Assessing the impact of chicken compost application and water regime manipulation on selected soil properties and furarium wilt of tomato

Thesis (M.Sc. Agriculture (Soil Science)) -- University of Limpopo, 2023

Soil properties such as physico-chemical and water holding capacity affect plant growth and the ability to resist soil-borne diseases. In tomato production, soil-borne disease such as Fusarium wilt, caused by Fusarium oxysporum f. sp. Lycopersici (FOL)cause serious yield losses and their severity is influenced by the interaction of soil biotic and abiotic factors. Despite their role as a store house for nutrients and a physical habitat for biological interactions, the influence of soil abiotic properties in driving mechanisms of disease suppression on Fusarium wilt and other soil-borne diseases, remain largely unexplored. Moreover, due to the nature of using organic amendments to improve soil physicochemical properties under greenhouse and field conditions as opposed to biological properties, which are amenable to analysis under laboratory conditions, the effects of physicochemical properties on disease development have only been briefly examined. To the best of our knowledge, the suppression of Fusarium oxysporum in tomato plants by physicochemical properties after amending soils with chicken compost and manipulating water-holding capacity, as exhibited in the current study, has not been reported previously. In line with these observations, the effects of amending soil with chicken compost coupled with manipulation of water deficit levels were investigated on soil physicochemical properties, plant growth parameters and subsequent suppression of Fusarium wilt of tomato. To achieve this, a 3 x 3 factorial pot experiment with four replications was performed under greenhouse conditions at the Green Biotechnologies Research Centre, University of Limpopo. The treatments included a control (non-amended soil), compost amended soil comprising of a mixture of 2/3 soil and 1/3 compost, mixture of 1/2 soil and 1/2 compost, irrigated to 100%, 60% and 30% water holding capacities. Pearson’s correlation analysis was employed to determine relationships between soil chemical and physical properties, plant growth parameters and disease suppression. Applied treatments yielded varying effects on measured parameters. For instance, soil organic carbon significantly increased in the order: no-compost < 25% compost < 50% compost soils with mean values of 39.4, 88.2 and 193.1 g kg-1, respectively. Increases in SOC were positively correlated with EC (r = 0.83), porosity (r = 0.81), air-filled porosity (r = 0.69), plant height (r = 0.68), fresh shoot weight (r = 0.81), fresh root weight (r = 0.57), chlorophyll content (r = 0.68), and negatively correlated bulk density (r = -0.81), shoot severity (r = -0.79) and vascular discoloration (r = -0.70). Moreover, no significant interaction effects of chicken compost and water deficit levels were observed in all the other soil and plant variables explored, except for SOC and EC. Effective suppression of Fusarium wilt was observed in soils receiving increased application rates of chicken manure, which correlated with increased gravimetric soil moisture and promotion of plant growth and development of tomato plants. Taken together, these results suggest the importance of SOC as a component of SOM in improving the fertility status of soils and of soil water relations, thus leading to the subsequent involvement in mechanisms of disease suppression. Such information advances our understanding of how soil physicochemical properties influences the suppression of Fusarium wilt; however, this needs to be tested in a wide range of soils and horticultural crops, and especially under field conditions.