|Brakke, Mary - UNIV OF FLORIDA|
|Baker, Jeffrey - UNIV OF FLORIDA|
|Jones, James - UNIV OF FLORIDA|
Submitted to: Soil and Crop Science Society of Florida Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2000
Publication Date: N/A
Interpretive Summary: Problem. Partial area irrigation was proposed for decreasing water use for irrigating citrus. Experiments were conducted by USDA-ARS scientists in Gainesville, FL as a part of research between the USA and Israel. Young Hamlin orange trees on Carrizo citrange, Swingle citrumelo, and sour orange rootstocks were trained to grow in split- root containers (4 sand-filled compartments) and then placed in controlled-environment chambers where 1/4, 2/4, 3/4, or 4/4 of the roots were irrigated each time 2/3 of the water was depleted. Accomplishment. Maximum photosynthesis occurred before 11:00 AM in all chambers, followed by midday depression of photosynthesis, but evapotranspiration (ET) remained nearly constant during the day. Photosynthesis and water-use efficiency through each day, as well as total new growth, was highest where all 4 compartments were irrigated (4/4) and lowest where 1/4 of the roots were irrigated. Benefit. This research indicates that citrus growers would probably get better growth and yield, and a higher water-use efficiency, by avoiding irrigation schemes that provide water to an insufficient fraction of the grove land area. Water stresses resulting from inadequate irrigation limit photosynthesis more than ET.
Technical Abstract: Young citrus trees were grown in controlled-environment chambers to determine evapotranspiration (ET), carbon exchange rates (CER) and biomass accumulation responses to partial wetting of root systems. One- year old 'Hamlin' orange scions [Citrus sinensis (L.) Osbeck] on Carrizo citrange [Poncirus trifoliata Raf x C. sinensis (L.) Osbeck], Swingle citrumelo (P. Trifoliata Raf x C. paradisii Macf.), and sour orange [C. Aurantium (L.)] rootstocks were established in 4-cell, split-root containers of coarse sand. Seven trees of each rootstock with 1/4, 2/4, 3/4, or 4/4 of the rooting volume irrigated (RVI) were grown in 4 separate chambers for 92 days and were irrigated at 2/3 depletion of available soil water. Daily maximum CERs occurred before 1100 EST in all chambers followed by midday depression of CER, whereas ET remained nearly constant during the day. CER and water-use efficiency (WUE) was highest for 4/4 RVI and lowest for 1/4 RVI. New biomass was linearly related to the fraction of RVI. Growth limitations by decreased RVI were least for the Swingle citrumelo rootstock. For citrus grown on soil with low water holding capacity, a large cutback on the portion of roots irrigated would likely have a detrimental effect on plant performance.