THE: SOIL AND WATER 147 



soil, by irrigation, by improving capillary conditions, by preven- 

 tion of loss, by decreasing transpiration, by drainage. In regions 

 where rainfall is deficient, especially during the crop season, it 

 may be necessary to store up the rain as much as possible. Sur- 

 face water may be conserved by plowing the soil before the rainy 

 season. Due regard should be paid to proper ditching, to prevent 

 washing. The subsoil may also be plowed and in arid regions (dry 

 land farming) it is packed after plowing so as to restore its capill- 

 ary spaces. In some dry regions a crop is grown only every alter- 

 nating year. The first year, the soil. is plowed, and the surface is 

 kept loose and porous so as to reduce the loss by evaporation; 

 the second year the crop is grown. 



The capillary condition of soils which are too loose and porous, 

 and also those too heavy and compact, is improved by incorporat- 

 ing vegetable matter with the soil. Capillary conditions may also 

 be improved by plowing of soil or subsoil when in suitable condi- 

 tion. 



Under-drainage, by aerating the soils, allows roots to go deeper, 

 and so places at their disposal a larger volume of soil containing 

 plant food and water. Since an excess of water keeps the soil 

 cold, drainage causes the land to warm up sooner in the spring. 



Losses of water by evaporation may be prevented by tillage. 

 Surface cultivation of the soil breaks up the capillary pores, and 

 prevents water rising to the surface. The following table of 

 King illustrates the effect : 



Water evaporated 



in 221 days. 



Inches 



Compact soil 7.98 



Stirred i inch 5.09 



Stirred 2 inches 4.20 



Stirred 3 inches 3.66 



Stirred 4 inches 3.60 



Compacting the soil by rolling increases evaporation, since it 

 increases the efficiency of the capillary pores. Rolling after plant- 

 ing grass seed is often advantageous, as it brings moisture to the 

 surface to sprout the seed. 



The destruction of weeds prevents loss by evaporation. In 



