66 RESULTS WITH BARLEY 



and a much greater residue at Woburn than at Rothamsted. 

 Can we explain these facts ? 



The far greater unused residue remaining in the soil after 

 the growth of a crop with ammonia salts at Woburn than appears 

 in the Rothamsted experiments is surely connected with the 

 much later date at which the ammonia is applied at Woburn, 

 and with the poverty of the Woburn soil in lime. Both of 

 these facts must tend greatly to retard the completion of 

 nitrification, and the subsequent distribution of the nitrates. 

 As wheat and barley do not apparently assimilate nitrogenous 

 food after flowering is completed, any nitrates formed after 

 this stage of growth would remain unused in the soil, and if not 

 subsequently lost, be available for the nourishment of the 

 succeeding crop. It will be recollected that the ammonia salts 

 are applied to the wheat at Rothamsted in March, but at 

 Woburn at the end of April or beginning of May. The ammonia 

 salts at Rothamsted are ploughed into the barley land at the 

 end of February, or commencement of March ; at Woburn they 

 are usually top-dressed in the middle of May. There is thus 

 apparently a good reason why a greater unused residue should 

 occur in the Woburn experiments. 



We have to account, however, not only for the occurrence 

 of a residue, but also for its preservation through the winter at 

 Woburn, and not at Rothamsted. The different character 

 and circumstances of the soils seems to explain this. At 

 Rothamsted the natural drainage provided by the chalk sub- 

 soil, aided in Broadbalk field by drain pipes, must greatly tend 

 to prevent any nitrates washed through the soil by autumn or 

 winter rains from returning to the surface so as to be of use to 

 the next crop. In the deep fine sand at Woburn the nitrates 

 may sink without being lost, and a rise in the water level of 

 the sub-soil, or capillary action, may bring them again within 

 the reach of the next crop. 



The greater residue from ammonia salts than from nitrate 

 of soda will be also due to the facts already mentioned. The 

 nitrate of soda is ready for immediate consumption as soon as 

 it reaches the soil. The ammonia salt must be nitrified, and 

 the nitrates distributed, before its nitrogen can be largely taken 



