Compost Update: Nov. 23, 2014

• When is a compost windrow (thermophilic compost) or a vermicompost ready to be applied in the orchard at Frog Hollow? Thermophilic composts have to reach a temperature of 130 F or more for three days and then have to be turned. This cycle continues for 15 days and the goal is to make sure that all parts of a windrow have been exposed to a temperature of 130 F or more. This is a way of killing most weed seeds, plant pathogens and human pathogens. On average the thermophilic compost at Frog Hollow is ready for application after 3 months of composting. After the heating cycles have subsided, there are several options to assess compost stability and readiness for application. First and foremost the windrow temperatures are checked to ensure that they are at 110 F or less (ambient temperatures are perfect), ammonia and carbon dioxide emissions are checked using colorimetric kits. Finally, the most important test is a biological analysis of a sample for the presence of bacteria, fungi, protozoa and nematodes. If the total biomass of these microbes reaches certain levels (indicating diversity), if the active part of the microbial biomass is at 10% or less (indicating stability), I conclude that the compost is stable and can be applied in the orchard. The colorimetric chemical tests for ammonia and carbon dioxide are used to confirm the biological analysis. I use the same tests (except for temperature measurements) to analyze vermicompost maturity.

•Applying immature compost can cause several problems. When the temperatures in a compost windrow are higher than 110 F, this is an indication that the microbes have not finished decomposing all the materials in the compost and consequently this compost will not immediately supply nitrogen and other nutrients to the roots of plants (at this time of the year the roots are storing energy reserves for the spring). If this immature compost contains a lot of carbon material (wood, cardboard, brown leaves), the microbes will scavenge soil nitrogen in order to decompose the woody material and this can cause nitrogen starvation in roots. Immature compost may contain phytoxins that can negatively affect root metabolism; phytoxins (such as very high ammonia levels) are produced naturally in a compost but have to be given time to be degraded. Immature compost does not have the ideal ratios of the various microbes because the metabolic activity is too high and will not be beneficial to the tree roots when applied. If the microbial activity is too high, roots can become starved of oxygen and this can promote the growth of pathogenic anaerobic organisms in the rhizosphere (region of soil where roots and microorganisms directly interact). Immature compost does not have an immediate effect on tree roots but can cause rapid phytoxic reactions in vegetable crops.

•No single parameter can give a sure indication of the stability of a compost. However, biological analysis coupled with temperature measurements is one of the best indicators of a good and stable compost.

•A new vegetable block will be planted in December and we are waiting for a compost windrow that was started on August 27th to cool down to 110 F or less. It looks like this compost will be down to 110 F at exactly 3 months.

•Next month planting holes have to be prepared for 700 new trees. The holes will be filled with compost and worms prior to planting. We have to estimate how many worms are presently available in our vermicompost beds. We also have to plan for the future and start breeding more worms (more on this in future blogs). During the summer months, the compost worms produce three cocoons per week. Each cocoon (can be compared to an egg) produces three hatchlings or 9 hatchlings per week per worm. I estimate that each cocoon takes 5-6 weeks in the summer at Frog Hollow Farm to mature and hatch. In 6 weeks, 54 hatchlings are produced per worm. In the winter, it probably takes 12 weeks to produce that many hatchlings. Next week we will have an estimate of how many worms we presently have at Frog Hollow. This number will probably be 2-3 million worms.

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