1,721,086 research outputs found
Response of paddy soil organic carbon accumulation to changes in long-term yield-driven carbon inputs in subtropical China
No full textA decrease in C inputs from the return of crop residues to soil has occurred in many regions worldwide in recent years. The effects of this. decline in C inputs could provide valuable information for assessing the long-term impact of litter C inputs on soil organic C (SOC) in rice paddy soils. The present study aimed to evaluate the response of rice paddy SOC accumulation to changes in actual C inputs in subtropical China, with emphasis on the response of C accumulation to declining C inputs. For this, we used a long-term field experiment on paddy soil in a rice-rice (Oryza sativa L.) cropping system running from 1990 to 2014. The four treatments were CK (control, no fertilizer), OM (organic matter application), NPK (N, P, and K fertilizer application), and NPKOM (NPK and organic matter application). Organic matter application for the OM and NPKOM treatments included rice straw and green manure that were left in the field after harvest and chopped, along with rice residues with stubbles and roots. In all treatments, C sequestration showed an increasing trend (from 0.207 to 0.8800 g kg(-1) yr(-1)) in the early and middle stages of the experiment (1990-2006) followed by a decreasing trend (from 0.429 to 0.064 g kg(-1) yr(-1)) in the late stage (2007-2014). The trends. were more pronounced for the OM and NPKOM treatments than for their CK and NPK counterparts. The changes in SOC stocks were consistent with changes in C inputs (p < 0.01). During the late stage, yield and litter inputs from crop residues and green manure decreased, quickly affecting SOC stock in paddy soils. This declining trend in annual rice yields was mainly caused by the decline in first rice yields, accounting for 42.3-91.5% of the decrease in annual C inputs..Insufficient P or N and K supply and unfavorable climatic factors (decreases in sunshine duration and both maximum and minimum temperatures) are possible reasons for the decline in first rice yields and green manure biomass in the late stage. Collectively, the results suggest that C stocks in high-productivity paddy soils respond very sensitively to a decline in C inputs. This raises the risk of loss of C stock in paddy soil if, in the long run, a large return of C to soil with crop residues or by other sources, e.g., green manure, cannot be achieved. (C) 2016 Elsevier B.V. All rights reserved
Loss of labile organic carbon from subsoil due to land-use changes in subtropical China
No full textTopsoil carbon (C) stocks are known to decrease as a consequence of the conversion of natural ecosystems to plantations or croplands; however, the effect of land use change on subsoil C remains unknown. Here, we hypothesized that the effect of land use change on labile subsoil organic C may be even stronger than for topsoil due to upward concentration of plantations and crops root systems. We evaluated soil labile organic C fractions, including particulate organic carbon (POC) and its components [coarse POC and fine POC], light fraction organic carbon (LFOC), readily oxidizable organic carbon, dissolved organic carbon (DOC) and microbial biomass down to 100 cm soil depth from four typical land use systems in subtropical China. Decrease in fine root biomass was more pronounced below 20 cm than in the overlying topsoil (70% vs. 56% for plantation and 62% vs. 37% for orchard. respectively) driving a reduction in subsoil labile organic C stocks. Land use changes from natural forest to Chinese fir plantation, Chinese chestnut orchard, or sloping tillage reduced soil organic C stocks and that of its labile fractions both in top and subsoil (20-100 cm). POC reduction was mainly driven by a decrease in fine POC in topsoil, while DOC was mainly reduced in subsoil. Fine POC, LFOC and microbial biomass can be useful early indicators of changes in topsoil organic C. In contrast, LFOC and DOC are useful indicators for subsoil. Reduced proportions of fine POC, LFOC, DOC and microbial biomass to soil organic C reflected the decline in soil organic C quality caused by land use changes. We conclude that land use changes decrease C sequestration both in topsoil and subsoil, which is initially indicated by the labile soil organic C fractions. (C) 2015 Elsevier Ltd. All rights reserved
To shake or not to shake: Silicone tube approach for incubation studies on CH4 oxidation in submerged soils
No full textAnaerobic oxidation of methane in paddy soil: Role of electron acceptors and fertilization in mitigating CH4 fluxes
No full textTo shake or not to shake: 13C-based evidence on anaerobic methane oxidation in paddy soil
No full textNitrogen fertilization alters the distribution and fates of photosynthesized carbon in rice–soil systems: a 13C-CO2 pulse labeling study
No full textInteractions between biochar and litter priming: A three-source C-14 and delta C-13 partitioning study
No full textAlthough it has been separately reported that biochar primes the decomposition of soil organic matter (SOM) or fresh organic matter, little is known about the simultaneous effects of biochar on SOM versus plant litter mineralization. We applied dual C-13/C-14 isotopic labels to partition soil CO2 efflux and C pools into three sources: SOM, litter and biochar. Biochar made by slow pyrolysis (400 degrees C) of C-14 labeled residues of rice (Oryza saliva, C3) and maize (Zea mays, C4) litter were added separately or in combination to a silty Fluvisol with a C3 isotopic signature and incubated at 25 degrees C over a period of 6 months. Biochar decomposition was very slow, with a mean rate of 0.017% d(-1). Approximately 63% of biochar-derived CO2 was produced in the first month. Mixing with litter reduced biochar mineralization by 14%. Addition of biochar alone to soil induced a cumulative positive priming effect (0.24 mg C g(-1) soil) on SOM decomposition over 183 days, a much smaller effect than litter-induced priming (1.05 mg CO2-C g(-1) soil). Compared to soils with only litter amended, biochar and litter added in combination decreased SOM mineralization by 19% while increasing litter mineralization by 6.9%, with no net changes in total CO2 release. Increased litter-but not SOM-derived C in microbial biomass in the presence of biochar suggested that biochar caused preferential microbial utilization of litter over SOM. Given that immobilization of mineral N in the soil-litter mixture was markedly enhanced following the addition of biochar, we proposed that the biochar-induced preferential microbial utilization of litter over SOM was due primarily to alterations in N cycling. In conclusion, the priming effects of litter on SOM are changed by the presence of biochar. (C) 2016 Elsevier Ltd. All rights reserved
Rapid decrease of soil carbon after abandonment of subtropical paddy fields
No full textPaddy field abandonment has become a major concern in China, particularly among traditional rice-cultivation regions. Abandonment results in the alteration of many processes affecting C sequestration and turnover, but the final effects on C stocks remain unknown. To examine the effects of paddy abandonment on topsoil organic C (SOC) content and stocks, a long-term experiment was performed in subtropical China, examining an abandoned paddy field with different pre-abandonment fertilization history (from 1991 to 2006 years) and SOC gradients (from 19.2 to 22.0 g C kg(-1)). Paddy field abandonment significantly reduced the topsoil SOC content and stock (0-20 cm). Eight years after cultivation ceased, SOC content and C stock had decreased by 9.9-20.9% and 10.2-20.8%, respectively, yielding a mean annual loss rate of 0.30-0.60 g C kg(-1)center dot yr.(-1) and 0.50-1.15 t C ha(-1)center dot yr.(-1), respectively. Soils with higher initial SOC content were more sensitive to abandonment than soils with low SOC levels. Dissolved organic C (DOC) was more sensitive to abandonment, as evidenced by the faster decrease of DOC than SOC. The rapid reduction of SOC content, combined with a strong decrease in DOC, indicates that post-abandonment C inputs into the soil were far lower than the concurrent SOC mineralization. The SOC content decreases was likely because of the shift from anaerobic to aerobic conditions. This change leads to faster litter decomposition and SOC mineralization, accompanied with decreasing SOC retention or stabilization by soil aggregates, mineral or Fe redox processes. Abandonment of paddy soils leads to switch from a C sink to a C source, resulting in high C losses. The succession of grasses in abandoned fields did not compensate for the losses of soil C stocks
Nitrogen fertilization modifies organic transformations and coatings on soil biogeochemical interfaces through microbial polysaccharides synthesis
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