| Maize is an important staple crop in China,and its yield plays a significant role in ensuring national food security.The application of nitrogen fertilizer is a major measure to increase corn production.However,the unreasonable application of nitrogen fertilizer not only leads to reduced efficiency but also limits yield growth.To further tap into the potential yield of corn and improve nitrogen utilization efficiency,a field experiment was conducted using spring cultivar Fumin 985 as the experimental material in Changchun,Jilin Province from 2021 to 2022.Five nitrogen fertilization treatments including N-fertilizer applied 100%at sowing(CK),40%at sowing,and 60%at V6(T1),40%at sowing,20%at V6,and 40%at VT(T2),40%at sowing,15%at V6,30%at VT,and 5%at R2(T3),40%at sowing,10%V6,30%at VT,and 20%at R2(T4)were implemented by drip fertigation.Fate of soil nitrogen,nitrogen absorption and metabolism of maize,photosynthetic characteristics of maize,grain-filling processes of maize and yield were studied.The main results were shown as below:1.Effects of nitrogen fate in soil by nitrogen topdressing.The content of available nitrogen(ammonium nitrogen and nitrate nitrogen)was maintained a higher value in the 0-20 cm soil layer by adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage.In 2021,compared with CK,the ammonium nitrogen content in the 0-20 cm soil layer of T3 treatment was significantly increased by 6.3%and 50.1%during the maize tassel and filling stages,respectively.The emission of ammonia and nitrous oxide was significantly reduced by adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage.The cumulative emissions of ammonia and nitrous oxide from T4 treatment are lower than those from CK,T1,and T2.The activity of soil urease was increased after harvesting by increasing the amount of nitrogen fertilizer applied during the grain filling stage.Soil urease activity of T4treatment was significantly higher than CK,T1,and T2 treatments in 2022,respectively.2.Effects of nitrogen uptake and key enzyme activity of nitrogen metabolism by nitrogen topdressing.The frequency of nitrogen application had a significant effect on the nitrogen uptake of maize.The change of nitrogen uptake with T4 treatment was significantly increased by 63.6%and 51.0%compared to T1 and T2 treatments,respectively.The nitrogen application increased the activities of NR,GS,and GOGAT in maize leaves.The NR and GS activities in the ear-leaf of T4 treatment were significantly higher than CK.NR activity in the lower ear leaf of T4 treatment was significantly increased by 84.3%,78.8%,and 57.5%compared to the CK,T1,and T2 treatments,respectively.In 2022,the activity of GOGAT in the ear-leaf of T4 treatment was significantly increased by 74.7%and 53.7%compared to T2 and T3 treatments,respectively.3.Effects of photosynthetic capacity of maize leaves by nitrogen topdressing.Adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage can delay the decrease of leaf area index(LAI).Compared with CK,the LAI of T4 treatment was significantly increased by 95.2%at 55 days after silking.SPAD value tended to stabilize during the grain-filling stage by adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage.Compared with CK,the decline of SPAD value at 45 days after silking was reduced by28.0%and 71.7%of T3 and T4 treatments,respectively.Net photosynthetic rate and the activity of phosphoenolpyruvate carboxylase of maize ear-leaf after silking were increased Adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage.The net photosynthetic rate of ear-leaf of T3 treatment was significantly increased by 36.7%,71.0%,and 18.4%compared with CK,T1,and T2 treatments at45 days after flowering,respectively.Compared with CK,the activity of phosphoenolpyruvate carboxylase in maize ear-leaf during the grain-filling stage was significantly increased by 20.6%of T4 treatment.4.Effects of grain filling period,accumulation of dry matter,and the activity of key enzymes by nitrogen topdressing.Adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage extended the grain filling period,promoted the accumulation of aboveground dry matter,and increased the grain weight.In 2021,compared with CK,the effective filling period of T4 treatment was significantly extended by 13.7 days,the time of maximum filling rate of T4 was delayed by 2.4 days,the grain weight of T4 treatment increased by1.2%.Adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage can improve activity of GBSS,SSS,and SS.In 2021,T4 treatment had significantly higher activity of GBSS,SSS,and SS in maize grains compared to CK,with increases of 44.7%,39.8%,and 14.6%,respectively.5.Effects of nitrogen use efficiency and yield by nitrogen topdressing.By adjusting the proportion of nitrogen fertilizer applied and increasing the amount of nitrogen fertilizer applied during the grain filling stage,the nitrogen use efficiency and yield of maize can be improved.In 2021,compared with CK,the nitrogen use efficiency of T1,T2,T3,and T4 treatments increased by 16.7%,77.1%,113.3%,and 114.5%,respectively.The grain yield of T4 treatment in2021 and 2022 were 13901 kg/hm~2 and 11918 kg/hm~2,respectively,which were significantly higher than CK and other treatments.In the semi-humid spring maize planting areas of the black soil region in Northeast China,implementing measure(40%at sowing,10%V6,30%at VT,and 20%at R2)can improve maize yield and nitrogen utilization efficiency while meeting the nitrogen requirements for maize growth and development. |
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