84 AGRICULTURE 



dred plants, and the grasses that form a sod or dense 

 covering over the entire surface. The surest and cheapest 

 way for the farmer to enrich his land and to make 

 larger profits in farming is by constantly adding vege- 

 table matter. 



Sale of plant-food in crops. If a farmer every year 

 hauls crops of grain, or hay, or potatoes from his field with- 

 out putting anything back, there will come a time when he 

 will say that the field is too poor to cultivate. Crops differ 

 greatly in the kind and amount of plant-food they remove 

 from the soil. The lint of cotton and the sugar of sugar 

 cane consist almost entirely of materials drawn from the 

 air, and so these products remove almost no plant-food. 

 Yet cotton may make the soil poorer because its clean cul- 

 tivation causes the loss of vegetable matter; because its 

 seed removes considerable plant-food; and most of all, 

 because it leaves the land without living roots during the 

 winter, and thus permits the rain to leach and to rob the 

 soil. Sugar cane may be an exhausting crop because the 

 stalks that are carried trom the field contain much plant- 

 food and because the leaves are generally burned. This 

 does not mean that exhausting crops should not be grown, 

 but that something must be returned to the land in exchange 

 for what is removed. 



Lack of drainage makes soils unproductive. All the 

 causes of soil-impoverishment mentioned are due to sub- 

 stances taken from the soil. They have all been forms 

 of subtraction. There is, however, an addition to the 

 soil that may make it poor. Too much water injures 

 (he soil and the crop if it is not drained away either by 



