VII.] 



EFFECT OF CLOVER CROP 



137 



Thus we see that the clover crop not only produced 

 nearly 4 tons of hay, which was removed from the land, 

 but left behind residues which increased the next wheat 

 crop from 4 to 5 quarters, and even caused a large 

 increase in the barley crop which came two years later, 

 in spite of the fact that a considerable amount of nitro- 

 genous manure had been applied to the intermediate 

 crop of swede turnips. It is, in fact, possible by growing 

 clover once during the rotation, to maintain the soil at a 

 moderate level of fertility without bringing in any 

 external source of nitrogen such as purchased fertilisers 

 or feeding stufYs, notwithstanding the continual removal 

 of nitrogen from the farm in the corn and the meat that 

 are sold away. The following example from the same 

 Agdell field will illustrate the point : — 



On one of the plots, which receives phosphoric acid 

 and potash but no nitrogenous fertiliser, clover is 

 grown once in the four years' rotation, and the swede 

 turnip crop is chopped up and ploughed in, thus re- 

 turning to the land the fertilising materials contained 

 in the plant, in the same way as is done when the turnips 

 are fed off with sheep. The following table (XV.) shows 



Table XV.— Conservation of Soil Fertility during 

 Rotation when no Nitrogen is Supplied. (Rothamsted.) 



that the nitrogen in the soil is not experiencing any 

 measurable loss, while the crop returns indicate that a 



