Sweet potato Nutrient Deficiency: Signs, Causes and the Fertilizer That Fixes It
Sweet potato nutrient deficiency is one of the first things to check when the leaves of your kamote (sweet potato) turn yellow, purple or burnt at the edges. On Philippine farms the usual ones are potassium, nitrogen, phosphorus, magnesium, boron, calcium, sulfur and zinc. 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 boron, calcium, sulfur and zinc 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 sweet potato nutrient deficiency you have, and a soil test confirms it. Each one below has its signs, its causes and its fix.
Sweet potato 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 and scorch at the edges and roll up, and roots stay small. | Muriate of potash 0 0 60, Sulfate of potash 0 0 50 |
| Nitrogen | old, lower leaves, the whole plant | Pale green vines that spread slowly, with the oldest leaves yellowing and drying. | Urea 46 0 0, Complete 14 14 14 |
| Phosphorus | old, lower leaves, the roots | Small, stunted vines with dark old leaves and purple red color under the leaves. | Single superphosphate 0 20 0, Complete 14 14 14 |
| Magnesium | old, lower leaves, between the veins | Older leaves yellow between the veins, sometimes with red or purple on top, and cup. | Epsom salt / magnesium sulfate, Dolomite |
Shows first on the young leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Boron | young leaves and the tip, the roots | Young leaves are distorted and brittle, and storage roots have hollow or brown spots inside. | Borax |
| Calcium | young leaves and the tip, the roots | Leaf tips die back and storage roots come out soft, small and misshapen, on very acid soil. | Agricultural lime, Dolomite |
| Sulfur | young leaves and the tip, the whole plant | Leaves yellow from the tip to the base, veins included, and vines stay short with few branches. | Ammonium sulfate 21 0 0, Single superphosphate 0 20 0 |
| Zinc | young leaves and the tip | Short internodes, small pale young leaves, and purple shoot tips. | Zinc sulfate, Agricultural lime |
Before you buy fertilizer for a sweet potato nutrient deficiency
So use the table to pick the likeliest sweet potato 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 sweet potato
Yellowing starts at the edges of the older leaves and turns into brown, scorched margins. Leaves may curl or roll upward at the edges, age early and drop, so the vine covers less ground. Vines wilt even in moist soil, and fewer and smaller storage roots form. You see it most at this stage: mid season, when storage roots bulk up.
Why potassium deficiency happens in kamote
Sandy and highly weathered soils, and fields planted to root crops for years, since roots carry away a lot of potassium. Acid soils hold less potassium.
How to tell it apart
Magnesium deficiency yellows between the veins of old leaves rather than burning the edges. Drought scorch shows on many leaves at once and recovers after rain. To be sure, soil test for potassium, and a leaf test. Look for edge scorch starting on the oldest leaves.
What to apply for potassium deficiency
Apply Muriate of potash 0 0 60 following the soil test, best split between planting and early vine growth. For quick help spray potassium sulfate at 10 g per liter (160 g in a 16 liter sprayer) in the morning, or 1 percent potassium chloride every 15 days. 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
- Sulfate of potash 0 0 50
- Complete 14 14 14
- Dolomite
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, add organic matter and wood ash, keep the soil pH above 6 with lime or dolomite, and give potash every season.
Nitrogen deficiency in sweet potato
Leaves turn an even light green, starting on the older, lower leaves. Vines grow slowly with fewer leaves, so the ground stays bare longer. The oldest leaves yellow, wilt and dry, and young leaves may show purple veins. You see it most at this stage: first two months, while the vines spread.
Why nitrogen deficiency happens in kamote
Sandy soils, soils low in organic matter, and rain that washes nitrogen out.
How to tell it apart
Sulfur deficiency yellows the young leaves too and veins do not stay green. Magnesium deficiency shows yellow between green veins. To be sure, check that yellowing started on the oldest leaves, then test the soil. A leaf test confirms it.
What to apply for nitrogen deficiency
Apply Urea 46 0 0 following the soil test. You can also give a urea spray of 10 g per liter (160 g in a 16 liter sprayer) every 15 days. Do not overdo nitrogen. It grows vines at the cost of roots. 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
- Ammonium sulfate 21 0 0
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 before planting and a balanced fertilizer such as 14 14 14. Split the nitrogen into two or three doses.
Phosphorus deficiency in sweet potato
Plants stay small and stunted with a poor root system. Older leaves turn dark green, and a purple red color shows mostly on the underside of the leaves. Yellow patches then spread unevenly and the oldest leaves die. You see it most at this stage: early growth.
Why phosphorus deficiency happens in kamote
Acid soils and volcanic soils that hold phosphorus tightly, and soils low in organic matter.
How to tell it apart
Iron deficiency can be confused with the dark old leaves, but it yellows the young leaves. Cold or wet weather also gives purple tints for a short time. To be sure, soil test for available phosphorus.
What to apply for phosphorus deficiency
Use single superphosphate for a quick fix, or bone meal and rock phosphate for the long term, following the soil test. Phosphorus is taken up best at pH 6.5 to 7.5. 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
- Rock phosphate
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, add organic manure with phosphorus fertilizer and correct strong acidity.
Magnesium deficiency in sweet potato
Older leaves yellow between the veins and age early, and may curl or cup. Red or purple color can appear on the upper side of old leaves, and the yellow parts turn brown and dead. Roots may come out small and misshapen. You see it most at this stage: mid season.
Why magnesium deficiency happens in kamote
Sandy and acid soils, and heavy potash, which blocks magnesium.
How to tell it apart
Potassium deficiency burns the leaf edges first. Nitrogen deficiency yellows the whole leaf evenly. 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. Apply magnesium and potash at different times. 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.
Boron deficiency in sweet potato
Young leaves become distorted and pale, stems are brittle, and leaf tips and edges yellow and die in spots. Storage roots develop poorly and can have hollow areas in the flesh, which ruins their sale. You see it most at this stage: root bulking.
Why boron deficiency happens in kamote
Sandy soils low in organic matter, high pH soils, and dry spells.
How to tell it apart
Calcium deficiency also hits the growing tips, but gives small, soft roots. Weevil damage leaves tunnels, not hollows. To be sure, soil test for boron. Cut roots to look inside. 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). Do not apply boron together with calcium or ammonium fertilizers. 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 for boron on sandy fields before planting. Test the soil every two or three years. Keep organic matter up with compost, manure or crop residues.
Calcium deficiency in sweet potato
Growing points and young leaves show dead spots and tip dieback, with some yellowing between the veins. Root growth is poor, and storage roots can be soft, very small and misshapen. You see it most at this stage: early growth to root bulking.
Why calcium deficiency happens in kamote
Very acid soils, and soils very high in phosphorus. 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 damages the tips, with brittle stems and hollows in the roots. 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 instead.
- 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, test the pH every few seasons and lime ahead of planting. Test the soil every two or three years. Keep potash in balance with magnesium and calcium.
Sulfur deficiency in sweet potato
Yellowing starts at the leaf tip and moves to the base, and the veins turn yellow too. Plants are badly stunted with small leaves and few branches, and leaves may curl or cup. Roots can be misshapen. You see it most at this stage: early growth.
Why sulfur deficiency happens in kamote
Soils low in organic matter, and burning crop waste, which drives off sulfur.
How to tell it apart
Nitrogen deficiency starts on the old leaves. Iron deficiency keeps the veins green. 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 a sulfur bearing fertilizer such as Ammonium sulfate 21 0 0 or single superphosphate. 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
- Single superphosphate 0 20 0
- Gypsum
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.
Zinc deficiency in sweet potato
Internodes stay short and young leaves show vein clearing and paling. Shoot tips may turn purple. You see it most at this stage: early growth.
Why zinc deficiency happens in kamote
Soils outside pH 5 to 7.5, and heavy phosphorus.
How to tell it apart
Phosphorus deficiency gives purple older leaves, not purple tips. Iron deficiency yellows young leaves between green veins. To be sure, soil test for zinc. 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. In severe cases spray 2 g zinc sulfate with 2.5 g lime (calcium carbonate) per liter in the morning. Do not apply zinc and phosphate together. 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, keep the soil pH between 5 and 7.5. Test the soil every two or three years.
A soil test is the surest check for any sweet potato 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 kamote needs. That saves money, because extra fertilizer is money lost.
Open the Nutrient Deficiency Finder, pick kamote, 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
Sweet potato nutrient deficiency questions
Why are my kamote leaves turning yellow?
What fertilizer fixes potassium deficiency in sweet potato?
What fertilizer fixes nitrogen deficiency in sweet potato?
What fertilizer fixes phosphorus deficiency in sweet potato?
How do I know which nutrient my kamote lacks?
Find the missing nutrient and fix it
With Libre + Anee, read the whole guide: how to tell the deficiency from look alikes, how to be sure, what to apply, and the fertilizers sold here that supply it.
The account is free, no credit card.
