Objectives Characteristics of potassium (K) uptake, utilization and transformation of sweet corn were studied for both high quality and high yield.

Methods Field experiments with a sweet corn cultivar (Zea mays L. saccharata sturt) ‘Yuetian 16’ (YT16) were conducted in 2015 and 2016. Seven nitrogen fertilizer rates were designed as N 0, 100, 150, 200, 250, 300, and 450 kg/hm², and using randomized complete block design with 3 replications. Aboveground plants were sampled to measure the dry matter weight, K content, K uptake, K harvest index and K use efficiency at flowering and milk-ripe harvest stages.

Results Significant differences in plant K uptake at milk-ripe harvest stage were found among 7 fertilizer N application rates. Under N 250 kg/hm², the differences of plant K uptake among the N rates were mainly due to the differences of the dry matter production and K content, and above N 250 kg/hm², the differences of plant K uptake among the N rates were mainly due to the differences of dry matter production. When the N application rates were increased from 0 to 250 kg/hm², the fresh ear yield, K uptake of ear, and the harvest index of K showed an increasing tendency. When the N application rates were in range of 0–450 kg/hm², both the dry matter production and plant K uptake were increased with the increase of N application rate. While with the increase of N application rate from 250–450 kg/hm², the fresh ear yield and K content of ear were kept stable, and the K harvest index showed a decreasing tendency. With the increase of N application rate (0‒450 kg/hm²), K requirement for producing 1000 kg of fresh ear yield was decreased firstly and then fluctuated. Above N rate of 250 kg/hm², both the K uptake and accumulation were increased, and the increase was mainly found in stem, sheath and leaf. N application rates significantly influenced the contribution of the K assimilated in roots and transformed from stem sheath and leaf after flowering to the ear potassium. The increase of N rate would not stop improving the transformation of K from stem sheath and leaf to potassium capacity of ear after flowering until the N rate was higher than 250 kg/hm². Under the N rate of 250 kg/hm², the K transformation from stem sheath, and leaf to ear would reach the peak, and the contribution rates to ear K from transformation of stem sheath, leaf and assimilation of root after flowering were 34.1%, 30.8% and 35.1%, respectively.

Conclusions N application rates significantly affect plant K uptake of sweet corn in the range of N application rate of 0‒450 kg/hm². Higher N inputs will stimulate the plant K uptake and transformation from vegetable organs to ears within the N range of 0‒250 kg/hm², while the transformation will not increase when the N rate is in the range of 250‒450 kg/hm², the fresh ear yield will not keep increasing, and the K use efficiency will be fluctuated as a result . Therefore, N application rate of 250 kg/hm² could be thought reasonable from the point of view of K use efficiency for sweet corn.