Irrigation from the Sixties: Flumen-Monegros

Abstract

In arid and semiarid areas, agricultural land use is mainly restricted, in the first place, by the availability of water for crop growth. The transformation to irrigation of about 600 000 ha in the Ebro Valley has led to high increases in yield and in diversity of crops. After the Spanish Civil War (1936-39), which was followed by II World War, the Spanish food production system was heavily disrupted and food shortages appeared. This put high pressure on the development of new irrigated schemes which had been planned many years ago. In the Flumen-Monegros area, the technology available in the late fifties was based on flood-irrigation systems, with no previous soil studies, an empirical land evaluation, no control of saltinization risk and, finally, levelling without topsoil preservation. The extension of salinity and/or sodicity-affected soils in the Ebro Valley (IRYDA, 1977) was 200 000 ha, from which 160 000 were located in Aragon, mainly in Bardenas, Cinca and Flumen-Monegros area. But Alberto et al. (1984) reckron this data in 300 000 ha. As a result of these studies, ILACO (1975) designed two experimental drainage plots. Although the existence of salt-affected soils was known, information about the extent, location and general functioning at landscape level of those soils was lacking in the area. Some of the problems related to land use and soil management which are present now in the area or can be expected in the near future are:

- Salinity-Sodicity: Diagnosis, monitoring and rehabilitation of salt-affected soils. - Soil structural degradation and surface crust formation. - Need for improved efficiency in water use: irrigation technology, water reuse, ... - Control of drainage-system degradation: open-air drains as well as underground drains. Several approaches at different scales have been adopted to work on these issues. Satellite images have been used to monitor land use and its temporal variability. Classical soil mapping at 1: 100000 level have been performed; in addition various detailed studies have been undertaken in model areas using the electromagnetic and four electrode sensors, micromorphological techniques, scanning electronic microscopy, and land evaluation procedures. The results have been presented in several papers: about salinity-sodicity trends in the Flumen sector (Herrero, 1987); about parameters related to water behaviour (Aragues, 1986); about soil porosity in plough horizons (Rodriguez-Ochoa, 1998); about translocation of solid materials (Rodriguez-Ochoa, et al. 1989; Porta and Rodriguez-Ochoa, 1991; Rodriguez-Ochoa, 1998); about degradation of underground drainage systems by mineral siltation (Herrero et al. 1989; Rodriguez-Ochoa, et al. 1989; Munoz, 1991; RodriguezOchoa, 1998).

Other studies performed in the area include: Soil-vegetation relationships (Herrero, 1981); laboratory trials with different amendments in the drainage trench infilling material (Porta et al. 1996); dispersive processes because of soil structural instability (Amezketa and Aragues, 1990; Aragues and Amezketa, 1991; Amezketa and Aragues, 1995) and degradation of the hydraulic conductivity of soils (Amezketa and Aragues, 1989; Aragues and Amezketa, 1991; Amezketa and Aragues, 1995). The trip to the Flumen-Monegros area undertakes some of these points, and the stops are located in some of the main soil units. Discussion will be centered on aspects of soil genesis, classification and mapping, land use and soil conservation.