Soil water components based on capacitance probes in a sandy soil

Understanding soil water movement is needed to manage irrigation to minimiz e water drainage, nutrient leaching below the root zone, and contamination of groundwater. We hypothesized that soil wafer content determined by capac itance probes can be used for irrigation scheduling and estimating soil wat er components. Objectives of this study were (i) to evaluate the performanc e of capacitance probes for optimizing irrigation management for 'Hamlin' o range trees [Citrus sinensis (L,) Osb.] on Swingle citrumelo [Citrus paradi si Macf. x Poncirus trifoliata (L.) Raf.] rootstock on a Candler fine sand soil (hyperthermic, uncoated, Typic Quartzipsamment) in Central Florida and (ii) to determine soil water balance components. Irrigation levels were de termined based on available soil water (ASW) and tree growth stage. The soi l water data measured at finite time interval by capacitance probes were us ed with irrigation and rainfall data to calculate daily evapotranspiration (ET) and drainage rates. Daily ET rates showed strong seasonal patterns and varied From <0.4 mm d(-1) in January to 5 mm d(-1) in July and August. The annual ET in 1997 was 920 mm or 53% of the total water input (irrigation a nd rainfall). The cumulative annual drainage in 1997 was 890 mm, or 47% of the total water input. Furthermore, 82% of the cumulative annual drainage w as contributed by rainfall. Irrigation based on monitoring soil water conte nt using capacitance probes minimized water drainage below the root zone in a system where rainfall contributed substantially to drainage.