Effects of drip fertigation and micro sprinkler irrigation on yield, root growth and water use in a South African apple orchard

摘要

In areas where summers are long, hot and dry the performance of deciduous fruit trees is highly dependent on irrigation (Naor et al, 1997; 1999; 2000; Naor, 2006). Irrigation is becoming increasingly sophisticated in line with pressure to improve theefficiency with which water, nutrients, energy, labour and capital are utilised. Micro sprinkler irrigation wets a continuous strip a metre or more wide on each side of the tree row centreline, and is widely used in deciduous fruit orchards. Drip irrigation wets a more localised area on both sides of the tree row frequently and wastes less water through wind drift and evaporation. Drip irrigation has also been found to improve yield and fruit size in apple (Naor et al., 1997,2000), possibly because theroots become concentrated in the wetted soil beneath the dripper line (Fig. 1). Densities of apple roots within 300 mm of the drip line may be three times higher than at greater distances (Levin et al, 1979). The ability to deliver water accurately to defined volumes of root zone soil enables irrigation to be scheduled with a high degree of precision. Accuracy is further improved by the increasing availability of reliable local weather data and crop factors, which enable water to be supplied at rates that match the seasonally changing requirements of the tree. Adjustment for deviations from the long term seasonal pattern due to heat wave conditions or precipitation is also possible where soil water sensors are utilised and weather forecasts are acted upon.