88 SOILS AND FERTILIZERS 



as to change the alkali from sodium carbonate to 

 sodium sulphate, a less destructive form, the reaction 

 being : 



Na CO + CaSO = CaCO + Na SO . 



2 3 ' 4 3 ' ? 4 



Many shrubs, as greesewood, and weeds, as Russian 

 thistle, take from the soil large amounts of alkaline 

 matter, and it is sometimes advisable to remove a 

 number of such crops so as to reduce the alkali. A 

 slightly beneficial effect is sometimes noticed on small 

 ' alkali ' spots where the ashes from straw are used, 

 forming potassium silicate. As a rule ashes are more 

 injurious than beneficial, on an ' alkali' soil. Irrigation 

 and thorough drainage, if continued long enough, will 

 effect a permanent cure. Irrigation without drainage 

 may cause a more alkaline condition by bringing to 

 the surface subsoil alkali. The waters from some 

 streams and wells are unsuited for irrigation on ac- 

 count of containing too much alkaline matter. Mildly 

 alkaline soils will usually repay in crop production all 

 the labor which is expended in making them pro- 

 ductive, and when brought under cultivation are fre- 

 quently very fertile soils. A small amount of alkaline 

 compounds in a soil is beneficial ; in fact, many soils 

 would be more productive if they contained more 

 alkaline matter. 



95. Improving Small Tracts of i Alkali ' Land. — 

 When the places are located so that they can be under- 

 drained at comparatively little expense, this should be 



