118 The Control oftlie Soil [pt, ii 



but there are many variants and many farmers indeed 

 have no fixed rotation but grow those crops that promise 

 to be profitable at the time. Among the crops introduced 

 in the rotation in the eastern counties are peas, sainfoin 

 and lucerne : elsewhere the number of crops varies and 

 there is taken one green or root crop to two grain crops. 

 It is not our business to discuss the rotations in detail 

 but only to consider their effects on the soil. The root 

 crop may be either swedes, kolil-rabi, cole, mangolds, 

 turnips or potatoes as convenience requires : in any case 

 its effect on the soil is to afford an opportunity for ex- 

 terminating weeds, and the frequency with which it is 

 taken is determined in part by this consideration. 



Now light soils are very prone to weeds, in particular 

 to charlock {Brassica sinajns). Heavy soils suffer less, 

 but still are liable to docks, thistles, etc. Charlock can 

 be kept down by spraying^, the others cannot. Some- 

 times the land will keep clean for four and sometimes 

 for five years : in that case two corn crops can be taken 

 in succession and a winter oat crop inserted between the 

 wheat and the roots: or the clover may be replaced by 

 a mixture of clovers and grasses which can be left for a 

 period of years. Again, the root crop may be eaten in 

 the field by sheep wherever the soil is not too wet, and 

 the soil then receives not only the fertilising constituents 

 derived from the crop but also those derived from the 

 added feeding stuffs. This furnishes an extremely useful 

 method of fertilising the soil for the next crop : it reduces 

 the losses of manure to a minimum (see p. 170), it saves 

 cartage of manure, and it enables rapidly grown catch 

 crops to furnish their quota to the organic matter of the 



^ A 3 per cent, solution of copper sulphate sprayed in early spring at the 

 rate of 50 gallons per acre 



