Potato (solanum tuberosum l.) yield and quality response to nitrogen, phosphorus and potassium fertilizer rates in Rwanda

Abstract

Potato is a strategic commodity with the potential to improve food and nutrition security and to generate income in Rwanda. Despite its potential, potato intensification remains low, translating into low yield. The low yield is occasioned mainly by the decline in soil fertility. In addition, farmers adapt a blanket fertilizer recommendation rate which is not sensitive to the actual crop needs. Field experiments were conducted in Birunga, Mudende [L1] and Buberuka, Rwerere [L2] highlands Agro-Ecological Zones (AEZs), during season A 2017 [S1] and B 2017 [S2] to determine the effects of rates of N, P and K on yield and quality of potato. The experiments were laid out using a Randomized complete block design with factorial arrangement, with four replicates. Factors were N rates (NX): (i) N0-0 kg ha-1, (ii) N50-50 kg ha-1 (iii) N100-100 kg ha-1; P2O5 rates (PX): (i) P0-0 kg ha-1, (ii) P50-50 kg ha-1, (iii) P100-100 kg ha-1and K2O rates (Kx): (i) K0-0 kg ha-1and (ii) K50-50 kg ha-1. Data collected included growth parameters, tuber yield components and quality attributes. Analysis of variance for the data, performed using SAS-version 9.2, revealed the existence of a significantly different soil fertility gradient, between the two locations and farms within both locations. The two locational and seasonal results showed similar response patterns with regard to effects of N, P, K and their combinations. Effects of location, N, P, K and N×P×K were found to be significant on all growth, tuber yield and quality traits except number of main stems per plant, while the effect of season was significant on all growth and yield attributes and non-significant on number of main stems per plant and all potato quality traits. With regard to tuber yield, L1, S2, N100, P100 and K50 factor levels and N100P100K50 combination performed better than other treatments. N100P100K50 recorded highest tuber yields: (32.73 ± 0.43) t ha-1 [L1] and (29.36 ± 0.41) t ha-1 [L2] and (31.05 ± 0.52) t ha-1 for pooled ANOVA. Contrarily to what happened at Rwerere (L2), effects of N100 and N50 on tuber yield as well as N100P100K50 and N50P100K50 were not significantly different from each other at Mudende (L1). With regard to potato quality, except N100P100K0, N50P100K0 and N0P100K0 found suitable for making potato salad, whole boiled and canned potatoes, all other treatments (with > 1.080, > 14%, > 20% and < 0.30% of specific gravity, starch, dry matter and reducing sugar content, respectively) were qualified suitable for making French fries, chips and flakes. N50P100K50 is recommended to Birunga AEZ whereas N100P100K50 is recommended to Buberuka AEZ. Further studies, using a wide range of fertilizer rates, will be necessary to determine optimal combination of N, P and K nutrient rates in both locations.