Evaluating Links Among Nutrient Management Practices,Soil Organic Carbon,Crop Productivity,and Yield Stability

In agro-ecosystems,fertilization practices must accomplish high and stable crop productivity,with maximum soil organic carbon(SOC)sequestration to address climate change and food security challenges.However,the impacts of these practices on SOC and crop yields are variable over the long-term duration,and an improved understanding of the factors influencing SOC sequestration and sustainable productivity is still needed to provide evidence-based management decisions.Therefore,we conducted a meta-analysis to evaluate the impact of long-term(?10 years)application of different fertilizer management practices adapted across China on crop productivity,yield sustainability,and SOC sequestration.Unbalanced mineral fertilizer(UMF),balanced mineral fertilizer(BMF),organic fertilizers(OF),combined unbalanced mineral and organic fertilizers(UMOF),and combined balanced mineral and organic fertilizers(BMOF)significantly enhanced the grain yield,and SOC sequestration compared with control(p<0.05).For UMF,the increases in SOC and grain yields were the least among fertilization practices.Comparing OF,BMF mostly produced more grain yields,but with a slight increase in C sequestration.The highest SOC sequestration rate of 0.43 Mg C ha^-1yr^-1was recorded in BMOF,among all the treatments.The data obtained indicated that SOC sequestration is highly time-dependent.Irrespective of fertilization mode,SOC gradually increased and attained the peak of sequestration rate in the initial two decades rather than at later stages of fertilizer addition.The linear fitted model indicated that an increase in SOC sequestration benefits sustainable productivity.The available data indicate that crop yields can be improved by 143 kg ha^-1 for rice(Oryza sativa),255 kg ha^-1 for maize(Zea mays),and 202 kg ha^-1for wheat(Triticum aestivum)with every 1 Mg ha^-1increase in SOC stock by fertilization in the root zone.Our understanding of how soil organic carbon(SOC)storage,crop yield,and yield stability are influenced by climate is limited.To critically examine this,the impact of long-term(?10 years)application of nutrient management practices on SOC storage,crop productivity,and yield stability were evaluated under different climatic conditions in China in the second study of this thesis.The cropping area of China was divided into four distinct groups based on local climatic conditions.Results indicated that the impact of nutrient management practices on SOC storage,crop yield,and yield stability varies under different climatic zone in China.The use of unbalanced mineral fertilizer(UMF),and balanced mineral fertilizer(BMF)led to a loss in SOC storage by 6%,and 11%under CM climatic zone and gains in DW,WM,and CD climates.Organic fertilizers(OF),combined unbalanced mineral and organic fertilizers(UMOF),and combined balanced mineral and organic fertilizers(BMOF)were able to sustain and enhance SOC storage under all climatic conditions.However,the largest increase in SOC storage across all climates was seen for BMOF.Corresponding values of crop productivity and yield stability were also highest for BMOF among all the nutrient management treatments.A linear-plateau model indicated that maximal yield responsive SOC stock(C_opt)levels ranged from 33.43 to 45.51 Mg C ha^-1for rice(Oryza sativa),maize(Zea mays),and wheat(Triticum aestivum)production.We concluded that BMOF can maintain and improve soil quality while producing high and stable crop yields.Because,under different climates,BMOF appears to be the most appropriate nutrient management strategy to enhance and sustain SOC storage,and crop productivity of croplands.Our findings demonstrate that it is essential to optimize nutrient management strategies according to the local climate to protect soil from SOC losses,and for achieving sustainable crop production.