Clover Clippings as Replacement for Chicken Litter in Compost
One of the elements of sustainable agriculture is reduction or elimination of off-farm inputs while maintaining soil productivity. A four-acre organic garden in Alabama has been enriching its soil with living mulches of clover and with compost which has depended on purchased chicken litter as the main nitrogen source. For a number of reasons the owners are questioning the sustainability of purchased chicken litter in their organic production system. The reasons include contamination risks, economic feasibility, and transportation problems. The growers speculated that they could mow the clover living mulch and use those nitrogen-rich clippings to replace the chicken litter in their compost.
1) Compare clover clippings with poultry litter as a nitrogen source for compost in terms of handling, cost and quality of compost as a complete fertilizer for organic vegetable production.
2) Determine the best carbon source for use in clover compost.
3) Determine if the fertility needs of a vegetable garden can be met by mowing and composting the clippings from a living mulch of white dutch clover growing in 2½-foot strips between the three-foot vegetable beds.
4) Host a field day to demonstrate clover composting to other growers and agriculturalists.
The project evaluated the use of clover clippings to replace chicken litter as the nitrogen source in compost. Normally the entire garden is planted with white dutch clover. At planting time the growers tilled the clover into the beds but left it growing in the walkways where it protects the soil from erosion and compaction, retains moisture, provides habitat for beneficial insects, suppresses weeds and adds nitrogen and organic matter. They fertilized the crops with compost made from organic matter (including clover clippings) produced on the farm and compared it with compost made from purchased chicken litter.
Comparable compost piles were maintained for one year. Some compost piles were made with chicken litter. The nitrogen source for the other compost piles was clover clippings. The goal was to produce soil fertile enough to grow vegetables without the use of off-farm nitrogen.
The study began in spring of 1995 when the clover was mowed, collected and piled for composting. A total of six compost piles were constructed: four using clover as the main nitrogen source and three using chicken litter:
Chicken litter/dried grass clippings, vegetable waste, straw, and other garden waste
Clover/dried grass clippings, vegetable waste, straw, other garden waste
Chicken litter/pine sawdust
Chicken litter/hardwood sawdust
Project investigators identified several differences in making compost with clover versus chicken litter. From a cost standpoint, the chicken litter must be purchased, while the clover requires only the labor to mow it. For two compost piles of comparable initial size, the costs were approximately $30 for a four-cubic-yard load of chicken litter as compared to $32 for four hours (at $8/hr) of mowing clover. The project farm is located in an area where chicken litter is readily available; the price might vary in other communities.
The piles were built by one or two people working on the ground with pitchforks and one person on a tractor equipped with a front-end loader. They discovered that the clover requires more pitchfork mixing than the chicken litter, which can largely be handled by the front-end loader. Subsequent turning of both piles is done with the front-end loader.
Making compost with clover clippings must be done within a limited time in early summer, which is already a very busy time for farmers. Once mowed the clippings quickly turn to slime if not combined with carbonaceous materials. The chicken litter may be stockpiled and used at a less busy time.
On this farm the clover provides beneficial insect habitat, protects the soil from erosion and compaction and suppresses weeds. Harvesting nitrogen by mowing the clover is considered a bonus, since the clover requires occasional mowing. For the growers the benefits of clover outweigh the advantages that the chicken litter has in terms of cost and ease of handling.
The compost piles were overwintered under fabric covers. Tests were conducted in June 1996 to determine amounts of macro- and micronutrients and organic matter in the finished compost. In experimenting with different carbonaceous materials the growers discovered that the hardwood sawdust immobilized nitrogen to the extent that it took much longer than the other piles to decompose. The hardwood sawdust piles were not analyzed for nutrients because they were not ready at the time of analysis.
The nutrient values of the compost piles made with a variety of carbonaceous materials were much higher than the other piles made with single ingredient carbon sources. Consequently, these compost piles made with clover or chicken litter will be the ones discussed below. Nitrogen and potassium levels were nearly the same in the two samples, but phosphorus was nearly three times higher in the chicken litter compost. Since soil tests indicated high levels of phosphorus in the soil (perhaps from past applications of chicken litter), the growers considered the lower phosphorus analysis of the clover compost to be a benefit. Copper was nearly three times higher and sodium and calcium were nearly twice as high in the chicken litter compost than in the clover compost.
The growers did not produce enough clover compost during the project to eliminate the need for other sources of nitrogen for the season. This was largely due to an extremely hot and dry summer, which limited the growth of the clover. However, the fertilizer values in the compost analysis indicate that the growers would need to produce approximately five tons of compost per acre for their four acre garden if they were to rely on the compost alone to supply the 80 to 120 pounds of nitrogen/acre that the garden requires. They produced approximately six tons of compost for the whole garden.
The growers decided that the clover compost was a better choice because: 1) the clover compost had comparable levels of nutrients when compared to the chicken litter compost but had significantly lower levels of phosphorus, sodium and copper which they did not want and 2) there was no real difference in cost between the clover compost and the chicken litter compost.
A field day was held June 4, 1995. The whole system of using clover as a living mulch in organic vegetable production was presented along with a demonstration of the composting project. The 42 attendees include farmers, extension personnel, consumers, home gardeners and one state agriculture department representative. The ripple effect of publicity after the field day resulted in a television report and two articles in magazines, plus several new members to the Alabama Organic Fruit and Vegetable Growers Association.
The project investigators presented a slide presentation at the Alabama Fruit and Vegetable Growers Association meeting and at the Southern Sustainable Agriculture Working Group conference. The investigators are also compiling a mailing list of people interested in receiving copies of the results at the completion of the study.