Many Kenyan farmers harvest five to seven tonnes of potatoes from an acre, according to available statistics. This is by far short of the optimal yield of between 16 and 20 tonnes or up to 400 sacks of 50 kilos.
At a cost of Ksh1,500 per bag, one is sure of Ksh600,000 per acre within only three months of planting. This can only be achieved when you plant the right seed, use the right inputs and follow apt agronomic practices.
To realise maximum yields, several factors should be considered when planting potatoes.
They include:
Soil testing
This is done to determine pH, which confirms availability of micronutrients; mineral and nutrient content of the soil before planting. The tests will give you indications on the following:
Nitrogen: Too much nitrogen will cause a lot of leaves and fewer tubers to be produced;
Phosphorus: Lack of phosphorus leads to poorly growing plants. Phosphorus needs to be given for a fast growing start, and more tubers, therefore, a better yield;
Potash: Sufficient potash will give more resistance to the plant during drought. The required amount depends on the potato variety, available potash in the soil, expected crop and weather.
Seeds
Use certified seeds;
Plant one variety only or separate them if more than one;
A large-sized potato is ideal for planting, contrary to popular practice where farmers select the small ones. Bigger ones have as many as six “eyes”. With each “eye” producing a shoot, a farmer is assured of more yields per plant. Small potatoes have only two “eyes”;
Treat the seeds with a fungicide against Rhizoctonia (Black scurf);
Some varieties have a long dormancy. Use seeds of an earlier seed crop;
If before planting, only the top sprout is there, remove it so that more emerge. Beware of infection;
Certain varieties can only grow in selected areas, because of soil type and climate. Seek the guidance from the Ministry of Agriculture extension workers.
Planting
Only plant seeds after they have sprouted, with the sprouts facing upwards. This ensures uniform growth;
Always plant a potato seed deep enough on a ridge and ensure there is a heap of soil;
Prepare the soil before planting to give you 15cm of loose ground. To do this mechanically, use a horizontal working rotovator;
To have a nice and equal field with plants, grade the seeds into several sizes;
Try to work properly with the row distances. It makes the ridging easier. If using a tractor for planting, use narrow wheels. Place the seed just on top of the untouched ground and make a little ridge above it;
Plant all seeds at the same depth; Spacing is 75cm between rows and 10 inches between tubers. This gives the roots expansion space and eases weeding.
Ridging
Ridging/hilling up helps in controlling weeds and gives the new tubers space to grow without becoming green because of exposure to light;
Shallow ridges will lead to poor yields. Potatoes should be planted at least eight inches deep for big tubers of between 45 and 60mm, while smaller ones of below 45mm in diameter require at least four inches deep;
Burying the seed this deep allows more roots to sprout, assuring the seed of a moist environment;
Ridge when the new plant is just emerging. If planting has been done properly, just 2cm of soil will be added on top of the original ridge;
Never bury new plants deeper than 4cm, as this will bring about an enormous decrease in yields;
Always be careful about the roots, they grow very close to the surface and if you damage them a lower yield will be the result.
Spraying programme
Potato blight is the most devastating disease capable of wiping out an entire plantation within a day. To guard against this, a farmer should get the right fungicide;
Monitor the crop on a daily basis;
Stick to a spraying programme. If it is a 10-day interval, it should remain so whether the disease has been detected or not. Farmers should seek advice from Ministry of Agriculture on the right programme;
There is more risk of attack during the wet season;
Spraying should commence when the plant attains a height of three inches.
Crop rotation
Do a good crop-rotation, and plant potatoes once in four years in the same field, otherwise nematodes will increase and you will never get rid of bacteria wilt;
During the rotational break, one needs to avoid planting crops of the same class (solanum tuberosum) such as tomatoes, which are normally attacked by the same diseases as potatoes.
Top dressing
Seek advice from agricultural officers whose decision is dependent on soil analysis results.
Weeding
When weeding, heap the soil around the plant to allow the roots to spread freely;
You could also apply selective herbicides;
Weeds that host bacterial wilt must be destroyed;
Beware of infections from other
fields (clean boots, machines,
wheels).
Irrigation
For regular growth, the plant requires a good water supply, especially when the stolons are developing and the number of tubers is established. When the soil is dry fewer tubers will be created. Drip-irrigation ensures the plant has sufficient water.
Harvesting
This is done in the third or fourth month after planting. To minimise tuber injuries, a forked hoe is recommended
Storage
Harvested potatoes should be stored in a dark room. Exposure to light makes them turn green. To avoid sprouting, temperature control is essential and a cold room recommended.
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