80 



THE EOTHAMSTED EXPERIMENTS. 



Nitrogen 

 rapidly 

 and slowly 

 available. 



Potash 



Potash of 

 the soil. 



General 

 results with 

 artificial 

 manures. 



Superphos- 

 phate for 

 spring- 

 sown crops. 



when it was so applied in addition, there was more effect 

 with the nitrate, with its more rapidly available nitrogen, 

 than with the rape-cake with its greater actual amount of 

 nitrogen, but in a less rapidly available condition. 



Comparing the produce of plot 2 with superphosphate with- 

 out potash, with that of plot 4 with superphosphate and 

 potassium, sodium, and magnesium sulphates in addition, it is 

 remarkable that, both in Series 2 with the ammonium-salts, 

 and in Series 3 with nitrate of soda, there is, over the whole 

 period of forty years, almost identically the same amount of 

 barley grain without as with the potash. There is, however, 

 rather more straw, and total produce, with than without the 

 potash. Thus we have, with the ammonium-salts an average 

 of 42f bushels without potash, and 43| bushels with potash ; 

 and with the nitrate of soda 45f bushels without, and 45| 

 bushels with potash. Of straw, however, there is with the 

 ammonium-salts an average of 2674 lb. without, and 2904 lb. 

 with the potash ; and on the nitrate plots 3018 lb. without, 

 and 3186 lb. with potash. 



It will afterwards be seen that where nitrogen and phos- 

 phoric acid were liberally supplied without potash, the avail- 

 able potash of the soil itself became deficient ; though this 

 deficiency was to the last comparatively little manifested in 

 the produce of grain. It is obvious, however, that with 

 gradual reduction in the amount of total plant, the yield of 

 grain must also in time materially diminish. 



So much for the influence on the barley crop of different 

 conditions of manuring, each continued for more than forty 

 years, on the same plot, and in a field of somewhat heavy 

 loam, with a raw clay subsoil, and chalk below giving good 

 natural drainage. 



It is seen that nitrogenous manures alone had much more 

 effect than mineral manures alone. It was obvious, therefore, 

 that the exhaustion induced by the continuous growth of the 

 crop was characteristically that of nitrogen. 



Both with and without nitrogenous supply, phosphates 

 were more effective than potash salts, showing that the avail- 

 able store of phosphoric acid in the soil became deficient 

 sooner than that of potash. With the shorter period of growth 

 of barley than of wheat, and its greater proportion of surface- 

 rooting, both nitrogenous and mineral exhaustion are sooner 

 developed ; and so far as mineral exhaustion is concerned, 

 the available supply of phosphoric acid was sooner exhausted 

 than was that of potash. Indeed, in ordinary agricultural 

 practice, it is clearly established that superphosphate is more 

 effective with the spring-sown than with the autumn-sown 

 cereals. 



