For years, farmers around the world have focused on growing single varieties of wheat; populations of identical individuals that have been selected for their yield and other desirable traits. More recently farmers and researchers have begun to look at mixtures of blends of different varieties, in order to benefit from the diversity in disease resistance – reducing the risk of one variety suddenly breaking down to a new race of Yellow Rust for example.
Last year we decided to put this theory to the test in Kenya with our environment, diseases, and varieties. Made up of a three-way mix of Robin, Kasuku, and AGV249 in equal quantities, the idea was to see if it is possible to benefit from the genetics of these three high-yielding varieties to slow or reduce the development of disease – thereby reducing the amount of fungicides required.
The downside is the need to identify varieties with similar uniformity for harvest – particularly having Kasuku in the mix and its risk of sprouting – but all varieties are very widely grown, high yielding and each has its strong points and weaknesses.
Robin is very susceptible to Stem Rust and Yellow Rust, Kasuku is fairly resistant to Stem Rust but weak against Yellow Rust, and AGV249 is highly resistant to both Rusts. This therefore gives us a good chance to observe the disease levels on individual varieties as well as the blend as a whole.
Why should it work? Physical separation between individual plants (harder for the disease to jump from one Robin plant to another Robin plant if there is a resistant plant in the way) and lower levels of inoculum in the crop etc.
The easiest way to test the theory? Plant the blend, and compare it to the yields of the three varieties when grown as ‘straights’ or individual varieties. We now have results from six trials, across three sites and two seasons. And they make interesting reading…
At all sites in 2022, the blend (black bars on the graph) did actually out-yield the average of the varieties when grown individually as straights (grey bars). This is where no fungicide was applied. When we sprayed four fungicides to the crop, there was no difference.
Bushel weight was particularly interesting. At Meru where Stem Rust pressure was greatest, bushel weight increased from 77kg/hl across the three varieties, to 79kg/hl in blend where no fungicide was applied. There was visibly slightly less Rust on the Robin heads, and intriguingly less Fusarium on the highly-susceptible Kasuku.
There is a lot of work still to be done but if you are one of the many farmers in Kenya growing wheat with one or no fungicide, trying a variety blend is a really good idea from what we have seen. If you regularly apply fungicides however, it is unlikely that you will see an obvious benefit.
A pure crop of Robin compared to Robin in the variety blend. Whilst the severity of the disease on the stems is similar, there was definitely a delay in the speed of the disease developing on the ears.
Biostimulants: Going Against the Grain
Last month I looked at a new fungicide and commented on how difficult it is for manufacturers to get conventional products approved with ever-increasing regulations and cost.
On the back of this, we have seen a lot of activity and promotion of biostimulant products over the past few years, promising to improve plant health, boost drought tolerance, crop quality and yields etc. Essentially, products which fit the familiar understanding of “a substance which is sprayed on a crop” but which is unregulated (i.e. easier to sell without expensive and time-consuming data).
In a recent fungicide trial on peas, for example, we compared a prominent biostimulant in the marketplace with three different fungicides. Although only one of the fungicide responses was statistically significant, they were very close, and all positive. The biostimulant on the other hand was negative; having seen in the past how sensitive peas are to injury from many commonly used sprays, I do not think that this was a random error.
Moving to a different crop, wheat, our biostimulant trial in Nakuru this year looked at five biostimulant products. Each was applied three times, and the crop was largely free of disease with minimal Stem Rust.
Ask questions about any chemical or biostimulant. If the seller believes in the product, it is reasonable that they would provide a sample free of charge for a trial.
Thankfully for the trial, the crop experienced a moderate level of stress during the dry June and July. This should have brought out and enhanced any stress mitigation effects from the biostimulants, but as the results show none of the yields (or Bushel Weights) were statistically different.
These are just two trials, yet the picture from other sites tells a similar story. Occasionally there are improvements in yield but these are the exception. Ultimately these products are not reliable nor consistent – something that independent research in other parts of the world has also found.
And be wary of the counter argument that “we need to find out how and where these products are likely to work and where they fit in”. Would you buy a phone, a motorcycle or a pair of shoes that the buyer was not able to confidently tell you when or how it would work?
Examining Soil Structure: Plotting your Path to Higher Yields
One of the biggest improvements farmers can make is getting their soil structure right. It doesn’t necessarily require big changes or expensive machinery, but it will improve productivity and make your crops more healthy and resilient.
Plough pans caused by years of disc ploughing and livestock are the single greatest barrier to higher yields that I see, and these require a number of simple steps including taking livestock off fields in the wet (or having dedicated livestock paddocks and dedicated cropping paddocks), deeper cultivation using a chisel plough, and leaving crop residues on the surface.
A well-structured soil with strong, stable crumby structure, plenty of pore space and holes, and lots of fine and bright roots
Varied cropping with a rotation also very quickly helps, with crops like canola and sorghum punching down through harder layers and opening up the soil structure. As with any project, measuring progress along the way is very helpful, so here are some simple tips to chart your journey:
- Dig a hole and visually assess. Record observations (you can find clear, simple guides online for Visual Soil Assessment methods)
- Shape of the soil particles (rounded and varied, rather than blocky and square)
- Direction of roots – downwards!
- Colour and density of roots – ideally bright white with lots of small fine roots (like cotton wool)
- Bulk density when comparably dry. Soil is made up of sand, silt, clay and organic matter, and a lot of air… and air requires empty space! The lower the density of soil, the more pores you have for air movement, for roots to grow through, for fungi and biota to explore. See the technique below*.
- Earthworm counts – there is no correct number, but on good soils in the Rift I expect to see one in every spade-full of soil. If you dig in three places and don’t find any worms, you have a problem.
- CO2 burst test. A laboratory test which measures respiration, as a proxy for all different types of life in the soil. This is quite subjective and depends on crop, season, recent weather etc, but it does at least give a numerical reference point to track over the years.
- Measure organic matter in a soil test – This varies across fields and takes time to build up, so don’t be angry with yourself if you don’t see immediate improvements.
*Soil bulk density – how to do it:
- Dig up a dry clod of soil – January or February is usually the best time to do this.
- Leave it to dry in the sun for a day or two, then
- Wrap it in kitchen cling-film.
- Weigh it, then put it into a full bowl of water.
- Remove the clod of soil from the water and top-up the water that was displaced, carefully noting the volume. The bulk density is the weight (kg) divided by the volume (litres).
Dry clods of soil, wrapped in cling-film, ready to weight and to measure the volume for calculating the bulk density.
Correction
Elatus Arc contains benzovindiflupyr, azoxystrobin and propiconazole – not as otherwise stated in November’s edition.
Till next time,
David Jones,
Independent Agronomist
