Abstract:
Ripening management is one of the core practices in sugarcane production to boost the sucrose content. Conventionally, in Ethiopian Sugar Industry, withholding irrigation through drying off the cane prior to harvesting is commonly conducted to facilitate the improvement of sucrose content. However, this method of ripening lacks accurate control of crop water supply and there is risk related to reduction in sugarcane and sucrose yield resulting from excessive withholding of water. Consequently, field experiments were conducted at Wonji-Shoa, Metahara, and Kessem Sugar Estates 1) to evaluate the responsiveness of sugarcane varieties to chemical ripeners; 2) to evaluate the effect of age of harvesting on the yield components, cane and sucrose yields of sugarcane, and 3) to evaluate the economic benefits of chemical ripeners. The first season experiment was aimed at evaluating the response of four sugarcane varieties (B52298, NCo334, C86-56 and SP70- 1284) to six chemical ripeners (2-chloroethylphosphonic acid (EthephonTM, 480 g ai L-1) @720 g ai ha-1, Fluazifop-p-butyl (Fusilade ForteTM, 150 g ai L-1) @ 25.6 g ai ha-1 , Trinexapac-ethyl (ModdusTM, 250 g ai L-1) @ 250 g ai ha-1, 2-chloroethylphosphonic acid (EthephonTM, 480 g ai L-1) @ 720 g ai ha-1 + Fluazifop-p-butyl (Fusilade ForteTM, 150 g ai L -1) @ 25.6 g ai ha-1, Trinexapac-ethyl (ModdusTM, 250 g ai L-1) @ 250 g ai ha-1 + Fluazifop p-butyl (Fusilade ForteTM, 150 g ai L-1) @ 25.6 g ai ha-1, and a none treated control.) at two locations viz., Wonji-Shoa and Metahara for early season (October) harvesting using a randomized complete block design in a factorial arrangement with three replications. A similar experiment was also conducted for mid-period (January) harvesting at Kessem sugar estate with variety C86-56 changed with C86-12. The results for the first season experiment combined over locations (Wonji-Shoa and Metahara) showed a significant (p = 0.025) and highly significant (p = 0.001) variety by ripener interaction in stalk height and sucrose content, respectively, while the main effect of ripener highly significantly (p < 0.01) affected stalk weight and sucrose yield. The variety C86-56 sprayed with combinations of EthephonTM + Fusilade ForteTM and ModdusTM + Fusilade ForteTM had the shortest stalk heights of 1.27 m and 1.29 m, respectively, as compared to the control (1.55 m). EthephonTM + Fusilade ForteTM combination resulted in the highest reduction of stalk weight (8.36%) while the lowest reduction was recorded in the sole ModdusTM treatment (6.31%) as compared to the control (1.17 kg). Among the ripener treatments, the ModdusTM + Fusilade ForteTM combination and EthephonTM + Fusilade ForteTM combination improved sucrose yield by 13.1 and 12.4%, respectively as compared to the control. However, in economic term, the ModdusTM + Fusilade ForteTM combination resulted in a net benefit of 6765.08 ha 1 and marginal rate of return of 1374%. Similarly, the study at Kessem showed that stalk height, stalk weight, sucrose content and sucrose yield were significantly (p ≤ 0.01) affected by the main effect of ripener. Overall, sucrose content (%) and sucrose yield (t ha-1) were improved by 2.64% unit and 2.15 t ha-1, respectively with the ModdusTM + Fusilade ForteTM combination treatment. In economic terms, the ModdusTM + Fusilade ForteTM combination treatment resulted in a net revenue of USD 5839.93 with marginal rate of return of 2393%. The second set of experiment was conducted at Metahara and Kessem sugar estates based on the results obtained from the first experiments, the ripener ModdusTM + Fusilade ForteTM combination treatment and two sugarcane varieties (B52-298 and SP70-1284) were used xix with the objective of determining the appropriate age of harvesting of cane treated with chemical ripener [(ModdusTM at 250 g ai ha-1 + Fusilade ForteTM at 25.6 g ai ha-1) combination sprayed and unsprayed (control)] using split plot design with three replications. The results showed that stalk height and stalk weight were significantly (p < 0.01) affected only by age and ripener combination at both plantations in the late period (June) harvesting, and in the early period (October) harvesting at Kessem. The 10 months age of harvesting ripener sprayed treatment in all the studies, and the 12 months age of harvesting ripener sprayed treatment in the late period study at Kessem had significantly (p