Ever since technical manager Dan Swart arrived at Bosman Adama in 2015, he and his team have been working to build up the soils, because healthy soils produce healthy vines; and healthy vines produce healthy grapes.
The first vineyards commenced their organic conversion in 2016. Today 16ha of vineyards are certified organic, another 6½ ha are in conversion, but the entire farm is farmed regeneratively.
The Compost Tea Project
Until recently, organic fertilisers were only available in pellets. These need considerable amounts of water to dissolve, so when distributed in the vineyards in Spring, often the pellet does not dissolve properly due to seasonal rainfall tapering off, and so it isn’t able to feed the vines as planned.
The solution was to erect a compost tea plant whereby a ‘tea’ can be brewed and fed directly into the drip irrigation system running through the vineyards. The ‘tea’ is brewed using a starter pack. This ‘tea’ builds up the naturally occurring micro-organisms in the soil so that no synthetic chemicals need to be applied. A natural balance is established within the soil, allowing the entire ecosystem between soil and vine to maintain itself.
The starter pack contains billions of bacteria, fungi, protozoa and beneficial nematodes that grow and multiply in the tea brewing process. These feed on each other and then release metabolic by-products and nutrients such as Nitrogen, which is vital for a plant to photosynthesize and produce healthy, robust grapes. For the plant to digest the Nitrogen, it needs Carbon which is also provided by the fermenting compost.
In addition, these micro-organisms cause the soil particles to clump together, making the soil structure more porous and therefore having a better water retention capacity. Hence less water is needed, and that means less electricity is used to pump the water.
While chemical fertilizers contain Nitrogen, the plants need excessive water to digest it and eventually the soil becomes depleted of organic matter, whereas this process builds it up, making it more resilient and nutritious. The more carbon available in the soil for the microbes to digest, the more nitrogen is made available to the plant for photosynthesis.
The compost tea is made in two 5 000 litre tanks with aerating pipes installed at the bases, and heating elements suspended over the tops. The tanks are filled with water and the customized tea starter (made specifically by Ecosoil in response to soil analysis on the farm) is added.
As the microbes from the tea increase, so the oxygen levels decrease which is why air is constantly bubbled through the system by the pipes. The tea is heated to 25C by the elements to allow the fermentation process to start. 24 Hours later, an additional bag of tea is added. After a total of 48 hours, the brewing process is complete and the tea consists of nutrient material and a wide variety of beneficial bacteria, protozoa and nematodes. This solution is them pumped into a tank, driven to the vineyard and pumped into the drip irrigation system.
The compost tea has been applied regularly for just more than a year now, and already soil tests show that the levels of carbon in the soil have doubled.
A sure sign that our soils a becoming increasingly healthy, and that healthy soils produce healthy grapes that produce good, naturally made wines.
