VII.] 



SLOW AVAILABILITY OF MANURE 



215 



mangold crops for the years 1900 and 1907, when crops 

 considerably above the average were grown, and com- 

 pare the yields obtained when farmyard manure was 

 used alone, with that given by a purely artificial dressing 

 containing nitrate of soda and by farmyard manure 

 supplemented by nitrate of soda : — 



Table LXVII.— Yield of Mangolds at Rothamsted, 1900 and 1907. 

 Roots only. 



The farmyard manure, though it contains about 200 

 lb. of nitrogen, cannot provide the rapidly growing 

 mangolds with as much nitrogen as does the nitrate of 

 soda containing 86 lb. of nitrogen, since it only grew 

 27-2 tons of mangolds against 33 tons with nitrate of 

 soda, and this notwithstanding the great accumulation 

 in the soil of the residues of thirty years' previous 

 manuring with dung. That only the nitrogen was 

 concerned in these differences is seen from the fact 

 that both the plots received the same phosphoric acid 

 and potasK The crop had by no means reached its 

 limit, for an addition of nitrate of soda to the dung 

 increased the crop to 41-4 tons ; and here, again, only the 

 nitrogen is concerned, because, on a further plot where 

 phosphoric acid and potash were added to the combina- 

 tion of dung and nitrate of soda, there was but a very 

 slight additional increase of crop. 



From other experiments it has been repeatedly 



