CROP ROTATION 23 



seedlings do not grow so well the second time in the same 

 solution, although the nutrient constituents may be 

 maintained at the same concentration. Certain organic 

 compounds which have been isolated from the soil and 

 their formulae determined are demonstrated to produce a 

 toxic effect when added to a nutrient solution in which 

 young plants are growing. Those who have investigated 

 this subject most thoroughly believe that the accumula- 

 tion of toxic compounds in the soil is an important factor 

 in the rapid decline of crops growing continuously on the 

 same land. 



Aside from the question of crop yields there are other 

 reasons along the lines of economy and convenience which 

 make it preferable to rotate a series of crops on dif- 

 ferent divisions of the farm rather than devote separate 

 fields to the growth of each crop continuously. Yet it 

 is seldom important to follow year after year a rigid rota- 

 tion. In fact, if a four or six year rotation is adopted, one 

 is likely, for some good reason or another, to make some 

 little change in his plans before more than one cycle of 

 the lotation has passed. With the frequent change in 

 value of crops and knowledge of important new crops 

 come changes in the rotation system. It is important 

 always to have a well-planned rotation under way, but 

 one should not hesitate to make changes that are in the 

 line of progress, to substitute a different crop for one that 

 has started off poorly, or occasionally increase the acreage 

 of a money crop at the expense of a less profitable one, 

 even though by such changes he may never actually 

 complete a perfect cycle of the rotation planned. 



23. Planning a rotation. — Any farm of good size 

 may have two, three, or more different rotations in prog- 

 ress, having a series of fields set apart for each rotation. 



