526 Report of Experiments with different Manures 
nitrate of soda (Plot 6), the estimated return of nitrogen was 
37*7 per cent, and with the larger amount (Plot 7) only 29'9' 
per cent, taking the average of the five years of its use ; but 
over the last four years the figures show rather more recovered 
than when the first year is included. It is worthy of remark, that 
the proportion recovered with the larger amount of nitrate 
(Plot 7), is higher than with the corresponding amount of nitro- 
gen in the form of ammonia-salts (Plot 4). 
With the same amount of ammonia-salts as was applied to 
Plot 4 (400 lbs.), and the mixed mineral manure in addition 
(Plot 10), the increased yield of nitrogen estimated as attribut- 
able to that supplied was 46*5 per cent, reckoning over the 
seven, but only 43"4 per cent, over the last four years ; indicating, 
therefore, that, even under these comparatively favourable con- 
ditions, the proportion recovered is diminishing rather than 
increasing from year to year. It is to be borne in mind, however, 
not only that the silica so specially required by Graminaceous 
crops was not supplied in the mineral manure in question, but 
also that the amount of ammonia-salts annually used (400 lbs., 
containing about 82 lbs. nitrogen) was very large. It is remark- 
able, too, that although when used alone (Plot 4), the ammonia- 
salts gave a less return of nitrogen than nitrate of soda containing- 
an equal amount of it (Plot 7), yet, when used in conjunction 
with the mixed mineral manure, the proportion estimated as 
recovered was less with the nitrate (Plot 15) than with the 
ammonia-salts (Plot 10). However, when the smaller amount 
of nitrate of soda was used with the mineral manure (Plot 14), 
the nitrogen estimated as recovered amounted to about 62 per 
cent, of that supplied ; that is, to more than in any of the experi- 
ments where the larger amounts of nitrogen were supplied, 
which gave larger, though not proportionally larger, amounts 
of produce. 
When to the mixed mineral manure and ammonia-salts, saw- 
dust or cut wheat-straw (Plots 1] or 12) was added, and 'their 
nitrogen reckoned in the supply, the proportions estimated as 
recovered are less than when they are not employed. 
Where the double or very excessive amount of ammonia-salts 
was applied in the first, second, third, and seventh years 
(Plot via), the proportion of nitrogen recovered was exactly 
the same over the seven years (and even more over the last 
four) as where the less amount of ammonia-salts with the same 
mineral manures was used (Plot 10). The increase of gross 
produce or hay was, however, not in proportion either to the 
increased supply or increased yield of nitrogen ; the large yield 
of it being due to a very high — perhaps an objectionably high — 
percentage in the produce in the years in which the large amount 
