TEMPORARY PASTURES. 363 



from lifting after they have been ploughed up is, in 

 some instances, felt for at least three years. 



While the grasses proper do not, like clovers, add 

 in the same way to plant food in the soil, they do add 

 materially to the supply of available plant food. Dur- 

 ing the processes of growth they search out and take 

 up plant food from the soil and subsoil, a part of which 

 is retained in the roots broken up and in the stubbles 

 that are buried. These, in their decay, furnish such 

 food for the crops that follow them in a form that is 

 easily accessible. The grass crops, in a sense, act the 

 part of scavengers in the soil for the crops that come 

 after them. Sir J. B. Lawes has estimated that when 

 grass lands are broken 5 to 10 tons of dry matter, roots, 

 leaves and stubbles are deposited in one acre by the grass 

 crop. 



Grass crops check the growth of weeds in the soil in 

 various ways. In some instances they crowd them out, 

 as in the case of bliie grass; in some, as when mowed 

 and properly pastured, they prevent them from seed- 

 ing; and in others, as when they are broken for a few 

 years, they cause the seeds of many weeds to perish 

 that are lying in the soils. Pastures and meadows of 

 any lengthened duration render most effective service 

 in this way, as is evidenced by their comparative clean- 

 liness when first broken up. 



So beneficent are the influences from introducing 

 grass crops frequently into the rotation, that it is 

 probably correct to say that the instimces are few in 

 which successful crop husbandry can be long conducted 

 in their absence. Due attention to this question would 

 Grasses — 24. 



