1910.] Conservation of the Fertility of the Soil. 121 



and even then not so much carbonaceous material would be 

 returned as is the case in the experiment, where it has been 

 necessary to cut up the roots and plough them in, but, on 

 the other hand, the manure made from the straw of both the 

 wheat and barley crops and from the clover hay would also 

 come back to the land. 



The evidence provided by this plot is strengthened by the 

 results obtained on the three other plots, on which the 

 recuperative operations of clover growing, and returning the 

 roots to the land, are either singly or together omitted ; under 

 such conditions the gross production is distinctly less, and 

 the fertility of the land is stationary or declining very slowly, 

 so that an equilibrium at a lower level of production has been 

 or will shortly be attained. 



We may then conclude from these Agdell Field results that 

 a conservative system of farming on the four-course system, 

 in which clover is grown at least once in every two rotations, 

 in which the roots are consumed on the land, and the dung 

 made by the straw and hay comes back to the land, will 

 maintain the fertility of the soil and support for an indefinite 

 period a gross production at about a 4 qr. of wheat 

 per acre level without any necessity for importing nitrogen. 

 The natural agencies of nitrogen fixation due to the growth 

 of the clover crop and the bacteria depending on the supply 

 of oxidisable carbonaceous matter returned to the soil are 

 capable of restoring sufficient nitrogen to the land to balance 

 such an output and to repair other unavoidable waste. 

 Of course, such a conclusion deals with nitrogen alone; it 

 assumes that the supply of phosphoric acid, potash, and 

 calcium carbonate is adequate, and, indeed, on much British 

 land the potash and calcium carbonate will be furnished by 

 the soil, while 4-5 cwt. of superphosphate per acre for the roots 

 will maintain or even increase the stock of phosphoric acid. 



The 4 qr. of wheat per acre level of production is, however, 

 a low one to aim at ; although it is the actual average pro- 

 duction of the country at the present time, it is below that 

 which a good farmer expects to-day, and must, indeed, attain 

 if he is to make a satisfactory profit on his land. But if the 

 general level of production is to be raised from the 4 qr. of 

 wheat to, say, the 5 qr. of wheat standard, then an external 



K 



