FARM LANDS OF NEW SOUTH WALES. 17 



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assimilating organisms which occur in the root-nodules of certain plants 

 depend, of course, upon the vigorous growth of these plants, and, without 

 irrigation, it appears hopeless to attempt to grow leguminous plants in these 

 districts. 



Prevention of Loss of Water from Soil. 



Even in the absence of irrigation a great deal can be done to ameliorate 

 the conditions of farming in the dry districts. There are large areas in the 

 State where it is out of the question to establish irrigation works — at all 

 events, for many years to come. It then becomes a question of conserving 

 within the soil the moisture present in the soil, and to counteract the con- 

 tinual loss of water which evaporates from the leaves of the plants and from 

 the surface. The planting of belts of trees to break the force of the winds is 

 a very important operation in this connection, since evaporation from both 

 leaves and soil is greatly accelerated by the passage of hot wind over the land. 

 Mulching of the surface soil, liming, thorough tillage, and a proper system 

 of drainage are all operations which result in the production of a fine spongy 

 texture in the soil, increasing its water-holding capacity and reducing the 

 amount of surface evaporation. 



The Value of Irrigation. 



There is no room for doubt that the soils of our arid districts are admirably 

 adapted for cultivation by means of irrigation ; abundance of water, properly 

 applied, being the only thing necessary to render them extraordinarily fertile. 



Irrigation fertilises. 



Irrigation is of value also on account of its direct fertilising effect, since 

 all water contains more or less saline matter in solution, which is retained 

 by the soil, and acts as plant-food. 



Saline Waters. 



There are, however, certain waters which contain substances which in 

 quantity are injurious to plant-life, and such waters must be employed with 

 caution. The most commonly occurring of these substances, as far as we are 

 concerned, are common salt and carbonate of soda. These salts have an 

 injurious effect both upon the plant and upon the soil. 



We have found by direct experiments in pots that the growth of wheat is 

 affected ty quantities as low as 05 per cent, to 15 per cent, of common salt, 

 whilst -2 per cent, prevented germination.* 



Carbonate of soda (alkali) affects the growth of the plant when present 

 to the extent of 1 per cent.; -3 per cent, prevents germination and growth. 



Our own observations on soils which had become charged with alkali from 

 continuous flooding without efficient drainage or correctives, show that such 

 soils are very rich in mineral plant-food, notably in potash, but deficient in 

 humus and in nitrogenous matter. Their capacity for water is reduced. The 

 soils become hard — so hard that some of the samples had to be taken by means 

 of a crowbar. The tendency of continued irrigation with alkaline water is 

 to destroy the organic matter, the soil becoming cemented together so as 

 to render tillage operations difficult, and finally impossible. 



A knowledge of the behaviour of these salts is of importance in view of the 

 fact that a large proportion of the water from New South Wales artesian 

 bores is charged with one or other of them. 



*F. B. Guthrie and R. Helms -Journ. Roy. Soc. N. S. Wales, XXXVI, p. 191. 



