At the moment, I am deliberating about the optimum time to apply compost and in what quantities.
In the spring, we applied 30t/ha immediately prior to a minimum tillage establishment of spring barley. But usually we plough and I do not want to invert the precious commodity eight inches under. So, my current thinking is to apply it to the second-year fertility building leys in the autumn.
The fungi-rich compost will be incorporated by the soil life and the nutrients captured by the variable root depths of the diverse ley. I am also reliably advised that 15t/ha on a regular basis might be more beneficial than infrequent applications of 30t/ha.
Making temperature-controlled aerobic compost is the closest I will get to alchemy. I source as much of the ingredients as possible from the farm. The windrows are made up of 30 parts carbon (straw, woodchip, and shavings from the horse livery) to one part nitrogen (horse manure, grass cuttings), with 10-20% imported green waste (Pas 100) and 10% clay soil.
The clay component is important, both as an inoculant and to promote soil aggregation which, by increasing the surface area, improves the soil’s capacity for moisture retention. Each windrow is approximately 40 cubic metres and is turned three or four times in the first two weeks whenever the temperature reaches 60-65degC. The composting process is complete within 7-8 weeks.
When I moved to Hemsworth in 2011, we faced a skewed organic rotation. All the fertility-building leys and straw had been auctioned off farm for several years in succession. The nutrient loss was compounded by it being a stockless system. It was a recipe for ever-diminishing returns.
The first remedial measures we took included importing hundreds of tonnes of chicken manure and mushroom compost. But this was never going to be a long-term, sustainable, desirable or affordable answer. During the first few years, I could not conceive of a way to make thousands of tonnes of compost on farm.
Then an alternative solution and the opportunity to join an Innovative Farmers trial presented itself. The trial was making and applying microbial inoculant (affectionately known as compost tea) to standing crops. The aim was to create a catalyst to increase microbial colonisation and thereby soil improvement.
Another reason for choosing compost tea applications was that it only required me to make 100kg of compost to brew 8,000 litres of tea, which is enough to treat 40/ha of crop.The three-year trials were interesting and instructive to participate in. But I learned more about the practicalities
of brewing and spraying compost teas than I understood about the complex science of how, why and when the applications did or did not
have a discernible effect.
We were very fortunate to work with the Organic Research Centre, Soilbiolab and Cranfield University, who designed the trial protocols and analysed the data. But after three years there were not enough consistent results of significance to warrant me making further investment in the system.
The compost tea trials have taken me full circle and we now make hundreds of tonnes of temperature-controlled, aerobically humified compost. There is a critical difference between rot and decomposition. The former is putrid, harbouring anaerobic bacteria and pathogens, while the latter is aerobic, fostering fungi and is sweet smelling.
Arable soils are often particularly deficient in fungi due to tillage and chemical applications. Humus-rich compost can stimulate soil biology, rebuild organic matter, restore carbon, reduce erosion, and enhance water and nutrient retention promoting plant health and disease resistance.
Including labour and depending on the ratio of imported ingredients, it costs me £5.50 to make one tonne of humus. Regular applications are an important part of our system in order to maintain optimum yields and continuously reinvest in soil health and resilience.