The current winter rainfall production season was certainly one of the driest across the whole of the Western Cape. Conservation Agriculture (CA) is included as part of the SmartAgri plan for weathering the climate changes expected for our province. This approach to production is based on minimal soil disturbance, biodiversity through crop rotation and the retention of crop residues on top of the soil.
In a dry year it is vital to use every single raindrop to its fullest extent to ensure production. The CA approach has again shown that it is highly efficient when dealing with very dry conditions. The system builds soil structure over time and this structure plays a vital role in moisture retention. Imagine a block of apartments underneath the soil, with larger and smaller spaces, where water can be stored. If we were still using the plow this structure would have been disrupted and broken down and the storage of water would have been minimal. The rotation of crop types and retention of residues helps building the organic material in the soil and with every 1% increase in organic material in the top 100mm of soil can hold roughly 140000 to 170000 liters of water per hectare more. Leaving the crop residues on top of the soil keep the soil cooler in summer and warmer in winter. During the growing season the residue helps lowering the evaporation of water by open soil and thus forces the available water to move through the plant which results in better yields.
It must be remembered that to take a crop such as wheat (the main cereal cash crop in the province) from a kernel to producing seed takes roughly 110mm of water. This only ensures that the plant will be able to reproduce itself. Commercial yields to feed people and ensuring a famers’ profitability lies in the efficiency of the amount of water received above the 110mm threshold. Several production areas in the Swartland received less than 100mm of rain during the season and in these areas there was either very low yields or no harvest at all. The best system of production will not be able to produce in such conditions.
The current CA trial sites of the Western Cape Department of Agriculture is situated at Langgewens (Swartland), Tygerhoek and Riversdale (Southern Cape). Rainfall for the production season at these sites were 173mm, 147mm and 126mm respectively. When taking the 110mm into account the crop yields (as can be seen in table 1) was produced on an excess of 63mm for Langgewens, 37mm for Tygerhoek and 25mm for Riversdale.
Table 1. Average yield for different crops at different localities
To convert to this system of production might be a little expensive at first, but the initial layout can be quickly recovered in a short span of time. The savings on fossil fuel inputs over time and the improved yield helps to offset the initial cost. Over time other inputs such as seed and fertilisers can be reduced, which not only has a cost saving benefit, but also an environmental impact. Producers could however convert older conventional planters, which might be more affordable.
The same base principles of CA can also be implemented in perennial crops such as fruit and vineyards resulting in improved water use efficiency. The results from these trials are communicated through Walk-and-talk’s, articles in Landbouweekblad, farmers’ days and an annual Conservation Agriculture conference.
Conservation Agriculture can help mitigate the adverse effects of climate change, but it must be realized that it is not an overnight success story. It takes time for the system to fully reach its potential. When one looks at the 3 driest years namely 2003, 2015 and 2017 the average wheat yield was 1 t/ha, 2.1 t/ha and 2.4 t/ha respectively. Full CA principles was implemented in 2002. Enough said.
Dr Johann Strauss
Direktorate Plant Sciences
Research and Technology Development Services
Western Cape Department of Agriculture