Growth of Tetragonia decumbens (dune spinach) in response to different PH and electrical conductivity levels in hydroponics

Abstract

The purpose of this research was to examine the growth of Tetragonia decumbens Mill. in hydroponics. A mother plant of T. decumbens was obtained from Assegaaibosch nursery in the south Western Cape province of South Africa. One hundred and eight plants were generated from the mother plant and cultivated in hydroponic system over 7 weeks. Four treatments were estimated with 9 sample replicates. Each treatment comprised of (silica sand) a soilless growing medium which was tested in aggregation with, 2 L head submersible pump. An analogue timer was used to control irrigation frequencies for all systems as follows: 2 ℓ/h for 15 minutes from 9 am - 5 pm at an intermission break of two hours during irrigation. Chapter 1 highlights relevant literature on research on leafy vegetables, food security, climate change, and hydroponics. It introduces empirical situations in which the research theme manifests itself. It defines the problems that need to be addressed and current gaps in scientific literature and research regarding T. decumbens. The chapter also delivers the rationale of the experiment and provides the aims and objectives of the study. Furthermore, it serves as an introduction to the research methods and procedures and scientific orientation concerning the research theme. It indicates the methods suitable for data collection and analysis. In chapter 2 the importance of T. decumbens and its availability as a traditional leafy vegetable was reviewed. It was found that T. decumbens has clear edible parts, recognized for its high nutritional value and drought-resistant traits and function in stabilizing dunes. Chapter 3 describes the growth characteristics of T. decumbens under various treatments and significant effects in terms of shoot growth, wet weight, and dry weight. Treatment 1 (T1) showed the highest individual mean value for vegetative growth, while the average from the T2-T3 displayed the highest average value. The lowest individual value for root growth was observed in the control. Overall treatments with nutrient application in hydroponics had improved shoot growth, while the control, T2-T3 showed sub-optimal root growth. For wet weight and dry weight, the highest individual mean value was found in treatment 1, while the highest average value was observed in T2 and T3. Chapter 4 discusses the nutrient uptake of T. decumbens under different fertigation treatments. The control consisted of 100% Silica sand with no nutrients; Treatment 1 (T1) - 100% Silica with 140g NPK /70 L; Treatment 2 (T2) - 100% Silica with 70g NPK/70 L; and Treatment 3 (T3) made of 100% Silica with 35g NPK /70 L, each of which was run for 2 hours every week at a pH range of 5.5 to 6.5. Post-harvest findings from the study showed that fertigation did not cause significant variability in the macronutrient concentrations of the species. However, micronutrient content was significantly affected. Chapter 5 discusses the estimation of chlorophyll production levels in the leaves of T. decumbens. Findings from this research show that fertigation regimes did not have a significant effect on the chlorophyll contents measured in leaves from week 1 to week 4 except in week 3 when a slight variability occurred. At week 3, the highest chlorophyll was recorded in T1 while T2 and T3 showed an equivalent chlorophyll content. Chapter 6 concludes the study with an urgent need in South Africa for more research into the commercial cultivation of wild species and an investigation into optimal propagation and growth requirements. Many stakeholders are re-kindling interest in the culinary use of Cape wild food plants. T. decumbens, has been revealed with phytonutrients that compare with or higher than most popular leafy vegetables present and are sourced for food security by as an alternative source of plant-based nutrients. Further studies would be required to investigate various growth substrates and, various fertigation regimes and how T. decumbens responds to these variables to further establish an optimal protocol for the cultivation of the plant in hydroponics.