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Good compost made better By Christine Ziegler Ulsh with Paul Hepperly, PhD |
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April 13, 2006: For many organic and sustainable farmers, compost is a sensible way to dispose of animal manure and crop waste and, at the same time, add organic matter and crop nutrients to the soil. The composting process is older than agriculture itself, having occurred in nature long before humans began to cultivate crops. Over the past decade or so, farmers and soil scientists at The Rodale Institute and other organizations began working together to make advances in compost technology, finding even safer and more effective and sustainable ways to convert waste materials into resources that build healthier soil with more balanced fertility. And now The Rodale Institute’s most recent research has the potential to take compost science one huge step forward: We’ve developed a new approach to composting, using amendments designed to mimic natural soil-forming processes, in order to keep more crop nutrients—particularly nitrogen and phosphorus—in the compost and out of the rainwater that washes through exposed piles during composting. Our goal is to keep these nutrients working for us on our farm and out of our streams, rivers, ground waters, oceans and air. With funding from the Pennsylvania Department of Environmental Protection (PA DEP), we began an experiment in 2005 to see how three different kinds of compost hold nutrients both in the pile and in the field, and how each affected crop responds. To date, we’ve compared the nutrient content, nutrient runoff and bacterial output of these three composts—broiler litter alone, standard broiler litter/leaf compost, and our new recipe—during the composting process. The results have been encouraging, indicating that our new recipe—which incorporates clay, calcium, and humic acid amendments in a standard leaf/ manure mix—has reduced nitrogen (N) losses from the compost pile by up to 90 percent and phosphorus (P) losses by up to 75 percent. The amendments also appear to accelerate compost maturation and reduce bacterial pathogens in the finished product. More benefits, similar procedure Fortunately for farmers and commercial composters, our new recipe doesn’t much change the process of making compost, which is very simple:
Compost can’t be beat as a means to recycle farm wastes such as manure, bedding, old hay, leaves, sawdust, and the like. And because it is such a valuable soil conditioner, compost also meets another criterion of farm friendliness: It solves two problems with one modest operation. As the years have progressed, agricultural science has learned more about why this simple process works and about how to tweak the handling and the components—material composition, particle size, moisture, pH, pile size, and turning method and schedule—to make a better product more quickly. Our own Compost Utilization Trial has shown that, while compost, synthetic fertilizer and raw manure each support competitive crop growth and yields, only compost significantly improves soil organic matter. Soil organic matter is the key to conditioning the soil for better performance during drought and guarding against excessive nutrient runoff in wet conditions. Only in recent years, as excess agricultural nutrients increasingly pollute the nation’s waterways, have people begun to question: How does compost affect the nutrient pollution picture? What quantities of nutrients are lost when compost is applied to the field? And what quantities of nutrients are lost during the composting process itself? Compost reduces N losses The Rodale Institute answered the first of these questions as part of its 10-year Compost Utilization Trial (CUT). Using lysimeters to collect water that passes through the crop root zone and soil of a farm field, CUT researchers determined that compost reduced nitrate nitrogen losses by 60 percent when compared with chemical fertilizer and 70 percent when compared with raw dairy manure. What’s more, the amount of nitrogen that remained in the soil after harvest was 4.5 times greater in the compost fields than in the chemically fertilized fields, and 1.5 times greater than in the fields fertilized with raw dairy manure. (Check out The Rodale Institute publication Water Agriculture and You for more detailed information on this landmark study.) Now, as part of our PA DEP-funded grant, we are also answering the second question by composting plain manure and our two different compost mixes on concrete drainage pads designed to capture any water that runs through the compost pile. This approach allows us to precisely measure nutrients and bacteria that are washed out of the compost as the piles mature.
Our three compost recipes are: 1) a standard mix of three parts leaves and one part manure; 2) our new (patent pending) amended mix that incorporates 14 cubic yards of leaves, 4 cubic yards manure, 2 cubic yards clay (taken from our farm subsoil), 90 pounds of gypsum (calcium), and 110 pounds of humic acid (leonardite coal dust); and 3) a plain manure “compost” (no leaves or other carbon materials added, with the exception of minimal bedding materials), which represents a worst-management scenario. Poultry manure (broiler litter) was used as the nitrogen source for the first round of compost in this study, which was initiated in May and finished in October of 2005. Data from the first part of the trial showed that, under slightly-lower-than-normal precipitation, the poultry manure (alone) leached 70 percent more ammonium nitrogen and 25 percent more ortho-phosphate (ortho-P) than standard composted manure. But when reported in actual weight, these nutrient losses were quite small; even the manure alone leached only 2.4 ounces of ammonium N and 1.4 ounces of ortho-P from a 20-cubic yard pile. Downpour reveals big differences However, after an extreme precipitation event in October—during which the farm received 10 inches of rain in two days—the manure-only pile lost 95 percent more ammonium N and ortho-P than either of the other composts. And the weight of the nutrients lost was more alarming: The manure-alone pile lost 18.3 pounds of ammonium N and 74 pounds of ortho-P, while the standard compost lost only 18.2 ounces of ammonium N and 49.9 ounces (3.1 pounds) of ortho-P. These results clearly show that, to prevent nutrient loss, standard compost is a superior way to manage manure waste and apply its nutrients to the field—far better than piling and applying manure by itself.
But our specially amended compost performed even better. During the summer period with lower rainfall, the amended compost lost 85 percent less ammonium N than the standard compost (only 0.11 ounces) and 71 percent less ortho-P (0.32 ounces). And after the extreme rain event, the amended compost leached the same amount of ammonium N as the standard compost (19.4 ounces) and 39 percent less ortho-P (30.56 ounces, or 1.91 pounds). This data demonstrates that the amended compost is a significant improvement over the standard compost recipes of old. We are currently performing a second round of compost-pad studies—using dairy manure as the nitrogen source for the compost—to corroborate our initial test. Thus far, the dairy manure has shown results consistent with broiler litter, with a large and clear advantage for amendments, including less leaching and even faster processing. Dairy manure also seems to offer more rapid and complete composting than broiler litter. During the coming 2006 growing season, we will apply both the dairy- and poultry-manure-based composts, along with raw dairy and poultry manure and chemical fertilizer, to corn fields fitted with lysimeters to see if the amended composts hold nutrients as well in the field as they do in the pile. We also incorporated the composts into potting mixes that we’re using to grow lettuce and test the composts’ influence on plant growth and nutrient content in the greenhouse. The development of the clay-calcium-humic acid compost amendment tests the theory of soil organic matter stabilization and soil aggregation proposed by Frank Stevenson, PhD, at the University of Illinois. New recipe shows some surprise benefits The amendment mix is designed to accelerate biogeochemical processes involved in soil aggregation. The reaction uses calcium ions (Ca++) as mortar to electrochemically attract and bind negatively-charged clay and humic acid particles, generating soil aggregates (or clumps). Clumps of soil, clay, calcium and humic particles create the storage structures needed to bind nutrients, thus preventing their loss through leaching or volatilization. In this way, the nutrients are captured in stable forms that resist losses to water and air but are available over time to help plants grow and develop. Our data indicate that this particle-and-nutrient binding process can have multiple benefits, some which came as a surprise.
First, our amendments trapped odors much more effectively than we expected. Amended compost cut the odors from the poultry manure within 10 days; more quickly than standard compost (long recognized for its ability to reduce odors), which took six weeks. Thus, the amendments could allow composters to work in urban environments without offending the neighborhood. Second, we found that the amended compost aggregated (clumped) conclusively within its first 10 days, again more quickly than we had hoped.
Third, the more stable N in the amended compost provided little food to support bacteria such as the E. coli pathogen (found in manure). Thus, E. coli was eliminated from the water that ran off the amended compost pile after only six weeks. The standard compost eliminated the E. coli by 12 weeks, and the poultry manure alone still leached it after six months (and probably still leaches it at the time of this writing). This data suggest that compost, particularly the amended compost, can go a long way to reduce potential pathogens, as well as excess nutrients, in the water supply. Fourth, the E.coli was eliminated by immobilization of organic nitrogen, rather than by pile temperature. We allowed pile temperatures to settle close to ambient temperature before turning and actually turned the piles only three times over their six months on the pads. Our goal in turning less often was to reduce N volatilization, but the reduced work load and elimination of E. coli are equally important benefits.
Fifth, because the amendment mix reduced nitrogen losses from the pile, N:P ratios were higher in the amended compost than in the standard compost or plain manure. This fact has very positive implications for field application, because higher N:P ratios allow farmers to apply more compost to satisfy a crop’s N requirement without over-applying P (which is usually over-abundant in our local soils). Finally, the amended compost was “finished” about 12 weeks earlier than the standard compost, based on temperature and soluble salt measurements (the manure-only pile is still far from being finished). The amendments quickly yielded a light, well-crumbled mixture that made a lovely potting mix (a bit more uniform in texture than the standard compost) and that is easier to apply due to its drier texture and granulation. By mixing the theory of a professor with some experimentation,
we are cooking up innovative changes in compost technology and performance
that promise to help farmers and regulators better deal with nutrient
loss issues, improve their soils, and protect our ground and surface
water resources. As more data comes in, we’ll update you on
the results and benefits of our amended compost. |
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