A nutrient management plan should serve as the foundation for meeting crop nutrient needs. Ultimately, it should address the 16 essential nutrients while also identifying fields that have high-priority conservation concerns related to nitrogen, phosphorus, and soil erosion. A nutrient management plan should be part of a farm operation’s conservation plan. It is considered an in-field practice.
A nutrient management plan should:
- match the nutrient needs of the crop with soil-available nutrients. It should identify any supplementary organic or commercial fertilizer applications required to ensure nutrient availability for crop production. Over-applied nutrients are subject to loss through tile or surface runoff, so the plan should attempt to limit soluble nutrients left in the soil at the end of the growing season. The plan should address the 4R’s of nutrient stewardship.
- provide a site-risk assessment of potential nitrogen, phosphorus, and sediment losses. The plan should consider inherent soil characteristics such as slope; soil hydrologic group; infiltration/ponding potential; and the presence of concentrated water surface flows in combination with management practices such as tiling, tillage, and phosphorus soil testl evels and nutrient placement. The risk assessment should identify fields where conservation practices should be implemented due to high loss potential of nutrients or soil erosion.
Figure 31. Soil sampling results are used in monitoring soilstable nutrients such as pH, phosphorus, and potassium. As samples are collected, it is also a good time to note erosion, wet areas, and other conservation concerns. Credit: The Ohio State University.
Crop nutrient needs should be assessed in all fields where forage or grains are harvested. While ideally, risk indexes should be calculated on all fields to evaluate for the potential loss of soil or nutrients, time might not allow a comprehensive evaluation. Fields with inherent soil conditions and management practices that result in potentially higher risk can be identified and evaluated. Narrowing the numbers of fields reviewed can be a timeefficient way to begin risk evaluation. Below are the risk tools provided by NRCS, along with inherent soil characteristics and management (also review Critical Resource Concerns).
For P concerns:
- The phosphorus risk tool is the Ohio P Risk Index.
- Fields with STP levels above 50 PPM should be assessed for phosphorus losses.
- Phosphorus concerns exist where it is estimated that 50 percent or more of the water leaving a site leaves via surface flows.
- Phosphorus concerns exist where fields have direct water contributions to ditches, streams, or rivers.
- Phosphorus concerns exist where there are C/D hydrology soils.
For N concerns:
- The nitrogen risk tool is the Ohio N Risk Index.
- Nitrogen concerns exist where highly leachable soil types and tiled fields have a greater transport of nitrogen.
- Nitrogen concerns exist where multiple nitrogen sources are used. These sources include organic sources (manure/biosolids); commercial fertilizer; and/or multiple split-timing sources such as preplant, starter, sidedressing.
For erosion concerns:
- The erosion risk tool is the Revised Universal Soil Loss Equation Version 2 (RUSLE2).
- Erosion concerns exist where soil slopes are greater than 4 percent.
- Erosion concerns exist where intensive tillage is used.
- Erosion concerns exist where concentrated surface flow in a field causes gully erosion.
- Erosion concerns exist where ditch design causes excessive bank erosion.
A nutrient management plan has economic and environmental benefits. The plan can identify better nutrient management practices that result in lower input cost, and it can provide a crop production environment that will not limit yield-increasing or economic returns. Practices that result in fewer soluble nutrients in the soil at the end of the season will result in lower environmental impacts and improved water quality in a watershed over time.
In Ohio, there are at least three potential reasons to have a nutrient management plan in place:
- It can be used to help farmers/landowners make informed nutrient decisions about a field.
- It is needed as a foundation for eligibility to participate in many cost-share programs offered by the local NRCS, SWCD, and other organizations.
- Ohio Revised Code 905.325 provides for an “affirmative defense” against private civil action from fertilizer application if a voluntary nutrient management plan approved by a local SWCD is in place, a person is a certified fertilizer applicator, and the proper application records are maintained.
Phosphorus is soil-stable and lost at low concentrations and at total pounds-per-acre rates in water flows. Unfortunately, only small amounts of phosphorus in an aquatic environment can trigger aquatic plant growth. The potential of water impacts from phosphorus lost from agricultural fields increases with soil erosion (particulate-bound phosphorus) or an increased soil test value (soluble phosphorus).
- STP is a good indicator for the potential of phosphorus movement offsite, but other management and soil conditions can result in higher or lower actual measured losses. As STP values increase, the elevated soil solution levels are exposed to loss through tile or surface water with water movement.
- Generally, fields with STP below 50 PPM can produce low levels of phosphorus runoff in water quality sampling.
- Fields at the 50–120 PPM range have shown DRP concentrations of 0.02–.40 PPM and 0.1–2.0 lbs of DRP load per acre.
- Fields at 120 PPM or higher tend to have annual edge-of-field losses of 2–5 lbs of DRP per acre. Tile water concentrations will be 0.08–1.50 PPM of DRP.
- Acute losses of phosphorus levels leaving the site can occur at the time of fertilizer application, especially with surface applications.
- Soil phosphorus levels are highly buffered and tend to move less than 3–4 PPM annually from just crop removal. Excessively high soil phosphorus levels result in added input costs without associated returns in the form of higher yield.
- Water concentrations of 0.05 PPM soluble phosphorus and annual loadings of less than 0.5 lbs per acre attain water quality targets for Lake Erie and would have beneficial targets for most Ohio watersheds.
By maintaining STP in agronomic ranges, the risk of phosphorus losses is reduced. Subsurface-placed phosphorus has shown reduction in phosphorus losses when compared to surface-applied phosphorus of up to 18 percent (see also Subsurface Placement of Nutrients). These two practices reduce the amount of phosphorus lost from an economic cost of inputs and water quality aspects.
Nitrogen in elevated levels in water leaving a field tends to be associated with excess application of nitrogen or weather conditions that limit crop yields and nitrogen uptake. Situations resulting in nitrogen loss are highly variable spatially and seasonally, but they can result in losses of 100 lbs of nitrogen or more per acre. It’s important to account for all sources and timings of nitrogen applications to ensure that excess rates are not applied. Nitrogen needs to be managed to reduce the rate to the actual need of the crop. This reduces the loss of nitrate-N during the nongrowing season.
Soil Test Recommendations
- The test should be taken within the 12 months prior to the development of the plan.
- Field landscapes should be divided into areas that represent crop production potential. Common factors used are soil type, past production practices, and harvested yield. Areas for sampling should not exceed 25 acres. Zone sampling and grid sampling are options to be considered. They result in more intensively sampled areas, and they attempt to identify variations that affect yield response. These intensively sampled zones should not exceed 12 acres.
- Soil tests should include, at a minimum, water pH, buffer pH (used for lime recommendation), organic matter, phosphorus, potassium, magnesium, calcium, and cation-exchange capacity.
- When sample results are received back from the lab, the first value that should be evaluated is pH, since pH affects soil solubility of nutrients and soil biological processes. If a sample reveals soil water pH less than 6.0 or buffer pH less than 6.2, the pH should be corrected (see Amending Soils with Lime or Gypsum). Then, the soil test should be retaken to assess soil nutrients. The repeat soil test will identify any increase in nutrient availability changes from liming.
- The soil test should be done according to adapted, recognized laboratory procedures developed for the region. An example is the Recommended Chemical Soil Test Procedures for the North Central Region (2015).
- Crop rotation plans should start with the current crop and continue for the next 3–5 years.
- Crop nutrient recommendations should be made according to calibrated crop response field trials. Compare the soil test analysis value to the crop yield and the added nutrients by replicated rate response trials. For Ohio, the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa (Vitosch et al., 1995) provides these recommendations for agronomic crops.
- Consider tillage and other equipment management that affects surface residues and soil disturbance.
- Consider field boundaries, current conservation practice inventory, presence of tile, and any concentrated surface water flows.
- Identify all sources of nutrients, including both organic and commercial fertilizer, that will be used on the farm to supplement soil-available nutrients.
- $4–$7 per soil sample collection
- $6–$18 per lab analysis per sample, depending on the test selected
- $500–$10,000 in professional assistance to develop the nutrient management plan, depending on the size of the operation and the complexity of the plan
- Enough fertilizer to meet recommendations
- $4–$6 per acre of application
Information from soil tests, cropping plans, and yield histories (used to determine field yield potentials) can be entered into computer programs to calculate nutrient needs. To meet nutrient needs, programs can balance added nutrients from multiple fertilizer and manure sources to prescribe amounts of nutrient sources to be applied. Some programs can identify field risk for nitrogen, phosphorus, and sediment losses while determining crop needs. This provides a nutrient plan that a farmer can take to the field for applications and to environmental professionals to discuss conservation plans.
Properly taken soil tests and crop yield responses provide a useful history. Crop response and soil test values can be used to understand localized nutrient responses. This history, along with on-farm trials, provides a valuable resource to use for the development of adaptive management recommendations. Recommendations can be fine-tuned from more regional recommendations to take into account a farm’s unique management system and soil resources.
Comparing the nutrient management plan to the actual result provides a record that can improve farm nutrient strategies. The farm can improve or define nutrient strategies that meet crop needs while preventing unneeded nutrient purchases. The goal is to continue to increase crop yields, improve nutrient use efficiencies, and lower soluble nutrients at the end of the growing season to limit environmental losses.