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Conservation agriculture can boost maize yields

Maize farmers who aim to practise no-tillage or conservation agriculture on their farms will benefit from considerably higher yields during dry seasons since these farming methods allow them to plant crops considerably closer together. So says Dr Stephano Haarhoff, who received his doctorate in agronomy at Stellenbosch University (SU). His research was conducted under supervision of Dr Pieter Swanepoel and Prof Nick Kotzé from the (SU) Department of Agronomy.
Dr Stephano Haarhoff
Dr Stephano Haarhoff

In his research, he investigated the influence of plant population (the number of plants per unit area) and row spacing on rainfed maize production in no-tillage- and conservation agriculture systems in North West and the eastern Free State. He believes, however, that some of the principles highlighted could also be considered by irrigation farmers.

Conservation agriculture is a comprehensive approach to soil and crop management that promotes the long-term sustainability of farming systems in terms of profitability and the soil-crop environment.

"With conservation agriculture, agronomic principles are applied, such as no-tillage, crop diversification, continuous soil-cover maintenance using crops or crop residues, and livestock integration into a farming system," elaborates Dr Haarhoff, who works as a small-grain research and development agronomist in Paarl. "Applying conservation agriculture can be very challenging because so much depends on the variable soil and climate conditions."

"The success of conservation agriculture and no-tillage is only possible when all these agronomic practices are applied together," he warns.

In South Africa, rainfed maize production systems are characterised by intensive soil tillage practices and the exclusive planting of maize year after year. This often leads to large-scale soil erosion and in the process resources like water and nutrients in the soil are not used optimally.

Eliminating conventional systems

"Farmers often still follow agronomic practices that are based on outdated research," he says. "New maize cultivars and improved planter technology nowadays enable them to think differently about the long-term sustainability of their farming systems by, for instance, considering conservation agriculture."

His research shows that large-scale soil erosion in production regions with high rainfall, like KwaZulu-Natal, Mpumalanga and the eastern Free State, can be combatted using cover crops, crop rotation and the management of sufficient crop residues.

"The same principles apply to the drier western production region (for example North West), but due to the lower rainfall received annualy it is more challenging to apply these principles," explains Dr Haarhoff. "For example, maintaining soil cover is more challenging because production volumes are lower and crop residues are utilised by livestock during winter months."

He says that because water is the limiting factor for maize production across the greater part of South Africa, farming principles must promote the storage and preservation of soil water.

"The large-scale soil erosion currently taking place all over our country's maize production regions must be combatted since it has a direct impact on the fertility of the soil and its ability to store water," Dr Haarhoff notes.

He believes integrating livestock such as cattle and sheep into these farming systems could improve farmers' cash flow throughout the year.

"It creates another source of income when cover crops and crop residues are used sensibly," elaborates Dr Haarhoff.

He says it is pointless for maize farmers who practise conservation agriculture to maintain existing approaches when it comes to plant population and row spacing. By making adjustments they could make farming systems considerably more productive and promote yield stability over the long term.

In the drier western production region of the country, in conventional farming systems, where intensive tillage is the order of the day, between 14,000 and 24,000 plants are planted per hectare. Rows are planted between 1.2 metres and 2.1 metres apart.

Tranforming management principles

Dr Haarhoff's research shows that farmers in this region who are practising no-tillage or conservation agriculture could aim for 35,000 to 40,000 plants per hectare, with rows planted 0.52 to 0.76 metres apart. He has found that the 0.76 metres row spacing is more beneficial than the narrower row spacing in dry seasons.

The calculations also look different for the eastern production regions which include the eastern Free State, Mpumalanga and KwaZulu-Natal, which enjoy more than 600 mm rain per year. Here, in conventional farming systems, between 35,000 and 45,000 plants are planted per hectare, with row spacings of 0.91 metres to 1.2 metres. Should no-tillage or conservation agriculture be followed in these regions, it could possibly change to 50,000 to 60 000 plants per hectare, planted between 0.52 metres and 0.76 metres apart.

Many farmers believe optimal maize root growth is not possible without soil tillage, but our root research has shown that it is possible when following the correct management principles.
"By increasing the plant population and decreasing row spacing, sunlight and soil water are used more effectively, and grain yields are increased," mentions Dr Haarhoff, who performed his field trials in Ottosdal and Reitz.

Dr Haarhoff also found that under no-tillage, plant population had no direct impact on root growth. Soil depth and seasonal rainfall played a greater role.

"Under no-tillage and in low-rainfall regions, maize roots are mainly concentrated in the deeper soil layers so that the plant can get sufficient soil water during dry periods," he explains.

He says it is therefore important for farmers to alleviate any compacted soil layers before switching to no-tillage and conservation agriculture.

In one of his field trials on this, he observed very high root volumes at a soil depth of 65 cm after only 30 days' growth. He did the root research in collaboration with Dr Elmi Lötze of SU's Department of Horticultural Science.

"Many farmers believe optimal maize root growth is not possible without soil tillage, but our root research has shown that it is possible when following the correct management principles."

His research was supported by, among others, the South African Society of Crop Production, the Maize Trust, Grain SA, AgriSETA and the National Research Foundation.

Dr Haarhoff offers the following advice to maize farmers who want to practise conservation agriculture:

i) Make sure the agronomic practices used for soil and crop management are economical and environmentally sustainable in the long run and do not only offer short-term solutions.

ii) By applying the correct agronomic practices that suit the challenges and needs of your own farm, the impact of climate conditions like variable rainfall can be reduced. No two maize farmers have the same farming system. Focus on the unique factors and challenges encountered within your fences.

iii) Resources, like available soil water and nutrients, can be maximally utilised by following the correct agronomic practices. Experiment on a small scale on your own farm with alternative farming methods and approaches – regardless of what the neighbours might say.

iv) Most South African maize farmers experience problems because they do not practise soil management optimally and only focus on short-term solutions. A good maize harvest starts with the soil and weather conditions, and the farmer can only manage the former. A farmer must approach soil management in such way that it promotes the success of alternative farming practices (like increasing plant population) while, at the same time, alleviating the negative impact of variable weather conditions.

About Engela Duvenage

Engela Duvenage is a freelance writer specialising in science and research related articles and press releases and is writer for the Faculty of AgriSciences, Stellenbosch University.

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