Sharpen Up On Crop Nutrition For 2025

As we move into 2025 and prepare for planting, think carefully about what you can do to set your soil up for a successful harvest. It should start with soil structure, fertility and nutrition.

For me, soil testing is absolutely crucial to making good planting decisions – too much and you are wasting money – and potentially risking seedling damage. Too little and you will not achieve the crop’s potential, losing out on profit.

A soil test report can be overwhelming, but the laboratory guides you through it and provides recommendations based on the knowledge that Cropnuts have accumulated over 25 years, and the trials that we have conducted on local soils here in Kenya.

I have taken a few key parameters that I look at for most situations:

Phosphorus is often the most limiting element in our soils. We can apply lime, nitrogen, potassium etc and only see a small improvement, but the majority of soils I see are low in P.

Over the years we have developed a table of soil test P level by crop, to show you how much phosphate needs to be applied to achieve the optimum yield. In our ‘Trials site A’ soil test for example, if we were planning to grow maize we would only need to apply around 40 kg/ha of phosphate (less than 100kg/ha of TSP or DAP), because the soil P level is 51ppm.

When I look at soil phosphate I also look at pH; whilst we don’t always see a yield improvement from applying lime unless the pH is 5 or below, it does have a big influence on phosphate availability in the soil. pH 6.0 for example should ensure that the P we have in the soil is very available to the plant, giving me confidence to only apply 40kg/ha.

Potassium is increasingly being marketed in fertiliser blends in Kenya but it is very rarely limiting. Levels above 250ppm are sufficient for most crops, and even potatoes don’t respond to K fertilisers at 400ppm in my experience.

Magnesium is often neglected and in lighter soils it is often around 200ppm – the level at which you would start to see classic yellow striping of deficiency on the leaves. A suitable blend or addition of magnesium sulphate at planting can remedy this.

I also like to track organic matter over time. Whilst not a nutrient as such, it helps nutrient availability, moisture retention, and supports soil life that is crucial to us. Do not get fixated on year-to-year variations; track the broad trend across the farm over time.

The last nutrient that is so often neglected is oxygen. Whilst not measured on a soil test, it is critical for the roots, fungi and bacteria to respire. A well-aerated soil smells sweet and pleasant as the organisms breath. This starts with soil structure and is one of the reasons that I regularly measure soil bulk density on clients farms and track them over time.

Soil compaction, where the particles are all squeezed together tight is the enemy of a well-functioning soil and deep crop roots and I see this so frequently where disc ploughs have been repeated used at the same depth, causing a hard pan to form.

Air cannot pass through this compacted layer of soil, water cannot infiltrate, and roots struggle to grow through it to bring up nutrients. The best advice I can give for the end of 2024 is to dig some holes in your shamba and push a knife into the side profile of the soil at various depths. It costs nothing and if you can find and repair compaction with a chisel cultivator, it could be the best gift you give your soil this Holiday Season!

I always get clients to do Grain Nutrient analysis on a few fields each year to help assess the success of the fertiliser program and identify what worked or did not. Grain Nutrient testing is particularly useful for phosphate which is handy for us in Kenya with generally low P soils. It has been very noticeable this year on a few fields that had to be re-planted after a failed crop, often after only 4-5 weeks – and did not have any fertiliser with the replanted crop – that these were very phosphate deficient. Because of how quickly P locks up on our soils especially, ALWAYS add some fertiliser when you re-plant.

Planning Critical for Successful Sunflowers in 2025

What percentage of Kenya’s shambas are left fallow after maize harvest in October? Many farmers use the opportunity to put beans in, but there is a huge opportunity to plant sunflowers in and to benefit from a completely different crop, rooting system and biology in the soil.

Sunflowers are very good at reducing Root Lesion Nematodes, something dry beans help multiply in the soil. These feed on the maize roots and reduce their size and ability to access nutrients and moisture. Sunflowers are also good at reducing Fusarium diseases which also damage maize roots, but what sunflowers do build up in the soil is mycorrhizal fungi.

More than almost any other plant, sunflowers are highly mycorrhizal which is very useful in helping subsequent crops in our low P soils.

Some consideration needs to be given to the herbicide program in the maize, so the planning process needs to start early next year before farmers begin applying herbicides. Products containing large amounts of clopyralid are not suited to following with beans or sunflowers within 9 months.

Mesotrione can also cause issues – six months is normally safe for 150g/ha of mesotrione. Atrazine needs caution too – 1,000g a.i. tends to last 4-6 months in the soil. Terbuthylazine tends to break down slightly quicker than Atrazine.

Halosulfuron, commonly used for Watergrass / Sedge control has 13 months plantback interval to sunflowers on many labels. This is absolutely the case in high-pH soils. Thankfully in many of our acidic soils around pH 5.5, I have rarely seen injury after 5 months. But exercise caution and always follow the label to avoid the risk of crop damage. Nicosulfuron and flumetsulam – also Group 2 herbicides – tend to break down similarly quickly in acidic soils too.

Topramezone has a 12-month restriction for crops not specifically listed and is commonly applied later on in the maize crop, so be cautious if you are planning to plant sunflowers.

Likewise saflufenacil has a 9 months restriction before sunflowers when used at the full label rate, but I tend to find in practice and on labels in other countries it is less.

So which maize herbicides are safe to follow with sunflowers? S-metolachlor, pendimethalin, linuron and metribuzin are all safe and have zero plantback to beans and sunflowers. It is important to consider these things now and planning accordingly for maize herbicides next year.

The are some very interesting forthcoming new varieties of sunflowers that will hopefully complete National listing trials in 2025. Hysun 33 is already registered and available and is a big improvement over KS Fedha (which is not well suited to oil extraction at all because of the husk content). Hysun is relatively tall and does lodge on volcanic soils, and is not the most competitive canopy to shade out weeds.

Pluto looks very interesting and brings high yields with good standing ability, relatively fast maturity and a competitive crop canopy. It has good Sclerotinia resistance too and is relatively short.

Wollf looks very good. In on-farm trials, the head size often looks small next to competitors but ends up out-yielding them by 10-15% on account of a very high specific weight and oil content. This is a very versatile and quick variety with great uniformity and harvestability (it has less pendulous heads than others so losses tend to be lower when cut with a cereal header).

Vollcano CL looks similar to Wollf but has the Clearfield trait – useful for reducing the risk of damage to Group B herbicide residues such as halosulfuron and nicosulfuron. It yields very well but can get late Sclerotinia infection in the heads in a very wet season.

2024 Lessons to Help Us Improve in 2025

I have made a lot of mistakes in 2024. Thankfully when we make mistakes we have an opportunity to remember, act and learn from them in future. Here are mine!

Peas without seed dressing. I am thrilled that we are close to eliminating seed dressing on peas. This wins on so many levels: less cost, less handling and seed breakage, less chemical use in the environment. Many labs offer an Ascochyta Seed Test service that gives growers the confidence to make the saving without risk, if the disease level on the seed is low. I will be advising growers to test all of their pea seed every season going forward.

Well-structured soils re-fill far quicker than we think. I have always been surprised at how the red soil in Kenya tend to perform relatively poorly when double-cropped. These sub-angular, blocky, friable clays have an inherently dense structure with limited pore space to allow water to penetrate to depth. Black Cotton soils on the other hand need a flexible approach and be cropped when the moisture is accessible rather than to a fixed, rigid schedule. I was very surprised earlier this year at how a crop of sunflowers thrived straight after sorghum; two heavy moisture-users, on a well-structured black soil.

Impala is a great variety but it has broken down to Stem Rust, so plan appropriately with the fungicides. I have been impressed by this variety for a number of seasons now; high high-yielding, great grain quality, relatively low sprouting risk for a white wheat, good Fusarium resistance and far less likely to lodge than Korongo. I would happily grown Impala in a three-way blend with Rocca and Cabernet in future.

Biostimulants are still not promising. I have tried and tried with Amino Acids and other products in randomised, scientific trials, without success for another year. The money is best spent elsewhere.

We can plant canola deeper than we thought. Choosing larger seeder varieties such as Blazer (if you are farm saving seed, screen out the largest seed >1.8mm) and reducing press wheel pressure can often achieve good establishment from as deep as 6cm. Allowing us to get the crop established before the rain and flowering in soft, wet conditions.

Late-planted peas has been a revelation. Logic would say that planting peas early before the onset of the rains and giving the crop a dry start free from disease would be the best approach. After all, this works well for Barley with Net Blotch, and in canola for Blackleg. The reality is somewhat different; delaying planting until the Ascochyta spores on infected stubble have been released and died is much more effective. Planting later also avoids the thick, dense canopy at the peak of the rains which collapses and makes harvest so difficult.

Legume Nitrogen has an intangible quality. In late-planted maize especially, that germinated well but later in May, it was very noticeable how residual Nitrogen from last year’s peas kept the crop well supplied when it was not possible to topdress. Nitrogen fixed by legumes also has an effect that is much greater than what the kg/ha is estimated to be on a soil test.

New wheat varieties are absolutely crucial to profitability, sustainability and resilience. The five new candidate varieties – Elexi, Fumettra, Rocca, Cabernet and Alverah, in our highest Stem Rust pressure trial site were higher yield without fungicide than the existing varieties with fungicide.

Fall Armyworm insecticides – be wary of manufacturers’ claims. Emamectin, indoxacarb, acephate, chlorantraniliprole and pyriproxyfen are all reliable and are very safe when used within the label guidance. I still find that maize grown in a rotation needs far less help against Armyworm, benefiting the farmer and the environment.

Soil structure is the most important thing in canola. Before you spend money on expensive seed, fungicides and fertilisers, ensure that you have inspected the soil structure and taken action to remedy compaction. I am increasingly surprised at how little phosphorus starter fertiliser maize requires compared to wheat, barley and maize. Take a soil test and act on it.

Till next time,

David Jones,

Independent Agronomist

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David is an independent agronomist in Kenya and a member of the Association of Independent Crop Consultants. David gives independent advice based on scientific trials and experience. Currently works with the Centre of Excellence for Crop Rotation.

Think Agronomy is brought to you by Cropnuts and the Centre of Excellence for Crop Rotation. We share the same vision for sustainable, dryland farming across Africa, and Think Agronomy is our independent voice to promote profitable, climate-resilient farming through better management of soil health, systems-based agronomy, crop diversification, and farm mechanization.