Field studies were conducted to evaluate the effect of various fertilizer placements on nutrient uptake, growth responses, storage root yield and leaf elemental concentration of Whatley/Loretan sweetpotato [Ipomoea batatas (L.) Lam.]. Vine cuttings were transplanted into 6.1 m rows with 0.3 m in-row spacing in a randomized complete block design with four replications. The fertilizer placement treatments comprised broadcast (Br), banded at two different widths (Ba), side dressing (Sd) or applied in various combinations of the above, and an untreated check. Fertilizer rates were 135, 35 and 133kg.ha-1 each of N, P and K based on soil test. At nine weeks after planting, the fifth fully expanded leaf from the tip of five plants was collected and analyzed for elemental concentration. The plants were harvested 101 days after transplanting and biomass data were collected. Vine yield for all placement treatments was equal to or exceeded that of the full rate broadcast. Yield of US # 1 roots was increased 78% and 72%, respectively, when 2/3 of the fertilizer was banded and tended to increase total storage root yield compared to the same, full or 2/3 the rate broadcast. Leaf N was highest with 1/3 Ba at planting with two side dressings, while leaf P was reduced by all treatments compared to the check. Leaf K was highest with 2/3 the rate Br at planting. Storage root N was lower than foliar N while root K increased with 1/3 Br combined with 1/3 Ba. Root Ca, Mg, Fe and B were not significantly affected by placement. Root Mn was lower than foliar Mn suggesting that sweetpotato distributes more Mn to foliage relative to storage roots. Generally, these results suggest that placement rather than quantity of fertilizer applied enhanced yield and elemental concentration.
Keywords: Broadcast fertilizer, Ipomoea batatas, banded fertilizer, side-dressing, elemental concentration, storage roots, plant nutrition