Mother Nature took pity on us this year when she decided to bless us with solid soaking of rain in the third week of April. The heavens opened on the 22nd of April and, cumulatively over two days, dropped a glorious 48 mm of rain on our thirsty vineyards. In comparison to what little rain fell in April of 2015, which was only 10mm, we were truly blessed by the rain gods! The rain we received created perfect conditions to sow our cover crop which will grow into the colder months of this year before our vineyards start to bud in Spring.
Why, you may ask, are we sowing a crop when we are already nurturing vineyards to produce grapes for fine wine? Sowing a cover crop in our vineyards has a multitude of benefits and is an integral part of our integrated soil and weed management strategy, both of which have a direct impact on grape quality.
By sowing a cover crop which is quick to germinate, after we have ploughed the soil, these tiny plants quickly grow and compete with many of the cooler season weeds which take advantage of the rains we have just had. Many open fields you drive past in the winelands at this time of year are already yellow with the flowers of such a weed called Ramenas or Wild Mustard. The cover crop we have chosen will germinate rapidly and very quickly outgrow weeds like Ramenas in our mid-rows and under our vines.
Our choice in what we sow as a cover crop was based on a few important factors and some lessons we have learnt in the previous year. We have chosen two different seeds this year, Bitter Lupins and Vetch or Wieke.
Bitter Lupins have hollow stems and an upright growth habit. Eventually these plants will be waist high and bear beautiful baby pink and lapis lazuli blue flowers closer to Spring time. The other seed choice Vetch, a much finer plant, has a creeping growth habit. By planting it with these Lupins not only will the Vetch creep along the surface while it grows it but also climb the Lupin stems to further develop a thick mat which helps to smother competing weeds underneath this mat.
Another important attribute that both Lupins and Vetch share is a special ability to form a symbiotic relationship with Rhizobium bacteria present in the soils. These bacteria are housed and protected in nodules on the plants’ root systems and in exchange for the housing and protection, these bacteria take inert Nitrogen, a form of Nitrogen plants cannot use, from the atmosphere and produce Nitrogen in a form the plant is able to use for growth. This marvellous symbiotic relationship turns these, seemingly, ordinary plants into plant-food factories. The beauty of this relationship is that any excess nitrogenous compounds produced by the bacteria that plant doesn’t need, are released back into the soil for our precious vines to access.
Conventional vineyard management calls for a full surface herbicide spray in spring time which kills weeds and the cover crop you have sown, to eliminate competition with the vines as they awaken from dormancy after a cold winter and begin to bud. We choose to leave our cover crop later than most, into the first portion of spring to allow seeds the cover crop has produced to ripen. Instead of spraying harsh soil damaging chemicals to kill the cover crop in the mid-row, as budding begins, we roll our mid-rows flat with a big, heavy roller.
By using Lupins and Vetch, as described above, the Lupins which have hollow stems will be rolled flat and the ripened seed pods will lie dormant in the soil until the following season and self-sow, thereby reducing our need to sow more seed the following year.
By choosing to use this roller and flattening the plants in the mid-rows we also have the added benefit of these flattened plants forming a thick mat of vegetative material on the soil surface. These flattened plants will eventually breakdown and increase the organic matter content of our soils thereby increasing soil health and richness. This also means that the root systems our Lupins and Vetch will remain intact and provide small channels in the soil. These channels that are formed help with water infiltration and keep our soils friable and soft. We found that we weren’t able to successfully roll the Wheat we sowed as a cover crop last year flat and had to mow our mid row. This mowing means wind blew away the plant-matter that were mown off and we lost that important organic matter.
The crop we have sown this season is growing beautifully and will soon completely fill the surface of the soil in our vineyards and continue to grow even in the cold of the winter. The importance of sowing a cover crop and the seed choice we make, at De Toren, has many functions for improving soil health and reducing our reliance on conventional chemicals for weed control. By improving and maintaining soil health our vines are better equipped for the coming growing season and they will be able to produce superior quality fruit which allows us to produce wines of such fine quality. We are always looking for ways to build on our integrated strategy in managing weeds and our soils to ensure, as custodians of this land, that we can refine our craft further and raise that bar of quality even higher.