ROTATION OF CROPS. 185 



PROBLEMS. 

 (Based on the foregoing plan of cropping on 160 acres.) 



1. How many pounds of each of the three kinds of plant foods 

 nitrogen, phosphoric acid and potash are removed per acre annually 

 according to the table given. 



2. If 50 head of stock including cattle, horses, sheep and hogs 

 produce 360 tons of manure, .6 per cent nitrogen, .3 per cent phosphoric 

 acid and .7 per cent potash, what is the total amount of each of these 

 plant foods produced per acre annually? 



3. If the 30 acre field of corn receives 360 tons of manure and 

 we calculate the value of roots of grass and clover, green material plowed 

 under and manure from pasturing at 80 pounds of nitrogen, 40 pounds 

 of phosphoric acid and 75 pounds of potash, what is the total amount 

 of each of the three elements nitrogen, phos. acid and potash received 

 every five years? 



4. Find the difference between the amount of plant food of each 

 kind removed by crops as given in the table and the amount restored 

 by manures, roots, plants, etc. 



5. Mix a fertilizer in the right proportion and amount to balance 

 the losses in fertility each year, occasioned in the foregoing method of 

 cropping and feeding and manuring. 



Facts About Rotation. 



1. Alfalfa, clover, soy-beans, cowpeas, vetch, crimson clover, or 

 some other legume should be a part of every crop rotation. 



2. Legumes, livestock, fertilizers, with a judicious rotation of crops 

 will build up a run-down soil. 



3. When clover fails we should sow some annual of the legume 

 family that will keep up the rotation as a nitrogen gatherer. 



4. Grain crops remove a large amount of phosphorus. 



5. Root crops remove much potash. 



6. Hay crops remove much nitrogen. 



7. Plants with shallow roots should follow roots that feed deep in 

 the soil. 



8. Non-cultivated crops should follow cultivated crops. 



9. Nitrogen producing crops should follow potash-using crops. 



10. Alfalfa, the true clovers, cowpeas, soy-beans, vetches, Japan 

 clover, and beans are nitrogen producing crops. 



11. Legumes leave in the soil more nitrogen than they take out, while 

 other crops use up nitrogen and do not gather any. 



12. The abundant use of fertilizers is often depended upon for a 

 time to take the place of crop rotation. 



