Reducing nitrate water pollution and irrigation water consumption at the river basin scale through the optimized allocation of a low-input perennial bioenergy crop within the existing cropping systems

The Pinios River Basin in Thessaly, Greece, is the country's most important agricultural region. However, intensive farming practices have led to the degradation of both surface water and groundwater quantity and quality. To address these issues within an energy vulnerable environment, the adoption of bioenergy crops into existing cropping systems offers a promising practice, combining environmental benefits at a river basin scale with the potential of producing renewable energy. The current study investigates switchgrass, a low-input, resource-efficient energy crop, as an ideal candidate for sustainable implementation in the irrigated cropland. Given the unavoidable conflicts with food, feed, and fiber production, a full examination of the environmental and economic implications is needed for its large-scale installation. The Soil and Water Assessment Tool (SWAT) was first used to develop a representative model of the Pinios River Basin and evaluate its current hydrological and nitrate (N-NO ₃ ) water pollution. A multi-objective Genetic Algorithm embedded in MATLAB was linked to SWAT and an economic component and after a large number of simulations, it identified optimum spatial allocations of the bioenergy crop in the agricultural land, with respect to the net farmers' income, biomass production and water quality and quantity. The analysis of the resulting trade-off curves demonstrated highly encouraging outcomes, with the most conservative solution achieving a 5% reduction in N-NO ₃ loads and a 5.6% reduction in irrigation water consumption across the entire basin. Furthermore, under this spatial allocation scheme, 0.44x10 ⁶ tons of biomass were produced from the bioenergy crop, while maintaining the total net agricultural income at the business as usual levels.