PROFESSOR BLACK'S LECTURE.

Evening Star, Issue 9832, 22 October 1895, Page 3

PROFESSOR BLACK'S LECTURE.

At Outrain, on a recent date, Professor Black gave a lecture, under the auspices of the Otago Agricultural and Pastoral Association, upon 'The Chemistry of Soils and Manures and Crop 3,' with special reference to phosphates of lime. There was a. large attendance, the majority being persons enfiged in farming pursuits in the district, he speaker explained that fifty bushels of wheat contained 10lb of phosphorus, the same quantity of phosphorus being contained in eighty bushels of oats, sixty bushels of barley, three tons of oaten hay, the same quantity of meadow hay, six tons of potatoes, twenty tons of turnips, swedes, or mangels, 1,400 gallons of milk, half a ton of cheese, or twelve fat sheep ; and pointed out that when produce to the above extent was raised off per acre such acre was impoverished to the extent of 101b of phosphorus. To replace this phosphorus on the ground, which every good farmer would see the necessity of doing, a man could use lewt of bonedust, which contained about 101b of phosphorus—the quantity required to replace what was removed by the above quantity of produce. The lecturer explained that there were two kinds of bonedust, one of which was worth from 30s to £'i per ton more than the other, the difference in value being due to the fact that from the inferior article about half the nitrogen had been removed by super-steam heating the bones before being made intc dust, whilst the other or more valuable kind retains all the nitrogen, aud therefore the ammonia of the original bones. The phosphorus might also be recovered in the ground by adding guano in the proportion pf, say, from 1001b to lewt of the best guanos, or from lewt to l.Jcwt of the inferior kinds. A third way of replacing the? phosphorus would be by the use of from lowt to 2cwt of super-phosphate, according to quality, which has an advantage over the two kinds of phosphate above mentioned of being to soma extent soluble in water, and since plants can absorb their mineral food only in solution ib is manifest that when the manure is presented in a soluble form the plants the more readily get the .use of it, Another curious source of phosphorus for manure is in what has been called basic slag, now imported into the colony. This basic slag is a by-product in the Bessemer steel manufacture, and there are something like two millions of tons of it produced per annum at the present time. Its composition is very varied, ranging between 25 per cent, and 50 per cent, of phosphate of lime. Besides phosphate of lime in this manure, there is. a considerable proporticn of burnt lime, which has a warming and sweeteuing effect on the soil and also forms part of the direct lime food of plants. The lecturer then went on to discuss the merits of lime as an article of manure. Among its other good points, he referred to the following :—(1) Lime is part of the direct mineral focd of plants, cultivated crops removing from 3lb to 2001b per acre, potatoes, turnips, and the clovers requiring the larger quantities. (2) Lime is good for burning up aud destroying the excess of vegetable matter when the accumulations of such arc an encumbrance to the soil, as in the case of old swamps which are being reclaimed. It is necessary, however, before applying the lime to t£.ke the proper means of drying the land thoroughly, otherwise the good quality of the lime will be to somo extent thrown away. (3) It releases from stubborn clays the potash, magnesia, and phosphates which they contain, thus rendering these ingredients available for the use of the Elants.- (4) Lime also sweetens sour soil y neutralising the free acids which it contains. It is for this purpose the very best application which the farmer can employ in seed time after a wet winter after water has been standing on his fields for weeks. (5) Quicklime applied in fine division rapidly warms a cold soil. It does so by slaking itself with the moisture which it finds in the soil, and, as everyone knows, lime in being slaked generates a great amount of heat. If, however, the lime were first slaked before being spread upon the field, such heating effects would not be produced. The lecturer therefore advised farmers who are applying lime in a cold, late spring, at seed time and after a cold winter, to pulverise the burnt lime without slaking it, and harrow it into the field a few days before the seed is sown. In this way the soil will get the full wanning and sweetening benefit of the lime. (6) It was discovered eight years ago by the great German agricultural chemist Hellriegel that lime is just the base which is best fitted for the growth of the nitrogen microbe, the functions of this wonderful microbe being to take the-nitrogen from the atmosphere, use it for its own purposes, and then transfer it into the substance of the plants on which it grows. Such plants, however, aro only those of the leguminous order, which includes peas, beans, lentils, vetches, lucerne, lupines, all the clovers, gorse, broom, the acacias, and indeed all plants which have a flower like the pea-blossom. In this connection the lecturer made the extraordinary statement that there is in the atmospheric air, resting on every acre of ground all round the globe, as much nitrogen as would, if sold at the present price of nitrogen in the manure market, bo worth something like two millions sterling, and, so far as the lectarer knew, the only way of utilising this valuable fertiliser is by means of such plants as are named above, affording as they do, on their roots, a home for this curious microbe.

A lecture similar to this waa given at

Mosgiel on Saturday night by Mr W. Goodlet, the professor's assistant. There was a large attendance, and Mr Qoodlet'a remarks were attentively listened to. Next winter, under the auspices of the A. and P. Society, Professor Black will give a course of these lectures all over the district. .