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COMPOST Don’t jump to conclusions


There are as many opinions as there are composters. With so many different composting proces- ses used all over the world, providing cut and dried answers and solutions is almost impossible, even though the opposite might seem true. I would like to use some examples to encourage rea- ders to investigate whether their apparently smooth composting process really is all it appears to be.


By Jos Buth, Mushroom Advice Network josbuth@gmail.com


Ammonia in relation to tricho- derma At a recently held meeting attended by a large audience of professional composters from all over the world, their unanimous answer to the question of whether there is a correlation between high or low ammonia values during pasteurisation and tricho- derma infections was a resounding: ‘no’. The shared opinion was that good hygiene is the most important weapon in keeping compost trichoderma-free and that there is no correlation between ammonia during pasteurisation and trichoderma. But is this true? On some companies, I notice signi- ficant correlations between the ammonia concentration during pasteurisation and trichoderma infections. On large, old com- panies using wooden trays and with very poor hygiene management and tunnel qua- lity that leaves a lot to be desired (a more common situation than you might imagine) I certainly do see a relationship between more ammonia and less trichoderma. Note – lower infections with higher ammonia


values! On modern tunnel plants that have optimal hygiene levels, you are unlikely to see any correlation between ammonia concentrations during pasteurisation and trichoderma infections as the strict hygiene reduces the infection pressure of tricho- derma to zero. Well constructed, properly functioning tunnels make an important con- tribution in this respect. Everything seems to be under control. On less professionally managed companies with poor quality tunnels, the relationship between ammonia and trichoderma is demonstrable. Com- mercial composting plants can also use this knowledge to their advantage.


Is a composting process that uses aerated floors from start to finish superior to a com- posting process with phases without aerated floors (wind- row composting)? The wording of the question influences the answer. The obvious answer is ‘yes’, but things are not that simple: on many


Windrow composting can be very successful provided extra attention is paid to the oxygen supply.


composting plants there are certain times when the horse manure, or already mixed raw materials (i.e. compost), are placed on concrete floors without any extra aeration. Whether the compost is stacked in a huge pile or formed into windrows obviously makes a difference. Many variables deter- mine the oxygen supply in the compost. In the USA I noticed with other professional composters an unmistakable difference if, immediately after adding poultry manure, compost is filled onto an aerated floor or not. With forced aeration, the compost tem- peratures rose higher during the bunker process and the high ammonia concentra- tion was dispersed easily from the compost during curing. The compost seemed to be better incubated with better pinhead formation – larger pinheads and a well- emerging first flush. Production was higher, at approximately 4.5 kg per m2 more. Until ... the opposite was proven true on another company. One of the larger companies in the USA, with two composting plants, equipped one plant with aeration in each stage of the phase 1 process, while on the other plant at the start of the process the compost spends a couple of days on a solid floor. The results there are identical. We shouldn’t jump to conclusions however. The significant difference between compos- ting on an aerated floor from start to finish of the process and a composting process with some days without forced aeration just after adding poultry manure usually makes that very clear. That the opposite was proven on another company has more to do in my opinion with the many other factors that influence the final results – for instance, how many times the material is turned with a compost turner. On another large site, where we ran a number of tests with forced aeration on the same day that poultry manure was added to the straw, we witnessed clearly large differences with more positive results. Some composters pre-wet straw or other raw materials like


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