above mentioned crops the following year. If it is used in this way, there is no danger of inducing rank growth.

Amount to Apply. In a few instances manures are wasted by too liberal use. For ordinary farm crops it is not customary to use more than eight to ten tons

Manure spread on the snow. There is no objection to this method of handling manure if the ground is fairly level and the snow not too deep. It is certainly better than to allow the manure to remain exposed in the barnyard

per acre, and on general principles it may be stated that somewhat frequent light dressings pay better than very large ones given at long intervals. On the other hand, the amount of manure produced on the average farm is so small when compared with the land to be fertilized that it would be utterly impossible to spread it over all the farm yearly. For this reason it is a good plan to apply the manure to one crop in a rotation, thus covering only a fraction of the farm each

year. The following rotation which is used by a well known dairyman is an example that will explain the last statement: Corn one year, grain one year, clover and timothy two or three years. The manure is applied the last year the field is in sod. A second rotation in common use is as follows: Corn (manured) grain, grain, clover. Chemical fertilizers are often used on one or both grain crops as well.

CHAPTER XVI

BARNYARD MANURE AND THE MAINTENANCE OF FERTILITY

Manure as a Crop Producer.-Some difference of opinion exists among farmers as to the relative value of barnyard manure and commercial fertilizers for crop production, but it is worthy of note that those who are most diligent in caring for the manure have most faith in its worth as a fertilizer. The fact that barnyard manure has been used so universally by agriculturalists for so many centuries is one of the strongest arguments in its favor. That the popular estimate of its value is established by scientific experiment is well shown by investigations carried on at Rothamsted. On certain plots, as has been mentioned, crops have been grown continuously with no fertilizer of any kind added, on other plots barnyard manure at the rate of 14 tons to the acre has been used every year, and on still others various combinations of commercial fertilizers have been tested. The following table gives the yields of barley and wheat from the unmanured plots, the plots dressed with barnyard manure, and the highest results obtained from the use of any combination of fertilizing materials. The tests extend over 40 years, but to shorten the table the results are given here in averages for five eight-year periods. (Fractions have been omitted.)

It will be seen that while both the fertilized plots gave much larger yields than the one receiving no addition of plant food, there is practically no difference between the plots dressed with barnyard manure and the best commercial fertilizers. This test is hardly fair to the barnyard manure as the quantities of commercial fertilizers applied were far in excess of anything used in general practice; the amount of nitrogen added to the wheat, for instance, being equivalent to that contained in 800 pounds of nitrate of soda, which would cost practically as much as the wheat would. bring on the market. In all probability, if these experiments had been conducted in this country the showing would have been more favorable to barnyard manure. It has been explained that the materials in the manure must undergo nitrification before the nitrogen.

Barnyard

Manure

Commercial

Fertilizers

becomes available to the plants and this process takes place so much more rapidly in this country than in England that it is easy to believe better returns might be obtained from barnyard manure under American conditions.

Lasting Effect of Manure.-Barnyard manure differs from other fertilizers in its lasting effect when applied to the soil. At Rothamsted, in connection with the above experiment, one plot was manured annually for 20 years and then received no manure for the next 20 years. In the accompanying table are given the yields of barley in averages for five year periods on the plot which was never manured, and the plot that had been manured the previous 20 years. The figures given for the second plot represent the effect of the residual manure, as no fertilizer was added during the period covered by the table.

The table shows that the effect of the manure was perceptible in yield for at least 20 years after the last application. It is more than likely that the more rapid rate of nitrification in this country might materially shorten the period in which the lasting effect of the manure would be observable, and perhaps the influence of the residual manure would have disappeared in a shorter time than twenty years.