Netsanet Ayele’s research while affiliated with Ethiopian Sugar Corporation and other places

Chemical ripening is a promising technology at Metahara and Kessem sugarcane plantations where conditions are not optimal for natural ripening in the early and late period of sugarcane processing. However, the harvest age at which sucrose yield could be maximized with application of ripeners has not been established. Thus, field experiments were conducted to determine the effects of harvest age and chemical ripeners on yield and juice quality of sugarcane. The experiments were conducted in the late period (June) harvesting at Metahara, and in the early (October) and late period (June) harvesting at Kessem. A split plot design with three replications was used where the main plot treatments were two sugarcane varieties, viz. B52-298 and SP70-1284, and the sub-plot treatment consisted of combinations of four harvest ages (10, 12, 14 and 16 months) and two ripener treatments [Moddus™ at 250 g ai ha−1 + Fusilade Forte™ (M + FF) at 25.6 g ai ha−1 combination sequentially sprayed and unsprayed control]. The results showed significant difference between the varieties for stalk height and stalk weight in early period study at Kessem with variety SP70-1284 being superior as compared to variety B52-298. Furthermore, harvest age and ripener combination significantly affected all yield and quality parameters, while there was a significant cane and sucrose yield response at Kessem at both sites and seasons. The highest cane yield was recorded in the unsprayed 16-month harvest age treatment, while the highest sucrose yield was recorded in the M + FF ripener combination 12-month harvest age treatment in all the studies. The economic analysis showed the highest marginal rate of return and net revenue in the M + FF ripener combination 12-month harvest age treatment and represents the best cane quality management practice for varieties B52-298 and SP70-1284 at these plantations.

The relatively high temperature at Kessem sugarcane plantation in Ethiopia was hypothesized to justify the implementation of chemical ripeners as a strategic intervention to combat poor cane quality. Accordingly, a field experiment was carried out to assess the responsiveness of four sugarcane varieties (B52-298, NCo334, C86-12, and SP70-1284) to five ripener treatments: 2-chloroethylphosphonic acid (Ethephon™, 480 g ai L−1) at 720 g ai ha−1, fluazifop-p-butyl (Fusilade Forte™, 150 g ai L−1) at 25.6 g ai ha−1, trinexapac-ethyl (Moddus™, 250 g ai L−1) at 250 g ai ha−1, 2-chloroethylphosphonic acid + fluazifop-p-butyl combination at the mentioned application rates, trinexapac-ethyl + fluazifop-p-butyl combination at the mentioned application rates, and an untreated control. The experiment was conducted in a factorial arrangement in a randomized complete block design (RCBD) with three replications. The results showed that stalk height, stalk weight, sucrose content (%), and sucrose yield (t ha−1) were affected by the main effect of ripener treatment, but there was no significant cultivar x ripener treatment interaction for the parameters collected. Overall, the sequential application treatment of trinexapac-ethyl followed by fluazifop-p-butyl 28 days later performed the best and improved sucrose content and sucrose yield by 2.64% unit and 2.15 t ha−1, respectively. In economic terms, the trinexapac-ethyl + fluazifop-p-butyl sequential application treatment resulted in a marginal rate of return of 2393%. Therefore, the sequential trinexapac-ethyl + fluazifop-p-butyl ripener program was identified as a promising ripening strategy to be evaluated on a commercial scale at the sugarcane plantations in Ethiopia.

Wonji-Shoa and Metahara sugarcane plantations experience reduced sucrose content (%) during the starting period of sugarcane crushing due to the combined influence of high (>27°C) temperature and the presence of high residual soil moisture. Studies elsewhere showed the potential of chemical ripeners in boosting the sucrose content (%), where natural ripening is deterred by these challenges. Accordingly, a field experiment was conducted to evaluate the responsiveness of selected sugarcane varieties to chemical ripeners at both plantations. The treatments consisted of a factorial combination of four sugarcane varieties (B52298, NCo334, C86-56, and SP70-1284) and six ripener treatments: (1) Ethephon™(720 g ai ha⁻¹), (2) Fusilade Forte™(25.6 g ai ha⁻¹), (3) Moddus™ (250 g ai ha⁻¹), (4) Ethephon™ (720 g ai ha⁻¹) + Fusilade Forte™ (25.6 g ai ha⁻¹), (5) Moddus™ (250 g ai ha⁻¹) + Fusilade Forte™ (25.6 g ai ha⁻¹), and (6) Unsprayed (control). The experiment was laid out in a randomised complete block design in a factorial arrangement with three replications. The results showed a significant () and highly significant () variety by ripener interaction in stalk height and sucrose content, respectively, while the main effect ripener highly significantly affected stalk weight () and sucrose yield (). The variety C86-56 sprayed with combinations of Ethephon™ + Fusilade Forte™ and Moddus™ + Fusilade Forte™ had the shortest stalk heights of 1.27 and 1.29 m, respectively, compared with the control. Ethephon™ + Fusilade Forte™ combination resulted in the highest reduction of stalk weight (8.36%), while the lowest was recorded in the sole Moddus™ treatment (6.31%). From the ripener treatments, the Moddus™ + Fusilade Forte™ combination and Ethephon™ + Fusilade Forte™ combination improved sucrose yield by 1.42 and 1.34 t ha⁻¹, respectively, compared with the control. However, in economic terms, the Moddus™ + Fusilade Forte™ combination treatment resulted in the highest marginal rate of return of 1244%. Therefore, the Moddus™ + Fusilade Forte™ combination ripener treatment was found to be promising to be evaluated at a commercial scale on immature sugarcane varieties B52-298, NCo334, and SP70-1284. 1. Introduction Sugarcane (Saccharum spp., hybrid) is cultivated in Ethiopia at a commercial level [1], as well as by smallholder farmers [2]. It also has broad socioeconomic advantages [3]. However, the per-capita sugar consumption of Ethiopia is one of the lowest in the world with about 5 to 6 kg per annum, and future sugar consumption growth is expected to be around 3–4% annually, which was forecasted to grow by 0.4 million tons by 2030 [4]. The total annual sugar production in the country was reported to be 400,000 tons in 2018, which only covers 60% of the annual demand for domestic consumption [5]. The country is endowed with a favourable climate, enormous land, and water resources for large-scale irrigated development of sugarcane [1] with an average sugarcane yield potential of 162 tons per hectare [6]. Nonetheless, the value of sugarcane is determined by the amount of recoverable sucrose per weight of cane [7]. In Ethiopia, sucrose is the main product of sugarcane processing [8], and its quantity principally depends on the quality of sugarcane supplied [9]. This suggests the need for maintaining quality using appropriate ripening management as an indispensable means [10]. Although the dry matter yield potential of sugarcane in the country is high [6], the quantity partitioned to sucrose varies depending upon the variety, age [11], season [8], soil fertility, irrigation [12], weed, pest and disease control [13], and the length of crushing season [7]. Nevertheless, air temperature and soil moisture are the major factors affecting the partitioning of sucrose in sugarcane [14]. At a higher temperature, from the total carbon fixed and stored, sugarcane partitions less carbon to sucrose [15]. The availability of soil moisture also reduces the sucrose content of sugarcane during ripening due to the high growth sink demand [16]. In the ripening phase, there should be a synthesis and rapid accumulation of sucrose with a concomitant reduction of vegetative growth and a decline in the level of monosaccharides (fructose and glucose) in stalks [12]. Wonji-Shoa and Metahara sugarcane plantations have a total area of 10,342 and 10,235 ha, respectively. Conventionally, to maximise the sucrose content (%) of cane harvested from these plantation areas, harvesting of sugarcane is conducted after drying off the cane by withholding irrigation for a specified period ranging from 5 to 9 weeks before harvesting [17]. However, the sucrose content of cane in the beginning (September to November) period is lower due to the presence of residual soil moisture coupled with the high temperature in July and August, and this has been reported to be a persistent problem at both estates [8]. This indicates the inadequacy of natural ripening [18], which resulted in the need for accurate control over crop water supply [19] and the reduction in cane and sucrose yield from the extreme withholding of water during drier periods [20]. Chemical ripeners have become an important technology to tackle challenges related to low sucrose content in many sugar industries of the world [12]. Ripeners used in sugarcane are plant regulators whose action consists of modification of plant morphology and physiology, which can alter plant production quantitatively and qualitatively [21]. The use of ripeners can provide gains in sucrose quality above those achieved by natural ripening [12, 19]. Ripeners can reduce plant height, increase sucrose content, advance plant maturation, and increase sucrose yield, and they can also present effects on enzymes that catalyse sucrose accumulation in the internodes [21]. The technology has potentially considerable impact in areas overwhelmed with poor natural ripening conditions [22]. The successful introduction of ripener technology could also facilitate the harvest of cane earlier in the season when it is relatively immature [23]. The chemical ripeners currently in use in many sugar industries include glyphosate (e.g., Roundup™), 2-chloroethylphosphonic acid (e.g., Ethephon™), fluazifop-p-butyl (e.g., Fusilade Forte™), and trinexapac-ethyl (Moddus™) [12]. In terms of their modes of action, glyphosate and fluazifop-p-butyl are herbicidal and suppress new tissue formation at a sublethal dose [24], while 2-chloroethylphosphonic acid and trinexapac-ethyl have a hormonal mode of action [25, 26]. The hormonal mechanism of improvement in sucrose content through 2-chloroethylphosphonic acid emanates from the active ingredient ethylene [25, 26], which reduces the demand for sucrose for vegetative growth [24]; but the mechanism for trinexapac-ethyl is related to its ability of inhibition of elongation of internode, resulting from the reduction in the level of GA1 [27]. Earlier works also confirmed the efficacy of sole application of glyphosate [24, 28], 2-chloroethylphosphonic acid [29, 30], fluazifop-p-butyl [30, 31], trinexapac-ethyl [32, 33], and combination of ripeners [23, 29, 30] in improving sucrose yield of sugarcane. However, to effectively use chemical ripeners at a commercial level, it is vital to generate information regarding the response of sugarcane varieties to these chemicals. In line with this study, reports from different sugar industries confirmed the need for evaluation of varieties for their response to chemical ripeners [23, 28]. In this regard, a preliminary study conducted at Metahara sugarcane plantation in the 1980s using fluazifop-p-butyl showed that the sucrose content (%) of varieties B41-227 and NCo376 were improved by 0.47 and 0.57% units, respectively, when compared with untreated control plots [29]. Although these studies showed improvement in juice quality of some sugarcane varieties, the emergence of new chemical ripeners, combination treatments, and sugarcane varieties necessitated another study that can provide up-to-date information to the estates. Therefore, this study was conducted to evaluate the response of selected sugarcane varieties to chemical ripeners at Wonji-Shoa and Metahara sugarcane plantations. 2. Materials and Methods 2.1. Description of the Study Areas The present investigation was carried out at Wonji-Shoa and Metahara sugarcane plantations from December 2017 to October 2018. Wonji-Shoa Sugarcane plantation is located in the Rift Valley of Ethiopia (8°31′N and 39°12′E), at an average elevation of 1550 masl. The plantation has a mean maximum and minimum air temperature of 26.9 and 15.3°C, respectively. Similarly, Metahara sugarcane plantation is located in the Rift Valley of Ethiopia (8°51′N and 39°52′E), at an average elevation of 950 masl. The plantation has a mean maximum and minimum air temperature of 32.6 and 17.5°C, respectively. The soils of the experimental fields of Wonji-Shoa and Metahara were clay (>54%) in texture. During the study period, Wonji-Shoa and Metahara sugarcane plantations obtained a total rainfall of 859 and 317 mm, respectively. As compared to the long-term annual average, both plantations experienced lower rainfall. Moreover, the distribution was not even at both locations (Figure 1). Maximum rainfall of 267 and 120 mm were recorded in April and August at Wonji-Shoa and Metahara, respectively. The mean annual minimum temperature recorded at Wonji-Shoa was 13.9°C and Metahara was 17.0°C. The mean annual maximum temperature recorded at Wonji-Shoa was 29.0°C and at Metahara was 33.2°C. (a)