Compost Handling in Agriculture Systems: Compost Transfer and Equipment Calibration

By Erica Rogers and Sarah Fronczak

Arranging for timely and safe application of compost once it has been delivered can help to safeguard maximum nutrient absorption by the soil and aids in reduction of environmental risks due to pile runoff. Michigan State University Extension recommends having a plan in place for transporting and applying compost before it is delivered or ready.

For compost that is not applied at the time of delivery, proper storage must be utilized as referenced in part 3 of this series. This includes the safe transfer of finished compost between locations, accurate calibration of spreading equipment, and the potential environmental implications that exist.

Understand and maintain transfer and application equipment of finished compost

One of the first things to consider is the type of equipment you plan to use for transferring and/or applying the finished compost. It may sound simple, but this is important in helping to prevent potential spills, which can ultimately affect surface waters and groundwater. The following are questions you should ask yourself:

• How much volume can the equipment safely hold?
• How will the compost be loaded into the transfer equipment?
• Do I have a route mapped out for getting the compost from point A to point B?

Be safe on the road and be aware of current road conditions

Michigan State University Extension recommends that applicators consider other safety precautions that should be taken into account such as current and forecasted weather conditions as well as road conditions. Rainy conditions may cause hydroplaning and poor visibility on the roadways, which could lead to accidents and spills. Winter weather including snow and ice, may cause roads to become slick and difficult to drive on, which could also lead to accidents and spills.

Other safety precautions include overall awareness when operating the equipment to transfer the finished compost. Nowadays, it is easy to become distracted while driving via texting, eating, and even being tired. Another important consideration is taking time to plan the best route possible, which may look like avoiding bridges and other surface water to reduce or eliminate any risk to water quality in the event of an accidental spill. Also, consider detouring around highly populated spaces like schools and hospitals to reduce odor complaints even though finished compost should have little to no odor. It is crucial to always share your plans to spread and the planned route with a trusted employee or family member, so if there are issues with equipment, someone knows your location.

Stockpiles must be properly managed

Another consideration when transferring finished compost is whether it will be land applied right away or stockpiled until land application occurs. If the compost will be stockpiled, it needs to be managed in a way that:

1. No leaching of nutrients from compost impacts the groundwater (meaning nutrients drain away from the compost and into the soil, eventually reaching the groundwater) and;
2. No contaminated runoff will flow onto neighboring property or into surface waters.

Additionally, it is important to protect the pile from excess moisture from both an environmental standpoint and a compost recipe standpoint. Too much water added to the pile can cause the compost recipe to be off, which can then cause odor issues. Additionally, the stockpile must be moved around from year to year in the field to allow vegetation to grow back from where the previous pile was located.

For more information about appropriate transfer practices, the Manure Hauler Certification Program can be utilized as a reference. While the Manure Hauler Certification Program discusses manure, many of the same principles can be applied to the transfer of finished compost.

Calibration of Spreading Equipment

Before any compost is applied, the spreader must be calibrated. Spreader calibration ensures that the right amount of compost is applied to achieve the desired soil health and plant protection. Spreader calibration also reduces the risk of ground and surface water contamination. Instructions on how to calibrate a large volume spreader can be found here.

A simple method can be used to determine the application rate for a small volume spreader. The first step is to determine the bulk density of the compost. This is done in three steps as follows:

• Step 1:  Weigh an empty 5-gallon bucket.
• Step 2:  Fill the bucket even to the top with compost and weigh the bucket. Repeat this step (at a minimum) of three times with new compost and average the weights.
• Step 3:  Subtract the Step 1 weight from the Step 2 weight and multiply by 40.5. The result is a bulk density of pounds per cubic yard.

The second step is to determine the volume of compost applied when the depth of application is known. A one-inch layer of compost applied over an acre always equals 135 cubic yards (assuming complete and uniform coverage and no compaction). For example, if a given compost has a bulk density of 500 lbs./cubic yard and a one-inch layer is applied over an acre, that one-inch layer equals 33.75 tons/acre (see calculations below).

• 135 cubic yards/acre X 500 lbs./cubic yards = 67,500 lb./acre
• 67,500 lbs/acre ÷ 2,000 lbs./T = 33.75 T/acre

The amount of compost applied, and the equipment used to apply it, depends on how the compost will be used. For example, blower equipment should be used to apply compost on steep slopes to hold the soil in place and stimulate plant growth for erosion control. When compost is used as mulch in an orchard, a small capacity side-discharge tractor-pulled spreader should be used. In both examples, different volumes of compost will be used to achieve the desired outcome.

Choosing the proper equipment for its intended use is critical in maximizing the benefits of compost. Compost can be applied with spinner, rear and side discharge spreaders, and blowers. Small volume spreaders are designed for locations such as orchards, vineyards, and small-scale vegetable growers, while large volume spreaders are typically designed for field crop use.

Records of compost application must be kept to be in conformance with the Michigan Department of Agriculture and Rural Development Right to Farm Generally Accepted Agricultural and Management Practices (GAAMPs) for Manure Management and Utilization, especially when finished compost is used as a nutrient source. The necessary compost application rate needed to meet the nutrient requirements of a planned crop are determined based on:

• Estimated crop yields
• Compost analysis for nutrient content
• Current soil test results

At a minimum, the following records should be documented on a per field basis: soil test results, dates of compost application, rate of compost applied, previous crop grown, yields on past harvested crops, and weather conditions at the time of application. In addition, the method used to calibrate the spreader and the date in which the spreader was calibrated should be documented.  

It’s important to remember that spreader calibration should be completed before any compost is land applied. Calibrating the spreader ensures that the proper rate of compost is applied and prevents the risk of ground and surface water contamination. Matching the right kind of spreader with the intended use maximizes the benefits of the compost. Finally, to be in conformance with Right to Farm, compost application information must be documented.

How much compost you apply, or the rate of application, depends on your nutrient management plan and will be discussed further in part five of this series.