[Effects of Biochar Application on Soil Organic Carbon Component in Eucalyptus Plantations After Five Years in Northern Guangxi].

To investigate the effects of biochar(BC) addition on soil organic carbon(SOC) contents and its fractions under different biochar applications, Eucalyptus waste twigs in Northern Guangxi were used to produce BC at 500℃. Additionally, we sought to clarify and define the carbon sequestration potential of soil and provide a basis for the preparation of biochar from Eucalyptus forest wastes and soil improvement. In a long-term positioning test of biochar application from 1997, six different treatments were selected:0(CK), 0.5%(T1), 1%(T2), 2%(T3), 4%(T4), and 6%(T5). The contents of SOC, light fraction organic carbon(LFOC), heavy fraction organic carbon(HFOC), easily oxidized organic carbon(EOC), dissolved organic carbon(DOC), particulate organic carbon(POC), microbial biomass carbon(MBC), and carbon stock(CS) following the different treatments were measured. The results showed that:① compared to that in the control, biochar application induced an increase in each soil organic carbon fraction with increasing application rate and reached a maximum under the T4 or T5 treatments; with the increase in biochar application, the contents of SOC, DOC, EOC, POC, MBC, and CS increased significantly by 101.62%, 67.46%, 143.03%, 164.78%, 110.88%, and 41.73%, respectively. ② The contents of LFOC and HFOC in the 0-10, 10-20, and 20-30 cm soil layers increased significantly by 41.41%-140.63%, 9.26%-87.04%, and -19.54%-106.90% and 15.32%-78.99%, 15.72%-75.25%, and 89.49%-148.64%, respectively, with the increase in biochar application. The average contents of LFOC and HFOC in the 0-30 cm soil layer also increased gradually. The soil carbon pool of the Eucalyptus forest was dominated by a relatively stable heavy fraction organic carbon. ③ The contents of carbon stock, soil organic carbon, and its fractions decreased with the increase in soil depth. In conclusion, the application of forestry waste biochar for five years could significantly increase the content of SOC and its components, thereby increasing soil organic carbon activity. Therefore, increasing the amount of biochar was an effective measure to enhance the carbon storage, soil stable carbon pool, and soil quality of the Eucalyptus plantation field. This study provides a reference for the resource utilization of forestry waste and improvements in soil fertility of Eucalyptus plantations.

[Effects of Reclamation on Soil Nutrients and Microbial Activities in the Huixian Karst Wetland in Guilin].

To investigate the effect of reclamation on soil quality in the Huixian Karst Wetland, samples from different soil levels were collected from marsh wetland, reclaimed paddy field, and reclaimed dry farmland, for analyzing soil nutrient (carbon, nitrogen, phosphorous, and potassium) contents, microbial biomass carbon/nitrogen (MBC/MBN), and microbial activity indicators[i.e. basal respiration (BR), potential respiration (PR), microbial quotient (qMB), and metabolic quotient (qCO2)]. The correlations between the soil nutrient contents and soil microbial activity indictors were examined. The results showed that:①Artificial reclamation led to the trend of slight acidity in the soil and a marked loss in soil nutrients, while, the pH value, soil water content (SWC), and the contents of soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), available phosphorus (AP), total potassium (TK), and available potassium (AK) decreased with reclamation. ②Among all the microbes, bacteria were the most numerous, followed by actinomycetes, and fungi were the least numerous. The microbial quantity decreased with the increase in the soil depth on the whole. The proportion of bacteria and actinomycetes were much higher in the paddy field, and that of fungi was the highest in the dry farmland. ③ In total, protease, sucrase, urease, catalase, and polyphenol oxidase activities decreased with the increasing of soil depths. Soil reclamation reduced the soil enzyme activities. ④qCO2 decreased after an initial increase in the marsh wetland, while it rose gradually in the reclaimed paddy field and reclaimed dry farmland. The contents of MBC, MBN, BR, PR, and qMB were the highest in the marsh wetland, followed by those in the reclaimed paddy field, with the lowest contents occurring in the reclaimed dry farmland. The trend of qCO2 contents in the 0-10 cm and 10-20 cm soil layers followed the order of marsh wetland > paddy field > dry farmland, but in the 20-30 cm and 30-40 cm soil layers, it showed the order dry farmland > paddy field > marsh wetland. The continuation of reclamation resulted in the decrease in soil microbial activity, and soil quality as well, especially in the dry farmland. Meanwhile, we should reduce the areas of paddy fields and dry farmlands under reclamation during the process of wetland ecological restoration in future. Conversion of farmlands to wetlands or lakes, to improve and increase the size of wetland ecosystems of nearby lands, should be done gradually.