Fruit Growing Research (Dec 2015)
INVESTIGATING SPATIAL DISTRIBUTION OF THE SOIL–WATER CHARACTERISTIC CURVES AND CONSEQUENCES IN IRRIGATION APPLICATION WITHIN A SANDY-LOAM SOIL IN AN INTENSIVE PLUM TREE ORCHARD
Abstract
The orchard plot has plum trees (Stanley cultivar grafted on Saint Julien rootstock), six years old, with 4 m between tree rows (ITR) and 2.25 m between trees in the row (IR). The relief is a gentle hillside with a slope of 0.075 m m-1 . Undisturbed soil samples were taken at field capacity (FC) from both IR and ITR positions, between 0 and 1 m depth, with a 0.1 m depth step, in cylinder metal cores of 0.05 m in both sizes. Soil water characteristic curves between the matric potential (soil suction, ψ, expressed as pF) and SWC (m3 m ) were determined in the lab according to van Genuchtenʼs method. BD for each sample was also determined. Highly significant correlations were found between the main soil physical indices used in irrigation application and bulk density. Thus, soil compaction in orchards deteriorates soil structure and decreases water supply to the fruit trees. Only about one quarter of the total water capacity of a soil is usually used as available water for plants. Most of this capacity for the investigated soils contains either immobile water (equivalent of the wilting point) or drainage water (from total capacity to field capacity). From the available soil water capacity, only half (i.e. 12.5% of total soil water capacity) is easily available, the rest being increasingly more difficult available to plants. Soil matric potential is lower and lower with decreasing soil water content within the available soil water capacity, or otherwise soil suction increases more and more under the same conditions. Thus, soil water availability decreases dramatically from field capacity to the wilting point, for uniform decreases in soil water content, and irrigation application under water stress reduces dramatically soil water availability for plants compared to fully irrigation.
