34 



THE TROPICAL AGRICULTURIST. 



[July i, i88z. 



keeping it alive, and afterwards had the satisfactioa 

 of planting it in the Jardin des Plantes at Paris. In 

 1838. at thn age of 100 years, it was cut down, h.aving 

 attained a height of 80 feet. 



The Elm, a wayside tree in Germany, a Vine-peg 

 in France, and an ornament of several avenues m 

 Madrid, is a puzzling tree to botanists, the genus be- 

 ing too mixed in char.aoter to reproduce itself true 

 from seed. The Wych Elm is our only undisputed 

 native, ripening its seed in our eliniate — the surest 

 tfst of a n.ative tree — .and extending fi-om the coast 

 villages in Sussex to the hauglis of tlie Teviot and 

 Tweed, and even to the HighlaciJs, All the varieties 

 of the British Elms may be referred to this Ulmus 

 montana, and to the old English Elm— Ulnins campestris 

 — which has smaller li'aves, throws up numerous suckers 

 — not a habit of the Wych Elm— and sometimes ilis- 

 plays a ti uuk of 90 feet loui! <aud 1.') feet girth This 

 is a constant free of avenues and parks in the southern 

 and midlnnd counties, .md of hedgerows in thevalleya 

 of the Th.imps and Severn. It is spread over Southern 

 H'urope, Western Asia, and Northern Africa, and it 

 has been naturalised in England, where it rarely ripens 

 its seeds, of wliich, indeed, only a portion ripens iu 

 France and Germany. The English Elm was rarely 

 found in Scotland before the Union, and only on sites 

 where it was known to liave been introduced. It has 

 been distributed over Ireland in modern times. Evelyn 

 spoke of it as biing rarely seen north of Stamford, 

 and as having been imported from Italy by our great 

 benefactors the Romans. Even Philip 11. admired the 

 stately form of our tree of lights and shadows, whose 

 open foliage admits the light and produces "the check- 

 ered shade," which is the charm of woods. He had 

 sat, perhaps, though not too often, with Mary — 

 "Under the shady roof 

 Of branching Elm, star proof," 

 aud on his return to a more congenial country he 

 transpori;ed to the Escurial some English Elms. 



Space will not allow us to add to this short selection 

 of travelling plants, and we have therefore omitted 

 the conifers, which have arrived from the East aud 

 West in this age of easy transit iu numbers too great 

 for enumeration. The same remark applies to the 

 plants introduced by private firms, aud to those 

 collected by Sir J. Hooker and other naturalists. — 

 H. E. — Gardeners' Olironide. 



THE PRODUCTION AND LOSS OF NITRATES 

 IN THE SOIL. 



Mr. Warington, chemist at Dr. Lawes's experimental 

 fariM at Rothamsted, in the course of a lecture at the 

 Royal Agricultural College, Cirencester, gave an inter- 

 esting account of the results of the investigations 

 carried out in the Rothamsted laboratory, of which the 

 following is a condensation. 



Nitrates, Mr. Warington commenced by explaining, 

 were produced as part of the living functions of a 

 very low order of living organisms, bacteria, present 

 in the soil ; tl)e action was analogous to that of the 

 vinegar plant, the former supposition of chemists, 

 viz., that nitrates were produced by mere surface 

 oxidation, was proved to be erroneous. The conditions 

 nece sary to nitrification were, first, th.at the soil 

 should be freely in contact with oxygen, for nitrific- 

 ation was a process of oxidation. Next, the soU 

 must be moist — the more wet the soil was, the more 

 would nitrification be assisted, provided the water 

 was not so abundant as actually to choke the pores 

 of the soil. Thirdly, the soil must contain some 

 salifiable base for the nitric acid to combine with 

 when it was formed, for if the b.ase was not present, 

 the jirocess of nitrification would so'in cease. In the 

 fourth place, a favourable temperature was necessary. 



Thw process of nitrification would take place, it was 



true, at a very low temperature, nearly at frtezing 

 point— he had had it going on at 3° C. (37° F.)— but 

 iu a summer temperature, the pro ess was wonderfully 

 aecderated. The French chemists, by whom the dis- 

 covery of nitrification as a vital process was first 

 m.ide, said that tlie most favourable tempfrature was 

 about 37° C. (98" F.), when it would take place ten 

 times more rapidly than it would at 14° C. (.57° F.) The 

 process went ou most rapidly iu the surface soil, and that 

 for two reasons — first, l)ecause there was ou the surtuce 

 a greater abundance of nitrogenous organic matter, the 

 remains of animal and vegetable life ; aud, secondly, 

 the surface soil came more freely into contact with 

 the oxygen of the air than was the case with the 

 subsoil. The production of nitrates in the soil was 

 asabjectof very great agricultural importance, because 

 sci ■ntitic .studies had clearly pointed out that, of .all 

 forms of nitrogen, nitrates were those most suitable 

 for plant food ; and in the case of cereal crops it 

 had been established that nitrates were practically the 

 only form of nitrogen which was adupted for the 

 wheat crop, aud on which it fed with advantage. 

 Thus, the crop of wheat or barley to be obt.ained from 

 the soil depended principally on the amount of nitrates 

 which that soil contained. The subject became of 

 new importance when they cousidered one of the 

 properties of nitrates, viz., their great solubility, and 

 their great diffusibility ; in fact, for them the snil had 

 no retentive power. With some other .substances this 

 was not the case — superphosphate, for instance, was 

 readily retained, but for nitrate of sodn the soil 

 possessed no retaining power, and the permanence of 

 it in the soil was at the mercy of the weather. It 

 would, therefore, very easily slip through their fingers, 

 and for that reason it was more worthy of their con- 

 sider.ation. 



From experiments on blocks of natur.al soil iu the 

 condition of bare fallow, it appeared that a consider- 

 able amouut of nitrates passed into the drainage water. 

 The amouut of nitric <a';id coming through was very 

 considerable about the month of July, the average 

 of five years for that month giving the amouut at 

 •2"7Slb. per acre. In the month of August the amouut 

 increased to 6681b. per acre. During all the autumn 

 months there was a great deal more nitric acid coming 

 through than in the spring months. That exactly 

 followed what he had told them about the facilities 

 afforded by summer temperature for the processot nitii- 

 fication, for it was after the summer, when the autumn 

 drainage began to fiow, that they got the greatest amouut 

 of nitrates coming through. The average of the two 

 sizes of drain gimges, 20 in. and 60 in. deep, showed 

 that during the five years they had in one case 44 '8 lb. 

 of nitrogen per acre per year draining through the 

 soil, and in the other case 42 -6 lb. of nitrogen per 

 acre per year. That was a very great amount of 

 nitrogen to pass through the soil in the drainage water, 

 and until those results were obtained thev had no 

 notion that such an amount would come away. An 

 average wheat crop of thirty bushels per acre only 

 contained 4.') lb. of nitrogen, and here they had an 

 average of 42 lb. aud 44 lb. being lost by drainage, the 

 highest amount in one year being 631b., and the 

 lowest 28 lb. He would now tell them the amount 

 of nitrates found in bare fallow. Sample? of soil had 

 been taken at Rothamsted, in two fields under bear 

 fallow, of the first depth of 9 in, the second depth of 

 9 in., and the third depth of 9 in. In one field the 

 whole of the 27 in. yielded 5S-81b. of nitrogen per 

 acre, and in the other the amouut was 56"5 lb. But 

 at the third depth of 9 in. th°y had not got to the 

 end of the nitric acid, and no doubt, if they had gone 

 still deeper, a further quantity would have Ijc^en found. 

 The greatest quantity of nitric acid was found in the 

 second nine inches. They generally found that the 



