Trade-Offs between Economic Benefits, GHG Emissions, and Nitrate, Phosphate, and Salinity Balances in Agricultural Land and Water Management

Abstract

Agricultural land, water, and fertilizer utilization significantly impact the nutrient and water balances and greenhouse gas (GHG) emissions. This study explores the impacts of agricultural water, land, and fertilizer management on the trade-offs between economic benefit, GHG emissions, and water, salinity, nitrate, and phosphate balances by employing crop growth, flow, and solute simulation models, linked with an optimization algorithm. The coupled models can simulate flow, crop growth, and nutrient transport, and capture the water and solutes interaction between the farmland soil zone and saturated groundwater zone, while considering spatial heterogeneity of soil, crop, fertilizer, and irrigation. The optimization model was used to find the trade-offs between the conflicting objectives of maximizing the net economic benefit and minimizing GHG emissions. The optimal water and land allocation schemes, fertilizer application, and crop type were obtained under wet, normal, and dry hydrological years. Then a simple rule was introduced based on the optimum results of the wet, normal and dry years. The proposed methodology was applied to the Dashteabbas irrigation network in southwest Iran. The results showed that the mass loading of salt, nitrate and phosphate decreases to water bodies by 7%, 37%, and 37%, respectively, and less land (−19%), water (−16%), and fertilizer (−35%) are exploited. Also, despite the lower net benefit of the optimum solution (12% lower than the current situation), the GHG emissions (28% lower than the current situation) would decrease, indicating that the introduced rule can help decision-makers to promote coordinated economic and environmental development in the agricultural irrigation systems.