International Water & Irrigation

22 Water restrictions applied later in the season, at the end of the fruit drop period, had less of an effect on reducing fruit drop. Possessing in-depth knowledge of the water stress effects on persimmon trees, as well as the appropriate timing to apply ROI strategies in the cultivar ‘Rojo Brillante’, may be of great utility in semi-arid areas to increase the fruit crop level. Based on the results from the abovementioned studies it was strongly suggested that Kc values for the application of ROI strategies should be followed. (Table Two) . A previous study concluded that some water restrictions applied at the end of fruit growth period might result in faster color development and can therefore accelerate fruit ripening. Water stress at that stage of the crop did not have an effect on the content of fruit total soluble tannins, both before and after the de-astringency treatment. This result would suggest that water deficit did not affect the level of fruit tannins at harvest or the effectiveness of the post-harvest treatment. The available information in the literature on the nutrient requirements of persimmon trees has been generally focused on studies conducted on non-astringent varieties cultivated in Asian countries such as South Korea, China and Japan, as well as Australia and New Zealand. Persimmon is a low-demanding crop for nutrients such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg), compared with other temperate tree species such as citrus, cherries or plums (Table 3) . Its root system is weak and therefore requires high soil porosity for a normal root development. Ameliorating the soil structure with high levels of soil organic matter is a recommended practice to improve the nutrient and water uptake efficiency. Soils with high organic matter content improve the canopy development and fruit size of persimmon. High soil organic matter content is particularly important to compensate for the weak root system of D. lotus rootstock and prevent restricted root development in compacted soils. Persimmon fruit Table One: Suggested crop coefficients (K c) for mature persimmon trees grown under limited water supply conditions in eastern Spain. Month K c March 0.20 April 0.45 May 0.57 June 0.40 July 0.90 August 0.96 September 0.70 October 0.70 November 0.60 Table Two: Comparison of crop nutrient removal rates between astringent “Rojo Brilliante” variety and non-astringent “Fuyu” variety of Persimmon. Persimmon “Rojo Bril- liante” (kg-t 1 ) Persimmon “Fuyu” (kg-t 1 ) Nitrogen 0.85 1.25 Phosphorous 0.39 0.25 Potassium 1.42 1.75 Calcium - 0.125 Magnesium - 0.06