Optimisation of stabilised hydrogen peroxide use for drip irrigation

Abstract Strong acids and chlorinated products are widely utilised for the maintenance of drip irrigation facilities worldwide. This research evaluated low concentration (10 ppm) of hydrogen peroxide (H2O2) products, in drip irrigation water, sourced from H2O2 containing high concentration (30,000 ppm) of an organic stabilizer (H2O2 High) and from H2O2 containing a low concentration (30 ppm) of the same stabiliser (H2O2 Low), evaluated in laboratory and field for effect on drip emitters, seed germination, seedling and crop growth, soil and water parameters. Findings from this research showed that seed germination was not impacted by H2O2 up to 5000 ppm. Positive effects on seed germination were noted for mungbean (Vigna radiata L.), egg plant (Solanum melongena L.), okra (Abelmoshus esculentus L.), chive (Allium porrum L.) and rocket (Eruca sativa L.) treated with 100 ppm H2O2. H2O2 High up to 1000 ppm did not negatively impact seed germination in other species tested. Root and shoot growth were enhanced in some species at lower concentration of H2O2 High, but were negatively impacted by higher H2O2 High concentrations for all crops except for corn. The negative effects on root and shoot growth were generally noted at higher concentrations (>1000 ppm). Therefore, continuous injection of H2O2 at low concentration (<100 ppm) in irrigation is unlikely to affect the seed germination and seedling growth. The impact of continuous injection of 10 ppm H2O2 on drip irrigation performance was evaluated in field trials. The emitter flowrates for surface drip single use tape on a chili (Capsicum frutescens L.) crop was not affected after 6 months of irrigation in either the control or H2O2 treatments. However, for above ground drip for table grapes (Vitis vinifera L.) and in subsurface drip for sugarcane (Saccharum officinarum L.) installations over four years, the emitter flow rate remained higher (2-16%) for H2O2 Low compared to H2O2 High and control. In aboveground drip, emitter clogging was reduced by 50% in H2O2 Low compared to the control and H2O2 High. The yield increases of 25, 10 and 4% in the sugarcane, chilli, and grape respectively probably due to H2O2 delivery proximal to root mass. H2O2 breakdown in soil was rapid, hence no residual H2O2 was found 10 minutes post irrigation. In tertiary treated wastewater (effluent), a single dose of H2O2 20 ppm was effective for suppression of algal blooms, whereas complete elimination was achieved by 2000 ppm by both products. In a circulating irrigation system, the emitter flow ceased after 900 hours due to biofouling in H2O2 High. In a bamboo (Bambusa spp. L) field trial using 20 ppm of products in non-circulating irrigation over 1966 hours, emitter flowrates were reduced by 50%. Drip emitter clogging was significantly reduced to19% for the H2O2 Low and 28% for H2O2 High compared to control (37%) of algae for effluent irrigation water. H2O2 High, unlike H2O2 Low, caused rapid emitter clogging in recirculating hard water irrigation, suggesting that HEDP in the presence of H2O2 caused Ca precipitation resulting in sudden emitter clogging. The degree of Ca precipitation in hard water increased with increasing HEDP inputs in irrigation. pH buffering of hard water delayed Ca precipitation. In the non-circulating irrigation higher concentration HEDP treatment in the hard water irrigation caused rapid emitters clogging. Low pH (≤6) increased solubility of Ca ions whereas higher pH led to precipitation causing crystal and amorphous Ca deposits. Continuous injection of H2O2 (10-20 ppm) in irrigation over a longer term did not show decline of soil biological functions (soil respiration, soil microbial biomass carbon and soil microbial diversity). H2O2 increased corn (Zea mays L.) yield by 9.2 and 70%, and coriander (Coriandrum sativum L.) yield by 2.3 and 15% for plants grown in vertisol and ferrosol, respectively, suggesting interaction effects, due to disproportionally greater decomposition of H2O2 to oxygen in ferrosol. In general, H2O2 Low injection in irrigation resulted not only in improved emitter performance, but also positive effects of crop growth, without noticeable negative impacts on soil. H2O2 High can acidify the rhizosphere, which may be of advantage in alkaline soil and/or irrigation water.