改变施肥管理后不同肥力稻田土壤CO2排放特征

利用一个长达30a水稻土长期定位试验,在保证原有定位试验继续正常开展的前提下,将原化肥处理改施有机肥,原有机肥处理改施化肥或者增施有机肥。通过观测田间试验2012—2013年双季稻轮作周期内不同肥力水平稻田土壤施肥管理改变后的土体CO2排放通量(FCO2),研究不同后续施肥管理对不同肥力红壤性水稻土CO2排放的影响。结果表明:变更施肥能明显改变CO2排放动态变化,其中长期施用有机肥处理改施化肥后其FCO2明显减小,长期施用化肥或有机肥处理增施有机肥后其FCO2显著增大。有机肥和土壤有机碳均可促进土体CO2排放,有机肥处理有机物料碳添加量与CO2-C年排放量呈极显著的正相关关系(r=0.9015**,n=21),单施化肥处理土壤有机碳含量与土体CO2-C年排放量符合线性方程:y=10.962x-68.86(R2=0.7507,n=9,P0.01)。长期施用有机肥土壤改施化肥会导致其有机碳矿化损失,土壤有机碳含量越高,矿化损失量越多,最终其有机碳水平将与长期施用化肥的土壤有机碳平衡值一致;长期施用化肥或有机肥土壤改施或增施有机肥可促进土壤有机碳积累,外源添加碳越多,土壤积累碳越多;相同有机肥施用量下土壤有机碳含量越高,有机物料表观分解率越大,积累于土壤中的有机碳越少,不同有机碳水平土壤在相同有机肥管理下其有机碳最终会达到相同的平衡值。在有机碳水平较低(20.46 g/kg)红壤稻田上增施有机肥是提升已培肥水稻土有机碳含量的可持续发展措施,而在有机碳水平较高(14.45 g/kg)红壤稻田上应避免改施化肥。总之,在有机碳含量较高或者较低的中国南方红壤性水稻土上,持续的有机肥施用是保持或者提高其有机碳水平的必要措施。

Effects of fertilization reforming on the CO2 flux in paddy soils with different fertilities

Paddy soils show significant potential of carbon sequestration. The soil organic carbon (SOC) content of red paddy soils have been reported to be steady after 30 years'' cultivation and it varies with different fertilization practice. In this study, three red paddy soils, which cultivated under different organic fertilization treatments in a 30 years fertilizer experiment in Changsha, China, was adjusted to the following seven treatments without compromising the original experiment: the original high organic fertilization treatment(HOM), the high organic fertilization treatment changed from the original normal organic fertilization treatment(N-H), the original normal organic fertilization treatment(NOM), the normal organic fertilization treatment changed from chemical fertilization (C-N), the chemical fertilization treatment changed from high organic fertilization treatment(H-C), the chemical fertilization treatment changed from normal organic fertilization treatment(N-C), the original chemical fertilization treatment(CF). CO₂ flux of the three original and four changed treatments was measured to study the effects of the following-up fertilization reforming on the CO₂ flux in red paddy soils with different fertilities in 2012-2013. The results clearly showed that the following-up changing of fertilization had obvious impacts on the dynamics of CO₂ flux. The CO₂ flux in the soils under long-term organic fertilization treatments decreased after the adjustment from organic fertilization to chemical fertilization. However, the CO₂ flux in the soils under long-term chemical fertilization treatments increased remarkably after the adjustment from chemical fertilization to organic fertilization. The results also indicated that both organic fertilizer and soil organic carbon (SOC) had important impacts on CO₂ flux. The amount of organic carbon inputted by organic fertilizers had a significantly positive relationship with the total amount of annual CO₂-C flux (r=0.9015^**, n=21), and the inherent SOC content (x) also had a positive relationship with the total amount of annual CO₂-C (y) (y = 10.962x-68.86, R² = 0.7507, n = 9, P<0.01) in the paddy soils received chemical in 2012. The fertilization reforming from organic fertilization to chemical fertilization would lead to the loss of SOC in paddy soils due to its mineralization, and the SOC loss increased with the rising of inherent SOC content. The SOC content in the paddy soils under long-term organic fertilization would be consistent with that in the paddy soils under long-term chemical fertilization after the fertilization reforming from organic to chemical fertilization for a certain time. The fertilization reforming from chemical to organic fertilization, or from low organic to high organic fertilization would lead to the SOC accumulation in paddy soils, and the accumulating rate of SOC had a positive relationship with the amount of the inputted organic material. Under same organic fertilization treatment, the apparent decomposition rate of organic material applied in the soils with high SOC content was larger than that in the soils with low SOC content, which would result in lower SOC accumulation. So, the paddy soils with different SOC content would have the same SOC level when they received same organic fertilization management for a certain time. As a conclusion, the sustained organic fertilization in red paddy soils with high or low SOC content is essential to maintain or improve the soil organic carbon content in Southern China.