Effect of macadamia husk compost on growth, yield and nutritional content of jute mallow (Corchorus olitorius) grown under different water regimes

Abstract

Jute mallow (Corchorus olitorius) can grow in poor soil and adverse climatic conditions; however, water stress and poor soil fertility are constraints to its production. The study aimed to improve jute mallow production by investigating the effects of macadamia husk compost (MHC) on growth, yield and nutritional content under different water regimes. A pot experiment was conducted for two seasons (2023/2024 and 2024/2025) at the Agricultural Research Council, Levubu, Limpopo province, South Africa. The treatments consisted of a factorial combination of three fertiliser levels (0 t ha-1 MHC, 30 t ha-1 MHC, and 60 t ha-1 MHC, and NPK (100:60:60 kg ha-1) and irrigation levels (30%, 60%, and 100% field capacity), arranged in a randomised complete block design, replicated 3 times. Macadamia husk compost and soil samples were analysed before and after planting to determine the effects of MHC and irrigation regimes on selected chemical and physical soil properties. The chlorophyll content was measured using a chlorophyll meter (CCM-200 PLUS, Opti-Science). Growth measurements such as plant height, stem diameter, number of branches, leaf fresh biomass, and leaf dry biomass of the jute mallow plants were investigated. Mineral content, including nitrogen, phosphorus, potassium, zinc, magnesium, boron, calcium, sulphur, and sodium were determined using a spectrophotometer. Total phenolic content, antioxidant activity, and total flavonoids were also analysed. The collected data were subjected to analysis of variance (ANOVA) using GenStat software version 17, and means were separated using Fisher’s least significant difference test at P≤0.05. The results showed that, the application of macadamia husk compost 30 and 60 t ha-1 enhanced SOC, SOM, C: N ratio, Mg, Ca, K, N, and P throughout the 2023/2024 and 2024/2025 cropping seasons. In addition, soil K, Na, P, and N increased under moderate irrigation at 60 % FC than in the control during the 2023/2024 season. Moreover, in the 2024/2025 cropping season, deficit irrigation at 30 % FC increased soil Ca, Mg, and K compared to the control. Furthermore, the interaction between MHC rates and irrigation levels significantly influenced soil chemical properties (e.g., SOC, SOM, K, Ca) and water-holding capacity. Fertiliser treatments enhanced chlorophyll content and the number of branches per plant at 49 days after transplanting (DAT) in both cropping seasons. Furthermore, plant height and stem diameter were significantly higher under soils amended with 30 t ha-1 MHC in 2024/2025 cropping season. Macadamia husk compost application increased jute mallow leaf yield in the 2024/2025 cropping season. Moreover, moderate irrigation at 60 % FC produced leaf yield comparable to that of the control at 100 % FC in the 2023/2024 cropping season. Furthermore, the interaction between 30 t ha-1 and 60 % FC and 60 t ha-1 and 100 % FC increased leaf fresh biomass in the 2024/2025 cropping season. Deficit irrigation at 30 % FC significantly reduced yield, while moderate deficit irrigation at 60 % FC maintained performance comparable to 100 % FC. In addition, application of MHC significantly increased the content of leaf phosphorus, potassium, magnesium, calcium, sulphur, zinc, copper, manganese, iron, and boron compared with the control (no fertiliser) and NPK fertiliser. Moderate irrigation at 60 % and 100 % FC produced comparable results for FRAP, TFC, and TPC. Moreover, interactions between 30 and 60 t ha-1 MHC and 30 %, 60 %, and 100 % FC positively influenced antioxidant capacities, as estimated by the FRAP assay, TFC, and TPC. There were positive associations found between the FRAP assay with TFC as well as TPC. It is evident from the results of this study that macadamia husk compost improved soil health, enhanced growth, yield and productivity of jute mallow, and increased its nutritional and phytochemical content and antioxidant capacity. In addition, moderate irrigation improved the chemical properties of the soil, growth, yield, and nutritional content of jute mallow. Furthermore, the interaction between macadamia husk and irrigation levels improved soil chemical properties, jute mallow yield, and its nutritional content. These results demonstrated the ability of macadamia husk compost to enhance production, nutritional composition, and yield of jute mallow, and the potential of MHC to mitigate the effects of deficit water in the soil and plants. Therefore, further research is needed to assess the combined influence of MHC and irrigation regimes on physiochemical properties of the soil, growth and yield and nutritional content of jute mallow in the field, in different environments, and other indigenous leafy vegetables.