134 RELATIONS OF SOIL TO WATER 



nous crops for this purpose, as the soil is then enriched 

 with nitrogen from the atmosphere. Lupins are commonly 

 employed in Germany for the amelioration of sandy soil. 



The water-holding power of a sandy soil is increased by 

 keeping it consolidated ; the treading of sheep in winter time 

 is thus beneficial. In a light soil, crops should be planted as 

 early as possible, so that the fullest root development may be 

 attained before summer begins. As soon as the season for 

 evaporation commences the surface of the soil should receive 

 a shallow cultivation, and a layer of loose earth should be 

 maintained on the surface throughout the summer. In the 

 garden, mulching is a still more effective plan for preserving 

 soil water. The temporary increase of water at the surface 

 obtained by rolling the soil has been already mentioned. 



We turn now to the opposite case of a clay soil, exhibiting 

 an excessive tenacity, hindering both root development and 

 the production of tilth ; retaining an injurious amount of 

 water after rain, and drying in summer time into a hard mass. 

 We seek in this case to diminish the coherence of the soil, 

 to make it more friable and more permeable to water. With 

 very stiff clay soils it may be impossible to remedy the 

 evils which they present in an economical manner, in which 

 case the land is allowed to remain permanently in grass. 

 When in grass, the clay soil becomes of great value ; the 

 excessive supply of water near the surface is then an 

 advantage, while under the protection of a sod a fairly good 

 natural tilth is finally obtained. In the case of clay soils 

 of a less extreme character a very considerable amount of 

 improvement is practicable. 



Deep autumn ploughing, and exposure of the ridged surface 

 to winter frosts, is a method of first-class importance for 



