522 EEPORT — 1880. 



estimate is more probably too liigli than too low. And here it may be mentioned 

 in passing, that numerous determinations of tlie nitric acid in the drainage water 

 collected from land at Rothamsted, which had been many years umnanured, indicate 

 that there may be a considerable annual loss by the soil in that way ; indeed, pro- 

 bably sometimes mucli more than the amount estimated to be amiually available 

 from the measured aqueous deposits from the atmosphere. 



It should be observed, however, that the amount of combined nitrogen, especially 

 of ammonia, is very much greater in a given volume of the minor aqueous deposits 

 than it is in rain ; and there can be no doubt that there would be more deposited 

 within the pores of a given area of soil than on an equal area of the non-porous 

 even surface of a rain-gauge. How much, however, might thus be available beyond 

 that determined in the collected and measured aqueous deposits, the existing 

 evidence does not afford the means of estimating with any certainty. 



The next point to consider is — What is the amount of nitrogen annually 

 obtained over a given area, in different crops, when they are grown without any 

 supply of it in manure ? The field experiments at Rot hamsted supply important 

 data relating to this subject. 



Thus, over a period of 32 years (up to 1875 inclusive), wheat yielded an average 

 of 20-7 lbs. of nitrogen per acre per annum, without any manure ; but the annual 

 yield has declined from an average of more than 25 lbs. over the first 8, to less than 

 16 lbs. over the last 12, of those 32 j-ears ; and the yield (it is true with several 

 bad seasons), has been still less since. 



Over a period of 24 years, barley yielded 18'3 lbs. of nitrogen per acre per 

 annum, without any manure ; with a decline from 22 lbs. over the first 12, to only 

 14'6 lbs. over the next 12 years. 



"With neither wheat nor barley did a complex mineral manure at all materially 

 increase the yield of nitrogen in the crops. 



A succession of so-called 'root crops' — common turnips, Swedish turnips, and 

 sugar beet (with 3 years of barley intei'vening after the first 8 years) — yielded, 

 with a complex mineral manure, an average'' of 26'8 lbs. of nitrogen per acre per 

 annum over a period of 31 years. The yield declined from an average of 42 lbs. 

 over the first 8 years, to only 13-1 lbs. (in sugar beet) over the last 5 of the 31 years ; 

 but it has risen somewhat during the subsequent 4 years, with a change of crop to 

 mangolds. 



"With the leguminous crop, beans, there was obtained, over a period of 24 years, 

 31'3 lbs. of nitrogen per acre per annum without any manure, and 45"5 lbs. with a 

 complex mineral manure, including potass (but without nitrogen). Without 

 manure the yield declined from 48-1 lbs. over the first 12 years to only 14'6 lbs. 

 over the last 12; and with the complex mineral manure it declined from 61 '5 lbs. 

 over the first 12, to 29'o lbs. over the last 12, years of the 24. 



Again, an ordinary rotation of crops — of turnips, barlej', clover or beans, and 

 wheat — gave over a period of 28 years an average of 36'8 lbs. of nitrogen per acre 

 per anniun without any manure, and of 45"2 lbs. with superphosphate of lime alone, 

 applied once every four years, that is for the root crop. Both without manure, and 

 with superphosphate of lime alone, there was a considerable decline in the later courses. 



A very remarkable instance of nitrogen yield is the following — in which the 

 results obtained when barley succeeds barley, that is when one gramineous crop 

 succeeds another, are contrasted with those when a leguminous crop, clover, inter- 

 venes between the two cereal crops. Thus, after the growth of six grain crops in 

 succession by artificial manures alone, the field so treated was divided, and, in 1873, 

 •on one half barley, and on the other half clover, was grown. The barley yielded 

 37'3 lbs. of nitrogen ])er acre, but the three cuttings of clover yielded 151 '3 lbs. 

 In the next year, 1874, barley succeeded on both the barley and the clover portions 

 of the field. AVhere barley had previously been grown, and had yielded 37'3 lbs. 

 of nitrogen per acre, it now yielded 39'1 lbs. ; but where the clover had previously 

 been grown, and had yielded 151 "3 lbs. of nitrogen, the barley succeeding it gave 

 69'4 lbs., or 30'.3 lbs. more after the removal of l51'3 lbs. in clover, than after the 

 removal of only 37'3 lbs. in barley. 



Nor was this curious result in any way accidental. It is quite consistent with 



