Nutrient Management Planning:
Win/Win and We Can Do Better

James Pease
Dept. of Agricultural and Applied Economics, VPI&SU

Laura VanDyke
Dept. of Agricultural and Applied Economics, VPI&SU

Darrell Bosch
Dept. of Agricultural and Applied Economics, VPI&SU

James Baker
Dept. of Crop and Soil Environmental Sciences, VPI&SU

Concern over agricultural nonpoint source pollution increasingly focuses on concentrated livestock operations, which attract particular attention because of the production, storage, and disposal of large amounts of nitrogen- and phosphorus-bearing manure. Improper manure disposal or excessive applications to crop and pasture land may have impacts on surface and ground water. High nitrate levels in water supplies have been directly related to regions of high animal concentration across the U.S. (Duda and Finan 1983; Kingery et al. 1993; Moore et al.1995). Since Virginia's dairy and poultry industries generate over 40% of the Commonwealth's agricultural production value, it is imperative to understand and remedy unsafe practices in the most cost-effective manner. The extent of pollution potential was indicated by Bosch et al. (1992), who estimated that 57% of crop and pasture land sites in Rockingham (Virginia's most intensive livestock production county) received manure applications in 1990. It was found that poultry farmers over applied nitrogen to farm fields by an average of 49 pounds per acre (relative to university recommendations) and over applied phosphate by 137 pounds per acre, while dairy farmers over applied phosphate to farm fields by an average of 93 pounds per acre. The study concluded that such practices posed a serious potential for nonpoint source pollution. Parsons (1995) found that 89 percent of 3,766 soil samples from Rockingham county rated either "very high" or "high" in phosphorus. Such soils do not require any additional phosphorus applications for optimal plant growth, either in the current year or for several years to come. It can be expected that soil nitrogen levels are also quite elevated.

In Virginia, a major public sector tool in controlling water quality pollution resulting from agricultural activities is farm nutrient management planning. The focus of such planning is farmer adoption of conservation practices designed to better manage the use of inorganic and organic fertilizers. These management practices are detailed in a written nutrient management (NM) plan. Although incentives or permitting regulations may sometimes be involved, farmers usually agree voluntarily to follow the NM practices detailed in the plan. Since nitrogen is considered to be the primary nutrient pollutant of the Chesapeake Bay, NM plans are designed to control nitrogen runoff and percolation from farm fields. However, evaluation of the on-farm environmental and economic impacts of NM planning is lacking.

In this study, the before-and-after effects of NM practices on farm profit and farm-level nitrogen losses were estimated for four Virginia livestock farms which had implemented a NM plan: a southwest dairy, a Shenandoah Valley dairy, a southeast crop/swine farm, and a Piedmont poultry farm. These farms were chosen in consultation with nutrient management specialists in the Virginia Department of Conservation and Recreation to represent a cross-section of livestock farm sizes and topographical/hydrological characteristics. The Erosion Productivity Impact Calculator (EPIC) was used to estimate changes in crop yields and potential nitrogen losses before and after the implementation of the plan (Williams et al.1989). EPIC is a computer model used to simulate multi-year interactions of weather, hydrology, erosion, nutrient cycling, plant growth, pesticide fate, soil temperature, economics, plant environmental control and soil tillage. EPIC estimates nutrient losses at the edge of the field and through the bottom layer of the root zone, and does not estimate nutrient loadings to water supplies. As such, the results estimated here should be taken as a measure of pollution potential rather than as pollution loadings. EPIC has been widely tested and used throughout the United States and other countries.

In consultation with a soil scientist, nutrient management specialists, and the farm operator, the major soils, slopes, and rotations on each farm were grouped into a manageable number (as many as 10 soils, 4 slopes, and 4 rotations across farms). For each soil, slope, and rotation combination, an identical daily weather series was randomly generated for one hundred simulated years, using 1953 to 1993 rainfall and temperature from the weather station nearest the farm as the expected probability distribution for weather parameters. Total nitrogen (N) losses are estimated as nitrate losses with runoff, organic nitrogen losses with sediment, and mineral nitrogen losses in subsurface flow and percolation. Volatization losses to the atmosphere are not considered for NM planning, and are not reported here. Phosphorus (P) losses, although not explicitly considered in NM planning, are estimated by EPIC and are reported.

Any changes in crop yields and production resulting from altered field management practices implemented in the NM plan, such as fertilization levels, crop rotations, or tillage, were estimated with EPIC, related costs or returns were estimated, and the impacts on farm net returns were analyzed using partial budgets. Investment costs, such as for manure storage, were considered as average annual values using straight-line depreciation, and annual costs were included for maintenance, repairs, and insurance. Additional costs such as pre-sidedress nitrogen tests, split nitrogen applications, and manure hauling costs included estimates for supplies, labor, and machinery. Information used in developing budgets was obtained primarily through interviews with the producers, supplemented by machine cost information and crop price information from secondary sources.

Nutrient loss abatement and changes in annualized net returns attributable to the farm's nutrient management planning are summarized in Table 1. As a result of the nutrient management plan, N applications were reduced by 21-47 percent across the four farms. Adoption of nutrient management practices resulted in significant reductions of potential nitrogen and phosphorus losses for each farm. Average annual N losses decreased by 23-45 percent, while phosphorus losses decreased by 0-66 percent. The principal pathway for nutrient losses before and after the plan was sediment erosion, as nutrients adhere to soil particles as they are washed off the field in rainfall runoff. The net impact of farm practice changes increased net farm income by $395-$4593 per year. Increases in farm income resulted primarily from reductions in commercial fertilizer purchases, which in turn were caused by more accurately crediting animal wastes for nutrient content. On the Piedmont poultry farm, however, income was increased by additional sales of poultry litter resulting from decreased litter application rates. On the Shenandoah dairy farms and the southeast swine farm, large reductions in nutrient losses were associated with installation of manure storage, which allowed the producer to store animal wastes until needed by growing crops. All farms spread manure on larger acreages after implementing the plan, thus lowering applications and losses on the smaller area formerly preferred for application.

Loss reductions vary widely within a farm. Nitrogen loss reductions on the Shenandoah dairy, for example, ranged from 5-50 percent depending on soil, slope, and crop rotation. As could be expected, losses with soil erosion are greater for row crops with no winter cover. Poorer quality soils with high potential for percolation losses resulted in higher losses for identical rotations and slopes. On all farms, as the field slope increases, the absolute magnitude of nitrogen loss reductions resulting from the plan is greater. For example, on the southwest dairy fields with Frederick soils and corn-rye-wheat rotations, nitrogen loss reductions are 9, 11 and 13.3 pounds per acre when slopes are 4.5%, 10.5%, and 16.5%. This suggests that greater nitrogen loss reductions may be possible by targeting high-loss potential soils, slopes and rotations within a farm for nutrient management.

Methods to investigate improved NM planning were investigated with a whole-farm linear programming model (LPNM). The Shenandoah dairy was chosen to be modeled. The variety of rotations, soils, and slopes present on the farm permit examination of the potential to further reduce nutrient losses beyond the levels of the current nutrient management plan through routing of manure and fertilizers according to the loss potential of individual fields and through changes in management practices and crop rotations. The model maximizes annual farm profit subject to resource constraints and parametrically varied whole-farm nitrogen losses. The model may 'choose' from a large set of alternatives within the resource base of the farm, including alternatives which involve timing and application amounts of fertilizer or manure to crops and pasture, or which vary crop rotations. Nitrogen losses for each alternative were estimated with EPIC. Budgets were constructed which reflect the variable costs of production of each alternative. Although the estimates of costs and nutrient losses vary slightly between the case farm analysis and the whole-farm linear programming analysis, the estimated case farm nitrogen losses were taken as the baseline to evaluate further nutrient loss reductions.

Results indicate that there is potential for an additional 15 percent reduction in nitrogen losses when the optimization model is allowed to maximize profits through choosing crop rotations and nutrient application practices based on field environmental loss potential. This additional loss reduction is achieved with no loss in farm income. The marginal cost of such additional loss reductions in terms of farm income begins to rise sharply as the whole-farm allowable N losses are further restricted. If N losses are restricted to 20 percent below after-plan losses, each additional pound of N loss reduction is achieved at a loss of nearly $5.50 in terms of net farm returns. If crop rotations are restricted to those chosen by the farmer in the nutrient management plan, flexible nutrient application practices can only reduce nitrogen losses by 5% below that of the existing NM plan.

Nutrient management planning is a cost-effective process to reduce nitrogen losses on livestock farms. On each of the studied farms, NM planning was a win-win investment that produced significant nitrogen loss reductions and moderate farm income increases. For livestock farms, manure storage, manure nutrient crediting, and proper timing of applications are keys to NM success. Large N losses occur when, in the absence of manure storage, heavy manure applications are made to limited land. Storage also allows proper timing of applications, which creates the potential for cost savings through reduced fertilizer purchases. Manure testing is a critical element in achieving such cost savings. Eliminating manure applications on fields with steep slopes, even if over applications are then made to more level fields, will have a significant impact on reducing soil erosion and related nitrogen/phosphorus losses.

NM plans are developed on a field-by-field basis, relying on operator preferences and NM specialist expertise to achieve a balance between profits and nutrient losses. There appears to be a significant potential to further reduce losses with whole-farm planning through manure routing and crop rotation selection based on field susceptibility to nutrient losses. In order to help producers implement practices which target the most sensitive areas of a farm, NM planners need spatially sensitive decision support systems.

Table 1. Nutrient Loss Abatement and Changes in Net Returns, All Farms

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