Our composting program is a big part of our sustainability goals, allowing us to ‘give back” to our soils in a very natural way. Healthy soils lead to healthy vines, and healthy vines produce balanced fruit and vibrant fermentations.
The compost cycle is fundamental to life on earth, and fascinating to understand. In a well-functioning natural system (somewhat simplified):
Animals feed off plants.
Animal waste and other dead plant material are decomposed by microbiology into their raw constituents.
Another set of microbiology (“humifying” microbiology) then creates short and long chain humus (a clay/organic complex) that serves as a resilient and long term storage of nutrients.
A further set of microbiology, fed by sugar and other stimulants from plants, then breaks down the humus to release nutrients to feed the plant
This last step is crucial, and is the fundamental difference between natural and conventional farming systems. Conventional agriculture feeds the plant directly though the use of artificial nutrients (often mined or created as the by-product of industrial processes), bypassing the first steps in the cycle. While this can be a cost effective practice in the short term, it can do significant environmental damage, including acidifying the soil, breaking down soil structure, reducing soil carbon and increasing the chances of damaging nutrient runoff. Pre-settlement reserves of long and short chain humus in agricultural soils were quickly depleted, and now generally replaced by artificial substitutes.
At Yarrh, we’ve gone some way to replicating (and accelerating) the natural nutrient cycle by introducing a composting program. We use winery waste (eg stalks, skins, seeds from the vintage), manures, straw, green waste and a little clay, to produce a highly humified compost (replicating Steps 2-3 above), then spread this through the vineyard. This composting process takes about 6 weeks, and first goes through a breakdown process (Step 2) for about 2 weeks, then through a build up process (Step 3) where humus is created, and a stable state reached.
When spread in the vineyard the cycle continues, with soil macro and micro biology incorporating the compost into the soil and reacting to stimulants from plants to release nutrients (Step 4). Rather than force feeding the vines, we allow them to decide what they want and when they want it.
We don’t yet have a fully functioning natural system, but the place is certainly looking a lot healthier and happier over the decade we’ve been doing this. The vines are strong, worms thrive, clovers go mad, and our soil’s water holding capacity buffers us from dry and hot conditions. We still need to supplement the natural system at times, but at much lower rates than we’d done in the past - mainly a small, well timed shot of nitrogen in late spring when vine demand peaks.
"This year we’re experimenting with alternative under-vine treatments. I love having full grass cover all through the vineyard floor, with all the microbial/nutrient cycling, soil structure and “living mulch” benefits that this treatment provides. However, we do have some concern that grasses immediately under the vine can rob the vine of water and nutrients, particularly in a drier year. This year, we’re experimenting with varying under-vine covers to see if we notice any difference in the vine and fruit development – from fully sprayed out, partially removed and mulched. We’ll monitor vine vigour, take petiole tests (measurements of vine nutrition status) and ultimately measure fruit composition to see what we can learn. Research in this area is somewhat lacking."
Our experimentation was interesting - in a dry season (typical but not always the case) there was a definite impact on vine vigour from leaving full grass cover in place, with Cabernet being the most significantly effected, and Shiraz barely noticing. Now, in addition to cyclical mulch and compost treatments, we selectively use a knockdown herbicide in the spring, to just tip the advantage to our vines in the critical first few months of growth. The grasses bounce back and we get the continued "living mulch" benefits for the rest of the season. This year we're trialing an even softer organic herbicide treatment. Tilling remains an option, but I'm reticent to disturb our delicate soils.