Activity means the difference between compost and air temperature. If excessively high compost temperatures higher than 28oC regularly occur during cultivation something has to be done with this activity. Too high compost temperature causes nutrient loss and quality problems during the first flush. Compost activity can be influenced by several factors. Firstly phase III compost always has higher activity than phase II compost. But even with incubated compost there are many differences. The longer compost is incubated in the tunnel the better colonised it is. Well incubated compost has a less noticeable temperature peak at the start of growth. The compost must have been incubated for at least 14 days but 16 to 17 days gives better consistency throughout the year. The filling weight also influences compost activity A filling weight of 95 kg/m2 creates more activity than a filling weight of 85 kg/m2 The minimum lower limit is 80 kg/m2.
Sheeting under the compost also gives more activity using perforated sheeting or omitting the sheeting altogether also creates fewer peaks in compost activity. A final factor is the amount of supplement added to the compost. The more supplement the higher the activity. Supplement amounts can vary from 5 kg/tons 18 kg/ton incubated compost (05 kg/m2 to 16 kg/m2). With supplements a good spread through the compost is very important.
Mark den Ouden, C point