356 Report of Experiments on the Growth oj Barley, 
used, was due to any action that they might have in increasing 
the available supply of mineral constituents within the soil, or that 
the effects of the residue of rape-cake were attributable to the 
mineral constituents it supplied. There can, indeed, be no 
doubt that, in all three experiments, the increased produce of 
barley was due to an increased supply of available nitrogen 
within the soil where it had been applied in the manures for the 
turnips. Still, in neither case is there as much produce of barley 
as without manure in the other (Hoos) field, where the barley was 
grown after several previous corn-crops. 
But experiments 5 and 6 afford conclusive evidence that it 
was of available nitrogen for the barley that the soil had become 
so exhausted by the growth of 10 successive crops of turnips. 
Thus, in the second year of barley, 1854, those portions of the 
mineral-manured turnip-plots which were left without further 
mranure (experiment 1) gave 19^ bushels of corn, and 12i cwts. 
of straw, per acre ; whilst a portion to which ammonia-salts, at the 
rate of 400 lbs. per acre, were applied (experiment 5), gave 52^ 
bushels of corn, and 39^ cwts. of straw ; and where 550 lbs. nitrate 
of soda, containing about the same quantity of nitrogen as the 
ammonia-salts, was applied (experiment 6), there were obtained 
54^ bushels of corn, and 42^ cwts. of straw. In fact, by the simple 
addition of ammonia-salts or nitrate of soda, from 3 to 3J times 
as much total produce (corn and straw together) was grown. 
Though not shown in the Table, it may be mentioned as 
remarkable, that although the produce without manure was very 
different in the two fields, that obtained when a given amount of 
nitrogen in the form of ammonia-salts or nitrate of soda was 
applied was very nearly identical in the different fields. The 
conclusion is that, in both, the mineral constituents, though 
abundant, were unavailing in the absence of a sufficiency of 
available nitrogen, but that when this was superadded, the 
amount of growth and produce was dependent on the amount of 
its supply, and the characters of the season. 
Lastly, in the third year of barley after turnips (1855), the 
Plot 5, which had received ammonia-salts in the previous year, 
gave about 6J bushels more corn, and 2j cwts. more straw, than 
the exclusively mineral-manured plots ; and Plot 6, which again 
received nitrate of soda, but only in small quantity (112 lbs. per 
acre), gave more than twice as much of both corn and straw as 
the purely mineral-manured plots. 
There is still evidence of another kind, which may be cited as 
showing that it was of available nitrogen that the turnips had 
rendered the soil so deficient for the after-growth of barley. It may 
be assumed that, on the average, between 25 and 30 lbs. of nitrogen 
would be annually removed from the Rothainsted soil by wheat 
