Soil water characterization for irrigation planning and operation at the BMC [Benguet Management Corporation] commercial mango plantation at Iba, Zambales [Philippines]

The study evaluated the soil water characteristics for the Benguet Management Corporation (BMC), a commercial mango plantation located at Iba, Zambales. Specifically, it sought to estimate volumes of water for irrigating mango at different levels of antecedent moisture, to determine relative rates of soil moisture accretion and depletion at three soil depths (25-, 50-, and 75-cm) during the dry season of October to December 1998, and to correlate statistically lagged soil moisture levels at three defined soil depths in different reproductive stages of mango, with daily rainfall. The soil textural class within the study site ranged from sandy loam, sandy clay loam, sandy clay, clay loam and clay.The resulting values of particle and bulk densities, porosity, field capacity, permanent wilting point, moisture characteristic curves and saturated hydraulic conductivity are generally within the range of values reported in literatures. The average volu me of irrigation water required to raise specified initial soil moisture levels to field capacity (0.3 bar) within the 75-cm root zone depth of each mango tree under the five phenological stages were computed. For initial moisture contents equivalent to 0.5, 0.7, 1.0, and 3.0 bars, the corresponding liters of water to be applied per tree in each of the phenological stages are as follows: 846.5, 1,108.0, 1,323.6 and 1,676.0 for bud break, 845.1, 1,165.1, 1,391.1 and 1,837.2 for full bloom, 890.0, 1,186.5, 1,404.6 and 1,817.3 for end of fruit drop, 745.1, 987.0, 1,175.8 and 1,615.5 for before harvest-stage. The differences in the amounts are due to variations in the texture in the soil depth considered. The observed total soil moisture (in mm) extracted within the 75-cm soil depth for phenological stage for 80 days from October1 through December 19, 1998 are as follows: 167, 134, 110, and 149 for the bud break, full bloom, end of fruit drop, and before harvest, respectively. T hese correspond to average daily moisture depletion (in mm/day) of 2.1, 1.7, 1.4 and 1.9, respectively for bud break, full bloom, end of fruit drop and before harvest treatment trees. Agronomically, bud break and before harvest phenological stages require greater consumptive use of water than the other mango phenological stages, but statistically these differences are not significant on a seasonal basis. The correlation analysis of lagged soil moisture with rainfall at three depths also yielded weak to moderate linear relationships. For the 1-day, 2-day and 3-day lagged soil moisture content, the 3-day lagged moisture content at the 25- and 50-cm depth in most treatment trees was significantly correlated with rainfall.