The Interplay Between Bioenergy Grass Production and Water Resources in the United States of America

Food-Energy-Water Nexus in compliance with Sustainable Development Goals for integrating and managing the core environmental verticals for sustainable energy and circular economy

Food, energy, and water resources are intricately interconnected, and nexus provides a holistic approach for addressing these complex links to minimize inefficiencies and waste. Nexus approach and circular economy are considered as effective solutions for sustainability. Quantification of these relations is the first step towards incorporating nexus modeling which helps sustainable production and consumption. For achieving the Sustainable Development Goals, understanding and effectively managing the FEW nexus becomes imperative. With an integral performance perspective, there is a need to address the interdependencies and trade-offs among food, energy, and water systems and challenges of economic, social and environmental sustainability. The aim of this study is to provide a comprehensive analysis of the FEW nexus, identify key opportunities and challenges, and propose integrated strategies for managing these core environmental verticals sustainably. The study addresses the accomplishment of these goals through nexus approaches and outlines the need for technological advancements for shared benefits among resources, contributing to conceptual development of nexus and circular economy. The results highlight the critical importance of adopting a nexus approach to advance sustainable development goals, enhance resource efficiency, and promote synergistic solutions across food, energy, and water systems.

Water impacts of U.S. biofuels: Insights from an assessment combining economic and biophysical models

Biofuels policies induce land use changes (LUC), including cropland expansion and crop switching, and this in turn alters water and soil management practices. Policies differ in the extent and type of land use changes they induce and therefore in their impact on water resources. We quantify and compare the spatially varying water impacts of biofuel crops stemming from LUC induced by two different biofuels policies by coupling a biophysical model with an economic model to simulate the economically viable mix of crops, land uses, and crop management choices under alternative policy scenarios. We assess the outputs of an economic model with a high-resolution crop-water model for major agricultural crops and potential cellulosic feedstocks in the US to analyze the impacts of three alternative policy scenarios on water balances: a counterfactual 'no-biofuels policy' (BAU) scenario, a volumetric mandate (Mandate) scenario, and a clean fuel-intensity standard (CFS) scenario incentivizing fuels based on their carbon intensities. While both biofuel policies incentivize more biofuels than in the counterfactual, they differ in the mix of corn ethanol and advanced biofuels from miscanthus and switchgrass (more corn ethanol in Mandate and more cellulosic biofuels in CFS). The two policies differ in their impact on irrigated acreage, irrigation demand, groundwater use and runoff. Net irrigation requirements increase 0.7% in Mandate and decrease 3.8% in CFS, but in both scenarios increases are concentrated in regions of Kansas and Nebraska that rely upon the Ogallala aquifer for irrigation water. Our study illustrates the importance of accounting for the overall LUC and shifts in agricultural production and management practices in response to policies when assessing the water impacts of biofuels.

Nitrogen Fertilization Elevated Spatial Heterogeneity of Soil Microbial Biomass Carbon and Nitrogen in Switchgrass and Gamagrass Croplands

The effects of intensive nitrogen (N) fertilizations on spatial distributions of soil microbes in bioenergy croplands remain unknown. To quantify N fertilization effect on spatial heterogeneity of soil microbial biomass carbon (MBC) and N (MBN), we sampled top mineral horizon soils (0-15 cm) using a spatially explicit design within two 15-m² plots under three fertilization treatments in two bioenergy croplands in a three-year long fertilization experiment in Middle Tennessee, USA. The three fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha⁻¹ in urea) and high N input (HN: 168 kg N ha⁻¹ in urea). The two crops were switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.). Results showed that N fertilizations little altered central tendencies of microbial variables but relative to LN, HN significantly increased MBC and MBC:MBN (GG only). HN possessed the greatest within-plot variances except for MBN (GG only). Spatial patterns were generally evident under HN and LN plots and much less so under NN plots. Substantially contrasting spatial variations were also identified between croplands (GG > SG) and among variables (MBN, MBC:MBN > MBC). This study demonstrated that spatial heterogeneity is elevated in microbial biomass of fertilized soils likely by uneven fertilizer application in bioenergy crops.