PHILOSOPHICAL SOCIETY

Nelson Evening Mail, Volume LVI, 31 July 1924, Page 4

PHILOSOPHICAL SOCIETY

LIME RESOURCES AND SOIL FERTILITY’

THE MINERAL BELT

The regular meeting of the Nelson Philosophical Society was held last night with the President (Professor Easterfield) in the chair. A letter was received from the City Council agreeing to the Society’s recommendations for the better protection of bird life in all the reserves to the east, of tlie city which are under the Council’s control; and the President intimated that, the. Society would have to nominate suitable persons who would be willing lo act as additional rangers in order to achieve the end in view.

LIME NEAR NELSON CITY

Mr J. A. Bruce read a paper on “Some Sources of Lime in the Vicinity of Nelson,” based on the examination and analysis of rocks and deposits occurring within a radius of seven or e.ight miles of the city. A few of the rocks containing lime were briefly described.

Reference was made by the writer to a deposit of shell limestone, of considerable importance at Stoke in tlie geological formation classified as the .Jenkin’s Hill beds. This deposit is on the foothills of Poor Man’s Valley near Mr Price’s residence. It outcrops in several places within an area of two or three acres either as a cemented mass of marine shells or merely as loose fragments of shell embedded in a mixture of silt and sand. As it yielded approximately 33 per cent, of calcium carbonate on analysis, a high value could be placed on its use for agricultural purposes. The size of the whole outcrop as well as its easily accessible position were points decidedly in its favour. To crush it into a somewhat finer state would be a comparatively simple matter. For the heavier types of soil found on the Waimea Plains and especially those of Stoke anil Richmond. this shell, which was available in large quantities, would be found very effective in reducing the acidity of soils and rendering them more productive. Within the same geological formation calcareous sandstone is found outcropping prominently at the Cliffs on the Rocks Road. This, was of interest- to agriculturists, as tlie whitish sandstone of the lower portions of the Cliffs contained about 20 per cent, of carbonate of lime. Tahuna residents and others bad used it with l a considerable amount of success for top-dressing soils. A calcareous shale of variable colour but typically blue grey occurs in the. municipal quarry on the eastern side of Botanical Hill. In contact with a narrow band of the Brook .Street igneous rock classified as augite porphyry, this calcareous shale occupies the major portion of the quarry. Analyses ’of rock selected from various parts of the quarry yielded on an average about 25 per cent, of carbonate of lime. The igneous rock contained a smaller proportion of lime carbonate.

On the western side of Botanical Hill at the rear of the Cawlhron Institute, the calcareous shale is again found in contact with igneous rock. An analysis of a composite sample yielded 30 per cent, of lime carbonate. Veins of calcite, a crystalline form of lime carbonate, are- found interpenetrating the rock masses on both sides of the hill. It was not surprising, therefore, said Mr Bruce, that the fertile market _ garden soil of the Wood had a low lime requirement. . The proximity of this type of rock, which weathered readily, had in all probability been a factor of considerable influence in the formation of the Wood soil.

The President, in congratulating Mr Bruce on his paper, said it was a good thing to know what the composition of the rocks in the district actually was. The lack of lime requirement in soils at the foot of Mount. Kaka and in the Wood was understandable when it was remembered that the water, seeping, out of the hills contained calcium carbonate. In place of the term calcareous shale it would be better to use that of calcareous mudstone or argillite. Mr T. Rigg, as. a Tahuna resident, said he could testify that, the,-Rocks Road material mentioned in the , paper' had an excellent effect on Tahuna sand, partly on account of tlie calcium, carbonate it contained and partly because of the rather coarse particles in it, which helped to keep the surface of the ground open.

SOIL FERTILITY

An illustrated lecture on “Soil Fertility” was delivered by Mr Bigg, who said that for the purpose of the farmer soil fertility must foe interpreted to mean the capacity of the soil for high production of ordinary farm, crops. Owing to th,e fact that, crops varied in their requirements,, any par-

ticular soil might have different values for different crops. The variation in fertility of a.particular soil for various crops was frequently small compared with the large deviations in fertility of two dissimilar soils for the same crop. Many factors were responsible for variations in the fertility of' different Nelson soils. Some of the more important of these factors were (1) soil texture, (2) soil acidity, (3) plant food content, (4) bacterial population, and (S) 'the presence of harmful substances. Soil texture played an important part in determining the amount of the water supply and the aeration of the soil. On this account soils of different texture were always associated with different kinds of crops. The small fruits, apples, peaches and hops were all susceptible to comparatively small variations in soil texture and for the best results required a soil of definite mechanical composition. Although agriculturists could the texture of heavy lands by liming and draining, and that of light lands by green manuring, it was seldom possible to remove completely defects that were due to bad texture. In a large number of Nelson soils, acidity seriously limited high yields of many leguminous plants. Barley and wheat were also adversely affected by acid conditions, and reduced yields and

those cereals were invariably obtained on acid soils. Soil acidity could always bo remedied by liming the land, and both ground limestone and slaked lime could be used for this purpose.: Perhaps the most important factor in the production of low fertility in many Nelson soils was their low content of phosphate. A great response to plioaphalio manuring was invariably obtained over a large range of Nelson soils, especially marked where liming had been carried out prior to manuring. Referring to the injurious effect of harmful substances, Mr Bigg remarked that it was commonly stated that magnesia was sometimes present in Nelson soils in such quantities as to cause sterility or low-yielding capacity. A large number of soils from different parts of the district, including the Mineral Belt, had been analysed in the chemical laboratory. of the Cawthron Institute, but no connection could be traced between high magnesian content and low soil fertility. It was interesting to note that several productive. Nelson soils contained higher percentages of magnesia in the hydrochloric acid extract of the soils

than those of certain samples from the Mineral Belt. Careful analyses of a number of different samples of Mineral Belt soil taken from widely separated parts of the Mineral Belt all agreed in disclosing a very low content of phosphoric acid. The amount of phosphate was so small that the infertility of the Mineral Belt could very well he taken to result therefrom ■ The lime-magnesia ratio of samples from different parts of the Mineral Belt varied widely even when the extract ions were made with dilute solutions. Mr’ Bigg also mentioned that a series of pot experiments conducted on Mineral Belt soil obtained from D'Urville Island showed conclusively that the low - content of phosphate was the factor concerned in ;.he production o.f pomyields of clover and grass. Experiments were in progress to ascertain whether trees responded in a similar way to phosphatic manuring. The president said it was frequently stated in the literature on the subject that the non-fertility of the Mineral Belt was due to the rocks there being rich in magnesia. When, however, they considered the small percentage of phosphoric acid shown by the analysis of Mineral Belt soils taken from four different localities it was not surprising that, they lacked fertility. What interested him part icularly when he visited D’Urville’lsland was to find that where stock had been put on to Mineral belt land that was fenced (lie growth i f rye grass and clover was quite as good as that on the ordinary Maitai Belt land on which sheep are run. The. lecturer, had made .comparisons of soils, and traced the connection between their composition and their texture and their fertility or otherwise, and by so doing had made it, evident that- if those points were studod with sufficient, care, there was practically no soil that could not bo made to grow healthy crops. Mr F. G. Gibbs said that the barrenness of the Mineral Belt was a subject of discussion .25 or 30 years ago. Then Hall’s book on the soil came out, and it was taken as settled, in view of what he. isaid about the effects of magnesia, that'it was the cause of the barrenness. Dr. Cockayne paid some attention to the Mineral BpU, and at bis request he (Mr Gibbs) made Certain investigations. One of the things that was' noticed should ; have put them on the right track, and that was the enormous root growth of some of the plants peculiar to the Mineral Belt. If they had only put two and two together they would have realised that the plants were hunting for food. The discovery which the Cawtlimn Institulejiad made with regard to the poor growth of vegetation on the Mineral Belt opened up a wide field for experiment that was worth while* following up. Mr J. .‘V. Bruce said he had treated some plants on the- Mineral Belt with superphosphate, and it would be interesting to ,=ee what the result would be. In reply to a remark by another speaker, Mr Gibbs said that the sharp line of demarcation noticeable at one point on the Dun .Mountain track where the bush ended was to some extent artificial, it being obvious that when people went up there to do mining they cleared a certain amount of forest. After, further discussion, the lecturer made a brief reply, in the course of which he said there certainly were points in connection with the investigation of Mineral Belt soils which should receive further attention. A vote of thanks was accorded to Mr Bigg by acclamation, and Mr \V. C. Davies’ services as photographer and lanternist were similarly recognised.