278 Bureau of Farmers' Institutes. 



In working by a system of crop rotation, certain general facts 

 should be kept in mind and carried into practice, principal among 

 which are the following: 



(a) Use of Remains of Preceding Crop. — The system of rota- 

 tion should be such as to utilize to the best advantage any plant- 

 food material furnished the soil by the preceding crop. Thus, 

 after a crop of clover, it is better to grow wheat and then oats 

 rather than the reverse, because the wheat has less power than 

 oats to utilize plant food. If oats were grown first, wheat might 

 be at a disadvantage unless additional plant food were furnished. 

 In general weak-feeding crops, unless specially fed, should pre- 

 cede strong-feeding crops in rotation, so that the former may 

 have the first chance at the more available forms of plant food. 



(b) Keeping Soil in Good Mechanical Condition. — Each class 

 of crops exercises a specific action upon the mechanical condition 

 of soils. Grass crops tend to make a soil compact; grain and 

 hoed crops tend to make the soil open and porous. It is desirable 

 that these conditions should be gradually alternated somewhat. 

 The amount and frequency of loosening and compacting must 

 depend upon the character of the soil. Sandy soils need more 

 of those crops that compact, while heavy clay soils need those 

 crops that will keep it more open. Rotation of crops should have 

 reference to these conditions and aim at the best mechanical con- 

 dition. 



(c) Alternation of Deep-Hooted and Shalloiu-Booted Crops. — 

 By including in a system of rotation crops that have both deep 

 and shallow root systems, the plant food is not taken entirely from 

 the surface soil but more or less from the subsoil. By such treat- 

 ment the soil is exhausted less quickly and requires less frequent 

 applications of plant food. Then, again, in many soils the potash 

 and lime are largely in the subsoil, the phosphoric acid and nitro- 

 gen being mainly in the surface soil. The growing of deep-rooted 

 crops also exercises a beneficial effect upon the mechanical con- 

 dition of the soil. 



(d) Alternation of Nitrogen-Gathering and Nitrogen-Consum- 

 ing Crops. — The value of nitrogen-gathering crops as green man- 

 ures has been already considered. In a four or five-year rotation 

 system, the use of a leguminous crop like clover will, with one 

 good application of stable manure, maintain the soil nitrogen un- 

 diminished. In all systems of rotation some nitrogen-gathering 

 crop should be included as an absolute essential. 



