SOIL MANAGEMENT. 31 



running water, maintained until the desired degree of 

 saturation has been reached. The alternate method is 

 to cover the surface with a sheet of standing water 

 until the soil has absorbed enough, when the balance 

 is drawn off; or, more simply, to place as much water 

 as is desired upon the land and allow this to be completely 

 absorbed. Flooding is used mostly for crops like the winter 

 cereals and lucerne. The preparation of the land for flooding 

 may be briefly described as follows : — When plougliing is com- 

 menced the entire fields are divided into lands about 10 to ]5 

 yards in width, so that after the ploughing and harrowing is 

 completed the land forms parallel ridges at the same distance 

 apart ; along these parallel ridges furrows are made by using 

 a double mouldboard plough, which throws the earth both ways 

 and thus forms distributing furrows. The ridge of earth on 

 either side of each furrow serves as a border, which prevents 

 the return to the furrow of the water after it has been thrown 

 out by damming. Too much care can hardly be exercised in 

 the preparation of the land by levelling and obtaining a desir- 

 able slope for crops like lucerne. Often where the land shows 

 a decided slope, a system of terracing may be found necessary, 

 the terraces, of course, following the contour of the ground. 

 In using the furrow method there is a danger of erosion. To 

 minimise this the furrows should closely follow the contour of 

 the ground. The furrows may be from two to five feet apart, 

 depending upon the crop and the soil. Difficulty is experienced 

 in obtaining an even distribution on account of variations in 

 the soil and the length of furrows. Where a furrow is unduly 

 long, the end nearest the supply receives generally considerably 

 more water than the further end. It is, however, a method 

 economical of water, giving a comparatively smaller evapora- 

 tion from the soil than flooding, because the w^hole of the sur- 

 face is not wet. In this connection it is w^orthy of note that a 

 wet soil surface loses water by evaporation more rapidly than 

 the same area of a free water surface. Furrow irrigation is the 

 only practicable method for inter-tilled crops like potatoes or 

 mangels. 



(e) The Kind of Crop Grown. — The duty of water or the 

 quantity of water needed to mature the crop will vary with the 

 different crops grown. " The absolute duty of water is the 

 total amount that the crop receives by irrigation, by rainfall, 

 and that contained in the soil. It is expressed as acre-inches. 

 The net duty of water is the amount actually delivered to the 



