Farmer Bone-Konsira Tumwesigye holds some potatoes in her hands. To get a good harvest, she must spray her field with fungicides on a weekly basis, a labor intensive, time consuming and expensive undertaking. Photo Credit: CIP

The climate-smart way to grow potatoes commercially

Mary Gateri
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[rt_dropcap_style dropcap_letter=”T” dropcap_content=”HE Irish potato is a major contributor to Kenya’s food security, household incomes and improved livelihoods. It stands as the second most important food crop after maize. However, unpredictable climatic changes such as flooding, drought, and extreme temperatures have impacted potato production negatively. Since potatoes are grown mostly by smallholder farmers, a lot of attention ought to be paid to these climatic changes if at all these farmers are to continue growing the crop sustainably. There is need to adopt climate-smart crop management practices — from planting to harvesting — to build resilience to these climatic risks, improve productivity and reduce environmental pollution.”]

Farm selection

Potatoes require fertile soil so the part of the farm that has laid fallow for some time could be of great help. If not, make sure the part selected has not been under any crops from the solanaceae family such as tomatoes or even potatoes.

The soils should have proper drainage and the crop should be in the open without shading from trees.

Land preparation

The area should be ploughed during the dry season to clear all perennial weeds. The ploughing ensures loosening of the soil at least 40-50 cm deep. The area should be hallowed to ensure the soil is sufficiently fine without big clogs.

Before preparations for planting, carry out soil testing to guide on the fertilisers to be applied. If lime is recommended, apply 2-4 weeks before planting. The analysis should also guide on manure application.

For best results, the manure should be well decomposed. Dig furrows 15 cm deep and 75cm apart. Use a sisal twine to ensure furrows run straight.

If manure is not broadcast prior to digging furrows, then it can be put on the furrows and mixed well with the soil.

It should be noted that soil testing is absolutely necessary for climatesmart production as it guides on the correct fertiliser and amount to be applied, thus improving yields and ensuring sustainability while avoiding environmental pollution.

Seed for planting

The best seed for planting is certified seed which can be sourced from KALRO or Kenya Potato Council. Most farmers have traditionally recycled seed that is planted year after year.

Such seed is not good for commercial purposes as disease builds up and vigour goes down so that yield decreases over time. Good planting material makes a difference in climate-smart agriculture. Certified seed has good field performance and high yields.

It is certified for purity and freedom from disease by Kenya Plant Health Inspectorate Services (KEPHIS). The variety selected should be adaptable to the local growing conditions for good results, e.g drought-tolerant, frost-tolerant or pest- and disease-tolerant.

A variety for commercial purposes should have good marketability. The quantity of seed required per acre depends on size as seed size influences spacing. Two sizes are planted.

  • Size 1 seed (the egg size) is 25 – 45 mm. It is the best seed for planting. Quantities required are 50 x 16 bags per acre.
  • Size 2 seed (big size) is 45 – 60 mm. Larger quantities of these are required (50 x 20 bags/acre)

It is advisable to check the number of sprouts per seed. It should be at least four. If only one sprouts, knock out the sprout to stimulate development of more sprouts.

The number of sprouts are related to the number of stems that are positively correlated to the yield (each stem carries 5 potatoes). Farmers are cautioned not to cut the seed to generate more seed as this encourages growth of microorganisms. Obtain fresh planting seed (certified seed) after every 3 seasons for best results.

Planting

In the absence of irrigation water, planting time becomes very crucial. The crop should be able to utilise all the available moisture in the growing season. Planting just before the rains ensures good moisture utilisation. Potatoes require a lot of water to maximise on yields and to obtain good quality.

[rt_blockquote_style blockquote_style=”two” blockquote_content=”Pest and disease management is very important for potatoes. Late blight and bacterial wilt are notorious diseases which require proper attention. In order of importance, cut worms, potato tuber moth, white flies and aphids are the major pests of potato in Kenya.” blockquote_icon_color=”#dd9933″]

Fertiliser application is done at planting. The type and rates are determined from soil test results.

Apply fertiliser on the furrows and mix well with the manure. Place the tubers with the sprouts facing up for faster and uniform emergence.

A spacing of 30 cm within rows is used for eggsized seed while 38 cm is used for the bigger seed. After seed placement, the seed is covered by ridging to ensure preservation of moisture during the growing period.

Crop management

Weed control after crop emergence is very important as weeds compete for nutrients with the crop.

Weeds are best controlled when a pre-emergence herbicide is used. This greatly reduces the volume of weeds. First weeding should take place 2-3 weeks after emergence while the second weeding should take place after 5-6 weeks.

Ensure proper earthing of the crop during weeding. Thereafter, do not disturb, just pull out persistent weeds.

Potatoes require proper nutrition for good yields and quality. Top dressing with CAN fertiliser is important 3-4 weeks after emergence. Avoid fertilising late in the season as this encourages canopy development at the expense of tuber growth. The amount to apply is as per soil test recommendation.

Pest and disease management is very important for potatoes. Late blight and bacterial wilt are notorious diseases which require proper attention. In order of importance, cut worms, potato tuber moth, white flies and aphids are the major pests of potato in Kenya. To manage these, do the following

  1. Ensure use of disease-free certified seed at planting
  2. Destroy any volunteers from previous cropping seasons.
  3. In case of late blight, apply fungicides when necessary. Before disease appearance, use one spray of Mancozeb. Thereafter, use contact fungicides e.g. Daconil every7-10 days interval to manage the disease. The choice of interval and fungicide to use will depend on the infection pressure.
  4. If bacterial wilt is noticed (wilting of lower leaves), uproot the infected plants and bury them at least 1 metre deep.
  5. For pest control, use Thunder or Tihan from Bayer E.A. at the recommended rates.
  6. Use proper harvesting and storage practices

Harvesting and storage

Potatoes are ready for harvesting when the leaves turn yellow and finally dry. In preparation for harvesting, dehalm the crop. This involves cutting the tops and leaving the tubers underground for 10 – 15 days to harden the skin for good storage. Potatoes are harvested by using a garden fork or a hard stick, which causes less injury. Gently dig up the stool and, using fingers, remove the tubers from the soil.

This is well achieved during dry weather. Potatoes are stored in heaps, gunny bags or bamboo baskets. Disinfect surfaces or containers before storing. Sort out and cull injured and diseased potatoes before storing. Make sure the storage area is kept dark as light will turn the tubers green and render them inedible.

Mary Gateri is a research scientist at Kenya Agricultural and Livestock Research Organization (KALRO).

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