QUESTIONS 73 



Since roots extend into the deeper layers of soil, the subsoil is 

 to be regarded as a portion of the feeding ground for crops. Sub- 

 soils which are porous, permiting air to enter freely, may contribute 

 considerable amounts of plant-food elements to crop needs. The 

 fact that in humid climates most feeding roots are to be found 

 in the tilled portion of the ground, especially in the heavier soils, 

 explains why the draft upon the surface layer is much greater. 



Exercises. Compare an average yield of one of your local crops with 

 the table of plant-food elements removed, and determine; the amount and value 

 of plant-food elements removed from one acre. 



2. Minor crops may be considered also. 



Projects in Crop Adaptations. On a given field lay off small strips along 

 one side where the soil is probably of average fertility. On these strips grow 

 several useful crops as oats, barley, rye, wheat, buckwheat, millet, sorghum, 

 corn, cowpeas, soybeans or others. Compare them in growth, yields, and study 

 their probable needs. Keep careful records and notes and from the trials 

 determine what crops are best suited to the soil. 



Buckwheat Project. Try the growth of buckwheat on poor soil and thus 

 decide whether it would aid in production of green manure for the improvement 

 of that soil. 



Projects on Poor Soil. Compare the growths of barley with oats on 

 poor soil. Determine which requires the richer soil for good returns. 



2. In like manner compare barley with rye, and compare oats with rye. 



3. Any one of these as barley (or other crops) should be grown on both 

 rich and poor soil. This will demonstrate the needs of the crop. 



Field Studies. Make studies of soil conditions in a field where grain 

 lodges badly. 



2. Collect whole plants of a number of grasses, legumes, grains, etc. 

 Compare their root systems to determine this depth of feeding. 



QUESTIONS 



1. Name the elements most commonly studied in relation to crop production. 



2. Are soil particles plant foods? What was taught at one time? 



3. In what forms do plants secure the elements they require? 



4. How much nitrogen, phosphorus, potassium and calcium is removed from 



one acre by a 65-bushel corn crop? By a 50-bushel oat crop? 

 By a 1500-pound tobacco crop? Which of these crops require the 

 most calcium? 



5. A man grew the following crops on an acre: 1st year, cabbage yielding 



15 tons; 2d year, corn yielding 12 tons; 3d year, barley yielding 40 

 bushels. How many pounds each of nitrogen, phosphorus and potas- 

 sium were removed from that one acre during those three years? How 

 much if there were 20 acres? 



6. A ten-acre field was cropped three years as follows : 1st year, sugar beets 



averaging 12 tons per acre; 2d year, wheat averaging 25 bushels; 3d 

 year, corn yielding 52 bushels per acre. How many pounds of each of 

 the important elements were removed from this field during these 

 three years? 



7. How much nitrogen is required to grow a bushel of corn? A bushel of oats? 

 In what part of crops is found the most phosphorus? The most potassium? 



The most calcium? 



