Introduction

In many developing countries, wild edible plants are a critical source of income and nutrition for millions of people1,2. Non-wood forest products play a vital role in tropical regions, supporting the livelihoods and well-being of local communities while also contributing to global markets. Rural populations, particularly those in poverty, often rely on these products for food, fodder, medicine, and income generation3. Beyond local subsistence, NWFPs are valuable traded commodities, circulating across local, regional, national, and even international markets. This trade not only helps meet daily subsistence needs but also generates employment and income for marginalized communities4.

Moringa stenopetala and Moringa oleifera are among the most valuable tropical tree species, contributing to nutritional diversification and helping to alleviate hidden hunger5. Moringa serves as a rich source of micronutrients that are often deficient in cereal-based diets. Nearly all parts of the tree are edible, providing highly nutritious food for both humans and livestock6,7,8. The flowers are an excellent nectar source for honey production, while the seeds yield oil suitable for cooking and industrial lubrication. Additionally, for decades, dried and crushed moringa seeds have gained attention as a natural coagulant, serving as an alternative to chemical coagulants like alum in water purification9,10. Beyond its functional uses, moringa is nutritionally dense, containing essential vitamins, minerals, amino acids, beta-carotene, antioxidants, anti-inflammatory compounds, and phytochemicals, as well as omega-3 and omega-6 fatty acids11,12.

In southern Ethiopia, smallholder farmers predominantly cultivate moringa in marginal, rain-fed environments. While the species is drought-tolerant, its productivity potential remains largely unrealized under natural growing conditions13,14. Furthermore, the current supply of leaves from naturally grown trees is insufficient to meet market demand, leading to high prices and limited availability15. Although irrigation is an established strategy for enhancing agricultural productivity in water-scarce regions16,17, systematic research on its application for optimizing M. stenopetala leaf production is lacking. While Fikremariam et al.18 studied nutrient composition in natural stands, no studies have systematically evaluated how supplemental irrigation at different frequencies affects both the biomass yield and the nutrient profile of M. stenopetala across harvests in eastern Ethiopia.

Despite its nutritional value, the consumption of indigenous vegetables like moringa is often stigmatized in many African and Asian communities, where it is associated with low socioeconomic status19. In southern Ethiopia, approximately 71% of moringa-growing households have cultivated M. stenopetala for generations, while the remaining 21% have adopted its cultivation more recently, within the past 2–17 years20.

The moringa tree has emerged as a significant commercial crop in Ethiopia and globally, with its derivatives being utilized in various value-added products. These include teas, beverages, cosmetics (such as lotions, shampoos, and conditioners), as well as traditional and modern medicinal preparations21. Despite its growing economic importance, there remains a notable lack of systematic management practices to enhance M. stenopetala cultivation for optimal leaf biomass production.

Currently, most leaves supplied to markets and households are harvested from naturally grown trees, leading to supply shortages that cannot meet increasing demand15. This production deficit has significantly driven up market prices; for instance, fresh leaves sell for approximately 50 ETB per kilogram, while fresh seed pods command around 100 ETB. In Addis Ababa, the price of powdered moringa leaves fluctuates between 50 and 200 ETB per kilogram, depending on seasonal availability15.

Current research on moringa nutrient composition remains limited, particularly regarding irrigated cultivation across different growth stages. While Fikremariam et al.18 examined naturally grown moringa trees without irrigation in southern Ethiopia, no studies have systematically evaluated the nutrient profile of irrigated moringa at various maturity levels. Implementing supplementary irrigation could address the current supply-demand imbalance by enhancing growth rates and increasing leaf biomass production22. While moringa is drought-tolerant, its productivity potential is unrealized under rain-fed conditions, and that no studies have systematically evaluated the nutrient profile under irrigation at different maturity stages in this region13,14. Irrigation efficiency has been established as a key factor in boosting agricultural productivity16, particularly in water-scarce regions where adequate water supply significantly improves yields17.

This study aims to fill this knowledge gap by evaluating the effects of different irrigation schemes on the leaf biomass yield and chemical composition of M. stenopetala in Eastern Amhara, Ethiopia. The specific objectives were to assess the impact of supplementary irrigation on leaf biomass production and to analyze variations in nutritional composition under different irrigation regimes.

Materials and methods

Description of the study area

The study was conducted at the Sirinka Agricultural Research Center sub-station in Kobo Woreda, located at 5°56’56” N latitude and 13°40’28” E longitude with an elevation of 1,450 m above sea level. The site experiences a semi-arid climate characterized by 648.4 mm annual rainfall and mean temperatures ranging from 18 °C to 34 °C. The soils are classified as Eutric Fluvisols, which typically exhibit significant moisture deficits, representing the region’s challenging growing conditions.

Experimental design and data collection

Seeds of M. stenopetala were collected from natural stands and homestead plantations across the Southern Nations, Nationalities, and Peoples’ Region. Seedlings were raised in a nursery using polythene tubes filled with a potting mixture of forest soil, sand, and manure in a 3:1:1 ratio. Once seedlings reached 33–40 cm in height with a root collar diameter of 10–15 mm, they were transplanted to the experimental field.

The experiment used a randomized complete block design with three replications. Four irrigation treatments were applied: T1 (control, no supplemental irrigation), T2 (intensive irrigation every 10 days), T3 (moderate irrigation every 15 days), and T4 (minimal irrigation every 30 days). Each plot contained 16 seedlings spaced 2 m apart, with 2 m between plots and 3 m between blocks.

Field management and data collection

Half-moon water harvesting structures were constructed for each tree. During irrigation sessions, each structure was filled uniformly over a 30-minute period. Deep trenches were excavated between plots and blocks to prevent cross-treatment water flow. All treatments received standard management practices including weeding.

Growth parameters, including root collar diameter, diameter at breast height, plant height, and survival rate, were monitored quarterly after planting.

Sample Preparation and laboratory analysis

Twenty-one months after planting, leaf samples were collected following the complete pruning of all treatments. The main stems were pruned to a height of three meters and the branches to one meter, in accordance with traditional farmer practices documented in the Konso/Dherashe district of SNNPR. This pruning method facilitates easier access for subsequent harvests.

For each treatment (10-day, 15-day, 30-day irrigation intervals, and a control), six kilograms of composite leaf samples were manually collected from the tree crowns during the early morning hours. The collected leaves were separated from the petioles and weighed using a precision balance. Drying was conducted by spreading the leaves on thin canvas sheets in a greenhouse to allow for uniform air-drying. The dried leaves were initially crushed by hand and then finely ground to a 2 mm particle size using a mortar and pestle. The processed samples were stored in paper bags at room temperature before being transported to the Horticoop Ethiopia laboratory in Addis Ababa for nutrient and proximate analysis.

Proximate and nutritional composition analysis

Proximate analysis was conducted following the standard methods of the Association of Official Analytical Chemists23. To determine moisture content, a 5 g sample of moringa flour was weighed into a crucible and dried at 105 °C until a constant weight was achieved through consecutive weighings. Ash content was determined by incineration at 550 °C for three hours. Protein content was analyzed using the Kjeldahl method, while crude fiber was measured through acid-alkali digestion. Lipid content was determined via Soxhlet extraction. All analyses were performed in triplicate. Phytate concentration was quantified according to the method of Latta and Eskin24, and tannin content was analyzed following the protocol described by Burns et al.25.

For mineral determination, 0.5 g of the flour sample was accurately weighed into a pre-cleaned ceramic crucible. The sample was ashed in a muffle furnace at 500 °C for four hours, cooled inside the oven, and then carefully removed. The resulting ash was quantitatively transferred to a labeled 50 mL centrifuge tube. The crucible was sequentially rinsed with 5 mL of distilled water followed by 5 mL of aqua regia, a process that was repeated until a final volume of 20 mL was achieved.

The solution was thoroughly mixed and centrifuged at 301.86 × g for 10 min using an IEC Central GP8 centrifuge. Mineral concentrations were determined by atomic absorption spectrophotometry (Buck Scientific Model 200 A), with specific wavelengths selected for each element according to the standardized methods of Novozamsky et al.26.

Treatments utilized at the field level

The field experiment employed four distinct treatment groups to evaluate the effects of supplementary irrigation on M. stenopetala including: Control: M. stenopetala grown under natural rainfall conditions without supplementary irrigation; Intensive irrigation: M. stenopetala receiving supplementary irrigation every 10 days; Moderate irrigation: M. stenopetala receiving supplementary irrigation every 15 days; and Minimal irrigation: M. stenopetala receiving supplementary irrigation every 30 days.

This gradient of irrigation frequencies was designed to systematically assess the water requirements and response thresholds of M. stenopetala under varying moisture regimes. The experimental setup allowed for a comparative analysis of growth parameters, biomass production, and physiological responses across different water availability conditions.

Data analysis

All collected field and laboratory data were systematically organized in Microsoft Excel and analyzed using SPSS Statistics (version 24.0) to evaluate leaf biomass production, growth performance, and nutritional composition across different harvesting times and irrigation frequencies. Data normality was assessed using a general linear model with one-way ANOVA, followed by Tukey’s HSD test for mean separation. The results are presented as mean ± SEM, with a significance level of p < 0.05.

Mineral element concentrations were determined via atomic absorption spectrophotometry (Buck Scientific Model 200 A) after wet digestion with concentrated nitric acid. The concentrations of calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), and sodium (Na) are expressed as percentages, while the concentrations of iron (Fe) and zinc (Zn) are reported in mg/kg.

Results

Growth performance and leaf biomass production of Moringa stenopetala

Trees under 10- and 15-day irrigation intervals exhibited superior growth. At the first harvest, these treatments resulted in significantly greater diameter at breast height, plant height, and number of branches per tree compared to the 30-day interval and the control. Survival rates were statistically similar across all treatments, though the 10-day treatment showed slightly lower initial survival due to waterlogging after transplanting.

Table 1 Growth performance of M. stenopetala at 12 months post-planting: RCD, DBH, Ht, SR, and branch number across irrigation treatments (P ≤ 0.05)
Full size table

Leaf harvests were conducted at 21 and 26 months after planting. Analysis of dry mass per tree at 21 months revealed significant differences among treatments (Table 2), with the lowest leaf yield observed in the non-irrigated control group. Dry leaf biomass yield was significantly influenced by irrigation. At the first harvest, the 10-day interval produced the highest yield (0.77 t/ha), followed by the 15-day interval (0.62 t/ha). Both were significantly higher than the 30-day interval (0.28 t/ha) and the control (0.21 t/ha). A similar trend was observed in the second harvest, confirming the positive effect of frequent irrigation on biomass accumulation.

Table 2 Mean dry leaf yield of the treatments at 21and 26 months age
Full size table

Proximate and mineral composition

Proximate analysis showed that irrigation frequency had a minimal effect on the nutritional quality of the leaves. Significant differences were found only for fat and ash content in the first harvest. Across all treatments and harvests, the leaves were rich in fat (11.7–13.8%), ash (5.9–6.0%), and fiber (9.7–10.6%). Crude protein content ranged from 3.2% to 3.8% (Table 3).

Table 3 Proximate composition of dried M. stenopetala leaf powder: moisture, crude fiber, fat, and ash content (% dry weight basis); phytate and tannin concentrations (mg/kg dry weight
Full size table
Table 4 Mineral composition of dried M. stenopetala leaf powder: macronutrients (Ca, K, P, Mg, Na as % dry weight) and micronutrients (Fe, Zn as mg/kg dry weight)
Full size table

Mineral analysis revealed that the leaves are a rich source of essential minerals. Iron and Zinc concentrations were particularly high, exceeding values reported from other regions (Table 4). All measured mineral elements were within the safe ranges recommended by the World Health Organization. Anti-nutritional factors, phytate (870–961 mg/kg) and tannin (164–220 mg/kg), were present but did not show a consistent pattern related to irrigation treatment. These findings demonstrate that moringa cultivation in the study area can provide substantial nutritional value, with biomass yield being the primary limiting factor for nutrient availability.

Fig. 1
figure 1

Map of the study area.

Full size image
Fig. 2
figure 2

Field performance M. stenopetala at different growth stages at Kobo research site.

Full size image

Discussion

Growth and biomass

Our findings confirm that supplemental irrigation is a key driver for enhancing the growth and leaf biomass production of M. stenopetala. The superior performance under 10- and 15-day intervals aligns with previous studies which identified water availability as a major limiting factor for moringa productivity10,22. The significantly lower yield in the control and 30-day treatment underscores the water stress experienced by the trees in this semi-arid environment. This supports the assertion that while moringa is drought-tolerant, its productivity is suboptimal without adequate water supply27.

The substantially higher leaf biomass from more frequent irrigation aligns with findings from the Sehal region22. Under optimal irrigation conditions, the trees demonstrated an annual growth potential of 2.5–3 m in height. However, our results contrast with a study in Sudan which found no significant effects of different watering intervals on tree development28.

Our study supports the conclusion that irrigation is more critical than fertilization for early-stage growth acceleration22. However, our findings also contrast with other reports which suggested that supplemental irrigation becomes unnecessary once trees are established, as natural rainfall alone can sustain growth29,30. This discrepancy may be due to the more arid conditions of our study site.

The initial lower survival in the 10-day treatment, attributed to waterlogging, highlights the sensitivity of young seedlings to excessive moisture, a critical consideration for early field management31. Once established, however, the trees under frequent irrigation showed remarkable growth.

Nutritional quality across irrigation regimes

A key finding of this study is that the nutrient composition of M. stenopetala leaves remained largely stable across different irrigation regimes. This suggests that the primary benefit of irrigation is to increase the quantity of biomass without diluting its intrinsic nutritional quality. The recorded levels of protein, fats, ash, and minerals are consistent with previous reports, confirming its value as a nutrient-dense food source32.

Our moisture content findings align with those of Hawa et al.28, though we observed lower crude protein levels. The fiber content was consistent with previous nutritional analyses by Abuye et al.33. These results corroborate a similar nutritional profile reported for M. oleifera in southern Ethiopia by Ambaye6.

Elemental analysis showed that the mineral content was in agreement with WHO standards for all nutrients except tannin, which exceeded recommended levels34. The iron (Fe) and zinc (Zn) values in the M. stenopetala samples from the Kobo irrigation schemes under different supplementary irrigation treatments were higher than those reported by Ambaye6 for samples from Tigray.

The presence of anti-nutritional factors like phytate and tannin is a known characteristic of moringa35. Critically, our data show that more frequent irrigation, while maximizing yield, did not lead to a statistically significant increase in these anti-nutrients compared to the other treatments. Therefore, the recommendation for a 10-day irrigation interval is based on a yield-maximization strategy. The levels found are not uncommon in plant-based foods, and their impact can be mitigated through processing methods such as cooking or fermentation35.

Conclusion and recommendations

Conclusions

This study demonstrates that supplemental irrigation significantly enhances the growth and leaf biomass yield of Moringa stenopetala in the semi-arid conditions of eastern Ethiopia. Irrigation at 10- and 15-day intervals resulted in superior tree height, diameter, branch number, and dry leaf yield compared to less frequent or no irrigation. Importantly, this boost in biomass production was achieved without compromising the nutritional composition of the leaves, which remained rich in essential fats, minerals, and protein across all treatments. The concentration of anti-nutritional factors was not significantly amplified by increased irrigation. Therefore, biomass yield, not nutrient concentration, is the primary variable affected by water management in this system.

Recommendations

For farmers aiming to maximize leaf biomass production where water is not a limiting constraint, implementing a 10-day supplemental irrigation interval is recommended. In contexts of water scarcity, a 15-day irrigation interval provides a substantial yield advantage over rain-fed cultivation while conserving water, making it a highly efficient and recommended practice. Future research should focus on determining the precise water requirements for M. stenopetala to develop water-saving protocols. Further investigation into processing methods to reduce anti-nutritional factors would also enhance the utility of the harvested leaves.

Limitations of the study

While this study provides valuable insights, certain limitations should be considered. First, the research was conducted at a single location over two harvest seasons; thus, the findings may benefit from validation across multiple agro-ecological zones and over a longer duration to assess inter-annual variability and long-term tree response. Second, the study focused on a specific set of irrigation intervals; a more granular analysis, including measurements of soil moisture content, would be necessary to determine precise water requirements and irrigation thresholds. Finally, the analysis of anti-nutritional factors was limited to phytate and tannin; a broader investigation including other compounds such as oxalates, or a study on the bioavailability of minerals in the presence of these anti-nutrients, would provide a more comprehensive nutritional assessment.