ObjectivesEffects of nitrogen application rates on sweet corn fresh ear yields, nitrogen translocation and use efficiencies under high yield conditions were studied in south China.

MethodsField experiments with a sweet corn cultivar (Zea mays L. saccharata sturt)‘Yuetian 16’ (YT16) were conducted in 2015 and 2016. Seven N application rates (N 0, 100, 150, 200, 250, 300, and 450 kg/hm²) were designed in the experiments in fields for successive two years. Aboveground plants were sampled to measure the dry matter weight, N content, N uptake rate, N harvest index, and nutrient use efficiency at the stages of the 8th and 12th full leaf expansion, tassel flowering stage and milk stage in order to study the characteristic of N uptake and utilization, N harvest index and agronomy efficiency of the sweet corn at milky stage, and N accumulation of plant, blade, stems and sheaths at different growth stages.

ResultsThe results showed that significant differences of fresh ear yield, total nitrogen accumulation amounts in plants, nitrogen agronomic efficiency, nitrogen recovery efficiency and nitrogen partial factor productivity at maturity stage were found among 7 fertilizer N application rates in two years. The fresh ear yields and amounts of total nitrogen accumulation in plants were increased at the first stage, and then slightly fluctuated with the increase of nitrogen application rates, and the nitrogen agronomic efficiencies were increased at the first stage, and then decreased, while the nitrogen recovery efficiencies and nitrogen partial factor productivity were continually decreased. Under the N 250 kg/hm² of nitrogen fertilizer rate, the fresh ear yield and amount of total nitrogen accumulation in plants of YT16 could reach to or near the maximum, which were 17544 kg/hm² and 145.6 kg/hm² in the average of two years, respectively, and the nitrogen agronomic efficiency of YT16 also reached to the maximum, 48.4 kg/kg, whereas the nitrogen recovery efficiency and nitrogen partial factor productivity were at medium level, which were 28.5% and 70.2 kg/kg in the average of two years, respectively. The fresh ear yield, total nitrogen accumulation and nitrogen agronomic efficiency reached to the highest under the N 250 kg/hm² of nitrogen fertilizer rate. Under the N 250 kg/hm², the translocation efficiency and nitrogen contribution proportion after the anthesis stage of YT16 in two years could be regulated effectively. As a result, the nitrogen translocation in stems and sheaths, leaf nitrogen translocation and the assimilated amount of nitrogen after the anthesis to fresh ear nitrogen accumulation were 48.8%, 10.2% and 41.0% in the average of two years, respectively. The nitrogen uptake in the whole plant continuously increased, and the maximum value appeared at the milky stage. The maximum N accumulation rate of the plant appeared at the period from 8 to 12 full expansion leaves. The N accumulation in leaves, stem and sheath changed as a single peak curve in the whole growth stage, and the maximum value appeared at tassel flowering stage. The maximum daily N accumulation in leaves, stem and sheath appeared at the period from 8 to 12 full expansion leaves, and from 12 full expansion leaves to tassel flowering, respectively. N supply significantly improved N uptake and accumulation in leaves, stem and sheath at various stages, but did not change the trend of N accumulation.

ConclusionsUnder this experimental field condition with many times of fertilization, as far as fresh ear yield and nitrogen agronomic efficiency were concerned, the most optimal nitrogen fertilizer rate was N 250 kg/hm².