The yield of potato (8.86 tonnes/ha), the second staple food and cash crop in Kenya is remained low due to a reduction in seasonal precipitation and low soil fertility. Drought or dry periods between rainfall seasons and increased temperatures, which leads to high crop evapotranspiration, are experienced in 70-80% of the smallholder farms. Among major elements require by potato, nitrogen is the most important influential element but it is deficient in most potato-growing soils in Kenya because of nutrient depletion with inadequate nutrient replenishment results from continuous production. Hence the introduction of supplemental irrigation with an adequate application of this nutrient could increase crop yields. Therefore, this study was conducted in Nakuru, one of the major potato growing areas in Kenya, to determine the effects of full supplemental irrigation (FI) and four nitrogen levels, N0(0), N1(60), N2(90) and N3(130 kg N/ha) on tuber yield, water use efficiency (WUE) and nitrogen use efficiency (NUE) of potato grown in a mollic Andosol in Kenya compared to conventionnel rain-fed potato production.
The results showed that tuber yield, marketable tuber yield and NUE significantly differed due to the interaction effect between irrigation and N-fertilization rate (P<0.001) whereas the WUE was statistically different due to the N-fertilization rate (P<0.001). The highest tuber yield 58.28 tonnes/ha was found in supplemental irrigation with an application of 130kg N/ha treatment. Full supplemental irrigation treatment increased marketable yield by 129.84, 94.63, 151.21 and 126.63% for 0, 60, 90 and 130 kg N/ha, respectively compared to rain-fed N-fertilization treatments. NUE increased statistically with an increase in N rate up to 90 kg N/ha, then tended to increase slightly as nitrogen rate increased further. An increase in potato tuber yield was positively correlated with number of tubers/plant (r=0.75), NUE (r=0.95), WUE (r=0.72) (P < 0.001).
The high potato yield and marketable tuber yield in mollic Andosol can be obtained when all water deficits of the growing season are eliminated with supplemental irrigation and an application of 130kg N/ha but it is essential to exploit water regimes for acceptable yield with water-saving.