利用方式对珠江三角洲耕层土壤团聚体分布及碳氮磷化学计量特征的影响

为探明利用方式对珠江三角洲农田耕层土壤团聚体特征和碳氮磷的影响，采集长期水田、旱地和水旱轮作的耕层土壤，对土壤团聚体组成、碳氮磷分布及其化学计量特征进行研究。结果表明，水田土壤以>2 mm团聚体为主，其含量占比显著高于旱地和水旱轮作两种利用方式，旱地和水旱轮作土壤则以<0.25 mm微团聚体为主。各粒级团聚体有机碳和全氮含量均表现为水田显著高于旱地、水旱轮作，而全磷含量变化规律不明显。水田土壤团聚体有机碳和全氮含量随粒径减小呈先升高后降低趋势，旱地、水旱轮作土壤的有机碳、全氮和全磷含量均随粒径减小呈降低趋势，三种利用方式碳氮磷主要集中在>2 mm和2~0.5 mm团聚体中。各粒级团聚体C：P和N：P表现为水田土壤显著高于旱地、水旱轮作，而C：N差异不显著（P>0.05）。水田和旱地土壤团聚体C：N、C：P和N：P随粒径变化规律与其团聚体养分表现出一致性，而水旱轮作则表现出相反规律。土壤碳氮磷与团聚体碳氮磷总体上呈显著正相关（P<0.05），表明团聚体碳氮磷对土壤养分具有良好的指示性，且随粒径减小指示作用增强。土壤团聚体C：P对利用方式变化最敏感，可作为反映该区域耕层土壤团聚体碳氮磷含量及化学计量特征的敏感性指标。水田土壤大团聚体及其碳氮磷含量较高，土壤结构良好，有利于团聚体对土壤养分的物理保护和土壤碳氮磷的积累。

Effect of land use on topsoil aggregate distribution and stoichiometric characteristics of C, N, and P in the Pearl River Delta

To explore the effect of different types of land use on the characteristics of topsoil aggregates and C, N, and P in the Pearl River Delta farmland, the composition of soil aggregates and the distribution of C, N, and P in paddy, dry land and paddy-upland rotation topsoil were studied. The size of the main aggregates in paddy was >2 mm, which was significantly higher than that in other types of land use; the main aggregates in dry land and paddy-upland rotation were <0.25 mm. The content of organic C and total N within different aggregate sizes in paddy was significantly higher than that in dry land and paddy-upland rotation, but the change of total P content was not obvious. The content of organic C and total N in paddy aggregates initially increased and then decreased with decreasing aggregate size. The content of organic C, total N, and total P in dry land and paddy-upland rotation aggregates decreased with decreasing aggregate size. The contents of C, N, and P in the three types of land use were mainly concentrated in aggregates >2 mm and 2~0.5 mm. The C:P and N:P ratios of each aggregate size in paddy were significantly higher than that in dry land and paddy-upland rotation but there was no significant difference in the C:N ratio, which indicated good coupling of C and N in soils. The C:N, C:P, and N:P ratios of each aggregate size in paddy and dry land were consistent with the variation of C, N, and P, while paddy-upland rotation showed the opposite regular pattern. There was a significant positive correlation between C, N, and P in soil and C, N, and P in aggregate(P<0.05), which indicated that C, N, and P in aggregate had a good indicative effect on soil nutrients, and that the indicative effect was stronger with decreasing aggregate size. The highest sensitivity value was observed for C:P, which could be used as a sensitive indicator to reflect the C, N, and P content and the stoichiometric characteristics of topsoil aggregates in farmland. In paddy field, the size of macroaggregates and their C, N, and P content were the highest, showing good soil structure. They are beneficial for the physical protection of soil nutrients and in promoting the accumulation of C, N, and P.