for Twenty Years in succession on the same Land. 3 1 3 
mineral constituents of the soil were insufficient for its full 
effect ; but when so supplied, the mineral manures, which alone 
had little effect, greatly increased the efficacy of the supplied 
nitrogen, 
The general result is, that whilst it is essential that there be a 
liberal provision of mineral constituents, the amount of produce 
was more dependent on the supply of available nitrogen within 
the soil than of any other constituent. The practical questions 
obviously arise — How much ammonia, or of its equivalent of 
nitrogen in some other form, will, on the average, be required to 
yield a given amount of increase of barley-grain, and its average 
proportion of straw ? and how much will the quantity vary, 
according to the amount applied per acre, to the supply of 
mineral constituents, and to the characters of the seasons ? 
The folding Table XXXIX. (facing this page) shows the 
amount of ammonia — or of nitrogen in nitrate of soda, or rape- 
cake, or farmyard manure, reckoned as ammonia — required to 
yield 1 bushel (52 lbs.) of increase of barley-grain, and its pro- 
portion of straw, under a great variety of conditions of manuring, 
and in each of the 20 seasons. In each case the increase is calcu- 
lated over the produce on the corresponding plot without nitro- 
genous manure ; that is, 1 A, 1 AA, 1 AAS, 1 C, over 1 O ; 
2 A, &c., over 2 O ; and so on; 1 N, and 2 N (with nitrate of 
soda), and 7 (with farmyard manure), are taken over the mean 
unmanured produce (1 O and 6-1). The average result for 
different periods, or series of years, is also given. Where there 
has been no change of manure, the averages are, as a rule, calcu- 
lated for the first half, the second half, and the total period ; and 
where there has been any change, for the periods so indicated ; 
also, for the sake of comparison, for corresponding periods in 
other cases. 
The five plots receiving 200 lbs. of ammonia-salts per acre 
per annum for 20 years are classed in the Table as Series I. 
Of these. Plot 1 A has had the ammonia-salts without any 
mineral manure ; 2 A with superphosphate ; 3 A with sul- 
phates of potass, soda, and magnesia : 4 A with superphosphate 
and sulphates of potass, soda, and magnesia ; and 5 A with 
superphosphate and sulphate of potass. Taking the average for 
the 20 years in each case, the quantity of ammonia required to 
produce 1 bushel increase of barley, and its proportion of straw, 
is, on the three plots with superphosphate 213, 2'41, and 2 l01bs.; 
on the plot with salts of potass, soda, and magnesia, without 
supr sphate, 3*59 lbs. ; and on the one without any mineral 
manure at all 3 68 lbs. 
Thus, taking the mean of the three experiments with super- 
phosphate, the amount of ammonia required is rather under 2^ lbs.; 
