The effect of fertilizers on the yield and quality of sweet potatoes

Abstract

The effects of major and minor fertilizer elements on yield and carotene and starch content of sweetpotatoes were investigated, and the following conclusions were drawn: 1. Excessive quantities of nitrogen decreased sweetpotato yields. The use of 82 pounds of N per acre was the highest rate needed in the four experiments. 2. The use of phosphorus fertilizers with rates of applications as high as 200 pounds of P₂O₅ per acre had no effect on yields. With the use of 300 pounds P₂O₅ per acre, a yield increase was obtained only on the Lares clay at Corozal. 3. No consistent increases in yields were obtained with increasing potassium additions to the soil. There was a yield response to the potassium applications on the Cataño loamy sand of the Loiza I experiment. There was no significant response to potassium on Lares clay at Corozal, on Cataño loamy sand at the Loiza II experiment, or on the Sabana Seca sandy clay loam at Sabana Seca. 4. The yields of marketable sweetpotatoes were increased by the use of potassium on Cataño loamy sand at the Loiza I experiment. 5. Filter-press cake used alone gave low yields on Cataño loamy sand. The use of filter-press cake plus fertilizer gave good results both on the heavy Lares clay and on the Cataño loamy sand. 6. The yields of sweetpotatoes were measurably affected by the use of lime in the acid Lares clay. The application of lime to raise the pH gave increased yields with increased soil pH. The Sabana Seca experiment showed yield increases from the use of calcium sulfate (gypsum). 7. No consistent yield increases were obtained from the use of magnesium oxide. 8. The use of boron gave significant yield increases in the Sabana Seca and Corozal experiments, but not in the Loiza experiment. 9. No yield increases occurred with the use of manganese and copper. 10. There was no effect on starch content attributable to any major- or minor-element treatment. 11. The use of nitrogenous fertilizers influenced the carotene content of the sweetpotatoes; where nitrogen applications produced yield increases there were also increases in the carotene content. 12. Increases in carotene content were obtained with phosphorus only when the yields were significantly increased by addition of phosphorus. 13. No significant effect on carotene content was noted for potassium, except for a decrease in one experiment on a Cataño loamy sand. 14. The carotene content of sweetpotatoes was measurably affected by the use of calcium carbonate on acid soils (pH 4.5). Increases in pH were accompanied by increases in carotene content. In most cases where yields were increased by liming, the carotene content increased appreciably. 15. No responses were obtained from the use of boron, magnesium, copper, and manganese on the carotene content of sweetpotatoes. No effects were obtained on yields by use of these elements, except boron on a Sabana Seca sandy clay. 16. A recommendation is made for sweetpotatoes of 600 pounds of a 8-6-16 formula per acre. 17. The yields of sweetpotatoes compared favorably with yields for the leading sweetpotato-producing States of Louisiana and North Carolina. 18. Yields were increased by planting in the shorter days of winter as compared to the longer summer days. Carotene content, however, was increased with spring as compared to winter plantings.