Differences In Nitrogen Supply And Nitrogen Fertilizer Utilization In Wheat Fields With Different Yield Levels

In response to the issue of significant yield differences and low nitrogen utilization efficiency in wheat production in the Huanghuaihai Plain,this study aims to investigate the differences in nitrogen transformation and supply characteristics in wheat fields at different yield levels,providing technical support for improving wheat yield and nitrogen fertilizer utilization efficiency,and reducing nitrogen fertilizer losses.A field experiment was conducted in Shijiawangzi Village,Xiaomeng Town,Yanzhou District,Jining City,Shandong Province during the wheat growth season from 2021-2022.The tested variety was a high yield wheat variety,Yannong 1212.The experiment selected three yield levels of wheat fields,with perennial yield levels of 10 500 kg hm^-2,9 000 kg hm^-2,and 7 500 kg hm^-2,respectively,expressed by S,H,and M.The main research findings are as follows:1 Difference of nitrogen transformation ability in wheat fields with different yield levelsThe intensity of ammonification in M wheat field was significantly higher than that in other wheat fields during pre sowing,jointing,and anthesis,while S wheat field was the lowest.There was no significant difference between overwintering and mature treatments.The intensity of nitrification and denitrification is consistent with the intensity of ammonification.This indicates that S wheat field can reduce the intensity of ammonification,nitrification,and denitrification,not only ensuring the supply of plants,but also reducing the loss of fertilizer nitrogen.The content of nitrate and ammonium nitrogen in the soil layer of S wheat field was significantly higher than that of other wheat fields during the overwintering period,20 days,30 days after anthesis,and 20 to 100 cm after maturity period.M wheat field had the lowest content,and the soil layer of 40 to 100 cm during the jointing period was significantly higher in S wheat field than other wheat fields.M wheat field had the lowest content.This indicates that the S wheat field ensures the demand of wheat plants for soil nitrate and ammonium nitrogen at various growth stages,ensuring timely supply of nutrients for wheat plants.The ammonia volatilization rate and N₂O gas emission flux in S wheat field were significantly lower than those in other wheat fields during the early sowing,jointing,and anthesis stages.There was no significant difference in overwintering and maturity stages.S wheat field reduced ammonia volatilization and N₂O gas emissions.2 Differences in nitrogen accumulation ability of wheat plants at different yield levelsDuring the anthesis period and 20 days after anthesis,the root dry weight density and root length density in the 0～100 cm soil layer in S wheat field were significantly higher than those in other wheat fields,while M wheat field had the lowest;The superoxide dismutase activity and soluble protein content in 0～40 cm soil layer were the highest in S wheat field,the lowest in M wheat field,and the highest in MDA content in M wheat field.S wheat fields can delay root aging and promote better absorption of nutrients and water in deep soil by wheat roots.The nitrogen accumulation of wheat plants from overwintering to maturity was significantly higher in S wheat field than in other wheat fields,while M wheat field had the lowest nitrogen accumulation;Except for the jointing to anthesis stage,the growth stages in S wheat field were significantly higher than those in other wheat fields,with M wheat field being the lowest;During the mature stage of wheat,the absorption of fertilizer nitrogen and soil nitrogen was significantly higher in S wheat field than in other wheat fields;The S wheat field significantly increased the nitrogen accumulation of wheat plants from sowing to jointing stage and from anthesis to maturity stage,and increased the proportion of soil nitrogen accumulation,which is beneficial for grain nitrogen accumulation.3 Differences in nitrogen transport capacity of wheat plants at different yield levelsThe content of free amino acids and soluble proteins in flag leaves after anthesis was significantly higher in S wheat field than in other wheat fields,while M wheat field had the lowest content;The amount of nitrogen transport from the vegetative organs to the grains and the accumulation of nitrogen in the grains after anthesis,as well as the contribution rate to the grains,were significantly higher in S wheat field than in other wheat fields,with M wheat field being the lowest;The nitrogen fertilizer utilization efficiency and soil residue rate were significantly higher in S wheat field than in other wheat fields,while M wheat field had the lowest;The nitrogen fertilizer loss rate in M wheat field is significantly higher than that in other wheat fields,while S wheat field is the lowest.This indicates that S wheat field has delayed the senescence of flag leaves after anthesis,increased nitrogen accumulation after anthesis,improved nitrogen fertilizer utilization efficiency,and reduced nitrogen fertilizer loss rate.The amount and rate of nitrogen accumulation in grains,as well as the duration of peak nitrogen accumulation in grains,also showed that S wheat field was significantly higher than other wheat fields,while M wheat field was the lowest.This indicates that the S wheat field can maintain a high grain nitrogen accumulation amount and rate during the filling period,prolong the duration of the peak nitrogen accumulation in grains,and is beneficial for increasing grain accumulation.4 Differences in grain yield and nitrogen utilization efficiency in wheat fields with different yield levelsCompared with M wheat field,the yield of H wheat field was improved by increasing the number of ears per unit area and the number of grains per ear.The number of ears per unit area increased by 12.84%and the number of grains per ear increased by 7.17%.Compared with H wheat field,S wheat field obtained high yield by increasing panicle number per unit area and 1000-grain weight by 12.67%and 6.73%respectively.In summary,this experiment explored the differences in grain yield and nitrogen utilization efficiency in wheat fields at different yield levels through indicators such as soil nitrogen transformation and plant nitrogen accumulation and transport.It indicates that with the increase of yield level,the senescence of roots and flag leaves is delayed,the nitrogen accumulation ability of plants is improved,the nitrogen fertilizer utilization rate is increased,and the loss rate is reduced.It can be seen that enhancing soil fertility and improving soil productivity is one of the main ways to achieve high yield and nitrogen fertilizer utilization efficiency.