February i, 1884.] 



THE TROPICAL AGRICULTURIST. 



603 



eed results ia fields that are full of wealth, yet will often 

 advance millious to some petty State which is beyond 

 hope of solvency. In conclusion I may add that consider- 

 able rivalry exists between the planters in several sugar- 

 growing provinces, and in the so-called contests that have 

 been held, subject to the decision of competent arbitrators, 

 the palm has alternated from one to another, Santiago 

 del Kstero, however, is at present the Iiolder of the 

 coveted distinction. — Cor., British Journal. 



JIAN L'RE,S— PRACTICE WITH SCIENCE. 



The fifteenth volume of the ninth edition of that stup- 

 endous work, the Enci/cfo/ffr^dia Britannia, iias recently 

 been issueii by the Mes,srs. Black, and amongst many 

 articles of the most varied interest there is one specially 

 attractivt; to agricultuj-al readers, niniely, Dr. Yoelckcr's 

 article on '• Manm-e." He defines the princiiial eoustituents 

 of manure to be nitrogen, iu the form of ammonia, nitr- 

 ates, and nitrogenous organic matters; organic matters 

 not containing nitrogen (humus) ; phosphoric acid, potash, 

 soda, lime, magnesia, silica, sulphuric acid, and chlorine, 

 by far the most important being the nitrogen, phosphoric 

 acid, and potash. 



With rcganl to nitrogen, Boussingault long ago proved 

 that plants do not possess the power of taking up by 

 their leaves and of assimilating the free nitrogen of the 

 atmosphere. A fractional percentage of the atmospheric 

 nitrogen undergoes couversion into nitric acid and ammo- 

 nia, which become dissolved by rain or dew, and so find 

 their way to thu soil, thus adding to the store of soil 

 nitrogen, but in altogether too insufiicieut a quantity to 

 meei ihe leijuirements of remunerative crops. At Kothara- 

 sted the amount of nitrogen annually deposited is 7-21 lb. 

 per acre, of which 6W lb. are iu the form of ammonia, 

 and 075 in the form of nitric acid. But it has been proved 

 that the loss of nitrogen iu the form of nitrates iu the 

 drainage water from cultivated soils is much greater than 

 the total amount supplied to the land in rain and dew. 

 The experiments on tus continuous growth of barley at 

 llothamsted from 1S.5J to 1875 afford direct evidence of 

 the iusufticieucy, not only of the atmospheric supply of 

 nitrogen, but likewise of that present in the soil in the 

 form of nitrogenous organic matter. 



The deep and moderately stiff soil at Rothamsted con- 

 tains the mineral elements of plant food in abundance, 

 so that it was possible to grow corn crops for over twenty- 

 five years without any manure. But the crops in the second 

 half were less than those in the first half of this period, 

 aud full crops were never obtained. While the appUc- 

 ation of niiueral manures alone produced only a slight 

 increase in the case of wheat, and not nmch better results 

 with barley, nitrogenous manures, on the other hand, 

 applied eitlier as ammonia salts or nitrate of soda, pro- 

 duce.l a strikingly large increase. While good crops of 

 wheat and barley can be grown by the annual addition 

 of M tons of farmyard mamnre per acre, the best results 

 are provi d to follow the use of a mixture of minaral and 

 nitrogenous manures. 



The quantity of nitrogen carried of iu the Rothamsted 

 crops was determined with these results:— Over a period 

 of thirtj-two years (to 1875) wheat yielded an average of 

 20-7 lb. of nitrogen per acre per aunum without any man- 

 ure, but the annual yield has decreased from an average 

 of over 25 lb. iu the first eight to less than 10 lb. in the 

 last twelve years, and since 1375 it has been still less ; 

 over a period of twenty-four years bailey, when unman- 

 ur..d, yielded an average of 183 lb. nitrogen per acre per 

 annum, but with a decline from 22 lb. in the fir.st twelve 

 to 14t; lb. in the last twelve years. Similar experiments 

 on oats, roots, pulses, and grass cups all show the steady 

 decline m produce when grown continuously without nitro- 

 geujus manures, and thus prove that the soil, and not 

 the atmosphere, is the chief source of nitrogen iu plants. 

 Great as was the eft'ect produced by the nitrogenous man- 

 ures, however, it was fouml that two-thirds of the nitrogen 

 supplii'd was unrecovered in the increase of crops when 

 the ammonia salts were sown on wheat iu autumu. But 

 wa.'u nitrate ol soda, which is always applied in spring, 

 w&i u.sed, the quantity of nitrogen unrecovered was not 

 e u h more than half that supplied. WTiat becomes of 

 the oae-half or two- thirds of the nitrogen wiioh is not 



recovered iu the increase of the crops ? Analyses of th e 

 drainage water from soils supply the auswer to this ques- 

 tion, l^igures are given showing how great may be the 

 loss of nitrogen by drainage when ammonia salts or nitrates 

 are liberally applied to the land in autnmn, or even when 

 applied in .spring if there be much heavy rain ; also that 

 a c{uantity of nitrogen, occurring as nitrates in drainage 

 water is increased correspondingly with the amount of 

 ammonia or nitrate put on the land. Besides the nitro- 

 gen removed in the crop and that lost in drainage, a 

 small proportion is found to be retained iu the soil itself, 

 but the amount depends on the nature of the manure ; 

 ammonia salts and nitrates yield but very small residues, 

 and exert little or no effect beyond the first year, while 

 bones, cake, aud such manures leave large residues of 

 nitrogen in the soil, which tell markedly on subsequent 

 crops. I'hosphoric acid aiKl potash pass but little into 

 the drainage water, but are retained almost entirely in 

 the land, while the less important miueral matters, lime, 

 magnesia, soda, chlorine, sulphuric acid, and soluble silica 

 pass iu large quantities into the draiuage water. Dr. 

 Voelckcr makes the following inferences : — First, that much 

 more nitrogenous material must be applied to the land 

 than would be needed to produce a given increase in the 

 crop, supposing all the nitrogen to be recoverable : aud 

 secondly, that nitrogenous organic matters when applied 

 to the land undergo decomposition, and are gradually 

 resolved into ammonia eompounds, which, after being re- 

 tained a short time by the soil, are finally oxj'dised into 

 nitrates, in which form they are most available and beue- 

 fici.al to plants, but are not ab.sorbed by the soil, aud are 

 readily washed out by rain. 



rhosphoric acid is next in value to nitrogen, partly 

 because of its natiu'al scarcity in cultivated soils, aud 

 partly because it is required alike by corn aud forage 

 crops in larger quantities than lime, magnesia, and other 

 minerals which are more abundant. I'hosphate of lime is 

 more or less assimilable by plants according to the more 

 or less porous condition of the phosphatic manuring mater- 

 ials. Hence the object of treating mineral phosphates 

 with sulphuric acid, and converting theiusolubie tribasic 

 phosphate of lime into a soluble svqjerphosphate. For 

 this manufacture alone, England imports over half a mil- 

 lion tons of phosphatic minerals per annum. 



As to the action in the soil. Dr. V'oelcker remarks: — 

 " The acid or soluble phosphate of lime iu superphosphate, 

 when applied to the soil is first dissolviil by the rain and 

 equally distributed iu a portion of tlie soil, iu which it 

 must be precipitated and rendered insoluble before it can 

 be assimilated by the plant." It is this intimate distri- 

 bution aud subsequent precijiitation iu :i most finely divided 

 state that would seem to c:uise the beneficial eft'ects of 

 superphosphate, and its superiority over undissolved phos- 

 phates. It supplies at ouce phosphoric acid, hme, and 

 sulphuric acid to the soil, and is much used in conjunc- 

 tion with nitrogenous materials. Superphosphates are manu- 

 factured of various strengths, the percentage- of tribasic 

 phosphate of lime, rendnvcl su'iible by acid, being taken 

 as the basis of valuation. 



Potash forms an important constituent of all crops, 

 particularly root crops. Sandy soils, as a rule,^ are poor 

 in potash, while clay soils usually contain sufficient. Au- 

 tumn cultivation, subsoiling, and similar means of facilit- 

 ating the free access to the air gradually liberate the 

 potHsh from the insoluble silicates in which it occurs iu 

 clays, aud then set it at the di.spo.sal of plants. Potash 

 occurs in farmyard manure, urine, all excrements in oil- 

 cakes, and largely in wood ashes. On most soils, in good 

 agricultural condition, the addition of potash maume gives 

 little or no effect, but on poor, sandy soils or worn-out 

 pastures, potash salts, used with superjihospbate, dissolved 

 bones, and guano, produce most beneficial results. 



The following remarks on the application of manures are 

 very valuable — "Farmyard mauure iu order to be must 

 beneficial, should be applied as quickly .as pos.sible after it 

 is made, the best time being autumn or early winter. 

 Nitrate of soila should be applied as a to]) dressing early 

 in spring; its effects will be seen in the first season only. 

 Ammonia salts, guano, dun;;, &c., .are best applierl to heavy 

 land in autumn or winter, either before the seed is sown 

 or after lilt; plant is fairly above ground, but in the case 

 of lighf'laud early in spring. The effect of UoneS iu the 



