EXHAUSTION OF THE SOIL.

Western Star, Issue 374, 21 August 1880, Page 5 (Supplement)

EXHAUSTION OF THE SOIL.

In the Agricultural Gazette of May 31, I noticed an extract from an American paper

relating to the subject of exhaustion of the soil. The editor writes, that he has been asked to furnish statistics of the average wheat crop in the States for forty years, in order to show whether there has been any decline in produce due to exhaustion. These statistics, he says, are not ’’forthcoming; but, from the average yields of wheat in New York, Pennsylvania, and Ohio, during twelve given years (between 1862 and 1878) taken from the reports of the Department of Agriculture, the editor thinks there is “strong presumptive evidence that land is not decreasing in fertility.” It is now exactly forty years since we began to exhaust a portion of one of my fields by continuous nnmanured wheat crops, it may therefore he interesting to show the evidence we are in a position to bring forward upon the subject of exhaustion as regards the soil at Rotha rusted. The produce of this unmanured land, I may mention, is one of the elements upon which we estimate the yield of the wheat crop of the country, each season, and we have recently submitted the figures to careful consideration in order to ascertain to what extent the produce now obtained has been affected by exhaustion. It would appear probable that the annual decline due to this cause may amount to from one quarter to one-third of a bushel of wheat per acre per annum. If we take the smaller quantity and add to it the ordinary proportion of straw, the result would he equivalent to about 40 lbs of produce; and, as there is hut little doubt that the hulk of the organic matter of the crop is obtained rom the atmosphere, the amount of matter annually taken from the soil by this 40 lbs of produce (including the nitrogen it contained) would be between 2 lbs and 3 lbs. The evidence derived from other experiments in the same field proves that the decline in produce is due to an absence of nitrogen, as also that the minerals are ih excess, but the actual amount of nitrogen that this 40 lbs of produce would have contained would be less than \ lb in weight! It will, I am afraid, appear to your agricultural readers something like an absurdity to suppose that lb, more or , less, of any substance upon an’acre of land, could have an appreciable influence upon a crop, I may observe, however, that this annual decline of 40 lbs of produce, small as it appears to be, amounts in forty years to 10 bushels per acre. !

Analyses of the soil made at different times show that the nitrogen is declining, and as the free use of minerals in an adjoining experiment does not prevent the decline of the crop, we can come to no other conclusion, than, that the gradual decline in the produce is due to the diminishing amount of nitrogen in the soil.. , ,

As far sis the wheat crop is concerned, it would appear that the total amount of produce to be obtained from any soil must depend very much upon the stores of nitrogen already in the land. It is true that the soil obtains a certain amount of ammonia from the rainfall, and it probably condenses more or less from the atmosphere; but, on the other hand, drainage' carries away every year more or leas nitrogen in the form of nitric acid ; and it is evident that the atmospheric supply, whatever it may amount to, does not suffice to prevent a decline of the crop ; it is therefore also evident that the source from which the forty crops obtained their supply, must have been the stores of nitrogen already existing in the soil when the experiment commenced ; further, it seems most probable that the yield of future crops will depend upon the amount of nitrogen liberated each year from the soil.

We have in these experiments a very interesting question opened in relation to the sources of fertility in soils, and exhaustion generally ; .it is, however, quite certain that the yield of the wheat crop in New York, Pennsylvania and Ohio, for the twelve years given in the American paper, could not possibly furnish any reliable information upon the subject,—J. B. Lawes.