Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/1999
Publication Date: 2/1/2000
Citation: FARES, A., ALVA, A.K. SOIL WATER COMPONENTS BASED ON CAPACITANCE PROBES IN A SANDY SOIL.. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 64:311-318. 2000. Interpretive Summary: Water leaching below the rootzone can contribute to leaching of soluble nutrients and agrichemicals. Minimizing leaching losses is important to decrease the non-point source pollution of groundwater by nutrients and agrichemicals. A clear understanding of soil water mass balance is important to fine tune irrigation scheduling aimed to minimize leaching losses below the root zone. Automated continuous measurement of soil moisture content, using capacitance probes, was being investigated in four year old citrus groves, with Hamlin orange trees on Swingle citrumelo rootstock, in a sandy soil. Using the soil water mass balance approach, evapotranspiration and drainage below the rootzone were calculated. The daily evapotranspiration values varied from <0.4 mm per day in January to 5 mm per day in July and August. The annual evapotranspiration was 920 mm. The total annual drainage below the rootzone was 890mm, however, 82% of the eannual total drainage below the rootzone was attributed to rainfall. Therefore, scheduling of irrigation using the capacitance probes to monitor the soil moisture content both within and below the rootzone was effective for minimizing leaching loss of water below the rootzone.
Technical Abstract: Understanding soil water movement is needed to manage irrigation to minimize water drainage, nutrient leaching below the rootzone, and contamination of groundwater. We hypothesized that soil water content determined by capacitance probes can be used for irrigation scheduling and estimating soil water components. Objectives of this study were (i) to evaluate the performance of capacitance probes for optimizing irrigation management for Hamlin orange trees (Citrus sinensis [L.] Osb.) on Swingle citrumelo (Citrus paradisi Macf.x Poncirus triboliata [L.] Raf.) rootstock on a Candler fine sand soil (hyperthermic, uncoated, Typic Quartzipsamment) in Central Florida and (ii) to determine soil water balance componenets. Irrigation levels were determined based on available soil water (ASW) and tree growth stage. The soil water data measured at finite time interval by capacitance probes were used with irrigation and rainfall data to calculate edaily evapotranspiration (ET) and drainage rates. Daily ET rates showed strong seasonal patterns and varied from <0.4 mm per day in January to 5 mm per day in July and August. The annual ET in 1997 was 920 mm or 53% of the total water input (irrigation and rainfall). The cumulative annual drainage in 1997 was 890, or 47% of the total water input. Furthermore, 82% of the cumulative annual drainage was contributed by rainfall. Irrigation based on monitoring soil water content using capacitance probes minimized water drainage below the rootzone in a system where rainfall contributed substantially to drainage.