不同培肥措施对红壤坡耕地土壤有机碳流失的影响

Effects of Fertility-Building Practices on Soil Organic Carbon Loss with Sediment in Sloping Cropland of Red Soil

基于侵蚀小区三年的田间监测(2015—2017年),分析不施肥(CK)、单施化肥(NPK)、化肥与秸秆覆盖(NPK+Str)、化肥与生物质炭(NPK+BC)、化肥与猪粪(NPK+OM)等五种培肥措施对红壤坡耕地水土流失及其有机碳流失的影响。结果表明,不同培肥措施地表径流表现为NPK+BC > CK > NPK > NPK+OM > NPK+Str(P< 0.05),泥沙流失量表现为CK、NPK+BC、NPK > NPK+OM > NPK+Str(P < 0.05),约有69%~83%径流和70%~90%侵蚀发生在花生生长季(4—8月)。与NPK相比,NPK+Str、NPK+BC和NPK+OM均显著增加泥沙中有机碳含量(P< 0.05),而有机碳流失总量以NPK+BC处理最多(C 52.1 t·km^-2·a^-1),NPK+OM和NPK+Str最少。泥沙中有机碳含量无明显的季节变化,但是78%以上泥沙有机碳流失量发生在花生生长季。说明NPK+Str和NPK+OM的培肥措施能有效减少红壤坡耕地土壤侵蚀,阻控有机碳流失,而NPK+BC由于生物质炭颗粒小、密度低而易流失,阻控土壤侵蚀效果并不显著。

【Objective】Soil is the largest carbon pool in the terrestrial ecosystem. Storage and sequestration of soil organic carbon (SOC) is an important factor affecting balance between input of organic carbon with organic matter incorporated into the soil and loss of SOC. Being a major hydraulic erosion stricken area in China, red soil sloping farmlands suffer serious soil erosion, which in turn drives heavy losses of soil organic carbon from the farmlands, posing a problem that should not be ignored. However, so far little is known about status of soil erosion on and SOC loss via soil erosion from red soil sloping farmlands subjected to different fertility-building practices, which seriously affects sustainable development of the local agriculture and eco-environment. Therefore, the objective of this study is to investigate effects of fertility-building practices on surface runoff and soil erosion, and to elucidate dynamics of organic carbon loss with erosion sediment from red soil sloping croplands.【Method】A field experiment was initiated in 2012 and designed to have 15 erosion plots laid out on a sloping cropland, for five treatments different in fertility building pattern and three replicates for each treatment. The 5 treatments include CK (zero fertilization), NPK (application of chemical NPK fertilizers), NPK+Str (application of NPK fertilizer plus rice straw mulch), NPK+BC (application of NPK fertilizer plus rice straw-derived biochar),and NPK+OM (application of NPK fertilizer plus swine manure). Peanut was planted in all the plots. At the lower end of each plot, a pit was dug for installation of a tipping bucket runoff flow meter connected with an rainfall event counter to keep real-time records of runoff, and entire process of a soil erosion event. A 300 mesh screen was placed under the bucket sm to collect sediment. Runoff, soil erosion sediment and organic carbon concentration in the soil sediment were monitored during the period of 2015-2017.【Result】Results show that in terms of volume of runoff, the five treatments displayed an order of NPK+BC > CK > NPK > NPK+OM > NPK+Str (P< 0.05), and in terms of sediment loss was in the order of CK≈NPK+BC≈NPK > NPK+OM > NPK+Str (P < 0.05). About 69%~83% of the surface runoff and 70%~89% of the soil erosion occurred during the peanut growing season (April - August). Compared with Treatment NPK treatments, Treatment NPK+Str, NOK+BC and NPK+OM significantly increased the concentration of organic carbon in the sediment (P < 0.05). However, Treatment NPK+BC was the highest in total organic carbon loss via soil sediment ( C 52.1 t·km^-2·a^-1), while Treatments NPK+OM and NPK+Str the lowest. No significant seasonal changes were observed in organic carbon content in sediment. About 78% of the loss of organic carbon with sediment occurred during the peanut growing season (April-August) in each year.【Conclusion】 All the findings in this study demonstrate that application of NPK Fertilizer plus rice straw mulch and NPK fertilizer plus swine manure (or Treatment NPK+Str and NPK+OM) can reduce soil erosion and organic carbon loss effectively, while application of NPK fertilizer plus rice straw-derived biochar (or Treatment NPK+BC) does not have much effect on soil erosion, and instead it increases the concentration of organic carbon in the sediment, which is attributed to characteristics of the local physical environment and texture of the rice straw-derived biochar, small in particle compositions, and low in density, and making it easy to get lost with surface runoff and erosion sediment and hard to retain in the soil. So it is not recommended to use biochar as supplement in fertility-building for soil erosion control in the red soil regions of China.