60 



EXPERIMENTS UPON WHEAT 



phosphoric acid comes into play prematurely and stops 

 development at a very early date, since it is acting in the 

 same direction as the heat and dry ness of the season. 



The indication of the 1879 and 1903 returns, that the 

 superiority of nitrate of soda over ammonium-salts is more 

 marked in a wet than in a dry season, is confirmed by a further 

 examination of the records over a series of years. Taking 

 the thirty years 1873-1902 and dividing them into two groups 

 according as the rainfall is above or below the average, and 

 then comparing the yields of the two plots, which receive equal 

 amounts of nitrogen, but one as nitrate of soda and the other 

 as ammonium- salts, we find that in the dry seasons the yield 

 from ammonium-salts is 86'6 per cent, of the yield from 

 nitrate of soda. In the group of wet seasons, however, the 

 yield from ammonium-salts is only 78 '8 per cent, of that given 

 by nitrate of soda, as shown in Table XXII. Thus the wet 

 seasons are on the whole more favourable to nitrate of soda 

 than to ammonium -salts. Presumably in the very wet and 

 cold seasons the conditions are unfavourable to the nitrifica- 

 tion of the ammonium- salts, and the immediately available 

 nitrate of soda is more effective. 



TABLE XXII. Broadbalk Wheat. Comparison of the yield of Dressed 

 Grain with Nitrogen as Ammonium-salts or Nitrate of Soda, in seasons 

 when the Rainfall was below or above the average, 30 years (1873-1902.) 



One of the most critical periods in determining the yield of 

 wheat appears to be the winter months ; if the wheat be sown 

 in October or early November Jt spends the next three or four 



