Irrigation. 15T 



the crust so soon as this silt has Ijecome dry enough to \y()rh. A'ou- 

 muddy, non-alkaline waters: ]3y these are meant fiesh waters, incliid- 

 ing- those that contain calcium carbonate and bicarbonate in solution. 

 These waters can be used on all soils without injury, provided they 

 are not applied in such quantities as to l)ring about secondary injurious 

 effects. No matter how " fresh " a water may be. it cannot be used 

 excessively without risk, as will be seen later. 



MetJiods of Applijinfj Water. — The two chief methods of apply- 

 ing water to the soil are (a) by flooding and (/>) by furrows, with 

 various modifications of these. In choosing the method to use in 

 applying water one should consider the soil, the quantity and quality 

 of the water, and of course the crop. In the case of a perennial forage 

 crop such as lucerne, the flooding method has most of the advantages, 

 for the crop shades the soil most of the time, thereby preventing 

 surface e\aporation. Then, again, the lucerne crop can stand very 

 severe cultivation without injury, so that deposits left by muddj- 

 waters on the land can be broken up. Cultivated crops such as 

 mealies, mangels, potatoes, sugar-beets, etc., could with advantage 

 be irrigated by the furrow method, for this method has the following 

 advantages: — Less water required: As a rule, less water will be 

 required to irrigate a certain area liy means of the furrow method. 

 The ideal principle in furrow irrigation is to apply a stream of just 

 sufficient strength to reach the end of the furrow without any over- 

 flow. Less 7cork once the land is furrowed: After the irrigation fur- 

 rows have been drawn (this can be done as a rule with a doubie-mould- 

 board plough), it is a simple matter to control the water distribution. 

 Less loss of water by evaporation : Since only about one-third of the 

 surface of the soil is actually wetted, it is obvious that the evaporation 

 must be less in the furrow method. Then, again, it is much easier to 

 establish a mulch over the wetted portion of the soil by cultivation 

 where furrows are used. Water penetrates wore readily into the sod : 

 We all know that if we wish water to enter readily into an empty tin 

 through a hole in the top, the Ciuickest way to accomplish this is to 

 punch a second hole in the top of the tin and to keep one hole above, 

 while the other is placed under the surface of the w'ater. The former 

 allows the air that is being replaced by water to escape readily. If 

 there were only one lioie, then the air escaping would have to bubble 

 up thrcmgh the water entering the tin. The same principle holds 

 when irrigating by the furrow method : the air being replaced passes 

 out through the ridge between the furrow. This means also that as 

 the water in the soil is used up by the plant roots atmospheric aii- 

 can readily enter to replace the water. In other words, furrow irriga- 

 tion facilitates the movement of air and water in the soil. This is a 

 very important consideration where, as in heavy soils, the supply of 

 oxygen in the soil often sets a limit to plant growth. Less danger 

 that hrak or alkali will accwmidate at the surface : Since furrow irri- 

 gation retards surface evaporation, there is less likelihood of an 

 accumulation of brak at the surface. Largely prevents formation of 

 crusts on surface : Some soils clod and cake badly after being irri- 

 gated. When only a small part of the surface is wetted as in furrow 

 irrigation this crusting is largely overcome. Better growth of crops : 

 On heavy soils, particularly, it will frequently be noticed that the 

 most vigorous plants are those grown on the edge of the bed. This 



