Critical shoot Nitrogen curve for potato varieties Asante and Tigoni in Kenya

Potato is a major crop in Kenya with its production area increasing as a result of people opting for potatoes than other crops. The production is however lower than what is expected due to several challenges, among them being low fertility, diseases and inadequate certified seeds. Nitrogen as one of the major plant nutrients has a greater influence in potato yields as well as the quality. Critical nitrogen dilution curves have been used as a precise method of managing nitrogen fertilization in farms. Use of chlorophyll meters is also increasing due to its ease in taking measurements. A survey with specific objectives of determining potato nitrogen status in the farmer’s field along Mau and West Aberdares potato growing gradients in Kenya. A field experiment with the aim of developing critical nitrogen dilution model for potatoes varieties Asante and Tigoni in Kenya, and determining the relationship between the total shoot nitrogen concentration and the chlorophyll content (SPAD index) in potatoes. The survey was carried out during long rains of 2012 in two transect in the rift valley and it involved administering a questionnaire and collecting of soil and leaf samples. Field experiments were conducted in a split plot design at the university of Nairobi farm during the short and long rains season of 2012 using potato varieties Asante and Tigoni with four nitrogen fertilizer levels (0, 45, 90, 135 N kg/ha). The survey revealed that majority of farmers (78%) use fertilizers but in levels lower than the recommended for Nitrogen. The critical nitrogen dilution model established is Nc= 5.8W-0.16 for variety Tigoni and Nc= 6.4W-0.18 for variety Asante with r2 of 0.41 and 0.50 respectively. A linear relationship between shoot nitrogen content and the SPAD index was established for the two seasons with r2 of 0.45 and 0.51. It can thus be recommended for extension service provider to use the tools in helping the farmers to apply adequate fertilizer in their crops.