Executive Summary
- The OXI-APP™ system was successful in keeping the filter rings clean and the discolouration and sedimentation inside the irrigation pipes to a minimum. This resulted in a significant decrease of salt deposits inside the irrigation pipes. Although the contamination in the dripper lines were not analysed, some of the following biotic and abiotic causes could be the reason for the green and brown sedimentation observed: insoluble Fe and Ca forms, green and red algae, iron bacteria, common bacteria, bacterial slimes, and sulfate reducing bacteria. Once the algae or bacteria forms a matrix inside the dripper lines, they trap oxidised Fe and insoluble Ca complexes. This is often referred to as a scale or rust build up. Based on the above observations, the OXI-APP™ system should result in less dripper blockages, better water distribution and minimal crop damage.
- The healthier, finer and deeper root system observed in the OXI-APP™ system resulted in less water saturation in the bottom of the bags. This more balanced air to water ratio resulted in a higher substrate and leaf petiole EC. This in turn stimulated the plants to form a significantly higher number of new bearing canes after pruning. Although the number of bearing canes were 16.4% higher in the OXI-APP™ system, they still managed to be of a greater length. The new cane leaves in the OXI-APP™ system also had a 6% higher chlorophyll concentration. The good substrate ‘air filled porosity’ and higher carbohydrate levels obtained from the increased crop biomass, should in turn favour the ‘cycle of energy production and demand’. This was demonstrated by the 25% higher root exudate brix in the OXI-APP™ system. In the larger scene of things, the root system will always benefit more in the short term, hopefully resulting in higher fruit yields and enhanced quality later in the season.
- The water oxidation observed with the OXI-APP™ system accelerated the conversion of ionic compounds to single ions. For this reason, higher electrical conductivity and higher total dissolved solids were measured at the drippers in the OXI-APP™ system. This is usually an indication of more plant available mineral ions in the fertigation water. The OXI-APP™ system increased the plant available sulphate, nitrate, ammonium, phosphate, manganese and iron levels significantly. The decrease in water pH, bicarbonate levels and total alkalinity will further enhance nutrient availability. This accelerated oxidation also resulted in an increased change of charge of manganese and iron to Mn3+ and Fe3+. These oxidised forms (Mn3+ and Fe3+) are less toxic to plants, and cannot be utilised by manganese and iron oxidizing bacteria as a food and energy source. Because these bacteria live in symbioses with micro-algae, a significant reduction in bacterial counts will result in less micro-algae clumps or cell-masses that causes dripper line blockages. The data supported this and showed a 40% reduction in the amount of algae and moss growth, as well as in the saprophytic fungi in the top of the substrate. In the long run this should increase aeration into the substrate, and lower the fungal inoculum concentration in the top of the substrate.
- Although no plant pathogens were detected in the water samples, there were high human pathogen counts in the untreated water (especially E. coli and total coliforms). The South African limits for human pathogens are < 1000 cfu/ml heterotrophic plant count, no E. coli, and < 10 cfu/100ml total coliforms. In both water samples the heterotrophic plate counts were less than 1000 cfu/ml. The OXI-APP™ system reduced the E. coli and total coliform counts significantly. This system can therefor be used to effectively lower the human pathogen counts in irrigation water and improve food safety for the export market.