CHOP EESIDUE3 87 



by drainage to a large extent. Eoot development will 

 also be prevented by excessive wet. After such a 

 winter the wheat crop generally is in a backward 

 condition, and finds itself in an impoverished soil. 

 A top dressing of nitrate in the spring is in such cases 

 of the greatest value. On the same land, after a dry 

 autumn and winter, no application of nitrate may be 

 required. In climates having a very severe winter 

 the nitrates are preserved from loss by the frozen 

 condition of the soil. In spring the melted snow is 

 removed mostly by surface drainage, the soil beneath 

 being still frozen ; the water produced by the snow 

 consequently does not remove the soluble matter of 

 the soil. 



Crop Residues.— The portion of the crop left in the 

 soil after harvest serves most important functions ; 

 on this residue (apart from actual applications of 

 organic manure) the maintenance of the humus, and 

 consequently of the nitrogen of the soil depends. The 

 quantity of residue left by different crops is very 

 different. From a crop of turnips, mangels, or 

 potatoes, practically no root residue remains in the 

 soil ; the residue, in the case of root crops is, in fact 

 limited to the leaves which may remain uneaten by 

 the stock. The residue of roots and stubble left by 

 an annual cereal crop is rather considerable, but poor 

 in nitrogen. The residues from deeply-rooted crops 

 which have long held possession of the soil, as sainfoin 

 and red clover, but especially lucerne, are very large, 

 amounting to many tons of dry matter, and contain- 

 ing 100 — 200 lbs., or even more, of nitrogen per acre. 

 In the case of permanent pasture, the effect of long- 



