Nutrient Loss Reduction Strategy Research Library

This is a summary of a full report published in 2020 (Christianson, 2020a) detailing agricultural conservation practice scenarios developed to meet water quality goals. Please see that report for additional details. The following article was featured in the 2021 NLRS Biennial Report. 

The Illinois NLRS was released in July 2015. The Science Assessment to Support an Illinois Nutrient Loss Reduction Strategy included example implementation scenarios detailing combinations of conservation practices, scales of implementation, and the associated level of nutrient load reductions that may be realized when fully implemented. Two of the example implementation scenarios met the 45% reduction goals set for both nitrogen and phosphorus; however, none of them reflected the interim reduction goals of 15% nitrate-N and 25% total phosphorus. In addition, tracking and reporting on some of the conservation practices, as described in the scenarios, has proven difficult. The purpose of this section is to provide additional implementation scenario examples that meet the interim nutrient reduction goals and provide additional scenario examples that meet the 45% reduction long-term goal, all with conservation practice scales that are more amenable for tracking and reporting. 

These additional implementation scenarios were developed by University of Illinois and funded by Illinois Environmental Protection Agency through a grant provided by U.S. Environmental Protection Agency. The intent is to align implementation scenarios with data available for tracking implementation across the state. Previous scenarios were set up without the knowledge of data availability, or how to potentially track progress with available data sources over time, such as conservation tillage practices on soil eroding greater than the tolerable level (>T). Many of these practices are excellent, though direct measurement of these systems would require data not currently available, or not consistently collected. There are six scenarios focused on nitrogen, phosphorus, or combined scenarios. The first three meet the interim water quality goals, while the last three focus on the 45% long-term reduction goals. Three additional scenarios were developed to highlight the potential use of new conservation practices that have yet to be assessed as part of the strategy.

Interim scenarios have undergone a simple cost optimization. Full scenarios required substantial adoption of practices; cost optimization was not attempted, since 100% adoption was largely required for all conservation practices. Further, the scenario development framework has been designed to allow new or updated costs to be incorporated as they are developed. In the future, new scenarios accommodating new information can be developed easily.

Point source reductions for phosphorus have been included in all scenarios. Urban stormwater was included as a line item, though this was not populated and will likely have little impact on the overall scenario development. Further, each scenario was broken into three distinct land use categories based on a combination of information available in the strategy, the science assessment, and available information on practice implementation. The three groups were general agricultural land consisting of corn and soybeans, tiled land, and non-tiled land. The two drainage categories are important to differentiate due to the applicability of certain conservation practices in the tiled landscape, such as denitrification bioreactors, and because data sources available to track this information make the distinction. Taking advantage of this information provides more detail and control over scenario development.

The science assessment was used to supply the agricultural conservation practice performance values (Table 3.6) for all scenarios. All nitrogen management practices are assumed to apply only to corn acres. The Policy Working Group has recently adopted a process to update or add conservation practice performance values to the strategy. As part of scenario development, a custom spreadsheet was developed to accommodate practice updates as they become available, so scenarios can be quickly modified using the most current scientific information. Potential additional practices may include some of the most highly funded practices by the U.S. Department of Agriculture’s Environmental Quality Incentives Program. Between 2008 and 2016, this program provided roughly $4.4 million in funding for water and sediment control basins, $3.9 million for grassed waterways, $2.9 million for heavy use area protection, $2.8 million for grade stabilization structures, and $2.5 million for terraces across Illinois.

Table 3.6. Conservation practice performance values that were part of the Illinois NLRS

The science assessment also developed costs associated with the various conservation practices. These costs included the expected life of each practice and the typical area treated by it. Full details can be found in appendix B of the Illinois Nutrient Loss Reduction Strategy. The science assessment noted five issues to consider when developing costs:

1. Costs represent a change from current practice.
2. The initial cost of practice investment (if lasting longer than a year) is amortized over the life of the practice with a discount factor of 6%. A lifespan of 20 years was most common. This is called the equal annualized cost.
3. A yield change due to implementing a practice was determined using the Illinois Agronomy Handbook as a general guide.
4. If per acre net returns on farmland are $55/acre, additional costs due to conservation practice implementation of even $10/acre would represent a substantial reduction in agricultural returns.
5. Some of the practices would require significant capital investment and may expose farmers to additional risk. Similarly, limiting the time available to do field operations (i.e., all field activities to be done in the spring), may also increase risk.

Each of the practices used in the scenarios had additional nuances, as discussed in the strategy. The resulting costs are summarized in Table 3.7. Cost development did not consider the human capacity issues that would be associated with a rapid ramp-up of conservation activities. In other words, the cost assumes the expense required to complete a given practice without competition for design, competition for installation capacity, or other technical skills requiring an expert.  

Table 3.7. Conservation practice costs included in the Illinois NLRS 

Scenario Summary

 A summary of the six basic scenarios is provided here for quick reference (Table 3.8). Costs were broken into annual cost and cost savings, as well as net annual cost. Cost savings are associated with reduced tillage management, phosphorus rate reductions to lower soil test phosphorus from high to optimum, and using the Maximum Return to Nitrogen application rate. Scenario details for combined interim water quality goals and full water quality goals are listed in the scenario results section. The total impacted area quickly rises above the estimated 22 million acres of row crops, due to the use of multiple practices on a given acre. For exam- ple, reducing nitrogen application rates to the MRTN would likely happen in combination with the addition of cover crops, or applying phosphorus based on the Illinois Agronomy Handbook recommendations for soil test phosphorus levels. These scenarios have also been refined based on stakeholder feedback, which was summarized in Christianson (2020a).

 The five extended scenarios were included to help answer questions surrounding specific types of activities and were intended to be “what if ” scenarios. Extended scenarios added more detail to tillage categories, saturated buffers as a conservation practice, perennials, nutrient manage- ment only, and in-field practices only. Since these scenarios did not, necessarily, align with the strategy, they are not discussed in detail here. More information on extended scenarios can be found in the full report (Christianson, 2020a).

The six basic scenarios are as follows:

N7:      Interim Nitrogen Reduction Goal of 15% from Benchmark

P7:       Interim Phosphorus Reduction Goal of 25% from Benchmark

NP7:    Interim Combined Reduction Goal of 15% for N and 25% for P from Benchmark

N8:      Nitrogen Reduction Goal of 45% from Benchmark

P8:       Phosphorus Reduction Goal of 45% from Benchmark

NP8:    Combined Reduction Goal of 45% for N and P from Benchmark

Table 3.8. Summary of agricultural conservation practices to meet water quality goals from the agricultural sector (estimates assume the point source sector meets goals)

*Practices may be implemented on the same acreage, though no data sources are available for estimating this. There are no estimates developed showing combined impact of practices on the same area. More significant digits available in full report.

Methods

 The backdrop for all scenarios was historical land use acreages and nitrogen and phosphorus loads. Background information was compiled accordingly and is shown in Table 3.9 for the 1997-2011 benchmark period. Many of these values were initially included in the strategy, though National Agricultural Statistics Service survey results, Cropland Data Layer, and Census of Agriculture values were also used. The corn to soybean ratio and the tiled to non-tiled ratio were used to proportionally distribute information on implementation potential for certain practices, like cover crops, when needed. Distinctions were made between tiled row crop agriculture and non-tiled row crop agriculture, due to data availability. Specifically, the NLRS Survey conducted by NASS asked questions distinguishing between these land management practices; some conservation practices, such as bioreactors, are only applicable in the tiled landscape.

Table 3.9. Background information for the 1997-2011 benchmark period for nutrient load in water and the 2011 benchmark period for agricultural management. These values were largely reported in the strategy; however, some extended calculations were added to facilitate proportionally distributing conservation practices.

As the scenarios developed here are from the view of the 1997-2011 benchmark period, the land use areas and ratios, along with nitrogen and phosphorus loads from this period were used. Information about conservation practice implementation during the benchmark period was collected from the strategy, where available, and from supplemental sources. For example, the existing cover crop area was not indicated in the strategy; however, the NLRS Survey conducted by NASS provides an estimate of the area using cover crops for 2011.

Maximum potential and practical area available to host specific conservation practices was estimated using a combination of background data and narrative provided in the strategy, the science assessment, literature, and the USDA Cropland Data Layer (USDA, 2018). Maximum potential area was included to add a realistic check against scenario development; however, the developed framework allows these maximum values to be updated with new information.

The maximum potential for buffers was estimated based on the equivalency of previous scenarios P1 and P2 (Illinois EPA et al., 2015), which were identical with the excepion of buffers being used in scenario P1 and cover crops being used in scenario P2. Making this equivalency for phosphorus, assuming all buffers were on non-tiled land with a phosphorus loss reduction efficiency for buffers of 50% and 30% for cover crops, resulted in approximately 12.3 million acres being treated by buffers. Buffers were the one practice included without a suitable data source to allow tracking.

Some effort was made to adjust the maximum potential implementable area by reducing to account for competing practices. For example, increasing perennial land requires a land use change, which was subtracted from applicable corn and soybean acreages. As these adjustments are not necessarily a direct subtraction from a given conservation practice, the initial maximums were divided by the total row crop area to develop a ratio. Land use changes in a given scenario were subtracted from corn or corn and soybean areas, but the practice maximum ratio was maintained. For example, the Maximum Return to Nitrogen practice could be implemented on an all-corn area, which is roughly 54% of the row crop landscape. A change to perennial would be subtracted from all row crop area, with the result multiplied by 54%, which would be the new maximum for the MRTN practice. Nitrogen management practices were treated in the same manner, though all nitrogen management practices were in direct competition with each other, meaning changing from 100% of nitrogen applied in fall to 100% of nitrogen applied in spring is in direct conflict with applying 50% of nitrogen in fall and 50% of nitrogen in spring.

The addition of cover crops is a major component in all scenarios, due to the relatively high nutrient loss reduction efficiency values for both nitrogen and phosphorus. To date, cover crop adoption across the state has been relatively low, though adoption is accelerating. Historic estimates of cover crop area have included winter wheat, which is technically not defined as a cover crop, but as a commodity and would, thus, factor into the base land use. Since tracking sources for cover crops (the NLRS Survey conducted by NASS) have not split these two apart, no effort was made here to split them. As cover crop adoption increases, this discrepancy will become less important, assuming winter wheat acreage stays relatively constant, as it has over the last five to 10 years.

Cost optimization included implementing the least expensive practice up to the practical maximum before moving to the next least expensive. End results were rounded.

Results

Figures 3.10 and 3.11 summarize acreages and provide a visual of the scenario. All nitrogen reduction results presented are for nitrate-N, as most of the conservation practices assessed focused on nitrate-N, which makes up over 75% of total nitrogen leaving the state (Illinois EPA et al., 2015).

Interim Goal: NP7 — Combined Reduction Nitrogen (15%; 61.5 million pounds) and Phosphorus (25%; 9.4 million pounds) 

This scenario includes increasing acres being managed at the Maximum Return to Nitrogen rate to 100% of corn acres, increasing nitrification inhibitors with all fall-applied nitrogen, increasing cover crops, and treating tile water with bioreactors. This scenario also includes increasing acres being managed with conservation tillage, cover crops, and increased phosphorus management based on soil test information and following the Illinois Agronomy Handbook recommendations for calculating phosphorus application, including limiting application where soil test phosphorus is above optimum. An estimated 59% of fields in 2008 tested above optimum. Note the total acreage needed is larger than the total row crop agriculture acreage. This indicates more than one practice per acre.

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Full Goals: NP8 — Combined Reduction Nitrogen (45%; 184.3 million pounds) and Phosphorus (46%; 17.3 million pounds)

This scenario maxes out MRTN, phosphorus management based on soil test phosphorus (as described in scenario P7), conservation tillage, cover crops, split nitrogen application on tiled land, nitrification inhibitors on fall-applied N on tiled land, bioreactors, and wetlands. Also, an increase in land treated with buffers was needed to close the nutrient loss reduction gap. As with the previous scenario, a treated area increased above the row crop area indicates more than one practice per acre.

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Conclusion

This type of planning is important to orient all stakeholders and provide some general guidance on the direction that conservation efforts could and should be going for the purpose of water quality. These scenarios are for information only; they are not prescriptive. All agricultural conservation activities are voluntary, so the numbers here represent hypothetical avenues to meet water quality goals. It is apparent with these scenarios that substantial effort is required to meet our nitrogen and phosphorus reduction goals. The primary benefit of having these scenarios published is to allow for conservation practice tracking to be correlated with associated metrics of accomplishment, so that an accurate story can be told. Since buffers are part of scenario NP8, a mechanism to track buffer implementation over time would be a helpful addition to overall tracking efforts. Finally, additional details surrounding all scenarios developed can be found in Christianson (2020a) and a presentation given at the 2020 Illinois NLRS Partnership Workshop (Christianson, 2020b), both of which can be found on the Illinois EPA’s website at www2.illinois.gov/epa/topics/ water-quality/watershed-management/excess-nutrients/Pages/NLRS-Scenario-Development.aspx.

Christianson, R. (2020a). 2020 Illinois Nutrient Loss Reduction Strategy Scenarios. Retrieved from Christianson, R. (Producer). (2020b). 2020 Illinois Nutrient Loss Reduction Strategy Scenarios - Presentation. Retrieved from www2.illinois.gov/epa/topics/water-quality/watershed-management/excess-nutrients/ Documents/Agriculture%20Water%20Quality%20Partnership%20Forum/2020/awqpf-presentation-christianson-102020.pdf.

David, M., McIsaac, G., Schnitkey, G., Czapar, G., & Mitchell, C. (2014). Science Assessment to Support an Illinois Nutrient Loss Reduction Strategy. Retrieved from IEPA, IDOA, & University of Illinois Extension (2015). Illinois Nutrient Loss Reduction Strategy. Retrieved from Springfield, IL: www2.illinois.gov/epa/Documents/iepa/water-quality/watershed-management/nlrs/nlrs-final-revised-083115.pdf. 

USDA. (2018). CropScape - NASS CDL Program. Retrieved from nassgeodata.gmu.edu/CropScape/.