From Global to Local to Global:

Attaining Long Run Sustainability in US Agriculture

Project Summary

The goal of this project is to leverage existing knowledge, models and data to understand and communicate the interplay between global change and local sustainability of US agriculture in the context of alternative national, state and local policies affecting agricultural productivity and environmental quality. In particular, the team will examine the tradeoffs between: 1) crop production, prices and food consumption, 2) nitrogen losses, and 3) groundwater depletion. Special attention will be paid to the role of current policies and institutions in governing these tradeoffs, as well as the impacts of prospective policies targeting land use, nitrogen applications and the allocation of groundwater.

Research Question #1: How do global drivers differentially affect local outcomes due to biophysical, economic and institutional heterogeneity?  Figure 1 provides an overview of the analytical framework to be employed which builds on SIMPLE (a Simplified International Model of agricultural Prices Land use and the Environment (Hertel and Baldos 2016; Baldos and Hertel 2013). The team will use a version which builds in a gridded representation of US agriculture (Figure 1B), informed by outputs from AGRO-IBIS (Kucharik 2003). Their analysis of the local impacts of global drivers of change will begin with projections to 2050 of the global change drivers outlined in Figure 1A, including: growth in population and incomes, investments in productivity-enhancing agricultural research and development, climate change and the demand for bioenergy (Hertel, Baldos, and van der Mensbrugghe 2016). These result in regional changes in crop production, land use and prices in the 15 non-US regions of SIMPLE-on-a-Grid – a model for which global outcomes have been validated over the period 1961-2006 (Baldos and Hertel 2013). For the US, the model will determine changes in crop production and prices, land use, groundwater withdrawals, nitrogen fertilizer applications and leaching -- all at the level of 5 arc minute grid cells (roughly 10 km square). Nitrate leaching as well as crop growth responses to nitrogen fertilization and irrigation, are based on transfer functions obtained from the AGRO-IBIS model (Kucharik and Brye 2003).

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Research Question #2: What are the regional, national and global impacts of local policies to control nitrogen runoff into ground and surface water?   The second research question focuses on local responses to farmers’ efforts to intensify production through increased use of fertilizers. The contribution of nitrogen (N) from the Upper Mississippi River Basin to the hypoxic zone of the Gulf of Mexico is a threat to sustainable cereal production in the US Corn Belt where states are required by the EPA Gulf of Mexico Hypoxia Task Force to develop a Nutrient Loss Reduction Strategy to reduce N and P loading by 45% by 2025 (US EPA 2007). Because of the magnitude of the problem and the costs of making large nutrient load reductions, the target date for reducing the hypoxic zone was recently extended from 2015 to 2035, with an intermediate goal of a 20% reduction in nutrient loads by 2025 (US EPA 2015; McIsaac et al. 2016). In addition to edge-of-field losses to surface waters, gaseous losses of N from fields occur as N2O; a greenhouse gas that is 300-fold more potent than carbon dioxide as a contributor to global warming and climate change.

This research focuses on the trade-off between the environment and food security embodied in the farmers’ choice of how much, when, and how to apply N in crop production. For example, evidence is emerging that alternative management strategies like cover cropping can recover and later release modest amounts of N (40 to 60 kg/ha) to a subsequent maize crop (Mahama et al. 2015). However, while N recovery from fertilizer N is often low and highly variable, release of N from residues is even far more difficult to predict and is influenced by soil texture, residue species and its N concentration, species being planted into the residue, and weather (Pituello et al. 2016). Because of this uncertainty and the risks and economic consequences associated with N-limited yields, producers are likely to over-apply fertilizer N (as “insurance”) even when cover crops are used. Taxation or government regulation of N will be aimed at reducing excessive applications. However, the team expects that the impacts of such regulation will be extremely heterogeneous. Indeed, some producers may benefit due to the ensuing rise in prices – a factor which will adversely affect consumers. Such regulations will also encourage expansion of crop production in other regions – both at the extensive and intensive margins. The team’s analysis will explore these tradeoffs.

Research Question #3: What are the regional, national and global impacts of local policies to restrict excess groundwater withdrawal?   Between 13 and 30% of the global freshwater supply exists as groundwater (Dragoni and Sukhija 2008), including over 95% of liquid freshwater supplies (Sophocleous, 2004). Groundwater is an essential part of the global water supply, often supplementing surface water supplies, especially in water-scarce areas, and providing a substantial portion of the water used for agricultural irrigation worldwide (Green et al. 2011; Reeves 2010; Alley 2001; Döll et al. 2012). Groundwater reserves have traditionally provided a buffer for cities and farms against drought, yet increasing withdrawals in many of the nation’s most important aquifers reduce the capacity of these underground stores to buffer water systems from continued scarcity. This is best exemplified in the Ogallala Aquifer in the central US and the San Joaquin aquifer in the central valley of California where groundwater depletion is occurring because of the annual abstraction of groundwater in excess of annual recharge (Wada et al. 2010), demonstrating the consequences of insufficient planning and the lack of scientifically-based policies in water management that reflect real-life decision-making: land subsidence, increased pumping costs, land degradation from irrigation overuse on high value specialty crops (Scanlon et al. 2012; Konikow, 2013).

The situation is further complicated by the fact that, in many cases, boundaries of groundwater aquifers do not correspond to those of watersheds, while well permits and withdrawal rates are tracked at the county level. The boundaries of land ownership may span any of these boundaries. Water law also provides a spatially variable set of conditions. The US, for example, has five different governing doctrines of groundwater law that vary by state (Dellapenna 2013). The third research question will focus on the consequences of alternative policies aimed at limiting unsustainable groundwater abstraction. These will include: outright bans on groundwater withdrawal in selected regions, quantitative regulation of withdrawals, taxation of groundwater pumping, and institutional reforms whereby the governing doctrine of groundwater law is altered in an attempt to achieve a more efficient allocation of this scarce resource. As with restrictions on fertilizer applications, the team will focus on the tradeoffs between local and global environment quality, and between food and environmental security.


Thomas Hertel
Distinguished Professor of Agricultural Economics
Laura Bowling
Professor of Agronomy
Sylvie Brouder
Professor of Agronomy
Nicole Kong
Assistant Professor of Library Science, GIS Specialist
Manjana Milkoreit
Assistant Professor of Political Science
Carol Song
Senior Research Scientist, Director of Scientific Solutions, Rosen Center for Advanced Computer (Research Computing), ITaP
Jeffrey Volenec
Professor of Agronomy

Principal Investigator Bio:

Thomas Hertel Distinguished Professor of Agrucultural Economics at Purdue University

Professor Hertel is Distinguished Professor of Agricultural Economics at Purdue University, where his research focuses on the global impacts of trade, climate and environmental policies. In 2013 he was awarded the inaugural Purdue University Research and Scholarship Distinction Award.

Dr. Hertel is a Fellow, and Past-President, of the Agricultural and Applied Economics Association (AAEA). He is also the founder and Executive Director of the Global Trade Analysis Project (GTAP) which now encompasses more than 15,000 researchers in 170 countries around the world). This Project maintains a global economic data base and an applied general equilibrium modeling framework which are documented in the book: Global Trade Analysis: Modeling and Applications, edited by Dr. Hertel, and published by Cambridge University Press in 1997. This book was selected as the publication of enduring quality by the AAEA in 2016.

At Purdue (from August 2008), he has developed autonomous navigation using natural fields for indoor, pedestrian, and UAV navigation. A sun sensor for compassing and a more sophisticated sun sensor for geolocation have been developed in his lab. His group has developed scalable methods for multi-UAV autonomous operations for specific surveillance tasks. He leads the Purdue portion of the AFRL’s Adaptive G&C ISHM Integration Requirements study.

Professor Hertel's recent research has focused on the impacts of climate change and mitigation policies on global trade, land use and poverty. During the 2011-12 year he was on leave at Stanford University, where he was engaged in inter-disciplinary research on these topics, along with initiation of a new course on Global Change and the Challenges of Sustainably Feeding a Growing Planet, which is now a permanent course offering at Purdue.