already discussed) that in a system of strictly animal husbandry, where nothing is sold from the farm except animals or animal products, the fertility of the land may be maintained indefinitely without the purchase of fertilizers, provided the manure is properly utilized. This assumes, of course, that as nearly as possible the full value of the fresh manure is realized and that the losses, which have been discussed, are avoided. Not only may the fertility be maintained in this way but it may actually be increased, as has been demonstrated by a number of farmers.

It has been shown that where the crop is allowed to remain on the ground to decay, and become a part of the soil, the fertility of the land increases from year to year. The fact was also brought out that the soil contains large quantities of potential plant food, especially of the mineral elements and that each year a certain portion of this potential food is becoming available. The question that suggests itself is whether the food rendered available each year is sufficient to make up for the 20 per cent lost in feeding the crops to animals. There seems to be no reason to doubt that this is so in case of the mineral elements even if not true of nitrogen. The 20 per cent loss in feeding falls nearly altogether on the nitrogen while very little of the phosphoric acid and potash are lost; so that it is easy to realize that the supply of these two elements can be maintained by the use of the manure and a good system of tillage. The experiments at Rothamsted indicate that the growth of a crop of clover adds 75 pounds or more of nitrogen per acre to the soil, and consequently this suggests a method of replacing the nitro

gen lost through feeding. Taking all things into consideration, it is evident that under the conditions mentioned above it is possible to keep a farm fertile indefinitely through the use of the barnyard manure produced upon it, supplemented by good tillage and the growth of leguminous crops. This statement holds true only where no crop is sold. In case the crop is sold the entire amount of fertilizing ingredients that it contains is removed from the farm. Where the farmer depends for his profit on the sale of animals and animal products, however, there is no doubt that the fertility can be maintained in the manner described, assuming that the farm was in a fair state of fertility at the start. Where large amounts of concentrates are used, as is often the case in dairy farming, there should be an increase in the fertility of the farm if the manure is properly handled.

Effect of Style of Farming on Fertility.-The facts brought out by this discussion of the subject of barnyard manure must have made it apparent that the losses in fertility are much greater in any system of farming where the crops are sold from the farm than where some form of animal husbandry is followed, especially if no commercial fertilizers are used. To bring this point more concretely before the reader the following diagram adapted from a Minnesota bulletin is given here.

To obtain the data upon which this diagram is based, four farms were assumed each containing 160 acres. On the first farm nothing but grain was raised, and all sold from the farm. The second was about equally divided between grain and stock farming, and the third

and fourth farms were devoted exclusively to stock raising and dairying respectively. In the last two cases a small amount of the farm produce was exchanged for mill products, which accounts for the slight gain in phosphoric acid, but it was assumed that no other concentrates or fertilizers were used. The decidedly smaller loss of nitrogen on the second farm, and the actual increase of nitrogen on the stock and dairy farms are due to the fixation of nitrogen from the growth of clover. The figures represent the number of pounds of the fertilizing materials lost or gained on the farm ir. one year. No more striking illustration of the effect of the system of farming on the fertility of the land could be desired.