Genotypic variation for potassium uptake and utilization efficiency in sweet potato (Ipomoea batatas L.)

Field experiments were conducted to study genotypic variation for potassium uptake and utilization efficiency in sweet potato for 2 years. In 1997, a field experiment was conducted using 84 genotypes under no potassium fertilization. In 1998, two field experiments were carried out. In experiment I, eight good genotypes evaluated from the previous experiment were tested at two K application levels: 0 and 270 kg ha⁻¹ of K₂SO₄. In experiment II, three special varieties with respect to pigment content were tested at five K levels from 0 to 600 kg ha⁻¹. A split-plot design with three replications was used.Variation existed among genotypes in K concentration, accumulation and potassium efficiency ratio (KER) in the field. Among various plant parts, petiole contained the highest K concentration and storage roots had the highest K accumulation at maturity. These changed considerably with genotype and K level. KER had significant positive correlation with root weight per plant, root:top ratio and harvest index (HI); and significantly negative correlation with K concentration and accumulation in the roots or whole plant at maturity.Based on KER, genotypes were identified as efficient and inefficient in potassium utilization. Yield increased generally in all genotypes with K application. The increase, however, varied among different genotypes. It was also found from this study that the fertilizer level that gave the highest yield was K₂ which is 300 kg ha⁻¹ of K₂SO₄. The yield increase as a result of K application was mainly due to the increase in root:top ratio which led to greater amount of photosynthate translocation to the storage roots causing their increase in size.Most of the quality parameters tested increased with increasing levels of K nutrition. Root dry matter (%), Brix (%), carotene content, anthocyanin content increased with K application. The extent of increase, however, differed with genotypes. Protein content generally tended to reduce with increase in K level. The degree of reduction also varied with genotypes.