BOSSES AND GAINS BY THE SOIL 275 



ticularly when the soil is water-logged or receives excessive 

 quantities of manure. Considerable losses of nitrogen take place 

 in cultivated soils. 



Organic matter is lost from all cultivated soils by oxidation. 

 The factors which influence the oxidation of organic matter have 

 been discussed in a previous chapter. 



Gains of Nitrogen by Bacterial Action. Considerable amounts 

 of nitrogen may be assimilated by legumes in connection with 

 bacteria. Crimson clover, according to the New Jersey Station, 

 may take up 200 pounds nitrogen per acre per year. Similar 

 studies at the Delaware Station 1 with various legumes showed 

 the yields to range from 31 to 140 pounds nitrogen per acre. 

 Velvet beans gained 213 pounds per acre in Alabama experiments, 

 172 pounds in Louisiana, and 141 pounds nitrogen in Florida. 

 Cowpeas gained 70 pounds in Alabama, 2 and 35 per cent, was 

 left in leaves and stubble if the vines were mowed. Like results 

 with other legumes showed an average gain of 122 pounds 

 nitrogen per acre for sixteen States. 



It is believed by some that appreciable quantities of free nitro- 

 gen may be fixed by soil bacteria, which have no connection with 

 legumes, especially when the soil receives manure or other 

 vegetable matter for the bacteria to feed upon. This subject 

 requires further investigation. Bacteria which have this power 

 are certainly present in the soil, but to what extent they aid in 

 maintaining the supply of combined nitrogen in the soil, is not 

 known. 



Losses in Cropping. This is due to the removal of plant food 

 in that portion of the crop which is taken from the land. The 

 amount lost in this way varies largely, depending on (a) the size 

 of the crop, (b) the kind of crop, (c) the portion of the crop 

 removed, and (d) the treatment of the residual portion, besides 

 the various factors which influence the amount of plant food 

 taken from the soil by the crop. 



The fact that the amount of plant food removed depends 



1 Bulletin No. 60. 



2 Bulletin No. 120. 



