9 ton/ha wheat, constant double cropping with Soybeans and 1,200mm annual rainfall. Zambia is a country of enormous agricultural potential but also immense agronomic challenges. We visited Somawhe Farm in Copperbelt Province to find out how they are adapting to the low grain prices, soil constraints and an alternating wheat and soya rotation…
You would imagine that Brian Jenkin’s (CEO at Somawhe) sandy soils should drain freely and be relatively forgiving. But the very fine textured sand suffers from significant sedimentation 20cm into the profile, blocking root growth and drainage. Combined with the 400mm of high magnesium irrigation water each year – identified by a simple irrigation water analysis at Cropnuts – it forms a hard pan at 20-25cm deep.
For this reason a Vaderstad Topdown is used to work the land ahead of Soybeans grown in the rainy season, breaking the pan and incorporating the large volumes of straw residue from the high-yielding wheat crops.
As the Soyabeans approach harvest, the patchy symptoms of withering crop caused by nematodes are prevalent across many of the pivots in particularly on the variety Spike, a variety that Mr Jenkins likens to a race horse. “When everything is going with the variety does well, but any unfavourable conditions see it really struggle more than the Dina”.
Bacterial Leaf Streak has been an enormous problem in recent years in both the Soyabeans and the Wheat – where it was misdiagnosed as Septoria until Cropnuts agronomist Stephan Nieuwoudt became suspicious and sent samples for laboratory analysis.
Wheat varieties come from both within Zambia and South Africa – and are notably more appropriate to the needs of larger scale farmers than CIMMYT type varieties. Although there is no extensive local variety testing, there is good data available on the varieties, albeit not as up to date as Australian or European farmers enjoy for example.
The serious nematode problems with Root Lesion, Root Knot, Stubby Root and Needle Nematodes in Soybean crops have been monitored by Mr Nieuwoudt over the past two years, and he notes that whilst nematodes thrive in sandy soils, they are exacerbated by the frequency of soybeans in the rotation and the low organic matter.
“Applications of Vydate (oxamyl) were made to the young growing crop 30 days after planting, but this had only limited activity. We are now exploring Biofumigant Mustard, grown as a cover crop then incorporated at early flowering”, added Mr Nieuwoudt, noting that this should have the double benefit of building soil carbon and Organic Matter but it also releases isothiocyanates into the soil which has a natural nematicidal effect – far more selectively than a chemical alternative.
Soybeans yield around 3 t/ha and nodulate successfully with in-furrow liquid inoculant, however he added that in the first year of soybeans nodulation is limited, even with high rates of inoculant applied.
Interestingly the farm is going back to inoculating the seed, and using the liquid applicator on the seeder to experiment with in-furrow nematicide options to see if they complement the Biofumigant Mustard cover crop.
Particularly impressive are the modifications made to the 90 Series John Deere seeders using Needham parts to improve the seeding accuracy, including narrower boots, upgraded bearings and flexible firming wheels. The Needham boot springs are also claimed to improve downforce – a major limitation with the standard 90 series in most no tillers opinions! Direct drilling wheat after Soyabeans will also mean only one Topdown pass a year, preserving at least some organic matter.
Precision Farming is a central part of the operation at Somawhe, with pivots divided into management zones based on soil conductivity maps, yield maps and knowledge of specific soil types and areas themselves.
Trials carried out on the farm by Stephan have been very successful at demonstrating the response to different nutrients across the major soil types, providing real confidence to adjust fertilizer rates, and whilst the rotation is clearly not ideal, Mr Jenkins pointed out that a major limitation in Zambia is the lack of developed markets for many crops resulting in a very small cropping choice of wheat, maize and soybeans.
Even with these constraints the farm is willing to adapt the system where the opportunity allows, trying biofumigant mustard and cover crops, Bacterial Leaf Streak seed treatments and new varieties. Ultimately, local agronomic expertise and evidence from field trials has allowed clear and confident decision making.
Dawn Equipment’s RowMow targets mechanical control of herbicide resistant weeds
There are very few farms to whom herbicide resistant weeds of some description do not apply, making Dawn Equipment’s new RowMow inter row weed cutter of pretty much universal interest.
Although still at concept stage, the principle is a high and low mini cut bar, guided between the crop rows to cut weeds down before they set seed.
— Underground Agriculture Co (@UndergroundAgri) January 24, 2019
Particularly relevant for shorter, wide row crops such as Soybean to control Amaranthus, Euphorbia or grasses, the principle is not new with ‘weed surfers’ having being employed by organic farmers to cut seed heads above the crop. Cutting BELOW the canopy is of far greater interest for shorter weeds however.
Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the futureof how we feed the planet. Agventure Ltd set up the Center of Excellence for Crop Rotation to help farmers diversify cropping systems and introduce techniques which have a long-term outlook to improve soil health. The Center of Excellence for Crop Rotation works extensively with Crop Nutrition Laboratory Services Ltd (CropNuts).
Till next time,
David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.