Performing Department
(N/A)
Non Technical Summary
California's San Joaquin Valley--a major agricultural region--faces transformative change. Local agencies are advancing actions to achieve groundwater sustainability, but this could result in at least 500,000 acres of cropland losing reliable access to irrigation. Our prior research shows that water-limited systems (dryland crops, especially with small amounts of supplemental irrigation to aid establishment) hold promise for stewarding lands facing irrigation cutbacks. These systems could provide a high-value use of water and a cost-effective way to manage hydrologic risk and reduce soil erosion and dust-related externalities of land fallowing. But many knowledge gaps remain.This interdisciplinary project will support data-informed land use decisions to manage water demand. Three inter-related activities will address knowledge gaps: 1) trialing and fine-tuning water-limited crops and management systems, 2) quantifying the implications of these systems for local water balances, and 3) advancing appropriate valuation of co-benefits of these systems relative to fallow, including dust mitigation in low-income rural communities. The broad aim is to generate agronomic, hydrological, and economic insights on the system-level benefits and tradeoffs at play in transitioning to water-limited cropping systems. This work will help land-use planners, resource managers, and public agencies at all levels understand where cropping system transitions may deliver net benefits for a broad set of stakeholders while also tracking and minimizing potential harm to vulnerable populations. Our focus is on the San Joaquin Valley, but the research is relevant for a much broader region of the western U.S. facing growing water scarcity in a changing climate.
Animal Health Component
0%
Research Effort Categories
Basic
0%
Applied
80%
Developmental
20%
Goals / Objectives
The long-term goal of this research is to ensure that land use and groundwater sustainability planning and implementation in the San Joaquin Valley are informed by targeted data and careful analysis. The San Joaquin Valley is in the midst of a major transformative moment, and there are likely to be winners and losers from changes in the use of scarce natural resources. Our goal is for this research to inform pathways towards more sustainable water use that maximize net benefits for a broad set of stakeholders while also tracking and minimizing potential harm to vulnerable populations. And while our focus is on one major farming region, we expect that the research will inform water and land management efforts across the American West, which is grappling with similar challenges of groundwater sustainability and water scarcity in a changing climate.Our research focuses on three interrelated scientific objectives:1. Pilot water-limited crop varieties and management approaches to better understand suitability and agronomic potential of water-limited crop substitution across the San Joaquin Valley.We will conduct controlled field trials to evaluate the genetic and management components of successful water-limited crop production at key sites. The activities under this objective will bolster empirical datasets for verification of novel dryland crop model parameterizations, as well as provide practical, extension-oriented advice and recommendations to growers and land managers implementing these systems.2.Develop a more nuanced understanding of net water balances for water-limited crops and other alternatives to fallowing on lands slated for groundwater demand reduction. This objective will generate data and approaches of direct relevance to land managers and planners as they devise and implement groundwater demand reduction programs.3. Assess the value of the potential benefits of water-limited cropping systems relative to fallow land across market and non-market dimensions. In addition to crop revenues, water-limited cropping and other alternatives to fallow may create benefits not only for water conservation, but also for soil health, air pollution mitigation, and other areas. However, primary valuation studies on relevant willingness to pay for these benefits are scarce. Better understanding the economic value of these benefits will help to inform public programs to incentivize improved land stewardship in response to the large-scale land transitions needed to manage growing water scarcity.
Project Methods
Objective 1 methods:Multi-year field trials will examine crop genotypes and management innovations that maximize crop performance under water-limited conditions.The trials will test 12 crop genotypes, including 3-4 varieties each of wheat, triticale, and barley, under fully irrigated and water-limited conditions. Genotype treatments will be crossed with early and late planting dates, with and without the addition of irrigation at sowing.We will implement a "mother and baby" trial design, with the full complement of treatments implemented at the UC West Side Research and Education Center (WSREC) near Five Points, CA, and a subset of treatments at the University Agricultural Laboratory at California State University, Fresno. Measurements to be collected at each site will include pre- and post-harvest soil water content, timing of key phenological stages (e.g., emergence, tillering, boot, flowering, maturity), and forage and grain yields for each genotype x irrigation x planting date combination, along with a fallow treatment. Soil cores collected at these trials will also contribute to objective 2, where they will be used to develop soil water retention curves for the purposes of parameterizing soil hydrological balance models. We will consider differences in representative soil types across trial plot locations--with clay loams at Five Points, and sandy loam at Fresno State. These differences may be relevant both for the assessment of water-limited crop establishment and yield performance and for the soil hydrological modeling under Objective 2.Objective 2 methods:We will leverage methods to estimate both above- and below-ground elements of net water balance in water-limited crops relative to fallow land.For the above-ground component, we will partner with OpenET to quantify consumptive water use across crop categories for reference sites (including the field trial sites described above) using the latest available land use classifications for the San Joaquin Valley. Land use classifications will be ground-truthed where necessary to improve confidence in comparative estimates of water balance between fallow and water-limited cropping alternatives. Additional exploratory work may expand this analysis to include consumptive water use from active habitat restoration areas and other non-irrigated land use alternatives to fallow, such as rangelands.For the below-ground component, we will use soil hydrological modeling to better estimate potential water returns to the system, considering consumptive use and water transport through the soil profile. Modeling will include testing of varying soil types, as soil hydraulic parameters mediate the balance between evaporation, transpiration, infiltration, and percolation. HYDRUS, a water flow and solute transport model, will be used to develop estimates for these elements of annual soil water balance at the reference sites mentioned above. As with the OpenET analysis, treatments to compare will include fallow, water-limited and fully irrigated winter crops across contrasting soil types. The Soil Survey Geographic Database (SSURGO) will be used to develop initial parameterizations of soil hydraulic parameters. Where needed, parameter specification will be fine-tuned with data from intact soil cores assessed for soil water retention and development of the van Genuchten soil hydraulic parameters that govern water flow. Management data will be gathered as inputs to the time-variable boundary conditions including: amounts and timing of irrigation and amounts of precipitation and fertilizer. Model outputs will be evaluated against yields and soil moisture from measurements taken in Objective 1.Objective 3 methods:The valuation exercise will consider three main benefit margins: dust mitigation, potential water use savings, and carbon sequestration. Quantification of net differences in these outcomes will be based on novel empirical estimation by the research team, inputs from other project objectives (for example, net water use estimation from Objective 2), and existing estimates from the literature. Valuation of these differences will rely on established benefit transfer techniques, market information (where applicable), and estimates of the social cost of carbon.Reductions in dust emissions on lands with established vegetative cover, relative to fallow, will be estimated based on an extension of Ayres et al. (2022). In this project, we will increase the spatial resolution of the observational units used in the estimation and test the robustness of the results to alternative methods for determining land cover types. Valuation of reduced particulate matter concentrations will proceed according to benefit-transfer of comprehensive willingness-to-pay estimates from Singh et al. (2018); an alternative estimate based on health damages from prevailing estimates of the value of a statistical life will also be produced (see for example Jones and Fleck 2020).Differences in water use on water-limited versus fallow parcels can impact future water availability in two ways: increased (or decreased) groundwater percolation and accumulation, and increased (decreased) soil water retention. Altered groundwater accumulation that results from adoption of water-limited systems will be valued as a shift in stored water according to the marginal value product generated by its use in a similar cropping system, as derived from the agronomic models improved as part of Objective 1. Valuation of net soil water retention, similarly, will be based on the profitability difference incurred in subsequent periods of agricultural production; production relationships (including those regarding establishment probabilities) from Objective 1 will inform a net profitability calculation for subsequent water-limited cropping relative to a fallow scenario that retains a different level of soil water.Previous work has identified important controls on the likely soil carbon sequestration potential of water-limited cropping systems relative to tilled fallow. Building on this understanding, we will construct a range of estimates for sequestered soil carbon relative to a baseline tilled fallow system and apply estimates of the social cost of carbon to monetize these spillover benefits. In particular, we will bound these benefits by drawing estimates of the marginal value of emissions from California's Cap-and-Trade auction results and more comprehensive estimates of the global value of avoided emissions from the environmental economics literature, as summarized by Ayres (2021).The profitability analysis will investigate profitability and break-even thresholds of water-limited cropping systems based on on-farm (private) revenues and non-market benefits streams. This analysis will draw on updated and improved agronomic modeling tools developed as part of Objective 1, as well as the valuation exercise's assessment of the three potential spillover, or non-market benefits described above (dust mitigation, water use savings, carbon sequestration).