Composting for Disease Suppression

PROJECT BACKGROUND
Harmony Valley Farm has a long history of compost production and use as a nutrient source for production of organic vegetables. Early composts were made form horse manure and bedding. Dairy manure with straw bedding, and later sheep manure with hay and straw bedding was used. All materials were from on farm animals. In 1991 all animals were sold and vegetable production increased from 20 acres to 50 acres. We purchased a heated and dried poultry manure for several years. Our subjective observation was an increase in weed germination and growth and an increase in foliar diseases. We also saw some research findings reported in the IPM Practioner that suggested disease could be suppressed by certain well made composts. (Quarles and Grossman, 1995)

We decided to go back to farm produced compost. With the aid of a 2 year grant from Wisconsin Department of Ag Trade and Consumer Production we trucked 300 ton of raw chicken manure, spoiled hay and sawdust bedding from a nearby bull breeding farm. During the course of that year we found our method of mixing and turning compost with a front end loader and manure spreader to be too slow for optimum making on this scale. In the spring of 1997 we purchased a used wildcat compost tuner and an IH Hydro 70 tractor to pull it at the necessarily very slow speed.

During a summer of 1996 visit to our farm our interest in demonstrating the disease suppressive potential of compost was shared with Dr. Bob Goodman. The ensuing relationship resulted in our 1997 compost field study.

PROJECT DESCRIPTION AND RESULTS
In the spring of 1997 we procured composting materials from 2 near by farms, goat manure with hay bedding and dairy manure with hay and corn stalk bedding. We also purchased additional stacks of corn stalks as an added carbon source.

As a result of research provided by Beth Kazmar we had a goal of achieving a carbon to nitrogen ratio of 20:1. We found it physically difficult to mix in enough cornstalk to achieve our goal with the high nitrogen goat manure. The goat compost started at approximately 15:1 and cow compost at 20:1.

We turned the windrows weekly for 8 weeks. Turning was initiated when temperatures, as monitored with 3 ft probes, started to fall from peaks of 140-150 degrees, and oxygen levels feel to 5-6%. After turning oxygen levels measured 12-20% and heat would return to 130 degrees after 24 hours. In early July the composts were heating to only 100-110 degrees and windrows were left to cure.

We chose to use the mid summer planted crops of turnip and winter radish because we thought it would give us sufficient time to make finished compost before planting. The time we allowed may not have been sufficient enough to cure either compost optimally; the goat manure, in particular, heated to higher temps and for a longer period than the cow manure.

The turnip and radish crops were chosen because, in addition to an advantageous planting time, we had observed a history of disease occurring in storage with both of these crops. Beth Kazmar had identified the diseases on the 1996 crop after several weeks of storage. With this history we expected to find several disease complexes on these crops again in 1997.

Test Plots
In July we spent considerable time calibrating our Knight Slinger spreader to ascertain the exact spreading rate at various speeds and gate openings. We secured sheets of fabric to the ground at measured distances from the side discharge spreader. We loaded the spreader with compost, weighed the spreader, spread the compost over the area where the fabric had been placed. We then weighed the compost left on top of the area covered by the fabric sheets, and we weighed the spreader with whatever compost remained in it. Through this process we were able to achieve a measurable degree of accuracy on the test plots. Test plot layout and design are described in table 1.

[Editor’s note: there are charts and tables that could not be posted online. If you would like to see these please email us at ncrsare@umn.edu or call us at 800-529-1342. Thanks]

On July 20th, when the field was ready, compost was spread from both sides of the plot. Total amount of compost was calculated to closely equalize the available nitrogen from the compost to that available from the NPK fertilizer was spread with a cyclone broadcast spreader.

A 3” rain delayed planting until August 5. Planting was done with a Stanhay belt spreader.

Weed control was accomplished with 2 cultivations and 1 pass with a Lely flex-tine weeder. The plots were virtually weed free.

Yield Results
Research that we have seen that showed disease suppression involved a high percent of compost in nursery media and per acre field application of compost as high as 93 tons. (Quarles and Grossman, 1995). Our application of 10 and 15 tons per acre compost was chosen because it is a realistic amount to use on a larger scale. Also, we feel it is significant to note that the test plots were on land that had a previous history of compost applications and incorporations of green manures. In this situation, it is not surprising to see only small differences in disease incidence between plots. The more than 10% yield increase in the Misato winter radish does have significant economic implications for out farm.

Our winter radishes store for several months and we’re able to sell them wholesale for $.50/lb. With a 10 ton per acre yield this 10% increase gave us $1000/acre increase in gross sales. Our harvest and packing costs run around 25% of sale price. So 10% yield increase gives us $750/acre net increase. If we could accomplish this increase on even half of our 50 acres it would mean a net profit increase of $18,750 for our farm.