Abstract
Field trials were conducted during the 2009/10, 2010/11 and 2011/12 dry seasons at the Teaching and Research Farm of the Kebbi State University of Science and Technology, Aliero located at Jega (Lat. 120 11’N; Long. 40 16 E and 300 m above sea level) in the Sudan savanna ecological zone of Nigeria. The aim was to study the effect of irrigation interval and NPK fertilizer rates on yield of three varieties of Irish potato (Solanum tuberosum L.) in the study area. Treatments consisted of three irrigation intervals (3, 6 and 9 days), four rates of NPK (20:10:10) compound fertilizer (0, 300, 600 and 900 kg NPK ha-1) and three varieties of potato (Bertita, Diamant and Nicola). Factorial combination of irrigation interval and fertilizer rates was allocated to the main-plots while varieties were assigned to the sub-plots in a split plot design, replicated three times. The size of each sub-plot was 4.5 x 3 m (13.5 m). Result revealed that mean tuber diameter was highest at 3-day irrigation interval. Mean tuber weight, tuber number per stand, tuber weight per stand and fresh tuber yield were highest when irrigated at 3- or 6-day irrigation interval. Mean tuber diameter, mean tuber weight, number and weight of tubers per stand and yield per hectare peaked at 600 kg NPK ha-1, with no further significant response at fertilizer rates beyond this level. Result of irrigation and fertilizer interactions indicated that yield was generally optimized under either 3-day irrigation interval at 600 kg NPK ha-1 or 6-day irrigation interval at 900 kg NPK ha-1. Therefore the use of 600 kg NPK ha-1 under 3-day irrigation scheduling or widening the irrigation interval to 6-day coupled with increased fertilizer rate up to 900 kg NPK ha-1 proved optimum for high fresh potato tuber yield. Also, any of the three varieties could be adopted for good yield in the study area.

Key words: Yield, Irrigation, NPK fertilizer, Potato variety, Sudan Savanna.