THE CHEMISTRY OF BUSH SICKNESS.

New Zealand Journal of Agriculture, Volume 5, Issue 2, 15 August 1912, Page 121

THE CHEMISTRY OF BUSH SICKNESS.

B.C. Aston, F.I.C., F.C.S.

The soils of the area in which <c bush sickness always in time develops are composed of air-borne pumice acid lava which has been so mixed with gases in the molten state that on cooling it presents a spongy structure with the hardness of rock. The size of the particles that go to make up the soil is such that generally they may be classed as coarse sands. This type of country is noted for the absence of surface creeks and pools, the drainage being excellent and very rapid. Where streams occasionally occur, they have eroded deep beds or gorges through the easily-transported pumice. There is no record of bush sickness having developed on any save pumice country. From its very nature it will be admitted that pumice soils must be exceptionally well ' aerated, and' those changes going on in the soil which benefit by an excess of oxygen here have optimum conditions under which they may take place. Analyses of pumice show that. it. contains every mineral nutrient necessary for plant-food, but, although these constituents are present in considerable amounts, some of them are not always present in a readily available state to the extent usually found in fertile soils. ' . <

The worst-affected country until recently supported a heavy growth of forest (see illustration, Agricultural Journal, Vol. iv, No. 5, p. 375), although a large area of land on . which sheep cannot be successfully reared has never supported forest and has been laid down 'in English grasses for over thirty years. . When the forest is . felled and burnt much of the organic matter in the soil is also destroyed; the soil is now, moreover, subject .to the action of the timber-ash, which is alkaline, and contains both potash and lime. These pumice soils suffer from two very great defects. When they were comparatively recentlygeologically speaking—ejected from the bowels of the -earth in a hot condition, they naturally contained no organic matter, neither did they contain colloidal clay, ' and although showers of mud and fine debris may at various times have fallen, they did not fall so as to form, with the coarse sands here spoken of, a more perfect mechanical

mixture of coarse and fine particles. To fill the soil-interstices it is not practicable to apply clay, but if a vegetable covering can be maintained for some years the accumulation of humus to a great degree remedies the mechanical defect. ■ The humus acts as a solvent of plant-food, and assists the decay of the pumice rock in situ without the intervention of surface running water, usually necessary for the formation of soils from the parent rock. I have previously pointed out (Agricultural Journal, Vol. iv, No. 5, p. 377) one of the chief ways of improving unproductive pumice soils is by increasing the humus and as the conditions , for the growth of clovers are extremely favourable,’ the growth of these and similar humus-producing plants must be an important factor m any system of soil-treatment adopted. On ploughable. lands green-manuring with leguminous' crops may prove of great service in hastening the accumulation of humus Turning to the chemistry of the soils, analyses of these from affected areas show that available phosphoric acid, extracted by 1-per-cent citric-acid solutions, is generally low in amount, suggesting that, dressing

the land with phosphatic fertilizers would prove beneficial to the pasture and profitable to the farmer*; but it is not to be thought that lack of phosphate is the immediate cause of the sickness, as there are many soils with just as little phosphate, on which the animals remain healthy. Moreover, the bones—the chief repository of phosphates m the animal—show no signs of malnutrition. If ' phosphatic manures, containing no iron when applied to the land, enable stock

depastured thereon to remain healthy continuously, it is probably due to some beneficial indirect action exerted by the phosphates. What this indirect action may be is not at present clear, though it may be said that phosphates are known to have a good effect in mitigating the injurious effects of manganese compounds when -present in excess. Lime, 1 it is interesting to note, has'the opposite effect,* and there is some evidence that lime has an injurious action on the feeding quality

of pasture on “bush-sick” lands. Should further experiments confirm this, it will be one of the most remarkable facts elucidated in this research, considering the. small amount of lime already present in the soil. The effect of manganese compounds on plant-life is one of the puzzles of agricultural chemistry. Analyses of the affected soils and grass from them have shown that manganese is present -in amounts greater than in ordinary soils and grasses. Lt may be detected .. in aqueous extracts, filtered through porcelain, and in citric-acid extracts (“available plant-food”) of pumice soils in very variable amounts. The oxidation of manganese compounds to higher and more toxic states in these well-aerated soils is a matter not to be lost sight of. About eight years ago I made analyses of sick animals’ blood, and found it extremely deficient in iron. Subsequent tests confirmed that analysis; this, together with analyses of soils and grasses, hinted that a deficiency of assimilable iron in the food might be the cause of the sickness. This suggested the application of iron compounds to the soil as a possible remedy. When therefore asked to suggest a series of schemes

{or top-dressing the pastures of the affected country, iron-sulphate was recommended by me for two farms situated widely apart. It is significant that of all the substances experimented with, iron-sulphate applied alone to pasture has been the most successful in enabling sheep (the animal most susceptible to the sickness) to be kept healthy over a period of eighteen months.* The ewes on the iron-dressed padlock on one farm successfully reared their lambs, with the death of only one, and at the time of shearing the lot were in excellent condition, being, in fact, the best of fifteen lots on four different farms, each lot having been pastured on an area receiving a dressing differing from the above, with one exception : this was the other irondressed paddock. Here one of two wether sheep died as the result of an accident; the remaining animal still survives in good condition. On the control (i.e., the untreated) paddocks of these farms, all the sheep became affected, except on one farm on which six wether sheep remained perfectly healthy when grazed on a field of 300. acres, including some standing bush. . It is possible that they were able, with their considerable range of 'food, to exercise some selection in their diet. Assuming that the sickness is caused by the deficiency of assimilable iron m the food, it would seem reasonable that m this large area there would be some vegetation not so deficient, which the animal, might instinctively prefer.

Summary, f

A great advance in our knowledge of the anaemic condition of stock , known as bush sickness, occurring on the pumice lands of the North Island, has been made during the past year. For the first time have been instituted, under the direction of Mr. Reakes, Director of the Live-stock and Meat Division, field experiments in which the pasture has been treated with various substances suggested by chemical theory. Generally speaking, the effect of the dressed pasture on the animals has been most beneficial, the animals having fattened to the /‘prime” condition, whereas on untreated adjacent , paddocks the ■animals have either died or become affected. Soluble iron salts proved

the most beneficial, and were almost entirely successful in enabling the stock to be kept healthy. Phosphates have been especially successful in the case of cattle.. As the experiments are still in progress, no advice can yet be given as to the treatment of these affected lands and, although this must be considered a progress report . merely, it may be said that the bulk of the evidence at present points to a lack of assimilable iron in the food-supply as being the cause of the sickness, though the presence of an excess of manganese may be a factor affecting the deficiency.

The sum of £2,561,000 is provided in the Austrian Budget of 1912 for expenditure on agriculture, as compared with £2,4/3,000 in 1911.

A society called the “ Guild of the Daughters of Ceres has been formed in England to forward the interests of women engaged in agriculture and horticulture.

Lord Strathcona, an old Lord Rector of the Aberdeen University, has endowed the new Chair of Agriculture at that University with a gift of £lO,OOO.

A sum of £5,000 has been voted by the American House of Assembly for further investigation into the natural and artificial sources of the supply of fertilizing-material and farm manures.

In Norway a certain number of farmers are nominated “ growers of the seed,” and an expert is engaged to instruct them in the cultivation of improved seeds and to supervise their work.

A report in the Board of Trade Journal, Bth February, 1912, states that an expenditure of £lO,OOO is authorized by the Brazilian Budget for 1912 for the establishment of an experimental wheat-growing area in the State of Rio Grande do Sul.

Cambridge University has received a grant of £14,500 from the Home Development Fund for the building and equipment of an extension of the School of Agriculture, chiefly for the accommodation of research institutes in plant-breeding and animal-nutrition. Oxford University will receive £9OO a year from the fund, in aid of investigations into the economics of agriculture. '

* Previous articles on this subject by the writer are to be found in the Journal of the Department of Agriculture, Vol. iii, 1911, p. 394, and Transactions of the . New Zealand Institute, Vol. 44, 1912, p. 288, and in Dominion Laboratory Report, 1911.

J«l’n‘.“ S VoI. s™. 26 We11 Sh ° OT by > illustration in the last number of this

* Kelly, “ The Functions and Distribution of Manganese in Plants and Soils,” Bull. No. 26, Hawaii Exp. Stn., 1912; also Guthrie and Cohen, Ag. Gazette, N.S.W., pp. 125 and 435, 1910. ’ - .

* This is the more remarkable as, of the substances tried—phosphates, lime, potash, nitrates and iron-sulphate—the last is the one which would possibly not have been thought of had the analyses not suggested it. . The opinions generally expressed by authorities are not favourable to the use of iron-sulphate' as a manure. Although essential to plant-growth, iron is required in such minute quantity that all soils are thought to contain sufficient. ■ When iron-sulphate proves beneficial the result is generally regarded as due to an indirect action and not to the supply of the plant-food, iron.

+ Should future research establish the “iron starvation ” hypothesis as a theory, it will open a most interesting field for experiment as to the cheapest method by which the remedy may be applied. Iron-sulphate is not produced in New Zealand, but there are large deposits of hydrated iron ore at Collingwood, and a use might be found for Taranaki ironsand. Practical considerations, however, rather suggest a phosphatic fertilizer containing a large amount of iron as being the most probable remedy.