Increasing Implementation of Conservation Practices to Protect Groundwater Quality

Increasing Implementation of Conservation Practices to Protect Groundwater Quality (Increasing Implementation) is an innovative, collaborative project led by the Southern San Joaquin Valley (SSJV) Management Practices Evaluation Program (or MPEP) Committee to increase implementation of practices that protect groundwater from pollution by nitrate in fertilizers applied to irrigated lands in the SSJV and beyond.

The MPEP was devised to complement other components of the Region 5 (Central Valley) Water Quality Control Board’s Irrigated Lands Regulatory Program general orders. This facet of the orders, along with the Groundwater Quality Management Plans, contains most of the actions to actually protect water quality, along with the most rigorous performance demonstrations. The MPEP moves beyond simple metrics that might indicate a problem to identifying solutions.

Seven coalitions, representing more than 7,100 growers farming approximately 1.85 million acres of irrigated land south of Fresno, formed the SSJV MPEP Committee to implement the MPEP. Their MPEP Workplan has been developed with extensive input from State and Central Valley Water Board staffs and with technical partners at United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), University of California (UC), California Department of Food and Agriculture (CDFA), and California State University (CSU). The Committee and technical team have also reached out to other irrigated lands coalitions and the dairy industry to exchange ideas and promote consistent approaches. The Central Valley Water Board conditionally approved the workplan in May 2017.

The Increasing Implementation Project helps to support implementation of the MPEP through its first three years.


The Increasing Implementation Project was awarded $2 million over three years by the United States Department of Agriculture Natural Resources Conservation Service Conservation Innovative Grant program. This award is matched with with member, partner, and collaborator contributions exceeding $2 million. In addition, the Committee funds other MPEP activities, either directly or (when available) with the assistance of outside funding.


Launched in late 2016, the Increasing Implementation Project has five main objectives:

1) Identify protective practices for Central Valley agriculture
2) Adapt the USDA’s Soil and Water Assessment Tool (SWAT) for Central Valley agriculture
3) Increase adoption of protective practices through intensive producer/advisor outreach and an online decision support tool
4) Assess adoption of protective practices by comparing a 2016 benchmark assessment with practices implemented throughout the project duration
5) Quantify the reductions in nitrate leaching at the landscape-level using SWAT.

Methods employed and practices will be readily available to similar water quality coalitions throughout California and beyond, and can be configured and tailored to meet distinct regional needs.

The SSJV MPEP Committee is partnering with NRCS, CDFA, UC, and CSU to implement the project, which mirrors the MPEP implementation model to protect groundwater quality.

This project is innovative because: 1) it is broad-based and producer-led, 2) it encompasses a broad range of technical partnerships and collaborators, 2) it adapts a proven tool (i.e., SWAT) to simulate agricultural nitrate leaching in the Central Valley; and 3) it is unprecedented in its potential to reduce nitrate leaching from irrigated lands toward groundwater.


This producer-led project leverages technical partners and a large community of collaborators to develop an innovative toolbox to help protect groundwater quality from nitrate due to fertilizers applied to irrigated crops in California. To support this effort, the Committee has contracted with a team of agronomists, horticulturalists, plant nutritionists, soil scientists (specialists in soil management, fertility, physics, chemistry, and modeling), and hydrogeologists.

This is a 3-year project and is organized into the following four technical tasks. A project timeline follows the discussion of the tasks.


• Task 1. Research and Producer Outreach with Technical Partners
• Task 2. SWAT Model Refinement and Landscape-Level Performance Assessment
• Task 3. Targeted Outreach and Training for Producers and Advisors in the SSJV
• Task 4. Management Practice Implementation

Task 1. Research and Producer Outreach with Technical Partners

This task supports Objectives 1 and 2, and includes initial evaluation of management practices, with a focus on identifying known protective practices to address the largest potential nitrate sources. Substantial work has been done on careful management of nitrogen and the irrigation water that may carry it beyond the root zone before it can be consumed by the plant. A good deal of this information can be readily recovered in the scientific and extension literature, as well as from knowledgeable scientists, producers, and producer-advisors. This task will focus on matching this knowledge to applicable field situations, and extending it to producers through early outreach.

Where existing knowledge needs to be supplemented, investigation priorities will be identified, planned, and implemented. We anticipate multiple priorities, which likely will include the following:

In addition, research activities have included development of yield-to-nitrogen-removed (Y-to-R) conversions for the majority of crops in the Central Valley. The Y-to-R conversions can be incorporated into NRCS practice standard 590, Nutrient Management. The ratio of applied nitrogen to removed nitrogen is a key performance metric to be shared with producers and to help guide them in evaluating nitrogen management, and in planning for efficient use of nitrogen.

Task 2. SWAT Model Refinement and Calibration and MaPP Decision Support Tool

This task supports Objectives 1, 2, 4, and 5 and includes SWAT model refinement and calibration, and development of the Management Practice Performance (MaPP) decision support tool. Model runs will evaluate alternative suites of management practices and quantify their effect on nitrate leaching, salts, and water balance in the Central Valley. Model features will include, but are not limited to, the following:

  1. Expanding the spatial domain of existing SWAT runs to model to the Central Valley, covering approximately 6.2 million irrigated acres.
  2. Updating the soil inputs to reflect more detailed mapping.
  3. Calibrating the crop models to reflect Central Valley cropping systems1 (e.g., yield, evapotranspiration, nitrogen budget).
  4. Updating the crop layers and suites of management practices to reflect the contemporary Central Valley, as well as potential future conditions.
  5. Refining irrigation water quality inputs to reflect applied surface/groundwater proportions, as well as salinity and nitrate concentrations.
  6. Developing a salinity sub-model, which is not currently operational in SWAT.
  7. Validating model results with existing data sets and field data, as necessary.

SWAT will be continually refined in an iterative process throughout the project, based on research and outreach activities.

This task also includes a landscape-level assessment of management practice performance (i.e., reduction in nitrate leaching) in the SSJV.

SWAT runs will be structured to assess a range of management approaches for each crop, over the entire extent of the Central Valley where this crop is grown. In this way, the performance of these alternative approaches can be rigorously, yet very efficiently assessed in a modeling environment. It is fair to say that such an assessment could never be performed without the aid of such a model, since field testing at this scale and intensity would be an immense and impractical effort, far outstripping the scale of all current agricultural research put together. Yet, the power of the analysis to inform grower decisions is great. The process can be summarized as follows:

  1. Develop suites of practices that represent the actual range of management approaches for each crop to be assessed. This must be done with knowledgeable experts and growers to ensure that a realistic range of cropping systems are accurately described.
  2. Partner with UC Davis pedologists who are working in conjunction with NRCS to use soil survey data to attribute Hydrus (an extremely rigorous soil physical modeling platform) to assess the innate, relative degree of risk of nitrate leaching for each California mapping unit.
  3. Multiple SWAT runs, each comprising one management approach per crop.
  4. Array SWAT model output (say, the rate of N leaching from root zones of each crop in each run), comparing results across the range of innate risk associated with mapping units. Make these results available in an easy-to-use, MaPP decision support tool, so that growers and grower advisors can use results to inform planning decisions.
  5. Review results relative to specific locations, and evaluate which management approaches would be expected to perform acceptably, with respect to reasonably minimizing the rate of unwanted nitrate loss from the root zone.

Growers can enter this process at Step 5, with the help of the MaPP decision support tool, to investigate the potential environmental performance of their actual, and many alternative management approaches, all without any site-specific field experimentation. While some approaches may be precluded by operational considerations (e.g., infrastructure, equipment, available labor or knowhow), there will be several options, increasing the likelihood that one or more will be usable, should the existing management approach need to be altered.

A conceptual graphic showing the data array described in Step 4, which is central to the MaPP decision support process, is shown in Figure 1.

Relative N Hazard Table
FIGURE 1. Conceptual illustration of N leaching response to relative N risk class for two suites of management practices for a crop class or group of crop classes. The performance metric shown on the vertical axis is N leaching rate, but other metrics could also be employed. The relative risk is a ranking of soil mapping units, based on their innate tendency to transmit nitrate through their root zones as determined by multiple hydrus model runs. This provides a convenient and meaningful set of classes across which to array performance results for multiple suites of management (management approaches). Only two suites (arbitrarily called Suite 2 and Suite 5) are shown in this example. The two suites perform acceptably over different ranges of innate risk, and thus have different geographic ranges of applicability. In this way site-specific soil conditions, management, and environmental outcomes can be viewed in a format that allows growers and grower advisors to assess their own operations, and consider management alternatives with some indication of how each will affect performance in each block.

Task 3. Target Outreach and Training for Producers and Advisors

In addition to outreach/training to occur as a part of technical partner projects (Task 1), the Project includes concurrent, targeted outreach to producers in the SSJV about protective practices and relevant resources. This supports Objective 3 and will focus on informing producers and producer-advisors about protective practices, with the aim of fast-tracking implementation.

Outreach and training activities will provide the following types of information:

Task 4. Management Practice Implementation

This task supports Objective 4 and includes implementation of protective practices throughout the SSJV. A number of improved management options (e.g., irrigation scheduling, system control and operation, and timely application of appropriate rates of nitrogen) have potential to increase nitrogen fertilizer efficiency and reduce the amount of residual soil nitrate at risk of leaching beyond the root zone.


The following timeline presents the schedule for the Increasing Implementation Project.

For More Information

For more information about the Increasing Implementation Project, contact the following project leaders:

Ms. Charlotte Gallock
Coordinator, SSJV MPEP Committee
Kings River Water Quality Coalition

Dr. John Dickey
Technical Program Manager

1SWAT includes a land cover/plant species database to simulate the growth of 120 crop types. Some California cropping systems are unique and extremely productive, and crop models developed in other locals do not have the productivity range to accurately represent these systems. In these cases, existing crop models will need to be modified to better reflect the high intensity, high-yield cropping systems implemented in the California Central Valley.