Sweet Potato (Ipomoea batatas) Fertilizer Trials on the Gazelle Peninsula of New Britain: 1954-1976.

Abstract

The influence of fertilizer on sweet potato yields was examined in 17 field and 6 pot trials on a young volcanic soil. Nitrogen (N) had the greatest effect on yield and it gave large yield increases, especially at grassland sites. In three fertilized plantings of a block cropped continuously with sweet potato (Soil Exhaustion Trial), however, nitrogen depressed tuber yield. It is suggested that different responses to N were due to varietal differences. Nitrogen increased top growth in all trials where this was assessed. Phosphate (P) improved top growth and yield in only a few trials. Negative responses to residual P occurred in most plantings of the Soil Exhaustion Trial. Large yield responses to applied and residual potash (K) fertilizer were recorded in the Soil Exhaustion Trial. Potassium did not affect top growth in any trial but it increased tuber number. No responses to other nutrients were recorded in field trials except a response to residual magnesium (Mg) in two plantings. In the pot trials there were top growth responses to N, P, K, Mg and manganese. Fertilizer (N-P-K or N-K) gave large yield increases in a rotation trial, especially in narrow rotations. A significant negative relationship was found between the magnitude of fertilizer responses and control yields. Soil analyses, fertilizer placement and the economics of fertilization are discussed. Recommendations for fertilizers for sweet potato are made for both grassland and former forest areas.