Tillage, Fertilizing and Rotation 119 



CONCLUSION 



In growing sweet potatoes, quality, which is measured 

 by size, shape and cooking, is a very important consid- 

 eration. These characteristics are largely influenced 

 by the soil, the rotation followed, and the fertilizer 

 applied. An abundance of phosphoric acid and potash 

 with smaller amounts of not too quickly available nitro- 

 gen are essential. A yield of 200 bushels of sweet po- 

 tatoes, not including vines, removes from the soil approx- 

 imately 30 pounds of nitrogen, 10 pounds of p^'hosphoric 

 acid and 30 pounds of potash. Fertilizers containing 

 a liberal supply of potash in comparison to the other 

 elements seem to give best returns under average con- 

 ditions, though clay soils do not respond so readily to 

 this element. In general, the best growers have found 

 a small amount of nitrogen and a larger percentage of 

 phosphorus and potash to give most profitable returns. 

 A quantity of each element somewhat in excess of the 

 actual amount removed from the soil by the plant should 

 be applied, as some will be lost by leaching. Twenty 

 pounds of pure nitrogen to the acre is the maximum that 

 should be used if high quality is not to be sacrificed to ex- 

 cessive yields. The New Jersey Station has found that 

 commercial fertilizers alone can be depended on to fur- 

 nish plant-food, but barnyard and green-manures are 

 valuable for supplying organic matter or humtts. Or- 

 ganic nitrogen is preferred to the more soluble forms. 

 Commercial fertilizer is best applied in the drill before 

 putting out the plants, while stable and green-manures 

 should be applied to crops preceding the sweet potatoes 

 in the rotation. Organic matter in the soil should be 

 well decayed. 



