Water erosion in sloping cropland poses a significant challenge in the Mollisol region of Northeast China, largely due to the clay-rich soils and the presence of a compacted plow layer. Therefore, enhancing the hydraulic characteristics of soils is crucial for preventing erosion and degradation in this area. This study investigated the effects of composite soil amendments, comprising super absorbent polymers, polyacrylamide, and organic fertilizer, on soil hydraulic characteristics at the runoff plot scale. The experiment was conducted with four application amounts: low (M1), medium (M2), high (M3), and ultra-high (M4). The infiltration capacity of soils was determined by the in situ infiltration method, the water-holding capacity of soils was measured with the constant head method, the soil structure was quantified by the Yoder wet sieve method and the sandbox method. The results showed that, compared with the control (CK), different amounts of composite soil amendments all increased the soil infiltration capacity (i.e., initial infiltration rate, steady-state infiltration rate, near-saturation and saturated hydraulic conductivity), among which the enhancement effect under the low suction at −0.5 hPa was significant. Soil water-holding capacity was also increased, in which the natural water content and maximum water-holding content were increased by 0.58–12.18 % and 5.53–18.73 %, respectively. Applying a medium amount of composite soil amendment (M2) best increased soil hydraulic characteristics. The mechanism is that the composite soil amendments enhance soil infiltration capacity by increasing macroporosity, while the enhancement of soil water-holding capacity is affected by the combined effect of macroporosity and the increase of large soil water-stable macroaggregates (>2 mm). Overall, the composite soil amendment effectively increased soil hydraulic characteristics and can be recommended in the Mollisol region of Northeast China.

The current literature provides compelling evidence of a robust connection between increased total organic carbon (TOC) content in soils and better soil physical characteristics. However, these studies predominantly relied on information gathered from soil surveys or soil incubation experiments. A primary limitation associated with such research is the inherent soil heterogeneity. To address this issue, we initially extracted organic carbon (OC) with highly enriched TOC soil specimens. Subsequently, we mixed this extract at various ratios with the original high-OC soil, creating four unique blends. Each blend was then used to cultivate B. chinensis, and the soil samples were retrieved afterwards for further analysis. The elevated TOC soil treatments displayed substantial macro-porosity and macro-aggregates (>0.25mm). The O-alkyl C fraction in high-OC soils exhibited heightened susceptibility to decomposition following H2O2 treatment; conversely, the proportion of alkyl C fractions remained remarkably stable in low-OC soils. No direct relationships were detected between the soil A/O-A ratio and aromaticity, or between the soil TOC content and its aromaticity. Correlation analysis revealed a positive association between soil macroporosity, macro-aggregates (>0.25mm), and soil TOC content, along with its active carbon fractions such as carbohydrate C. Our study revealed that increasing levels of soil TOC, specifically certain reactive carbon fractions, significantly enhance soil physical properties. However, it is noteworthy that the rate of soil OC accumulation does not invariably reflect changes in its quality. This finding paves the way for a novel perspective on the regulatory mechanisms of SOC related to soil physical characteristics.

Drainage difficulties in the waterlogged areas of sloping cropland not only impede crop development but also facilitate the formation of erosion gullies, resulting in significant soil and water loss. Investigating the distribution of these waterlogged areas is crucial for comprehending the erosion patterns of sloping cropland and preserving black soil resource. In this study, we built varied models based on two stages (one using only deep learning methods and the other combining object-based image analysis (OBIA) with deep learning methods) to identify waterlogged areas using high-resolution remote sensing data. The results showed that the five deep learning models using original remote sensing imagery achieved precision rates varying from 54.6% to 60.9%. Among these models, the DeepLabV3+-Xception model achieved the highest accuracy, as indicated by an F1-score of 53.4%. The identified imagery demonstrated a significant distinction in the two categories of waterlogged areas: sloping cropland erosion zones and erosion risk areas. The former had obvious borders and fewer misclassifications, exceeding the latter in terms of identification accuracy. Furthermore, the accuracy of the deep learning models was significantly improved when combined with object-oriented image analysis. The DeepLabV3+-MobileNetV2 model achieved the maximum accuracy, with an F1-score of 59%, which was 6% higher than that of the model using only original imagery. Moreover, this advancement mitigated issues related to boundary blurriness and image noise in the identification process. These results will provide scientific assistance in managing and reducing the impact in these places.

Taking Bijie tobacco planting area in Guizhou Province as the study area, based on the analysis of different influential factors on soil pH, the main controlling factors of soil pH variation were discussed, the spatial variation characteristics of soil pH were obtained by geostatistical interpolation method, and then the suitability grades of carbon-based organic fertilizer for improving acidified soil in this area were divided. The average value of soil pH in Bijie tobacco growing area is 6.5, the average value of soil pH in Dafang and Weining counties are both only 6.2, while those in Zhijin, Jinsha and Qianxi counties are all higher than 7.0. The comparative analysis shows that soil parent rock and soil types are the main controlling factors of soil pH variability in Bijie tobacco growing area. From the perspective of spatial distribution characteristics, soil pH distribution is higher in the east than those in the middle and west. Soil pH is higher in the northwest of Jinsha County, the east of Dafang County, and the middle of Qianxi County; lower in the south of Weining County, the middle and north of Hezhang County, and the middle and west of Qixingguan as a whole. The area proportion of soil pH is about 44.1% in the appropriate grade（5.5＜pH＜7.0）, while the proportion higher and lower than the appropriate level is 36.7% and 19.2%, respectively. The suitable application area of carbon-based organic fertilizer is mainly distributed in the west and central and some areas of the east,while the unsuitable application area is mainly distributed in the east and central. At the township level, the key application of carbon-based organic fertilizer is mainly concentrated in Weining, Qixingguan and other counties, the unsuitable application areas are mainly distributed in Qianxi, Zhijin and Dafang counties, while the general application areas are mainly distributed in Zhijin, Nayong and Jinsha counties. This study can provide a scientific basis for the precise application of carbon-based organic fertilizer for the purpose of regulating soil acidity.

Soil degradation in the Mollisol region of Northeast China is ubiquitous partly due to poor soil hydraulic characteristics. Improving soil hydraulic characteristics thus delivers benefits to soil sustainability. In this study, the effects of organic amendments on soil hydraulic characteristics were explored at the laboratory scale. Soil samples were subjected to three low-cost and eco-friendly organic amendments, including corn straw juice (CSJ), fulvic acid (FA), and humic acid (HA). The soil infiltration capacity, soil water characteristic curve (SWCC) and soil water retention capacity were determined by using a steel-ring method and a centrifuge method. The parameters of the SWCC were fitted by a van Genuchten (VG) model, and the specific water capacity [C(h)] was calculated. In addition, bulk density (BD), macroporosity, and soil organic matter (SOM) were measured, and the relationships between the variables and processes were evaluated. The results indicated that the soil infiltration capacity (i.e., initial infiltration rate, cumulative infiltration, and steady infiltration rate) was significantly increased in the CSJ and FA treatments (p < 0.05) but decreased in the HA treatment compared to the control (CK) treatment. All the selected organic amendments improved the soil water release and supply capacity, and the CSJ2 treatment showed the best effect. The incorporation of CSJ, FA, and HA significantly improved the soil water retention capacity by increasing the saturated soil water content, field capacity, and plant available water capacity (p < 0.05). Such changes were significantly associated with macroporosity and SOM (p < 0.05). In this sense, our results showed that the CSJ treatment with 4 L m(-2) and 50% volumetric concentration could be an effective soil amendment to improve the soil hydraulic characteristics in Mollisols and deserves further research.

Nitrate nitrogen (nitrate-N) is crucial for the development of tobacco quality. However, how to enhancing soil nitrification in tobacco plantation is still an immediate concern that requires attention. This study aimed to examine the impact of mixed organic manure on soil nitrification in tobacco cultivation regions. We selected an Ultisols field, which was planted with tobacco from Yunnan province, to explore the impact of adding various organic manures (F1-F6: regular organic manures, F7: mixed organic compost which was derived from crop residues), on soil gross N mineralization and nitrification. This study was conducted through a 75-day indoor leaching experiment, with constant temperature (25 degrees C) and humidity (65% of field water capacity). The results showed that F4 significantly (p <.05) enhanced soil N mineralization, and had the highest mineralized-N and potentially releasable mineralized-N (N-0) due to its highest organic carbon (OC) and total-N, which amounted to 422 mg kg(-1) and 705.7 mg kg(-1), respectively. F7 exhibited a significant increase (p <.05) in the rate of soil N mineralization, with the highest firstorder mineralization rate constant (k(1)) of 0.090 d(-1). Moreover, it displayed a substantial increase (p <.05) in nitrate-N content and potentially releasable nitrate-N (N-p), measuring 41.5 mg kg(-1) and 41.3 mg kg(-1), respectively. Furthermore, F7 exhibited the highest first-order nitrification rate constant (k(2)) of 0.076 d(-1). It also demonstrated a considerably higher net nitrate-N/ mineralized-N ratio of 33.5%, which was significantly (p <.05) greater than that of F1-F6 (nitrate-N/mineralized-N ratio: -7.06 to 1.86%). At day 15 and day 45, F7 exhibited the highest nitrate-N concentration and nitrate-N/mineralized-N ratio (28.1 mg kg(-1) and 49.7%) in comparison to F1-F6, which had lower nitrate-N concentrations (ranging from 0.4 to 6.9 mg kg(-1)) and nitrate-N/mineralized-N ratios (ranging from 0.4 to 11.9%). These results indicate that the addition of mixed organic compost significantly enhances soil nitrification compared to regular organic manures. Therefore, it suggests that incorporating mixed organic compost improves soil nitrification in Ultisols.

Deriving an accurate three‐dimensional (3D) spatial distribution of heterogeneous soil pollutants at contaminated sites using traditional spatial interpolation methods, such as inverse distance weighting (IDW), is challenging; especially when only limited borehole data are available. This study presents a novel IDW‐COV method, where weighting is determined by optimizing relative importance between feature distances of covariates and spatial distances to soil sample locations. The method was tested by mapping the 3D distributions of Cr (VI) and total Cr at a Cr salt production workshop (Site A) and a legacy Cr slag stacking site (Site B). The results were compared with those of IDW, the soil land inference model (SoLIM), and the SoLIM combined with IDW method (SoLIM‐IDW). The proposed IDW‐COV method returned the highest accuracy, with R 2 values of 0.83 for Cr (VI) in Site A and 0.75 for total Cr in Site B, compared with 0.65 and 0.57 for IDW, 0.16 and 0.58 for SoLIM, and 0.73 and 0.61 for SoLIM‐IDW. This study highlights the importance of considering differences in explanatory power between multidimensional covariate and geographical spatial distance when incorporating multisource auxiliary data into weighted average estimators and provides guidance for mapping 3D distributions of heterogeneous pollutants from sparse soil borehole data .

土壤酸碱度是影响蓝莓树体正常生长的重要环境因子之一,量化表征土壤酸碱度变化对保持蓝莓正常生长、提高经济效益的影响幅度至关重要.本文利用Meta分析方法系统地集成国内外87篇文献,共筛选12个蓝莓品种,利用文献中已提取数据组定量化拟合土壤pH变化对不同品种蓝莓树体生长的影响差异.结果表明:根据土壤pH变化对蓝莓树体生长的影响幅度判断,蓝莓各品种的最适土壤pH分布在4.4～5.0之间;利用量化拟合关系式的|k|值,将蓝莓生长对土壤pH变化的敏感性分为高敏感型、低敏感型和迟缓型3个类型,不同敏感型蓝莓的最适土壤pH范围分别为4.2～5.6、3.5～5.5和3.2～5.7;利用土壤pH对蓝莓树体生长的影响幅度为评价依据,将土壤pH适宜性划分为最适、适宜、有碍和不适4个等级.蓝莓种植户可依据土壤pH对蓝莓树体生长的影响幅度来调节蓝莓土壤pH,并依据蓝莓对土壤pH变化的敏感性来适当放宽或严格调整蓝莓土壤酸碱环境.

BACKGROUND The availability of soil nitrogen (N) decreases as the structure of agricultural soils degrades. Traditional methods focus on organic amendments that indirectly affect the porosity and N content of soil. Due to the low efficiency of such amendments, new materials, particularly highly porous materials, are needed to improve the quality of soil, which has opened new directions. RESULTS The addition of 2 to 7 mm of porous clay ceramic (PLC) significantly increased the fresh weight of Brassica chinensis. The soil aeration porosity (>50 mu m) increased by 0.69% on average in response to 1% PLC application. Soil NO3--N, NH4+-N and mineral N increased by 3.3, 1.3 and 4.6 mg kg(-1) on average, respectively, following a 1% PLC application rate. The initial N content of the high PLC treatments was the lowest in the incubation experiment. The parameters of soil N mineralization, i.e. potentially mineralizable N (N-0), the first-order rate constant (k) and the mineralization composite index (N-0 x k), increased obviously as the amount of PLC increased. Porosities larger than 1000 mu m were significantly more positively correlated with the parameters of soil N mineralization than those <500 mu m. The Pearson correlation coefficients suggested that high porosity, mineral N and N-0 values had significant positive relationships with the fresh weights in double seasons. CONCLUSION The application of PLC increased soil aeration and enhanced the availability of soil N, which yielded large vegetable harvests in clayey soils in the short term. (c) 2022 Society of Chemical Industry.

[目的]查明区域土壤氯素含量和烟叶氯素风险可为烟区科学管理提供依据.[方法]本研究基于毕节植烟区2059个土壤采样点,通过经典统计学和地统计学方法,研究了毕节烟区土壤氯离子含量及烟叶氯素风险的空间分布特征.[结果]研究结果表明:土壤氯离子平均含量为29.4 mg kg-1,烟叶无氯素风险(20～30 mg kg-1)的样点比例仅为12.2％,而低氯风险2级(＜10 mg kg-1)的比例高达40％,与低氯风险1级(10～20 mg kg-1)的比例之和超过60％;烟叶高氯风险2级(＞45 mg kg-1)与高氯风险1级(30～45 mg kg-1)比例之和为26.3％.各县区中,织金县土壤氯离子含量较低,而七星关区含量最高;紫色土和石灰土存在较大面积的烟叶低氯风险区域,而黄棕壤和粗骨土的部分区域存在高氯风险;页岩和碳酸盐岩土壤的烟叶低氯风险较大,而玄武岩和砂岩土壤的高氯风险相对较大.从空间分布看,烟叶低氯风险主要分布在南部和东部地区,高氯风险主要分布在西部地区和中北部局部区域.[结论]毕节烟区土壤氯离子存在较强的空间变异性,烟叶低氯与高氯风险并存,在田间管理时应依据烟叶氯素风险等级科学制定区域氯肥施用方案.

土壤容重是影响作物生长的重要土壤属性,也是土壤改良的重要依据,对土壤容重空间分布及影响因素的了解有助于生产管理及土壤改良方案的实施.本研究通过系统采样,测定了毕节市植烟区653个样点的土壤容重、机械组成及有机质含量,分析了土壤容重的空间分布特征,探讨了影响土壤容重的因素.结果表明:毕节市植烟土壤容重平均为1.20 g/cm3,变异系数为12.4％.在空间上,土壤容重以西部为高,中部略低.土壤母质及土壤类型对土壤容重影响较大,其中,红色风化壳及砂页岩类土壤容重较高,而粗晶岩发育土壤容重最小;土壤类型中,以紫色土容重最高,而水稻土最低.土壤有机质含量与土壤容重呈负相关(P<0.01).依据植物生长特性,结合土壤质地分级,本研究给出了七星关与威宁的部分地区为土壤容重改良的重点区.

为研究玉溪烟区烟叶镁含量的分布状况和影响因素,采集玉溪烟区烟叶和土壤样品,通过描述性统计、方差分析、相关性分析及回归分析的方法,明确了烟叶镁含量的整体分布状况及在不同海拔高度和坡度区间的分布特征,分析了其与土壤全氮、全磷、速效钾、有效镁、有效硼和氯离子之间的关系.结果表明:玉溪烟区烟叶镁平均含量为4.28 g/kg,变幅为0.94～9.17 g/kg,41.2％的烟叶镁含量处于适宜范围(4.0～15 g/kg).除1700～1900 m海拔区间的烟叶镁含量均值(4.67 g/kg和5.57 g/kg)处于适宜范围外,<1700、1900?2000 m和>2000 m海拔区间的烟叶存在轻度缺镁(2.0～4.0 g/kg)状况.除5° ～10°坡度区间的烟叶存在缺镁状况外,<5° 和>10°坡度区间的烟叶镁含量(4.55 g/kg和4.34 g/kg)处于适宜范围.烟叶镁含量与土壤全磷和有效镁含量呈极显著线性正相关(P<0.01),与速效钾、有效硼和氯离子含量呈显著线性正相关(P<0.05).在玉溪烟区需要适当增施磷、钾、镁和硼肥,进一步调控氮肥和氯肥的施用.

以2019年玉溪烟区9个植烟县34个主要植烟乡镇各1个代表性烟田的土壤和烤烟为研究对象,分析了土壤速效钾和有效镁及其交互作用对烤烟化学及感官品质的影响.结果表明:土壤速效钾和有效镁平均含量分别为325.9 mg/kg和207.9 mg/kg,变幅分别为93.0～713.0 mg/kg和40.0～610.0 mg/kg,土壤速效钾和有效镁缺乏的烟田分别占14.7％ 和23.5％.随着土壤速效钾含量的增加,烟叶钾含量先增后减,烟叶镁含量递增,烟碱和总氮含量先降后增,总糖含量、还原糖含量、糖碱比和氮碱比递减,其中土壤速效钾含量与烟叶镁含量呈显著正相关(P<0.05).随土壤有效镁含量的增加,烟叶钾含量递减,烟叶镁含量递增,烟碱含量先增后降,总氮含量递增,总糖含量、还原糖含量、糖碱比和氮碱比先降后增,其中土壤有效镁含量与烟叶钾、镁含量分别呈极显著负相关和正相关(P<0.01).土壤速效钾和有效镁含量的增加能分别显著提升烟叶清甜香和香气量(P<0.05).土壤钾镁交互作用对烟叶总糖、还原糖含量及氮碱比均产生显著影响(P<0.05).因此,为提升玉溪烤烟品质,应在适当施用镁肥的基础上增施钾肥,并同时关注氮肥等其他肥料对烤烟钾镁的影响.

Soil structure and organic carbon are key factors that reflect soil quality in sustainable agricultural production. Many studies have concentrated on soil aeration under intensive anthropogenic agricultural practices, but the relationship between soil aggregate stability and soil organic carbon (SOC) functional groups is poorly understood, particularly in degraded greenhouse vegetable fields converted from paddy fields. To solve this problem, soil samples were collected from local vegetable fields and adjacent paddy fields. Conventional open-air vegetable fields and greenhouse vegetable fields, both with a 6-8-year cultivation history following conversion from paddy fields, were considered. SOC functional groups were characterised by C-13 cross-polarisation magic-angle-spinning nuclear magnetic resonance (C-13 CPMAS NMR). The results showed that the mean weight diameter (MWD) values of water-stable soil aggregates in the open-air vegetable fields and greenhouse vegetable fields decreased by 64.6% and 66.7%, respectively, compared with those in the paddy fields. Similar results were obtained for the soil aggregate distribution, and soil aggregates in the greenhouse vegetable fields and open-air vegetable fields were mainly in the 0.25-2 mm size classes. Among all SOC functional groups, O-alkyl C exhibited the greatest decrease after the conversion of paddy fields to vegetable fields, no matter whether greenhouse vegetable fields or open-air vegetable fields. The degradation of soil structure decreased the physical protection of SOC functional groups by soil aggregates, and therefore, decreased the total SOC content and labile C functional group fractions in bulk soil. At the soil aggregate scale, the decrease of O-alkyl C mainly occurred in microaggregates (0.053-0.25 mm), while aromatic C decreased significantly in macroaggregates (>0.25 mm) in the greenhouse vegetable fields converted from paddy fields. Correlation analysis showed that O-alkyl C was significantly positively related to MWD and the proportion of large soil macroaggregate (>2 mm). This result suggested that soil aggregates become fragile in long-term vegetable cultivation after conversion from paddy fields, and a large loss of O-alkyl C might be the main reason for this phenomenon.

为研究适合滇中地区烤烟生产的有机肥类型,通过田间小区试验分析并比较了不同硝态氮比例的有机肥对烤烟性状与品质的影响.试验共分常规纯化肥处理(CK,N用量为113 kg/hm2)、化肥+常规有机肥处理(1H,N用量为79 kg/hm2+34 kg/hm2)、化肥+促硝氮有机肥处理(2H,N用量为79 kg/hm2+34 kg/hm2)、化肥+促硝氮有机肥处理(3H,N用量为79 kg/hm2+34 kg/hm2)等4个处理.结果表明,从烤烟农艺性状来看,2H和3H处理均不同程度提升了烤烟农艺性状,新型促硝氮有机肥处理的SPAD值均低于1H处理和CK;从烤烟经济性状来看,3H处理产量最高,达到1842 kg/hm2,2H处理为1841 kg/hm2,两者增产率均为10.5％;从烤烟化学成分来看,施用新型促硝有机肥能提高烟碱、总糖、还原糖、总磷、总钾含量,降低总氯含量,使烤烟内在品质渐趋合理.从烤烟评吸指标来看,施用促硝氮有机肥能提高烟叶香气质量,其中2H处理的评吸综合分值达74.3分,较CK(67.7)表现出优势.总之,提升有机肥的硝态氮比例可以有效促进烤烟生长,同时在产量方面也具有提升作用,为替代无机氮肥和提升有机肥质量,增加养分供给和促进土壤环境改善提供了参考.

【Objective】The role of biochar-based organic fertilizers in improving soil fertility and health, in general, has gained a lot of attention in recent times. It is the premise of scientific fertilization to make clear which planting areas are suitable for applying biochar-based organic fertilizer and which areas are not.【Method】Based on 2 059 soil samples in Bijie tobacco planting area of Guizhou Province, this study analyzed the distribution characteristics of soil pH and the spatial changes of soil properties,such as organic matter, available calcium, available magnesium, clay content and cation exchange capacity（CEC）. Based on the overall consideration of soil pH and soil acid-base buffer potential, the suitability grade of biochar-based organic fertilizer application in the Bijie tobacco planting area was obtained. 【Result】The results showed that the average pH value of all sampling points in Bijie tobacco growing area was 6.5, which was weakly acidic. The average pH values of Dafang County, Qixingguan District and Weining County were only 6.2, 6.3 and 6.3, respectively, while those of Zhijin County, Jinsha County and Qianxi County were more than 7.0. The contents of organic matter, available calcium and magnesium, clay and CEC in tobacco planting soils in different counties were different, which led to the differences of soil acid-base buffer index between different counties. In all counties, the comprehensive index of acid buffer in Dafang and Weining was 0.96, while that in Zhijin was 1.23. Generally,there was a positive correlation between the pH value and the buffering potential of each parent rock soil type. The pH value of sandstone coarse bone soil and yellow soil was lower, and the value of the acid-base buffering potential index was also smaller.Also, the value of carbonate limestone soil with higher pH value was higher than that of other soil types. The suitability grade of biochar-based organic fertilizer calculated by pH value and acid-base buffer composite index showed that except for the purple soil of sand shale, the soil types derived from sandstone and sand shale were the most suitable application grade, and it was very necessary to apply a biochar-based organic fertilizer to improve soil pH value in these soil types. Carbonate and calcareous soils were not suitable for the application, which indicates that biochar-based organic fertilizer is not suitable for the two soil types without changing the current soil pH and acid-base buffer potential. The remaining soil types from other parent rocks belong to the suboptimal grade, and a certain amount of biochar-based organic fertilizer should be applied to these soil types to moderately increase the pH value, to keep the soil pH in a better state.【Conclusion】From the township level, the town numbers of key application, general application, and unsuitable application grades were 82, 144, and 32 respectively. The key application towns of biochar-based organic fertilizer were mainly concentrated in Weining County, Zhijin County, and Hezhang County. The towns with general application grade were more, and most of them were distributed in Dafang County and Qixingguan District. The unsuitable application towns for biochar-based organic fertilizer are mainly concentrated in Qianxi County and Jinsha County.This study fully considered the effects of soil pH value and acid-base buffer potential on the suitability of biochar-based organic fertilizer, and identified the key application, general application and unsuitable application towns in the Bijie tobacco planting area. This study provides a scientific basis for the accurate application of biochar-based organic fertilizer in the Bijie tobacco planting area and also enriches the research connotation of soil management division in the tobacco planting area.

Soil iron (Fe) performs vital functions in the biogeochemical cycles of soil environments. The amount and profile allocation of various Fe parameters can be used as sensitive indicators of soil development and pedogenic processes. This study aimed to evaluate the potential of ground-based hyperspectral imaging (HSI: 400-1010 nm) spectroscopy to predict and map six Fe parameters indicative of pedogenic processes: total Fe (Fe-t), dithionite-citrate-bicarbonate (DCB)-extracted Fe (Fe-d), oxalate-extracted Fe (Fe-o), weathering index (Fe-W), active ratio (Fe-A) and crystallinity ratio (Fe-C). In total, 17 intact soil profiles at a depth of 100 +/- 5 cm were collected to acquire HSI images. Four non-linear machine learning techniques, namely, random forest (RF), XGBoost, CatBoost and support vector machine regression (SVMR), were implemented and compared with linear partial least squares (PLS) to identify the models with the best performance for different soil Fe parameters. Our results indicate that the four non-linear machine learning models outperformed PLS for most soil Fe parameters, with low root mean square error (RMSE) and high Lin's concordance correlation coefficient (LCCC) values. Based on the testing set, SVMR showed better performance over the other tested models for Fe-t (RMSEP = 2.645 g kg(-1), LCCCP = 0.89), Fe-d (RMSEP = 0.972 g kg(-1), LCCCP = 0.97), Fe-o (RMSEP = 0.273 g kg(-1), LCCCP = 0.97), Fe-W (RMSEP = 0.035, LCCCP = 0.97), Fe-A (RMSEP = 0.033, LCCCP = 0.97) and Fe-C (RMSEP = 0.031, LCCCP = 0.97). According to the LCCCP values, soil Fe-t was predicted to be in substantial agreement by SVMR, and the other soil Fe predictions were considered to be in near perfect agreement. Moreover, SVMR required lower computational costs. Given these results, the combination of HSI spectroscopy and SVMR is recommended due to its more reliable estimation and profile mapping of the selected soil Fe parameters than that of PLS, RF, XGBoost and CatBoost. Highlights Hyperspectral imaging was used to map six soil Fe parameters of intact profiles. Nonlinear machine learning models were compared to select the most suitable model. Nonlinear techniques outperformed the linear PLS model in most cases. SVMR showed higher comprehensive performance than other models. Hyperspectral imaging combined with SVMR is recommended to map soil Fe in profiles.

Soil structure degradation in greenhouse vegetable fields reduces vegetable production. Increasing aeration porosity is the key to ameliorating soil structure degradation. Thus, we tested the effect of a porous material, porous clay ceramic (PLC), on the amelioration of soil structure degradation under greenhouse vegetable production. A 6-month pot experiment was conducted with four PLC application levels based on volume, i.e., 0% (control), 5% (1P), 10% (2P), and 15% (3P) using Brassica chinensis as the test plant. At the end of the experiment, soil columns were sampled, and the aeration pore network was reconstructed using X-ray computed tomography (CT). The degree of anisotropy (DA), fractal dimension (FD), connectivity, aeration porosity, pores distribution, and shape of soil aeration pores and plant biomass were determined. The DA, FD, and connectivity did not significantly differ as the PLC application rate increased. Nonetheless, aeration porosity significantly linearly increased. The efficiency of PLC at enhancing soil aeration porosity was 0.18% per Mg ha–1. The increase in aeration porosity was mainly due to the increase in pores > 2 000 μm, which was characterized by irregular pores. Changes in aeration porosity enhanced the production of B. chinensis. The efficiency of PLC at increasing the plant fresh weight was 0.60%, 3.06%, and 2.12% per 1% application rate of PLC for the 1P, 2P, and 3P treatments, respectively. These results indicated that PLC is a highly efficient soil amendment that improves soil structure degradation by improving soil aeration under greenhouse conditions. Based on vegetable biomass, a 10% application rate of PLC was recommended.

Greenhouse vegetable production (GVP) is developing rapidly and farming practices strongly affect soil quality. However, quantitative evidence of the differences in soil macropore structure between organic and conventional greenhouse vegetable cultivation is still unavailable. In this study, we sampled paired organic and conventional greenhouse vegetable soils from the tilled and plough pan layers at sample sites south of Nanjing, China. Using industrial computed tomography (CT) scanning technology to measure soil macropore characteristics, we examined the effects of different farming practices on soil macropore structure, as well as the main factors that influenced soil macropore characteristics. Organic greenhouse vegetable (OGV) production was associated with a greater quantity and quality of soil macropores compared with conventional greenhouse vegetable (CGV) production. The total macroporosity in the tilled soil layer averaged 16.9% in OGV soils, more than twice that of CGV soils. OGV soils exhibited an improved pore size distribution with a greater relative abundance of transmission pores (50-500 mu m) and a decreased relative abundance of large macropores (>1,000 mu m). Pore size and shape data suggested that OGV soils had fewer soil cracks but more biopores than CGV soils in the tilled layer, as well as more root biopores in the plough pan layer. Furthermore, macropore morphology was improved in both the tilled and plough pan layers of OGV soils. In particular, macropore connectivity was nearly 10 times greater in the tilled layer of OGV soils. Soil organic matter (SOM) content was the dominant factor influencing most macropore characteristics (total macroporosity, connectivity, and relative porosity of 100-1,000 mu m pores, all small macropores and elongated medium macropores). We suggest that greater SOM content and consequently better soil macropore structure in OGV soils was dependent not only on greater organic manure input, but also on the non-application of chemical fertilizer. Highlights Farm management affects soil macropore structure in greenhouse vegetable production. Compared soil macropore structure in organic and conventional greenhouse vegetable cultivation. OGV had greater quantity and quality of soil macropores than CGV. Greater SOM in organic farming contributed to the better soil macropore structure.

Conversion of rice-wheat rotation (RWR) to conventional vegetable cultivation, especially vegetable cultivation in plastic sheds, readily causes soil structure degradation, and organic manure is commonly applied to mitigate such degradation. Although many studies have focused on changes in SOC properties or structural soil parameters, additional details about the changes, such as the relationships between SOC fractions and soil aggregates during unique land-use changes, are unknown. Here, we studied the changes in soil aggregation, and SOC parameters in 14-year-old plastic-shed vegetable fields (PVFs) and open-air vegetable fields (OVFs) covered with organic manure, with adjacent RWR fields serving as a control. The vegetable fields were converted from RWR fields. SOC fractions were analyzed by using C-13 solid-state NMR spectroscopy, and the aggregate classes were divided as follows: large macro-aggregates (>2 mm), small macro-aggregates (2-0.25 mm), micro-aggregates (0.25-0.053 mm), and silt and clay particles (<0.053 mm). PVFs had higher SOC and MBC than OVFs and RWR fields. In terms of the SOC fractions, the proportion of O-alkyl C decreased as RWR (53.90%) > PVF (43.21%) > OVF (35.37%), in contrast to the trends in the carbonyl C and aromatic C fractions. The aggregateassociated C, especially that associated with large macro-aggregates and micro-aggregates, in the PVFs was highest among the treatments. The O-alkyl C fraction in large macro-aggregates decreased in the order RWR (44.67%) > OVF (35.76%) > PVF (32.40%), consistent with the results for micro-aggregates. Furthermore, there was a significant (P = 0.05) positive relationship between macro-aggregates (>0.25 mm) and the active C fractions, in contrast to the relationships with stable fractions. It suggested that plastic-shed cultivation might have a more positive effect than open-air cultivation on soil structure and the carbon stock when large amounts of organic manure are applied; moreover, the SOC quantity and quality affect soil aggregation differently.