.VI Agricultural Chemistry. 



The evaporation from a saturated soil is greater than from a 

 water surface and as the soil drys the rate of evaporation rapidly 

 diminishes. The average annual evaporation from a bare loam 

 at Madison, Wisconsin, is about fifteen inches. "While soils of 

 various character evaporate equal amounts while saturated, 

 they exhibit great differences as drying proceeds. A soil of 

 coarse particles and loose texture dries quickest and to the 

 greatest depth. Consequently it appears to be good practice 

 to avoid deep tillage in early summer, if land is intended to carry 

 a crop. 



Evaporation from the soil is diminished by protection from 

 sun and wind. Economy of water is best effected by mulching 

 with straw. Keeping the surface stirred to a depth of an inch 

 or two, thus providing a mulching of loose dry soil, is an excel- 

 lent practice and forms a fundamental part of successful culti- 

 vation in dry climates. 



The greatest evaporation of water takes place from the soil 

 when it grows a crop. The water in a soil growing barley and 

 in an adjacent bare fallow was determined at Rothamsted, Eng- 

 land, at the end of June during the drought of 1870. It was 

 found that down to 54 inches below the surface the barley soil 

 contained 9 inches less water than the fallow soil. The injurious 

 effect of weeds in the summer time is largely due to their robbing 

 the soil of water. 



With dry soils the farmer should aim to increase the amount 

 of humus. Crops should be sown early and the land kept solid ; 

 very shallow summer cultivation should be resorted to. Such 

 land may possess distinct advantages. It furnishes the earliest 

 crops to market gardeners, the soil being easily wanned. A little 

 rain will wet it to a considerable depth and the whole of the 

 water it contains is available to plants. 



A soil, when drained, is seldom too wet because of its power to 

 retain water. The trouble is more often due to want of drain- 

 age ; the remedy for such a soil is deep tillage and draining. Ap- 

 plications of lime or an increase in the humus content may bo 



