One thing is certain in animal agriculture. There is manure, and it happens year-round. But handling that manure changes with the seasons. Weather has major impacts on manure application strategies, and winter manure handling brings additional considerations. Snow cover, winter precipitation, frozen ground and winter melts all complicate the management of manure.
Climate change predictions indicate that wetter winters, more extreme storm events and weather variability will create increasingly challenging conditions for farmers needing to apply manure outside of the growing season. Manure management in the Northeast is only going to get trickier.
Peter Wright, formerly of New York State National Resources Conservation Services, addressed some of these concerns at the recent Dairy Environmental Systems and Climate Adaptation Conference, held at Cornell University. The impacts of climate change, Wright said, will be accompanied by increased environmental regulations, including water quality management. Decreasing the carbon footprint of agriculture will become a main focus, and mitigating greenhouse gas emissions and eliminating runoff concerns will play a major role in farm manure management decisions. With all of these pressures, managing manure with as little detrimental impact as possible will require changes in handling.
Manure is a nutrient-laden, all-natural fertilizer, and its use in crop production is an important part of the equation on most farms. Whether deposited by rotationally grazed livestock, spread in its solid form, stored and applied in its liquid form, composted, separated or anaerobically digested, manure in all of its forms needs to be handled appropriately.
Proper manure management will help to reduce runoff from fields, as well as to reduce odors and greenhouse gas emissions. Nitrogen and phosphorus, both present in manure and both of which contribute to eutrophication of waterways, can run off of fields,. In addition, volatilization of nitrogen left on the surface of the soil causes the release of nitrous oxide, a greenhouse gas.
“It is critical for farm managers to understand that while we may not notice a loss of a pound or so of phosphorus per acre, if there are enough farm acres in a watershed, this is enough phosphorus to potentially have significant impact on water quality,” Karl Czymmek, Senior Extension Associate, Prodairy Field Crops and Nutrient Management, Cornell University, said. “It is also critical to understand that phosphorus losses happen with or without manure application: fields that are fertilized and have runoff or soil erosion are contributors too.”
While manure isn’t the only contributing factor to runoff, proper manure application, year-round, is warranted. Managing manure through daily spreading, which is less and less common as farm size grows, eliminates the need for manure storage, but applying manure under adverse conditions is not an acceptable practice. If precipitation is predicted in the next 24-48 hours, soil is saturated, snowmelt is predicted, snow coverage exists, or when the ground is frozen, spreading manure isn’t a good practice.
Spreading manure in the summer, when the crops can actively utilize the manure nutrients, will become one standard method of reducing winter manure application concerns. Increasingly warmer summers will be conducive to double cropping, Wright said. Because less than optimal weather conditions for applying manure in the colder months are expected to increase, increasing manure storage volumes, separating out manure solids and covering liquid manure storage need to become standard practices, Wright said.
There are other risk factors which that intensify the negative impacts of winter manure spreading. Sloped land, proximity of surface water, tile drainage systems, inlets and ditches, liquid manure and lack of crop residue or cover all negatively impact manure application. The method of manure application also has a substantial impact.
While more farms store their manure in some form prior to its field application, situations still arise when the manure storage is full, and the manure needs to be applied to the crop outside of ideal conditions. Although solid-liquid manure separation and coverage of liquid manure storage will help to increase storage capacity, in general liquid manure is more likely to run off when spread on fields than is manure in its solid form. No matter the form, some states ban spreading during certain months, while others have restrictions limiting the conditions under which application can occur.
“Manure spreading in Vermont is banned from December 15th through April 1st,” Scott Magnan, a custom applicator in St. Albans, said. “Adequate storage through those months is needed. The farms in the area have made huge improvements to structures and in management practices to control runoff. If broadcast spreading is needed late in the year we try to apply to low runoff areas away from stream and waterways.”
Contact with the soil is important in preventing runoff from occurring. During spreading of manure, the time period during which the manure can dry is critical. Liquid manure is more likely to runoff after surface application, no matter the weather conditions.
“The main concern is that manure runs off of the soil when rain or snow comes. A period of time when manure is in contact with the soil, crop residue, or cover crops, without precipitation, reduce s the chances of runoff losses,” Bill Verbeten, of Empire Ag Imagery LLC, and formerly of Cornell Cooperative Extension, said. “Partially or fully incorporating the manure into the soil,” and doing so when weather conditions are optimal, are best practices for manure handling.
In the winter, getting manure into contact with the soil is complicated by the freeze/thaw cycle, and by snow coverage. Spreading on snow should be avoided, and rain and melting conditions lead to runoff concerns. Because new snow coverage can obscure where manure was recently spread, marking the end-point when spreading frequently can decrease overlap.
“In the past we have spread on snow covered ground, but as environmental regulations become stricter, this practice is avoided. We have been able to inject manure into one to three inches of frost with our current injector,” Magnan said. “If the frost becomes much deeper, we can no longer pull through. We have also had issues with frost when the top starts to melt and the tractor spins out on the slick surface.”
Injecting or incorporating manure into soils with this critical one to three inches of frost is one of the best tools for winter manure application. Spreading, too, works well during this occurrence, if it is done where significant crop residues exists, and if local laws allow. Some residues, such as hay, offer more protection from runoff than others, and heavier residue is preferred.
“It’s a wonderful way to apply manure,” Wright said of frost injection. “But it may not be a way you can count on,” moving into the future, as changing weather patterns may create less of an opportunity for the proper conditions to occur.
Proper conditions for frost injection develop rapidly. Above freezing daytime temperatures, plus bare soil and night temperatures which that fall below freezing combine to create the frost layer. This frost layer can support heavy equipment without compaction.
Magnan is purchasing a new injector this fall, which utilizes uses disks instead of points. This “cuts and rolls” instead of “pulling and ripping” through the frost layers, and the machine is designed specifically for these harsh conditions.
Equipment and storage preparation
“Equipment preparation is important, and all tanks and pumps should be drained at night. Plug in the block heaters on the tractors at night. A few minutes spent at shutdown can save you hours the next day,” Magnan said. “Accurate spreader calibration means less chance of runoff from over-application. GPS equipment helps in accuracy, and flow meters and valves on tanks allow rates to be set.”
Wright advised that farmers plan on separating manure solids out, capturing value for use in bedding. This also decreases manure hauling costs “because you’re not hauling all that liquid.”
Storage for liquid manure should be covered, eliminating rainfall and capturing greenhouse gases. Without covers, and without designing storage to account for the increased winter rainfalls predicted for the Northeast region, manure storage facilities will be inadequate. With winter field conditions for manure application also increasingly limiting application windows, combined with increased environmental regulations, farmers will be facing a crisis if manure storage capacity isn’t adequate. Filled storage leads to application at “inopportune times,” Wright said.
Management of tile drainage systems is another area which that Wright recommends improving. Blocking drainage after harvest, to allow the soil to absorb nutrients, and the use of bioreactors, joined to every tile line, are needed improvements to nutrient handling. Both phosphorous and nitrogen discharges from tile drainage will increase with warming trends, Wright said.
“Tile can improve drainage, but it’s impact on manure runoff can be quite variable,” Verbeten said. Increased
Tile drainage areas are already known to be hydrologically active areas of concern. Applying manure to fields where tiles are flowing from field drainage is risky as runoff issues are highly likely to occur.
If winter weather conditions are not optimal for manure application, yet storage is inadequate, reducing the manure application rate, applying manure to fields with the least chance for runoff issues, and applying smaller amounts of manure more frequently, rather than a large amount at once, are some recommendations to decrease negative impacts.
“Manure management is among the top priorities for farms that are positioning themselves for the future. This will mean having manure systems that can function in a range of expected weather conditions and enough manure storage capacity to avoid applications in poor conditions such as when the soil is frozen solid or when significant rainfall or snow melt is expected,” Czymmek said. “Anything we can do to keep soil, residual nutrients and manure on the land will help us to maintain productivity of farm fields and will limit offsite degradation where the extra fertility can create problems.”
Cover Photo Courtesy Scott Magnan