长期施肥对浙江稻田土壤团聚体及其有机碳分布的影响

以浙江省稻田长期定位试验站为依托,研究长期不同施肥措施对土壤团聚体及其有机碳分布的影响。研究结果表明,与不施肥对照(CK)相比,栏肥与化肥配施(NPKOM)、单施栏肥(OM)、秸秆与化肥配施(NPKRS)和单施秸秆(RS)处理均显著提高了2 mm和2~0.25 mm水稳定性大团聚体的含量和团聚体平均重量直径(p0.05),强化了团聚体对土壤有机碳的物理保护作用。此外,长期有机无机配施(NPKOM和NPKRS)处理显著提高了各个粒级团聚体中有机碳含量,并且显著增加水稳定性大团聚体有机碳的贡献率,而长期单施化肥和单施秸秆处理并未有效增加土壤总有机碳含量。不同施肥处理下,2~0.25 mm粒级团聚体有机碳占土壤总有机碳的34.2%~48.6%,是土壤有机碳的主要载体。利用傅立叶变换红外光谱(FT-IR)技术对2~0.25 mm和0.053 mm团聚体进行结构表征,发现长期单施有机肥或者有机无机配施下芳香族C较CK提高29.9%~45.2%,较NPK处理提高22.3%~36.6%,提高了土壤有机碳的芳构化。在有机碳积累方面,施用有机肥,尤其是栏肥与化肥配施,同时强化了团聚体对有机碳的物理保护以及促进了化学抗性有机碳组分的积累,是加强稻田土壤有机碳库积累的合理施肥模式。

Effect of long-term fertilizer application on distribution of aggregates and aggregate-associated organic carbon in paddy soil

Soil samples collected from a 17 years old long-term fertilizer field trial in Zhejiang Province, China were analyzed to evaluate the influence of organic amendments and chemical fertilizers on the distribution of aggregates and aggregate-associated carbon in paddy soil. The fertilizer treatments included the control (no fertilizer applied, CK), combination of chemical fertilizers and rice straw (NPKRS), combination of chemical fertilizers and organic manure (NPKOM), chemical fertilizers (NPK), rice straw alone (RS), organic manure alone (OM). Wet-sieving method was used for the evaluation of physical stability of aggregates and their distribution of particle-size fractions. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the inherent chemical composition of soil organic carbon (SOC) at the molecular level in the aggregates. It was found that the fertilizer treatments had significant effect on the mass distribution of aggregate size fractions and aggregate stability. In comparison with the CK, the NPKOM, OM, NPKRS and RS treatments significantly (P<0.05) increased the proportion of >2 mm and 2~0.25 mm water stable aggregates, and the values of mean weight diameter, indicating that these fertilizer treatments enhanced formation of macroaggregates and therefore improved the physical protection of SOC by macroaggregates. The SOC content of the bulk soil and all aggregate size fractions, as well as the contribution of macroaggregate-associated (i.e., >2 mm and 2~0.25 mm) SOC to total soil organic C were significantly higher in the NPKOM and NPKRS treatments than that in the CK. However, there was no significant difference in the accumulation of SOC between the control and the NPK or RS treatment. The 2~0.25 mm aggregates accounted for 34.16~48.6% of the total SOC content in all treatments, suggesting that 2~0.25 mm aggregates were the main carrier of SOC in the paddy soil. The FTIR spectra of the 2~0.25 mm and <0.053 mm aggregates showed that the ratios of aromatic-C to the total SOC in the NPKOM, OM, NPKRS and RS treatments were 29.9~45.2% greater than that in the CK, and were 22.3~36.6% greater than that in the NPK treatment. The greatest ratio of aromatic-C to the total SOC was observed in the NPKOM treatment. The FTIR spectra also indicated small but consistent increases in aliphatic-C groups in soils treated with organic amendments. The increases in the proportion of aromatic-C and aliphatic-C were mainly attributed to the inputs of recalcitrant compounds derived from organic amendments, and/or to the reduction in H-bonded O-H hydroxyl groups of phenols induced by biochemical processes in soils treated with organic amendments. Our results indicated that both the enhanced physical protection and increased proportion of chemically recalcitrant organic compounds contributed to the carbon accumulation in the paddy soil treated with organic amendments, with the most prominent enhancement being observed in the NPKOM treatment. Long-term application of organic manure and chemical fertilizers combined appeared to be a sustainable and environmentally friendly strategy to achieve both high agricultural production and soil carbon accumulation.