黑土团聚体结合碳对不同有机肥施用量的响应

Response of aggregate-associated carbon in Mollisols to application rate of organic manure

以连续11年化肥配施不同剂量有机肥的黑土为研究对象,采用团聚体分组与闭蓄态微团聚体分离技术,研究土壤团聚体及其内部组分有机碳对不同有机肥施用量的响应,以期从团聚体尺度揭示黑土有机碳的物理稳定性机制。试验设置4个处理:OM0,仅施化肥;OM1,低量有机肥(7.5 Mg hm-2 a-1)+化肥;OM2,中量有机肥(15 Mg hm-2 a-1)+化肥;OM3,高量有机肥(22.5 Mg hm-2 a-1)+化肥,各处理化肥用量相同。结果显示,与单施化肥相比,有机培肥处理土壤有机碳水平均有显著提升,低量、中量和高量有机肥处理分别提高了7.1%、12.4%和15.7%。有机培肥促进了土壤的团聚化作用,随着有机肥施用量的增加,250—2000μm团聚体含量增加,粉粘粒含量降低,土壤团聚体的稳定性增强,但与中量有机肥相比,高量有机肥输入对土壤团聚化的作用并不明显。有机培肥加速了土壤大团聚体的周转,大团聚体周转速率随着有机肥施用量的增加而加快。有机肥输入并未影响粉黏粒结合有机碳浓度,表明在无有机肥投入的传统管理措施下,黑土粉黏粒已接近或达到碳饱和水平。随着有机肥输入的增加,微团聚体有机碳小幅增加,大团聚体有机碳增加趋势明显,而当有机肥用量最大时,微团聚体有机碳无显著变化,仅大团聚体有机碳仍继续增加,表明高量有机肥投入下微团聚体有机碳库已达到饱和,而更多的新增碳流向大团聚体。对大团聚体内部组分解析发现,高量有机肥处理下大团聚体有机碳的增加主要归因于粗颗粒有机质的增加。这些结果表明,黑土团聚体对有机碳的固持存在由小到大的等级饱和机制,随着有机肥输入的增加,粉粘粒最先达到饱和,然后是微团聚体,而更多的新增碳向周转不断加速的大团聚体富集,固持在活性相对较强的有机碳库—粗颗粒有机质之中。

This study used fractionation of aggregates and microaggregate-within-macroaggregate techniques to determine the organic carbon(C)content in aggregates and subfractions within aggregates of Mollisols after 11 years of continuous manuring in combination with mineral fertilizers.We aimed to explore the physical protection mechanisms of organic C stabilization of Mollisols at the soil aggregate level.The following four treatments were selected:OM0,only mineral fertilizers with no manure application;OM1,organic manure at the lowest level(7.5 Mg hm-2 a-1)plus mineral fertilizers;OM2,organic manure at the medium level(15 Mg hm-2 a-1)plus mineral fertilizers;and OM3,organic manure at the highest level(22.5 Mg hm-2 a-1)plus mineral fertilizers.Chemical fertilizers were applied at the same rate in each treatment.We found that organic manuring at various rates in combination with mineral fertilizers significantly enhanced the soil organic C(SOC)content.The SOC content in the OM1,OM2,and OM3-treated Mollisols was increased by 7.1%,12.4%,and 15.7%,respectively,compared to that with OM0 treatment.Organic fertilization greatly facilitated the macroaggregation processes and enhanced the aggregate stability compared with OM0 treatment.The proportion of small macroaggregates(250—2000μm)increased,whereas the proportion of the silt-plus-clay fraction decreased in response to an increase in the organic manure addition rates.However,there was no significant difference between the OM2 and OM3 treatments in the weight proportion of aggregates or their mean weight diameters.The turnover rate of macroaggregates increased with an increase in the application rates of organic manure.Organic manuring did not affect the C concentration of the silt-plus-clay fraction,which indicated that the silt and clay particles had approached or reached the C saturation level under the traditional management practices without organic manure input.An increase in the organic manure input slightly increased microaggregate C and significantly increased macroaggregate C.When organic manure was supplied at the highest level,microaggregate C did not change significantly,and only macroaggregate C continued to increase,which indicated that the microaggregate C pool had reached saturation and that additional C was sequestered in macroaggregates.Physical separation of the macroggregates into subfractions showed that the increase of organic C in macroaggregates was mainly attributable to the increase of coarse particulate organic matter in macroaggregates(coarse iPOM).These results suggested that C saturation occurred in a hierarchical fashion in a Mollisol.As the C input increased,the silt-plus-clay C pool saturated before the microaggregate C pool and,consequently,additional C input only accumulated in a relatively labile C pool,the coarse iPOM within macroaggregates,which has a relatively faster turnover rate.