for Twenty Years in succession on the same Land. 315 
to ammonia, was proportionally hi<iher over the last ten years, 
than was the increase in the actual produce of corn per acre. 
Further, the actual produce of straw per acre was uniformly, and 
that of the total produce (corn and straw), taking the average of 
the plots, rather lower, over the last ten years. That the total 
produce was lower rather than higher over the later years, 
seems to afford evidence that, with this smaller dressing of 
ammonia-salts, there was little or no effect in succeeding, from 
accumulation in preceding years. 
When, as in Series II., double the quantity,or 400 lbs. ammonia- 
salts, was aj)plied per acre per annum for the first six years, the 
average amount of ammonia required to yield 1 bushel of in- 
crease was, according to the same mode of calculation, without 
mineral manure, 4*81 lbs. ; with superphosphate, 5'06 lbs. ; with 
mixed alkali-salts 6"38 lbs. ; and with superphosphate and mixed 
alkali-salts, 5*86 lbs. Thus, the amount required appears to be less 
without, than with either of the mineral manures, less with super- 
phosphate than with superphosphate and mixed alkali-salts, and 
less with the latter than with mixed alkali-salts without super- 
phosphate. The apparently more favourable result without than 
with mineral manure, is explained by the fact, that the increase 
by ammonia-salts is, in each case, calculated over the produce by 
the corresponding unmanured or mineral-manured produce, as the 
case may be ; and as the produce by mineral manures, especially 
if containing phosphates, was so much higher than that without 
manure, there is so much more to deduct from the produce 
with ammonia-salts in addition ; and hence, though the produce 
by the ammonia-salts with mineral manure is much higher, the 
increase so reckoned as due to the ammonia only is less. 
During the next ten years, the quantity of ammonia-salts was 
reduced from 400 lbs. to 200 lbs. ; and during the last four years 
the ammonia-salts were replaced by 275 lbs. of nitrate of soda, 
estimated to contain the same amount of nitrogen as 200 lbs. 
ammonia-salts, namely 41 lbs. = 50 lbs. ammonia. Over both 
of these periods the result is much more favourable with each of 
the four conditions as to mineral manure than during the first 
six years, and also relatively much more so where the super- 
phosphate was employed. This depends in part on the fact 
that, whilst the produce without manure or by the mineral 
manures alone, which is the standard over which the increase by 
ammonia is calculated, declined perceptibly from year to year, 
that where ammonia was used either did not decline at all, or 
did so much less rapidly ; and hence the increase calculated as 
due to the ammonia (or nitrogen reckoned as ammonia) is 
higher. 
In reference to these results it should further be observed, that 
