224 Journal of Agriculture, Victoria. [lo April, 191 2. 



escape for surplus water exists it is necessary to underdrain to get the 

 «ame result. 



(3) Evaporation from the surface. All soils are subject to this loss and 

 the amount may represent the total annual rainfall. According to Greaves 

 the yearly amount evaporated from a water surface in the vicinity of Lon- 

 don equals 20.6 inches. There is more loss than this from a soil kept fully 

 saturated. While fully saturated all soils lose water at the same rate. As 

 different soils are allowed to dry those with largest particles (sands) lose 

 water fastest. After a time those with finest particles (clays) lose most 

 because they have most to lose. Finally, both kinds of soils come to a 

 balance losing or gaining moisture according to the humidity of the air. 



Evaporation may be greatly diminished by protecting the soil from the 

 action of sun and wind. Under ordinary circumstances as the soil loses 

 moisture by evaporation, more water reaches the surface from below. It 

 rises by capillary attraction through the pores of the soil. The smaller 

 these pores are (within limits) the higher the water will rise; if they are 

 very large it will practically not rise at all Leaves or loose litter spread 

 on the surface have very wide pores and water cannot rise through them. 

 At the same time they prevent rapid evaporation because they shield the 

 soil surface from sun and wind. 



Litter spread on the surface to limit evaporation is called a mulch. 

 Instead of spreading litter the soil itself may be used as a mulch. For this 

 purpose it is only necessary to stir it to a depth of 2 or 3 inches when 

 it is not too wet. By this means the surface pores become too large to raise 

 the water above the lower layer of the stirred soil. The stirred soil soon 

 appears to dry while an unstirred portion may appear to remain wet, but 

 that is because in the latter case the water is continuing to rise to the surface 

 and dissipate by evaporation, while in the former case no water is rising to 

 the surface and none is lost, because the surface layer is not getting any 

 from underneath to lose. Beneath the apparently dry surface water is 

 being saved from loss in the body of the soil. Working with a 3-inch soil 

 mulch on a clay loam, Professor King of Wisconsin found that 63.13 per 

 cent, of the evaporation on similar unmulched land was saved in 100 days. 



When referring to the water requirements of a wheat crop it was ob- 

 served that about 400 tons probably was required to produce i ton dry in- 

 crease, equal to approximately 100 tons for each ton of the crop in the 

 green sappy state. In greater or less degree the same is true for the re- 

 quirements of weed plants, and so weeds, whether in the crop or on fallow, 

 rob the land of much moisture. As the making of a soil mulch, whether 

 on fallow land or by way of intertillage in growing crops, kills weeds at 

 the same time as it makes a mulch it has thus a double effect in conserv- 

 ing moisture. 



The particular importance of soil moisture conservation in Australian 

 farming arises in large part from the powerful evaporation which occurs 

 ■during the summer months. In some ways the conditions are special 

 and more exact information is required. With this object, experiments 

 are being conducted during the present season bearing on the relation of 

 soil moisture to the requirements of the plant, to the conditions for nitri- 

 fication in soils, and to different methods of bare fallowing and inter- 

 tillage. To the reporting of the results of the experiments designed 

 under those heads the present article will serve us as an introduction. 



