66 CULTIVATION METHODS AND ROTATIONS FOR GREAT PLAINS. 



ble amount of plant food unless it is plowed under for green manure 

 or is allowed to decay upon the surface. But, nevertheless, certain 

 crops leave the land in poorer condition for a subsequent crop of 

 some particular kind than it was before they were raised. These 

 are designated as " exhaustive" crops, and include wheat, oats, bar- 

 ley, rye, and millet. Their ill effects upon subsequent crops may be 

 due to a reduction of the available plant food ; to an increased growth 

 of weeds, fungi, or injurious insects ; to a change in the physical con- 

 dition of the soil, particularly its water content; or to a reduction in 

 the quantity or activity of beneficial lower organisms. " Restora- 

 tive" crops have the opposite effect. They leave the soil in better 

 condition for certain crops than it was before. Among restorative 

 crops may be mentioned corn, potatoes, beans, peas, clover, alfalfa, 

 most cultivated crops grown in the Great Plains, and perennial grasses 

 grown for meadow or pasture. " Intermediate " crops are those that 

 have, in some respects, a beneficial effect upon certain crops which 

 follow them, while in other respects their influence is detrimental. 

 The sorghums, cane, milo, and kafir belong to this class. Their ben- 

 eficial effects are due to the fact that, like all cultivated crops, they 

 reduce the amount of weeds in subsequent crops; their detrimental 

 effects upon subsequent crops seem to be due to the fact that they 

 are able to exhaust the soil moisture to a greater extent than any 

 other crops commonly grown in the Great Plains. 



(2) In addition to and in a certain measure independent of the 

 above-mentioned classification is the problem of crop sequence, or 

 the relations which two crops bear to each other independent of any 

 apparent difference in the conditions of the soil brought about by 

 their growth. For instance, two crops may be equally exhaustive, 

 but when grown consecutively, better results will be obtained if they 

 are grown in one sequence than when the opposite sequence is fol- 

 lowed. Oats following wheat generally give better results than 

 wheat following oats. Or, again, a restorative crop may have a 

 more beneficial effect upon some certain exhaustive crop which fol- 

 lows it than it has upon some other equally exhaustive crop. Wheat 

 generally responds more readily to the effects of a corn crop than 

 does oats. 



(3) The effects of the preparation of the land — time and depth of 

 plowing, disking instead of plowing, the amount of harrowing and 

 packing of the seed bed, etc. — depend not only upon the crop for 

 which preparation is being made, but also upon the crop grown the 

 preceding year and the previous soil treatment. 



(4) The selection of the varieties or strains of the crops grown 

 which are best adapted to the particular locality and to the rotation 

 planned and the determination of the quantity of seed to use and of 

 the method and time of seeding are also of great importance. 



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