Modelling the economic tradeoffs between allocating water for crop production or leaching for salinity management

Abstract

Salinisation threatens the sustainability of irrigation agriculture and needs to be managed through leaching practices. Under conditions of water scarcity a tradeoff exists between allocating water for salinity management and production. Currently no model in South Africa is able to model explicitly the impact of salinity management through leaching on the economic efficiency of irrigation farming, taking the opportunity cost of water under limited water supply conditions into consideration. The main objective of this paper is to develop a robust non-linear optimisation model that is able to determine endogenously the impact of declining irrigation water quality on the economic efficiency of irrigation farming. A data envelopment framework was used to integrate recently developed soil water salinity crop-yield production functions and leaching functions to model the complex interactions involved in water allocation decisions. Results showed that it is profitable to reduce the area irrigated under limited water supply conditions in order to release water for leaching purposes. When more water, but still a limited amount of water, is allocated to the farmer, his willingness to pay for water will increase if irrigation water deteriorates. Thus, the conclusion is that leaching is profitable irrespective of the water supply conditions.

An Assessment of Irrigation Water Quality and Selected Soil Parameters at Mutema Irrigation Scheme, Zimbabwe

“…There is need for development and implementation of agronomic and water management strategies in the scheme to ensure sustainable crop production. The use of surface water to complement the groundwater source should be considered where it can be used as a dilution or a pre-planting flushing of salts to beyond the root zone [5,20,48,49]. Thus, integration of the surface and groundwater sources could help reduce the problem of salinity in the scheme.…”

“…The main cause of salinization and sodification is the use of poor quality irrigation water and continued use of this water leads inexorably to increasing salinization and sodification problems and ultimately results in increased cost of production and crop failures [14,[17][18][19][20]. Salinization is especially serious where groundwater is used for irrigation with the problem being coupled by conversion from natural deep rooted trees and shrubs to commercial shallow-rooted crops that cause the water table to rise and bring more salts with it to the upper layers [8,21].…”

A Review of Soil-Improving Cropping Systems for Soil Salinization

“…Under limited water supply of suboptimal quality, the farmer has to compromise between allocating all irrigation water to plant the maximum area possible without applying a leaching fraction, thus assuming some reduction in crop yield per unit area or alternatively reducing the cultivation area but allocating some water for leaching, thus eventually increasing crop yield per unit area [52]. Modeling suggests that leaching of the excess salt from the soil once salinity levels exceed the crop's salinity threshold is more profitable [52].…”

“…English et al [76] argued that in light of the limited water availability and dubious quality, economically efficient irrigation will develop into the new paradigm of irrigation management. Matthews et al [52] explained how farmers' willingness to pay more for water increases as water availability and quality decrease. They also suggest that under limited supply of irrigation water, it is more profitable to reduce cultivation area in order to allocate enough water for leaching.…”

Designing the Path for Soil Salinity Management: Lessons Learned and Future Perspectives in Morocco

“…Table 1 provides a non-exhaustive list of selected examples from genetic improvement for salt-tolerance, agronomic practices and irrigation management. Under water scarcity conditions, a trade-off exists between allocating water for salinity management and production [5]. Thus, leaching practices are not relevant option in arid and semi-arid areas.…”