The best fertilizer for cassava is one that is rich in potassium, moderate in nitrogen and low in phosphorus, applied about three to four weeks after planting. Cassava is often called a crop that grows anywhere. It does. But it doesn’t yield well everywhere, and on worn-out soil the missing ingredient is usually potassium.
That surprises a lot of growers. They see a big, leafy plant and assume it is well fed. Then they lift the roots and find a disappointing harvest. Cassava can grow plenty of leaves and stems on nitrogen alone. What it needs to fill its roots is potassium.
This guide covers what cassava needs, how much fertilizer trials suggest, when to apply it and how to spot a hungry crop.
What cassava needs
- Potassium (K): the big one. It moves sugars and starch into the roots. Research across West Africa found potassium to be the main nutrient limiting cassava yield.
- Nitrogen (N): needed for leaves and early growth, but too much pushes the plant into leaves and stems at the expense of roots.
- Phosphorus (P): needed in smaller amounts. Cassava works well with soil fungi (mycorrhizae) that help it find phosphorus, so it copes on low-P soils better than many crops.
- Secondary nutrients: magnesium, calcium and sulphur matter on very weathered soils, and zinc on some.
One study of nutrient uptake put cassava’s optimum uptake ratio at roughly 5.1 parts nitrogen to 1 part phosphorus to 4.7 parts potassium. In other words, the plant takes up almost as much potassium as nitrogen.
How much fertilizer does cassava need?
There is no single rate that suits every field. It depends on the soil, the variety and the price of fertilizer against the price of roots. Published trials give a sense of the range:
| Source and setting | Rate tested or found |
|---|---|
| Trials on Ultisols low in N and K | Optimum root yield at about 90 kg N, 18 kg P and 75 kg K per hectare |
| Potassium trial (Pakistan) | Growth and fresh root yield peaked at about 80 kg K per hectare |
| West African calibration study | Rates up to 100 kg N, 50 kg P and 170 kg K per hectare tested; K was the main limiting nutrient |
| Nigerian extension guidance (potassium-rich NPKS blend) | About 200 kg NPKS per hectare (around 20 g per plant), plus about 120 kg urea per hectare later |
Two practical points stand out. First, potassium rates are often as high as nitrogen rates, or higher. Second, on soils that have grown cassava for years without potassium, the response to K can be dramatic.
Which fertilizer to use
Most cassava programmes use one of these:
- A compound NPK such as 15-15-15, or better, a grade with more potassium, for the first application. See NPK ratios for how to read a grade.
- MOP (muriate of potash, 60% K2O) as the main, low-cost potassium source. Unlike tobacco, cassava is not a crop where chloride is a major concern. Read more in MOP fertilizer.
- Urea as a later nitrogen top-up on poor soils. See how to use urea as fertilizer.
- Organic matter such as compost or manure, which improves the soil and supplies some potassium. Compare options in organic vs chemical fertilizers.
When to apply fertilizer to cassava
Timing matters as much as the product. A widely used extension recommendation is:
- At planting: no fertilizer on the cutting itself, which can burn new roots. Some growers place potassium in the planting row.
- About 3 to 4 weeks after planting: the main NPK application, once the cuttings have rooted. Place it in a ring or band a short distance from the stem, not touching it, and cover it with soil.
- About 14 to 16 weeks after planting: a nitrogen top-up with urea, where the soil is poor.
Applying fertilizer too early wastes it, because young cuttings have few roots to take it up.
Soil pH and cassava
Cassava tolerates acid soils better than most crops. Studies found it handled low pH and high aluminium better than maize and soybean, with an optimum around pH 5.5. In one trial on a clay soil, yields only suffered when the pH fell below 4.3. So lime is rarely the first priority for cassava, unless the soil is extremely acid or the crop follows one that needs lime.
Signs of nutrient deficiency in cassava
| Nutrient | Typical sign |
|---|---|
| Potassium | Short, highly branched plants with very short upper internodes; leaf edges may curl upward in dry weather |
| Nitrogen | Pale, yellowish leaves across the whole plant and slow growth |
| Phosphorus | Thin stems and small leaves, sometimes with yellowing of lower leaves |
| Magnesium | Yellowing between the veins of lower leaves |
Potassium deficiency is easy to miss. Researchers note that cassava moves nutrients poorly to its upper leaves, and many deficient plants look normal. A leaf analysis of the fourth or fifth leaf from the top, at 3 to 4 months, is the reliable check: below about 1.5% K suggests the crop is short of potassium.
Common mistakes
- Too much nitrogen. Lush tops, poor roots.
- No potassium on old cassava land. The commonest cause of falling yields.
- Fertilizing the cutting at planting. Risky for young roots and largely wasted.
- Ignoring weeds. Weeds in the first three months take the fertilizer you paid for.
Buying fertilizer for cassava in bulk
Agromer supplies NPK compounds, including custom formulas from European factories, along with urea, potash (MOP) and DAP to importers, distributors and large growers. For cassava programmes, we can look at potassium-rich NPK grades. Tell us the grade, quantity, packaging and destination port.
Frequently asked questions
What is the best fertilizer for cassava?
A potassium-rich fertilizer with moderate nitrogen and a little phosphorus, such as a high-potassium NPK, or NPK plus MOP. Potassium is the nutrient that most often limits cassava yield.
How much NPK should I apply to cassava per hectare?
It depends on the soil. Trials on soils low in nitrogen and potassium found optimum yields at about 90 kg N, 18 kg P and 75 kg K per hectare. A soil test and local recommendations will give the right rate for your field.
When should I apply fertilizer to cassava?
The main application is usually 3 to 4 weeks after planting, once the cuttings have rooted. On poor soils, a urea top-up follows at around 14 to 16 weeks.
Is urea good for cassava?
Urea can supply part of the nitrogen, usually as a later top-up. Too much nitrogen makes cassava grow leaves and stems instead of roots.
Can I use MOP on cassava?
Yes. MOP is a common, low-cost potassium source for cassava, which is not as sensitive to chloride as crops such as tobacco.
What soil pH does cassava like?
Cassava tolerates acid soils well, with an optimum around pH 5.5. It handles low pH better than maize or soybean.
How do I know if my cassava needs potassium?
Look for short, highly branched plants with very short upper internodes. Because many deficient plants show no symptoms, a leaf test at 3 to 4 months is more reliable.