Research was conducted at the Nubaria Horticultural Research Station, El-Bohira Governorate in Egypt's calcareous soil to determine the effect of humic acid amendments and flood irrigation scheduling on the development and growth of Prunus domestica L. (Kelsy plum). The research was conducted over a four year period beginning in 2005 when the plum fruit trees had developed for 2 years having budded on a Mariana rootstock. Tests were conducted during 2006- 2009 growing seasons.
The main and interacting effects of flood irrigation frequency and humic acid amendments were tested using a split-plot design experimental set-up. Kelsey plum was planted at a spacing of 4 x 5 m under a flood irrigation system in calcareous soils. The trees were irrigated under three regimes, which were: 5-day (I1), 10-day (I2) and 15-day (I3) interval. The humic acid treatments (thereafter referred to as HA) included: humic acid soil application around tree's trunk (T1), foliar application (T2), soil and foliar application (T3) and a control (T4) whereby no humic acid treatment was made. HA treatments were applied on the months of April, May, June and July during each of the years (2006-2009). During 2006 and 2007 vegetative growth measurements and leaf mineral contents were measured. In 2008 and 2009 when the plum trees had attained maturation and had reached their reproductive stage, the fruit quality and yield were determined.
Each of the humic acid additions in either soil or foliar application method increased the physical attributes (vegetative) of the trees during the first and second seasons of growth relative to the control. The combined foliar and soil applications of humic acid (T3) increased tree height and Trunk Cross-sectional Area (TCA); shoot number, length and diameter during 2006 and 2007 seasons compared to all other treatments. The largest combined effect of irrigation and humic acid treatments during the vegetative seasons (2006 and 2007)on the plum trees was observed for the T3 I2 treatment, followed by the T3 I1 and T1 I2 in that order. The vegetative growth parameters highlighted the importance of humic acid and its usefulness in increasing water use efficiency for the 10-day irrigation interval as compared to the 5-day interval. Foliar and soil humic acid treatment significantly induced high leaf contents of both macro- and micro- minerals (N, P, K, Fe, Mn and Zn). The soil mode of application T1 was inferior to the foliar mode of humic acid application (T2) during the growing seasons of 2006 and 2007.
In the two studied years 2008 and 2009, the highest yield with good fruit quality was obtained from trees under T3, so it recommended.