HORTICULTURE 121 



The first class is the least extensive of the three, the extent of 

 injury depending upon the value of the crops that may be grown on 

 the land when dry. The greatest danger of serious loss in this kind 

 of land is that alkali may accumulate in injurious quantities with 

 the lapse of time. In the irrigated region there is very little seepage 

 water which does not contain some alkali in solution, which tends to 

 accumulate to an injurious degree in saturated land. Inquiry into 

 the history of lands which have become badly affected with both al- 

 kali and water show that when injury first became noticeable such 

 lands could have been protected from further injury with as much 

 profit as attended the reclamation of lands affected by water only. 



It is to the second class that most of the lands belong which now 

 need drainage in the irrigated sections. Alkali accumulations usu- 

 ally follow accumulations of seepage water. If one admits that this 

 condition is a forerunner of total abandonment, surely no argument 

 is necessary to convince him that such lands belong to the class that 

 should be drained. Lands of the third class are principally those in 

 the virgin state, having enough alkali uniformly distributed through 

 the soil to a depth of 6 feet to cause crop failure after a few years of 

 irrigation, because of insufficient underdrainage. If irrigated 

 lightly, the alkali will in time become concentrated at the surface, 

 and if irrigated copiously, without underdrainage, water-logging will 

 follow. 



Alkali and Ground Water. The relation of alkali to drainage 

 is important and must be taken into account. In speaking of alka- 

 lies in his book on "Soils," Hilgard says: 



"They are the natural result of a light rainfall, insufficient to 

 leach out of the land the salts that always form in it by progressive 

 weathering of the rock powder, of which all soils largely consist." 



Ordinary alkali is made up of one or more of the following 

 salts in varying proportions: Sodium chloride (common salt), so- 

 dium sulphate (Glauber's salt), magnesium sulphate (Epsom salt), 

 calcium chloride, and calcium sulphate, all of which are white alka- 

 lis, and sodium carbonate (sal-soda), or black alkali. The latter is 

 so called on account of the dark stains on the ground caused by the 

 dissolution of the soil humus or vegetable matter. These salts and 

 also the mineral plant foods are readily soluble in water, so that in 

 the humid countries the constant leaching removes not only the in- 

 jurious salts but also part of the plant foods. This accounts for the 

 intrinsic fertility of the arid lands as compared with humid lands. 

 The account of the origin of alkali naturally suggests the control by 

 irrigation and underdrainage. 



Of the fundamental principles, those relating to ground water 

 and its movements are perhaps the most important. There is no 

 question that seepage is an actual accompaniment of all irrigation. 

 It has been found in all irrigated countries, doing damage and re- 

 quiring drainage. The sources of supply are leakage from canals, 

 surface applications, and precipitation. If the soil has the capacity 

 for discharging this water as fast as it is supplied no damage will be 



