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Potatoes: using well-rotted manure and compost.
Potatoes are a major cash and food crop in Kenya’s highlands, and they respond well to organic matter. They are also easily ruined by disease that spreads through seed, soil and infected plant waste. This guide covers what to apply, how to plant, and what to keep out of your compost heap.
The numbers that matter
These figures come from KALRO, the Kenya Agricultural and Livestock Research Organization, and from the Ministry of Agriculture’s SHEP PLUS potato guide. Hectare and acre figures are as each source gives them.
Soil, site and seed
Soil and site
- Choose well-drained medium loam. Avoid poorly drained or rocky soil.
- The Ministry’s guide gives a pH range of 5.5 to 7.5. Have the soil tested, especially if it may be acidic.
- Break the soil up well so air can reach the roots.
- Avoid fields that grew tomatoes, chillies or eggplant in the last two seasons.
Seed tubers
- Use certified, disease-free seed.
- Choose tubers 25 to 35 mm across, with 4 to 5 sprouts each.
- Plan on roughly 16 to 18 bags of 50 kg per acre (the Ministry’s guide gives 800 to 1,000 kg per acre).
- Do not cut seed tubers to stretch your supply.
SOURCES: KALRO, WARE POTATO PRODUCTION; MOALF/SHEP PLUS POTATO GUIDE
Manure, compost and fertiliser
| Input | Rate | Notes |
|---|---|---|
| Well-decomposed manure or compost | 5 to 10 t per hectare (KALRO) | Applied as a basal dressing. Well-rotted manure helps prevent black scurf. The Ministry’s guide recommends compost or manure but gives no rate. |
| DAP | 500 kg/ha, or 200 kg per acre | Applied in the rows at planting and mixed into the soil. |
| On acidic soils | MAP at the same rate as DAP (KALRO). The Ministry’s guide gives TSP at 80 kg and CAN at 120 kg per acre. | Let a soil test decide. |
Whichever fertiliser you use, keep the tubers from touching it. Mix it into the soil in the furrow first. The two sources do not give a rate that combines manure with a reduced fertiliser dose for potatoes, so treat the manure and DAP rates as separate recommendations and ask your extension officer how to combine them on your soil.
Planting step by step
- Prepare the fieldPlough thoroughly to remove weeds, then make furrows 75 cm apart and 10 to 15 cm deep.
- Add manure and fertiliserPut the well-rotted manure or compost and the DAP in the furrow and mix it into the soil.
- PlantPlace seed tubers every 30 cm with the sprouts facing up. Cover them completely with soil. Plant shortly before the rains begin.
- Earth upPile soil along the rows until the ridges stand about 25 cm high. Stop weeding and ridging once the plants cover the ground between rows, and avoid working in the crop when the soil is wet.
SOURCES: KALRO, WARE POTATO PRODUCTION; MOALF/SHEP PLUS POTATO GUIDE
Keep disease out of the field and the heap
Healthy seed, clean fields and rotation protect your crop more than any input does.
| Problem | What to know | What to do |
|---|---|---|
| Bacterial wilt | No chemical cure once a crop is infected. The germ can persist in soil for up to 4 years. | Avoid fields that had wilt. Use certified seed from a wilt-free field. Rotate crops. Burn infected debris. Do not bring in soil from affected fields. Clean your tools. |
| Late blight | Water-soaked spots on leaflets that enlarge and turn brown, with white mould under the leaf. | Plant tolerant varieties and certified seed, and remove infected plants. KALRO advises spraying registered fungicides, so consult your extension officer. |
| Black scurf | A fungal disease on tubers. | Use well-rotted manure, not fresh. |
| Common scab | Rough patches on tuber skin. | Rotate for two years or more. |
What this means for your compost heap.
Do not put wilt-infected plants or tubers into compost. The Ministry’s guide says to burn infected debris. We have not found a source showing that composting reliably destroys the germ, so the safe course is to keep infected material out of the heap altogether.
Rotate with crops outside the potato family, such as maize or beans. Tomatoes, chillies and eggplant are in the same family as potatoes and share their diseases.
SOURCES: KALRO, WARE POTATO PRODUCTION; MOALF/SHEP PLUS POTATO GUIDE. FUNGICIDE NAMES IN THE MINISTRY GUIDE ARE FROM A 2018 LIST: CHECK CURRENT REGISTRATION WITH THE PEST CONTROL PRODUCTS BOARD.
Harvesting for good skins
- Wait for maturity. Harvest 3 to 4 months after planting, depending on variety. Early harvests have low dry matter and soft skins that let infection in.
- Cut the haulms. Cut or pull the vines about two weeks before harvest so the skins harden.
- Keep tubers covered. Fully covered tubers are less likely to turn green and are safer from potato tuber moth.
The Ministry’s guide puts the average Kenyan yield at 3,200 kg per acre, and says good husbandry and clean planting material can raise it to 6,000 to 8,000 kg per acre.
SOURCES: KALRO, WARE POTATO PRODUCTION; MOALF/SHEP PLUS POTATO GUIDE
Questions people ask
Can I use fresh manure on potatoes?
The sources recommend well-rotted or well-decomposed manure. Well-rotted manure helps prevent black scurf. Compost fresh manure first.
Can compost replace DAP?
The sources give separate rates for manure and for DAP, and do not say compost can replace the fertiliser. A soil test and your extension officer can tell you how much, if any, fertiliser your soil needs.
Can I save my own seed?
Only from a clean crop. Bacterial wilt and other diseases travel on seed, so certified seed is the safer choice.
What can I plant after potatoes?
Crops outside the potato family. KALRO advises avoiding tomatoes, chillies and eggplant in the two seasons before potatoes, and rotating to manage wilt and blight.
Can I compost potato haulms?
Only if the plants were healthy. Burn plants infected with bacterial wilt, and do not compost them.
Want to make the compost for your potatoes?
We train farmers and groups to produce well-rotted compost from their own farm waste.