ARS | Publication request: Soil Water Sensor Needs for the Evaluation of Hydraulic Lift in Crop Plants

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2007
Publication Date: March 21, 2007
Citation: McMichael, B.L., Lascano, R., Gitz, D.C. 2007. Soil Water Sensor Needs for the Evaluation of Hydraulic Lift in Crop Plants. International Soil Moisture Sensing Technology Conference, March 19-21, 2007, Waikiki, Honolulu, Hawaii. 2007 CD-ROM.

Technical Abstract: Hydraulic lift (HL) in plants is defined as the process by which water is redistributed from wet soil zones to drier soil zones through the plant root system in response to gradients in water potential. Water is released into the dry soil when plant transpiration is low (night) and reabsorbed by the plant when higher transpiration rates are resumed (daylight). The crops in our area, consisting mainly of cotton, are increasingly being produced under dryland and limited irrigation conditions due to a decreasing water supply. Rainfalls during the growing season in the area generally come in the form of high intensity short duration events and are frequently less that 10mm per event. In many cases, the plant is unable to take advantage of these rainfall events due to runoff and/or high evaporation since there may be an absence of viable roots in the upper (0-10 cm) soil profile. We have hypothesized that since HL would probably not be of a sufficient magnitude to meet total transpirational demand, there may be sufficient water transferred to maintain roots in the dry soil zone in a viable condition to absorb water in case of a rainfall event. Preliminary results with cotton using a split root system for growing roots of the same plant in both wet and dry soil have shown that HL did in fact occur. The amount of water transferred was very small (on the order of 0.006 m3/m3 difference in water content) but amounted to approximately 11-32 % of daily evapotranspiration rates of from 2-6 mm/day. Subsequent preliminary results using stable isotope (deuterium) as a tracer have also confirmed the occurrence of HL. We have also documented genetic variability for HL on a limited basis in cotton. One particular difficulty we have encountered is to be able to document the small changes in soil water content accurately and consistently. Also, new techniques for water content measurement needed to evaluate HL on a large scale must be devised in order to determine genetic variability for the trait. These and other issues concerning the measurement of HL will be discussed further.