Effect of timing and methods of mineral fertilizer application on Irish potato (Solanum tuberosum L.) performance in Musanze and Nyaruguru Districts, Rwanda
Irish potato is among the most important tuber crops produced in Rwanda and is among priority crops on which the national programme of intensification and development of sustainable production systems is primarily focused, but so far its yield is still below the genetic potential. A field experiment was therefore conducted to investigate the effect of timing and methods of mineral fertilizer (N.P.K 17-17-17) application on growth, yield and yield components of Irish potato - cruza variety in Kibeho (Nyaruguru District) and Kinigi (Musanze District) during the long rainy season (mid-February - June) of 2012. The experiment was laid out as a RCBD with a factorial arrangement, and replicated three times. The factors were timing of fertilizer application (Tx); (i) T ,-100% of the fertilizer applied at planting time , (ii) T2. 50% of the fertilizer applied at planting and the remaining 50% applied at weeding time (two weeks after emergence) (iii) T3 _75% of the fertilizer applied at planting and 25% at weeding time (iv) T4- 50% of the fertilizer applied at planting and 50% at earthing up time (four weeks after emergence) and (v) T, - 75% of the fertilizer applied at planting and 25% at earthing up time and methods of fertilizer application (Fx) at two levels; (i) localised placement (F2) and (ii) row banding (F,). The treatments were; F,T" F,T2, F,T3, F,T4, F, r, F2 T" F2T2, F2T3, F2T4 and F2Ts- Agronomic parameters; emergence rate, number of shoots per plant, stem height, canopy cover, number of tubers per plant, tuber grades and tuber yields, and soil chemical properties (soil pH, organic carbon, total nitrogen, available phosphorus, exchangeable bases and CEC) were measured. Regarding times of application, the crop performed better in split than in single fertilizer application with potato yields (14.73 t ha-' at Kibeho and 17.00 t ha-' at Kinigi) and yield components being significantly higher in T2 across fertilizer application methods. The Irish potato yields (13.81 t ha-' at Kibeho and 16.09 tha-' at Kinigi) and yield components were significantly higher with localised placement (F2) than row banding (F,) across the fertilizer times of application. The correlation between stem height, canopy cover and number of tubers per plant with tuber yield was positive and significant. Timing and methods of fertilizer application and their interactions had 'no significant effect (P>0.05) on the measured soil chemical properties. For enhanced Irish potato production, fertilizer should be applied in two splits, with the second portion applied at weeding time (two weeks after emergence), and using localized fertilizer placement method.