| The soil carbon pool levels play a critical role is the biggest one in the earth surface system. Increasing soil organic carbon mitigating greenhouse effects cultural sustainability and, maybe more important, in global climate changes. Fertilization affected significantly soil organic carbon stability,soil CO2 emission. However, little information is known for SOC characteristic under fertilization. So that,throng arrangement of field fertilization measurement,pot experiments and laboratory incubation , a systematic study was made on the composition of soil aggregates,the quantitative dynamics of fractions of soil organic carbon, and explored the effect of different fertilizations on soil organic carbon emissions on citrus orchards. The main results indicated that:(1) Fertilization to some extent improved the content of large aggregates, organic fertilizer and co-application of manure and chemical fertilizers treatments were best. The content of water stable aggregate ranged from 80.68%~91.49% in 0-20 centimeters soil layer, 25% compound fertilizer+75%organic fertilizer(T5) treatment was highest, but single application of compound fertilizer (T2) and applied strain organic fertilizer residue ware not significant. The content of water stable aggregate ranged from 70.39% ~79.91% in the lower 20 ~ 40cm of soil, and other fertilization treatments was not significant.(2) In the 0-20cm soil layer, the MMD value was between 2.03~3.15, single application of organic manure and compound fertilizer best; in 20-40cm soil layer, the fertilization of the WMD value were significantly higher than no-fertilization, but fertilization treatments were not significant. The mean mass diameter (MMD) of soil aggregates was larger in 0~20 cm than in 20~40 cm soil layer. The MMD was positively correlated with the amount of>0.25 mm water stable aggregates.(3) The results of content soil organic carbon before and after fertilization ,showed that the content of soil organic carbon in treatments of organic fertilizer increased the range of between 1.53%~15.7% on flied experiment, but chemical fertilizer and without fertilizer treatment reduced 7.14%, 20.19%; the content of soil organic carbon in treatments of organic fertilizer increased 14.18%~245.69% on pot culture experiments, while treatments of chemical fertilizer and no fertilizer reduced 1.81% and 11.78%. The contents of total organic carbon in treatments of organic fertilizer were higher 23.8%~43.6% than treatment of CK in the 0-20cm soil layer, also its increased 19.8%~41.9% in 20~40cm soil layer. The contents of total organic carbon in treatments of manure and manure combination chemical fertilizer increased rate of between 29.42%~156.47% on pot culture experiments. This shows that organic fertilizer is conducive to promoting the accumulation of soil organic carbon content.(4) Under different fertilization, the content of organic carbon all increased with increment of aggregate size, and the organic carbon was rich in the 5~0.25mm soil aggregate. In the same size, especially of the organic fertilizer, organic carbon content of aggregates increased significantly, and the organic carbon content of different size class aggregates significantly were higher than CK, suggesting that manure application was beneficial to the accumulation of SOC. On 0~20cm soil layer, >5mm and 2~5.0mm aggregate sizes increase of organic carbon accumulation in soil organic carbon is more prominent; surface soil organic carbon accumulation by the various aggregate sizes of organic carbon accumulation affected, affected by the lower layer is not obvious.(5) Fertilization will help improve the content of soil active organic carbon and their ratio, organic fertilizer and organic fertilizer compound fertilizer treatment were higher than single application of fertilizer treatment. Under field experiments, fertilization increased the contents of MBC(Microbial biomass Carbon),DOC(Dissolved Organic Carbon),EOOC(Readily Oxidizable Carbon),LF(Light Fraction),LFOC(Light Fraction Organic Carbon) by 45.61%~200.78%,107.09%~255.38%,158.63%~963.55%,37.74%~178.55%,58.81%~279.47% in 0~20cm soil layer. However, the content of active organic carbon were no significant in 20~40cm soil layer.The results of pot experiments were in keeping with the field.(6) Soil organic carbon and active soil organic carbon in surface the correlation analysis showed that there were extremely significant relationships between soil organic carbon and active soil organic carbon or among fractions of soil organic carbon. Therefore, the activity of organic carbon can be considered to reflect stable indicators of soil organic carbon.(7) Soil organic carbon mineralization culture test results showed that: compared with the control treatment, fertilization were promoted soil respiration rate in a short time, expertly the effect of organic fertilizer. The rates of soil respiration were higher during the prophase incubation for different treatments, then decreased and afterwards a little varied. Daily mineralization of soil organic C during incubation accords to the relations of logarithm. With the increase in the amount of soil sample, the amounts of cumulative release of soil respiration increased with each treatment for each site. The amounts of cumulative release of soil respiration in organic manure or high proportion of organic fertilizer with chemical fertilizer treatments were more than that in inorganic fertilizers treatments.(8) Increasing the organic manure, the temperature sensitivity of soil respiration are also different. The rang of soil Q10 values was 1.49~2.08 for different fertilization, CK treatment Q10 values smallest, single application of organic fertilizer Q10 value is the largest, organic fertilizer processing Q10 values of soil was higher than that of chemical fertilizer and the CK treatment. Add meal organic fertilizer treatments of soil temperature coefficient Q10 values was between 1.49 ~2.64, C4(25% nitrogen+75% organic manure) Q10 value the most, and there is significant difference between fertilization treatments. |
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