Quantifying the effect of inorganic and organic mulches of 2 soil types on nutrient uptake and fruit quality of Cripps’ Pink apples

The project was an addition to an established project and comprises bearing, ‘Cripps’ Pink’ trees on M793 on a light, sandy and heavier, silt soil on Lourensford. A clean, cultivated control was compared to a geotextile fabric, compost, wood chips and vermi-casting/wood chips mulch. Irrigation and fertilizer practises were applied according to commercial recommendations and noted. During the last 2 of the 4 season, irrigation was reduced by changing nozzle delivery. Nevertheless, over irrigation was indicated and masked possible positive contributions of the mulches. Results differed between the first and subsequent two seasons of the trial and coincided with the reduction in irrigation volumes. After the first 2 seasons, no significant nutritional trends could be identified (Kotze 2012). After 4 seasons, woodchips improved leaf P, K and Ca levels in the heavy soil.  Compost had a more pronounced effect on fruit nutrient levels and improved the levels of P, K and Mg in the heavy soil.  In contrast, the vermi-castings resulted in more changes in nutrient levels at the sandy soil, with a positive effect on fruit P, K and Mg. The same trend was observed in the leaf nutrient levels. The geotextile mulch did not improve any nutrient levels, either the leaves or the fruit, compared to the organic mulches, but showed higher nutrient levels for most nutrients in the tree compared to the control, in both sites. Mineral analyses of vermi-castings indicated the highest nutrient levels of all organic mulches at application, as well as after a growing season, but did not result in a higher leaf or fruit nutrient status. The woodchips mulch showed higher yield efficiency and lower shoot growth compared to the control at both sites. The negative effect of compost on yield could not be explained. None of the treatments had a negative effect on fruit quality.