Abstract form

Saline water irrigation effect on soil organic carbon sequestration
Tahar GALLALI
UR Pedology 04/UR/10-02. Faculty of Science. Campus Universitaire. Tunis 2092.
Tunisia
Contact e-mail: gallali.tahar@planet.tn
In arid zones, low precipitation combined with very high evapo-transpirations are
expressed, on a pedogenetic level, by organic matter-depleted soils. The use of
irrigation to compensate the high water demand does only aggravate the organic stock.
In fact, the highly mineralised water induces a solubilisation of the SOM as fulvates or
even as sodium humates.
In this paper, we propose to study the balance of organic matter in terms of increased
salinization. This is an open field experiment undertaken in the alluvial plain of the
Medjerda Valley (Northern Tunisia) on a clay- silty soil with irrigation waters varying
from freshwater (EC = 0,3-0,5 mmhos /cm at 25°C, SAR= 1,1-1,6) to mineralized
waters (EC= 4,7-5,4 mmhos/cm at 25°C, SAR= 7,0- 9,0). After twenty-five years
experiments, the organic matter balance carried out on 1.5 m soil depths is established
as follows:
-Organic Carbon: 148.5 Tons/ha in the freshwaters irrigated soils against 139.6 Tons/ha
in saltwater irrigated soil.
-Organic nitrogen: 18.1 Tons/ha against 16.8 Tons/ha respectively.
In effect, the increase in salinity results on one hand, in less important long-term
organic restitutions, and on the other hand, by an increased solubilisation as hydrosoluble
carbon.
Key words: Salinization, organic matter, arid zone, Tunisia.
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