Browsing by Author ". Calton. W.E."
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Item Soil Salinity Related to the Clearing of Natural Vegetation(1943) Milne, G.; . Calton. W.E.; AmaniIn 1940 the late Mr. Milne visited a group of sisal estates in the low-lying country at the foot of an escarpment where encroaching soil salinity had been reported. He left a comprehensive report which is of general interest because it points to a closer relation between soil conditions of upland and adjacent lowland than is generally realized and the phenomenon may repeat itself elsewhere. The conception of a catena or topographic sequence of soils implies that each type in the series is inter-related and affects the other. Here, where the problem centres on two very mobile soil constituents—water and soluble salts—the catenary aspect is important; in fact, without appreciation of it, the appearance of toxic amounts of salt and the possibilities of encroachment or recession are largely unpredictable. The following summarizes Mr. Milne's report. The junior author was concerned with the investigation and was responsible for the analytical work. The damaged sisal was on low ground adjacent to the flats of a river. At the time it was planted the soil conditions, as judged by the natural vegetation (grasses and herbs), were considered normal, though evidently the water-table was near the surface during the rains. At first the sisal grew satisfactorily and several cuts of good leaf were obtained, but for some time, and especially after 1939, large areas had been dying, together with all weeds and other vegetation except a salt-bush Suaeda monoica Forsk,(locally called" N yonya" and well known as a dominant in saline soils) which was not there originally. In some places so much salt had been accumulated on the soil surface that it was collected by natives. The steady spread of the salt even into areas well above swamp level was noticed. Preliminary soil samples sent to the Laboratory confirmed that a high concentration of salts, about 6 per cent, was present in the surface soils where sisal had died completely. A sample from an area of dying sisal showed 1.5 per cent salts, and an adjacent area of still healthy sisal had about 0.7 per cent at 18 in. depth, though there were only traces near the surface. The salts were chlorides and sulphates of sodium and magnesium with traces of sodium carbonate at depth in one area. A study of the problem in the field showed that it involved the conditions of soil formation and water balance in the whole of the stretch of country, which is a narrow strip of sloping ground lying between the foot of the high escarpment and the flood plain of the river running roughly parallel to it.
