Effect of split applications of oil cake on leaf nutrient contents, tree growth, and fruit quality in non-astringent persimmon trees

Oil cake, widely used as an organic source of nutrients in horticultural production in South Korea, is a by-product when oil is extracted from various oilseeds. Split applications of oil cake were supplied to evaluate their effects on tree growth and fruit production in organic, non-astringent persimmon (Diospyros x kaki Thunb.) trees in 2009 and in 2010. Treatments included a single annual application of oil cake at 150 kg N ha(-1) in April (single application), two applications in April and July (105 and 45 kg N ha(-1), respectively; two-split application), or three applications in April, June, and August (60, 45, and 45 kg N ha(-1), respectively; threesplit application), as well as zero application of oil cake (control). All applications of oil cake significantly increased the amount of ground-cover vegetation compared to the control. The single and two-split applications increased soil organic matter (OM), K2O, CaO, and MgO concentrations, and cation exchange capacity to a soil depth of 0-30 cm in 2010. Oil cake applications increased soil porosity in 2010, as well as overall chlorophyll (SPAD values) and macronutrient concentrations in leaves in 2009 and 2010. Single and two-split applications stimulated water-sprout development, reduced the light intensity inside the tree canopy, and increased fruit drop. Fruit yield was higher in the two-split [24.7 metric tonnes (MT) ha(-1)] and three-split application trees (25.0 MT ha(-1)) compared to zero application control trees (19.8 MT ha(-1)) and single application trees (21.0 MT ha(-1)) in 2010. A single application resulted in soft fruit and slow skin colouration during maturation. Total soluble solids contents were higher in the control and three-split application trees in both years. The three-split application in 2010 increased the estimated production income by approx. 21% compared to the zero application, and by approx. 33% compared to a single application of oil cake.