Abstract. Using the simulation model MACRO, this paper investigates the likely consequences of reduced irrigation inputs on the water and salt balance and crop growth in a drained, saline clay in a Mediterranean climate (Marismas, SW Spain). The model was first successfully validated against field measurements of the soil water and chloride balance, water table depths and drain outflows in the 1989 growing season. Three-year simulations were then performed assuming two different irrigation applications (60 and 75% reductions from the 1989 amount) and two different frequencies (12 or 6 irrigations per growing season). The model predictions suggested that reduced irrigation may lead to up to a 15%) increase in the chloride content of the soil profile after 3 years. Also, despite overall reductions in water discharge, slight increases in chloride leaching via field drains ( c. 4 to 8%) were predicted. The model demonstrated that encroachment of salt into the soil profile may he exacerbated by the non-equilibrium nature of water flow and solute transport ('by-passing flow') in structured clays. With reduced water supply for irrigation, more frequent applications may give marginally better crop yields for the same quantity of irrigation but at the expense of slightly increasing salt concentration in the root zone. 相似文献
In hummocky morainal landscapes, soil distribution in well-drained landscape positions tends to follow a consistent pattern. Soils in depressions, however, are more difficult to predict reliably. This study had two objectives: (1) to determine the parent material and landscape properties controlling the formation of the different depressional soils; and (2) to use these controls to identify quantitative, terrain-based predictors of soil type in depressions. Only two terrain attributes, specific dispersal area (SDA) and elevation relative to open water bodies, were required to distinguish three main soil groups: Gley Recharge, Non-gley Recharge, and Discharge soils.
Specific dispersal area is the downslope area draining flow from a given grid cell. Gley Recharge soils occur primarily at points with SDA of less than 2 m2 m−1, regardless of elevation within a given site, because most of the runoff flowing to a point with very low SDA values will pond or infiltrate vertically rather than flow downslope. Non-gley Recharge soils and Discharge soils both occur at points with SDA of greater than 2 m2 m−1. The majority of the Non-gley Recharge soils occur above 5-m elevation relative to an open water body and the majority of the Discharge soils occur below 5-m elevation relative to an open water body, reflecting the importance of solute cycling in the development of discharge conditions. Buried and depositional soils could not be predicted from current terrain attributes because their profile characteristics were derived from the paleosurface. 相似文献