Soil water content beneath summer-dormant and summer-active swards in a seasonally semi-arid environment
✍ Scribed by R.W. Snaydon
- Publisher
- Elsevier Science
- Year
- 1972
- Weight
- 836 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0002-1571
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✦ Synopsis
Soil water content was measured, over a period of 2Y2 years at Canberra, Australia, beneath summer-active swards (close-spaced and wide-spaced lucerne), and beneath summer-dormant swards (Phalaris and cocksfoot with subterranean clover). The measurements were made fortnightly, using the neutron scatter technique, at 0.25 m intervals down to 1.5 m.
Seasonal patterns of change in soil water content were similar beneath all swards, but the changes beneath close-spaced lucerne were less than those beneath wide-spaced l,~cerne or grass swards at 0.5-1.25 m depth. 75% of the changes in soil water content beneath all swards occurred in the top 0.75 m of soil. At depths greater than 1.0 m, soil water contents remained constant, and soil water potentials were less than -15 bar beneath close-spaced lucerne; small changes (2% by volume) were recorded beneath other swards.
Evapotranspiration from summer-active and summer-dormant swards was similar even during summer. Less than 15% of summer evapotranspiration was supplied from the soil water store, but 30% of evapotranspiration was supplied from the soil store during spring. 75% of the variation in E T throughout the investigation was accounted for by variation in rainfall; only a further 4 and 3%, respectively, were accounted for by variations in Epa n and available soil water.
The rate of water withdrawal was linearly related to soil water content at each soil depth, but, at a given soil water potential, withdrawal was four times greater from the top 0.5 m of the soil than from soil deeper than 1.0 m.