Effect Of Long-term Fertilization On Composition And Stability Of Aggregates In Brown Earth And Black Soil

This paper deals with the effects of long-term fertilization on aggregate distribution,δ¹³C value of aggregate and aggregate stability by aggregate separation methods(wet sieving and dry sieving )and aggregate breakdown methods(fast wetting,wet stirring and slow wetting). Soils samples were collected from two long-term experiment locations in Shenyang Agricultural University and Jilin Academy of Agricultural Sciences.The fertilization treatments in the Brown earth experiment location included control(no fertilizer),chemical fertilizer(inorganic fertilizers),high manure(high-rate organic fertilizers) chemical fertilizer plus high manure(high-rate organic- inorganic fertilizers ),and the fertilization treatment in the Black soil experiment location included control(no fertilizer),chemical fertilizer(NP, NPK) and chemical fertilizer plus manure(high-rate organic- inorganic fertilizers).The effects of different fertilization treatments on aggregate-protected C and change of carbon pool were studied using incubation experiment.The objectives of the study were to compare the changes of aggregate distributions and SOC,total N content and storage between the Brown earth and the Black soil under long-term different fertilization.The main results are as follows:1.Aggregate size distributions in Brown earth and Black soil were all dominated by 0.25～1mm.Inorganic fertilizer plus manure application effectively enhanced micro-aggregate 0.05～0.25mm content in Brown earth and micro-aggregate 1～2mm content in Black soil.2.The most storage of SOC was in aggregate 0.25～1mm in all treatments..Great amounts of the new SOC were accumulated in the aggregates 0.05～0.25mm.Increase of SOC storage was the most obvious in inorganic fertilizer plus manure(organic- inorganic fertilizers) treatment of Black soil,and the new SOC was greatly accumulated in the aggregates 1～2mm and 0.05～0.25mm.3.Whether Brown earth or Black soil,manure and chemical fertilizer plus manure application increased total N content in soil.Chemical fertilizer plus manure application significantly increased total N content associated with 0.25～1mm aggregate.C/N in fertilizers treatments of Black soil was lower than those in no fertilizer,which indicated that the accumulation rate of total N was larger than the accumulation rate of total C in Black soil.4.Mean weight diameter(MWD) of aggregates in fast wetting treatment in Brown earth and Black soil was lower than that in wet stirring and slow wetting treatments.MWD of aggregates in M2 treatment of Brown earth was significantly higher than other treatments. MWD of aggregates in medium-rate organic fertilizers treatment of Black soil was significantly higher than other treatments.According to relative slaking index(RSI) and relative mechanical breakdown index(RMI) of aggregates,aggregate stability in Brown earth and Black soil was the most stable in no fertilizer,inorganic fertilizers and NPK treatment, respectively.5.The fast wetting caused the most severe disruption to aggregates under different wetting treatments in aggregates of Brown earth and Black soil.The wetting time had obvious effect on aggregate stability.The effect that SOC improved aggregate stability was more evidence under fast wetting and wet stirring.6.Manure and inorganic fertilizer plus manure application could increased the contents of unprotected macro-aggregate C and unprotected micro-aggregate C.Macro-aggregate had positive effect on microaggregate-protected C.Increasing of macro-aggregate content could contribute to protection of soil C.