20 THE HANDBOOK FOR PRACTICAL FARMERS 



value of a ton of manure as an average for several rotations over 

 a long period of time has been about three dollars. At the same 

 station eight tons of manure applied on the corn and on the 

 wheat in a five-year rotation has given a gross return of four 

 dollars and sixtj^-nine cents per ton. 



The returns that may be expected from a ton of manure 

 depend upon the condition of the soil, the value of the crop and 

 the quantity of manure used. In general the largest returns per 

 ton of manure will be secured: (1) from soils that are deficient 

 in organic matter; (2) when used on crops of high value per 

 acre ; (3) when used in moderate quantities. Within reasonable 

 limits the smaller the application per acre the larger the returns 

 per ton of manure although the total acre value of the crop 

 increase will be less. For example, if one-half of a field is 

 manured at the rate of five tons per acre and the other half at 

 the rate of ten tons, the acre yield from the latter will be much 

 larger than from the former but the increase derived from the 

 ten-ton application will not be twice that received from the 

 lighter application. In general farm practice the use of from 

 five to ten tons of manure per acre on each of two non-legumes 

 in the rotation is about as much as can be used with profit. 

 These light applications can be made most effectively by the use 

 of a manure spreader. By the use of the spreader the labor cost 

 is materially reduced and the same amount of manure can be 

 made to go farther than when spread by hand and a more even 

 distribution is secured. 



For most soils the effectiveness of the manure is greatly 

 increased by re-inforcement with acid phosphate or with raw 

 ground phosphate rock at the rate of fifty to sixty pounds of 

 the phosphate for each ton of manure. This material may be 

 used in the stable under the bedding as an absorbent, or it may 

 be mixed with the manure in the storage shed or on the spreader 

 as it is being hauled to the field. 



Green manuring crops. — All of the methods, such as tillage, 

 drainage, etc., employed for making plant food materials avail- 

 able tend to decrease the amount of organic matter or humus in 

 the soil, because the conditions that are favorable for making 

 plant food available, also favor the decomposition of the organic 

 matter. The plowing under of green crops to restore the organic 

 matter and thus keeping up the fertility of the soil was advocated 

 by Roman writers more than two thousand years ago and has 

 been practiced by progressive farmers ever since. 



Two classes of plants are in conmion use for green manuring 



