On water availability in saline soils
P. H. Groenevelt A , C. D. Grant B C and R. S. Murray AA Visiting scientist from Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada.
B School of Earth & Environmental Sciences, University of Adelaide, Waite Campus, PMB No. 1, Glen Osmond, SA 5064, Australia; CRC for Plant-based Management of Dryland Salinity.
C Corresponding author; email: cameron.grant@adelaide.edu.au
Australian Journal of Soil Research 42(7) 833-840 https://doi.org/10.1071/SR03054
Submitted: 2 May 2003 Accepted: 19 May 2004 Published: 12 November 2004
Abstract
We present a formulation for the effect of the osmotic pressure of the soil solution on the availability of soil water for plant uptake in the extreme case that the reflection coefficient of root-cell walls is always unity. We also present a new equation to fit the water retention curve, which allows for an inflection point and is solidly anchored at both the wet end (saturated water content) and the dry end (water content at 150 m head, the permanent wilting point). By differentiating the fitting-equation one finds the differential water capacity, which is subsequently multiplied by a weighting function to account for the impediment caused by soluble salts. The weighted differential water capacity is then integrated over the entire range of the matric head from zero to infinity. This produces the integral water capacity and constitutes the total amount of water the soil can hold and release to a hypothetical plant that behaves like a perfect osmometer. We illustrate the approach using data found in the literature for a wide range of soil textures. In this paper the lower boundary of water availability in the presence of soluble salts is defined and calculated as would be registered by a perfect osmometer (reflection coefficient of unity). The upper boundary of water availability is found by setting the weighting coefficient at unity at all times, which implies a reflection coefficient of zero, and in turn that the salts in the soil solution have no influence on the availability of water (as would be registered by a tensiometer). The upper and the lower boundaries constitute the envelope within which the actual availability of water to real plants occurs, and implies a variable reflection coefficient plus the occurrence of active plant osmo-regulation. This establishes a framework within which water availability to real plants experiencing real osmo-matric conditions can be evaluated.
Additional keywords: integral water capacity, plant-available water, salinity, osmotic pressure, water retention curve, curve-fitting.
Acknowledgments
We thank the referees of this paper for their thoughtful reviews. We are indebted to Dr Neville Robinson, mathematician at Flinders University, Adelaide, for his blessing of the mathematics contained in this paper.
Breazeale EL, McGeorge WT
(1955) Effect of salinity on the wilting percentage of soil. Soil Science 80, 443–447.
Gardner WR
(1965) Dynamic aspects of soil-water availability to plants. Annual Review of Plant Physiology 16, 323–342.
| Crossref | GoogleScholarGoogle Scholar |
van Genuchten MT
(1980) A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal 44, 892–898.
Groenevelt PH, Grant CD
(2004) A new model for the soil water retention curve that solves the problem of residual water contents. European Journal of Soil Science 55, 479–485.
| Crossref |
Groenevelt PH,
Grant CD, Semetsa S
(2001) A new procedure to determine soil water availability. Australian Journal of Soil Research 39, 577–598.
| Crossref | GoogleScholarGoogle Scholar |
Hillel, D (1980).
Koorevaar, P ,
Menelik, G ,
and
Dirksen, C (1983).
MathSoft (1998).
Richards, LA (Ed.) (1953).
Richards LA, Weaver LR
(1943) Fifteen atmosphere percentage as related to the permanent wilting percentage. Soil Science 56, 331–339.
Robertson LS, Kohnke H
(1946) The pF at the wilting point of several Indiana soils. Proceedings of Soil Science Society of America 11, 50–52.
Rose, CW (1966).
Zimmermann U,
Schneider H,
Wegner LH,
Wagner HJ,
Szimtenings M,
Haase A, Bentrup FW
(2002) What are the driving forces for water lifting in the xylem conduit? Physiologia Plantrium 114, 327–335.
| Crossref | GoogleScholarGoogle Scholar |
