780 



EOTHAMSTED EXPERIMENTAL STATION. 



[Dec, 



sufficient amounts of these were added. It is now known that 

 the full action of artificial manures is exerted oniy when the 

 conditions are satisfactory for the growth of plants. Organic 

 matter as supplied by farmyard manure improves the condi- 

 tions for the root crops, facilitating the production of tilth and 

 increasing the water-holding capacity of the soil. It also 

 improves the growth of clover. At Eothamsted recently it 

 has been shown that farmyard manure causes less variation in 

 yield from year to year than does artificial manure; further its 

 use involves less risk of deterioration of soil when the course 

 of cropping is abnormal. In the Broadbalk wheat field many 

 of the plots have received a manurial treatment deliberately 

 deficient in one or more essential constituents; in all the con- 

 tinuous growth of wheat may be regarded as abnormal cropping. 

 In consequence soil exhaustion iD most plots is manifested by 

 a progressive diminution of the yield; the actual diminution is, 

 of course, irregular owing to the varying seasons, but from a 

 long series, such as that furnished by the Broadbalk experiment, 

 comparable figures may be obtained representing the mean 

 value by which the yield, in bushels per acre, decreases in each 

 year; these figures measure the mean annual diminution. This 

 result is set out in Table I, where the results of continuous 

 wheat growing are given. See also Fig. 1. 



Table J. — Comparison of Farmyard with Artificial Manures 

 (R. A. Fisher). Broadbalk Field. Continuous Wheat. 







Ave rase 



*lean annual 



Percentage of 



Plot No. 



Treatment. 



yield, bush. 



diminution. 



relative vari- 



per acr \ 



bush, per 



ance a se ridable 







1852-1920: 



acre. 



to weath'T. 



2b 



Farmyard manure, 14 tons 

 annually 



31-549 



031 



2-78 



3 and 4 



NTo manure 



12-2*9 



■097 



6-20 





Complete mineral manu: e 



1 4 * 1 80 - 



•09! i 



5-84 



G 



As 5 -f single Ammonium 



22-581 



141 



6 01 • 





salts 







5-11 



7 



As 5 + double Ammonium 



31 -367 



,., 





salts 







4-18 



8 



As 5 -I- treble Ammonium 



35-694 



•092 





salts 









10 



Double Ammonium salts 



19-501 



•157 



11-iO 





alone 







10-32 



11 



As 10 4- superphosphate 



22-046 



•219 

 •181 



12 



As 10 + Super + Sulph. 



Soda 



28-319 



7-28 



13 



As 10 + Super 4- Sulph. 



30-209 



•123 



5*55 





Potash 







6*3S 



14 



As 10 -f Super -f Snlph. 



27-765 



•231 





! Magnesia 







I 



10-16 



17 ) alter- 



, Minerals alone, or double 



14-510 



092 



18 f nate 



ammonium salts alone 



29 006 



•114 



4*55 



in alternate rears - 









