20 Journal of the Department of Agriculture. 



drainag-e will gradually raise the water-table, rendering any deep- 

 rooted crop that may be in occupation of the soil unthrifty, and 

 accumulating- the bralc of the soil nearer and nearer to the surface 

 will finally render the soil unfit for any agricultural purpose. The 

 deeper the soil the longer this evil will be developing, provided the 

 same amount of water is applied to the shallow as to tlie deep soil. 

 If the soil, however, is deep enough it is possible to irrigate it success- 

 fully, even if very brak, provided one has a good water and the 

 lequisite skill. The basis of the method of handling the water under 

 these circumstances is by a first heavy Avatering to drive tlie brak deep 

 down so as to leave several feet, if possible, of dry soil between the 

 ground water and the depth to which the irrigation water has 

 penetrated. Subsequent waterings should be sufficient in quantity 

 to meet the needs of the crop, but no more. It will usually happen 

 that after a few years the brak which had been driven down has com- 

 menced to rise again ; it is again driven down by a heavy watering. 



(c) The Soil is Not Permeable hut the Drainage is Good. 



This is a condition that not only occurs naturally, but is also 

 created as a result of irrigation. It is evident that the good drainage 

 cannot be made use of until the soil has been rendered permeable. A 

 special instance of tlie kind is the occurrence of hard pan at a less or 

 greater distance beloAv the surface. The worst type of hard pan is 

 that due to the cementing action of sodium carbonate. Such a pan is 

 almost entirely impervious to water, unless this latter contain consti- 

 tuents such as gypsum, which are able to destroy sodium carbonate. 

 It cannot be too strongly emphasized tliat tlie irrigation of an imper- 

 meable soil is a very hazardous undertaking. 



(d) Tlie Soil is ] mpeniieahle and tlie Drainayc is Bad. 



It would be difficult to imagine a more adverse condition of the 

 soil. Usually such land is impossible of utilization. 



Having outlined the more important types of soil conditions and 

 the principles underlying the treatment they should receive, I now 

 proceed to a few happenings that are common in irrigation practice. 



The Appearance of Beak after Irrigation. 



Let us suppose that we have a paraffin tin full of soil, and 

 further, that we make the soil thoroughly wet by pouring water on 

 the top of it. If, now, we place this tin in the sun the soil will 

 sooner of later dry out. The soil loses the water added to it by the 

 l)rocess known as evaporation. The water at the surface is lost first, 

 and as it is lost more rises from below to take its place, so that finally 

 there is none remaining in the tin. The last water to be lost is 

 naturally that which penetrated deepest. 



Now, let it be supposed that in filling- the tin we mixed some salt 

 in with the lower soil. The water which penetrates down to the lower 

 soil will dissolve the salt, and finally will carry it towards the surface, 

 where the water will evaporate and, since it cannot take the salt with 

 it into the air, leave the salt behind. Thus by watering soil which 

 contained salt in its lower layers we have brought the salt from the 

 lower layers to the top layers. Something of the same kind occurs 



