Research paperIrrigation scheduling and soil moisture dynamics influence water uptake by Huanglongbing affected trees

- Good and frequent irrigation management is necessary particularly on the extremely well drained sandy soils of Florida.
- The results showed that Daily irrigation would reduce water stress in trees affected by citrus greening and would be appropriate to implement on Florida's sandy soils.
- The findings should improve our understanding in estimating irrigation water demand of Huanglongbing affected trees in Florida and other citrus producing regions.

Improved understanding of citrus water use and soil moisture distribution in Huanglongbing (HLB) (Candidatus Liberibacter asiaticus) affected groves is critical for devising appropriate recommendations for optimizing water use and sustaining citrus yields. Thus, a study was conducted to investigate soil moisture movement and water use patterns in central, south-central and southwest Florida. Treatments included: 1) daily irrigation (Daily), 2) University of Florida Institute of Food and Agricultural Sciences recommended scheduling characterized by irrigating every two days to replace water used by crop evapotranspiration (IFAS), and 3) irrigation scheduled half the number of days between irrigation recommended by IFAS and Daily (Intermediate). The total irrigation was designed to meet estimated crop water use (ETc) for mature citrus equaling 1127 mm, 1138 mm, and 1211 mm, and 1211 mm per year at Avon Park, Arcadia and Ave Maria, respectively. Field capacities (FC) and available water capacity (AWC) varied between 0.062 cm3 cm−3 to 0.11 cm3 cm−3, with AWC estimated to be 86% to 91% of FC. Irrigation set points for irrigation scheduling were estimated at 33 and 50% of allowable soil water depletion (ASWD) and varied between 0.020 and 0.033 cm3 cm−3 while 50% ASWD varied between 0.031 and 0.050 cm3 cm−3. Daily water use largely varied between 0.02 and 0.18 g/d/cm2 in Summer 2013, 0.01-0.15 g/d/cm2 in Fall 2013 and 0.01 and 0.24 g/d/cm2 in Spring 2014. Water use pattern was largely of the order Daily > IFAS > Intermediate. Moisture contents were similar among irrigation schedules varying between 5-20%, 1-14% and 5-25% at 15-, 30-, and 45-cm soil depths, respectively, increasing with depth possibly as a result of uptake in the top 30 cm. These findings should help in refining limits for available water contents and estimating irrigation water demand to sustain citrus productivity of HLB infected trees.