SOIL SURVEY

Waikato Independent, Volume XLIV, Issue 108, 1 October 1947, Page 2

SOIL SURVEY

WORK OF GOVERNMENT BUREAU ■ PHYSICAL ANALYSIS An outline of the work done by the Soil Bureau of the Department of Scientific and Industrial Research at Wellington was given by an officer of the Bureau when he made a recent visit to the Soil Survey Division at Christchurch. He explained that the Soil Bureau was made up of four sections —the soil chemistry, soil physics, soil survey, and soil biotics divisions. The biotics division studied micro-organ-isms in the soil and plant relationships. "The soil chemistry division does chemical.and some physical analysis of soils," he said. "It investigates the "soil chemical side of problems, and one' of the methods used is the X-ray technique. It can be particularly useful applied to soil classification. This approach is not novel, as it has been used overseas for some years. The idea started in the early part of the century and was first used in the examination of crystalline structures."

It was explained that many soil properties were directly determined by the type of clay in the soil. By clay was meant very small mineral particles ' less than .062 millimetres in diameter. These clays could be divided into three 1-ough groups—the mont-morillonite or expanding lattice type the hydrous mica or illite group, and the kaolinite group. By using. X-ray technique it was possible to tell which of these groups was prominent in a soil because each clay group gave a characteristic X-ray diffraction pattern on a photographic plate. In this process X-rays were passed through small clay samples to produce characteristic lines on a photographic plate. These lines were determined by the internal atomic structure of the clay being examined. This test was a qualitative one, and was useful only for identification. Other methods made use of thermal analysis or the electron microscope, but this was not yet available in New Zealand., At' the Wellington laboratory X-ray work was started in 1945. Chemical analysis showed what soil-forming processes had developed the soil under examination. For example, they showed how much of the soluble plant foods had been leached out by water. Composite sample* from selected paddocks were analysed and gave a useful relative measure of fertility expressed in chemical terms. Physical analyses were used to show how compact a soil was and whether it was likely to compress or slump if large buildings were erected on it. Tests carried out recently on the hospital site at Cashmere showed the soil to be sufficiently stable to carry the buildings. Samples of soil from all over New Zealand had been sent to the Soil Biotics Division. Plants, sensitive to the lack of certain elements, were grown in pots of these soils and then studied for any symptoms of mineral deficiencies.