Effects of nitrogen topdressing amount at various stages on nitrogen efficiency of maize and soil nitrogen balance under mulched drip irrigation

Objectives Effects of nitrogen topdressing amount at various stages on maize yield, nitrogen accumulation and distribution, residual characteristics of nitrogen in soil, nitrogen balance in soil-crop system and nitrogen use efficiency under mulched drip irrigation were studied to provide accurate and efficient implementation of maize mulched drip irrigation fertilization management in the semiarid region of Songnen Plain.

Methods In 2015 and 2016, with maize as a test crop, field trials with large ridge and double row under mulched drip irrigation were conducted. There were three topdressing levels of nitrogen fertilizer, 90(T90), 120(T120) and 150(T150) kg/hm². Topdressing nitrogen fertilizer was applied at leaf age index 30% (V6), 60 % (V12) and 100% (R1). The five distribution ratios for topdressing nitrogen fertilizers at the three stages were set as: 5∶5∶0(A1), 3.3∶3.3∶3.3 (A2), 4∶5∶1(A3), 3∶5∶2 (A4) and 2∶5∶3 (A5). Meanwhile, no nitrogen fertilizer (CK) was set as comparison. Maize yield, nitrogen accumulation, distribution and inorganic nitrogen content in the 0–100 cm depth of soil were investigated and analyzed. The nitrogen balance of soil–crop system and nitrogen use efficiency were calculated.

Results The two-year test results of 2015 and 2016 showed that the yields in the two years were increased by 13.88% to 75.72% and 13.73% to 88.50% compared with the CK. The increase in grain yield of the T120A4 treatment was the most obvious, and the two-year yields were 11643 kg/hm² and 12952 kg/hm², which were significantly higher than those of other treatments. At the same time, it could effectively regulate nitrogen absorption, accumulation and distribution of maize plants, so that the nitrogen accumulation amounts in maize vegetative organs were increased by 3.23 to 50.49 kg/hm², 4.61 to 40.70 kg/hm² and 2.65 to 25.48 kg/hm² at 45, 60, and 75 days after the jointing compared with other treatments. Its grain nitrogen accumulation amounts were significantly increased by 8.51% to 74.90% at 75 days after the jointing compared with other treatments. In the nitrogen balance of soil-crop system, the nitrogen accumulation amounts in plants of the T120A4 treatment were significantly higher than those of other treatments (5.58%–65.01%). The total inorganic nitrogen residue in 0–100 cm soil layer of maize farmland was 123.75 kg/hm² and the proportion of inorganic nitrogen in the 0–60 cm soil layer was 78.33%, both were at a moderate level. In the same time, the nitrogen surplus and loss in the soil–crop system under the T120A4 treatment were 9.94 kg/hm² and 133.70 kg/hm², all at the lowest level, which effectively reduced the risk of nitrogen leaching. The nitrogen fertilizer partial productivity, agronomic efficiency and apparent utilization rate of the T120A4 treatment were increased by 8.66 to 31.53 kg/kg, 11.76 to 26.28 kg/kg and 3.54% to 52.89% compared with other treatments. In the interim, its soil dependent rates for nitrogen were 1.70% to 32.64% lower than those of other treatments. It could significantly increase the nitrogen proportion of maize plants absorbed from fertilizers.

Conclusions In this experiment, the treatment of 120 kg/hm² nitrogen fertilizer was topdressed, and the ratio of topdressing nitrogen at 30%, 60% and 100% leaf age index was 3∶5∶2 was the best nitrogen fertilizer application practice by considering maize grain yield, nitrogen balance, nitrogen absorption and nitrogen utilization efficiency.