64 RESULTS WITH BARLEY 



At Rothamsted there is very little evidence of any practical 

 effect being produced on subsequent crops from the unused 

 residue of a previous manuring with ammonia salts. 



We have seen that in the wheat field .at Rothamsted, 

 where at present- 100 Ibs of ammonia salts are applied in 

 autumn and 300 Ibs. in March, only about 40 per cent, of the 

 nitrogen of the ammonia appears, in an average season, in the 

 increase of crop obtained. What becomes of the remaining 60 

 per cent, we do not exactly know. What we know is that by 

 the month of June nitrates generally cease to be found in the 

 drainage waters from such plots as 6 and 7, where a full supply 

 of ash constituents is joined with the ammonia. On such 

 plots, but not on others, the nitrates have thus apparently 

 disappeared at this time from the upper two or three feet of 

 soil. In agreement with this fact we find that the following 

 wheat crop, if grown without nitrogenous manure, shows no 

 effect from any unused supply of nitrates remaining in the soil. 

 We must however bear in mind that the evidence of the 

 drainage waters is confined to those seasons in which the drains 

 run, that is to say, it is limited to seasons in which there is no 

 deficiency of rain. In seasons of drought, or on plots receiving 

 a deficient supply of ash constituents,, there must be some 

 residue of unused nitrate left in the soil at harvest. 



During forty years, an application of 400 Ibs. of ammonia 

 salts has alternated each year between plots 17 and 18 ; there 

 is thus every year a crop grown without any application of 

 ammonia, but with the residue remaining of the previous 

 year's manure at its disposal. The average of the forty crops 

 with ammonia salts has been 30-6 bushels, the average of the 

 forty crops following an application of ammonia has been 15-2 

 bushels. The average of forty crops on plot 5, which has 

 received no ammonia salts whatever in the whole period, is 

 15-0 bushels. No residue of the ammoniacal manure thus 

 remains to benefit the next season's crop. In only one 

 instance in Broadbalk field, where an immense dressing of 

 800 Ibs. of ammonia salts had been applied on plot 16, was 

 there a distinct effect produced on a subsequent unmanured 

 crop. 



