Dynamics of nitrogen use efficiency of maize and alkali-hydrolyzable nitrogen content of red soil under long-term application of organic and inorganic fertilizers

Objectives Optimum yield of maize relies on sufficient nitrogen (N) supply. Studying the change in maize N absorption and utilization and the soil N surplus caused by long-term application will provide a theoretical basis for sustainable productivity of maize and scientific management of soil nitrogen in red soil areas.

Methods A double cropping maize experiment was conducted in Jinxian, Jiangxi Province, including five fertilization treatments, a control without fertilizer (CK), conventional chemical fertilizer (NPK), double amount conventional chemical fertilizer (DNPK), single organic fertilizer (OM), and conventional chemical fertilizer plus organic fertilizer (NPKM). The periodical changes of maize grain yield and biomass, and the N contents in plants and soils, N uptake and N use efficiency (NUE) were calculated at 10-years intervals.

Results Compared with CK treatment, the average grain yield of maize across 35 years under the treatments of NPKM, DNPK, OM, and NPK was increased by 3.36–9.07, 3.31–5.64, 2.46–6.72, and 1.91–3.70 times, and the N absorption was increased by 5.20–11.93, 4.33–7.02, 3.66–5.90, and 1.80–3.64 times, respectively. During the 0–10 years, there was no significant difference in grain yield among the four treatments, and no significant difference in maize N uptake among NPKM, DNPK and OM treatments, but they were sll significantly higher than NPK. Between 11–20 years, the grain yield and N uptake under NPKM and DNPK treatments were significantly higher than NPK and OM treatments. During the 21–35 years, the yield and N absorption of NPKM treatment were significantly higher than all other treatments. The N partial productivity of NPK and DNPK treatments increased from 0 to 20 years, and then decreased from 21 to 35 years, while that of NPKM and OM treatments kept increasing, and was significantly higher than that of NPK and DNPK treatments from 31 to 35 years. The soil N exhibited surplus in all the N treatments. In the first 30 years, NPKM treatment had the highest surplus, which was 13.63%–37.48% and 133.95%–208.24% higher than those of DNPK and NPK treatments, respectively. However, during 31–35 years, there was no significant difference in N surplus between DNPK and NPKM treatment. The soil alkali hydrolyzable N was positively correlated with N surplus at 0–20 cm soil layer (P<0.05), with every 10 kg/hm² increment in average N surplus, soil available N content increased by 1.00, 1.20, 1.60, and 2.80 mg/kg during 0–10 years, 11–20 years, 21–30 years, and 31–35 years, respectively.

Conclusions In the first 20 years, applying chemical fertilizer alone increased the maize N absorption and fertilizer partial productivity, but subsequently decreased, while organic and inorganic fertilizer combination or organic fertilizer alone consistently improved the N use efficiency, promoted maize yield. Nitrogen surplus significantly increased the alkali-hydrolyzable N in the topsoil, and the improvement effect of combined application of organic and inorganic fertilizer was higher than other inputs.