By: Pat Murphy
Yahara Pride Farms has initiated a long-term study of bedpack manure composting to document the environmental and agronomic performance of the practice.
The projected benefits of composting manure include:
- Prevent the land application of bedpack manure on frozen and/or snow covered ground where runoff is more likely to occur.
- Reduce the volume of manure that is handled decreasing the time/cost of land application.
- Increase the nutrient density of the compost encouraging the distribution of nutrients further from the livestock production facility.
During the winter of 2017/2018, 4066 cu. yds. of bedpack manure was diverted from land application to composting. During the winter of 2018/2019 an additional 2258 cu. yds. of bedpack manure was windrowed for composting. This action prevented an estimated 55 acres of winter manure spreading. Modeling done for the YPF Phosphorus Report estimates a reduction of up to 2 lbs. of phosphorus per acre, per year when winter spreading of bedpack manure is eliminated.
The volume reduction achieved by composting bedpack manure is highly dependent on the amount of carbon present in the material. Bedpack manure with high carbon levels (straw highly visible in the manure) can be expected to achieve a 50 – 70 percent reduction in volume.
Dense manure is significantly less efficient achieving a 30 – 40 percent reduction in volume. The reduction in manure volume and weight correlates directly to the reduced cost of transporting composted manure.
Additional unanticipated benefits
Soil sampling for the nitrate form of nitrogen below a temporary composting stack documented a minimal increase in soil nitrate levels (3 ppm. at 6-inch depth, 1 ppm at 12-inch depth) vs. 9 ppm in the adjoining cropland planted to corn (6-inch depth).
Minimal leachate runoff occurs from composting stacks that are being aerated (turned). Aerating the stack causes heating and a reduction in moisture and allows the stack to absorb precipitation that falls on them while being turned.
Farmers have learned that additional manure can be added to a compost stack that is being turned without disrupting the process. This alternative offers an additional manure management option when fields are wet or inaccessible. A heating compost pile also reduces fly problems that are typically associated with unmanaged manure stacks.
Overcoming resistance to widespread adoption
Farmers are conditioned to complete field work when operating conditions permit. If you wait, you may not get another chance to complete the field operation in a timely manner. Late winter field application of manure offers the benefits of frozen soil conditions (limits compaction risk) and a relatively low demand for labor/equipment.
Yahara Pride Farms estimates that the cost to build and turn a manure compost stack is slightly greater than the savings achieved by volume reduction and nutrient concentration. To achieve widespread adoption of manure composting, a combination of incentive payments and timely access to compost turning equipment will need to be provided.
The in-field composting of bedpack manure poses a significantly lower environmental risk when compared to field stacking of raw manure with low carbon content. Current temporary and permanent compost facility siting guidance is over-designed relative to the risk. The increased costs and limitations of the current policies reduce the viability of manure composting as an alternative best management practice.
The first turning of compost stacks this spring was delayed until the soil near and under the stacks thawed and firmed up. This delay increased turning efficiently, reduced rutting of the work area and did not significantly reduce the efficiency of the composting process.
The manure began heating immediately upon being stacked. The stacks continued to compost at a slow rate until the first turn which significantly raised temperatures and decomposition activity.
When composted bedpack manure is applied following the harvest of a hay crop, the plants respond immediately with vigorous regrowth. Topdressing hay with compost significantly reduces the amount of pathogens applied and will not burn the newly emerging shoots/leaves of the hay regrowth.
The microorganisms and stable carbon in the compost improves soil condition and provides less of a shock to the soil nutrient/organism equilibrium.
Yahara Pride Farms is considering augmenting finished compost with composted sewage sludge to increase the nutrient content of the mixture to more closely approximate commercial fertilizer. It is hoped that the increase fertilizer value will justify hauling the material greater distances from the farmstead, encouraging greater distribution of nutrients within and outside of the watershed.
An additional benefit is that all the nutrient sources contained in this material are generated within the watershed reducing the importation of commercial fertilizer sourced nutrients.
Pat Murphy is has been a member of AgriEnvironmental Advisors LLC since 2015, providing conservation planning and environmental assessment services to farmers and agribusiness. He provided state-wide leadership on conservation planning, resource assessment and development of non-engineering conservation practice standards as the NRCS State Resource Conservationist from 2001-2015. Pat consults with YPF on composting and other conservation initiatives for the group. Contact Pat at (608) 772-2602 or firstname.lastname@example.org