Not only is there general accordance in the character of the results in different localities, when the averages of a number of years are taken, but the noneffect of the residue from previous application of ammonium-salts is as marked in the sandy soil at Woburn as in the very different soil at Rothamsted. Reference to Table X. will illustrate this. Stackyard field, Woburn, received mineral manure, and ammonium-salts=86 lbs. nitrogen, for five successive years. The field was then divided, one portion receiving the same manure as before, and the other the mixed mineral manure, but no nitrogen. In the next year, 1883, the portion which had received nitrogen in the previous year received mineral manures only, and conversely the other portion, which had received mineral manures only in 1882, received both mineral manure and ammoniumsalts. It is seen that in each year, 1882 and 1883, the portion which received the nitrogenous manure yielded large crops (434 and 45 bushels); whereas, the portion on which mineral manures alone succeeded ammonium-salts and large crops, yielded very small crops-13 and 17 bushels, respectively, against 143 and 17 bushels on the plot where the same mineral manures were used year after year. It is thus seen that there was no available and effective residue where the ammonium-salts had previously been applied. It may be stated, however, that in 1884 there was notable effect from unexhausted residue of nitrogenous manure; the explanation probably being that there had been very little rain, and consequently very little loss by drainage during the winter of 1883-4.

TABLE X.-Wheat grown year after year on the same land. Stackyard

Harvests.

Field, Woburn.

Dressed Grain.

Bushels.

1 Mixed Mineral Manure alone. 2 Mix. Min. Man. and Ammonium-Salts=86 lbs. N.

Having illustrated the soil conditions necessary for the growth of wheat, it will be well to call attention to one practical application of these long-continued field experiments. For thirty-two years (1852–83) an estimate has been made of the average produce of wheat per acre in the United Kingdom, based upon the yield at Rothamsted on the unmanured, the farm-yard manured, and three of the artificially manured plots taken as one. From this the total yield of the country has been calculated; to this the imports have been added, and the quantity required for seed deducted, the final figure showing the total amount available for consumption, and from this the consumption per head of the population has been reckoned. It may be said at once that these results proved to be very near the truth. But the point of interest to a wheat-growing and wheat-exporting country like America is, the evidence which the results afford as to the constantly increasing requirements of a largely importing country like Great Britain.

The following table (XI.) shows that during the thirty-two years, 1852-3 to 1883-4 inclusive, the area under wheat in the United Kingdom has been reduced

by about one-third.

The average yield per acre is estimated at 28 bushels, but owing to recent bad seasons, the average for the whole period of thirty-two years was only 27 bushels, that for the first sixteen years having been 281, but that for the second sixteen years only 25. Thus there has not only been a reduction in area under cultivation, but in yield per acre, also; this, however, is probably temporary, whilst the reduction in area will doubtless continue.

TABLE XI.—Particulars of Home Produce, Imports, and Consumption of Wheat, in the United Kingdom-32 years, 1852-3 to 1883–4.

The great increase of population which has taken place within the period covered by the table, has, of course, necessitated greatly increased consumption, and the comparison of the home production and the foreign importation for successive periods, becomes of much interest. The table shows that the average annual consumption over the four successive periods of eight years each, increase as follows:

These amounts were supplied from home produce and importation as follows:

Thus, over the first eight years, only one-fourth of the wheat consumed was obtained from foreign sources, whilst over the last eight years, nearly twothirds of the entire consumption were imported. It is probable that the home produce will still decline, consequent chiefly on reduction of area under cultivation; whilst with increase of population, imports must increase, and doubtless our supplies will be largely drawn from this continent.

It has been stated that, excluding recent bad seasons, the average yield of wheat per acre of the old arab le soils of Great Britain, is twenty-eight bushels. Comparing this yield with that of the United States, as shown in Table No. XII, we find, on the authority of the U. S. Census Bureau, that the general average of localities and years is 11.9 bushels per acre, a yield which is not equal to that of the continuously unmanured plot at Rothamsted, and which is considerably less than half the average yield of Great Britain under ordinary cultivation. This may be partly due to a shorter period of growth, and to rapid maturing, or in some localities to deficiency of rain; but it is probably largely also due to want of sufficient labor to clean the land, and to consequent luxuriance of weeds.

Referring to the table, we find the general averages of the different sections of the States ranging from 15.1 bushels per acre in New England, to 7-3 bushels in the South Atlantic and Eastern Gulf States. Even the Northwest and Minnesota, including much prairie land, give very meager average produce for such rich soil. So long as wheat is grown on such lands under the conditions frequent, and indeed almost inevitable, in the case of new settlement,that is, growing it year after year, with deficient cultivation, luxuriance of weeds, and the burning of the straw,-only low yields per acre can be expected. The result is due to the fact that, under such conditions, fertility is cheap and labor dear. But with increased density of population, more mixed agriculture must be adopted. Stock must be kept, the farm kept freer from weeds, the

straw used instead of being burnt, and the manure from it, and from the consumed food, returned to the land. Then, and not till then, will the fertility of the rich prairie soils be conserved, and not wasted, as is too often the case under the necessities of the first breaking up, and the sparse settlement of the country. That your rich prairie soils can, and should, yield more produce than they do, is clear from the high yields obtained occasionally, under favorable conditions of cultivation.

TABLE XII.

Average yield per Acre of Wheat and Indian Corn in the United States. From Signal Service Reports. Six years, 1875–1880.

Turning to Indian Corn, Table XII shows that the yield of that cereal is very much higher than that of wheat; and the yield of nitrogen per acre in those corn crops would doubtless be much greater than in the wheat crops of the same localities. This is probably in part due to the high condition of the soil under which the crop is generally grown, corn generally following clover in the rotation. It is, however, doubtless in part due to the growth of corn extending much further into the late summer and autumn, the period during which nitridication is the most active in the soil, and when therefore the supply of nitrates to the plant will be greater under the same conditions of soil than in the case of wheat. This would be a very interesting subject for investigation, in the field and in the laboratory, tracing the nitrogen at various periods in the soil, in the plant, and in the drainage waters.

The following table (XIII) gives estimates of the yield of various crops on some Manitoba prairie soils:

TABLE XIII.-Estimates of the yield of various Crops in Manitoba. Summary of Statistical Returns-seven years, 1876-1882. Quantities in Bushels per Acre.

The above estimates are founded on the reports of numerous farmers, and it is seen that the average yield of wheat for seven years (1876-1882) is assumed to be twenty-nine bushels. This is, however, doubtless too high, even for exclusively virgin prairie soils, under the condition of cultivation incident to new settlement, and the result is probably accounted for by the fact that the records come chiefly from the more intelligent and better farmers. From returns since supplied to me from the Department of Agriculture at Ottawa, the average produce of wheat in Manitoba was, in 1880, 20.1 bushels, and in 1882, 24.0 bushels, instead of 29 and 32 bushels as above, whilst the average produce in 1883 is estimated at 21.8 bushels.

In connection with this subject of the average yield of wheat of different countries, it will be of interest to contrast the condition of soils of very different history, as to their percentage of nitrogen, and, so far as we able, of carbon also.

Table XIV (see next page) shows the characters in these respects of exhausted, arable soils, of newly laid down pasture, and of old pasture soils, at Rothamsted; of some other old arable soils; of some Illinois and Manitoba prairie soils; and lastly, of some very rich Russian soils.

From these results there can be no doubt that a characteristic of a rich virgin soil, or of a permanent pasture surface-soil, is a relatively high percentage of nitrogen and of carbon, and a high relation of carbon to nitrogen. On the other hand, a soil that has long been under arable culture is much poorer in these respects; whilst an arable soil under conditions of known agricultural exhaustion shows a very low percentage of nitrogen and of carbon, and a low relation of carbon to nitrogen.

Finally, it has been maintained by some that a soil is a laboratory, and not a mine. But not only the facts ascertained in our own and in other investigations, but the history of agriculture throughout the world, so far as we know it, clearly show that a fertile soil is one which has accumulated within it the residue of ages of previous vegetation, and that it becomes infertile as this residue is exhausted; and enormous as are the accumulations in the prairie lands of the American continent, it is still desirable to postpone, rather than to accelerate, the time of their exhaustion.