ROTATION OF CROPS.

New Zealander, Volume 1, Issue 33, 17 January 1846, Page 4

ROTATION OF CROPS.

Professor Danhen) *'On the Chemical Principles involved in the Rotation ot Crops." — Pi of. Daubeny marie some itsmarks on the chemical pnnciples involved in the 'otation of ciops, stating the conclusions whicli he had deduced fioin «i st-iiesof experiments, cariied on -.vitliin the Botanic Gaiden at Oxford, and intended to asceitdin the late of diminuiion in the produce of several plots of gtound thai had been sown for ten years, either continuously with the same, or successively with diilVient crops, in either case without the addition of manure thioughout the couiseot" thetnals. Lie stated that although, as> might have been anticipated, a dnniuutioii in

the latter years ptoduce took place both 111 the permanent and in the shifting crops, and a smaller average amount was obtained in the lonner than in' the latter, yet that after the expiration of ttie whole period the ground still continued unexhausted ; and that an anal) sis of it showed it still to contain sufficient of the phosphates to supply materials for 19 crops of barley, sufficient of potass lor 15, and sufficient of soda for 43. The actual diminution then of produce during the latter years he attributed to the circumstance of these ingredients not being in a soluble condition, it being found that from the I soil solongdrawn upon, water impregnated with i carbonic acid, took up much less of the above ingredients, than it did from the same that had not been so cropped, and but recently manured. The greater diminution in the permanent than in the shifting crop he attributed to the circumstance of the latter being supplied with a larger amount of organic indtter, derived from the fallow crop intercalated, owing to which the crops would be more fully developed through the influence of the carbonic acid and ammonia, which would be imparted to it by the decomposition of the humus. He pointed out, how the mere introduction of healthy plants into a soil might aid in rendering the phosphates and alkaline salts, locked up within the laiter, more speedily soluble, and hence inferred that a laiger amount of these substances might be extracted, where the plants were stimulated into activity by the presence of decomposing oiganic matter. He was also led to enquire whethei, in the event of a scantier supply of one of the alkalies or of the earths that was common, a plant would substitute ad libitum another which might be presented to it in greater abundance To determine this, he obtained from Mr. Way, late assistant to Professor Graham, an anal)sis of three samples of six different kind of crops, — viz., potatoes, barley, turnips, hemp, flax and teans; one sample being that cultivated for ten successive years in the same ground without manure ; the second from a similar plot which had grown different crops for the same period without manure j the third from a plot in a contiguous part of the garden which had been recently manuied. From the results obtained, it would appear that the aggregate amount of bases, in the three samples, was about the same ; but the proportion of these bases one to the other varied considerably, a circumstance at h'rst sight appearing to confirm the theory of substitution. The author however, conceives that this may be explained by supposing a different degree of developement of the several parts or proximate principles in the respective samples, as he finds a great discrepancy in the amount of phosphoric acid in gluten and in starch, and thinks it probable that the same diversity may extend to other of the principles contained in each plant. That potass is better adapted for the organization of a plant that soda, seems to follow from the circumstance, that whilst the soil usually contained an excess of soda, the plant always was most rich in potass. The author therefore, in accordance with the views of Leibig, throws out as a conjecture, that the soda found in the ash may be that circulating through the vegetable tissue, and contained on the top, whilst the potass is actually assimilated, and constitutes a part of the vegetable tissue. The fotmer, as Leibig supposes, may be useful in conveying carbonic acid to the plant, but cannot be substituted for potass, at least without injury to its healthy condition. It appears also, from the analysis referred to, that land plants have not the power of decomposing common salt, so that this substance cdiinot, as has been supposed, be serviceable to vegetation, by supplying it with alkali. We may also infer that it does not follow because a soil is benefitted by manuring that it is destitute of the ingredients which the manure supplies, since it may happen that these ingredients are present in the soil in an insoluble, and therefore not an available condition. Chemical and mechanical means may no doubt be effectual in bringing into a soluble condition the phosphates, and alkaline salts thus locked up within the soil, but as this is brought about by Nature herself, we are counteracting her beneficial effects when we waste the products of these operations, ready prepared for our hands, as is done in suffering to jun to waste the various excrementitous matters which are placed at our disposal. The analysis given may also show, from their great discrepancy with those of Sprengel, the importance of that investigation of the constituent* of the ashes of plants, now about to be undertaken under the auspices of Hie Royal Agricultural Society. The author also conceived that the line of research which he had pursued might be useful as an illustration of that system of scientific book-keeping, which he had proposed at a former meeting of the Association, at once as an useful article to the agricultural student, and as a means of introducing greater precision into the conduct of our expeiiments in such subjects.