I’m just preparing a presentation I’m giving in the Netherlands tomorrow, and I came across two pictures I took in the vineyards at Waterkloof in Stellenbosch, South Africa. The first is of one of their vineyards that has been managed biodynamically from the start, which is above. [It’s not an old vineyard.] The soils had a loose structure and were quite pliable.
The second, below is from a vineyard that was previously managed with herbicides. It has just been converted to biodynamics. The two vineyards are only a few paces apart, and share the same soil type, but the vineyard managed with herbicides is like a road.
Clean cultivating using herbicides (most commonly glyphosate, which is relatively benign) has profound effects on the soil structure. It has effects on the soil microlife, too. It’s generally a really bad idea, but it saves lots of money, and the vineyards look very tidy and orderly.
Gradually, people are beginning to appreciate the importance of what goes on below the ground in viticulture. Plant roots exude a range of organic nutrients such as organic acids, sugars, amino acids, nucleosides and mucilage. This encourages the development of a community of microbes, including some – called plant growth-promoting rhizobacteria (PGPR) – that interact with the roots in specific ways, including altering the root structure itself. They promote nutrient uptake and can help plants tolerate drought stress, among other things.
A recent paper by Patricia Piccoli (above) and colleagues looked at what’s taking place under the ground in Catena’s Adrianna vineyard, in Mendoza, Argentina – and specifically which bacterial strains are present in the soil. They took root and soil samples every 10 cm to a depth of 80 cm. These were placed in sterile pots and then taken to the laboratory, where the work of characterizing the various bacteria present began. After culturing and examining the various isolated strains, Patricia analysed the DNA to identify the species present. In all, 11 strains of soil bacteria were isolated, and these were from 10 different genera. Of these, two were selected as having characteristics of plant growth promoting rhizobacteria (PGPR). These were Bacillus licheniformis and Pseudomonas fluorescens, both of which produced the plant hormones abscisic acid (ABA), indole-3-acetic acid (IAA) and the gibberellins A1 and A3. They also colonized roots of Malbec grape vines grown in controlled conditions in pots. Vines that had these bacteria on their roots showed ABA levels that were increased 76-fold by B. licheniformis and 40-fold by P. fluorescens, when compared with controls. These bacteria slowed down the rate of water loss in the vines, and this slowing of water loss correlated with increased ABA levels. Because the levels of ABA found were so high, Patricia and colleagues think this indicates that the increase is due to production by the bacteria plus production by the vine as a response to the interaction with the microorganisms.
The bacteria also increased the production of terpenes, which are associated with plant defence against microbial attack. Interestingly, high levels of terpenes were found in the aerial part of the vine whereas the bacteria were present just on the roots. This suggests that these bacteria are able to cause what is known as induced systemic resistance in vines, because the synthesis of terpenes was found mainly in leaves, which would be the part of the vine mainly subject to any microbial attack.
There’s a lot happening under the ground that’s really important in viticulture, and we don’t know enough about it. But killing soil life by using herbicides is clearly a silly thing to do.