Site ManagementMajor considerations in site management are:
Soil ConservationTo manage land application of biosolids properly, you must control runoff and erosion. Erosion decreases soil productivity, increases sediment loads in streams, and could carry biosolids into surface waters. A well-managed permanent cover, such as pasture and hay crops, has the lowest potential runoff and erosion. To reduce soil erosion in row crops, tillage operations must be managed carefully. Improving infiltration and slowing water that flows over the soil surface controls erosion. Organic matter in the biosolids helps form stable soil aggregates which increases the porosity and infiltration rate of the surface soil.
Effective erosion control may require additional conservation practices. Appropriate conservation practices vary widely depending on crop, soil, landscape, climate, etc. Consult with your local Natural Resources Conservation Service (NRCS) office to discuss appropriate conservation practices for your site.
Highly Erodible LandCertain parts of Washington State are classified as highly erodible. Biosolids applications could conflict with required soil conservation plans if biosolids incorporation requires more tillage operations than normal. Before applying biosolids, growers should contact their local NRCS office to review their plan and avoid reducing surface crop residue levels below the requirement. Conflicts between biosolids application and conservation compliance are most likely in the drier areas (below 16 inches annual precipitation) that use a winter wheat-summer fallow system.
The following management practices help maintain surface soils on highly erodible sites:
Vehicle Traffic PatternOne option is to spread vehicle traffic as evenly as possible over the whole field. The other option is to use the same lane for all traffic, which reduces the area compacted, but requires remediation (such as subsoiling) on the lane itself. Where wind erosion is a problem, vehicle traffic should be kept away from the edge of the field to avoid dust problems.
Water ManagementMany agricultural areas face problems because of too much or too little water in the soil. To manage these problems, farmers drain or irrigate their farmlands. Both of these practices must be considered when planning biosolids applications.
Ground WaterGroundwater should be at least two feet below the soil surface, and static or receding before biosolids are applied.
IrrigationCrop yields are higher on irrigated land than on dryland, so the demand for nutrients is greater, allowing for higher application rates. Irrigation increases the potential for both leaching and runoff. Farmers can reduce leaching and runoff with an irrigation system that is properly designed and managed.
Practices that can reduce leaching and runoff include:
Application Equipment & Operation
Transfer EquipmentTransferring biosolids between vehicles and storage is by gravity or pumping, depending on the solids content of the biosolids and the position and configuration of the storage vessel.
The easiest way to unload a trailer from the treatment plant is by gravity. For gravity transfer:
MethodsThe suitable application methods for winter applications are:
Forest Application SystemsThere are three general methods for applying biosolids to forests:
Forest Application VehiclesMany application vehicles have been designed for agricultural applications, but can be modified for forest use by mounting a spray nozzle and pump on the tank. Application vehicles can also be custom-made. Depending on site needs, options include a specially designed all-terrain vehicle or a heavy-duty truck chassis with rear-mounted tank. Liquid application vehicles can be filled by a traveling tanker, directly from on-site storage, or may itself be an over-the-road multi-purpose vehicle that is filled at the wastewater treatment plant. Throw-spreaders or manure spreaders can be filled by loaders, or may be custom-fit with self-loading clamshells.
Calibrating Application EquipmentCalibrating application equipment is an essential part of biosolids application and record keeping. Because of the nature of the material and limitations of the application equipment, it is difficult to deliver the exact application rate planned. In most circumstances it is reasonable to expect actual application rates to be within15% of the planned rate.
Calibrate biosolids spreaders by determining the area applied per load. You can adjust either the ground speed of the spreader vehicle or the biosolids discharge rate. You will need truck scales to determine the weight of biosolids in the spreader, and a measuring wheel to measure the actual length and width of the application area in the field.
If you are applying liquid biosolids that vary in percent total solids, you will need to recalibrate the spreader as the solids content changes. Material with 4% total solids should be applied at half the rate of material with 2% total solids to maintain the same application rate in dry tons per acre. This recalibration is very important at low solids content, because a small error in calibration can result in a large error in the application rate.
At the end of each day you should verify the calibration by measuring the total area spread, and comparing the actual number of loads applied with the projected number based on area covered.
See our Spreader Calibration Worksheet.
For more detailed information see our Application Rate page.
Copyright © Washington State Department of Ecology|
Privacy Notice | Site Info | Accessibility | Contact the web team |