THE DISTRIBUTION OF FERTILIZERS 203 



should be kept down by the frequent use of cleaning or 

 smother crops. Fertilizers suit weeds as well as economic 

 crops, and much of their fertilizing value may be lost unless 

 weeds can be removed either by cleaning or smothering. 



The Four-Course Rotation. The best known rotation 

 is the Norfolk four-course, introduced from Flanders in the 

 early part of the eighteenth century. The common four-course 

 rotation consists of turnips, barley, clover and wheat. Where 

 climatic and soil conditions interfere with the growth of 

 wheat, oats may take its place, or replace the barley crop, 

 where the soil is not in a sufficiently fine condition to give a 

 good barley plant. The four-course rotation receives for the 

 turnip or swede crop about 15 tons of farmyard manure per 

 acre, 5 cwt. of superphosphate and | cwt. of sulphate of 

 ammonia, with, on lighter soils, J cwt. muriate of potash in 

 addition. As all these manures require to be placed in drills, 

 there is no difficulty in using one of the compound manures 

 alluded to on p. 185. 



The second year's crop barley usually receives no 

 manure at all. In the barley is sown rye grass and clover, 

 or some similar mixture, which, after the barley has been 

 removed, receives dressings of about 2 cwt. superphosphate, 

 Jcwt. sulphate of ammonia and Jcwt. muriate of potash. 

 The sulphate of ammonia may be kept back until later and 

 divided between two top dressings, one in the early spring 

 and one later on before the hay ripens. It is distinctly 

 advantageous in this case to keep the sulphate of ammonia 

 distinct, because the farmer can then take the opportunity 

 of correcting for climatic conditions. Sulphate of ammonia, 

 like all other nitrogenous manures, stimulates feeble plants 

 whatever may be the cause of their unsatisfactory growth. 



The third year's crop clover ma}^ receive a small 

 dressing of about J cwt. of sulphate of ammonia, a part of 

 which may be kept back to be applied at a later period of 

 growth. Where the land is in poor condition, or the farm- 

 yard manure rather short in quantity, the amount of sulphate 

 of ammonia may be increased with advantage. In many 

 variations of this rotation, potatoes take the place of roots, 



