The removal of organic matter and iron oxides could increase and decrease soil CEC in tropical and subtropical regions, but the quantitative information is insufficient so far about the change of soil CEC, the influen...The removal of organic matter and iron oxides could increase and decrease soil CEC in tropical and subtropical regions, but the quantitative information is insufficient so far about the change of soil CEC, the influence factors and their contribution. In this study, the subhorizon soils of 24 soil series in the tropical and subtropical China were used, pH, particle size composition, organic matter, iron oxides of these samples were measured, and also CECs were measured and compared for the original soils and after the removal of organic matter and iron oxides. The results showed that, compared with CEC of the original soil, the eliminating organic matter increased soil CEC significantly by 2.28% - 56.50% with a mean of 24.02%, but the further obliterating iron oxides decreased soil CEC significantly by 0.75% - 20.30% with a mean of 7.73%. CEC after the removal of organic matter and iron oxides had positive correlation with iron oxides (p < 0.01) and negative correlation with sand content (p < 0.01 and p < 0.05). CEC after organic matter eliminated was mainly decided by iron oxides (51.68%), followed by silt content (22.19%);while CEC after iron oxides obliterated was mainly determined by iron oxides (50.55%). The increase of CEC after organic matter eliminated was co-affected by the contents of clays, slits, iron oxides and pH (22.00% - 27.34%), while the decrease of CEC after iron oxides obliterated further was dominated by the content of organic matter (66.92%). More other soil parameters should be considered for higher predicting accuracy in the regression model of soil CEC after the removal of organic matter and iron oxides, and the recommended optimal models obtained in this study were as follows: for soil CEC after organic matter eliminated, CEC = 1.665 <span style="white-space:nowrap;">−</span> 0.546pH <span style="white-space:nowrap;">−</span> 0.024OM + 0.053Fe<sub>x</sub>O<sub>y</sub> <span style="white-space:nowrap;">−</span> 0.001Silt + 0.007Clay + 0.972CEC<sub>original</sub> (R<sup>2</sup> was 0.923, RSME was 1.55 cmol(+)<span style="white-space:nowrap;"><span style="white-space:nowrap;">∙</span></span>kg<sup><span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>1</sup>, p < 0.01), while for soil CEC after iron oxides further obliterated, CEC = 1.665 <span style="white-space:nowrap;">−</span> 0.546pH <span style="white-space:nowrap;">−</span> 0.024OM + 0.053Fe<sub>x</sub>O<sub>y</sub> <span style="white-space:nowrap;">−</span> 0.001Silt + 0.007Clay + 0.972CEC<sub>original</sub> (R<sup>2</sup> was 0.923, RMSE was 1.55 cmol(+)<span style="white-space:nowrap;"><span style="white-space:nowrap;">∙</span></span>kg<sup><span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>1</sup>, p < 0.01). Further research is needed in the future as for exploring internal functional mechanism in view of soil electrochemistry and mineralogy.展开更多
Cation exchange capacity (CEC) is one of the most important properties of soils. The NH<sub>4</sub>OAc (pH = 7.0) exchange method is usually recommended to determine CEC (CEC<sub>1</sub>) of al...Cation exchange capacity (CEC) is one of the most important properties of soils. The NH<sub>4</sub>OAc (pH = 7.0) exchange method is usually recommended to determine CEC (CEC<sub>1</sub>) of all soils with different pH values, particularly for studies on soil taxonomy. But comparatively the BaCl<sub>2</sub>-MgSO<sub>4</sub> forced-exchange method is more authentic in determining CEC (CEC<sub>2</sub>) of tropical and subtropical highly-weathered acid soils. But so far little is known about the difference between CEC<sub>1</sub> and CEC<sub>2</sub>. In this study, the physiochemical data of 114 acid B horizon soils from 112 soil series of tropical and subtropical China were used, CEC<sub>1</sub> and CEC<sub>2</sub> were determined and compared, the influencing factors were analyzed for the difference between CEC<sub>1</sub> and CEC<sub>2</sub>, and then a regression model was established between CEC<sub>1</sub> and CEC<sub>2</sub>. The results showed that CEC<sub>2</sub> was significantly lower than CEC<sub>1</sub> (p < 0.01), CEC<sub>2</sub> was 14.76% - 63.31% with a mean of 36.32% of CEC<sub>1</sub>. In view of the contribution to CEC from other properties, CEC<sub>2</sub> was mainly determined by pH (45.92%), followed by silt (21.05%), free Fe<sub>2</sub>O<sub>3</sub> (17.35%) and clay contents (12.76%), CEC<sub>1</sub> was mainly decided by free Fe<sub>2</sub>O<sub>3</sub> content (40.38%), followed by pH (28.39%) and silt content (27.29%;and the difference between CEC<sub>1</sub> and CEC<sub>2</sub> was mainly affected by free Fe<sub>2</sub>O<sub>3</sub> (50.92%), followed by silt content (26.46%) and pH (21.80%). The acceptable optimal regression model between CEC<sub>2</sub> and CEC<sub>1</sub> was established as CEC<sub>2</sub> = 2.3114 × CEC<sub>1</sub><sup>1.1496</sup> (R<sup>2</sup> = 0.410, P < 0.001, RMSE = 0.15). For the studies on soil taxonomy, the BaCl<sub>2</sub>-MgSO<sub>4</sub> forced-exchange method is recommended in determining CEC of the highly-weathered acid soils in the tropical and subtropical regions.展开更多
Clay CEC is one of identification indexes of the LAC-ferric horizon which is the diagnostic horizon of ferrosols in Chinese Soil Taxonomy, and it is defined as soil CEC × 1000/clay content, rather than the measur...Clay CEC is one of identification indexes of the LAC-ferric horizon which is the diagnostic horizon of ferrosols in Chinese Soil Taxonomy, and it is defined as soil CEC × 1000/clay content, rather than the measured CEC of the extracted clays;however, such a calculation method would definitely lead to an overestimation of clay CEC because it doesn’t remove the contribution to soil CEC from other soil parameters. In this study, the physiochemical data of the subhorizons from 82 soil series in the tropical and subtropical regions in south China were used, clay CEC was calculated according to the current formula and measured after clays being extracted, the measured and calculated clay CEC were compared, the influencing factors were analyzed for their difference, and the new algorithms were established for clay CEC. The results showed that the measured clay CEC was 21.86% - 99.53% with a mean of 66.88% of the calculated one (significantly lower at p < 0.01), and their difference was significantly correlated with the contents of clays, sand and OM, and mainly decided by the contents of clays and Fe<sub>2</sub>O<sub>3</sub> (the contribution was 52.51% and 25.36%, respectively). By comparison of established regression models of clay CEC with other soil parameters, two new algorithms were recommended for clay CEC as follows: 1) Clay CEC = 10.32 <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.14pH <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.05OM <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.11Fe<sub>2</sub>O<sub>3</sub> + 0.01Silt <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.01Clay + 1.17CEC<sub>soil</sub>, R<sup>2</sup> = 0.705, P < 0.01;2) Clay CEC = <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>3.40 + 0.01Sand + 0.02Silt + 1.05CEC<sub>soil</sub>, R<sup>2</sup> = 0.589, P < 0.01).展开更多
In the Wondo Genet, Ethiopia, the common agricultural land uses include maize, shade coffee, khat and sugarcane. The objective of this study was to examine the impact of perennial land uses on soil organic carbon (SOC...In the Wondo Genet, Ethiopia, the common agricultural land uses include maize, shade coffee, khat and sugarcane. The objective of this study was to examine the impact of perennial land uses on soil organic carbon (SOC), soil N and base cations. Four sites having maize and one or two of perennial land uses and with similar site characteristics were identified for this study. Soils (0 - 30 cm) were sampled at corners of a plot (20 × 20 m2) placed in each land use at each site. Results indicated that the SOC storage of the shade coffee plantations were 86% and 125% higher compared with adjacent maize land uses with the absolute differences being 50.7 and 54.4 Mg·ha-1, respectively. The soil N stock was 109% and 126% higher for the shade coffee than the maize land use while the absolute differences were 5.7 and 4.7 Mg·ha-1 for the same sites. Among perennials, the higher SOC storage in the shade coffee is attributable to the increased litter input and reduced soil disturbance in the system. While the higher soil N in the shade coffee was attributed to reduction of leaching, N uplift, and the increased litter quality and input. The high relative increase in shade coffee in SOC and soil N at Finance site was ascribed to the finer soil texture and low SOC and soil N at the compared adjacent maize farm. Although not significant, the relative increase in SOC (34%) and soil N (43%) in the sugarcane at the Finance as well as the relative increase in SOC (7%) and soil N (9%) in khat at Gotu as compared to Chaffee site was attributed to mainly the management differences. The shade coffee has the greatest potential for SOC storage and for increasing N stock, while khat and sugarcane have the least potential.展开更多
文摘The removal of organic matter and iron oxides could increase and decrease soil CEC in tropical and subtropical regions, but the quantitative information is insufficient so far about the change of soil CEC, the influence factors and their contribution. In this study, the subhorizon soils of 24 soil series in the tropical and subtropical China were used, pH, particle size composition, organic matter, iron oxides of these samples were measured, and also CECs were measured and compared for the original soils and after the removal of organic matter and iron oxides. The results showed that, compared with CEC of the original soil, the eliminating organic matter increased soil CEC significantly by 2.28% - 56.50% with a mean of 24.02%, but the further obliterating iron oxides decreased soil CEC significantly by 0.75% - 20.30% with a mean of 7.73%. CEC after the removal of organic matter and iron oxides had positive correlation with iron oxides (p < 0.01) and negative correlation with sand content (p < 0.01 and p < 0.05). CEC after organic matter eliminated was mainly decided by iron oxides (51.68%), followed by silt content (22.19%);while CEC after iron oxides obliterated was mainly determined by iron oxides (50.55%). The increase of CEC after organic matter eliminated was co-affected by the contents of clays, slits, iron oxides and pH (22.00% - 27.34%), while the decrease of CEC after iron oxides obliterated further was dominated by the content of organic matter (66.92%). More other soil parameters should be considered for higher predicting accuracy in the regression model of soil CEC after the removal of organic matter and iron oxides, and the recommended optimal models obtained in this study were as follows: for soil CEC after organic matter eliminated, CEC = 1.665 <span style="white-space:nowrap;">−</span> 0.546pH <span style="white-space:nowrap;">−</span> 0.024OM + 0.053Fe<sub>x</sub>O<sub>y</sub> <span style="white-space:nowrap;">−</span> 0.001Silt + 0.007Clay + 0.972CEC<sub>original</sub> (R<sup>2</sup> was 0.923, RSME was 1.55 cmol(+)<span style="white-space:nowrap;"><span style="white-space:nowrap;">∙</span></span>kg<sup><span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>1</sup>, p < 0.01), while for soil CEC after iron oxides further obliterated, CEC = 1.665 <span style="white-space:nowrap;">−</span> 0.546pH <span style="white-space:nowrap;">−</span> 0.024OM + 0.053Fe<sub>x</sub>O<sub>y</sub> <span style="white-space:nowrap;">−</span> 0.001Silt + 0.007Clay + 0.972CEC<sub>original</sub> (R<sup>2</sup> was 0.923, RMSE was 1.55 cmol(+)<span style="white-space:nowrap;"><span style="white-space:nowrap;">∙</span></span>kg<sup><span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>1</sup>, p < 0.01). Further research is needed in the future as for exploring internal functional mechanism in view of soil electrochemistry and mineralogy.
文摘Cation exchange capacity (CEC) is one of the most important properties of soils. The NH<sub>4</sub>OAc (pH = 7.0) exchange method is usually recommended to determine CEC (CEC<sub>1</sub>) of all soils with different pH values, particularly for studies on soil taxonomy. But comparatively the BaCl<sub>2</sub>-MgSO<sub>4</sub> forced-exchange method is more authentic in determining CEC (CEC<sub>2</sub>) of tropical and subtropical highly-weathered acid soils. But so far little is known about the difference between CEC<sub>1</sub> and CEC<sub>2</sub>. In this study, the physiochemical data of 114 acid B horizon soils from 112 soil series of tropical and subtropical China were used, CEC<sub>1</sub> and CEC<sub>2</sub> were determined and compared, the influencing factors were analyzed for the difference between CEC<sub>1</sub> and CEC<sub>2</sub>, and then a regression model was established between CEC<sub>1</sub> and CEC<sub>2</sub>. The results showed that CEC<sub>2</sub> was significantly lower than CEC<sub>1</sub> (p < 0.01), CEC<sub>2</sub> was 14.76% - 63.31% with a mean of 36.32% of CEC<sub>1</sub>. In view of the contribution to CEC from other properties, CEC<sub>2</sub> was mainly determined by pH (45.92%), followed by silt (21.05%), free Fe<sub>2</sub>O<sub>3</sub> (17.35%) and clay contents (12.76%), CEC<sub>1</sub> was mainly decided by free Fe<sub>2</sub>O<sub>3</sub> content (40.38%), followed by pH (28.39%) and silt content (27.29%;and the difference between CEC<sub>1</sub> and CEC<sub>2</sub> was mainly affected by free Fe<sub>2</sub>O<sub>3</sub> (50.92%), followed by silt content (26.46%) and pH (21.80%). The acceptable optimal regression model between CEC<sub>2</sub> and CEC<sub>1</sub> was established as CEC<sub>2</sub> = 2.3114 × CEC<sub>1</sub><sup>1.1496</sup> (R<sup>2</sup> = 0.410, P < 0.001, RMSE = 0.15). For the studies on soil taxonomy, the BaCl<sub>2</sub>-MgSO<sub>4</sub> forced-exchange method is recommended in determining CEC of the highly-weathered acid soils in the tropical and subtropical regions.
文摘Clay CEC is one of identification indexes of the LAC-ferric horizon which is the diagnostic horizon of ferrosols in Chinese Soil Taxonomy, and it is defined as soil CEC × 1000/clay content, rather than the measured CEC of the extracted clays;however, such a calculation method would definitely lead to an overestimation of clay CEC because it doesn’t remove the contribution to soil CEC from other soil parameters. In this study, the physiochemical data of the subhorizons from 82 soil series in the tropical and subtropical regions in south China were used, clay CEC was calculated according to the current formula and measured after clays being extracted, the measured and calculated clay CEC were compared, the influencing factors were analyzed for their difference, and the new algorithms were established for clay CEC. The results showed that the measured clay CEC was 21.86% - 99.53% with a mean of 66.88% of the calculated one (significantly lower at p < 0.01), and their difference was significantly correlated with the contents of clays, sand and OM, and mainly decided by the contents of clays and Fe<sub>2</sub>O<sub>3</sub> (the contribution was 52.51% and 25.36%, respectively). By comparison of established regression models of clay CEC with other soil parameters, two new algorithms were recommended for clay CEC as follows: 1) Clay CEC = 10.32 <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.14pH <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.05OM <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.11Fe<sub>2</sub>O<sub>3</sub> + 0.01Silt <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span> 0.01Clay + 1.17CEC<sub>soil</sub>, R<sup>2</sup> = 0.705, P < 0.01;2) Clay CEC = <span style="white-space:nowrap;"><span style="white-space:nowrap;">−</span></span>3.40 + 0.01Sand + 0.02Silt + 1.05CEC<sub>soil</sub>, R<sup>2</sup> = 0.589, P < 0.01).
文摘In the Wondo Genet, Ethiopia, the common agricultural land uses include maize, shade coffee, khat and sugarcane. The objective of this study was to examine the impact of perennial land uses on soil organic carbon (SOC), soil N and base cations. Four sites having maize and one or two of perennial land uses and with similar site characteristics were identified for this study. Soils (0 - 30 cm) were sampled at corners of a plot (20 × 20 m2) placed in each land use at each site. Results indicated that the SOC storage of the shade coffee plantations were 86% and 125% higher compared with adjacent maize land uses with the absolute differences being 50.7 and 54.4 Mg·ha-1, respectively. The soil N stock was 109% and 126% higher for the shade coffee than the maize land use while the absolute differences were 5.7 and 4.7 Mg·ha-1 for the same sites. Among perennials, the higher SOC storage in the shade coffee is attributable to the increased litter input and reduced soil disturbance in the system. While the higher soil N in the shade coffee was attributed to reduction of leaching, N uplift, and the increased litter quality and input. The high relative increase in shade coffee in SOC and soil N at Finance site was ascribed to the finer soil texture and low SOC and soil N at the compared adjacent maize farm. Although not significant, the relative increase in SOC (34%) and soil N (43%) in the sugarcane at the Finance as well as the relative increase in SOC (7%) and soil N (9%) in khat at Gotu as compared to Chaffee site was attributed to mainly the management differences. The shade coffee has the greatest potential for SOC storage and for increasing N stock, while khat and sugarcane have the least potential.
