Potato (Solanum tuberosum L.) Response to Crop Residues and Varying Combinations of Inorganic Potassium Fertilizer in Wolaita, South Ethiopia

Abstract

Emerging research evidence indicates that Potassium (K) is a limiting nutrient in Ethiopian soils. However, its fertilizer is costly and rarely available, especially in communities facing severe poverty. As a result, the researcher looked for locally available organic sources of potassium in the areas. Field experiments were conducted on potato crops to identify the best optimum and optional potassium fertilizer (KF) sources in soils from two sites representing areas where potassium deficiency had been previously identified by studies from the Ethiopian soil information system (Ehiosis). Treatments included residues and mixes with fixed rates as KF sources (organic and inorganic); these are 100 % optimum potassium chloride (KCl) standardized by previous research and used as check, potato residue (PR) equivalent of optimum KCl, PR equivalent of 75 % optimum KCl, PR equivalent of 125 % optimum KCl, PR of 50 % combined with 50% of KCl, PR of 25% combined with75 % of KCl, PR of 75 % combined with 25 % of KCl, PR of 50% combined with coffee husk (CH) of 50 % to optimum KCl and CH of 50 % combined with 50 % of KCl laid in RCBD (randomized complete block design). The previously identified research optimum standards were 150 kg ha-1 and 120 kg ha-1 KCl for Abota-ulto and Gututo-ampokoysha sites respectively. Results showed difference in both treatments and locations. The highest marketable tuber yield (MTY, 30.99 tha-1) and total tuber yield (TTY, 35.4 tha-1) were obtained from the combined application of PR equivalent to 50% of optimum KCl and 50% of KCl, which resulted in a 33.5% and 30% yield advantage over the lowest yield, respectively. Total tuber number per plot (TTNPP) and average tuber weight (Av.TW) also showed superior results with the same application. Plant height, total dry biomass, and specific gravity showed inconsistent trends among treatments. Locational yield and yield components were higher at Abota-ulto than Gututo-ampokoysha. Partial budget analyses indicated that the highest net benefit and acceptable marginal rates of return were achieved at Abota-ulto (107.4%) and at Gututo-ampokoysha site (168.38%) with the highest net benefit also resulting from the application of 50% PR with 50% KCl and this treatment was identified optimum. Finally, potato residue has been found to have greater nutrient potential. A balanced combination of PR with KCl has been identified as the best integration, and has been selected as the optional K-source over the CH combinations. Key words: Potassium fertilizer, Potato production, Marketable yield, Economic feasibility