| Low soil organic carbon（SOC）levels and high seasonal nitrogen（N）fertilizer losses are significant challenges in improving the quality of cultivated land in low-and medium-yield fields of the ancient Yellow River alluvial plain.SOC is a key factor affecting nitrogen conservation.Therefore,increasing SOC can improve soil comprehensive fertility and reduce N fertilizer losses.However,the quantitative relationship between SOC level and N fertilizer losses and its targeted improvement strategies need to be further clarified in the ancient Yellow River alluvial plain.Therefore,meta-analysis methods,field positioning experiment and 15N in-situ tracing experiment were comprehensively used in this study to clarify the main influencing factors for N fertilizer losses and their relationships between N fertilizer losses and SOC contents,explore effective measures for rapid enhancement of SOC,and generate the optimal solutions for simultaneously increasing SOC and reducing N fertilizer losses.Through meta-analysis,global 15N tracing data were integrated to analyze the effects of natural factors,soil physicochemical indexes and N fertilizer application on the total N fertilizer losses in the current season.The results showed that the effects of natural factors and soil physicochemical indexes on the N fertilizer losses ratio of crops in the current season were mainly affected by average annual rainfall and soil p H in wheat season,p H and SOC content in rice season,SOC and rainfall in maize season.The total N fertilizer losses increased significantly with the increase of N fertilizer application rate.Under conventional N fertilizer application rate,increasing SOC level by 1 g/kg can reduce N fertilizer losses ratio by 0.78%～2.75%.By optimizing N fertilizer application rate and increasing SOC level,N fertilizer loss could be reduced by 25.61～64.49 kg N/ha/season under the premise of ensuring crop yield.The effects of no-tillage,biochar application and polyacrylamide（PAM）application on SOC,soil aggregate,soil available nutrient content and crop yield were investigated by field experiment in the ancient Yellow River alluvial plain.The effects of improvement measures on SOC and soil fertility were analyzed.The results showed that compared with conventional management,SOC content of typical middle-low yield fields in the ancient Yellow River alluvial plain was increased by 6.7%～30.2%and 13.7%～21.7%by applying biochar and no-tillage（P<0.05）,respectively.Application of biochar and PAM significantly increased the content of macroaggregates in soil aggregates by 0.9%to 13.9%and 1.8%to 14.5%（P<0.05）,respectively.Applying biochar could significantly increase the average weight diameter of aggregates by 4.3%to 18.0%（P<0.05）.Over two years of no-tillage combined with biochar and PAM applications,SOC content increased significantly by 4.20 g/kg,which was the highest among all treatments.The combination of practices also exhibited a increase of crop yield increased by 6.3%～12.9%compared to conventional treatment.Therefore,biochar+PAM+no-tillage could be considered as an integrated optimization measure for increasing grain yield and soil fertility.Through 15N in-situ tracing study,the effects of improvement measures on the direction and total loss of nitrogen fertilizer in the current season were quantified,and the reduction effect of improvement measures on the total loss of nitrogen fertilizer in the current season was analyzed.The results revealed that although rotary tillage combined with biochar and PAM application significantly increased SOC content by 6.8%～22.1%and reduced gorss N fertilizer losses by9.1%in wheat season,it could also lead to an increase in fertilizer-N losses during the corn season（10.2%）.No-tillage combined with biochar and PAM application significantly reduced fertilizer-N losses（11.3%～12.8%）,and increased soil TN（4.9%）,available phosphorus（43.54%）,and available potassium content（20.1%）in both cropping seasons.Therefore,although increasing SOC content can enhance nutrient retention capacity,the establishment of soil improvement measures should also consider the interaction between materials and tillage practices on seasonal fertilizer-N losses.No-tillage combined with biochar and PAM application can be a promising solution for increasing SOC and fertilizer-N losses in the Yellow River Old Course region. |
