Estimated reading time: 6 minutes
Producers must realise that they are farming not only above the soil but also below it.
Sustained vegetative cover is needed to protect the soil surface and support microbial life below the soil. Productive and healthy soil depends on this cover. Prof Jan Myburgh, a veterinarian and toxicologist at the University of Pretoria’s Department of Paraclinical Sciences, says the practice of cultivating fields and then leaving them bare for long periods is detrimental to soil health. Producers must realise that they are farming not only above the soil but also below it. They are, in fact, microbial farmers too.
Prof Myburgh, who is also a founding member of the non-profit organisation Save Our Rivers, emphasises that the biological life below the soil surface is just as important as the vegetation above it. When soil is left fallow or bare, the microbial population decreases dramatically, as their energy source is indirectly dependent on photosynthesis.
Plants use solar energy to produce sugars, some of which are supplied to soil microbes by the roots. This process creates a subterranean ‘feeder’ that sustains the microbial community, which in turn supports the plants. A lack of vegetation means no food for the microbes, causing the subsurface ecosystem to wither. When crops are replanted later, this microbial community has to rebuild itself virtually from scratch.
Drought resilience
Maintaining soil cover does more than just protect against wind and water erosion. It also keeps the subsurface biological system active. A healthy microbial population promotes soil biology, improves nutrient cycling, and supports plant growth. At the same time, plant roots increase the soil’s organic matter and carbon content. During mowing or grazing, the plant roots stay behind and break down into valuable organic matter that is converted into carbon. This, in turn, serves as a nutrient for microbes, improving soil health and water retention.
Because Southern Africa is a drought-prone area, producers need to keep soil organic matter content as high as possible. Doing so not only helps preserve nutrients but also improves the soil’s water retention capacity. With predictions indicating that the next major drought is at our doorstep, one of the most important steps is to monitor soil quality and biology. High organic content enables the soil to retain water, so rainwater stays on the farm rather than running off into nearby rivers or streams. This is a key strategy for conserving water for drier periods and strengthening the sustainability of the farming operation.
Cover crop utilisation
Cover crops, says Prof Myburgh, do not necessarily have to be incorporated into the soil or left on the land to rot. They can be utilised through grazing, mowing or as hay. He warns against following a rigid approach and planting cover crops solely to build up organic matter. “Should roughage or grazing be in short supply, grazing or mowing cover crops can be highly beneficial. They don’t simply have to be left on the land.”
Cultivating cover crops offers producers the opportunity to plan and experiment with different crop combinations. Mixtures of legumes, grasses, herbs, and flowering plants are used to promote soil health and support production goals. However, producers must decide in advance how the cover crops will be utilised – whether for grazing, haymaking or as permanent ground cover.
There is no single recipe for successfully planting cover crops. Each farm’s conditions are unique, and the choice of crops and management system must be adapted accordingly. Integrating cover crops with minimum- or no-till systems can create a win-win situation by improving long-term soil health while providing an additional source of livestock feed and income.
Choose the right species
An article in SA Graan/Grain highlights how the decline in fertility and production capacity of many South African croplands has increased the need for effective fallow-planted pasture systems in the country’s grain-producing regions. The article “Integrated crop and pasture-based livestock production systems: Integrating pasture-planted lands with grain crop systems” was written by several experts, including Prof Wayne Truter.
Prof Truter is a trained livestock and pasture scientist affiliated with the University of the Free State. He is also an expert in agricultural and environmental sciences. He believes that cover-cropped pasture in crop rotation systems has the potential to reverse declining soil health and improve livestock productivity while also limiting environmental problems. However, the characteristics of cover-cropped pasture species need to be understood.
The success of these systems depends on the right choice and combination of species, as the wrong combination can adversely affect subsequent crops.
Each crop has a specific function:
- Legume pasture fallows and cover crops are primarily used to increase soil nitrogen levels. These crops fix atmospheric nitrogen, making it available to subsequent crops.
- Grass pasture fallows and cover crops contribute to the buildup of soil organic matter (SOM), the recycling of excess nutrients, and the reduction of soil compaction. They also help to limit erosion and weed pressure, while improving soil structure and carbon sequestration.
- Brassica crops such as radishes and turnips are used to increase soil porosity, reduce compaction, and improve soil structure thanks to their higher levels of organic matter. They can also promote weed suppression.
- Some cover crops are used to suppress insect pests, diseases, and weeds or to attract beneficial insects to the fields.
Cover and cash crops
Prof Truter believes that various fallow or cover crops can be planted with, between or after cash crops in South Africa’s summer rainfall area. These crops perform best in a multi-species mixture and can be utilised over a short period through ultra-high-density grazing. The ideal scenario is to have a variety of living roots in the soil year-round, which improves soil health.
Table 1 provides an overview of the main established fallow species that can serve as livestock feed for cattle, sheep, pigs and chickens, and even fish.
Table 1: Significant cultivated pasture fallow crops that can serve as livestock feed. (Source: Truter et al., 2014)
The following crops can be used to follow up maize or soya bean plantings, or as a late intercrop or winter cover crop:
- Grasses such as stooling rye, annual ryegrass, oats or triticale. These grasses build up SOM, recycle nutrients, and relieve soil compaction.
- Brassica crops (oilseed or tillage radishes or turnips). These help recycle nutrients, reduce compaction, and suppress weeds and diseases.
- Vetch. These can be planted as a nitrogen source.
With late intercropping, these winter cover crops can be planted between mature maize rows. The cover crops will germinate and grow slowly under the mature maize canopy. Once maize is harvested in autumn or winter, the cover crops will already be established and will resume growth, saving valuable time. The intercrop will usually grow more throughout winter and spring than any cover crop sown after the maize.
Crops such as babala, forage sorghum, cow peas, soya beans, mung beans, dolichos lablab, velvet beans, sun hemp, and jack beans can be planted as green catch crops during the cash-crop growing season. Concluding this process depends on the need to conserve soil water for the next crop.
Non-climbing crops such as cow peas or velvet beans, and climbing plants such as dolichos lablab, can be planted as intercrops during the growing season, around the same time as maize. They can also be sown as an intercrop two to eight weeks after maize. However, later plantings tend to have a smaller impact on the maize yield. The earlier the catch crop is sown, the greater the soil protection and weed suppression benefits. In small-scale systems, catch crops also serve as a food source, and their residues can be used as animal feed. – Christal-Lize Muller, Stockfarm
For more information or references, email Prof Jan Myburgh at jan.myburgh@up.ac.za or Prof Wayne Truter at truterwf@ufs.ac.za
