Effect of highly processed calcined kaolin residues on apple productivity and quality

Abstract

Calcined kaolin-based particle films (PKPF) are effective in reducing insect, heat, photosynthetically active radiation (PAR) and ultraviolet radiation (UV) stress in plants due to the reflective nature of the heat-treated particles. The purpose of this study was to determine the effects of PKFP treatments applied at moderate (3%) and high rates (12% w/v) on apple physiology, yield and quality and the interaction with ambient ozone levels for a 6 year period. Fruit mass was increased by applications of PKPF at 3% and 12% in 4 of 6 years in non-irrigated treatments and in 2 of 6 years in irrigated treatments. Red fruit color was increased (lower hue angle) over the control in 5 of 6 years and in 2 of 5 years the 12% PKPF had improved red color over both the 0% and 3% PKPF non-irrigated treatments. PAR interception over 6 years, adjusted for LAI, was greatest for the control, least for the 12% PKPF, and 3% PKPF was intermediate. Reduced PAR interception below the canopy was likely due to greater PAR reflection within the canopy. Whole canopy temperature was significantly higher for the control (26°C) and lower for the 3% and 12% PKPF treatments (24°C). Fruit mass increased in the PKPF treatments, relative to the irrigated control treatment (%), with increasing maximum ozone levels during May. In laboratory studies, ozone degradation was greatest for alfalfa, least for calcined kaolin and the addition of alfalfa to calcined kaolin increased degradation proportionately. The present study confirms that calcined kaolin is an effective catalyst for ozone degradation and organic materials, such as alfalfa, are even more effective, due to the direct reaction with carbon molecules. Whole canopy gas exchange measurements (1000–1600HR) over a 10 day period in 2011 indicated that the 2.7% PKPF+0.3% alfalfa dust consistently had higher photosynthesis, 0.3% alfalfa was intermediate, while the control and 3% PKPF had the lowest photosynthesis rate. Whole canopy ozone degradation indicated that the 2.7% PKPF+0.3% alfalfa dust consistently had the greatest ozone degradation, 3% PKPF and 0.3% alfalfa were intermediate and the untreated control had the least ozone degradation. There is evidence that the 0.3% alfalfa stimulated a small amount of microbial growth on the leaf surface while the 2.7% PKPF+0.3% alfalfa stimulated a much greater amount of microbial growth. This synergistic effect may be due to the increased surface area in the particle film providing habitat for microbial populations and the reflection of UV by the particles that can be deleterious to microbial growth within that habitat. Data support the concept that chronic ozone damage is moderated to a significant degree by the use of surface treatments that catalyze ozone degradation in a particle film. The use of PKPF may be one tool to mitigate not only increased ozone stress but also heat stress from increased growing season temperatures in the future.