No. 7. DEPARTMENT OF AGRICULTURE. 453 



while the chief effect of the clover has been to extract phosphorus 

 from the soil for its own growth and for the use of succeeding crops. 



There is another point to be considered in reference to nitrogen. 

 On land that is capable of furnishing sufficient nitrogen for even a 

 5U-bushel crop of corn, the clover crop will undoubtedly draw a third 

 of its nitrogen from the soil and not more than two-thirds from the 

 air. Consequently, since two-thirds of the nitrogen in the entire 

 plant is removed in the tops, the roots and stubble will leave no more 

 nitrogen in the soil than the plant takes from the soil. How, then, 

 can we maintain the supply of nitrogen in the soil? By plowing 

 under sufficient clover or by applying sufficient farm manure, or bet- 

 ter, by both of these means. 



If all the crops grown in rotation are fed, including the corn 

 stalks, containing a total of 526 pounds of nitrogen from four acres, 

 and if three-fourths of this, or 81)5 pounds, are returned in the ma- 

 nure, we have sufficient to replace the 086 pounds removed in the 

 corn and oat crops and we may assume that the 160 pounds removed 

 by the clover came from the air. Of course some additional nitro- 

 gen will be saved in the straw and stalks which are used directly for 

 bedding, and not for feed. 



How shall the grain farmer maintain the nitrogen in his soil? 

 Possibly this can be done by growing an additional legume catch 

 crop in the corn and plowing under everything produced except 

 the grains and the clover seed, preferably only one corn crop being 

 grown in the rotation. 



The problem of maintaining the nitrogen becomes easier if we 

 extend the rotation to include about two years of pasture, using a 

 mixture of red clover, alsike, timpthy and red top instead of seed- 

 ing red clover only with the oats. In this case three grain crops, 

 as corn, oats and wheat, or corn two years and oats one year, could 

 be grown during the six-year rotation, the land being kept in meadow 

 or pasture one-half the time. 



It is one thing to say that farm manure has a value, but quite 

 another thing to say what that value is or to what it is due. 



The positive or intrinsic value of farm manure lies in the amounts 

 of valuable plant food which it contains. It also possesses an im- 

 portant indirect value as a soil stimulant, due to its power as it 

 ferments and decays, in contact with the soil, to liberate from the 

 soil plant food that would not otherwise become available so quickly. 

 There is still another distinct value in farm manure due to the fact 

 that it makes the soil more porous and spongy and thus increases 

 the power of the soil to absorb and retain moisture and to resist 

 surface washing. In other words, this third value of farm manure 

 is due to improvement in physical condition. 



The value of farm manure for its physical improvement of the 

 soil is commonly fully appreciated and frequently even overestimated 

 by popular agricultural writers, while its value for plant food which 

 it supplies and that which it liberates from the soil is sometimes 

 almost ignored. 



There is no good excuse for erroneous teaching regarding these 

 different values, because there exists a vast amount of positive in- 

 formation both from ^practical experience and from exact scientific 

 investigations. 



Thus, organic matter from peat beds hauled out and spread on the 

 land and incorporated with the soil produces no such effects on crop 



