Problem Solving

Top dressing in potato field is important for tuberisation process and must be done in good time because when this process is delayed it results in underutilization of the fertilizers hence low yield.  When correct amount and type of fertilizers are timely used there is no need for booster fertilizers especially after flowering since it may not be used for the intended purpose.  Flowering in potato is mostly done after tuberisation process is already done. So when potatoes are flowering the farmer needs to ensure that the field has correct moisture levels for bigger tubers.

Generally it is advisable that application of second dose of nitrogenous fertilizer such as CAN or Urea be done when the crop is 14 to 21 days after planting and plant height is about 15 to 25 cm.  However, in tropical regions such as Malawi it is advisable to use CAN than Urea because Urea evaporates or volatilizes when exposed to sun and also encourages more vegetative growth and watery or soft starch tubers that is very susceptible to rotting. Apply the fertilizer in the grooves in  the soil surface 5 cm away from stems. Apply about 30 g of the fertilizer using 10 cupfuls of cup No.5 per metre. This mainly applies when the crop is grown for seed.  For ware potatoes the grower may apply 20 g per metre of ridge length using 5 cupfuls of cup No. 5. It should be noted that too much fertilizers or too close to the plant can burn the stems and leaves of the potato plant. Also note that nitrogen fertilizer such as Urea evaporates or volatilizes when exposed to sun. This justifies why hilling up (or banking) of plants should be done immediately after second fertilizer application. Adding soil around plants helps tubers and stolons (underground stems that carry tubers) to be kept in the soil. If stolons come out of the soil they will produce stems with leaves instead of tubers. Soil test results may also be necessary to guide the farmer on the quantity of CAN or Urea to apply per hectare of land. Where no soil test exists, 200-250 kg of CAN per hectare may be applied or 150-200 kg of Urea (46%N) per hectare may be applied for potatoes grown for seed whereas 150-200 kg/ha of CAN may be applied to achieve high tuber yield. Nevertheless, it is strongly recommended that for commercial farming soil test be conducted.

The nutrient requirement of potatoes is very high. It has a shallow root system and also a very short growing period during which it must bulk up yield. Nutrients must be readily available in correct and balanced amount.  Tuber quality is also significantly affected by plant nutrition. Phosphorus deficiency and Nitrogen or Potassium excesses can decrease specific gravity leading to small tubers hence low yields. Growth disruptions, because of fluctuations in nitrogen supply, can cause misshapen tubers with brown centres or hollow centre. Potassium deficiencies can result in increased black spot bruise at harvesting, darkened colour, and storage problems. Excess Nitrogen, on the other hand, can delay tuberisation and slow skin development at maturity. Vines with excessive nitrogen can create an environment more conducive to infection by certain pathogens. Calcium deficiency has been associated with internal brown spot. The potato plant has a poorly developed root system. Fertiliser is therefore mainly applied in the planting furrows at the time of planting. It should preferably be placed at the same level as, or under, the seed tubers.  It is recommended that potato planters be equipped with bins for fertiliser application. If the phosphorus requirement is very high, some of the phosphorus may be broadcast and incorporated into the topsoil. The rest is then applied in the planting furrows along with the nitrogen (N) and potassium (K). Nitrogen top dressings are applied on either side of the plant row, after the rows are ridged and irrigated. Potatoes respond well to fertilizers. Being a root crop, they respond well to phosphorous and nitrogen.