Effects of Fertilizer Placement and Nitrogen Forms on Soil Nitrogen Diffusion and Migration of Red-Yellow Soil in China

A better understanding of nitrogen (N) diffusion and transformation in soils could reveal the capacity of the biological inorganic N and improve the efficiency of N fertilizers. A field micro-plot experiment was carried out to study the effects of fertilization methods (mixed uniformly with 12 cm top soil, placed in holes at a 12-cm depth, or placed in furrows at a 12-cm depth) and forms of N fertilizers (urea and ammonium phosphate) on the dynamics of soil N’s vertical diffusion and horizontal migration in red-yellow soil. The soil inorganic N ( NH4+-N and NH3--N) content following point deep placement was greater than that from mixed or furrow applications. Under point placement, the migration of soil inorganic N in urea and ammonium phosphate treatments occurred in the 6 - 15 cm layer at a horizontal distance of 0 - 9 cm. However, the nutrient preservation capability of the soil receiving ammonium phosphate was greater than that receiving urea under point deep placement. Thus, point deep placement had a tendency to increase the inorganic N in the soil and reduce inorganic N loss, which probably occurred due to the reduced soil volume with which the N fertilizer was mixed. According to crop growth and fertilizer requirements, the optimized fertilizer placement and N species resulted in a continuously high nutrient supply to crops for 90 d. However, the effects of point deep placement on increasing the N-use efficiency and reducing N loss have to be evaluated under natural field conditions.

Soil Fertility Comparison between Rotations of Tobacco-Rice (TR) and Rape-Rice (RR)

Tobacco-planting plays an important role in ensuring the high-quality tobacco raw materials supply and the local social and economic development in Chenzhou City. In recent years whether tobacco-planting is better for the maintenance and improvement of soil fertility than other crop-planting has been highly concerned. In this study, 16 soil fertility indicators and soil integrated index (IFI) were compared by 21 pairs of fields in Chenzhou city under the rotations of tobacco-rice (TF) and rice-rice (RR), and results showed that, comparing the mean values of soil fertility indicators, the contents of OM, TN, AN, AK, S and IFI were extremely significantly higher in TR than those in RR (p < 0.01), the contents of Cu, Ca, Mg and Fe were significantly higher in TR than those in RR (p < 0.05), but Mn content was significantly lower in TR than those in RR (p < 0.05). Meanwhile the contents of TP, TK and AP were insignificantly higher in TR than those in RR, and the contents of B, Mo and Zn were insignificantly lower in TR than those in RR. The above significant differences in soil fertility indicators were mainly due to relatively higher fertilizer inputs and less nutrient removal during tobacco-growing season than during rape-growing season, the net increase of N, P2O5 and K2O are 8.61, 5.25 and 24.89 kg per 667 m2 respectively in tobacco-growing season, while the net decrease of N, P2O5 and K2O are 8.88, 4.70 and 4.62 kg per 667 m2 respectively in rape-growing season. C.V. of soil fertility indicators and IFI were meanly lower in TR (52.25% and 15.95%, respectively) than those in RR (63.07% and 22.12%, respectively). Comparatively, tobacco-planting can improve soil fertility better than rape-planting when rotated with late rice in Chenzhou city. For tobacco-planting, Mg fertilizer should be applied for 23.8% TR fields, while more N, K, Ca, Mg, S and B fertilizers should be applied for 42.86%, 23.81%, 14.29%, 47.62%, 80.95% and 47.62% RR fields, respectively.

Experimental Investigation on Fracturing Behaviors after Liquid Nitrogen Pre-Injection in High-Temperature Sandstone

The fracturing process of sandstone is inherently complex due to its loose internal structure and deformation adaptability.Liquid nitrogen pre-injection has emerged as a promising approach to damage reservoir rocks,effectively reducing fracture pressure and establishing intricate fracture networks,thus offering a potential solution for reservoir reconstruction.To unravel the fundamental mechanisms governing sandstone fracturing behaviors following liquid nitrogen pre-injection,sandstone fracturing experiments were conducted under varying durations of liquid nitrogen injection,rock temperature,and in-situ stress conditions.The experiments showcased the evolution of injection pressure and fracture characteristics under different testing conditions,complemented by electron microscope analysis to elucidate the factors driving the complex fracture characteristics of sandstone.The findings revealed a significant decrease in fracture pressure after liquid nitrogen pre-injection,accompanied by a notable increase in the complexity of the fracture network and the roughness of the fracture surface.Moreover,prolonging the duration of liquid nitrogen injection and elevating reservoir temperature further contributed to reducing fracture pressure,consequently enhancing fracture complexity and surface roughness.Conversely,the application of confining pressure amplified fracture pressure while intensifying the degree of fracturing.Notably,the investigation highlighted the increased presence of microcracks in sandstone resulting from liquid nitrogen preinjection,facilitating fluid diffusion during fracturing and yielding lower fracture pressures,thereby enhancing the effectiveness of sandstone reservoir reformation.The research results can provide theoretical guidance for geothermal reservoir reconstruction.

Content, Density, Illuviation Mode and Depth of CaCO₃in Soils of Semiarid-Arid Qilian Mountains—An Altitude Sequence Study of the Hulugou Watershed

The parental material of soils in the Qilian Mountains of northwest China is mainly aeolian loess containing CaCO3 which may remain in soils under the semiarid-arid climate. To disclose the CaCO3 characteristics change with the altitude and the terrain attributes, we surveyed 18 soil profiles in an altitude sequence from 3076 m to 4510 m in the Hulugou Watershed in the Qilian Mountains, measured CaCO3 contents of all genetic horizon samples, analyzed the densities, illuviation modes and depths of CaCO3 in the profiles, extracted values of the terrain attributes of the profiles including altitude slope, aspect, plane curvature, profile curvature and terrain wetness index (TWI) from the 90 m resolution SRTM3 DEM data on ArcGIS 9.3 platform. We found that CaCO3 weighted content of the profiles ranged from 1.30 g·kg-1 to 93.09 g·kg-1, CaCO3 density from 0.05 kg/m2 to 75.69 kg/m2, CaCO3 illuviation depth from 12 cm to 54 cm. CaCO3 illuviation modes could be divided into three types, i.e., no illuviation mode in which the profile has only A horizon or CaCO3 content -1, middle illuviation mode in which CaCO3 accumulated in a middle horizon, and down illuviation mode in which CaCO3 content increases with the depth. CaCO3 weighted content, density and illuviation depth had significant correlation with certain terrain attributes. In general, the altitude sequence is an effective way to study CaCO3 characteristics in the alpine region, and the data of terrain attributes which can influence the precipitation and its redistribution in soil are potential in predicting soil CaCO3 characteristics in the alpine region.

Study on Climate Changes for Flue-Cured Tobacco Growth in Chenzhou City of Hunan Province

Chenzhou city is the most typical region of Nanling Hill Ecological Zone of flue-cured tobacco with of aroma style of burnt sweet and pure sweet in China and is the largest planting region of flue-cured tobacco in Hunan province. It is of significance to study the changes of climatic parameters with time because climate is the most important factor in determining the growth, yield and quality of flue-cured tobacco. In this study, the data of climatic parameters including cumulative sunshine hours(S), mean temperature (T) and cumulative precipitation (P)from 1952 to 2018 in Chenzhou were used to analyze their changes at the scales of year, whole field period and growing period of flue-cured tobacco. The results showed that at the scale of year, the cumulative S, mean T and cumulative P were ranged from 1029.0 h to 2072.1 h, from 17.1°C to 19.5°Cand from 897.1 mm to 2244.6 mm, with the means of 1449.7 h, 18.1°C and 1482.5 mm, respectively. At the scale of whole field period of flue-cured tobacco, the cumulative S, mean T and cumulative P were ranged from 298.1 h to 807.2 h, from 21.2°C to 23.9°C and from 416.7 mm to 1102.7 mm, with the means of 514.8 h, 22.3°C and 719.0 mm, respectively. At the scale of growing period of flue-cured tobacco, the annual cumulative S were ranged from 70.0 h to 257.2 h, from 77.3 h to 322.5 h and from 131.2 h to 300.3 h in the periods of rooting, flourishing and maturing with the means of 127.8 h, 190.4 h and 197.2 h, respectively. The mean temperatures were ranged from 14.2°C to 18.9°C, from 22.2°C to 26.1°C, and from 25.8°C to 29.6°C with the means of 16.4°C, 24.1°C and 28.0°C, respectively. The annual cumulative P were ranged from 69.9 mm to 553.9 mm, from 133.1 mm to 485.6 mm and from 46.4 mm to 356.8 mm in the periods of rooting, flourishing and maturing with the means of 262.5 mm, 299.9 mm and 153.9 mm, respectively. At the year scale, cumulative S annually decreased by 7.587 h, mean T annually increased by 0.02°C, while cumulative P changed irregularly with insignificantly increasing about by 0.184 mm annually. At the scale of whole field period of flue-cured tobacco, mean T annually increased by 0.0195°C, while both cumulative S and P changed irregularly with insignificantly decreasing by 1.64 h and 1.62 mm annually, respectively. At the scale of growing period of flue-cured tobacco, all climatic parameters changed irregularly except cumulative S in significant positive compound function in the maturing period. Meanwhile, the slight decreasing tendency of cumulative sunshine hours and the slight increasing tendency of cumulative precipitation are disadvantageous while the slight increasing tendency of cumulative precipitation in the maturing period is positive for the growth and quality of flue-cured tobacco.

Available Contents and Spatial Distribution of Soil Microelements of Tobacco Fields in Liupanshui City

The contents of soil microelements can affect the growth, yield and quality of tobacco, but it is not clear of the status quo of soil microelements in tobacco fields in Liupanshui city. In this study, soil samples of the plough layers (0 - 20 cm) were collected from January to March in 2021 from 500 typical tobacco fields in Liupanshui City (100, 180 and 220 fields in Zhongshan, Shuicheng and Panzhou, respectively), the particle size composition, pH, the contents of organic matter (OM), available boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) were measured and discussed. the results show that the mean contents of B, Cu, Fe, Mn, Mo and Zn are 0.92, 2.55, 66.47, 47.26, 0.39 and 3.96 mg/kg, respectively, and among which, B, Cu and Zn are at the high grades while Fe, Mn and Mo are at the very-high grades. There are significant differences in B, Fe and Zn among the three regions, while Cu is significantly different between Zhongshan and Shuicheng, Mn is significantly different between Panzhou with Zhongshan and Shuicheng, and Mo is significantly different between Zhongshan and Panzhou. The proportions of fields deficient in microelements are relatively low, no field is Fe-deficient, and the fields deficient in Mo, B, Cu, Zn and Mn are only account for 10.40%, 9.40%, 7.40%, 2.80% and 2.00% of the total fields respectively. B-deficient fields (green and light green colors, the same below) are mainly scattered in the northwest of Zhongshan and in the north and south of Panzhou, Cu-deficient fields mainly in the middle of Shuicheng and Panzhou, Mn-deficient fields mainly in northern Zhongshan, central Shuicheng and north of Panzhou. Mo-deficient fields are mainly in the middle of Shuicheng and the middle and east of Panzhou, while Zn-deficient fields are mainly in the middle of Shuicheng and the middle and east of Panzhou. Altitude is negatively correlated with Mn (P < 0.05), pH is negatively correlated with B (P < 0.05), Fe and Mn (P < 0.01), and OM is positively correlated with Fe and Zn (P < 0.01). Sand is negatively correlated with B (P < 0.05), Mn and Mo (P < 0.01), but positively correlated with Zn (P < 0.01). Silt is positively correlated with Mo (P < 0.05);clay is positively correlated with B (P < 0.05) and Mn (P < 0.01), but negatively correlated with Zn (P < 0.01). In conclusion, most of the fields do not need to apply micro-fertilizers in Liupanshui, but the fields deficient in microelements should be considered to use the corresponding fertilizers.

Quantitative Estimation of the Changes in Soil CEC after the Removal of Organic Matter and Iron Oxides

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 − 0.546pH − 0.024OM + 0.053FexOy − 0.001Silt + 0.007Clay + 0.972CECoriginal (R2 was 0.923, RSME was 1.55 cmol(+)∙kg−1, p < 0.01), while for soil CEC after iron oxides further obliterated, CEC = 1.665 − 0.546pH − 0.024OM + 0.053FexOy − 0.001Silt + 0.007Clay + 0.972CECoriginal (R2 was 0.923, RMSE was 1.55 cmol(+)∙kg−1, p < 0.01). Further research is needed in the future as for exploring internal functional mechanism in view of soil electrochemistry and mineralogy.

New Algorithm of Clay CEC for Soils in Tropical and Subtropical Regions of South China

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 Fe2O3 (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 − 0.14pH − 0.05OM − 0.11Fe2O3 + 0.01Silt − 0.01Clay + 1.17CECsoil, R2 = 0.705, P < 0.01;2) Clay CEC = −3.40 + 0.01Sand + 0.02Silt + 1.05CECsoil, R2 = 0.589, P < 0.01).

Comparison of Highly-Weathered Acid Soil CEC Determined by NH₄OAc (pH = 7.0) Exchange Method and BaCl₂-MgSO₄Forced-Exchange Method

Cation exchange capacity (CEC) is one of the most important properties of soils. The NH4OAc (pH = 7.0) exchange method is usually recommended to determine CEC (CEC1) of all soils with different pH values, particularly for studies on soil taxonomy. But comparatively the BaCl2-MgSO4 forced-exchange method is more authentic in determining CEC (CEC2) of tropical and subtropical highly-weathered acid soils. But so far little is known about the difference between CEC1 and CEC2. In this study, the physiochemical data of 114 acid B horizon soils from 112 soil series of tropical and subtropical China were used, CEC1 and CEC2 were determined and compared, the influencing factors were analyzed for the difference between CEC1 and CEC2, and then a regression model was established between CEC1 and CEC2. The results showed that CEC2 was significantly lower than CEC1 (p < 0.01), CEC2 was 14.76% - 63.31% with a mean of 36.32% of CEC1. In view of the contribution to CEC from other properties, CEC2 was mainly determined by pH (45.92%), followed by silt (21.05%), free Fe2O3 (17.35%) and clay contents (12.76%), CEC1 was mainly decided by free Fe2O3 content (40.38%), followed by pH (28.39%) and silt content (27.29%;and the difference between CEC1 and CEC2 was mainly affected by free Fe2O3 (50.92%), followed by silt content (26.46%) and pH (21.80%). The acceptable optimal regression model between CEC2 and CEC1 was established as CEC2 = 2.3114 × CEC11.1496 (R2 = 0.410, P < 0.001, RMSE = 0.15). For the studies on soil taxonomy, the BaCl2-MgSO4 forced-exchange method is recommended in determining CEC of the highly-weathered acid soils in the tropical and subtropical regions.

A Brief Study on pH, Exchangeable Ca²⁺and Mg²⁺in Farmlands under Tobacco-Rice Rotation in Xuancheng City of South Anhui

pH, exchangeable Ca2+ and Mg2+ of soil can influence the yield and quality of flue-cured tobacco. Xuancheng city is the dominant tobacco-planting region in Anhui province since 2008. A general soil survey was conducted in Xuancheng city to understand the current situations of pH, exchangeable Ca2+ and Mg2+ of farmlands under tobacco-rice rotation and to decide whether continuous applying dolomite powders to abate soil acidification. In total 124 topsoil samples (0-20 cm) were collected from the typical farmlands and soil pH, exchangeable Ca2+ and Mg2+ were measured. The results showed that soil pH and Ca2+ and Mg2+ in Xuancheng city were generally in the suitable grades, pH ranged from 4.56 to 8.42 with an average of 5.87, exchangeable Ca2+ ranged from 1.01 cmol(1/2Ca2+) kg-1 to 100.55 cmol(1/2Ca2+) kg-1 with an average of 11.07 cmol(1/2Ca2+) kg-1, and exchangeable Mg2+ ranged from 0.14 cmol(1/2Mg2+) kg-1 to 2.86 cmol(1/2Mg2+) kg-1 with an average of 0.81 cmol(1/2Mg2+) kg-1, all spanned from the low grades to the high grades. To the whole Xuancheng city, 37.10%, 62.10% and 72.58% of the surveyed farmlands were in the low grades of pH, exchangeable Ca2+ and Mg2+, respectively, while 52.42%, 25.00% and 20.97% of the farmlands were in the suitable grades, respectively. pH had an extremely significantly positive Napierian logarithm correlation with exchangeable Ca2+ and an extremely significantly positive power correlation with exchangeable Mg2+. In total about 338.2 kg·hm-2 of Ca2+ and 202.4 kg·hm-2 of Mg2+ are annually input into the farmlands, while about 110.4 kg·hm-2 of Ca2+ and 7.4 kg·hm-2 of Mg2+ are annually moved out from the farmlands, exchangeable Ca2+ and Mg2+ were annually increased by 225.2 kg·hm-2 and 187.6 kg·hm-2 in the farmlands, respectively. It is necessary to monitor the farmlands dynamically in order to decide whether continuous applying dolomite powders which should be dependent upon the specific conditions of individual farmlands.

Predicting Base Saturation Percentage by pH—A Case Study of Red Soil Series in South China

pH and base saturation percentage (BSP) are two basic indexes in identifying soil types in Chinese Soil Taxonomy. Some studies proved that there is significant correlation between BSP and pH, thus it could save the cost of laboratory work if we can infer BSP directly from pH. In this study, the measured values of BSP and pH of 162 and 232 horizon samples from 48 and 55 red soil series surveyed from 2009 to 2011 in Fujian and Guangdong respectively were adopted from Soil Series Database to set up the optimal correlation model between BSP and pH. The results showed that: 1) BSP ranged from 2.30% to 94.02% with a mean of 25.07%, while pH from 3.42 to 6.91 with a mean of 4.98 for the total soil samples. 2) There were significant differences in pH between different soil types (R2 were 0.624 for Ferralosols, 0.507 for Ferrosols, 0.515 for Argosols, and 0.456 for Cambosols, p 2 were 0.580 for Quaternary red clay, 0.434 for granite, 0.642 for sandstone, and 0.712 for basalt, p 2 were 0.623 for dryland, and 0.404 for forest land, p 0), their probability density curves were mainly in flat or normal curves (y = 6.84x2 &#8722;45.86x + 81.52, R2 = 0.494, p < 0.01).

Change of Tillage Layer Thickness of Farmland in Anhui Province of Eastern China

Tillage layer thickness (TLT) of farmland could be regarded as one of physical indexes in assessing soil productivity and quality. In recent years, tillage layer shallowing was found in China in various regions, mainly due to the adoption of non-tillage or rotary tillage practices, but only little rough and non-quantitative information is available so far on the issue. This research took Anhui, a typical agricultural province in Eastern China as an example and compared the TLTs of 87 typical profiles on provincial scale and 210 on county scale from 1980s to 2010s. The results showed that TLTs of 3.7% and 17.2% of samples in 1980s and 2010s respectively were larger than 20 cm. From 1980s to 2010s the mean TLT increased from 16.3 to 17.4 cm on the provincial scale and from 15.0 to 15.5 cm on the county scale respectively. In the middle and southern regions the mean TLTs increased by 0.4-0.7 cm on the provincial scale and 0.3-3.2 cm on the county scale respectively, but decreased by 2.0 cm in northern region on the county scale. The mean TLT increased by 0.8 cm for paddy-field and 1.4 cm for dry-land on the provincial scale. TLT was influenced comprehensively by the factors of soil texture, the depth of rotary tillage and the farming positivity of the farmers. Generally, TLT of farmland with coarse soil texture was higher than that of farmland with fine soil texture, in 1980s TLT in region of poor-economic condition usually was deeper than in region of good-economic condition, and the adoption of rotary tillage led widely TLTs of farmlands to about 15 cm in 2010s.

Contents and Changes of Potassium in Plough Layers of Xuancheng, South Anhui Province

Xuancheng City is the dominant tobacco-planting area of Anhui province due to the high quality of the tobacco leaves. However, the potassium content in the tobacco leaves shows a gradual decreasing trend in recent years, which may be attributed partly to the possible low potassium content in topsoil of tobacco-planting farmland. Therefore, the content data in the year of 2005-2007 of rapidly available potassium (RA-K) of 7730 topsoil samples mainly under double rice rotation or wheat/rice-rice rotation at that time and the content data of slowly available potassium (SA-K) and RA-K of 124 typical topsoil samples in the year of 2015 under tobacco-rice rotation were used and compared in order to disclose the status of topsoil potassium and to provide a guidance for reasonable potassium fertilization in Xuancheng. The results showed that in 2005-2007 RA-K content ranged from 1 mg&#183kg-1 to 844 mg&#183kg-1 with an average of 68 mg&#183kg-1, and 82.7% of topsoil samples were insufficient in RA-K (-1). Comparatively in 2015 SA-K content ranged from 230 mg&#183kg-1 to 1340 mg&#183kg-1 with an average of 595 mg&#183kg-1, and 13.7% of soil samples were insufficient in SA-K (-1);RA-K content ranged from 46 mg&#183kg-1 to 352 mg&#183kg-1 with an average of 134 mg&#183kg-1, and 25.8% of soil samples were insufficient in RA-K (-1). The above data show that RA-K content has increased gradually in farmland topsoil mainly due to fertilization since 1980s, particularly to farmland under tobacco-rice rotation, but insufficient RA-K in topsoil is still widely and serious for farmland under double rice rotation or wheat/rice-rice rotation. Under tobacco-rice rotation, RA-K insufficiency usually occurred in the farmlands which plant tobacco less than 3 years, indicating more potassium fertilizer should be applied.

Study on Exchangeable Cation Determining Base Saturation Percentage of Soil in South China

Base saturation percentage (BSP) is an important soil chemical index in soil fertility and soil taxonomy. However, it is still unclear what exchangeable cation dominates BSP of soil in south China. Therefore, in this study, the data of BSPs and exchangeable H+, Al3+, Ca2+, Mg2+, K+ and Na+ of 109 and 45 horizon samples of 50 and 28 soil species in red soil and yellow soil groups in the Database of Chinese Soil Species were used to explore further the characteristics of BSPs and exchangeable cations as well as the correlation between BSPs and exchangeable cations. The results showed that the concentrations of exchangeable cations in both red soil and yellow soil groups were in an order of Al3+ (4.55 ± 1.47 and 4.22 ± 1.2 cmol(+)/kg) > Ca2+ (0.32 ± 0.21 and 0.36 ± 0.24 cmol(+)/kg) > H+ (0.23 ± 0.13 and 0.19 ± 0.10 cmol(+)/kg) > K+ (0.16 ± 0.09 and 0.16 ± 0.11 cmol(+)/kg) > Mg2+ (0.13 ± 0.09 and 0.11 ± 0.08 cmol(+)/kg) > Na+ (0.08 ± 0.06 and 0.11 ± 0.06 cmol(+)/kg). For red soil group, Al3+ concentration was significantly higher than those of other exchangeable cations, Ca2+ and H+ concentrations were significantly higher than those of K+, Mg2+ and Na+;while for yellow soil group, Ca2+, H+ and K+ concentrations were significantly higher than those of Mg2+ and K+. BSP of red soil group was codetermined by Ca2+, Al3+, Mg2+ and Na+, with the contributions of 33.81%, 19.82% and 14.49%, respectively;while BSP of yellow soil group was codetermined by Al3+, Ca2+, Mg2+, K+ and Na+, with the contributions of 24.91%, 21.55%, 19.91% and 14.21%, respectively. A higher concentration of exchangeable cation does not mean the higher importance of the cation to soil BSP.

Evolution and significance of soil magnetism of basalt-derived chronosequence soils in tropical southern China

Soil samples were collected from eight basalt- derived chronosequence soils with the ages of 0.01, 0.58, 0.92, 1.33, 2.04, 3.04, 3.76 and 6.12 Ma respectively from Leizhou Peninsula and northern Hainan Island of tropical southern China. Magnetic parameters of magnetic susceptibility (MS), percentage of frequency-dependent magnetic susceptibility (FDS%), anhysteretic remanent magnetization (ARM), saturation isothermal remanent magnetization (SIRM), soft and hard isothermal remanent magnetization (IRMs and IRMh) of the collected samples were measured to study the evolution and the significance of the magnetism with soil age. The results show that the magnetic parameters changed fast from Primosols to Ferrosols (0.01 ~ 0.92 Ma) but slowly at Ferralosols stage (1.33 Ma~), it suggests a stable phase occurred for soil magnetism at Ferralosols, the existence of this phase could be supported by the little changes in the contents of clay, Fet and Fed. Obvious differences existed in the values of magnetic parameters between Ferralosols and other soil types (Primosols and Ferrosols), FDS%: Ferralosols > 10%, Primosols and Ferrosols –8· SIm3·kg–1, Primosols and Ferrosols > 8000 × 10–8 SIm3·kg–1, thus, it is possible to differentiate Ferralosols from other soil types in tropical region by using magnetic indices.

A Brief Study on Using pH_H₂Oto Predict pH_KClfor Acid Soils

pHKCl and pHH2O are two basic necessary indexes to reflect the acidity of asoil. Predicting pHKCl?directly from pHH2O?could save the cost of laboratory work. In this study, the values of pHKCl and of 442 and 310 horizon samples from 126 and 98 soil profiles (0 - 120 cm in depth) surveyed from 2014 to 2015 in Guangxi and Yunnan were used to establish the optimal correlation model between pHKCl and pHH2O. The results showed that: 1) pHKCl is lower than pHH2O, pHKCl?was 0.07 - 1.99 units with a mean of 0.99 units lower than for Guangxi, while 0.03 - 1.90 units with a mean of 0.89 lower than pHH2O?for Yunan. 2) There is significant positive correlation between pHKCl?and pHH2O, the optimal correlation models between pHKCl?(y) and pHH2O?(x) for Guangxi and Yunnan are y = 0.1963x2 &minus;1.0512x + 4.338, R2 = 0.836, p 0.1859x, R2 = 0.769, p pHKCl?with exchangeable H+ and Al3+ (R2 = 0.487, 0.716, p pHKCl?is dominated by exchangeable Al3+, followed by exchangeable H+, and their contribution to pHKCl?were 71.1% and 28.7%, respectively.

Brief Study on Microelement Contents in Topsoils of Farmlands in Xuancheng, South Anhui

The available contents of microelements in the topsoil can influence the yield and quality of flue-cured tobacco. Xuancheng is the dominant tobacco-planting region in Anhui province since 2008. In this paper, the topsoil available Fe, Mn, Cu and Zn contents of 4197 farmlands mainly under rice-rice rotation and wheat-rice rotation in 2008 and of 124 typical farmlands under tobacco-rice rotation in 2015 in Xuancheng city were analyzed in order to disclose the changes and spatial distributions of these microelements and to instruct the reasonable application of the microelement fertilizers. The results showed that the topsoil average available contents in the farmlands under rice-rice rotation or wheat-rice rotation in 2008 were 105.9 mg·kg-1 for Fe, 19.6 mg·kg-1 for Mn, 4.5 mg·kg-1 for Cu, and 3.0 mg·kg-1 for Zn, respectively, increased by 33.14%, 64.29%, 51.11% and 36.67%, respectively, compared with those in the 2nd Soil Survey in 1980s, and the historic, once intensive and overall application of microelement fertilizers was attributed to the great increases. The topsoil average available contents in the farmlands under tobacco-rice rotation in 2015 were 31.1 mg·kg-1 for Fe, 9.8 mg·kg-1 for Mn, 2.1 mg·kg-1 for Cu, and 0.3 mg·kg-1 for Zn, respectively, decreased by 70.63%, 50.00%, 53.33% and 90.00%, respectively, compared with those of the farmlands under rice-rice rotation or wheat-rice rotation in 2008, and the net deficiencies in the input and output of microelements were attributed to the significant decreases in the topsoil microelements. It is necessary to monitor the farmlands under tobacco-rice rotation dynamically and in time in order to decide whether applying microelement fertilizers or not.

Study on Chemical Characteristics of Rainfall in Tobacco-Growing Regions of Chenzhou, Hunan Province

In order to clarify the chemical properties of rainfall in typical tobacco areas in Chenzhou City, Hunan Province, and analyze its potential for soil and flue-cured tobacco planting, rainfall samples in 2020 were collected by rainfall instruments in Fangyuan Town and Aoquan Town of Guiyang County, and the chemical properties that are closely related to the quality of flue-cured tobacco were determined, such as pH, EC, total nitrogen (TN), nitrate nitrogen (), ammonium nitrogen () and ion concentrations (K+, Na+, Ca2+, Mg2+, , Al3+, , Cl−,). The results show that the pH values of rainfall samples at Fangyuan and Aoquan monitoring sites are in the range of 4.92 - 6.17 and 4.93 - 5.69 respectively, with an average of 5.27 and 5.27 respectively. The acid rain characteristic is very obvious, which is mainly dominated by . The variation of rainfall EC has seasonal characteristics. EC is low from January to September, in the range of 6.09 - 56.72 and 11.83 - 30.93 μS/cm respectively, besides, it is high from October to December, in the range of 102.63 - 174.60 and 25.05 - 86.37 μS/cm respectively. The annual deposition of TN was 22.19 and 20.76 kg/hm2/yr respectively, which were higher than that in the western regions with less human disturbance, but lower than or equal to that in the developed agricultural regions in eastern China. The proportion of in the annual deposition of TN was higher than that of at two monitoring sites, with an average of 56.51% and 38.86% respectively. Ammonia volatilization from agricultural activities contributed more to rainfall nitrogen content. The ratios of ammonium nitrogen to nitrate nitrogen deposition at two monitoring points were 1.84, 1.81, 1.86 and 1.34, 1.46, and 1.29 during the whole year, summer and autumn, winter and spring respectively. The ratio is higher in summer and autumn than in winter and spring. The weighted average equivalent concentrations of the main ions at two monitoring sites were 238.88 μeq/L and 211.21 μeq/L respectively, and the orders of the ion concentrations were slightly different. Both the concentrations of and are higher, while Mg2+, and Al3+ are lower. , and are mainly from human activities with a contribution rate between 91.90% and 99.35%. Ca2+ mainly comes from soil and ground dust, besides, Cl− and Mg2+ mainly come from marine sources and K+ mainly comes from terrestrial sources. In general, the acidic rainfall and higher concentration are beneficial to reducing the high pH value of soil in Aoquan tobacco area and improving the quality of flue-cured tobacco. Higher concentrations of and in rainfall are not conducive to the improvement of flue-cured tobacco quality, because of the high content of soil available sulfur in Chenzhou tobacco area and the characteristics of flue-cured tobacco’s preference for ammonium.

Iron loss of paddy soil in China and its environmental implications

Iron(Fe)is an important element for the terrestrial and marine ecosystems through its biogeochemical cycling on the Earth’s surface.China has a long rice cultivation history,with extensive rice distribution across many types of paddy soils.Paddy soils are the largest anthropogenic wetlands on earth with critical roles in ecosystem functions.The periodic artificial submergence and drainage during paddy soil evolution result in significant changes in soil moisture regime and redox conditions from the natural soils,which facilitate the increase of Fe solubility and mobilization.However,there is a lack of systematic assessment on the magnitude of the migration and loss amount of Fe from paddy soils.In order to quantify the Fe loss and assess the dynamic evolution of Fe in the soils after rice cultivation,seven paddy soil chronosequences derived from different landscapes(bog,plain,terrace)and parent materials(acidic,neutral,calcareous)with cultivation history from 0 to 2,000 yr were studied.Results showed that the rates and trajectories of Fe evolution showed distinct patterns among the studied seven paddy soil chronosequences.However,net losses of Fe from 1 m soil depth occurred at all studied paddy soil chronosequences regardless of the original landscapes and parent materials.Fe in the paddy soils derived from the calcareous lacustrine sediments in the bog area showed a slight accumulation during the initial stage(50 yr)of paddy cultivation,with a loss rate of0.026 kg m^(-2)yr^(-1) during the 50-to 500-yr time period.For the paddy soils developed on the calcareous marine sediments in the plain area,Fe evolution was dominated by the internal movement in soil profiles through coupled reducing-eluviation reactions in the surface horizons and oxidation-illuviation in the subsurface horizons within 1,000 yr of paddy cultivation,with an averaged net loss rate of 0.029 kg m^(-2)yr^(-1) during the 1,000-to 2,000-yr time period of rice cultivation.In contrast,Fe in the paddy soils derived from the acidic and neutral parent materials in the plain and terraced upland areas was rapidly lost during the initial stage of paddy cultivation,with a maximum loss rate of 1.106 kg m^(-2)yr^(-1),while the Fe loss rate decreased gradually with increasing paddy cultivation age.Soil pH,CaCO_(3),and organic matter contents of the original soils,the length of time of paddy cultivation,landscape types and positions,and changes in soil moisture regime and redox condition induced by artificial submergence and drainage were the main factors controlling the rates and trajectories of Fe loss during paddy soils evolution.The amount of Fe loss caused by rice cultivation at the national scale was estimated based on the data collected from this study and the literature.The Fe loss fluxes of paddy soils in China were about 46.4–195.7 Tg yr^(-1),and the amounts of Fe losses from paddy fields nationwide were about 5,121.5–9,412.2 Tg.Quantifying Fe loss from paddy fields is important to scientifically assess the impact of paddy cultivation on the Fe biogeochemical cycle.

Machine learning methods for predicting the uniaxial compressive strength of the rocks:a comparative study

The uniaxial compressive strength(UCS)of rocks is a critical index for evaluating the mechanical properties and construction of an engineering rock mass classification system.The most commonly used method for determining the UCS in laboratory settings is expensive and time-consuming.For this reason,UCS can be estimated using an indirect determination method based on several simple laboratory tests,including point-load strength,rock density,longitudinal wave velocity,Brazilian tensile strength,Schmidt hardness,and shore hardness.In this study,six data sets of indices for different rock types were utilized to predict the UCS using three nonlinear combination models,namely back propagation(BP),particle swarm optimization(PSO),and least squares support vector machine(LSSVM).Moreover,the best prediction model was examined and selected based on four performance prediction indices.The results reveal that the PSO–LSSVM model was more successful than the other two models due to its higher performance capacity.The ratios of the predicted UCS to the measured UCS for the six data sets were 0.954,0.982,0.9911,0.9956,0.9995,and 0.993,respectively.The results were more reasonable when the predicted ratio was close to a value of approximately 1.