THE ROTATION OF FARM CROPS 61 
as good a money crop as oats and has a big advantage over 
oats since it is building up the land instead of running it 
down. 
Rotation IMPROVES THE PHysicAL CONDITION oF THE SoIL 
AND INCREASES ITS FERTILITY 
The roots of the different crops are of great aid in pul- 
verizing (and fining) the soil. When deep rooted legumes are 
grown in rotation they utilize and bring to the surface plant 
food which lies beyond the reach of the short rooted cereals. 
‘When the roots of these legumes decay this nitrogenous plant 
food is left in the surface soil to be used by the succeeding 
grain crops. 
While there is a slight improvement in the physical con- 
dition of the soil when different grain crops alone are rotated, 
the greatest benefits of rotations are derived from the legumes 
included. For this reason at least one leguminous crop 
should be included in every crop rotation. 
The increase in the fertility of the soil as a result of crop 
rotations is due entirely to the additional nitrogen stored in 
the soil by the legume. If the leguminous crop is taken off 
the land each time it is grown it is doubtful if any nitrogen 
is added. When soy beans and cowpeas are grown and the 
hay is taken off and no manure is returned it is believed that 
nitrogen is actually taken from the soil rather than added. 
If soy beans and cowpeas are grown for the seed, the straw 
should be returned to the land after the seed has been 
threshed out. Since a good supply of nitrogen is essential 
for the profitable growing of grain crops, and the only cheap 
way to get this nitrogen is by growing legumes, every effort 
should be made to leave as much of the crop on the land 
as is possible. 
We wish to say, right here, that crop rotation alone will 
