Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/1999
Publication Date: 6/1/2000
Citation: PARAMASIVAM, S., ALVA, A.K., FARES, A. AN EVALUATION OF SOIL WATER STATUS USING TENSIOMETERS IN A SANDY SOIL PROFILE UNDER CITRUS PRODUCTION. SOIL SCIENCE, 165:343-353. 2000. Interpretive Summary: A clear understanding of redistribution of water in the soil profile following rain and/or irrigation is important to fine tune irrigation scheduling to minimize leaching below the rootzone. Soil water distribution was studied in a Tavares fine sand (96% sand - an Entisol) with 25 year old Hamlin orange trees, using tensiometers installed at various depths. Irrigation was scheduled when the 15 and 30 cm dpeth tensiometers read 10 centibars in January to June, or 15 centibars in July to December. Using the soil moisture characteristic curve, the soil water tension data was transformed into soil water content data to determine the water content in the rooting depth (0-90 cm) and below this depth (90-150 cm). This study demonstrated that tensiometer is a valuable tool to evaluate the distribution of soil water content in agricultural soils as basis to improve irrigation scheduling in coarse texture soils to minimize water leaching below the rootzone.
Technical Abstract: Redistribution and depletion of soil water in a Tavares fine sand (Typic Quartzipsamments) profile were evaluated after irrigation or rain in a commercial citrus grove with under-tree microsprinkler irrigation. Tensiometers were installed at 15-, 30-, 90-, and 150-cm depths in five clusters along the dripline of 25-year-old Hamlin orange trees on Cleopatra amandarin rootstock. Irrigation was scheduled when the soil water potentia at the 15- and 30-cm depths exceeded either -10 Kpa (Jan. To June) or -15 Kpa (July to Dec.) To replenish the water deficit (below field capacity) in the top 90 cm of the soil profile. The tensiometers placed at 15- and 30- cm depths responded to changes in soil water regardless of irrigation or rainfall. Tensiometer readings at various depths were used to estimate the water content at corresponding depths using the van Genuchten analytical relationship equations. Total soil water contents within the rootzone (0 to 90 cm) and below the rootzone (90 to 150 cm) within the monitoring dept (0 to 150 cm) were also calculated to estimate the water available for the trees and water that drained below the rootzone. Results showed some leaching does occur during months when there is heavy rainfall. This study demonstrated that tensiometer readings can be used to calculate the soil water content at various depths within the soil profile. Therefore, duration of irrigation can be adjusted to minimize leaching below the rootzone. Because optimal irrigation management is important to minimize nutrient leaching below the rootzone, tensiometer-based irrigation scheduling is an important component of nutrient and irrigation best management practices for citrus in sandy soils.