The History of a Field newly laid down to Peimanent Grass. 17 
2,000,000 lbs. of soil, corresponding to 0-231' per cent, in the 
2,000,000 lbs., instead of 0-2414 per cent, on 1,908,978 lbs. as 
given in Table V. of the actual experimental results. 
It will be seen, therefore, that in endeavouring to estimate 
the loss or gain in the nitrogen of a surface-soil, under any- 
particular mode of treatment, we have to face a very complicated 
problem, and one which is not generally recognised. It is, 
however, essential to meet the difficulty, if we would arrive at 
anything like trustworthy conclusions. 
Adopting the plan of calculation above described, we have — 
reckoning in each case 2,000,000 lbs. of dry surface-soil per 
acre — estimates of the percentage of nitrogen, and of the actual 
amounts of it, in lbs. per acre, in 1856, when the land was 
arable; estimates for 1866, the time from which our records of 
manure and produce commence ; direct determinations in 1879, 
when the first samples were taken ; and direct determinations 
also for 1888, when the last samples were taken and analysed. 
The following Table shows the results so obtained, and also the 
estimated gain of nitrogen, per acre per annum, over individual 
periods, and the total period : — 
Table VI. — Nitrogen per Cent, in Surface-Soil (dry) ; also 
ACTUAL Quantities and Gain, in lbs. per Acre, at dif- 
ferent Periods. 
Nitrogen 
Dates 
Number 
o£ years 
Per cent, in 
Per acre 
total 
Gain 
surface- 
soil (dry) 
Per acre 
total 
Per acre 
per annum 
18S6 
1866 
1879 
1888 
10 
13 
10 
per cent. 
0-1520 
0-1749 
0-2046 
0-2345 
lbs. 
3,040 
3,497 
4,091 
4,690 
lbs. 
457 
594 
599 
lbs. 
} 45-7 
59-9 
33 
1,650 
50-0 
Taking into consideration both the treatment of the land as 
to manuring, and the amounts of crop grown, there can be no 
doubt that there would be greater accumulation of nitrogen 
within the surface-soil over the later than over the earlier years ; 
and it is seen that, according to the calculations, there was an 
estimated average gain of 45-7 lbs. per acre per annum over the 
period from 1856 to 1879, but of 59-9 lbs. per acre per annum 
over the last ten years. It is probable that the average gain 
was rather less per acre per annum over the first ten years, and 
VOL. 3tXV. — S. S. C 
