Effects of pre-harvest irrigation regime and crop level on yield, fruit size distribution and fruit quality of field-grown ‘Black Amber’ Japanese plum

Abstract

SummaryThe effect of pre-harvest irrigation level and crop level on yield, fruit size distribution, fruit growth and fruit quality was studied on field-grown ‘Black Amber’ Japanese plum in a commercial orchard in a semi-arid zone. Differential irrigation treatments were applied at stage III of fruit growth, from mid-May until harvest. Crop coefficients during the month prior to harvest ranged from 0.24 to 1.17 and from 0.13 to 1.33 of potential evapotranspiration in 2001 and 2002, respectively. Fruit growth and midday stem water potential were measured throughout the season. The yield from each experimental tree was harvested on 19 and 24 June, 2001 and on 19 June, 2002. The yield was weighed and fruit size distribution was determined with a commercial grading machine. The optimum crop coefficient appears to lie between 0.6 and 0.8 of the potential evapotranspiration. Fruit yield and size increased with increasing irrigation rate. Limitation of availability of assimilates was apparent in the low irrigation treatments at high crop levels. Relative fruit growth rates in all treatments decreased dramatically during an extremely warm, dry week, when temperature and vapour pressure deficit exceeded 40°C and 8 kPa, respectively. The decrease in relative fruit growth rate during this week was inversely proportionate to the irrigation level.The soluble solids content in the fruit juice decreased with the increase in the irrigation level.