Yield characteristics, carbon capture and chemical composition of moringa oleifera under diverse planting population and agro-ecological conditions of the Limpopo Province

Abstract

Moringa oleifera is a multipurpose fast growing tree which is widely cultivated in tropical and subtropical regions of the world due to its numerous benefits. The benefits include medicinal use, industrial use, soil fertility, water purification, climate change mitigation as well as of nutritional value for humans and livestock. Recently, many areas globally have been rendered vulnerable to climate change as well as food insecurity. Climate change increases irregularities of rainfall and temperature patterns in semi-arid conditions. One practical way to address this challenge in the agricultural sector is to introduce more trees crop species which are found to be more tolerant than annual crops under harsh growing conditions. Moringa is one species that could be considered under variable climatic conditions for positive outcomes through climate change adaptation and mitigation as well as life sustenance against food insecurity threats. Production of moringa in South Africa is exclusively for leaf processing and consumption. To date, there is no documented information available about seed and oil yield production of moringa mainly in the Limpopo Province of South Africa. The aim of the study was to generate knowledge on moringa growth, nutritional composition, seed and oil yield production as well as its response to drought through gaseous exchange parameters, as influenced by plant density under diverse agro-ecological locations in Limpopo Province. The study was conducted in the Limpopo Province, South Africa, from November 2013 to January 2016. The study area falls within the semi-region which is characterized by low and erratic rainfall which predominately falls in summer as well as extremely low or high temperatures. A survey was conducted from November 2013 to September 2014 in five districts of the Limpopo Province. Focus group discussion, questionnaires and field observations were used for data collection. A total of 150 moringa growers formed part of the focus group and a questionnaire was administered to only thirty-one farmers, who constitute the population of farmers producing moringa within an area of 0.25 ha or more. A second study was conducted at two experimental sites in the Limpopo Province of northern part of South Africa to evaluate for the first time, the effect of plant density and cutting interval on biomass production and chemical composition of moringa grown under two diverse climatic conditions. Four different planting densities (435 000, 300 000, 200 000 and 100 000 plants/ha) were arranged in a randomized complete block design and experimental samples were replicated four times. A third study was conducted over two years to achieve additional objectives which included evaluation of gaseous exchange, biomass, seed, and oil yield. Untreated seeds of Moringa oleifera were used for establishing the trial at densities of 5 000, 2 500, 1 667 and 1 250 plants ha-1, with eight replicates. The same study was used to achieve the objective on gaseous exchange in comparison with other two naturally growing tree species of mopane (Colophospermum mopane) and marula (Sclerocarya birrea) trees growing within the moringa trial vicinity. The study was further used to evaluate the effect of planting density on biomass, grain, oil yield production and nutritional composition of Moringa oleifera trees. The last part of the study was carried out in the five districts of the Limpopo Province to determine the influence of soil physical and chemical properties on the nutritional composition of moringa leaves. The farms that were identified during the survey were also used to achieve other objectives of the study. In order to determine soil and leaf nutritional composition, soil samples were collected and analyzed for physical and chemical properties. The harvested leaves were dried at room temperature and their nutritional compositions were determined using standard methods. Findings from the studies revealed the following: The survey indicated that there are potential moringa farmers in all the districts of the province, with the intention to commercialize the tree. Majority of farmers grow moringa on 0.251.0 ha and have been producing the crop for the past 2 years. The study on planting density and cutting frequency revealed satisfactory nutritional composition in the leaves across the cutting frequencies and that, an increase in the plant density led to enhanced biomass production. The study on the monthly and seasonal gaseous exchange revealed significant differences in net photosynthetic rate, transpiration, sub-stomatal CO2 and stomatal conductance. However, planting densities of Moringa oleifera had no significant effect on all the gaseous exchange parameters measured. In a comparison of moringa with other tree species growing in the vicinity of moringa, the results differed significantly in gaseous exchange. The highest activity in photosynthetic rate (A), stomatal conductance (gs), transpiration rate (E) and sub-stomatal CO2 (Ci), as well as higher stomatal density, was found in moringa. The findings from the biomass, seed yield and oil yield study showed that the increase in measured biomass, seed and oil yield increased with increasing planting density. However, seed oil concentration was non-significant. Findings from the ecology study revealed that moringa improved soil nutritional composition; mainly in areas where the trees were more than three years old as compared to control soils where moringa had not been planted. The soil nutritional composition differed with soil textural classes with the clay soils recording higher nutrient ion values. The study revealed that moringa can be produced in many locations of the Limpopo Province without negatively affecting leaf nutritional composition. Moringa leaves contain high level of nutrients even under marginal production areas irrespective of the planting density. A population of 5000 plants ha-1 can be used for seed and oil yield production where temperatures are favourable for improved farmers’ livelihoods. The results strongly showed with no doubt, the superiority of moringa in capturing more carbon among the three species. Moringa maintained good leaf yield even under drought condition, which is an indication of its potential to act as a good sink for carbon dioxide absorption. It can, therefore, be recommended for many parts of Limpopo Province for climate change mitigation and adaptation strategies and food security.

KEY CONCEPTS: agro-ecology, biomass, climate change, commercialization, drought, food security, gas exchange, leaf chemical composition, location, Moringa oleifera, oil, seed, soil textural class, survey, trees, weather, yield