Long-term effects of irrigation and date-palm production on Torripsamments, Saudi Arabia

Abstract

Specimens of soil profiles from four date-palm orchards under irrigation for periods ranging from 10 to 230 years, were compared with one another and with a profile from the nearly barren desert. Soil properties were recorded through field and laboratory observations. Distribution and mass of plant roots in each layer to a depth of 135 cm were also measured, as was the quality of the irrigation water used in each orchard. The data indicate changes in several characteristics of the soils after they were put under irrigation. Some differences were also observed among the profiles in the orchards in relation to their ages. Differences were found in the amounts and distribution of calcium carbonate, the levels of organic matter, the values of strength and bulk density, and possibly in the amounts and distribution of the clay fraction. Total amounts of carbonates are several times larger in profiles from the older orchards than in the one from the desert. Most of that difference is in carbonates of claysize. The largest amounts of carbonates occur in the same layers as where the greatest mass of plant roots is found. Levels of organic matter are two to three times as high in the profiles in the orchards as in that in the desert, with the biggest difference between the barren profile and that in the orchard of 10 years old. Amounts of the clay fraction are greater in the profiles under irrigation, with a tendency for the amounts to increase with time. Greater amounts of clay are attributed chiefly to precipitation of carbonates in that fraction. The profiles in the orchards developed increasing strengths and decreasing bulk densities over time. Differences among the profiles thus indicate not only that pathways of genesis have been altered under irrigation but that some effects become evident in a short space of time and are gradually enhanced over longer periods.