长期施肥对栗褐土有机碳矿化的影响

【目的】 土壤有机碳矿化是土壤中重要的生物化学过程，与土壤养分的释放、土壤质量的保持以及温室气体的形成密切相关。本文以 25 年长期定位施肥试验为依托，对栗褐土土壤有机碳矿化速率、有机碳累积矿化量的动态变化进行研究，为科学管理土壤肥力、增加栗褐土碳汇、减少温室气体排放提供依据。 【方法】 田间试验开始于 1988，共设置 8 个施肥处理:不施肥 (CK)；单施氮肥 (N)；氮磷肥合施 (NP)；单施低量有机肥(M₁)；低量有机肥与氮肥合施 (M₁N)；低量有机肥与氮磷肥合施(M₁NP)；高量有机肥与氮肥合施 (M₂N)；高量有机肥与氮磷肥合施 (M₂NP)。于 2013 年玉米播种前，采集耕层 (0—20 cm) 土壤样品，采用室内培养方法，对土壤碳矿化释放 CO₂ 的数量和速率进行测定，并利用一级动力学方程计算出土壤有机碳库潜在矿化势和周转速率。 【结果】 各肥料处理不同程度地提高了栗褐土总有机碳含量，以高量有机肥与化肥配施作用最为显著。与 CK 相比，M₂N、M₂NP 处理土壤总有机碳含量增加了 121.1%、166.8%。不同处理土壤样品培养有机碳矿化速率均在第一天达到峰值，随后急剧下降。5 d 后，下降趋缓，不同处理 CO₂ 产生速率趋于一致。培养期间，各处理矿化速率变化符合对数函数关系。长期施用不同肥料均可以提高栗褐土有机碳的矿化速率，其大小顺序为:有机肥与化肥配施 > 单施有机肥 > 单施化肥 > 对照。培养 57 d 后，各处理土壤有机碳累积矿化量为 555.0～980.3 mg/kg，以 M₂NP、M₁N 的累积量较高，为对照的 1.77 倍、1.73 倍。长期施肥栗褐土有机碳矿化率呈下降趋势，以处理 M₂NP 下降最明显，与对照相比，降低了 6.3 个百分点。施肥处理土壤的潜在矿化势均高于对照，M₁N、M₂NP 最高，为 923.7 mg/kg 和 926.4 mg/kg，较对照增加了 74.0% 和 74.5%。不同施肥处理均可明显提升土壤有机碳的周转速率，减少周转时间，其中处理 M₁NP、M₂NP 效果最为明显。 【结论】 长期施用化肥、有机肥及有机无机肥配施可有效促进栗褐土有机碳的积累，提高有机碳的矿化速率和周转速率，降低有机碳的矿化率 (累积矿化量占有机碳总量的比率)，加强了土壤的固碳能力，以 M₂NP 处理的效果更佳。

Effect of long-term fertilization on organic carbon mineralization of cinnamon soil

Objectives]Mineralization of soil organic carbon is an essential process of biochemistry in soils, which is closely related to release of soil nutrients, maintenance of soil quality, and formation of greenhouse gases. This paper is to study the effects of different fertilizing treatments on dynamic changes of soil organic carbon mineralization rate and cumulative decomposition in Cinnamon soils for better managements of soil fertility, increasing carbon sinks and decreasing greenhouse gas emissions.[Methods]Since 1988, a field experiment was conducted in 8 different fertilization treatments: no fertilizer (CK), inorganic N (N, 120 kg/hm2), inorganic N and P (NP, P2O575 kg/hm2), low amount of organic manure (M1, 22500 kg/hm2), low amount of organic manure plus inorganic N (M1N), low amount organic manure plus inorganic N and P (M1NP), high amount organic manure plus inorganic N (M2N) and high amount organic manure plus inorganic N and P (M2NP). Soil samples were collected at 0–20 cm depth before sowing in 2013. Carbon dioxide cumulative emission and mineralization rate were determined by incubation method. First-order kinetic model was used to calculate potential mineralization and turnover rates.[Results]All the long-term fertilization treatments increased total organic carbon in the 0–20 cm depth of soil. The effects of manure combined with chemical fertilizer application, especially M2N and M2NP were more obvious than those in CK total organic C in M2N and M2NP was increased by 121.1% and 166.8%, respectively. The incubation results show that mineralization rates of soil organic carbon in all the treatments are the highest in the first day and then decreased rapidly. After 5 days incubation, the mineralization rate decrease slowdown. The changes of mineralization rates of soil organic carbon of all the treatment were in agreement with the logarithmic function relationship. Long-time fertilization enhanced the mineralization rates of soil organic carbon in the Cinnamon soils in the following order: manure with chemical fertilizer > manure > chemical fertilizer > CK. The cumulative CO2during 57 days incubation period was in the range of 555.0–980.3 mg/kg. The M2NP and M1N had the highest amounts which were 1.77 and 1.73 fold higher than in CK, respectively. The percentage of cumulative CO2-C in TOC during the 57 days incubation period in all the fertilization treatments were lower than in comparing to CK. The M2NP treatment decreased the most with 6.3% lower than that in CK. The potential CO2-C evolved from the fertilization treatments were all higher than that from the CK, especially the M1N, and M2NP that produced 923.7 mg/kg and 926.4 mg/kg, which were 74.0%and 74.5% higher than CK. The fertilization treatment increased the turnover rate of soil organic carbon significantly and reduced the turnover time. Among the fertilization treatments, M1NP and M2NP showed strong impact on these.[Conclusions]Long-term application of chemical fertilizer, manure, and manure with chemical fertilizer can effectively increase the accumulation of organic carbon in Castano-cinnamon soils and increase organic carbon mineralization rate and turnover rate. However, the fertilization treatments reduce the cumulative mineralization rate (the ratio of accumulated mineralization amount to total organic carbon), and enhance the soil carbon sequestration capacity. Among these treatments, application of 45000 kg/hm2manure, 120 kg/hm2and P2O575 kg/hm2shows the most significant impact.