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The effect of biochar on soil respiration (Rs) over one maize-growing season was studied after 5 years of consecutive application in an intensive cropland in the North China Plain. The experiment was carried out in randomly arranged plots with four treatments being evaluated. Three replications were conducted per treatment: a control plot without biochar addition (CK), biochar incorporated at 4.51 t [ha.sup.-1] [year.sup.-1] (BC4.5), biochar incorporated at 9.01t [ha.sup.-1] [year.sup.-1] (BC9.0), and incorporated wheat straw (SR). The Rs was determined throughout the growing season of maize in 2012. Soil temperature and moisture were measured simultaneously at 5 cm depth. The results showed that the seasonal and diurnal variations of Rs in the four different treatments were approximately equal, and there was a positive correlation between Rs and soil temperature. The Rs values of treatments BC4.5 and BC9.0 were significantly lower than of SR but not CK. Significant correlations between Rs and soil temperature and soil moisture were observed. Soil temperature had a stronger effect on Rs than did soil moisture, and Rs was more sensitive to soil temperature in the biochar treatments than in the SR and CK treatments. The application of biochar and straw increased the soil active organic carbon content, but an obvious relationship between Rs and the soil active organic carbon content was not found. Additional keywords: carbon emission, soil active organic carbon, straw return., Introduction Biochar produced during the pyrolysis of biomass is considered a promising material for the mitigation of global climate change and the improvement of carbon sequestration (Lehmann 2007). Woolf et [...]

The effects of biochar on alkaline soils in high-yielding agricultural fields remain poorly understood. Nitrate variation in soils due to biochar application without a change in soil pH, is a great concern relating to both crop yield and nitrate leaching. In this study, we monitored changes in dynamics of soil nitrate accumulation and effects on grain yield due to biochar application in a temperate, high-yielding region. Biochar derived from corncob was applied to an alkaline soil at biochar rates (kg [ha.sup.-1]) of 0 (CK), 2250 (C1), and 4500 (C2) for each of two crop seasons in 2007. A treatment with 750 kg biochar-based fertiliser [ha.sup.-1] (CN) for each of two crop seasons was also included. Biochar had no significant effect on soil water content to 1 m soil depth. Biochar tended to increase the soil cation exchange capacity (CEC) in the 0-20 cm soil layer and nitrate retention to 1 m soil profile, but there was no significant difference between biochar treatments and CK. Grain yield of C1, C2, and CN was improved by 10.3%, 16.9%, and 15.5% compared with CK, respectively, but only C2 was significantly different from CK. Grain yields of winter wheat with biochar application showed a trend similar to soil CEC and average soil-nitrate retention, suggesting that the increases in grain yield were mainly attributable to improvements in soil CEC and soil nitrate retention due to biochar application in the alkaline soil. In conclusion, the effects of biochar on soil water retention, soil nitrate retention, and grain yield were very limited in alkaline soil in a high-yielding region. Additional keywords: biochar, black carbon, nitrate, soil CEC, yield., Introduction Application of biochar has been proposed as a novel approach to increase soil carbon sequestration and mitigate the greenhouse effect. In addition, the effects of biochar in increasing crop [...]

Land use change is an important factor affecting soil carbon and nitrogen cycle, and this is a hot spot in the study of global climate change. Based on the fixed depth method (FD) and the equivalent mass method (ESM), we explored the effects of land use change on soil organic carbon (SOC) and total nitrogen (TN) storage from the perspectives of forest reclamation and farmland vegetation restoration in Karst area. The storage of SOC and TN significantly decreased after the forests were converted to grassland, eucalyptus and farmland. On average, the SOC and TN losses calculated by the FD method were 47.4% and 41.6%, respectively, the losses of SOC and TN calculated by ESM method were 54.8% and 49.7%. The SOC and TN storage increased significantly after abandonment of farmland to grassland or planting eucalyptus. On average, the SOC and TN stocks calculated based on the FD method increased by 60.5% and 49.7%, while the SOC and TN calculated by the ESM method increased by 85.5% and 70.8% respectively. The difference between FD method and ESM method was analyzed, it was concluded that FD method ignored the difference of soil bulk density after land use change. Soil bulk density was significantly increased after forest destruction. The loss of SOC and TN storage was overestimated by the FD method. Soil bulk density decreased after vegetation restoration, FD method will underestimate the enhancement of SOC and 85.5% and 70.8% respectively. The difference between FD method and ESM method was analyzed, it was concluded that FD method ignored the difference of soil bulk density after land use change. Soil bulk density was significantly increased after forest destruction. The loss of SOC and TN storage was overestimated by the FD method. Soil bulk density decreased after vegetation restoration, FD method will underestimate the enhancement of SOC and TN storage. It is suggested that the ESM method should he used to estimate the impacts of land use change on SOC and TN storage. [ABSTRACT FROM AUTHOR]

A 3-year field experiment with randomized block design was conducted to study the effects of biochar amendment on the soil bulk density, cation exchange capacity (CEC), and particulate organic matter C (POM-C) and N (POM-N) contents in a high-yielding cropland in the North China Plain. Four treatments were installed, i.e., chemical NPK (CK), chemical NPK plus 2250 kg·hm-2 of biochar (C1), chemical NPK plus 4500 kg·hm-2 of biochar (C2), and 750 kg·hm-2 of biochar-based slow release fertilizer (CN). Comparing with CK, treatments C1 and C2 significantly decreased the bulk density of 0-7.5 cm soil layer by 4.5% and 6.0%, respectively, and the treatments with biochar amendment increased the CEC in 0-15 cm soil layer, with an increment of 24.5% in treatment C2. Biochar amendment also increased the C (POM-C) and N (POM-N) contents in 0-7.5 cm soil layer, e.g., the POM-C and N contents in treatment C1 and C2 were 250% and 85%, and 260% and 120% higher than those of the CK, respectively. After three years of biochar amendment, the soil had obvious improvement in its physical and chemical properties, and played more active roles in soil carbon sequestration and greenhouse gases emission reduction. [ABSTRACT FROM AUTHOR]

Land use change is an important factor affecting soil carbon and nitrogen cycle, and this is a hot spot in the study of global climate change. Based on the fixed depth method (FD) and the equivalent mass method (ESM), we explored the effects of land use change on soil organic carbon (SOC) and total nitrogen (TN) storage from the perspectives of forest reclamation and farmland vegetation restoration in Karst area. The storage of SOC and TN significantly decreased after the fore-sts were converted to grassland, eucalyptus and farmland. On average, the SOC and TN losses calculated by the FD method were 47.4% and 41.6%, respectively, the losses of SOC and TN calculated by ESM method were 54.8% and 49.7%. The SOC and TN storage increased significantly after abandonment of farmland to grassland or planting eucalyptus. On average, the SOC and TN stocks calculated based on the FD method increased by 60.5% and 49.7%, while the SOC and TN calculated by the ESM method increased by 85.5% and 70.8% respectively. The difference between FD method and ESM method was analyzed, it was concluded that FD method ignored the difference of soil bulk density after land use change. Soil bulk density was significantly increased after forest destruction. The loss of SOC and TN storage was overestimated by the FD method. Soil bulk density decreased after vegetation restoration, FD method will underestimate the enhancement of SOC and TN storage. It is suggested that the ESM method should be used to estimate the impacts of land use change on SOC and TN storage.

A 3-year field experiment with randomized block design was conducted to study the effects of biochar amendment on the soil bulk density, cation exchange capacity (CEC), and particulate organic matter C (POM-C) and N (POM-N) contents in a high-yielding cropland in the North China Plain. Four treatments were installed, i.e., chemical NPK (CK), chemical NPK plus 2250 kg x hm(-2) of biochar (C1), chemical NPK plus 4500 kg x hm(-2) of biochar (C2), and 750 kg x hm(-2) of biochar-based slow release fertilizer (CN). Comparing with CK, treatments C1 and C2 significantly decreased the bulk density of 0-7.5 cm soil layer by 4.5% and 6.0%, respectively, and the treatments with biochar amendment increased the CEC in 0-15 cm soil layer, with an increment of 24.5% in treatment C2. Biochar amendment also increased the C (POM-C) and N (POM-N) contents in 0-7.5 cm soil layer, e.g., the POM-C and N contents in treatment C1 and C2 were 250% and 85%, and 260% and 120% higher than those of the CK, respectively. After three years of biochar amendment, the soil had obvious improvement in its physical and chemical properties, and played more active roles in soil carbon sequestration and greenhouse gases emission reduction.

In Quzhou County, Hebei Province where now intensive farming system is operated, original grassland and farming land under different tillage, crop straw return and fertilization measures were studied using isotope carbon for the analysis of the impact on soil organic carbon (SOC) properties. The research indicated that after change into farmland (34 years), SOC is significantly reduced and for 1 m of soil layer, the scope of reduction is from 13.3%-35% and this decrease happens in 0-40 cm of soil layer. After 8 years of fertilization, SOC can be increased at 0.83 g x kg(-1). No-tillage can significantly increase the SOC especially in 0-10 cm but plough will increase the SOC at 10-15 cm and 15-20 cm. Change of delta13 C of SOC due to land use change mainly happens in 0-20 cm, where input of organic materials from maize stored. In soil layer of 0-5 cm, only maximum 18% of SOC is from crop residues and in 15-20 cm, this percentage is about 5%.