Common grassland management practices include animal grazing and the repeated addition of lime and nutrient fertilizers to soils. These practices can greatly influence the size and distribution of different soil aggregate fractions, thus altering the cycling and storage of carbon (C) and nitrogen (N) in grassland soils. So far, very few studies have simultaneously addressed the potential long-term effect that multiple management practices might have on soil physical aggregation. Here we specifically ask whether and how grazing, liming and nutrient fertilization might influence C and N content (%) as well as C and N pools of different soil aggregate fractions in a long-term grassland experiment established in 1991 at Silwood Park, Berkshire, UK.We found that repeated liming applications over 23 years significantly decreased the C pool (i.e. g C Kg^− 1 soil) of Large Macro Aggregate (LMA > 2 mm) fractions and increased C pools within three smaller soil aggregate fractions: Small Macro Aggregate (SMA, 250 μm–2 mm), Micro Aggregate (MiA, 53–250 μm), and Silt Clay Aggregate (SCA < 53 μm). Soil C (and N) accrual in smaller fractions was mainly caused by positive liming effects on aggregate fraction mass rather than on changes in soil C (and N) content (%). Liming effects could be explained by increases in soil pH, as this factor was significantly positively related to greater soil C and N pools of smaller aggregate fractions. Long-term grazing and inorganic nutrient fertilization had much weaker effects on both soil aggregate-fraction mass and on soil C and N concentrations, however, our evidence is that these practices could also contribute to greater C and N pools of smaller soil fractions.Overall our study demonstrates how agricultural liming can contribute to increase C pools of small (more stable) soil fractions with potential significant benefits for the long-term C balance of human-managed grassland soils.

中文翻译：

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长期草地管理对不同土壤团聚体碳氮库的影响

草原的常见管理做法包括放牧动物以及向土壤中反复添加石灰和营养肥料。这些做法会极大地影响不同土壤团聚体组分的大小和分布，从而改变草地土壤中碳（C）和氮（N）的循环和存储。到目前为止，很少有研究能够同时解决多种管理措施可能对土壤物理聚集产生的长期影响。在此，我们具体询问在1991年在伯克希尔郡希尔伍德公园建立的一项长期草地实验中，放牧，石灰和营养施肥是否以及如何影响碳和氮含量（％）以及不同土壤团聚体组分的碳和氮库，英国。我们发现，在23年内重复施石灰会显着降低碳库（例如，克C Kg^{− 1}土壤）中的大型宏观骨料（LMA> 2 mm）部分和三个较小的土壤骨料部分中增加的碳库：小型宏观骨料（SMA，250 μm–2 mm），微型骨料（MiA，53–250μm）和淤泥粘土骨料（SCA <53μm）。较小部分的土壤C（和N）的累积主要是由于石灰对总部分质量的积极影响，而不是土壤C（和N）含量（％）的变化所致。撒石灰的影响可以用土壤pH值的增加来解释，因为该因素与较大的土壤C和N含量较小的聚集体显着正相关。长期放牧和无机养分施肥对土壤团聚体质量以及土壤碳和氮浓度的影响要弱得多，但是，我们的证据表明，这些做法也可以促进土壤分数较小的碳和氮库的增加。