Sugarcane has been monocropped in South Africa for over a century, but recently local cane farmers began looking at crop rotation to improve and sustain soil health. Field trials are currently determining the viability and effectiveness of rotating cane with soya beans, reports Lloyd Phillips.
Over time, monocropping reduces soil fertility and production potential. The South African cane industry is a textbook case, especially where fields planted to sugarcane are ratoon-cropped for as long as 10 years before replanting.
With few or no fallow periods or crop rotation, the soil doesn’t recover between plantings, forcing growers to increase quantities of expensive fertilisers, pesticides and herbicides to sustain yield and quality. It’s not a recipe for financial and environmental sustainability.
Recently the cane industry began experimenting with rotating cane and soya beans. Two trials are underway in Zululand, one under irrigated conditions on the Crookes Brothers’ Riversbend Estate at Nkwalini and the other under rainfed conditions on the UVS Marsabit Estate outside Empangeni. “I feel very positive about these trials,” says UVS Marsabit’s farm manager, Warren Poustie. “I’m already noticing earthworms moving into the soil – I hadn’t seen them for years. We hope to produce at least a break-even 2t soya bean crop, but we’re already saving R1 000/ha on weed control by rotating with soya beans, plus R2 000/ha to R3 000/ha on soil preparation. We should have the potential to increase cane yield by R3 000/ha to R3 600/ha for the first year after the soya bean planting. “I estimate a total potential benefit of R12 000/ha over the average eight-year cycle of the cane crop following soya beans.”
Selecting soya beans bean
Six months ago canegrowers in KZN joined SA Sugarcane Research Institute (SASRI) agronomists and extension specialists, as well as independent grain crop experts, to find the practical, viable, cost-effective and beneficial crop urgently needed for rotation with sugarcane. Soya beans sounded ideal and the wheels were put in motion for the trials. “Soya beans are the world’s most important source of protein and edible oils and an undisputed champion for crop rotation value,” explains Dr Michiel Smit, a senior agronomist at SASRI and author of Your Guide To Successful Soya Production, published by the Agricultural Research Council Grain Crops Institute.
“Belonging to the legume family, soya beans are an annual crop that can fix high amounts of inert atmospheric nitrogen, as much as 360kg/ha, improve soil structure, immobilise heavy metals and improve the soil microbial population,” he says. “Planting soya beans as a break crop gives cangegrowers the opportunity to bring problem grasses under control cost-effectively and disrupt pest cycles. Soya beans are in short supply in South Africa and considered a high-value crop. Wheat and maize farmers take full advantage of this when they rotate their crops with soya beans, so we decided to try it with sugarcane.”
Benefits for farmers
Riversbend’s general manager Tiaan Viljoen and agricultural manager Herman Badenhorst say alongside the benefits of rotation, soya beans will also generate additional income to offset the low international raw sugar price.
They’re taking advantage of cheaper farm-to-processor transport costs for soya beans than cane, as moisture makes up a significant portion of a truckload of cane.
Tiaan explains, “Monocropping left our fields virtually sterile, and major weeds like water grass and creeping grass are continually increasing. All this restricts our efforts to produce good cane yields containing high-quality sucrose.
Trials underway
“SASRI, the soya bean seed companies and independent agronomists taught us how to plant, manage, harvest and market soya beans. They’ve taken responsibility for scientifically monitoring the trials and will release their findings to the sugar industry.”
Both the irrigated and rainfed trials planted a wide variety of soya beans bean cultivars. All are Round-Up Ready so the crop isn’t damaged when herbicides are used to kill weeds.
Soya bean fields were planted in October, November and December to monitor which cultivar and planting date is best for the hot and humid Zululand climate.
Nothing has been harvested yet, but the November plantings seem to be performing best so far in terms of stands and pod yields.
Planting row widths were also varied, from 750mm to 900mm. In wider rows, weeds tend to get a strong foothold before they’re killed by herbicide, but the narrower inter-row spacing produced a good soya bean canopy, shading out weeds without excessive competition between the soya bean plants.
Equipped for prep and planting
“We can get two crops out of a single soil preparation for soya beans. After harvesting, soil conditions remain ideal for the replanting of seedcane,” explains Tiaan. “Soya beans need a good soil tilth to germinate, so we plough and disc the soil to break up large clods, then use a conventional grain planter.”
The KZN north coast isn’t a traditional, commercial, grain cropping region, so planters for the trials have been difficult to come by. Fortunately, stakeholders sourced a seven-row and a four-row planter, both second-hand, from Winterton and Bergville grain farmers.
These planters will be shared among cane farmers interested in rotating with soya beans, or groups of cane farmers can buy a planter together.
A combine harvester will be brought in from northern KZN to harvest the trials at the appropriate time. The Dundee KZN branch of Afgri has committed itself to buying the soya bean crop from the trials. A biodiesel manufacturer in Empangeni has also expressed interest in buying part of the crop.
Farming with soya beans
SASRI’s regional extension manager in Zululand Tom Fortmann says, “The cane farmers will have to be taught the need to inoculate soya bean seed with Rhizobium bacteria before planting, which is critical in getting the plants to fix nitrogen. It’s cheap, but the long-term benefits are significant.” Tiaan believes because the soya bean crop is planted between long sugarcane cycles, the best option is to inoculate the seed with a dry Rhizobium and spray liquid inoculant behind the planter’s disc openers. This will make for better Rhizobium nodule distribution on the soya bean plant roots.
Soya bean seed companies agree care must be taken during handling and the dry mix inoculation process to prevent seed damage.
They add it’s practical to leave the soya bean stubble on the field after harvesting because it helps protect against wind and water erosion. As it becomes brittle very quickly, it won’t cause problems at cane-planting time. For more information contact Tom Fortmann on (035) 772 5871, fax (035) 792 2680 or e-mail
[email protected]. |fw
