FARM AND STATION.

Otago Witness, Issue 2102, 7 June 1894, Page 11

FARM AND STATION.

(Continued from page S.) AGRICULTURAL CHEMISTRY. A SERIES OF LECTURES DELIVERED BY PROFESSOR BLACK AT THE OTAGO UNIVERSITY. IV. — Lecture on Phosphates. There is another kind of phosphatic material in the manure market. It is a by-product in the Bessemer process for making steel. It is Bold under various names — "basic slag," "basic cinder," "Thomas phosphate," " Thomas slag " feeing the more common. There are now over 700,000 tons of it made annually in Europe and America. It is made as follows :— Most iron ores contain a small proportion of phosphorus, and the cast iron made in the blast furnace still retains the phosphorus of the ore. From this cast iron Bessemer steel is made by blowing air through it in the molten state in a kind of crucible called a " converter." For many years after the invention of this Bessemer process only those kinds of cast iron were " converted" which contained little or no phosphorus, as that process left in the steel all the phosphorus contained in the cast iron. Thomas (hence the name of the manure), in order to remove the phosphorus from the molten cast iron, lined the" converter " crucible with a mixture of burnt lime and magnesia, and also threw a quantity of the same mixture into the molten charge in the "converter." This lime and magnesia mixture, as Thomas anticipated, had the effect of taking up the phosphorus and fixing it as phosphate of lime, which, with the magnesia and some oxides of iron and manganese, floats on the heavy liquid metal, and is skimmed off, forming the " basic cinder," or Thomas phosphate manure referred to. The most valuable constituent of this "basic slag" is its phosphate of lime ; but it also contains at first a considerable proportion of quicklime, which, after standing exposed to the air for sometime, and especially after undergoing a long sea voyage, becomes gradually changed into carbonate of lime. There is a peculiarity about the phosphate of lime of this manure. Being found to be more readily soluble in water than ordinary bone earth or tricalcic phosphate (usually called insoluble phosphate of lime), it was suspected that it differed in composition from that compound, and .as the result of the analyses of many samples, ' agricultural chemists in England and Germany have proved that Thomas phosphate contains an extra or fourth molecule of lime, over and above the three molecules of lime present in the ordinary insoluble phosphate — that, in short, instead of containing 54- per cent, of lime, it contains 61 per cent, of that constituent. This extra quantity of lime, it seems, makes the Thomas phosphate more easily dissolved by water than bonedust or guano or coprolites or any other kind of tricalcic phosphate. The presence of the oxides of iron and manganese was at first objected to as likely to be hurtful to young plants ; but -that objection is removed now by the oxidation of the lower hurtful oxide of iron into the higher oxide by tbe grinding and exposure to the air to which it is subjected before its application to the soil. It is insisted on by the agricultural experts that this Thomas phosphate be ground to very fine powder before it is sent into the market. They require that it should be sifted through a sieve containing about 3600 holes to the square inch to bring out its soluble quality, and therefore its manurial value, to perfection. Many practical field experiments have been made in England and Germany with this phosphate against other phosphatic manures on many kinds of soil, and for different crops. These, it is claimed, while proving its inferiority to good superphosphates, have shown that for the immediate crop (the crop sown with it) it is superior to the insoluble phosphates — guano, bonemeal, ground coprolites, &c. Wagner, the great German authority, after many trials, strongly recommends it for cold, damp, sour lands. Its extra molecule of lime, acting much in the same way as quicklime would act, probably warms and sweetens and helps to dry up this dampness by combining with the moisture and with the obscure acids to which the sourness is due. The same authority says that it is very nearly equal to superphosphate for the immediate crop. The dark, unpromising appearance of this slag manure will prejudice Farmers against it. It has been introduced into the colony, and I have analysed samples of it from Southland and Canterbury, and also obtained in Dunedin. As there are many qualities of this manure, not differing much from each other in appearance, its proportion of phosphate of lime should be guaranteed to the purchaser, and an analysis should also state the degree of fineness, as upon this the activity and value of the manure greatly depend. What a confusion must exist in the minds of farmers about these four different kinds of phosphate of lime, all of which are in the market :—: — 1. There is the monooalcic phoßphate, CaH 4 P a O 8 , contained in superphosphates, and constituting from, say, 9 per cent, to 30 per cent. of that manure, and all of it soluble very readily in water, and therefore immediately available for the crops of the current season. 2. Dicaloic phosphate, or reverted phosphate, Ca,H,P a O 8 , contained to a greater or less extent in old superphosphate, made from mineral phosphates, with a stinted supply of sulphuric acid. This variety of phosphate in respect of solubility holds a place intermediate between the soluble monocalcio and the insoluble tricalcic to be mentioned presently. In rainy seasons, or on wet, sour land, this dicalcio variety is by some people preferred to the more soluble and more acid superphosphate. 3. The tricalcic phosphate or insoluble phosphate, Ca 3 P a O 8 . This is the kind of phosphate occurring in Nature as coprolite, apatite phosphorite, estreradourite, sombrerite, the guanos, raw bones, bonedust, bonemeal, &c. Though called " insoluble " it dissolves 6lowly, as already explained, in the carbonic acid soil water, and this gradually presents itself to the growing plants in a suitable form. 4. The "Thomas phosphate," "Thomas Blag," "Thomas cinder," "Basic cinder" (Ca.j.PzO:,), or "Basic Bessemer slag, "described above as a by-product of tfie Bessemer steel works. This phosphate, in a state of fine dust, is more soluble in water, and therefore more active in the soil, than the tricalcic phosphate. Its free lime also is a good base for the operations of the nitrogen and fermentation microbes — those grand manufacturers of nitrites and nitrates in the soil. In regard to the proportion of lime and phosphoric acid in these four kinds of phosphate?, as they are offered for sale, with their moisture and organic matter and sulphate of lime (for those of them which contain this last ingredient)! it may be said that the richest in

amounts to between 17 and 30 per cent., making it equal in that essential constituent to from 38 to 65 per cent, of phosphate of lime. Agricultural experts are not quite agreed as to the marrarial value of this manure. Voelcker, the late great English authority, as the result of field experiments (similar to those which Mr P. Patullo is carrying on here), got from it in oats and peas, larger returns than from the other manures he tried against it. Voelcker's results are tabled below :—: — With Oats. Crop per Acre. Manure per Acre on Moderately .2 „; .9 Heavy Land. .% . iij: 6Jcwt ground coprolites 65 1 3-5 scwt coprolites treated with sulphuric acid (mineral superphosphate) ... 72J2 lOswtrodunda phosphate (likeour Green Island phosphate) 7832 3icwt bonemeal, with 3ulphuric acid (bone superphosphate) • 61 J 2 4Jcwt precipitated phosphate 66 19-10 No manure 60 1J 3cwt raw bonemeal 61£1 3-5 20 tons of dung (farmyard manure) ... 70§2 1-10 10 tons of dung and scwt coprolites, with acid (superphosphate) 67 2 10 tons of dung and 6&cwt ground coprolites 62^2 5 tons of chalk 72 2 1-7 3cwt coprolites, with sulphuric acid (superphosphate), and 2ic wt Peruvian guano 64^2 With Peas "~~ ~ ~" Crop per Acre. S co .3 Manure per Acre on L'ght Land "3 .o5 |IJf_ No manure 39 2 1-7 53 wt ground coprolites ... 42 21 scwt ground coprolites and acid (mineral superphosphate) -WJ3 scwt' rodunda phosphate (like Green Island phosphate) 43J2J 4cwt precipitated phosphate 40J 2J3cwt of raw bonemeal 43J2 1-7 3cwt bonemeal and acid (bone superphosphate) 42-] 2J 3cwt coprolites superphosphate and 2Jcwt Peruvian guano 43 2i I have not any information as to the percentage of phosphoric rcid in the " rodunda " experimented on; and as this manure ranges I from 19 to 38 per cent, of that essential constituent (equal respectively to 40 per cent, and

These quantities take account only of the phosphorus to be replaced per acre without regard to its state of solubility, and without regard to other fertilising materials in the manure, as, for example, the nitrogen, ammonia, lime, potash, &c, which most of the above manures also contain. The quantities of manure named above would, however, be a very hand-to-mouth kind of treatment of the soil. It does not leave any margin of phosphorus to improve the soil permanently, or with which to grow future crops, or for laying down in grass. It does no more than leave the soil just where it was before the crops mentioned above were raised from it. A farmer who owns the land he is cropping, or who has a long lease of it, would deal generously with his fields and put in not a hundredweight or even less of these manures per acre, but three or four hundredweight per acre ; and he would thereby be laying in material for big crops in the future. His land to the farmer is, in one thing, like his bank to the merchant. He cannot take out of it more than he puts into it. The land contains a certain ascertainabie amount of phosphorus to begin with. Let that represent the capital or principal or sum to his credit in the bank. He raises a crep of, say, 50 bushels of wheat to the acre, and sends that away to London. By doing so ho draws 101b of phosphorus from every acre of that paddock, which of course is then 101b of phosphorus poorer. This is like drawing a cheque on his account with the bank. The manure he puts on then to restore this 101b of phosphorus is like paying a sum into the bank to keep his account healthy. If the farmer keeps crop, crop, cropping away it will be only a question of time when the original stock of phosphorus will be so far reduced as to raise crops not worth growing — diminishing year after year, in step with the diminution of his phosphorus. The farmer should farm in euch a way as to improve the value of his land by increasing the phosphates in the soil. This he will do by putting into it as much phosphates, &c., by manuring as he takes out of it by cropping. Wo must not, however, overlook two other sources of available phosphorus in the ground itself. (1) All soil consists of solid particles of greater or smaller size, and all more or less porous in texture ; and mixed with these particles there are stones of different sizes, which are not porous in any effective sense. Now a growing crop — by the root hairs and root terminal spongioles — draws phosphates from the loose, porous particles, but not from the interior of the stony matter. Gradually, however, assisted by good cultivation and free exposure to the weather, these stony particles get decomposed and broken up and converted into soil, bringing into use now any phosphates they may

the bones they take with them did not come from his paddock. There are about 1,800,000 sheep and lambs — not to speak of the frozen beef — exported frozen from New Zealand every year. There is also a large quantity of wheat and oats. The phosphorus sent away in this way is very considerable, but there is no help for ib. It would not, however, be a bad rule for the farmer to follow if he were to replace on his land under cultivation every year a little more phosphorus, lime and potash than he knows he is removing from it in his grain crops and potatoes, and sheep and cattle, milk and cheese. Of course, this could not be done on the uncultivated lands on the runs ; but these do not need it much, as they are not being impoverished by cropping, and it will be time enough to deal with them when they come into cultivation. A little bonednet scattered here and there from year to year would not, however, hurt them much. The price of 1001b of bonedust or good guano, or of lowt of good superphosphate, is not prohibitive. With a crop of 50 bushels of wheat, I suppose the price of three bushels, in a bad season like this, would restore the phosphorus taken away. The price of three or four bushels of oats out of crop of 80 bushels would not hurt much. And, of course, with smaller yields of wheat or oats less phosporus will be removed, and therefore a less quantity of phosphatic manures would be required to replace it. The lecturer announced that the next meeting of the class would be held at Eempthorne, Prosser, and Co.'s Chemical and Manure Works, at Burnside, all of which are to be in full swing next Saturday for the occasion. The manager of the freezing works, also, has kindly promised to show the students through, and explain the various operations of the freezing process. Our next article will include an account of what they will see and learn during that visit. Note. — In lasfc issue "apatites," by a printer's error, appeared as " apatiles."

phosphoric acid is the tricalcic, as it occurs in the Maiden Island, Abrolhes, and Coral Queen guanos, bonedust, bonemeal, and the mineral phosphates, ranging in all these from about 18 to 32 per cent., Coral Queen, Abrolhes, and bonedust being about 24- or 25 per cent., and mineral phosphates up to 30 or 32 per cent. In all these kinds of tricalcic phosphate there is no sulphate of lime, and in the mineral phosphates there is no nitrogen. The lime in all of them ranges from 21 to 37 per cent, and both the phosphoric acid and the lime are in the insoluble state. In point of phosphoric acid the " Thomas basic slag " comes next to the tricalcic, as it contains from 16 to 19 per cent, of that valuable constituent. Its proportion of lime ranges from about 18 to 30 per cent. The other two kinds of phosphatic manures — namely, the superphosphates (both the pure and partly reverted), contain from 10 to 18 per cent, of phosphoric acid and very varying proportions of lime, a good deal of which is in a soluble condition as sulphate of lime and soluble phosphate of lime. For rapid effect the superphosphates are far ahead of the others, reverted phosphates and Thomas phosphate coming next ; then the guanos and bonedust, and, last of all, the mineral phosphates. An admixture of Thomas phosphate with superphosphate has been tried with success on heavy, damp, and clay lands. Alone the Thomas phosphate is said to be inferior to mineral superphosphates on dry, light, chalky, or lime lands ; but, on clay lands, it is said to be equal or superior to these. The points which the farmer should get guaranteed in his phosphatic manure are (1) the percentage of soluble phosphate of lime ; (2) the percentage of reverted phosphate of lime ; (3) the percentage of insoluble phosphate of lime ; (\) the percentage of nitrogen or of ammonia (he can remember that 14 parts of nitrogen will make 17 parts of ammonia) ; (5) the origin of the manure, whether mineral, bone, or guano ; (6) the state of division of the manure. All these six points should be taken into account in valuing a phosphatic manure. If the manure contains potash salts, the percentage of these should also be stated. The process for ascertaining the proportion of phosphoric acid, lime, and nitrogen in phosphatic manures was described, and will be given in detail in a future lecture. Besides the mineral phosphates — apatite, coprolifces, phosphorite, sombrerito, &c, all of which are true phosphates of lime — there is another, known as "rodunda" phosphate, so called from the name of the island on which it is found. It consists chiefly of phosphates of alumina and iron. A modified variety of it. occurs on Green Island, near Dunedin, and has been analysed here. The phosphoric acid in it

82 per cent, of phosphate oE lime), there is an I have contained. A soil therefore nearly exunsatisfactory vagueness in the statement of j haußte( i of available phosphates may, by a the returns trz>m it. - „ ... , .. „ One thing about it is this : it must be ground !eaßon! eaBon of active f »Uow— ploughing and harrowto fine flour, passing through a sieve of 60 wires ln S and " cc exposure to the air— be restored to each way to the inch, or 3600 holes to the inch, a fertile state for a time by this bringing forto bring out its best effects. This fine ward of the phosphorus previously locked up in grinding, as already stated, is also essen- tbese hard stony particles. (2) Long-roobed plants tial to the success of the "Thomas basic (old clovers, &c), given time enough, will gather slag." The rodunda or Green Island phos- in from below (lft, 2ft, or 3ft or more down, phate is not suited for treatment with acid, according to the nature of the soil and the age of It cannot, therefore, be made into a super- the plant — far under the depth to which the roots phosphate. The Green Island variety shows an of a grain crop would reach) the phosphates, lime, advantage over the original "rodunda" in the and potash down there, and send them up into natter of nitrogen, as, so far as I know, there is the stem and leaves above ground. These no mention at all of that element in the latter, stems, then, eaten off or decaying or ploughed while in the Green Island I have found up to in, will thus bring into the surface soil and 1£ per cent, of nitrogen. This suggests a guano within the reach of the subsequent grain crop origin for this Green Island deposit. this additional contribution of fertilising The above results, published by the highest materials. Hence another explanation of the English and American authorities, show that, in enriohing effects of old clover pastures, money value, the rodunda phosphate (finely The lecturer pointed out that it would be ground) is superior to the best kind of mineral quite possible to impoverish a field by pasturphosphates. I do not know what quantity of ing iti as in oattle raising or dairying. That this manure is lying on Green Island ; but, dairying would do so is self-evident from the being so accessible to the market, it seems fact that 1400 gal of milk contain 101b of phosetrange that it should be neglected. Fashions phorus, or just as much of that precious elechange in manures as in other things, and I ment as is contained in 50 bushels of wheat, have no doubt the Green Island phosphate will The phosphorus in the milk comes from the have its turn. I should like to see it tried, grass, which, in its turn, comes from the soil, after passing through a 60- wire sieve, by Mr It might easily happen, however, that if the Fatullo in his field experiments. Before quit- pasture contained much clover (old and thereting the phosphates I must point out the fore long-rooted) and other long, wanderingquantities of the various kinds that are required rooted and enterprising fodder plants, these tor putting into the soil the phosphorus that might for a long time take up from below in the the different crops take out of it, assuming that manner already explained as much phosphorus the yield per acre of the different crops is as as is removed by the dairy cows, follows :—: — That cattle-raising would impoverish the land 50 bußhels of wheat * n thelong run is evident from similar considera80 bushels of oats tions. Given, for comparison, the practice of 60 bushels of barley two contiguous farmers — both feeding cattle for 18cwt of peas the butcher. One of them (call him A) raises 6 tons of potatoes , , his own bullocks from calves calved on his own irtonloESls} Ca^LXr yy e and "*** g-und from bi 8 o o 2J tons of oaten hay own paddocks to the size of three or four year old 3 tons of meadow hay big bullocks. They are sold away with all their Or that UOOgal of milk or half a ton of cheese b ° aes * n *k, cn V * d ° n> * kn ° w wh l at fche w . ei S. hfc have been produced per acre, or bone material of ea ?£. bullock would be, but whatever it is, for a dozen sheep. In each of these cases about something like one-tenth or one-twelfth of it 101b of phosphorus will have been removed from *™ uld _ bbcb b e bones » containing, as all bones do, the soil per acre. To restore the 101b of phos- about 55 per cent. of phosphate of lime, phorus per acre there will be required— all . of which has thus been produced lb ib and removed from the soil. The other Of Maiden Island guano, about 75 farmer (call him B) also fattens cattle Lacepede guano 75 for the market, but he buys them as store Steamed bones 78 cattle off the runs, puts them on his paddocks Abrolhes guano 80 to 85 as big lean hungry beasts, but with all their SsaSf?osSSSa.(»w) ::: IS b r s i te&d l /"VrN - On h v aßt r s Thomas phosphate 100 to 130 they put on tat, which contains neither phosSuperphosphatos (good quality) 110 to 140 phorus nor nitrogen, and the lean of beef, Chesterfield guano, from ... 100 to 160 which does not contain much phosphorus, but a Inferior superphosphates ... 150 to 250 good deal of nitrogen. And when he sells them Farmyard manure (dung; ... 3to 4 tons. away he has the satisfaction of knowing that