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Agronomy Journal Abstract -

A Field Study of Plant Resistance to Water Flow in Alfalfa1


This article in AJ

  1. Vol. 76 No. 5, p. 765-769
    Received: Nov 28, 1983

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  1. A. S. Abdul-Jabbar,
  2. D. G. Lugg,
  3. T. W. Sammis and
  4. L. W. Gay2



The objective of this study was to investigate the plant resistance to water flow (Rp) in alfalfa (Medicago sativa L.) under field conditions. Plant resistance was computed using Ohm's law analog from leaf water potential (ψ1), transpiration rate (T), soil resistance (Rs), and soil water potential (ψs). A pressure chamber was used to measure ix hourly throughout the 3 days, 18, 19, and 20 Aug. 1982. Evapotranspiration rate (ET) was measured continuously using the energy balance-Bowen ratio method, and T was assumed to equal ET because the alfalfa completely covered the soil, thus limiting evaporation from the soil. The leaf area index was 4.3. Soil resistance was computed from root radius and root length density data, and had a value of 698 h, which was much smaller than the calculated value of (Rp). Soil water potential was calculated from soil moisture content data obtained using a neutron probe. Using this approach, Rp was almost constant throughout the day from 0730 to 1500 h, with an average value of 1.97 × l05 h. From 0730 to 1500 h, (Rp) was not significantly correlated (P<0.05) with the water potential gradient (ψ1ψs) (r=0.08). In addition, & was not significantly correlated with values of T above 0.2 mm/h (r= −0.32). Plant resistance to water flow in alfalfa was similar to reported values for other crops.

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