MANURE 507 do not possess the power of taking up by their leaves and of assimilating the free nitrogen of the air. This conclusion has been verified by the extensive researches of Messrs Lawes, Gilbert, and Pugh. The nitrogen contained as nitric acid and ammonia in the air, and descending upon the land in the shape of rain, dew, or snow, though, without doubt, adding to the supply of nitrogen in the soil, is altogether insufficient to meet the requirements of re munerative crops. The experiments of Messrs Lawes and Gilbert and Professor Way show that the average proportion of nitrogen deposited annually upon one acre of land at Roth -misted, St Albany amounts to 7 21 lb, of which quan tity G 46 lb occur as ammonia and 75 lb as nitric acid. The further investigations of Dr Voelcker, Professor Frankland, and Messrs Lawes and Gilbert upon the drainage water from cultivated soils show that a consider able quantity of nitrogen in the shape of nitric acid passes into land drainage, and that this loss of nitrogen is much greater than the total amount supplied to the land by the rain and dew. The results which Messrs Lawes and Gilbert obtained in their experiments on the continuous growth of barley at Rothamsted from 1852 to 1875 afford, as is shown in the following table (I.), direct evidence of the insufficiency of the atmospheric supply of nitrogen, and of that present in the soil in the form of nitrogenous organic matter. TABLK I. Messrs Lawes and Gilberts Experiments on the Growth of Wheat and Barley, year after year on the same Land, without Manure, and with different kinds of Manure. Manures per Acre per Annum. Produce per Acre (Average per Annum). Dressed Corn. Total Straw. Quantity. Weight per Bushel. 12 Years 1852-63. 12 Years 18G4-75. 24 Years 12 Years 1852-75. 1852-63. 12 Years 24 Years 1864-75.1852-75. 12 Years 12 Years 24 Years 1862-63. 1864-75 1852-75. Wheat, t 1. Unmanured continuously bush. 15J | 181 } 22| I 38 35f 211 j- 301 271 341 39J } 4 ri I 60ft 46f bush. 12f 131 21J 37 35 16} 21| 20| 29 321 44 46f 50f bush. 14 i ii 211 37J 35J 18} 251 241 3l| 36 45J 48J 48J ft 56J 65} 57f 591 511 . 52J 62J 51 i 51 52 51 J 53J ft 59 59J 58 60J 60f 53J 541 64| 53| 65J 55 55i ft 57| 68} 561 59 60 M 53 53* n 541 53| 54| cwts. 14} 161 231 421 34| 12} 151 1-11 19ft 2^1 291 34| 271 cwts. 9| U? 181 401 32J 9J 10j 10i 15} cwts. 12| 14J 201 411 88| 11 13| 12| 17J 21J 27 J BU 28i 2. Mineral manures alone (200 lb sulphate of potash, 100 ft sulphate of soda, 100 lb sulphate of magnesia, and 3 cwts. of superphosphate made from 200 lb bone ash, 150 lb sulphuric acid of 1-7 specific gravity, and water) ... 3. Ammonia salts alone for 1845, and each year since ; mineral manure in 1844 (equal parts of sulphate and muriate of ammonia of commerce) 4. Ammonia salts and minerals. (The same minerals as in No. 2, and GOO lb 5. F.irmyard manure (14 tons every year) Barley* 1. Unmanured continuously 2. Mineral manure alone (200 lb sulphate of potash, 100 lb sulphate of sodr, 100 lb sulphate of magnesia, and 3j cwts. of superphosphates) 3. Superphosphate alone (">k cwts.) 4. Ammonia salts alone (200 lb) 5. Nitrate of soda (275 lb) C. Ammonia salts and minerals. (The same minerals as in No. 2, and 200 ft ammonia salts.) 26 J 28 29j 7. Nitrate of soda and minerals. (The same minerals as in No. 2, and 275 lb nitrate of soda.) 8. Farmvard manure (14 tons every year) Tho Tlothamsted soil is a moderately stiff one, of con siderable depth, and contains naturally the mineral elements of plant food in abundance ; thus it has been possible to grow corn crops for over twenty-five years without any m inure (Plots 1). The crops in the second period of twelve years were, however, less than those of the first period, and in neithar case were full crops obtained. While the application of mineral manures alone (Plots 2) produced only a slight increase in the case of the wheat, and rather better, though poor, results with barley, nitrogenous manures, applied to the land either in the shape of ammonia salts or nitrate of soda, produced a strikingly hrge increase. The experiments further show that while good crops, both of wheat and barley, can be grown by the annual application of 14 tons of farmyard manure per acre, the best results are obtained by the use of a mix ture of mineral and nitrogenous manures. In Messrs Liwes and Gilbert s experiments the amount of nitrogen removed in different crops was determined with the following results : over a period of thirty-two years (to 1875), wheat yielded an averageof 20 7 ft) of nitrogen per acre 1 Previous cropping : 1839, turnips with farmyard manure ; 1840, barley; 1841, pease; 1842, wheat; 1843, oats; the last four crops unmannred. First experimental wheat crop in 1844. Wheat every year since ; and, with some exceptions, nearly the same description of manure on the same plots each year especially during the last twenty-six years (1852 and since). Unless otherwise stated, the manures are sown in the autumn before the seed. Area under ex periment about 13 acres. 2 Previous cropping : 1847, Swedish turnips with dung and super phosphate of lime, the roots carted off; 1848, barley; 1849, clover; 1850, wheat; 1851, barley manured with ammonia salts. First ex perimental crop in 1852. Barley every year since. per annum without any manure, but the annual yield has decreased from an average of over 25 fib in the first eight to less than 16 K) in the last twelve years, and since 1875 it has been still less ; over a period of twenty-four years, barley, when unmanured, yielded an average of 18-3 lb nitrogen per acre per annum, but with a decline from 22 lb in the first twelve to 14 - G in the last twelve years. Experiments similar to those on wheat and barley have been made on oats, root crops, leguminous and grass crops, all showing the gradual decline in produce when grown continuously without nitrogenous manures, and prov ing that the soil and not the atmosphere is the chief source of nitrogen in plants. In face of these results the "mineral theory" of Liebig, which attached but small value to nitrogen applied to the soil in the form of nitro genous manures, and maintained the sufficiency of the ammonia of the atmosphere for supplying the needs of the plant, cannot be accepted without reserve. Notwithstanding the great effect produced by the nitrogenous manures, two-thirds of the nitrogen supplied was unrecovered in the in crease of crops when the ammonia salts were supplied to wheat in autumn. When, however, nitrate of soda was used, which is always applied in the spring, the quantity left unrecovered was not much more than half that supplied. The following table (II.), by Messrs Lawes and Gilbert, shows the amount of nitrogen recovered, and the amount not recovered, in the increase of the crop for 100 supplied in manure, to wheat and to barley respectively, the result being in each case the average over a period of twenty
years :