Abstract
Sweet potato is a strategic food security crop in southern Ethiopia, yet its productivity remains below potential due to erratic rainfall and sub-optimal field management. A field experiment was conducted during the 2024 cropping season at Jinka University to evaluate the effects of supplementary irrigation depth and vine planting orientation on growth and yield of sweet potato. The treatments consisted of five irrigation depths (0, 3, 6, 9, and 12 mm) and three planting orientations (vertical, horizontal, and inclined) arranged in a factorial Randomized Complete Block Design with three replications. Growth parameters, yield components, and total tuber yield were recorded and analyzed using ANOVA. Planting orientation significantly affected tuber length, tuber diameter, and total biomass. Vertical planting produced the longest tuberous roots (13.6 cm), greatest diameter (7.0 cm), and highest total biomass (2,755 g plot⻹). Supplementary irrigation improved growth and yield, particularly when combined with vertical planting. A significant interaction effect was observed for tuber length and total biomass, indicating that irrigation response depended on planting orientation. The results demonstrate that integrating vertical vine placement with moderate supplementary irrigation enhances sweet potato productivity under the agroecological conditions of Jinka. These findings provide practical guidance for improving water use efficiency and root yield in moisturelimited environments of southern Ethiopia.
Introduction
Sweet potato (Ipomoea batatas L.) is one of the most im-portant root crops grown in tropical and subtropical regions of the world, including Sub-Saharan Africa. Sweet potato is a member of the family Convolvulaceae, with characteristics such as its ability to perform under a wide range of agroeco-logical conditions, low input requirement, and high caloric productivity per unit area [1-2]. Sweet potato is very critical for food security, income, and nutritional improvement, par-ticularly for smallholder farmers in developing countries. Sweet potato is one of the most important root and tuber crops grown in Ethiopia, particularly in the southern and southwestern regions, where it serves as a food security and cash crop [3]. Sweet potato performs very well under tropical
conditions and is capable of growing under adverse conditions, but its yield is still far below its potential yield. Its yield is significantly low compared to the experimental and global yield, particularly because of sub optimal agronomic practic-es, moisture stress, lack of access to improved technologies, and poor crop management [4].
Moisture availability is among the most critical factors affect-ing sweet potato growth and yield. Although the crop is rel-atively tolerant to drought, prolonged moisture stress during critical growth stages particularly tuber initiation and bulk-ing can significantly reduce tuber number, size, and overall yield[5-6] . In rain-fed systems such as those predominant in Southern Ethiopia, rainfall is often erratic in both amount and distribution, resulting in frequent dry spells during the growing season. These conditions make reliance on rainfall alone
unreliable for achieving stable and high sweet potato yields. Supplementary irrigation has been identified as a practical strategy to mitigate moisture stress and stabilize crop pro-duction under rain-fed agriculture. It involves the application of additional water during periods when rainfall is insufficient to meet crop water requirements [7]. For sweet potato, ap-propriate supplementary irrigation can enhance vine de-velopment, leaf area expansion, tuber initiation, and tuber bulking, ultimately leading to improved yield and quality [8]. However, excessive irrigation or poorly managed water ap-plication may result in excessive vegetative growth, reduced tuberization, and increased susceptibility to diseases [9]. Therefore, determining the optimal irrigation depth is essen-tial for efficient water use and sustainable productivity.
Despite the recognized importance of supplementary irriga-tion and planting methods, their combined effects on sweet potato growth and yield have not been adequately studied under the specific agroecological conditions in Ari Zone. The area is characterized by seasonal rainfall variability and in-creasing pressure on water resources due to climate change and population growth. Farmers in the region often rely on traditional planting practices and have limited empirical guid-ance on optimal irrigation depth and planting methods for sweet potato production. As a result, yield variability remains high, and resource use efficiency is often low.
Understanding the interaction between supplementary irri-gation depth and planting methods is therefore essential to develop site-specific recommendations that enhance sweet potato productivity while ensuring efficient use of limited wa-ter resources. Generating locally relevant scientific evidence can support improved agronomic decision-making and con-tribute to sustainable crop intensification in the region.
Sweet potato production in Southern Ethiopia, including in Ari Zone areas, plays a vital role in household food securi-ty, particularly during periods of cereal crop failure. Despite its importance, productivity remains low due to a combina-tion of biophysical and management constraints, among which moisture stress and inappropriate planting methods are prominent. Addressing these challenges is critical to improving farmers’ livelihoods and strengthening local food systems.
