Basal application of equal ratio of citrate and water soluble potassium fertilizers is conducive to potassium accumulation across sweet potato growth stages and formation of tuber yield

Objectives Sufficient K nutrition across the whole growth cycle is a key measurement for efficient sweet potato production. We investigated the effects of different ratios of citrate and water soluble potassium fertilizers on the K accumulation and yield of sweet potato, in order to increase the potassium fertilizer use efficiencies and sweet potato yields.

Methods A field experiment was conducted in cinnamon soil at Ruyang of Henan province. The test citrate and water soluble potassium fertilizer was silicon potassium fertilizer (K₂O 25%, SiO₂ 15%, CaO 14%) and potassium sulfate (K₂O 52%). Under the same total K₂O rate, five water and citrate soluble potassium fertilizer ratio treatments were set up: T1 (100% : 0%), T2 (75% : 25%), T3 (50% : 50%), T4 (25% : 75%), and T5 (0% : 100%), taking no K application as control (CK). At the 30, 60, 90, and 120 days of transplanting, plants were sampled for the determination of stem length, biomass, K content, and the tuber yield at the end. Potassium fertilizer use efficiency were calculated.

Results Compared with CK, all the potassium treatments significantly increased the stem length, stem thickness, and biomass of sweet potato. At the 30 days, T1 treatment was recorded the highest promotion effect in the growth and biomass, and the other treatments did not show significant differences. At 60, 90 and 120 days, T3 was recorded the highest promotion effects, the stem length, thickness, and biomass in T3 treatment were significantly higher than those in T1 and T5 treatment. Compared with T1 and T5, T3 treatment significantly increased K content and K accumulation of sweet potato in the 60, 90 and 120 days, thereby achieved the highest K harvest index, partial factor of K productivity, agronomic efficiency and apparent utilization efficiency of K.

Conclusions Under the same potassium rate, basal applying water and citrate soluble potassium fertilizers in equal ratio is conducive to the sufficient supply of K nutrition across the whole growing period of sweet potato, thereby increase the potassium accumulation, yield formation, and the potassium utilization efficiency at last.