Characteristics Of Organic Carbon Stock And Carbon Fixation Capacity In Orchard Soils By Different Managing Measures

The red soil hilly region in the Southern China, in which C storage is large, and land use and vegetation cover changes strongly, is an important ecological area in the world, and has an important impact on the global C cycle and the seasonal fluctuation of atmospheric CO2. Meanwhile, the region is also an important production base of the tropical and subtropical economic fruit and tea in China, However, due to longly irrational exploitation and use of land resources, soil erosion and land degradation is serious. But now study on soil organic carbon in the orchard of the evolution and stable mechanism is still strongly weak. Therefore, in this research we choose location experiment and mathematical modeling to investigate soil organic carbon in the orchard and its quality of the evolution, and analyzed its response on growing years, reclamation mode, herbage interplanting, fertilizer management, evaluated soil carbon fixation capacities under different reclamation modes, draw the following conclusions:â‘´There was different distribution characters of soil organic carbon in the orchard on microhabitat distribution and redistribution slope. Soil organic carbon content in clean-tillage orchard showed less outward along the trunk in the horizontal direction. But there was no significant difference in soil organic carbon along the trunk in herbage interplanting orchard. Soil organic carbon under different cultivating systems decreased with soil depth in vertical direction. On slope re-distribution, soil organic carbon content with different cultivating methods varied inconsistent, for example, the downhill bits> middle slope> upper slope under clean tillage treatment, the middle slope> downhill bit> upper slope under herbage interplanting. Herbage interplanting reduced the horizontal heterogeneity of soil organic carbon in orchards, but increased the vertical variation.⑵The characteristics of soil organic carbon in orchards had been shown to vary by growing years. The 60's citrus orchard compared with 30's citrus orchard, 0-100cm soil organic carbon storage increased more than 30.30%, micro-aggregates (<0.25mm) carbon storage increased by 20% to 80%, the heavy fraction of organic carbon increased by 29.27%, resistant organic carbon content increased by 31.94%, black carbon content increased by 4.09%. As organic carbon which combined with micro-aggregates was protected by physical, and resistant organic carbon and black carbon is recalcitrant organic carbon in soil, this indicated that the carbon sequestration capacity of 60's citrus orchard is higher than 30's citrus orchard.⑶Compared with 30's citrus orchard, soil particulate organic carbon, light fraction organic carbon, dissolved organic carbon and microbial biomass carbon in the ratio of total organic carbon in 60's citrus orchard were all lower. It showed that more than 30 years after planting period, there is degradation risk of soil organic carbon quality with the increasing of growing years.â‘·Compared with the clean tillage orchard, R0.25, MWD, and GWD of soil aggregates in peach orchard under different herbage interplanting increased by 2.1% to 2.4%, 1.6% to 8.9% and 2.3% to 12.2%, respectively. Soil total organic carbon content increased by 12.0% to 15.3%. The particulate organic carbon, light fraction of organic carbon, dissolved organic carbon and microbial biomass carbon content increased by 34.1% to 52.7%, 40.7% to 52.6%, 52.3% to 99.0% and 22.5% to 42.2%,, respectively. It showed that herbage interplanting was conducive to improve orchard soil structure, increase soil fertility.⑸Soil organic carbon storage of <0.25mm soil aggregates in herbage interplanting orchard was significantly higher than that of clean tillage orchard, resistant organic carbon content in soil was also increased by 15.3% to 20.1%. It showed that herbage interplanting was conducive to increase the stability of soil organic carbon stock.⑹The results on field and laboratory experiments showed that compared with the clean tillage, soil respiration rate, potential mineralization of organic carbon (C₀), easily mineralizable organic carbon content (C1) and initial potential mineralization rate (C₀k) under herbage interplanting were significantly higher in nectarine orchards. But there was no significant difference among the treatments of intercropping Arachis pintoi and Chamaecrista rotundifolia. It showed that herbage interplanting could increase microbial activity, and be conducive to the transformation of soil carbon and nitrogen and the improvement of soil fertility.⑺Compared with no fertilizer and only chemical fertilizer, soil organic carbon content in citrus orchard under different fertilizers treatments was not significantly different. With only application of organic fertilizer of mushroom residue and mixed application of inorganic and organic fertilizer on soil, dissolved organic carbon, microbial biomass carbon, particulate organic carbon and light fraction of organic carbon increased by 26.39% to 75.97% and 13.95% to 58.66 %, 76.46% to 264.25% and 5.97% to 118.74%, 23.02% to 73.71% and 17.97% to 66.58%, 31.07% to 70.61% and 17.34% to 52.74%, respectively. It showed that the short-term reasonable application of organic fertilizer can not significantly increase the total organic carbon content in surface soil, but can significantly increase the active organic carbon content in citrus orchard.â‘»By mixed application of inorganic and organic fertilizer on soil, there was no significant increase of potential carbon mineralization in the ratio of total organic carbon with the increasing of the amount of organic fertilizer in citrus orchard. Compared with no fertilizer and only chemical fertilizer, resistant organic carbon content and organic carbon stock of soil micro-aggregates in citrus orchard under organic fertilizer treatments increased by 23.77% to 44.27% and 22.78% to 43.12%, 3.67% to 9.24% and 1.80% to 7.28%, respectively. It showed that mixed application of inorganic and organic fertilizer on soil can increase the accumulation of soil organic carbon.⑼Soil carbon sequestration potential under different management systems was evaluated with the implication of Jenny's model, The results showed that: the equilibrium value of soil organic carbon(EV) and carbon sequestration potential(CS) in landings clean tillage orchard increased by 29.69% and 174.56% than those of the longitudinal clean tillage orchard, respectively. EV and CS in landings herbage interplanting orchard increased by 20.09% to 22.89% and 48.23% to 52.86% than those of landings clean tillage orchard, respectively. EV and CS in orchard interplanting with Arachis pintoi orchard increased by 2.33% and 3.13% than those of orchard interplantingwith Chamaecrista rotundifolia, respectively. It showed that herbage interplanting was conducive to enhancing soil carbon sink.