Despite potato yield potential, its intensification level remain low in Rwanda, translating into low yield occasioned mainly by the decline in soil fertility. Field experiments were conducted in Birunga, Mudende [L1]) and Buberuka, Rwerere [L2] highlands Agro-Ecological Zones (AEZs), during September- December 2016 and March-June 2017 crop growing seasons to determine the effects of varying rates of N, P and K on potato tuber yield and yield components. The experiments were laid out using randomized complete block design with factorial arrangement, with four replicates. Factors were N rates (NX) i.e N1-0 kg ha-1, N2 – 50 kg ha-1, N3 – 100 kg ha-1 ; P2O5 rates (PX) i.e P1-0 kg ha-1, P2 – 50 kg ha-1, P3 – 100 kg ha-1and K2O rates (Kx) i.e K1- 0 kg ha1and K2- 50 kg ha-1. Number of tubers per plant, fresh tuber weight, small tuber yield, medium tuber yield, large tuber yield and total tuber yield were measured. Analysis of variance, performed using SAS-version 9.2, revealed that interaction effects of N×P×K were very highly significant on all parameters. Generally, N3×P3×K2 performed better than other treatments and recorded highest tuber yields in all situations: (32.73 ± 0.43) t ha-1[L1] and (29.36 ± 0.41) t ha-1 [L2] and (31.05 ± 0.52) t ha-1for pooled ANOVA. Contrarily to what happened at L2, N3P3K2 andN2P3K2 were not significantly different at L1. N2P3 K2 is recommended to L1 whereas N3P3K2 is recommended to L2.

This study assessed soil fertility in potato farms of Birunga and Buberuka highlands agro-ecological zones (AEZs). It compared nutrients levels (N, P, K, Mg, Ca, Na, S, Mn, Cu, Zn and Fe) and other parameters (pH, organic carbon [OC], cation exchange capacity [CEC], base saturation [BS], bulk density [BD] and texture) of soil samples. ANOVA revealed that pH of soils (5.53-6.50) varied from slightly to moderately acidic, BD fell below optimum for plant growth (Lessthan 1.8gcm-3), texture was sandy loam to sand clay loam. Soil fertility for OC (3.33-5.53%), N (0.15-0.31%) and CEC (10.08-18.60 meq/100g) varied from low to medium; and medium to high for BS (34.78-61.91%); was qualified medium for P (5.75-9.20 ppm), K (0.21-0.54 meq/100g), S (6.46 - 8.15 ppm) and majority of micronutrients. Values from Birunga AEZ were higher than ones from Buberuka AEZ except for BD, CEC, clay, silt, Na and Fe. There were significant differences between farms within locations for all parameters and significant differences between locations for all parameters except Na and Mn.