Effects Of Soil Management Regimes On The Distribution Of Aggregate Associated Carbon, Nitrogen And Its Organic Carbon Mineralization On Lou Soil

Soil aggregates play an important role in soil structure. It also had great influence in theprotection of soil organic carbon and sustaining and supplying of nutrient elements. Thisstudy investigated the effects of soil management regimes on the distribution of aggregateassociated carbon, nitrogen and its organic carbon mineralization on Lou soil based on the21-year long-term experiment on Lou soil in Guanzhong Plain, Shaanxi province, China. Thesoil management regimes were cropland abandonment (Set aside), bare fallow withoutvegetation (Fallow) and a wheat-maize cropping system (Cropping). The Cropping wascombined with the following nutrient management treatments: control (CK, no nutrient input),nitrogen only (N), nitrogen and potassium (NK), phosphorus and potassium (PK), NP, NPK,straw plus NPK (SNPK) and two levels of manure plus NPK (M1NPK and M2NPK). Themain results obtained are as follows:1. Soil management regimes had significantly affected the distribution of dry aggregatesand water stable aggregates in the surface and subsurface soil layers (0-10and10-20cm).Fallow treatment increased the proportion of microaggregates (<0.25mm), while the set asidetreatment increased the proportion of macroaggregate (>2mm) as well as aggregate stabilitycompared with the cropping treatment. The distribution of dry aggregates and water stableaggregates were significantly impacted by fertilization in all soil depths under cropping.Generally, various fertilization regimes decreased the proportion of>1mm aggregates andincreased the proportion of0.25-1mm aggregates compared with the control. However,long-term fertilization didn’t notably affect the aggregate stability on Lou soil.2. Soil management regimes had significantly affected the distribution of organic carbonand nitrogen in dry aggregates in the surface and subsurface soil layers. Fallow treatmentreduced the SOC and nitrogen contents in all aggregates compared with the croppingtreatment. There were no significant effects on the SOC and nitrogen partitioning by fallowtreatment under the cropping in the0~10cm soil depth, but the SOC and nitrogen partitioningin <0.5mm aggregates were increased in the10~20cm soil depth. While the set aside treatment increased the SOC and nitrogen contents in all aggregates in the0~10cm soil depthand decreased them in the10~20cm soil depth compared with the cropping treatment.However set aside significantly increased the allocation proportions of SOC and nitrogen in>2mm aggregate over the cropping treatment. The SOC and nitrogen contents in dryaggregates were higher in the NP, NPK, SNPK, M1NPK and M2NPK treatments than in thecontrol. The allocation proportions of SOC and nitrogen in aggregates in the treatments whichreceived mineral fertilizers had not an obvious trend over the control. There were nosignificant effects on the SOC and nitrogen partitioning in the organic and inorganic fertilizertreatments compared with the control treatment in the0~10cm soil depth. The allocationproportions of SOC and nitrogen in>2mm aggregate were lower, and the allocationproportions of SOC and nitrogen in <0.5mm aggregates were higher in the treatments whichreceived manure addition along with NPK than the control in the10~20cm depth.3. Soil management regimes had significantly affected the distribution of organic carbonand nitrogen in water stable aggregates in the surface and subsurface soil layers. Fallowtreatment reduced the SOC and nitrogen contents in all aggregates compared with thecropping treatment. The SOC and nitrogen partitioning in>2mm aggregate were increased inthe fallow treatment compared with the cropping treatment in the0~10cm depth. Howeverfallow treatment neither affected the SOC and nitrogen partitioning in <0.25mm aggregate inthe0~10cm depth nor the SOC and nitrogen partitioning in all aggregates compared with thecropping treatment in the10~20cm depth. No significant differences were observed for thecontent of SOC in all aggregates and the nitrogen content except for in0.5-1mm aggregateby set aside treatment compared with the cropping treatment in the0~10cm depth. Thecontent of SOC in>0.25mm aggregates and the content of nitrogen in all aggregates weredecreased in set aside treatment compared with the cropping treatment in the10~20cm depth.The SOC and nitrogen partitioning in>2mm aggregate were higher in the set aside treatmentthan in the cropping treatment. Compared with the control, the SOC and nitrogen contents inall aggregates, especially in marcoaggregates, in the NP, NPK, SNPK, M1NPK and M2NPKtreatments were increased. The allocation proportions of SOC and nitrogen in0.25-0.5mmaggregate were increased, but the allocation proportions of SOC and nitrogen in>2mmaggregate were decreased in the mineral fertilizer treatments than in the control. Theallocation proportions of SOC and nitrogen in>2mm aggregate were lower, and theallocation proportions of SOC and nitrogen in0.25-1mm aggregates were higher in thetreatments which received manure addition along with NPK than the control.4. Soil different management regimes and fertilization had significantly affected the soilorganic carbon mineralization of dry aggregates. Fallow and set aside treatments didn’t affect the mineralization proportion of SOC compared with the cropping treatment. The stability ofSOC in set aside treatment was comparatively higher than the cropping treatment. Themineralization rates of SOC in all aggregates and cumulative mineralization of SOC in <2mm aggregates were increased in the0~10cm depth, and the contribution of>2mmaggregate to the cumulative mineralization of SOC was increased, the contribution of0.25-2mm aggregates to the cumulative mineralization of SOC were decreased in the set asidetreatment compared with the cropping treatment in all soil depths. Although fertilization didn’taffect the mineralization proportion of SOC, the mineralization proportion of SOC had anupward trend in fertilization treatments over the control. Fertilization treatments increased themineralization rates and cumulative mineralization of SOC in all aggregates as well as thecontribution of <0.25mm aggregate to the cumulative mineralization of SOC.In conclusions: Long-term cropland abandonment increased the proportion ofmacroaggregates as well as aggregate stability, promoted the accumulation of SOC andnitrogen in macroaggregates, and had comparatively higher stability of SOC. Long-termfertilization significantly influenced the distribution of aggregates, increased theconcentrations of SOC and nitrogen in all aggregates, and promoted the accumulation of SOCand nitrogen in0.25-1mm aggregates. However there was no notably effect on mineralizationproportion of SOC in all aggregates by fertilization.