Environmental Benefits of Improved Water and Nitrogen Management in Irrigated Sugar Cane: A Combined Crop Modelling and Life Cycle Assessment Approach

Abstract

The application of irrigation water and nitrogen (N) fertilizer in excess of crop demand reduces profitability and has multiple detrimental impacts on the environment. N dynamics in agroecosystems are extremely complex, and mechanistic crop models are most often required to quantify the impact of improved management practices on reducing fertilizer N losses. In this study, Life Cycle Assessment (LCA) methodology and mechanistic modelling was used to quantify the environmental benefits of improved management of water and fertilizer N by sugarcane farmers in a case study in Pongola, South Africa. A baseline scenario, representing farmer intuition-based irrigation scheduling management, and two additional scenarios in which water, and water and N were more rationally managed, were compared. Results show that improved water and N management can lead to a 20% reduction in non-renewable energy consumption per functional unit (FU), with sustained or even increased yields. Total GHG emissions can potentially be reduced by 25% through more efficient water and N management.Limiting the rates of fertilizer N applied, made possible by decreasing N leaching through improved irrigation scheduling, resulted in the highest reductions for both impact categories.While total water consumption was very similar between the scenarios, more efficient use of † Bénéfices environnementaux de la gestion raisonnée de l'eau et de l'azote en canne à sucre irriguée :Approche combinée de modélisation de la culture et d'analyse du cycle de vie à Pongola, Afrique du Sud  Correspondence to: M. van der Laan,

Impact of agricultural practices on energy use and greenhouse gas emissions for South African sugarcane production

“…Both studies show irrigation and fertilizer production as the two largest contributors to energy input, but we show a 50% greater impact from irrigation. In both studies, diesel fuel was noted as the third greatest energy contributor but the earlier study reported 30% lower diesel use, contributing to the lower overall energy input (van der Laan et al, 2015). Renouf et al (2010) reported GHG emissions of sugarcane production in Australia to be between 50 and 100 kg CO2-e/t cane for several growing regions.…”

Irrigation and the Environmental Tragedy: Pathways Towards Sustainability in Agricultural Water Use

“…LCA is increasingly used in the irrigation sector. Recent works have explored pathways to improved, less impacting water use and N fertilization in sugar cane production (Van der Laan et al, ), investigated trade‐offs between energy and water use in tomato production (Payen et al, ), defined water and soil salinization as a new impact category (Payen et al, ), combined LCA with economic analysis to explore the eco‐efficiency of cotton in Pakistan (Ullah et al, ) and of paddy rice in Thailand (Thanawong et al, ), and compared the environmental impacts of different groundwater pumping systems (Pradeleix et al, ). Overall, these research works demonstrated that optimizing the use of chemicals and addressing the issue of non‐point‐source pollution in irrigation have benefited a great deal from LCA applications.…”

Towards ecologically sustainable crop production: A South African perspective

“…If the complete life cycle of agricultural products is considered, agriculture"s footprint rises to 26-36% of the global anthropogenic footprint (Barker, 2007 Emissions associated with fertiliser production, storage and transport accounted for 41% of total CO 2 equivalent emissions. The generation of electricity for irrigation of sugarcane was estimated to contribute approximately 25% of CO 2 equivalent emissions (van der Laan et al, 2015). The simulations of van der Laan et al (2015) also demonstrated that more judicious use of water and N fertiliser in irrigated sugarcane could reduce GHG emissions by 25% and non-renewable energy consumption by 20%, while achieving equal or even slightly higher yields.…”

“…The generation of electricity for irrigation of sugarcane was estimated to contribute approximately 25% of CO 2 equivalent emissions (van der Laan et al, 2015). The simulations of van der Laan et al (2015) also demonstrated that more judicious use of water and N fertiliser in irrigated sugarcane could reduce GHG emissions by 25% and non-renewable energy consumption by 20%, while achieving equal or even slightly higher yields.…”