Growth and phenological responses of selected improved coffee varieties (Coffea arabica L.) to Vermicast application

Organic soil amendment is important for sustainable coffee production; however, efforts to establish its scientific basis have been insufficient. This study evaluated the phenological and growth responses of selected CBD-resistant coffee varieties to different vermicast application rates at Wonago, Gedeo, during 2022–2023 under irrigation. A 4 × 6 pot experiment was arranged in a randomized complete block design with three replications. Treatments consisted of four coffee varieties (74112, 74110, Kotti, and Fayate) and six levels of cow dung vermicast (4.5, 6.3, 8.1, 9.9, and 11.7t ha−1, plus a control) were considered as treatments. ANOVA showed that both variety and vermicast significantly affected seedling girth, number of primary branches, leaf number, leaf chlorophyll content, leaf area, specific leaf area, primary branch length, biomass, and dry weight of seven-month-old coffee seedlings. In addition, node number, seedling height, and days to 50% emergence were significantly influenced by the interaction between variety and vermicast. Variety Kotti exhibited the highest biomass, seedling girth, leaf chlorophyll content, leaf area, and specific leaf area, possibly in relation to this variety is native to the study area, while variety 74112 produced the highest number of primary branches, primary branch length, leaf number, and seedling dry weight. Application of 9.9 and 11.7t ha−1 vermicast shortened the number of days to first emergence and 50% emergence. As the vermicast rate increased up to 9.9t ha−1, seedling growth improved for most parameters; however, when the rate exceeded 9.9t ha−1, a slight decline was observed, possibly because some growth regulators in the vermicast became dominant in the growth process. Further studies are suggested to determine the levels and types of growth hormones present in cow dung vermicast.