Effects of nitrogen application on potassium uptake and utilization of sweet corn in south China

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.