Weight of Dry Produce of Wheat Per Acre.
| Straw and Grain. | |
|---|---|
| 1863 | 9330 lbs. |
| 1879 | 3859 lbs. |
In order to ascertain the increase due to the nitrogen of the salts of ammonia or nitrate of soda, we must deduct from the crop the produce obtained, where mineral manures without nitrogen were used. In 1863 this amount was three thousand pounds, and in 1879 it was one thousand two hundred pounds. Deducting these amounts from the gross produce in each case, leaves six thousand three hundred and thirty as the produce due to the nitrogen in the season of 1863, and two thousand six hundred and fifty-nine as the produce due to the nitrogen in 1879.
But in each case we applied the same amount of nitrogen, eighty-seven pounds; and as the amount of nitrogen in a wheat crop, as carted from the field, contains less than one per cent. of nitrogen, it is evident that if all that was contained in the manure had been taken up by the plant, the increased crop should have weighed eight thousand seven hundred pounds instead of six thousand three hundred and thirty. Thus even in our best year, some of the nitrogen applied failed to produce growth; and when we come to the bad year we find that only twenty-six and a half pounds were taken up out of the eighty-seven pounds applied, thus leaving more than two-thirds of the whole unaccounted for.
Seasons are only occasionally either very bad or very good. What we call an average season does not differ very much from the mean of the best and worst years, which in this case would be represented by a crop of four thousand four hundred and ninety-four pounds, containing nearly forty-five pounds of nitrogen. I may say that, although I have employed one per cent. to avoid fractions in my calculations, strictly speaking three-quarters of a per cent. would more nearly represent the real quantity. If, however, on the average, we only obtain about forty-five pounds from an application of about eighty-seven pounds of nitrogen, it is evident that not more than one-half of the amount applied enters into the crop.
Now in dealing with a substance of so costly a nature as ammonia, or nitrate of soda—the nitrogen contained in which substances cannot cost much less than twenty-five cents per pound by the time it is spread upon the land, it becomes a question of importance to know what becomes of the other half, or the residue whatever it may be, which has not been taken up by the crop. Part is undoubtedly taken up by the weeds which grow with the wheat, and after the wheat has been cut. Part sinks into the sub-soil and is washed completely away during the winter.
I, myself, am disposed to think that the very great difference in the size of the Indian corn crops, as compared with the wheat crops in the States, is partly accounted for by their greater freedom from weeds, which are large consumers of nitric acid, and, in the case of the wheat crop, frequently reduce the yield by several bushels per acre. It must, however, be borne in mind that, though the wheat is robbed of its food where there are weeds, still if there were no weeds, the amount of nitric acid which the crop could not get hold of, would, in all probability, be washed out of the soil during the ensuing winter. I come to the conclusion, therefore, that the nitrogen alone, which would be required to produce one bushel of wheat, would cost not much less than fifty cents; and that, in consequence, wheat-growing by means of artificial manures, will not pay upon very poor land.
I have said that the land, about which I was consulted, had not been plowed for several years, and that although nature had done all she could to clothe the soil with vegetation, the most disheartening feature in the case was, the poverty of the weeds. A thistle may be a giant or a dwarf, according to circumstances; here they were all dwarfs. The plaintain, which I believe is sometimes sown in these districts for food, has a very deep root; here the plants were abundant, but the leaves were very small and lay so close to the ground, that, as the manager informed me, “the sheep were often injured from the amount of sand which they swallowed with the leaves when feeding.”
At Rothamsted, the analyses of the rain water passing through the ordinary soil of one of my fields, which has been kept free from vegetation, have shown that the amount of nitric acid liberated in a soil, and washed out each year, is very large. Taking the ten years during which these special experiments have been in progress, I should think that the loss of nitrogen would be equal to, or possibly exceed, the amount of that substance removed by the average crops grown in the United States.
The results obtained by the rain gauges, are further completely confirmed by those in an adjoining field, where wheat and fallow have been grown alternately for twenty-seven years. The liberation of nitric acid, during the year of rest, produced for a time a large growth of wheat, but it was done at a very great waste of the fertility of the soil, and the produce is now, in proportion, considerably lower than that grown on the continuously unmanured land.