During the 2013 Pumper and Cleaner Environmental Expo in February, Bruce Fox, of Allied Septic Services, gave a presentation on the challenges of land application. He talked about allowable application rates based on the type of crop grown. Someone in the audience asked how the rate was established. Fox responded that his firm hired a professional crop consultant to establish the accepted rate of application.

The audience member followed up, wanting to know the precise method of calculating the application rate. The questioner talked about the need for a nutrient management plan. I thought it would be a good idea to explore the development of a nutrient management plan and all that is involved, and hopefully clear up how rates are established for land application of domestic septage.

According to the federal Natural Resources Conservation Service (NRCS) nutrient management practice standard 590, the purpose of such a plan is to “manage the amount [rate], source, placement [method of application], and timing of plant nutrients and soil amendments.” In Fox’s discussion he said that the land-applier should act and think like a farmer. Farmers understand and use nutrient management plans.

SETBACKS & EROSION CONTROL

In addition to establishing rates of application, nutrient management plans include other elements important to properly managing the application of nutrients to a crop. The criteria required of land application sites includes observance of setback distances for lakes, streams, drainageways, other buildings, roads, etc. Additional requirements establish runoff and erosion control measures to eliminate the impact on surface waters. And other conservation practices may be required and incorporated into the plan.

In terms of establishing the rate of nutrient application, standard 590 states “At a minimum, determination of rate must be based on crop/cropping sequence, current soil test results, realistic yield goals, and NRCS-approved nutrient risk assessments.” To make these determinations, most state land grant universities provide a crop and nutrient guide including established rates of application. So if you are interested in the nutrient recommendation for a given crop, this guide is the one to be consulted for your area.

Recommendations vary from state to state based on soil, climate and crop conditions, so what may be true for your location may not hold true in another region. Fox and I actually found this to be true for our two states, Pennsylvania and Minnesota. Pennsylvania does not allow application of nitrogen to alfalfa since it is a legume and has the ability to fix its own nitrogen. In Minnesota, nitrogen application is allowed since, if nitrogen is available, the alfalfa will use that input rather than fix its own, resulting in higher yields.

There are other good reasons not to land-apply to alfalfa, as the plants don’t stand up to traffic and have a susceptibility to frost heave problems. But this is a good example of differences between university recommendations.

The first step toward establishing a nutrient application rate is to determine a realistic yield goal. Realistic yield goals must be established based on historical yield data, soil productivity information, climatic conditions, nutrient test results, level of management and local research results considering comparable production conditions. Estimates of yield response must consider factors such as poor soil quality, drainage, pH, salinity, etc.

STATE RULES VARY

This was a part of the question from the audience because the expected yield on the grass crop was not what the questioner thought. As I just explained, the expected yield in Pennsylvania may be very different from Indiana or Minnesota. Other aspects that need to be addressed in terms of application rate are the source of the nutrients, how they are applied and the timing of the application to correspond with when the crops are able to use the nutrients.

Another feature considered the amount of residual nutrients available from previous years’ application. This is important for land application because as a biosolid is being applied, not all of the nitrogen becomes available the first year. So for succeeding years the residual needs to be considered as a part of the application program.

For land application, according to the federal 503 guidelines, nitrogen is the nutrient used to determine how much septage can be applied. So once the Maximum Allowable Nitrogen Application (MANA) rate is determined in pounds per acre per year for the specific crop, the amount of septage applied is determined by the following equation:

Maximum allowable septage application rate (gallons/acre/year) = MANA divided by 0.0026

0.0026 is a constant based on an average amount of nitrogen per gallon of septage as determined by the U.S. Environmental Protection Agency.

Hopefully from this discussion you see that the nutrient management plan needs to be developed for your specific location and crop, in accordance with your state and local requirements, and that what is appropriate for another state will probably not apply in your state.