长期施肥对红壤性水稻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,与土壤养分释放、土壤质量保持以及温室效应密切相关。揭示稻田生态系统在长期施肥下土壤有机碳固存与矿化特征,旨在正确评价施肥对全球气候变化的影响。【方法】本研究以33年长期定位试验为依托,对红壤性水稻土土壤有机碳累积及矿化动力学特征等进行系统研究。长期定位试验始于1984年,选取其中5个处理：不施肥处理（CK）,施氮磷钾化肥处理（NPK）,施70%化肥+30%有机肥处理（70F+30M）,施50%化肥+50%有机肥处理（50F+50M）,施30%化肥+70%有机肥处理（30F+70M）,于 2017 年早稻种植前采集耕层 （0—20 cm） 土壤样品,采用室内培养方法,测定土壤碳矿化释放 CO₂-C量和速率等,并采用一级动力学方程拟合土壤潜在可矿化有机碳量（C₀）、易矿化有机碳量（C₁）和周转速率常数等。【结果】各施肥处理均不同程度地提高了土壤总有机碳含量,NPK处理有机碳含量显著高于CK,较CK提高了27.32%。化肥配施有机肥处理（70F+30M、50F+50M 和30F+70M）土壤有机碳显著高于NPK处理（P<0.05）,平均较NPK处理提高了31.31%,以50F+50M和30F+70M处理较为显著。各处理有机碳矿化速率均在培养后的第1天达到峰值且差异显著,排序为50F+50M>30F+70M>70F+30M>NPK>CK,随后下降,11 d之后趋于稳定,稳定后各处理的土壤有机碳矿化速率大小排序为：30F+70M>50F+50M>70F+30M>NPK≈CK。在整个培养期,土壤有机碳矿化速率与培养时间呈对数曲线关系。培养35 d结束后,NPK处理较CK未能显著改变土壤有机碳累积矿化量（P>0.05）,70F+30M、50F+50M和30F+70M处理土壤有机碳累积矿化量显著高于NPK处理（P<0.05）,分别较NPK提高了50.99%、70.85%和86.39%。各处理土壤有机碳累积矿化率（累积矿化量占有机碳总量的比率）变化范围为3%—4%,30F+70M处理显著高于NPK处理（P<0.05）。施肥处理均不同程度地提高了土壤潜在可矿化有机碳量,以30F+70M处理最高,较NPK提高了1.19倍。不同施肥处理较不施肥均未明显改变土壤有机碳周转速率及半周转期。土壤潜在可矿化有机碳量（C₀）、易矿化有机碳量（C₁）、累积矿化量及累积矿化率均显著受土壤有机碳含量及投入碳量的影响,且呈现正相关关系。土壤潜在可矿化有机碳量（C₀）/土壤有机碳比值与所投入碳量呈现显著正相关（P<0.05）;土壤有机碳的周转速率常数（k）与土壤有机碳及投入碳量均未呈现显著性相关性。【结论】长期化肥配施有机肥可有效提高红壤性水稻土有机碳的矿化速率及促进有机碳的积累,并未显著改变土壤有机碳的矿化率,有利于红壤性水稻土的养分供应及固碳。

Effects of Long-Term Fertilization on Mineralization of Soil Organic Carbon in Red Paddy Soil

【Objective】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 greenhouse effect. Revealing the characteristics of soil organic carbon sequestration and mineralization in rice field ecosystem under long-term fertilization are aimed at correctly evaluating the impact of fertilization on global climate change. 【Method】Based on the 33-year long-term stationary experiment, systematic study of soil organic carbon accumulation and mineralization dynamics of red soil double-rice cropping field in red paddy soil was carried out in this paper. Five fertilization treatments were selected form the long-term stationary experiment which began in 1984, including CK (no fertilizer), NPK (application of chemical), 70F+30M (70% NPK plus 30% organic fertilizer), 50F+50M (50% NPK plus 50% organic fertilizer) and 30F+70M (30% NPK plus 70% organic fertilizer). Soil samples from tillage layer (0-20 cm) were collected before early rice planting in 2017. The amount and rate of CO₂-C released by soil carbon mineralization were determined by incubation method. First-order kinetic model was used to calculate potential mineralization (C₀), easily mineralizing organic carbon (C₁) and turnover rates. 【Result】 All the long-term fertilization treatments increased total organic carbon in the 0-20 cm depth of soil. The content of total organic carbon under NPK treatment was significantly higher than that under CK treatment, 27.32% higher than that under CK treatment. Chemical fertilizer combined with organic fertilizer treatments were all higher than that under NPK treatment (P<0.05), which was 31.31% higher than that under NPK treatment on average. The effects of treatments of 50F+50M and 30F+70M were more obvious. The incubation results showed that mineralization rates of soil organic carbon in all the treatments reached the peak value on the first day and the differences were significant, and the order was: 50F+50M>30F+70M>70F+30M>NPK>CK, then they all decreased and stabilized after 11 days. The order of soil organic carbon mineralization rate after stabilization was: 30F+70M>50F+50M>70F+30M>NPK≈CK. During the whole incubation process, the relation between SOC mineralization rate and incubation days followed the logarithm law. After 35 days incubation, compared with CK, NPK treatment did not significantly change soil organic carbon accumulation mineralization (P>0.05). The cumulative mineralized SOC under 70F + 30M, 50F + 50M and 30F + 70M treatments were significantly higher than that under NPK (P<0.05), with increased 50.99%, 70.85% and 86.39%, respectively. The cumulative mineralization rate of soil organic carbon (the ratio of cumulative mineralization to total organic carbon) under all treatments varied from 3% to 4%, and 30F+70M was significantly higher than NPK (P<0.05). The potential mineralizable SOC in soil were enhanced in varying degrees by adding fertilizers, among which 30F+70M was the highest with 1.19 times higher than NPK. Fertilization did not cause significant changes in turnover rate and half turnover period of SOC. C₀, C₁, cumulative mineralization and cumulative mineralization rate were significantly affected by soil carbon and input carbon content, and showed a positive correlation. C₀ / soil organic carbon was positively correlated with input carbon content (P<0.05), and the rotation rate constant (k) of soil organic carbon was not significantly correlated with soil organic carbon and input carbon. 【Conclusion】 In summary, long-term chemical fertilizer combined with organic fertilizer increased mineralization rate and the accumulation of SOC in red paddy soils, but not significantly changed the mineralized SOC to SOC ratio. This was very useful for nutrient supply and carbon sequestration of red paddy soils.