Canopy Tree Management and the Effect on Water Infiltration Rate.

The distinctive properties of volcanic soils are largely attributable to the formation of noncrystalline materials (allophane, imogolite, ferrihydrite) containing variable charge surfaces, and the accumulation of organic matter. Phosphorus fixation and strong acidity, are the primary chemical limitations to agricultural productivity. Volcanic soils generally have high physical fertility and mature soils are relatively resilient to erosion and compaction. Volcanic areas include a wide variety of landscapes. On lowlands, the tephras may have produce deep fertile volcanic soils going from 1 to >10 m depth. In hilly landscapes the tephras may be of variable thickness due to erosion, leading to shallow bedrock and thinner soil profiles. Macadamia nut (Macadamia spp.) trees will perform well on a wide range of soil types from heavy sandy soils and lava rock soils to heavy clay soils if the soil is well drained. Nevertheless, they do best in deep, rich soils with a pH of 5.5 to 6.5. A multi-faceted study to quantify the effects of canopy management on surface biomass, tree health and water infiltration was established on two separated Macadamia nut orchards. Soil samples were analyzed for moisture content, and bulk density, while field tests were carried out to determine water infiltration rates using a “Mini-Disk Infiltrometer”. Later SURFER software was used to visually represent the spatial variability. The results showed an increment in surface biomass on pruned areas, however, no relationship between water infiltration and total nut yield was observed. Water infiltration was recorded between 0.08 cm hr^-1 to 0.53 cm hr^-1 (0.03 to 0.21 in hr^-1). Volcanic ash soils dominated by allophane and imogolite clay shows high water holding capacity and low bulk density which is a determining factor. An increase of surface biomass was positive, stimulating a reduction of soil erosion.