Suitable nitrogen application rate for spring maize under full straw mulching in black soil area of central Jilin Province

Objectives This study investigated the suitable N application rate, accumulation, and distribution characteristics of spring maize in the black soil area of central Jilin Province. Maize straw was returned to the field in full for many years.

Methods This experiment was conducted in Gongzhuling City, Jilin Province, from 2017 to 2019. The main plot was nitrogen level at 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240), 300 (N300), and 360 (N360) kg/hm². The subplot was maize cultivar. The dry matter, nitrogen uptake and yield composition of maize organs at different growth stages were measured in Fumin 985 and Xiangyu 211.

Results Increasing N fertilizer application (P<0.05) affected maize yield, with differences across the years, cultivars, and their interactions. N0 treatment yield decreased across the years, and the yield in 2018 and 2019 was 10.9% and 26.2% lower than in 2017, respectively. The yield of N180 in 2017 was increased by 23.2% and increased by 55.1% in 2019 compared with N0. Xiangyu 211 yield was higher than Fumin 985 from 2017 to 2019; the suitable N application rate for Xiangyu 211 was slightly higher than Fumin 985. The dry matter accumulation in spring maize increased at first and subsequently decreased with an increase in N level. The dry matter accumulation in stem and leaf and N accumulation in the treatments reached the maximum value from silking to milk stage. The dry matter accumulation in stem, leaf, and grain under N180 was the highest at the maturity stage. Under different N application levels, the distribution ratio of N accumulation after anthesis increased first and then decreased. There were (P<0.05) differences in the total N content based on the straw theory. The amount of N returned by straws increased gradually across the years. In 2017, the quantity of N re-entry under N300 treatment was the highest (68.9 kg/hm²), surpassing N0 and N360 treatments by 155.0% and 15.2%, respectively. In 2019, N re-entry under N240 treatment was the highest (109.9 kg/hm²), exceeding N0 and N360 treatments by 156.7% and 33.4%, respectively. The fitted models for 2017 and 2019 showed that maize's optimal economic yield and N fertilizer dosage were 13028 kg/hm² and 162 kg/hm², respectively.

Conclusions The practice of returning straw to the black soil in Jilin has been in existence for a long time. Although inter-annual conditions and cultivars affect maize yield, nitrogen fertilizer remains important for high and stable maize yield. Using the appropriate quantity of N fertilizer was beneficial to increasing dry matter accumulation and distribution of maize from the silking to filling stage, thereby increasing maize yield. The optimal N application rate to maintain maize yield at 12–13 t/hm² was 160–165 kg/hm².