70 THE farmers' handbook. 



Evaporation. 



The soil-water evaporates in two ways. The water absorbed by the root 

 diffuses throughout the cell-system of stems and leaves, and evaporates 

 through the breathing-pores of the leaf. Water is also lost by evaporation 

 from the surface of the soil. 



Both kinds of evaporation are increased by high temperature, dryness of 

 the atmosphere, or a high wind — that is to say, evaporation is most rapid in 

 hot, dry weather and a windy day; it is slowest in cool, moist weather and 

 calm air. 



The advantage of shelter in the shape of trees is, therefore, quite obvious 

 as a means of cooling and moistening the air and breaking its force, and 

 thus preventing too rapid evaporation. It is, unfortunately, largely ignored 

 in New South Wales, where most of the trees are religiously " cleared," and 

 the crops protect themselves against drought as best they can. 



I do not know of any other method for checking the evaporation from the 

 leaves which has been successful, though one or two have been suggested. 



With regard to the evaporation from the surface-soil, the case is different. 

 Evaporation from the surface can be checked by mulching. A covering of 

 leaves or farmyard manure, or any other form of mulch, protects the surface- 

 soil from the heat and the dry winds which cause rapid evaporation, and 

 thus prevents the too great loss of moisture; or the same result can be 

 obtained by hoeing or stirring the surface-soil, which has the effect of break- 

 ing or widening the capillary tubes at the surface, and by this means pre- 

 venting the upward motion of the water, for a time at least, and until the 

 water has found out the new channels. Hoeing, therefore, which is gene- 

 rally practised for the removal of weeds, has another equally beneficial 

 action, and it should be done, even where there are no weeds. 



The above remarks show how important a matter is the texture of a soil in 

 its relation to moisture, the ideal soil being one of a fine tilth, from which 

 excessive moisture drains readily away, in which there is free movement of 

 air and water, and in which too rapid evaporation is checked. 



Humus. 



Closely connected with the soil's texture and its consequent relation to 

 moisture is its content of humus. Humus is the black or brownish matter 

 in the soil produced by the slow decay of organic matter, whether of animal 

 or vegetable origin. It is not a definite chemical compound, but a mixture 

 of a number of different compounds, the nature of which varies, both with 

 the original matter and with the age of the product. 



Over that considerable portion of the State's arable land on which the 

 rainfall is limited or uneven, the need of retaining within the soil whatever 

 moisture is received as rain is one of paramount importance in the treat- 

 ment of the land. The maintenance of the soil's fertility in these areas 

 becomes largely a question of conserving this sometimes scanty supply, and 

 soil-treatment having for its object suitable means of maintaining the most 

 favourable conditions as to moisture will claim the most serious considera- 

 tion of the farmer. 



As the land taken into cultivation gradually extends so as to include more 

 and more of the area within the belt of reduced rainfall and approaching to 

 serai-arid conditions, this question of the conservation of soil moisture 

 becomes of increasing importance. 



