Of the corn suppose we sell one-half the grain and keep the other half and the fodder for use on the farm.
Suppose the oats be made into oat hay and be fed on the farm and the cowpeas be turned under.
Assuming that the cowpeas take half their nitrogen from the air.
This will mean that in the course of three years we take out of the soil of each acre in the crops:
| Nitrogen. | Phosphoric Acid. | Potash. |
| 258 pounds. | 103 pounds. | 219 pounds. |
but we return to the soil in crop refuse and manure from the stock:
| Nitrogen. | Phosphoric Acid. | Potash. |
| 256 pounds. | 87 pounds. | 197 pounds. |
This assumes that we have taken from the farm in products sold:
| Nitrogen, pounds. | Phosphoric Acid, pounds. | Potash, pounds. | |
| Cotton Lint | 2 | 1 | 2 |
| Corn | 28 | 12 | 10 |
| Animal products | 11 | 3 | 10 |
| Totals | 41 | 16 | 22 |
The plant food charged to animal products is twenty per cent. of that in the grain and forage fed to the stock.