Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : The structural instability of soils of the old and new land of Al-Hassa Oasis, Saudi Arabia.

Auteur : Al-Jabr, Mohammed A.

Université de soutenance : University of Salford

Grade : Doctor of Philosophy (PhD) : 1989

Résumé
Soil structural stability is desirable for plant growth and soil structural compaction. Its effect on plant growth lies in its indirect influence on the relationships between air, water and soil and through its control of the pore size distribution, which in turn, controls the physical and chemical properties of the soil. Salinity, wind and water erosion are a major problem in arid areas. These conditions, together with high evaporation rate, lead to soil structural deterioration. Al-Hassa Oasis, Saudi Arabia, experiences such problems in its two major areas of agricultural operation, the Old Oasis and New Lands, which show differential problems of soil structural stability. These areas are : (1) The Old Oasis where cultivation has been in progress for many thousands of years. (2) Newly reclaimed areas cultivated only for two decades. Two types of soil stability were measured. Osmotic stability was assessed using a chemical dispersion technique. Water stability was measured using a modified wet-sieving method comprising two stage sieving and examination of the water stable aggregates surviving the wet sieving. The results show complex relations which are difficult to explain. The main difficulty lies in the fact that while clay mineralogy is similar in both areas, the respective behaviours of the soils to stability experimentation and analysis vary sharply from one area to another and from one site to another. The results showed that the Old Oasis soils are relatively richer in the soil constituents (organic matter, CaCO$\sb3$ and iron as a binding agent) that positively influence both osmotic and water stability. The realtively low osmotic and water stabilites of soils of the New Land resulted from deficiences in these constituents in addition to a high sand content. The possibility of reducing or eliminating stability problems using PVA was investigated and the effect of simple simulated management practices by controlling drying of treated and untreated soils. It was shown in both osmotic and water stability analysis, that the treatment with PVA aided aggregation and reduced dispersion more effectively in the Old Oasis soils which have high organic matter, CaCO$\sb3$ and iron content than the New Land soils.

Présentation : EThOS (UK)

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