| Field 1. | Field 2. | Field 3. | |
| 1st year or 1905 | Cotton. | Oats, harvested in spring, followed by Cowpeas. | Corn, followed by oats, planted in fall. |
| 2d year or 1906. | Corn, followed by oats, planted in fall. | Cotton. | Oats, harvested in spring, followed by Cowpeas. |
| 3d year or 1907. | Oats, harvested in spring, followed by Cowpeas. | Corn, followed by oats, planted in fall. | Cotton. |
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 cowpeas to plow under. All cotton and corn refuse is plowed under.
What effect will such a system have on the conditions necessary for plant growth? Suppose we follow the crops on Field 1. 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.
Such a yield of crop would take from the soil the following amounts of plant food per acre:
| Nitrogen, pounds. | Phosphoric Acid, pounds. | Potash, pounds. | |
| Cotton (whole plant) | 103 | 41 | 65 |
| Corn (whole plant) | 84 | 26 | 61 |
| Oats (whole plant) | 32 | 13 | 27 |
| Cowpea | 78 | 23 | 66 |
Now suppose we sell the lint of the cotton, keeping all the rest of the plant, including the seed, on the farm and turning it back into the soil.