Fertilizer application
Fertilizers are fast acting inorganic materials supplying one or more key nutrients to the plant.
Nutrients required by the potato crop may be supplied either through:
Organic - commercial organic fertilizers, farmyard manure, compost, liquid tea, green manure and minjingu rock phosphate).
Inorganic fertilizer; Diammonium phosphate (DAP), nitrogen-phosphorus-potassium
(NPK), triple superphosphate (TSP), monoammonium phosphate (MAP), calcium
ammonium nitrate (CAN) and Urea.
Customized and blended fertilizer according to crop specific and soil test result is advisable.
It is important to note that:
Liming is highly recommended for acidic soils.
Micronutrients are supplied through foliar sprays in cases of deficiency but it is advisable to apply through field grade fertilizer.
It is important to consider target yield during nutrient application rate. For instance,to produce 56 tons’/Ha potatoes requires about 235 kg N/Ha, 31 kg P/Ha and 336 kg K/Ha according to Westermann (2005). Although, the recommended rate in Kenya is 90 kg/Ha and 230 kg P/Ha based on the commonly used fertilizer (DAP), experts do not recommend the blanket application rate because of the following reasons: Potato is a heavy feeder of K which DAP does not have because it contains only nitrogen and phosphorus; DAP has too much P which could cause long term acidity if used for a long time; and lastly it is advisable to split N applications during the lifetime of a crop because loses of N occur much faster and cannot survive until crop maturity.
Different fertilizer companies formulate different fertilizers for potato crops.
Fertilizers used for planting potato are;
• DAP (Diammonium Phosphate)
• NPK (17:17:17; 20:20:20; 23:23:0)
• Blended NPK (14:28:14+Te, NPK 18:0:21+Te)
• Single Superphosphates (SSP)
• Triple superphosphates (TSP)
Steps in applying fertilizer
• Divide the land or furrow into 4 equal quarters.
• Divide available fertilizer into 4 equal portions.
• Allocate each quarter portion of fertilizer to each quarter portion of land.
• Apply each portion of fertilizer to the allocated portion of land and cover with soil awaiting seed placement.
Irrigation
Soil moisture from rains can be supplemented by irrigation. The irrigation methods available are drip, sprinkler and furrow.
Drip irrigation
- This type of irrigation is quite more effective and it may not contribute to establishment and spread of foliar diseases
- However, it is more expensive than sprinkler irrigation and many smallholder farmers may afford the method.
Sprinkler irrigation
-This method may not cover all parts of the field adequately.
- It may spread foliar diseases due to an extension of availability of moisture in the canopy. Prolonged moisture on the leaves creates a favorable environment for the growth of fungal and bacterial pathogens.
- In this method infections can easily spread from the upper leaves to lower leaves as water drains down the crop.
Furrow irrigation
-Maintenance and monitoring of drainage in the furrows is very key in this type of irrigation to avoid water logging. Waterlogging is a favorable condition for anaerobic conditions and spread of soil borne disease caused by pathogens in the field.
It is important to note that:
Consistent water supply is key in the emergence stage, tuber setting and tuber bulking stages.
Water stress during the above mentioned stages leads to misshapen tubers and low yields.
A farmer should plan for irrigation based on these critical periods which should be done either early in the morning or late afternoon to minimize evaporation
