226 THE FIRST BOOK OF FARMING 



Each of these crops occupies one-third of the 

 farm each year, and yet the crop on each field 

 changes each year so that no one kind of crop is 

 grown on any field oftener than once in three years. 

 The cotton is grown for market, the corn partly to 

 sell, partly to feed, the oats to feed and the cow- 

 peas to plow under. All cotton and corn refuse is 

 plowed under. 



What effect will such a system have on the con- 

 ditions necessary for plant growth? Suppose we 

 follow the crops on Field I. Cotton, corn, and oats 

 are humus wasting crops but the pea crop which is 

 grown the third year is plowed under, and largely, 

 if not entirely, remedies the loss by furnishing a 

 new supply of organic matter, and the ill effects 

 which we noticed would follow the loss of organic 

 matter due to the continuous growing of cotton are 

 avoided, soil texture is preserved, soil ventilation is 

 not injured, and the power of the soil over water is 

 preserved. 



What is the effect on plant food in the soil? 



Before answering this question let us see what 

 amounts of plant foods these crops take out of the 

 soil. 



We will assume that the soil is a good loam at 

 the start and will produce : 



One bale of five hundred pounds of lint cotton 

 per acre, sixty bushels shelled corn per acre, thirty 

 bushels oats per acre, or two tons cowpea hay per 

 acre. 



