66 AGRICULTURE. [CH. 



monia, and if any other double silicate exists in the 

 soil naturally, or has been produced there by any 

 artificial means, such double silicate will, by exposure 

 to the air, take in from the atmosphere a valuable 

 store of ammonia ready for the next crop. 



129. The exposure of the soil by ploughing also 

 enables it to derive full advantage from the frosts 

 and rains of winter. We have in this way a break- 

 ing up of the soil going on through many months, and 

 much of the dormant matter of the soil is thus ren- 

 dered active, and available for vegetation. 



130. That which is accomplished by the plough is 

 also favoured and promoted by those lesser operations, 

 which assist in bringing the earth into a finer condition 

 for the growth of a crop. There are times when 

 stirring is preferable to the ploughing of the land. 

 When land has been ploughed up before winter, and 

 exposed to the winter's frosts, it is often better to keep 

 the fine earth thus obtained upon the surface, rather 

 than bury it. The use of a stirrer, whilst it moves the 

 land, and gives it the looseness desired for the roots, 

 does not bury the finely broken earth which is on the 

 surface, and which is most valuable as a seed-bed for 

 the next crop. 



131. When the surface of the land is not sufficiently 

 fine for a seed-bed, then we find the crushing of the 

 roller, and the gentle stirring of the harrow, 

 assist in breaking the lumps on the surface into a finer 

 condition. The fineness of the soil is a most 

 important point, when required as a seed-bed in which 

 seeds can make a successful growth. In a rough soil 

 a small seed will fall from one lump to another, until 

 it has got too deep in the soil to make proper growth, 

 and it therefore becomes necessary, by the use of 

 rollers, to crush the rough lumps in the soil to prevent 

 waste of seed. 



132. A fine condition of earth is also necessary 

 for a seed-bed in order that the early growth may 



