Farm Manure. 



139 



the farm each year. The following three-year plan of rotation 

 will explain the above statement; corn, 1 year; grain, 1 year; 

 clover, 1 year ; the manure is applied to the clover sod. The fol- 

 lowing table brings out clearly the relation of plant food removed 

 by such a rotation as described above, and the quantity returned 

 by the application of 10 or 15 tons of farm manure of average 

 composition once in 3 years. No account is taken of losses by 

 drainage or the gain in nitrogen to the soil of probably 50 pounds 

 per acre, by the growth of the clover. 



"We see from this table that it would require once in 3 years 

 the application of about 15 tons of manure of average composi- 

 tion to replace the plant food removed by the three crops. 



Relation of manure to maintenance of fertility. At the Rot- 

 hamsted Experiment Station, England, experiments to determine 

 the relative value of farm yard manure and commercial fertilizers 

 have been carried on over a very long period of time. On certain 

 plots, crops have been grown continuously with no fertilizer, on 

 other plots with barn yard manure at the rate of 14 tons per acre 

 annually, and on still others, various combinations of commercial 

 fertilizers have been tested. The tests extend over 40 years and 

 are given in the following table as averages of five 8-year periods. 



