[Effects of Replacing Chemical Nitrogen Fertilizer with Organic Fertilizer on Active Organic Carbon Fractions, Enzyme Activities, and Crop Yield in Yellow Soil].

Taking the typical yellow soil in Guizhou as the research object, four treatments were set up： no fertilization （CK）, single application of chemical fertilizer （NP）, 50% organic fertilizer instead of chemical nitrogen fertilizer [1/2（NPM）], and 100% organic fertilizer instead of chemical nitrogen fertilizer （M）. The effects of organic fertilizer instead of chemical nitrogen fertilizer on organic carbon and its active components, soil carbon pool management index, soil enzyme activity, and maize and soybean yield in yellow soil were studied in order to provide theoretical basis for scientific fertilization and soil quality improvement in this area. The results showed that the replacement of chemical nitrogen fertilizer by organic fertilizer significantly increased soil pH, organic carbon （SOC）, total nitrogen （TN） content, and C/N ratio. Compared with those in the CK and NP treatments, the content and distribution ratio of soil active organic carbon components and soil carbon pool management index （CPMI） were improved by replacing chemical nitrogen fertilizer with organic fertilizer, and the effect of replacing chemical nitrogen fertilizer with 50% organic fertilizer was the best. Compared with those in the NP treatment, the 1/2 （NPM） treatment significantly increased the contents of soil readily oxidizable organic carbon （ROC333, ROC167）, dissolved organic carbon （DOC）, and microbial biomass carbon （MBC） by 22.90%, 8.10%, 29.32%, and 23.22%, respectively. Compared with those under the CK and NP treatments, organic fertilizer instead of chemical nitrogen fertilizer increased soil enzyme activities. The activities of catalase, urease, sucrase, and phosphatase in the 1/2 （NPM） treatment were significantly increased by 21.89%, 8.24%, 34.91%, and 18.78%, respectively, compared with those in the NP treatment. Compared with that of the NP treatment, the maize yield of the 1/2 （NPM） and M treatments was significantly increased by 44.15% and 17.39%, respectively. There was no significant difference in soybean yield among different fertilization treatments. Correlation analysis showed that soil SOC was significantly positively correlated with ROC333, ROC167, ROC33, DOC, MBC, and soil active organic carbon components, and CPMI was significantly positively correlated with soil organic carbon and its active components （P<0.01）. Corn yield was significantly positively correlated with soil enzyme activity, CPMI, total organic carbon, and its active components （P<0.05）. Therefore, from the perspective of yield increase and soil fertility, 50% organic fertilizer instead of chemical nitrogen fertilizer was conducive to improving soil quality and soil fertility, which is the key fertilization technology to achieve a high yield of crops in the yellow soil area of Anshun, Guizhou.

[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.

[Evolution Characteristics of Soil Active Organic Carbon and Carbon Pool Management Index Under Vegetation Restoration in Karst Area].

Vegetation restoration affects the carbon cycle of terrestrial ecosystems by changing the rate of carbon input and conversion. In order to explore the evolution characteristics of soil active organic carbon components and carbon pool management index during vegetation restoration in karst areas, the soil of a grassland sequence(5, 10, 15, and 20 a), shrub sequence(5, 10, 15, and 20 a), and garden sequence(5, 10, and 15 a) in a karst area was taken as the research object, and the adjacent farmland was taken as the control(CK). The effects of different vegetation restoration years on the evolution of soil organic carbon(SOC), readily oxidizable organic carbon(ROC333, ROC167, and ROC33 were all soil active organic carbon that could be oxidized by 333, 167, and 33 mmol·L-1 KMnO4), microbial biomass carbon(MBC), dissolved organic carbon(DOC), and carbon pool management index(CPMI) were analyzed. The results showed that compared with that of CK, the average grassland, shrub, and garden SOC contents in the 0-40 cm soil layer increased by 70.77%, 114.40%, and 50.17%, respectively. In the 0-20 cm soil layer, with the increase in restoration years, the SOC content of the grassland sequence and garden sequence increased first and then decreased, and that of the shrub sequence increased first, then decreased, and then increased again. ROC333, ROC167, and ROC33 were consistent with the SOC change trend of the corresponding sequence. In the 20-40 cm soil layer, the change trend of ROC333, ROC167, and ROC33 of each sequence was inconsistent with the SOC of the corresponding sequence. In the 0-40 cm soil layer, the MBC content of the grassland sequence decreased first, then increased, and then decreased, and the maximum value of MBC in each soil layer was in G15. The shrub sequence in the 0-10 cm soil layer increased first, then decreased, and then increased, and in the 10-40 cm soil layer it increased first and then decreased. The garden sequence increased first and then decreased in the 0-30 cm soil layer and gradually increased in the 30-40 cm soil layer. Kos of the three sequences decreased first, then increased, and then decreased, whereas L and LI showed the opposite of Kos. CPI increased first and then decreased; the CPMI of the grassland and garden sequences increased first and then decreased, whereas the CPMI of the shrub sequence increased first, then decreased, and then increased again. The contents of SOC, ROC333, ROC167, ROC33, and MBC and the annual growth of Kos were shrub>grassland>orchard, and the annual growth of DOC and CPMI were orchard>grassland>shrub. The contents of SOC and its components in the three sequences decreased with the increase in soil layer and had obvious surface aggregation. Redundancy analysis showed that alkali-hydrolyzable nitrogen(AN) was the main environmental factor affecting soil active organic carbon components and soil organic carbon pool under the vegetation restoration in the karst area. In summary, soil active organic carbon components and CPMI evolved with vegetation restoration years. Different vegetation restorations could increase the content of SOC and its components in karst areas to a certain extent, and shrub restoration promotes the accumulation of SOC.

[Effects of Organic Fertilizer Replacing Chemical Fertilizer on Organic Carbon Mineralization and Active Organic Carbon in Dryland Yellow Soil].

At present, the effect characteristics and mechanism of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil remain unclear. In order to explore the effect of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil, we used soil with no fertilization (CK), only chemical fertilizer (NP), 50% organic fertilizer replacing chemical fertilizer (1/2(NPM)), and 100% organic fertilizer replacing chemical fertilizer (M). We examined the indoor mineralization culture of organic carbon and explored the characteristics of soil organic carbon and the change in active organic carbon under the condition of organic fertilizer replacing chemical fertilizer. The results showed that organic fertilizer replacing chemical fertilizer increased soil pH, organic carbon (SOC), total nitrogen (TN), and C/N. During the culture period, the soil organic carbon mineralization rate of all treatments decreased sharply in the initial stage (2-4 days), decreased slightly in the middle stage (4-20 days), and tended to be stable in the last stage (20-60 days). After fertilization, the cumulative mineralization of soil organic carbon significantly increased by 7.9%-27.7%. Compared with that in the NP treatment, the cumulative mineralization of soil organic carbon decreased by 5.2% in the 1/2(NPM) treatment and increased by 12.2% in the 1/2(NPM) treatment. Before mineralization culture, the substitution of organic fertilizer for chemical fertilizer had no significant effect on soil recalcitrant organic carbon (ROC) but significantly increased the content of microbial biomass carbon (MBC). The content of dissolved organic carbon (DOC) was significantly increased in the 1/2(NPM) treatment and decreased in the M treatment. After 60 days of culture, the content of soil active organic carbon in all treatments decreased compared with the initial content, of which MBC decreased the most (30.6%-41.2%). The accumulated mineralization of organic carbon was significantly positively correlated with soil pH and SOC and significantly positively correlated with the initial value of MBC and the change value before and after culture. To summarize, 100% organic fertilizer replacing chemical fertilizer significantly promoted soil organic carbon mineralization and reduced soil organic carbon stability; 50% organic fertilizer replacing chemical fertilizer inhibited soil organic carbon mineralization, which was beneficial to soil sequestration and fertilization; and 50% organic fertilizer replacing chemical fertilizer significantly increased soil active organic carbon content, and MBC was used as the main carbon source in the process of soil organic carbon mineralization.

[Effects of thinning on soil active organic carbon contents and enzyme activities in Larix principis-rupprechtii plantation]. / é—´ä¼å¯¹åŽåŒ—è½å¶æ¾äººå·¥æž—åœŸå£¤æ´»æ€§æœ‰æœºç¢³å«é‡åŠé ¶æ´»æ€§çš„å½±å“.

The effects of thinning on soil active organic carbon and related soil enzyme activities were investigated in a Larix principis-rupprechtii plantation in Taiyue Mountain. With the increases of soil depth, the content of soil labile organic carbon, soil nitrogen content and enzyme activities all reduced. For each soil layer, moderate thinning increased soil carbon and nitrogen contents dramati-cally. The activities of sucrase (SC) and peroxidase (PEO) and the activities of polyphenol oxidase (PHO) and urease (UE) in the layer of 0-10 cm could be significantly improved by low thinning and moderate thinning, respectively. For the 10-50 cm layer, the activities of SC and UE were reduced by low thinning, while moderate thinning markedly reduced the activities of cellulase. Results from redundancy analysis showed that dissolved organic carbon (DOC) was the main factor affecting soil enzyme activity in both 0-10 cm and 20-30 cm soil layers and that soil organic carbon (SOC) contents affected the activities of PHO and SC in 10-20 cm soil layer. The microbial biomass nitrogen (MBN) mainly affected the activities of PHO, PEO and UE in 30-40 cm soil layer. The contents of total P (TP) and readily oxidized carbon (ROC) played an important role in affecting soil enzyme activities in 40-50 cm soil layer. The results indicated that thinning could dramati-cally affect soil active organic carbon content and soil enzyme activity in L. principis-rupprechtii plantation. Moderate thinning treatment could obtain the highest soil nutrients and achieve better soil chemical properties such as soil pH, water content and organic matter content than other treatments, which could improve vegetation structure, litter and nutrient cycling process. Therefore, we recommended moderate density adjustment (1404-1422 trees·hm-2) to L. principis-rupprechtii plantation to promote soil carbon and nitrogen retention.

[Characteristics of soil organic carbon and its fractions in subtropical evergreen broad-leaved forests along an urbanization gradient.] / åŸŽå¸‚åŒ–æ¢¯åº¦ä¸Šäºšçƒ­å¸¦å¸¸ç»¿é˜”å¶æž—åœŸå£¤æœ‰æœºç¢³åŠå ¶ç»„åˆ†ç‰¹å¾.

Subtropical evergreen broad-leaved forests were selected along an urban (Guangzhou) - suburban (Dinghushan) - rural (Huaiji) gradient in the Pearl River Delta, from which soil samples in different layers were collected. The changes in total organic carbon (TOC), recalcitrant organic carbon (ROC), and active organic carbon (AOC) including readily oxidizable organic carbon (ROOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC) of samples were examined along this urbanization gradient to reveal the influence of urbanization on forest soil organic carbon. Results showed that no significant differences in both TOC and ROC contents were observed in 0-5 cm soil layer along the gradient. In 5-60 cm soil layer, the TOC content was significantly higher in the rural forest than that in the suburban and urban forests, the ROC content was the highest in the suburban forest and no significant difference was observed between the urban and rural forests. The ROOC content was significantly lower in the suburban forest than in the rural (0-60 cm soil layer) and urban (0-10 cm soil layer) forests. The MBC content was significantly lower in the urban forest than that in the suburban and rural forests. The suburban forest had significantly lower WSOC than the urban forest (0-10 cm soil layer). In 0-20 cm layer, the percentage of AOC to TOC of the urban and rural forests was significantly higher than those of the suburban forest, while the percentage of ROC to TOC was the lowest in the rural forest. The significant difference in the percentage of ROC to TOC was only observed in 5-10 cm depth layer between the suburban and urban forests. The results indicated that urbanization increased the active components of soil organic carbon and reduced the stable ones, which could be detrimental to organic carbon accumulation in soils. The rural forest soils were more sensitive to the urbanization.

[Effects of different winter cover crops on soil organic carbon in a double cropping rice paddy field.] / 不同冬季覆盖作物对双季稻田土壤有机碳的影响.

In a double cropping rice field experiment, effects of five winter cover crops on the total organic carbon (TOC), active organic carbon (AOC), carbon pool management index (CPMI) and organic carbon storage were studied in three soil layers (0-5, 5-10 and 10-20 cm).Winter cover crops of ryegrass (Ry), Chinese milk vetch (Mv), potato (Po), and rape (Ra) between two rice crops were compared with fallow as control (CK). The results showed that the TOC and AOC contents under Ry, Mv, Po and Ra treatments were higher than those of CK in all three la-yers. Meanwhile, the TOC and AOC contents in Po treatment were higher than those of other treatments. Compared with CK, the AOC, activity index (AI), carbon pool index (CPI) and CPMI in the soil were improved through the recycling of winter cover crops straw. The AOC, AI, CPI and CPMI in the studied layers increased in order of Po>Mv>Ry>Ra>CK. The results indicated that the recycling of winter cover crops straw promoted the storage of SOC in the 0-20 cm soil profile as compared with CK. The strongest effect of the winter cover crops on the SOC storage occurred in Mv treatment, followed by Mv and Po treatments, and the SOC storage increased with the increasing soil depth.

[Effects of Biochar Pyrolyzed at Varying Temperatures on Soil Organic Carbon and Its Components:Influence on the Soil Active Organic Carbon].

Soil active organic carbon is the most important carbon pool and a good indicator in ecosystem management due to its great significance in soil carbon cycling and soil quality.In order to investigate the effect of biochar (BC) addition on soil organic matter fractions,apple tree twigs were used to produce BC at 300,400,500 and 600℃,respectively.Elemental analysis and Fourier transform infrared (FTIR) spectroscopy were used to determine the characteristics of BC.Four kinds of BC were added into soils at five application rates (0,0.5%,1%,2% and 3%) and incubated at 25℃ in lab for over 360 days.Soil organic carbon (SOC),microbial biomass carbon (MBC),water soluble organic carbon (WSOC) and readily oxidized organic carbon (ROC) were measured during the incubation.The mass fraction of carbon (C) in the generated BC ranged from 62.20%-80.01%,while hydrogen (H) ranged from 2.72%-5.18% and Oxygen (O) ranged from 15.98%-30.92%.The increasing temperature increased the mass fraction of C,while decreased the O and H mass content,as well as the ratio of H/C and O/C.The addition of BC significantly increased SOC,and the treatments amended with BC500 had the highest increments.Compared with the control treatment (CK),the addition of BC produced at temperatures below 400℃ increased the contents of MBC,WSOC and ROC during the incubation,at the end of the incubation,BC300 treatments significantly increased the contents by 38.25%,82.09% and 63.53%(P<0.05),respectively;BC400 treatments significantly increased the contents by 26.07%,65.61% and 48.09%(P<0.05),respectively;while lower contents of MBC,WSOC and ROC were found in the treatments amended with BC produced at temperatures above 400℃ after 40-60 d incubation.After 360 d of incubation,the contents of MBC,WSOC and ROC were significantly decreased by 0.27%,13.48% and 14.67% in BC500 treatments and 7.80%,14.66% and 15.79% in BC600 treatments (except for the MBC in BC500 treatment)(P<0.05).The relative contents of ROC ranged from 3.39% to 15.65%,BC application decreased the relative content of ROC,suggesting that the increase was in proportion to the stability of organic carbon in the soil.Considering the content and quality of SOC,when the BC products were applied to the Loutu soil,500℃ was the optimal temperature for preparing apple-derived BC due to its significant increase of the soil organic carbon and a slight decrease of the relative content of soil active organic carbon.