Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Plants, Soils, and Climate

Department name when degree awarded

Soil Science

Committee Chair(s)

H. B. Peterson


H. B. Peterson


In saline soils, which are characterized by an appreciable quantity of neutral soluble salts, plant growth is adversely affected due to the increase in osmotic pressure and the consequent decrease in the physiological availability of water. In addition, growth may also be restricted through the accumulation of toxic quantities of various ions within the plant.

On the other hand, alkali soils, whether saline or non-saline, are characterized by a high content of exchangeable sodium in the cation-exchange complex. One reason of low productivity on these soils is the unfavorable physical conditions induced by the dispersing action of the sodium ions. It was pointed out by Ratner (1935) that the influence of exchangeable sodium upon the physical properties of the soils is very clearly defined even when there are only small amounts of exchangeable sodium in the soil. Recent studies have shown that when a soil containing more than 10 or 15 per cent of the exchangeable sodium is cultivated and irrigated, it becomes dispersed, disaggregates and becomes relatively impermeable to water and air. Plant growth under these conditions is restricted by a number of factors involving nutrient availability, poor gaseous interchange and lowered water availability.

In contrast to the above mentioned effects of exchangeable sodium on the soil structure, sodium also possesses some harmful chemical effect on plant growth and nutrition. High exchangeable sodium in soil due to hydrolysis and formation of sodium carbonate results in injury to plant roots and unfavorable soil reaction. It upsets the nutritional balance, precipitates calcium and magnesium as insoluble carbonates and antagonizes their uptake. Thus plants suffer because of the low availability of these nutrient elements.

Several worker, Ratner (1935), Thorne (1944), Joffe and Zimmerman (1944) and Bower and Wadleigh (1948), have studied the effects of various levels of exchangeable sodium on the growth and nutrition of plants and have sought to find out the limits of exchangeable sodium when the plant growth begins to decline and finally when growth ceases. However, as yet no definite attempt has been made to evaluate the chemical effects of exchangeable sodium on plant growth independent of its adverse effect on soil structure.

Although as yet not economically feasible for general agricultural use, aggregating agents can be an effective research tool for investigational work on alkali soils. By their use, plant response to different levels of exchangeable sodium or different Ca:Na ratios may be studied on "conditioned" soils in the absence of poor structure and accompanying conditions of deficient aeration and low water-movement rates ordinarily present in alkali soils.

The introduction of synthetic exchange resins known as 'Amberlites', also, makes it possible to study the direct chemical effects of exchangeable sodium on plants as separate from its adverse physical effects on the cultural medium. It has been pointed out by Bower and Wadleigh (1948) that Amberlites do not disperse and their physical properties are not affected to any measurable extent when sodium saturated.

This work is an attempt to correlate the various levels of exchangeable sodium to plant growth and nutrition while keeping the adverse effects of poor structure of the cultural medium as low as possible.



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