TEMPORARY PASTURES. 361 



renewing of permanent pastures is discussed in Chap- 

 ter XVI. (see page 392). The methods of renewing 

 these will also apply, in great part, at least^ to the re- 

 newal of temporary pastures. 



Influence- on Succeeding Orops. — Although the true 

 grass crops are not nitrogen gatherers in the sense in 

 which clover and other legumes are, yet it is important 

 that they shall be grown in rotation, in all or nearly 

 all instances, when tilling arable soils. Growing them 

 thus in the rotation is less necessary when clovers form 

 a part of the regular rotation, but even when clovers 

 are grown, it will usually be found advantageous to 

 grow grasses also. Among the benefits which result 

 from growing grasses in the rotation are the following: 

 1. They supply the land with humus. 2. They fur- 

 nish plant food in a more readily available form. 3. 

 They tend to check the growth and increase of weeds. 



It is not easy to over-estimate the value of a supply 

 of humus in the soil. It would probably be correct to 

 say that it is well nigh impossible to grow good crops 

 without keeping the land sufficiently supplied with 

 humus, or in other words, vegetable matter. Such mat- 

 ter in the soil promotes aeration in stiff soils and ren- 

 ders them more friable, increases the power of all soils 

 to hold moisture, aids in the chemical transformation 

 of inorganic substances in the soil and renders sub- 

 stantial service in preventing soils from being washed 

 away by an excess of water or from being lifted by the 

 winds. Some soils, more especially those composed of 

 fine clay particles or fine deposit when long cultivated 

 withoiit any replenishment of humus, become so im- 



