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We’ve already covered our thoughts on how we might better manage the undervine area, but now we want to focus on the bulk of the area of any vineyard, the midrow sward. Many vineyards I’ve seen practice what I call “recreational mowing”, never allowing the midrow grass to get very tall before mowing again. This certainly makes the vineyard look tidy, but burns diesel and employee hours, compacts soil, and, in most cases, is of no benefit at all to the vines or to wine quality. In this case, focusing on aesthetics has a tangible price tag, and perhaps less tangible negative effects on vineyard soils. That said, I’d rather have mowed grass than tilled out midrows entirely, which is sadly the norm in some vineyards.
Some vineyards in NZ choose to plant cover crops in their midrows, generally alternating them with grassed down tractor rows. The reasons for this are varied, including provision of habitat for predators/parasitoids of pests (shown in the NZ context by Wratten et al, 2012) and bees, nitrogen fixation, and soil carbon building. The standard method for full season cover cropping involves spraying and/or tilling out the row to eliminate grass competition before seeding the cover crop mix in the autumn and spring. Direct drilling into a grass row, even if it’s mown down very low, does not get the same strike rate and subsequent growth of the cover crop, unfortunately. Postharvest cover crops are seeded and grow all winter before they are mowed or tilled before budburst to reduce frost risk, and summer crops are mowed before harvest. If the seed bed is tilled before both plantings, it is unclear how much soil carbon gain this cover cropping method may offer, since disturbing the soil hastens organic matter breakdown by soil microbes. In a three year study we did in NZ, there was no carbon gain using a winter cover cropping regime versus grass. A potential better, and more cost effective, way to allow full season groundcover and to reap the benefits of cover crops, is to utilise a roller crimper, rather than a mower, to manage the cover crop rows.
Crimpers knock down and kill plants that have lignified, and require about 1/10 of the energy of a flail mower (Hunt, 1977). We want to emulate organic row crop production with this new midrow management paradigm (Kornecki, 2016). In this method, the terminated winter crop serves as a mulch/weed mat for the “cash crop” (summer cover crops for a vineyard), which are sown in the same pass, or shortly after, the crimping. Because the previous cover crop is left more or less entire, it breaks down much more slowly than mowed or tilled-in fragments, and so covers the soil and retains moisture for the germinating cover crop, which can greatly improve strike and growth in regions that have dry summers. It also suppresses weeds that would compete with the cover crop. At the end of the summer, the cover crops are crimped and the winter crop seeded into the stubble again. The process repeats each year, with the aim being a diverse cover crop sward that is active for as much of the year as is possible, and managed with a simple three-point linkage piece of equipment and no more tillage. This regime has the potential to speed carbon gains in soil and reduce fossil fuel usage, both of which move our vineyards towards carbon neutrality, or maybe even negativity. Our soils will benefit in terms of water infiltration, water holding capacity, and increased nutrient cycling, all of which will likely have positive impacts on the vines and the wines.
In this new management archetype, since the tillage only happens once at the outset, and because it retains soil moisture which can allow for more plant growth before the summer gets too dry in the unirrigated midrow, we hypothesise carbon gains will be faster than standard cover cropping and mowed grass.
We’ve done work with hemp as a cover crop, which grew relatively tall right next to Sauvignon blanc vines with no negative effect on productivity, fruit composition, or fruit health, so we do not anticipate huge devigouration of the vines by allowing permanent cover other than grass in New Zealand. We saw higher carbon (by combustion) at 40-80 cm in the hemp treatment, but not in the 0-40 cm sample. Perhaps a more diverse sward will have a greater effect throughout the soil profile.
Much like undervine cover crops, we’re curious to find specific species and mixes that work in well with a crimper regime. There are many in the regenerative community touting cover crop mixes with an exorbitant number of different species in a single mix, but we have our doubts on the efficacy of those compared to mixes with fewer species that are known to work in well together and are adapted to the soils and climate of the site. Finding a suitable mix that could be a jumping off point for those interested in dabbling with crimp rollers is all part of working towards information to support development of best practice resources for the community. At the end of the day, we’re farming grapes, and if trying to improve the soil comes at the expense of the quality or economic viability of the vineyard, we won’t be able to recommend the approach.
Applicable research that supports continuous improvement is all about sustainability, and we think some of these changes in management can be steps towards that goal. Looking after the soil in the vineyard in a thoughtful way will unequivocally have positive effects on the grapes and wine produced.
Hopefully we can secure some funding to start a sustainable ground cover programme. If we can get it going, we’ll certainly keep everyone updated via posts and this blog.
Watch this space.
Literature cited
Culman, S. W., Snapp, S. S., Freeman, M. A., Schipanski, M. E., Beniston, J., Lal, R., ... & Wander, M. M. (2012). Permanganate oxidizable carbon reflects a processed soil fraction that is sensitive to management. Soil Science Society of America Journal, 76(2), 494-504.
Hunt, D. 1977. Farm Power and Machinery Management—Laboratory Manual and Workbook. 7th ed. Ames, IA Iowa State University Press. 365 p.
Kornecki, T. S. (2016). The effects of combined cover crop termination and planting in a cotton no-till system. Applied Engineering in Agriculture, 32(5), 551-560.
Wratten, S. D., Gillespie, M., Decourtye, A., Mader, E., & Desneux, N. (2012). Pollinator habitat enhancement: benefits to other ecosystem services. Agriculture, Ecosystems & Environment, 159, 112-122.
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