of Europe and has problems with high evaporation rates, and high risks of desertification exist including soil quality loss and soil erosion. Farmers in this semiarid region use polyethylene covers on their irrigated croplands to reduce evaporation to enhance crop yield. When farmers abandon the acres, they leave the plastic covers on the fields. Up to now research has been concentrating on the effects of plastic covers on crop yield and microclimate under these covers but there is little known about the effects of plastic covers and irrigation on soil quality, erosion susceptibility, and hydrology after abandonment of these fields. The research question in this paper is: How do the former irrigation practices and plastic soil covers affect organic C content, aggregate stability, hydrological properties, and erosion susceptibility? Organic C content and aggregate stability are important soil quality parameters that are easy to measure. Beside these two parameters, soil crusting, infiltration rates, and sediment yields have been determined for a set of irrigated fields that have been abandoned at different times (up to 20 yr) and where plastic covers have been used. The properties of these fields were compared with control sites with comparable periods of abandonment and substrate, but where only classical rain fed cropping systems have been applied. It was expected that leaving plastic remains in the soil after abandonment would be harmful to soil quality and would lower infiltration. The first associations with seeing the plastic are those of garbage and pollution. In fact, most of the indicators of soil quality considered in this survey turned out to be better or the same on the fields where irrigation and plastic covers had been used, when compared with control fields. Organic C contents were up to 40% higher on fields where plastic sheets remain and soil aggregates were more stabile. Fields where plastic had been mixed with the soil by tillage showed lower erosion susceptibilities.