To contact the SSJV MPEP Committee, send an email to outreach@formationenv.com.


What is the MPEP?

The Management Practices Evaluation Program, or MPEP, is a required component of the Central Valley Regional Water Quality Control Board Irrigated Lands Regulatory Program. The MPEP will evaluate and demonstrate which agricultural management practices are effective in protecting water quality, and how these practices have been or will be implemented to minimize nitrate leaching to groundwater. A Workplan describing activities to be completed as a part of the MPEP received Conditional Approval from the Central Valley Regional Water Quality Control Board in May 2017.

Why is the MPEP important?

The Central Valley Regional Water Quality Control Board is obligated by law to develop and issue permits (referred to as Waste Discharge Requirements) to potential sources of water pollution, to protect specified uses of those waters (including drinking water and irrigation of crops). The MPEP is one of several required actions in the permits issued to Central Valley irrigators. The penalties for failing to comply with these permits vary, but they include large fines and/or orders to cease operations.

On the positive side, the MPEP is the part of the permit that allows growers to demonstrate that they are protecting water quality as part of their operations, and (as a possible result) to avoid more cumbersome requirements that could be imposed to curb ongoing, unabated pollution. This type of demonstration is the main goal of the MPEP, and should limit the long-term costs to comply with these permits.

The implementation of MPEP is in the hands of Irrigated Lands Regulatory Program (ILRP) coalitions run by growers, which distinguishes the ILRP’s regulatory approach from similar regulatory programs elsewhere and from other environmental regulations where regulators may prescribe practices.  MPEP is a grower initiative to develop practice recommendations and implementation in response to regulatory orders to protect groundwater quality.

Is the MPEP just about nitrate leaching into groundwater? If so, how do we know that is a real problem?

The current focus is on minimizing nitrate leaching, but the overall Irrigated Lands Regulatory Program (ILRP) also pertains to other constituents that could be construed as pollutants (e.g., sediment in runoff, pesticides, and salts). If at some point other constituents need to be addressed by growers, the MPEP would likely serve the same functions for those constituents.

The SWRCB SBX2 1 Report to the Legislature (http://groundwaternitrate.ucdavis.edu/) was one of several lines of evidence that supported the expansion of the ILRP to limit losses of applied nitrogen into underlying groundwater.

What geographic areas are involved?

The Southern San Joaquin Valley MPEP includes areas within the Buena Vista Coalition, Cawelo Water District Coalition, Kaweah Basin Water Quality Association, Kern River Watershed Coalition Authority, Kings River Watershed Coalition Authority, Tule Basin Water Quality Coalition, and Westside Water Quality Coalition. These coalitions are organized as the SSJV MPEP Committee (Committee). The Committee is also working with other water quality coalitions implementing an MPEP in other areas of the Central Valley. At the moment, the MPEP is only required to be carried out in high-vulnerability areas, but results are applicable on all irrigated lands.

Does the MPEP require grower reporting?

No, the MPEP has no specific grower reporting requirement. The MPEP may, however, use anonymous information collected as part of the ILRP’s Nitrogen Summary Report and Farm Evaluation to make sure that growers’ operations are correctly represented.

How long will the MPEP continue?

The permit allows 8 years for development of the MPEP, including 2 years for work planning and 6 years for implementation of the first phase. The planning timeframe began in January 2016, and implementation began in May 2017. While this appears to be a long period, it is worth noting that most growers select practices annually, so modifications often take a year to implement and more time to assess. Over a duration of only 6 growing seasons, substantial planning, investigation, interpretation, outreach, and implementation must occur. In addition, implementation progress is required to be assessed and reported. This is handled directly by the Irrigated Lands Regulatory Program coalitions.

How much does the MPEP cost and who is paying for it?

The MPEP is a grower-directed program, so program activities and therefore the cost, will depend on what the coalitions decide is necessary and helpful to their growers. As of early August 2020, a total of $3.1M had been spent, of which about $2.1M was reimbursed by grants obtained by the Committee. Additional work has been performed by partners with funds not administered by the Committee, funds generally supplied by various grants they obtained with Committee support. Average annual per-acre grower costs to date are thus about 11 cents for the 1.85M-acre SSJV. However, much of the work benefits the entire 6M irrigated, non-dairy acres in the Central Valley. On this basis, the program cost is about 3 cents per beneficiary acre. Grant funding agencies have included USDA NRCS (thorough Conservation Innovation Grants) and the CA Department of Food and Agriculture Fertilizer Research and Education Program (FREP).

Who is helping the coalitions with the MPEP?

The coalitions are collaborating with several technical partners, including the USDA NRCS, the CA Department of Food and Agriculture, and the University of California Cooperative Extension.  These partners help to plan technical approaches, identify known, protective practices, assess and quantify fate and transport through modeling, work with cooperating growers, perform focused field studies, explain sound practices to growers and their advisors, and develop information and tools that facilitate application of practices that protect groundwater quality. In addition, the coalitions use private-sector consulting scientists to help them work effectively with these partners.

Will the program change and become more difficult?

There will almost certainly be some changes over time. However, coalitions are working with the Regional and State water boards to maintain the most important and useful parts of the permits, and to limit new elements that threaten grower confidentiality, add new and cumbersome processes, monitoring, or reporting, or that are otherwise unworkable or unhelpful. We think that when we comply with existing permits, and strive to make and document rapid progress through processes like the MPEP, that this strengthens the case that the current permit conditions are sufficient.

What crops are included in the MPEP?

All crops irrigated for commercial purposes are included in the MPEP, except for those included under other permits, such as rice, and fields irrigated with dairy effluent. The MPEP will prioritize groups of crop, soil, and groundwater conditions, focusing on situations with the greatest potential to minimize nitrate leaching.

Isn't it dangerous to assess our own performance? Isn't that the State's job?

The orders require that growers assess their own performance; it is not optional. This is common in environmental programs, partly because the owner of a business or operator of a facility knows so much more about how to best to maintain and improve their own environmental performance. The Central Valley Regional Water Quality Board usually sets up the framework of the program or permit, and then works with the permit holders to make sure that the goals of the program are met as the operation works within that framework.

What about all the improvements growers have already implemented related to management of agrichemicals and water?

The MPEP recognizes that existing management practices already include the careful use of crop and soil information to determine appropriate nitrogen rates, and careful handling and application of fertilizer to ensure that it is taken up by the crop. It recognizes similar care taken with irrigation. These approaches are therefore built into the assessment. This should result in recognition of existing cropping systems that are already protective of groundwater, and expansion of these approaches where this could provide even broader benefit.

Will the MPEP specify a set of required management practices?

No, the MPEP’s purpose is not to mandate specific practices. We know that growers need flexibility to adapt practices to their specific situation, whether that be the nature of their operation, the soil they farm on, or the commodity that they grow. The MPEP is designed to preserve this flexibility to the maximum extent possible. Rather than prescribing, the approach is similar to that employed by NRCS and Cooperative Extension: practices are related to specific performance objectives and field situations, and then the grower can fashion a solution that fits their operation based on this and other information. The difference is that there will be even more focus on the pollutants that the Central Valley Regional Water Quality Board is most concerned about, and right now that is mainly nitrate.

It is possible that in specific areas, certain management practices will be encouraged, or even required as part of Groundwater Quality Management Plans that the Central Valley Regional Water Quality Control Board also requires of coalitions. The MPEP aims to minimize these types of requirements by getting out ahead of them with good performance, and with evidence of that good performance.

Will all practices that decrease nitrogen leaching result in lower yields?

Some could, but the opposite can also occur. For example, we know that more efficient irrigation and/or fertigation systems and operations often result in less water and/or N stress, and that higher yields can result, often with similar or lower N rates. Since more N is being recovered and N rates are not increasing, it is intuitive that less N is subject to leaching. This is borne out by monitoring of these systems for many crops. One interesting effect of this type of outcome is that the N balance (a Regional Board metric) plummets, partly because of higher yields.

Are the specific conditions of my field considered, and if so, how?

The most detailed soil data that is readily available comes from NRCS’ soil surveys, which are now available digitally. Climatic information is similarly available from the California Irrigation Management Information System (CIMIS) and other sources. This allows site-specific data on growing conditions to be efficiently incorporated into landscape-level (considering many, diverse fields at once) assessments in computer models. A widely-used watershed model developed by the USDA Ag Research Service in conjunction with many others have been adapted for use in California with NRCS as a major supporter. By using this soil and climatic information in this model, estimates of the amount and quality of water moving through soils and interacting with crops reflects field-specific soil properties and climatic conditions to the greatest extent practicable with current technology.

How will modeled estimates of nitrate leaching be checked?

Landscape-level results will be compared to runs of more detailed, site-specific models and to site-specific field measurements. The landscape-level model will then be adjusted as necessary to improve the accuracy of its estimates.

Is the MPEP mainly a bunch of new studies, field monitoring, monitoring wells, modeling, or what?

The schedule does not allow for complete dependence on new studies, since they take several years to develop and complete. Fortunately, FREP, UCCE, commodities groups, USDA, and many others have been studying efficient use of N fertilizer for some years. The focus is on ensuring that this knowledge is available and useful to growers, on encouraging or doing high-priority new work, and on using available information to assess how practices affect groundwater. The assessment involves modeling that is rigorously checked against field observations. Where groundwater quality data are needed, observations from existing wells will be used to the maximum extent possible, but some new monitoring wells may also be needed.

Will the MPEP include monitoring wells?

The focus of the program is on understanding what happens in the soil and how it relates to management practices. This usually requires using operational and site information, sometimes with measurements in the crop root zone. Monitoring wells are rarely used for this purpose because groundwater quality, e.g., in domestic wells, does not tell us enough about where a contaminant came from or, if it happened to come from an agricultural field, why it was leached from the soil. A limited number of monitoring wells may need to be installed at research sites specifically developed to monitor groundwater conditions in response to advanced practices.

Some groundwater information will be needed to understand long-term trends in regional groundwater quality. These data may be from samples taken in existing wells managed by others, from those shared with other groups who need to monitor groundwater, and from a few wells that coalitions install to answer a specific question that cannot be addressed another way. The coalitions manage this regional “Groundwater Trend Monitoring” separately from the MPEP.

Will the MPEP include field studies?

The agricultural research community has been working on soil fertility and efficient use of nitrogen for decades, producing a great deal of useful information that is being assimilated into the performance assessment and outreach parts of the program. After all, using existing knowledge gets quicker results, and allows us to focus new studies (there are a couple) on pressing questions for which answers are as yet unclear. This approach is consistent with a widely accepted standard for scientific inquiry: begin by understanding what is already known, then frame a new and relevant question before launching into costly experimentation.

Will the MPEP include individual field sampling?

Other than specific field studies and samples growers take for their own information, no. It is quicker and less costly to work with growers to use data that they already have about their management and fields than it is to collect new data.

How will the MPEP relate management practices to groundwater quality?

This is one of the most challenging parts of the program and it requires bringing several approaches together to establish this relationship. First, root zones that produce very little leaching nitrate cannot reasonably be assumed to be big sources of nitrate going to groundwater. Therefore, understanding what is happening to water in the root zone, before it moves downward toward groundwater, is crucial. Aquifers are large, and reflect the combined influence of many individual fields. We use a soil-water-crop model to evaluate nitrate leaching and groundwater recharge through cropland as a function of management, crop, and soil characteristics. The results characterize a reasonably accurate representation of the true pattern of water and nitrate emanating from root zones, which is the type of input needed to understand how underlying groundwater will be affected.
Second, we collaborate with university partners to determine groundwater quality impacts at the landscape (e.g., township, groundwater sub-basin, or regional) level. Long-term groundwater quality calculations can be made with new simulation tools that reflect the amount of water and nitrate that are recharging from irrigated lands but also account nitrate and recharge from other sources, and for the legacy effects past nitrate leaching across these landscapes. The results can help to predict future groundwater quality trends and to set appropriate expectations for when improvements in water quality at domestic and public water supply wells might be seen.
Third, groundwater quality trends can be measured directly in existing or new wells, so that this is another requirement in the Central Valley Irrigated Lands permits. To achieve this goal efficiently, Coalitions are working together and with neighbors and partners to develop a regional well network, utilizing existing wells wherever possible.

What about other sources of pollution besides irrigated crops?

The landscape-level model used to assess management practices will incorporate other nitrate sources, such as industrial, dairy, and septic systems, so that water quality relationships of irrigated lands are assessed in a realistic context.

Will the MPEP identify specific fields as sources of nitrate leaching?

In a sense, yes. In 2019, a Groundwater Protection process was added to Central Valley Irrigated Lands permits, requiring that field-specific N management (applied N and yield) information be considered along with other factors to estimate N leaching from lands in each township. Further, the effects of this leaching on underlying groundwater quality must be assessed, and reductions necessary to achieve water quality objectives need to be determined. Although field-specific information is used in this calculation, the results are to be reported at the township level.

Otherwise, the MPEP is not focused on assessing individual fields, but rather on assessing the performance of classes of management practices, crop, and soil combinations over time. The results of these assessments will be made available to growers to help them to assess their own performance. You will be able to compare the results for several alternative suites of practices, in terms of their effect on N leaching for the specific combination of crops and soils that comprises your field.

Could assessment methods account for various irrigation and fertigation regimes?

If the exact regime is known for a site, it can be reflected in modeling for that site. So, modeling can be quite specific and results should show the effects of each management regime.

How does the assessment account for different management practices by growers? For example, if a grower is using smaller but more frequent N applications or applies the N toward the end of irrigation sets, how is this represented?

The modeling to date considers a relatively common multiple application scenario for most drip and microspray irrigated crops. It applies this regime to all fields. The simple reason for this is that nitrogen management summary reports contain no information about nitrogen application other than the amount applied, so there is currently no basis on which to customize application timing for each field. Since something must be specified, a regime that is fairly common and efficient is one of several that is modeled. These management regimes were developed with people knowledgeable about each crop. Methods can be changed in the future as more is learned or as farming methods evolve.

Is it assumed that the effects of growers’ efforts to improve nitrogen use efficiency will show up in the N balance (N applied minus N removed)?

They might. When systems become more efficient, more of the applied N is captured by the crop. There is thus less leachable N and a generally lower risk of N leaching.

Is the N balance itself sufficient to predict N leached?

No. The N balance is a helpful metric and indicator of leachable N, but is inadequate by itself to estimate leaching losses. This is why the coalitions opted for a platform that is more robust than a partial N balance. Monitoring and modeling results demonstrate clearly that over the long term, leaching is always less than the N balance due to other things that happen to N besides being incorporated into crop yield. The distribution of N among these alternative fates is driven by timing, form, or placement components of fertilization, and by irrigation management. Of course, the effects of management in any given location are also dependent on local climate, soil, and crop factors. Almost none of this is reflected in a simple applied-minus-removed N balance.

How does the amount of N applied affect the N balance?

This can be thought about several ways: for a single field, for groups of fields of a single crop type, and across different crop types.

Single field: When yield is constant, applying more N increases the N balance because it is not going into yield. If more N is applied to support a larger yield, since N applications are rarely 100% efficient, some of the N applied normally contributes to an increased N balance.

Groups of fields of a single crop type: Across large numbers of fields, N balance tends to increase with the N rate. This is often true when fields receiving more N also tend to have higher yields (for the same efficiency reason cited above). Increases are steeper when fields with higher N rates have similar or lower yields than the less heavily fertilized fields.

Across different crop types: The relationship between N applied and N balance is much messier across different crops, because factors affecting recovery of applied N by the crop differ markedly among crops.

How do the meaning and use of the A/R and A-R (applied N/N removed from the field, and the difference between N applied and that removed from the field) differ?

Both have been identified as usable metrics in Irrigated Lands permits, so either can be used. A-R is the more commonly used, representing the pounds of N per acre that is subject to leaching in a given year or season. However, since other things happen to N not taken up by plants, A-R does not reflect leaching as such. Nevertheless, it is widely and correctly accepted as an index of general leaching risk.

The A/R metric, on the other hand, has no units and is not a physical quantity, but rather one way to express efficiency. Growers using 70% of 30 and 300 lb/acre N applications will have the same A/R. A/R is mathematically more erratic and more likely to be high when there is no real problem, or low when there is.

In terms of metrics, the SSJV MPEP tends to emphasize A-R as one way to indicate the level of leaching risk. Use of A/R efficiency indicators is limited to comparing among alternative systems for the same crop.

How does the MPEP assessment relate to the SBX2-1 N balance in terms of methods and findings?

Similarities are that applied N and that removed by crops are considered in both, but otherwise the two assessments are very different.

The goal of the SBX2-1 assessment is to assess historical N balances, whereas the MPEP must assess the influence of current or possible future management on underlying water quality.

The SBX2-1 was a simple N balance, in which applied N could either be taken up (each crop has an estimated demand), lost as gas (as a fixed proportion of applied N), or leached. This simple balance was calculated for each field each year. This accounting tool is not in the same “family” of physically based, complex watershed models as the SWAT model employed in the MPEP. SWAT is a better fit for the MPEP, but was not needed to meet the objectives of SBX2-1.

The MPEP assessment links SWAT to NPSAT, a groundwater assessment tool set developed by UC. SBX2-1 does not contain an explicit groundwater component because it was not needed to achieve its objective. Neither assessment addresses processes between the bottom of the root zone and the water table, other than to assume that recharging water does not change much as it flows through these layers.

The SBX2-1 N rates were developed by estimating the available N sources from regional manure production and fertilizer sales, and then apportioning that total amount onto land in proportion to (but sometimes much greater than) crop needs. The N supply drove that assessment. The MPEP is more demand-driven, and assesses N rates in the range from those recommended as agronomically sound (low end) upward through the range reported by growers (sometimes exceeding the strictly agronomic rate). In general, the SBX2-1 rates are in the range of 2.5 to 3 times these rates.

How are NMP summary information used in MPEP assessments?

They are used as a reference point to ensure that the full range of N rates and yields that growers report are considered for each crop. In the Groundwater Protection assessment, they are used to select the N rate/yield combinations to apply to each field within a township.

If the assessment does not recognize improvements, then how will growers’ benefit from better management?

Eventually, sufficient detail to capture the combined effects of practices on leaching outcomes will be needed. Coalitions endeavored to select and develop a platform that would enable growers to do just this. Modeling will never be a perfect solution, but it allows us to recognize nuances of management better than any approach except site-specific monitoring, which is prohibitive due to the astronomical cost and difficulty of obtaining reliable monitoring results for vast acreages.

Could the assessment be seen as a strictly regulatory activity and not a method to provide positive feedback to growers for improvements that they achieve?

The Irrigated Lands permits require an assessment, but the method of assessment is up to growers and it was up to their coalitions to develop it. As such, these tools belong to the grower coalitions. How they are used is up to them. Of course, whatever assessment method is used, it is only useful if the results are credible to others. Thus, coalitions have worked to ensure that scientific, regulatory, and stakeholder partners are informed about and have the chance to become comfortable with assessment methods as they have been developed.ges.

Where can I find information on management practices that minimize nitrate leaching?

To start sharing information as quickly as possible, the coalitions compiled numerous resources at https://agmpep.com/. The site includes a calendar of outreach events related to nutrient management, hosted by a wide variety of entities. The site also includes a directory of publicly available agricultural management practice tools and resources. The directory is an evolving collection of resources, and is not intended to be comprehensive, or to replace site-specific management recommendations.

In addition, and as results of the MPEP become available, the coalitions transmit these to growers through other modes of communication, including meetings, mailings, and online tools.

Can I help in some way? What if I have a question or suggestion?

We are always interested in questions and input from grower-members. Attend a meeting and/or feel free to contact us. Some of our studies require grower-cooperators. Feel free to let us know if you are interested. Please send email to agoutreach@plantierra.com. We look forward to hearing from you.