Cassava Nutrient Deficiency: Signs, Causes and the Fertilizer That Fixes It
Cassava nutrient deficiency is one of the first things to check when the leaves of your kamoteng kahoy (cassava) turn yellow, purple or burnt at the edges. On Philippine farms the usual ones are potassium, nitrogen, phosphorus, zinc, magnesium, calcium, sulfur and boron. This guide shows where each one starts, how to be sure, and the fertilizer that fixes it.
Start with one question: did the change begin on the old leaves or on the young ones? Potassium, nitrogen, phosphorus and magnesium move inside the plant, so a shortage shows on the old, lower leaves first. But zinc, calcium, sulfur and boron stay where the plant first put them, so the young leaves and the growing tip show it first. After that, the color and the pattern narrow down which cassava nutrient deficiency you have, and a soil test confirms it. Each one below has its signs, its causes and its fix.
Cassava nutrient deficiency signs, old leaves and young leaves
Shows first on the old leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Potassium | old, lower leaves, leaf edges and tips | Older leaves yellow between the veins and scorch at the edges. Plants branch a lot and sprawl. | Muriate of potash 0 0 60, Complete 14 14 14 |
| Nitrogen | old, lower leaves, the whole plant | Pale green plants with short stems and small leaves, yellowing from the bottom up. | Urea 46 0 0, Complete 14 14 14 |
| Phosphorus | old, lower leaves, the roots | Stunted plants with a few yellow lower leaves and purple under the leaves, and late harvest. | Single superphosphate 0 20 0, Complete 14 14 14 |
| Magnesium | old, lower leaves, between the veins | Lower leaves turn yellow between green veins and cup inward. | Epsom salt / magnesium sulfate, Dolomite |
Shows first on the young leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Zinc | young leaves and the tip, between the veins | Young leaves have narrow, pale lobes that curl up, on short internodes. | Zinc sulfate, Agricultural lime |
| Calcium | young leaves and the tip, leaf edges and tips | Upper leaves curl and get brown to black spots at the tips and edges, on very acid soil. | Agricultural lime, Dolomite |
| Sulfur | young leaves and the tip, the whole plant | The young upper leaves yellow first, and stems are thin and weak. | Ammonium sulfate 21 0 0, Gypsum |
| Boron | young leaves and the tip | Small deformed young leaves on short stalks with brown gummy spots on the stalks and stem tips. | Borax |
Before you buy fertilizer for a cassava nutrient deficiency
So use the table to pick the likeliest cassava nutrient deficiency, then read its section below. Also keep in mind that dry soil, standing water, cold nights, a pest or a disease can look the same. That is why it pays to check the roots and the whole field first.
Potassium deficiency in cassava
Yellowing between the veins starts on older leaves and moves up. Leaf edges die and turn brown, and the dead area spreads inward. Plants branch too much and sprawl, leaves are smaller and narrower, and roots carry less starch. You see it most at this stage: from about 3 months after planting, as roots bulk.
Why potassium deficiency happens in kamoteng kahoy
Fields planted to cassava year after year, since roots take away a lot of potassium, and sandy, acid soils. Cassava draws more potassium from the soil than it does nitrogen or phosphorus.
How to tell it apart
Magnesium deficiency also yellows between veins but without edge scorch. Mite damage gives speckled, bronzed leaves, with mites under the leaf. To be sure, soil test for potassium. Check the oldest leaves for edge scorch.
What to apply for potassium deficiency
Apply Muriate of potash 0 0 60 following the soil test, split in parts. Put one third of the nitrogen and potash in at planting, then split the rest at 2.5 and 5 months. Give a potassium sulfate spray of 10 g per liter (160 g in a 16 liter sprayer) in the morning for quick help. A usual dose is 2 to 3 bags of Muriate of potash 0 0 60 per hectare, half at planting and half when the roots or tubers start to swell.
- Muriate of potash 0 0 60
- Complete 14 14 14
- Sulfate of potash 0 0 50
Sold here with potassium: Atlas Muriate of Potash (MOP) by Atlas Fertilizer (0 0 60), Simplot Sulfate 0 0 50 by Nutranta, Potassium Nitrate by Parafield (13 0 46) and Qrop Mix Production 14 0 23 plus 13 Cao by Farmtech Agriland (14 0 23 with 9.3 percent calcium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to potash fertilizer, and the page on potassium deficiency in every crop. In anee.io, Anee, the smart farm technician, reads a photo of the leaf and tells you which nutrient is short.
To keep it away, the national recommendation is 8 bags of Complete 14 14 14 per hectare. A rate matched to your field can yield more, for example 180 kg N, 70 kg P2O5 and 250 kg K2O per hectare. Return leaves and stems to the field.
Nitrogen deficiency in cassava
The whole plant turns pale to light green, starting on the older, lower leaves and moving up. Stems are short and leaves small, and new leaves come slowly. Roots are fewer and smaller, with less starch. You see it most at this stage: first 3 to 4 months.
Why nitrogen deficiency happens in kamoteng kahoy
Soils low in organic matter, sandy soils, and fields cropped for years without fertilizer.
How to tell it apart
Potassium deficiency burns the leaf edges. Sulfur deficiency yellows the young upper leaves first. To be sure, check that yellowing starts at the bottom of the plant. Soil test.
What to apply for nitrogen deficiency
Apply Urea 46 0 0 following the soil test, split with the potash. You can also give a urea spray of 10 g per liter (160 g in a 16 liter sprayer) every 15 days. A usual side dress is 1 to 2 bags of Urea 46 0 0 or 2 to 4 bags of Ammonium sulfate 21 0 0 per hectare, 30 to 45 days after planting.
- Urea 46 0 0
- Complete 14 14 14
Sold here with nitrogen: Atlas Granular Urea (46 0 0) by Atlas Fertilizer, Amigo Planters Ammonium Chloride by La Filipina (25 0 0), Agripower 46 0 0 (Locally Blended) Coated by Green Acres Agri Tech and Calcipro by Ramgo (15.5 0 0 with 18.8 percent calcium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to urea fertilizer, and the page on nitrogen deficiency in every crop.
To keep it away, use compost or manure and a balanced fertilizer at planting.
Phosphorus deficiency in cassava
Plants are stunted with a small root system. A few lower leaves turn yellow while the upper leaves stay green, and the underside of leaves may turn purple. Maturity is late and roots are small with less starch. You see it most at this stage: early growth.
Why phosphorus deficiency happens in kamoteng kahoy
Acid upland soils. Skipping phosphorus fertilizer brings it on, and it can cut the harvest to about half.
How to tell it apart
Potassium deficiency also yellows lower leaves but scorches the edges. To be sure, soil test for available phosphorus.
What to apply for phosphorus deficiency
Put all the phosphorus in at planting, using Superphosphate, 16 20 0 or 14 14 14 at the soil test rate. Use single superphosphate for a quick fix and rock phosphate for the long term. A usual basal dose is 4 to 6 bags of Complete 14 14 14 per hectare in the furrow at planting.
- Single superphosphate 0 20 0
- Complete 14 14 14
- 16 20 0
Sold here with phosphorus: Philphos 18 46 0 (Di Ammonium Phosphate), Atlas Super Gro (16 20 0) by Atlas Fertilizer, Amigo Planters Granular Single Super Phosphate by La Filipina (0 18 0 with 11 percent sulfur) and Triple Super Phosphate by Newman Chemicals (0 46 0). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to 16 20 0 fertilizer, and the page on phosphorus deficiency in every crop.
To keep it away, apply phosphorus each crop and add organic manure.
Zinc deficiency in cassava
Young leaves turn yellow between the veins and the leaf lobes become narrow, pale and curl upward. Leaf tips die, internodes stay short and leaves are deformed. Maturity is delayed. You see it most at this stage: early growth, from the first weeks after planting.
Why zinc deficiency happens in kamoteng kahoy
Sandy soils low in zinc, soils outside pH 5 to 7.5, and heavy phosphorus. On sandy soils, zinc shortage is a common reason for low cassava yield.
How to tell it apart
Mite damage also distorts young leaves but with speckling. Mosaic virus gives a yellow and green mosaic with twisted leaves. To be sure, soil test for zinc and pH, or a leaf test. In a soil test, less than 0.8 ppm of zinc is low.
What to apply for zinc deficiency
Give about 20 kg Zinc sulfate per hectare to the soil, or in severe cases a spray of 2 g zinc sulfate with 2.5 g lime per liter in the morning. Mixing 18.75 kg of zinc sulfate per hectare into the soil with the NPK gives the best yield and return. Give the soil dose at planting or when the rains begin, and sprays on young growth.
- Zinc sulfate
- Agricultural lime
Sold here with zinc: Harvester Zinc Sulphate Heptahydrate by Universal Harvester (22 percent zinc), Petbowe Zinc Sulphate Monohydrate (33 percent zinc), Tierramino ZN by Unilox Far East Resources (7 0 0 with 10 percent zinc) and Liquid Chelate Zinc with Sulfur by Sagrex (10 percent zinc and 5 percent sulfur). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to fertilizer with zinc, and the page on zinc deficiency in every crop.
To keep it away, add zinc sulfate with the basal fertilizer on sandy fields, and do not apply it together with phosphate. Test the soil every two or three years.
Magnesium deficiency in cassava
Yellowing between the veins starts on older leaves and moves to younger ones while the veins stay green. Leaves curl or cup inward, and in extreme cases turn whitish and die. Plants are stunted. You see it most at this stage: mid season.
Why magnesium deficiency happens in kamoteng kahoy
Sandy soils, acid soils and heavy potash.
How to tell it apart
Potassium deficiency scorches the leaf edges. Zinc deficiency narrows the young leaf lobes. To be sure, soil test for magnesium.
What to apply for magnesium deficiency
Give about 80 kg magnesium sulfate per hectare in bands near the plants. Do not apply magnesium and potash at the same time. Put the soil dose in before planting or when the rains begin. Sprays show results in 10 to 14 days.
- Epsom salt / magnesium sulfate
- Dolomite
Sold here with magnesium: Dolomite by A6 Agrisource (24 percent calcium and 11 percent magnesium), Agsmart Kieserite Granule (20 percent sulfur and 16.3 percent magnesium), DDDD Planter's Choice Magnesium Sulphate Monohydrate by Modern Time (15.1 percent magnesium) and Zetryl MAG 9 by Zetryl Chem (9 percent magnesium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to complete fertilizer, and the page on magnesium deficiency in every crop.
To keep it away, use Dolomite over the long run on acid soils. Test the soil every two or three years. Lime acid soil with Dolomite rather than plain lime.
Calcium deficiency in cassava
Upper leaves curl and twist, and dead spots form at the tips and edges that grow brown to black. Stems are short and brittle, leaves small, and roots shallow. You see it most at this stage: early growth.
Why calcium deficiency happens in kamoteng kahoy
Very acid soils, soils high in phosphorus, and boron shortage, which calcium needs to work. Heavy potash or ammonium fertilizer, salty soil and dry spells keep calcium from reaching fruit and young leaves.
How to tell it apart
Boron deficiency also deforms young leaves, with gummy brown spots on the leaf stalks. To be sure, soil pH and calcium test. A soil test for calcium and pH, and a leaf test, confirm it.
What to apply for calcium deficiency
On acid soils, lime about 250 kg per hectare where the pH is 5.5 to 6. About 840 kg per hectare in two splits where it is 3.5 to 4.5. On alkaline soils use Gypsum.
- Agricultural lime
- Dolomite
- Gypsum
Sold here with calcium: Planters Products Lifelime (36.2 percent calcium), Dolomite by A6 Agrisource (24 percent calcium and 11 percent magnesium), Calcipro by Ramgo (15.5 0 0 with 18.8 percent calcium) and Philphos Gypsum (22.2 percent calcium and 17.4 percent sulfur). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to fertilizer for tomatoes, and the page on calcium deficiency in every crop.
To keep it away, lime acid soils ahead of planting. Test the soil every two or three years. Keep potash in balance with magnesium and calcium.
Sulfur deficiency in cassava
Yellowing appears first on the upper, younger leaves and moves down. Shoots and roots grow less, stems are thin and weak, maturity is late and root yield drops. You see it most at this stage: early growth.
Why sulfur deficiency happens in kamoteng kahoy
Soils low in organic matter and burning of crop waste.
How to tell it apart
Nitrogen deficiency starts on the lower leaves. To be sure, soil and leaf test for sulfur. In a soil test, less than 10 ppm of sulfate sulfur is low.
What to apply for sulfur deficiency
Use Ammonium sulfate 21 0 0 or single superphosphate in the program. Give about 25 kg sulfur dust per hectare on sulfur poor soils, or Gypsum on alkaline soils. Give it at planting or with the first side dress.
- Ammonium sulfate 21 0 0
- Gypsum
- Single superphosphate 0 20 0
Sold here with sulfur: Atlas Ammosul 21 0 0 by Atlas Fertilizer (21 0 0 with 24 percent sulfur), Philphos Gypsum (22.2 percent calcium and 17.4 percent sulfur), Harvester Sulphate of Potash by Universal Harvester (0 0 50 with 17.5 percent sulfur) and Agsmart Kieserite Granule (20 percent sulfur and 16.3 percent magnesium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to ammonium sulfate fertilizer, and the page on sulfur deficiency in every crop.
To keep it away, add organic matter and stop burning crop waste. Test the soil every two or three years.
Boron deficiency in cassava
Young leaves come out small and deformed on short leaf stalks, with abnormal edges. Brown, gummy spots form on the leaf stalks and the growing part of the stem, stems turn brittle and root growth drops. You see it most at this stage: early growth.
Why boron deficiency happens in kamoteng kahoy
Sandy soils low in organic matter and dry spells.
How to tell it apart
Calcium deficiency also curls young leaves but without gummy spots. Zinc deficiency narrows the leaf lobes. To be sure, soil test for boron. In a soil test, less than 0.5 ppm of boron is low.
What to apply for boron deficiency
Give about 10 kg Borax per hectare to the soil, or a borax spray of 1 g per liter (16 g in a 16 liter sprayer). Keep boron and calcium applications apart. Give boron before flowering: flowers and fruit set need it most.
- Borax
Sold here with boron: Etifert 11 (Borax Decahydrate) by Zetryl Chem (11 percent boron), Fertibagra 15G by Unilox Far East Resources (14.6 percent boron), B17 (Boric Acid) by Newman Chemicals (17 percent boron) and Better Yield by Bacphil Planters Fertilizer (0 0 0.9 with 10 percent boron). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to foliar fertilizer, and the page on boron deficiency in every crop.
To keep it away, test sandy fields before planting. Test the soil every two or three years. Keep organic matter up with compost, manure or crop residues.
A soil test is the surest check for any cassava nutrient deficiency. Before you buy, ask your Municipal Agriculture Office where to send a soil sample. The DA regional soil laboratories test soil, and the result says how much of each fertilizer your kamoteng kahoy needs. That saves money, because extra fertilizer is money lost.
Open the Nutrient Deficiency Finder, pick kamoteng kahoy, say where the leaves changed first and what you see, and get the fertilizers sold here that fix it.
- Anee, the smart farm technician, reads a photo of the leaf
- The cropping calendar dates every fertilizer application of your season
Cassava nutrient deficiency questions
Why are my kamoteng kahoy leaves turning yellow?
What fertilizer fixes potassium deficiency in cassava?
What fertilizer fixes nitrogen deficiency in cassava?
What fertilizer fixes phosphorus deficiency in cassava?
How do I know which nutrient my kamoteng kahoy lacks?
Find the missing nutrient and fix it
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