Allocating marginal water sources to irrigation: effects on soil hydroecological functioning

Abstract:

The challenge of meeting the projected doubling of global demand for food by 2050 is monumental. It is further exacerbated by the limited prospects for land expansion and rapidly dwindling water resources. A promising strategy for increasing crop yields per unit land requires the expansion of irrigated agriculture and the harnessing of water sources previously considered ‘‘marginal’’ (saline, treated effluent, and desalinated water). Such an expansion, however, must carefully consider potential long-term risks on soil hydroecological functioning. It seems that long-term use of treated wastewater (TW) for irrigation of orchards planted on heavy soils cause to yield reduction and crop damages. In terms of water quality, TW are characterized by higher concentrations of sodium and dissolved organic content that affect both soil exchangeable sodium percentage and soil wettability. The long-term use of TW for irrigation of clayey soils causes significant changes in the soil hydraulic properties that might affect the water and air regime in the root zone. These might affect the chemical and biological conditions in the root zone, affecting plant nutrition, root development and microbial activity. The emerging availability of desalinated water (DS) for irrigation, on the other hand, expands management options and improves yields while reducing irrigation amounts and salt leaching below the root zone towards groundwater. Therefore, the primary challenges to the sustainability of agroecosystems when marginal water sources are allocated to irrigation lies with the hazards of saline and sodic conditions, and the unintended consequences on soil hydroecological functioning. Multidisciplinary approaches that combine new scientific knowhow with legislative, economic, and societal tools are required to ensure safe and sustainable use of water resources of different qualities. New scientific knowhow integrating key biophysical processes with ecological interactions at appropriate spatial and temporal scales should be developed.