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Soil pH is an essential indicator for assessing soil quality and soil health. In this study, based on the Chinese farmland soil survey dataset and meteorological dataset, the spatial distribution characteristics of soil pH in coastal eastern China were analyzed using kriging interpolation. The relationships between hydrothermal conditions and soil pH were explored using regression analysis with mean annual precipitation (MAP), mean annual temperature (MAT), the ratio of precipitation to temperature (P/T), and the product of precipitation and temperature (P*T) as the main explanatory variables. Based on this, a model that can rapidly estimate soil pH was established. The results showed that: (a) The spatial heterogeneity of soil pH in coastal eastern China was obvious, with the values gradually decreasing from north to south, ranging from 4.5 to 8.5; (b) soil pH was significantly correlated with all explanatory variables at the 0.01 level. In general, MAP was the main factor affecting soil pH ( r = -0.7244), followed by P/T ( r = -0.6007). In the regions with MAP < 800 mm, soil pH was negatively correlated with MAP ( r = -0.4631) and P/T ( r = -0.7041), respectively, and positively correlated with MAT ( r = 0.6093) and P*T ( r = 0.3951), respectively. In the regions with MAP > 800 mm, soil pH was negatively correlated with MAP ( r = -0.6651), MAT ( r = -0.5047), P/T ( r = -0.3268), and P*T ( r = -0.5808), respectively. (c) The estimation model of soil pH was: y = 23.4572 - 6.3930 × lgMAP + 0.1312 × MAT. It has been verified to have a high accuracy ( r = 0.7743, p < 0.01). The mean error, the mean absolute error, and the root mean square error were 0.0450, 0.5300, and 0.7193, respectively. It provides a new path for rapid estimation of the regional soil pH, which is important for improving the management of agricultural production and slowing down soil degradation.

Improving soil structure is key to improving soil quality and nitrogen utilization efficiency (NUE) in global cropping systems. Soil sieving is a direct means of dividing soil activity into components with different practical functional significance. In order to have a more intuitive understanding of nutrient turnover and NUE under different soil particle sizes, we identified the key soil particle sizes that affect N cycling in cropping systems. An in-situ field experiment was conducted in Mollisol for three years using the 15 N isotope tracer technique to examine the effect of soil structure on maize growth, nutrient uptake, and 15 NUE. We artificially destructed the soil structure by sieving it into four particle size classes: (i) unsieved soil (CK), (ii) <0.5 mm size (A), (iii) 0.5-2 mm size (B), and (iv) 2-5 mm size (C). Then each year, the physical properties of the soil, 15 N loss and retention rate ( 15 NRR), the 15 NUE, 15 N absorption, and distribution, as well as maize growth and yield, were measured. The results showed that the 0.5-2 mm size (B) and 2-5 mm size (C) improved soil physical properties and increased the uptake of 15 N by maize (especially in the leaves and grains), thereby increasing maize yield. The B and C particle sizes had lower soil 15 NRR and higher alkaline hydrolysable N content than the other treatments in the depth. We concluded that the B sieving treatment is the key aggregate fraction to increasing maize 15 NUE and yield and minimizing the negative effects on soil N retention capacity. Furthermore, the B treatment is key to affecting crop nutrient absorption and utilization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

A three-year field experiment was conducted to analyze the effects of straw enrichment and deep incorporation on the humus composition and the structure of humic acid (HA) in black soil. The differences in the HA structure between different straw returning methods were detected by three-dimensional fluorescence spectroscopy and 13 C NMR technology. The purpose of this paper is to provide a theoretical basis and data support for improving the straw returning system. Four different treatments, including no straw applied (CK), straw mulching (SCR), straw deep ploughing (MBR), and straw enrichment and deep incorporation (SEDI: harvested the corn straw from four rows together with a finger-plate rake and then crushed and buried them in one row in the 20∼40 cm deep level in the subsoil with a wind-driven input cylindrical plough), were used in this study. Our results showed that compared to CK treatment, SEDI significantly increased the contents of organic carbon (SOC), soil humic acid carbon (HAC), fulvic acid carbon (FAC), and humin C content (HM-C) in the subsurface soil layer by 27.47%, 34.33%, 19.66%, and 31.49%, respectively. Among all the straw returning treatments, SEDI treatment had the most significant effect in increasing the contents of HEC, HAC, and FAC. Straw returning not only reduced the degree of condensation and oxidation of the HA structure but also increased the proportion of alkyl C and enhanced the hydrophobicity of the HA structure in subsurface soil. Moreover, SEDI treatment significantly increased the proportion of aliphatic C/aromatic C of the HA structure in subsurface soil and improved the aliphatic property of HA, which had a significant effect on the HA structure compared to other treatments., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2021 Shuang Zheng et al.)

The purpose of this study is to analyze the effects of different straw returning modes on the structure of humic acid (HA) in soil by fluorescence spectroscopy and infrared (IR) spectroscopy. Four different straw returning modes, including straw returning to topsoil (St), straw returning to subsoil (Ss), straw mixing with topsoil (Smt), and straw mixing with subsoil (Sms), were used in this study; the soil HA was analyzed after 12 months of corn straw returning by a combination of fluorescence spectroscopy and IR spectroscopy. Based on the results, it was established that IR spectroscopy can estimate the complication and oxidation degree of soil HA and also evaluate its aliphaticity and aromaticity. Monodimensional fluorescence spectroscopy could preliminarily determine the changes in the humification of HA through the fluorescence intensities. The intensity ratio of I 456 /I 380 calculated from synchronous-scan fluorescence spectra could be used to evaluate the humification degree of soil HA. The total luminescence spectra of HAs provided more information on the fluorophores in the structure, including the amount and peak position of lignin-like structures and phenol-like or naphthol-like structures. Among the four straw returning modes, Ss is the most beneficial for reducing the oxidation degree and increasing the aromatization and humification degree of subsoil HA. It is believed that fluorescence spectroscopy and IR spectroscopy are relatively simple and sensitive methods for analyzing soil HA., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2019 JinFeng Gao et al.)

Drived by the soil microorganisms, the decomposition and transformation of cellulose plays an important role in the formation of humic substances. The techniques of infrared spectrum combining with element analysis were adopted to compare the structural differences of humic-like substances (HLA, humic-like acid; Hu, humin) extracted from the microbial residues formed in the liquid shake-flask culture (70 days), in which the single fungi (Trichoderma viride, Penicillium and Aspergillus niger) and mixed strains participated. The results showed that: (1) The combination of two techniques could clarify the molecu- lar structure of HLA extracted from the microbial residues, however, it remained to be further discussed in terms of analyzing the structures of Hu; (2) Trichoderma viride was beneficial to the condensation of HLA extracted from its microbial residue, but Penicillium was more favorable to the degradation of HLA. (3) The oxidative degradation of HLA fractions extracted the microbial residues was implemented by Penicillium and mixed strains. Both of the mixed strains and Aspergillus niger were helpful to transfer the inorganic N compounds from the culture media into the organic N components of HLA and Hu extracted from the microbial residues, simultaneously increase their amino C contents and then provide the indispensable N source for the humification process.

Biogas slurry is not suitable for liquid fertilizer due to its high amounts of volatile materials being of complicated composition and peculiar smell. In order to remove volatiles from biogas slurry efficiently, the dynamic headspace and gas chromatography-mass spectrometry were used to clear the composition of volatiles. Nitrogen stripping and superfluous ozone were also used to remove volatiles from biogas slurry. The results showed that there were 21 kinds of volatile compounds in the biogas slurry, including sulfur compounds, organic amines, benzene, halogen generation of hydrocarbons and alkanes, some of which had strong peculiar smell. The volatile compounds in biogas slurry can be removed with the rate of 53.0% by nitrogen stripping and with rate of 81.7% by the oxidization and stripping of the superfluous ozone. On this basis, the removal rate of the volatile compounds reached 99.2% by chloroform and n-hexane extraction, and almost all of odor was eliminated. The contents of some dissolved organic compounds decreased obviously and however main plant nutrients had no significant change in the biogas slurry after being treated.

The effects of different microbial communities on the structural characteristics of humus from the black soil amended with wheat straw were studied by FTIR Spectroscopy. The results indicated that (1) The structure and amount of functional groups in the water soluble substances (WSS) was tremendously influenced by the tested microorganisms, of which the amino and aryl ether was degraded rapidly in the inoculation process, and in the meantime, the content of hydroxyl groups was significantly reduced. The bacteria was helpful to increasing the amount of aliphatic hydrocarbons, while the other inoculated treatments were contrary. At the end of culture, the phenols and polysaccharides were gradually consumed, but the content of carboxyl groups had an increasing trend. (2) In the aspect of reducing hydroxyl groups of fulvic acid (FA), the role of actinomycetes was the biggest. The fungi had the biggest effect in improving the net generation of FA content. In addition, the fungi was conducive to improve the contents of carboxyl groups and carbohydrates of FA fraction. Except the mixed strains, the other treatments were all beneficial to the degradation of polysaccharide in the FA fraction, whose rate was greater than the decomposition of lipids. (3) The bacteria, actinomycetes and fungi were all helpful to reducing the amount of aliphatic hydrocarbons of HA fraction except the mixed strains. The content of carboxyl was effectively increased by fungi, but the effect of bacteria was contrary. The tested microorganisms could consume and utilize the polysaccharides of HA fraction, which could transform the humic-like fractions from plant residues into the real humus of soil.

The changes in surface hydroxyl structures and their absorption peaks after the adsorption of Cu2+ on the hematite and bayerite were studied by FTIR spectroscopy under the different pH values and Cu2+ concentrations. The result indicated that: (1) with the increase of Cu2+ concentrations, the H-O-H and OH deformation vibration of the hematite participated in the adsorption and Cu2+ combined with the Fe-O structure strongly, then Fe-O-(Cu) had been formed on the hematite surface. (2) In acid conditions, H+ in the solution destroyed the O-H structure of hematite surface and the existence of NO3- prompted the production of a new peak (1 131 cm(-1)). With pH value increasing, the hydroxy structure of hematite surface changed gradually from stretching vibration to deformation vibration, then the structures of Fe-OH and Fe(3+) -O(2-) constantly changed. (3) The adsorption of Cu2+ on the bayerite happened in the high wave position. With the Cu2+ concentration increasing, the free OH bending vibration, the OH- stretching vibration and its H-O-H bending vibration were all involved in the adsorption, and at the same time, Al3+ of Al-O was gradually replaced by Cu2+, which enhanced the vibration intensity of the low waves position. (4) With the increase in pH, the Al-OH bending vibration and Al-O stretching vibration changed gradually, which indicated that AlOCu+ and AlOCuOH structure had been formed on the bayerite surface after the adsorption.

By using the CERES-Maize crop model and Century soil model in Decision Support System of Agrotechnology Transfer (DSSAT) model, this paper studied the effects of crop management parameters, fertilizer N application rate, soil initial N supply, and crop residue application on the maize growth, crop-soil N cycling, and soil organic C and N ecological balance in black soil (Mollisol) zone of Jilin Province, Northeast China. Taking 12,000-15,000 kg x hm(-2) as the target yield of maize, the optimum N application rate was 200-240 kg N x hm(-2). Under this fertilization, the aboveground part N uptake was 250-290 kg N x hm(-2), among which, 120-140 kg N x hm(-2) came from soil, and 130-150 kg N x hm(-2) came from fertilizer. Increasing the N application rate (250-420 kg N x hm(-2)) induced an obvious increase of soil residual N (63-183 kg x hm(-2)); delaying the N topdressing date also induced the increase of the residual N. When the crop residue application exceeded 6000 kg x hm(-2), the soil active organic C and N could maintain the supply/demand balance during maize growth season. To achieve the target maize yield and maintain the ecological balance of soil organic C and N in black soil zone of Jilin Province, the chemical N application rate would be controlled in the range of 200-240 kg N x hm(-2), topdressing N should be at proper date, and the application amount of crop residue would be up to 6000 kg x hm(-2).

Soil and plant samples were collected from the sunflower growing area in the west of Jilin province. A variety of ancillary methods were used to determine the soil element content. Then the rare earth elements geochemistry in soil was studied, and the correlation of REEs in this region with other elements and the quality of plant was investigated. The results show that, (1) REE content of the soil in Nong'an is relatively higher to those in Daan and Tongyu. Distribution pattern of rare earth elements in soil for the right tilt of the light rare earth enrichment patterns which is consistent with the national distribution pattern of rare earth elements; (2) REE contents in the three studying areas in the soil are different, and this primarily relates to the soil parent materials; (3) The REEs which positively correlate with soil available potassium are Se, Fe2O3, Ti, P, Mn, Cu, Zn, Cr, Mo, B, F. The protein content of sunflower seeds has a negative correlation with REE. With the exception of Lu, all REEs show a similar correlation.

Petroleum contamination in soil decreases with the increase in the distance of soil to the drilling well. Accordingly, an abandoned petroleum well which had been exploited for about twenty years in Songyuan city of Jilin Province, China, was selected to investigate the structural characteristics of soil humic acids (HAs) under different petroleum contamination levels. Surface (0-20 cm) soil samples were collected at 0.5, 1.5, 3.5, 5.5 and 7.5 m deep from well head, and the petroleum contents were respectively 153.3, 148.4, 129.2, 50.5 and 5.62 g x kg(-1). HAs were extracted with 0.1 mol x L(-) NaOH and 0.1 mol x L(-1) Na4 P2O7 and were characterized with elemental analysis, Fourier transformed infrared (FTIR) spectroscopy and solid-state 13C cross polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy. Results showed that the atomic C/H, O/C and (N+O) /C ratios of HAs increased from 0.74, 0.41 and 0.45 for 7.5 m to 0.80, 0.83 and 0.88 for 0.5 m, respectively. The relative intensity of the peaks assigned to aliphatic carbon (2 921, 2 851 and 1 454 cm(-1)) in the FTIR spectra gradually decreased with increasing contamination levels, while that of the peak assigned to aromatic C(1 600 cm(-1)) increased, and the calculated absorption intensity ratio of 2 921 to 1 600 cm(-1) (2 921/1 600) declined from 0.22 for 7.5 m to 0.11 for 0.5 m. The solid-state 13C NMR data suggested that the relative content of alkyl C(0-50 ppm ) decreased from 49.9% for 7.5m to 30.9% for 0.5 m, while that of O-alkyl C(50-110 ppm), aromatic C(110-160 ppm) and carboxyl C(160-190 ppm) increased respectively from 20.1%, 13.1% and 14.3% to 28.0%, 18.8% and 19.3%. These results showed substantial chemical, structural, and molecular differences among these HAs. The aliphaticity and hydrophobicity of HAs decreased while aromaticity and polarity increased with the increase in petroleum content. Namely, HAs tended to become aged in molecular structure. Therefore, it is imperative to renew and activate the aged HAs by adopting appropriate measures for the remediation of petroleum contaminated soil.

In high-temperature and aerobic condition, speciation of heavy metals were studied during composting process of chicken manure and maize straw. The results showed that total weight of composting material was reduced and content of heavy metals was increased during composting process. No significant changes were found in total amount of heavy metals during composting process. The speciation of heavy metals could be affected significantly by composting. Ni and Cd's percentages of Fe-Mn oxides fraction increased by 5.0%-8.7%. Cu and Cr's percentages of organic fraction were increased by 14.1%-19.1% and 22.0% -28.7%, respectively. Hg, Pb, As, Zn's percentages of residual fraction were increased by different extents. Hg, Pb, Cr, As, Cu, and Zn's percentages of stable fraction all increased. The increasing range of Cu was the highest, which was 10.9%. Composting could reduce the biological activity and toxicity of heavy metals. The inoculating complex microbial strains had no significant influence on the speciation of heavy metals in chicken manure.

An abandoned petroleum well which had been exploited for about twenty years in Songyuan city of Jilin Province, China, was selected to study the compositions and characteristics of soil humus using revised humus composition method and Simon-Kumada method. Soil samples were collected at 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5 and 10.5 m apart from the well head. Results show that the petroleum contents increase from 0.08 g/kg (10.5 m to the well head) to 153.3 g/kg (0.5 m to the well head). With the increase in petroleum content, the contents of soil organic carbon and water soluble organic carbon increase; for total soil humus, the contents of extractable humus (HE) and humic acid (HA) decrease whereas that of humin (HM) increase; the percentage of HA/HE (PQ 72.0%-8.05%) decrease and HM/HE ratio (31.4-76.7) increase; for different combined humus, the contents of loosely combined humus (HI) and stably combined humus (HII) have a decrease tendency while that of tightly combined humus (HIII) increase; the HI/HII ratio (0.19-0.39) shows an increase tendency, whereas HI/HIII ratio (0.032-0.003) and HII/HIII ratio (0.096-0.009) decrease; the PQs of HI (3.21%-1.42%) and HIII (58.1%-35.5%) also decrease, and the range of PQ change is less in HI than in HII; the color coefficient (deltalogk) of water soluble organic matter (WSOM) decreases, whereas no obvious change for HA. The above results indicate that petroleum hydrocarbon promotes the formation of HM but not HA. The decrease in HA is mainly due to the restraining effect of petroleum hydrocarbon on the formation of stably combined HA. Petroleum hydrocarbon leads molecular structure of WSOM more complex but no effect on molecular structure of HA.

The properties of organic matter in steppe chernozem, steppe wind-blown soil and cultivated wind-blown soil were studied by analyzing the status of organo-mineral complex and the combined status and composition of humus. The results showed that different types and utilization patterns of soil had very different effects on the properties of soil organic matter. The amounts of total organic carbon, biomass C, heavy fraction C, extractable humus (HE) and loosely-combined humus and the humification degree were higher in steppe chernozem than in wind-blown soil. Steppe soil had higher amounts of total organic carbon, biomass C, heavy fraction C, HE and different combined humus than sunflower wind-blown soil, but humification degree had no obvious difference.