By Jaco Engelbrecht | www.visualviticulture.co.za
We have a little experiment on a farm in the Voor-Perdeberg area. It is a block of Cabernet Sauvignon with supplementary irrigation (not the one in the photo, that is Cinsaut for The Blacksmith Barebones). The soil form is Klapmuts of the Malmesbury Shale family, with a moderate water permeability.
We put two continues loggers in the block. One on the vine row without mulching, the other (4 rows away) on the vine row with straw mulching, about 20cm thick. The goal of the experiment is just to monitor soil temperatures and fluctuations in the top 30cm region, where your fine roots are and microbial activity is crucial.
So what would you like in that top soil? Ideally, little fluctuation and moderate temperatures.
So, here is the reading without mulching:
Soil temperature does not only fluctuate violently from day to night due to direct solar radiation, but has gone above the threshold of 28ºC 12 times, rendering microbial activity slow or even non-active. This has a negative effect on fine root development and nutrient availability, brought forth from microbes and bacteria working in the top layer of soil.
Here is the reading with straw mulching on the surface:
Wow! BIG difference. Clearly very little fluctuation from day to night. Soil temperature is in the ideal range, never even lifting above 22ºC and once dropping down to 18ºC, compared to the chilling minimum of the no-mulch that almost dropped to 16ºC once.
The temperature is constantly between 19.8º and 21.6º, ideal for microbial activity, compared to the no-mulch that ranges between 18ºC and 33ºC. This does not only have a detrimental effect on soil life, but plays a direct role in soil water loss from the topsoil, and further impacts water use in the subsoil.
Mulching not only provides a better microbial and bacterial living environment, but saves water, improves soil structure (once the microbes and organisms has broken it down to usable organic material) and improves soil health.
With this Ill Niño still pounding us with dry, windy weather, mulching is no longer an option – it is a necessity.
Jaco Engelbrecht is a passionate viticulturist based in the Coastal Region of South Africa. He has been a viticulturist for nine years and have since consulted more than a hundred wine producers and been involved on even more wine farms.