Abstract:As the material basis of food security, fertilizer plays an important role in supporting grain yield, agricultural product quality and human nutrition and health. Stepping into the new era, under the great situation of the national social economy, especially the green transformation of industry and agriculture, fertilizer innovation is facing the great challenge of synergistic realization of multiple objectives including food security, resource efficiency, environmental friendliness, nutrition and health, green and low carbon. In order to solve this major problem, the concept and industrialization pathway of green intelligent fertilizer were put forward in this paper. Through systematically elaborating the interactive principle of soil, plant, microorganism, fertilizer and environment, this study put forward a new academic idea for creating green intelligent fertilizer that matches soil, crops and climate and environmental conditions, and proposed its theoretical framework, key scientific issues, research and development pathways and future breakthroughs of green intelligent fertilizer. This study can provide new insights and reference for the design and implementation of holistic solutions for the green development of the whole industrial chain of multi-disciplinary cross-innovation and integration of industry and agriculture, aiming at promoting the green transformation and upgrading of China's chemical fertilizer industry and ultimately supporting the green development of agriculture.

Abstract:Herbicides are important inputs in the agricultural chain of production required for the improved productivity of black soil granary. Nevertheless, the high-frequency and high-intensity application of herbicides in the black soil region in northeastern China might lead to their residual accumulation in soil. Thus, this affects the growth of after reap crops and becomes the bottleneck of crop rotation and planting structure adjustment. Therefore, research on the herbicide pollution process and key abatement technologies are of great scientific significance to ensure green sustainable development of agriculture in the black soil region. This paper systematically analyzed the research progress and development trend on herbicide pollution process and abatement technology in the black soil region. The scientific and technical problems existing in this research field was pointed out. Besides, we also put forward research ideas and key directions of herbicide pollution process and abatement technology in the black soil region in China, so as to promote the development of herbicide pollution and remediation theory and technology in the black soil region in China.

Abstract:Cropland is an important source of the potent greenhouse gas nitrous oxide(N₂O). The cultivated black soils located in Northeast China play a vital role in national grain production. It has been demonstrated that the growth rate of N₂O emissions from Chinese croplands is slowing down but still accelerating in the black soil area of Northeast China. Aiming at comprehensively assessing N₂O emissions and understanding the production mechanisms, in this study, we summarized and characterized the N₂O emission intensity, production processes and influencing factors from the black soils in Northeast China. The results showed that the average N₂O-N emissions from unfertilized and inorganic-fertilizer applied black soils were 0.56±0.29 and 1.49±1.09 kg·hm^–2, respectively. The inorganic fertilizer-N induced N₂O emission factor(EF)was 0.45%±0.42% on average across the black soils in Northeast China. Both the background emissions and the EF values were generally lower compared with those of other uplands in China and black soils in other countries. This was likely due to the limitation of denitrification by labile carbon under normal rainfall conditions, and thus the N₂O emissions were predominately derived from nitrification. It was found that the freeze-thaw cycles could greatly promote denitrification and result in large pulses of N₂O fluxes during spring thaw, which might dominate the annual emissions. Compared with croplands in other regions of China, studies on the N₂O emissions from black soils in Northeast China are largely limited. In future research, the in-situ observations of N₂O emissions from black soils in different regions of Northeast China should be strengthened, and the mechanisms involved in freeze-thaw induced N₂O emissions should be clarified. This will facilitate the evaluation of the response of N₂O emissions from black soils to global climate change. Also, there is a need to strengthen researches on the effects of crop residue returning, manure application, etc. on N₂O emissions, to facilitate the development of win-win strategies for enhancing soil quality and simultaneously reduce N₂O emissions from black soils.

Abstract:Compared with the constant charge soils that distribute in temperate regions, the variable charge soils in tropical and subtropical zones are unique soils, with highly variable particle surface charges. Investigations on the surface chemical characteristics of variable charge soils have received considerable attentions. The potentiometric acid-base titration method is the most straightforward approach to qualitatively and quantitatively identify the surface chemical characteristics of variable charge soils. In this paper, the characteristics of variable charge soils are briefly described and the concept and difference of point of zero charge (PZC) is described and classified according to (i) the conditions for surface charge measurement, (ii) the modes of expression for PZC, and (iii) measurement methods for surface charge of soil colloidal particles. On this basis, the influence of the acid-base potentiometric titration setup conditions on the observed PZC, including co-existing ions, ionic strength of the solution, pre-equilibrium time, titration ranges, reaction atmosphere and titration method, is summarized and discussed. Furthermore, the research progresses on the application of potentiometric titration combined with surface complexation model (SCM, including diffuse layer model, basic stern model, triple layer model and distribution multi-site complexity and so on) to analyze the acid-base buffering capacity of variable charge soils were further summarized. Moreover, how related factors such as clay mineral composition, metal oxides, organic matter and other factors, affect the acid-base buffering capacity of variable charge soils are discussed. We believe that future studies on the variable charge soils could be carried out with the hope to:(1) establish a typical acid-base potentiometric titration method for all types of soils; and (2) verify if the combination of various surface complexation models could accurately quantify the acid-base buffer capacity of variable charge soils. It is hoped that this review can help soil science beginners to understand the basic concepts of variable charge soils, invite more researchers to pay more attentions to variable charge soils, and further encourage sustainable utilization of soil resources.

Abstract:Intensive vegetable production system with a high amount of phosphate fertilizer will cause phosphorus (P) resources waste and environmental risks caused by high accumulation of P in the soil. One of the effective methods to reduce P input and increase P use efficiency in vegetable fields is rhizosphere regulation, which could also improve P absorption and utilization by vegetables. This paper summarizes the major modules of rhizosphere communication, including plant-plant communication (vegetables intercropping root interactions), plant-microorganism communication (vegetable root and mycorrhizal fungi and rhizosphere bacteria interactions) and microorganism-microorganism communication (P solubilizing microorganism with rhizosphere microorganisms in vegetable fields) in promoting vegetable root development. Importantly, we discussed the mechanism (s) for activating soil accumulated P to increase the absorption and utilization of P by vegetables and its mechanism. In addition, different artificial regulation modules, such as increase P absorption and utilization of vegetables by applying P microbial fertilizer, and relieving the obstacles of continuous cropping of vegetables are discussed. Finally, the paper evaluated the direction of the rhizosphere communication in high-input systems to provided a theoretical basis for promoting the green and sustainable development of P fertilizer management in high-input vegetable planting systems.

Abstract:[Objective] Black soil of Northeast China suffered serious degradation due to intensive farming in the past decades. To protect Black soil, conservation tillage is encouraged to be applied in this region. However, some studies have reported that this practice may reduce crop yield. Thus, our objective is to evaluate the suitability of conservation tillage and deep tillage in Black soil of Northeast China.[Method] We collected 543 yield comparisons from 61 papers published in international and domestic journals. After synthesis and grouping of required data, we analyzed the impacts of conservation tillage and deep tillage on crop yield and their influencing factors using meta-analysis as well as random-forest methods.[Result] Overall, crop yields were slightly increased under conservation tillage(+1.21%), but significantly enhanced under deep tillage(+12.3%) as compared with traditional rotary tillage. Conservation tillage caused a higher yield only at Liao River Plain(14.6%), whereas deep tillage increased yield by 10% across three plains including Sanjiang, Songnen and Liao River. Under conservation tillage, the yield effect size was most influenced by the mean annual temperature(20% contribution), mean accumulated temperature >10℃(19% contribution) and aridity index(16% contribution). For deep tillage, the most important factor was the topographic slope(14% contribution). Also, conservation tillage increased soil organic C mainly in the top layer and when combined with straw mulching reduced soil temperature remarkably and increased soil moisture. This observation was the main reason for yield reduction under this practice. Deep tillage reduced soil bulk density and penetration resistance significantly, leading to an increase in crop yield. After synthesizing the yield effect size and factor contribution, our results indicated that wind erosion sensitive regions such as western Liaoning and Jilin provinces as well as eastern Inner Mongolia are highly suitable for conservation tillage. On the other hand, the cold, humid, low-lying areas are more suitable for deep tillage, e.g., Sanjiang Plain and the typical Black soil belt.[Conclusion] This study evaluated the suitability of tillage practices in the Black soil of Northeast China based on the effect size of tillage on crop yield. The synthesized results suggest that conservation tillage is more suitable for dry and wind erosion sensitive regions or slopping lands where it can increase crop yield and protect soils as well.

Abstract:[Objective] Black land is a valuable land resource, which plays an important role in ensuring food security in the northeast region of China. In order to slow down the erosion and degradation of black soil farmland and improve farmland fertility, new soil management practices need to be developed.[Method] In this study, woody peat and bentonite were added to a typical eroded and degraded black land. The saturated hydraulic conductivity, air permeability and relative gas diffusion, water holding capacity, organic carbon content and crop yield were evaluated by the combination of indoor simulation and field in-situ observation.[Result] The results showed that:under indoor conditions, (1) adding 2% or 4% woody peat decreased the saturated hydraulic conductivity by 14.3% or increased it by 9.9%, increased the air permeability by 18.9% or 4.1%, increased the relative gas diffusion by 15.5% or 6.6%, increased the organic carbon content by 39.4% or 71.5%, and increased the yield of potted maize by 2.0 times or 1.9 times respectively; (2) adding 1% bentonite decreased the saturated hydraulic conductivity, air permeability and relative gas diffusion by 63.2%, 55.3% and 7.6%, and increased the organic carbon content and yield of potted maize by 1.0% and 1.1 times, respectively; (3) adding 2% or 4% woody peat and 1% bentonite decreased the saturated hydraulic conductivity by 65.8% or 73.1%, decreased the air permeability by 33.2% or 32.8%, increased the relative gas diffusion by 0.2% or 4.7%, increased the organic carbon content by 37.8% or 70.6%, and increased the yield of potted maize by 1.9 times or 1.5 times. The saturated hydraulic conductivity, relative gas diffusion, organic carbon content and soybean yield increased by 75.0%, 32.0%, 36.1% and 43.2% respectively, and the air permeability decreased by 45.2% when woody peat was added to the eroded farmland. Also, the saturated hydraulic conductivity, air permeability and relative gas diffusion decreased by 39.1%, 44.4% and 44.0% respectively, while the organic carbon content and soybean yield increased by 3.6% and 4.2%, respectively, when bentonite was added to the eroded farmland. Even though there was no significant difference in organic carbon content and soybean yield; the soil saturated hydraulic conductivity, relative gas diffusion, organic carbon content and soybean yield increased by 134.4%, 28.0%, 36.0% and 26.3% respectively, and the air permeability decreased by 38.2% when woody peat and bentonite was added to the eroded farmland. The addition of woody peat and bentonite could improve the water holding capacity of black land soils, and bentonite can retard the decomposition of organic carbon.[Conclusion] In general, the mixed addition of woody peat and bentonite has the best effect, which can effectively improve the soil aeration permeability, water holding capacity, organic carbon content and crop yield, and also help to accumulate organic carbon in the soil. It is an effective measure to rapidly improve the degraded black soil.

Abstract:[Objective] Understanding the behaviours of solute transport in soils is of great importance to agricultural management, resource utilitzation and environmental protection. Introducing boundary-layer theory to solve solute transport problems provides a simple and accurate alternative method to predict solute profile distribution and estimate transport parameters. Appropriate selection of boundary layer solutions requires an overall understanding of the characteristics of boundary layer solution accuracy under different conditions.[Method] This study compared the accuracy of the polynomial solution, exponential solution, combined solution, logarithmic solution and small flux solution based on multiple parameter combinations. Solute front movement with time in soil column experiments was further used to evaluate the performance of boundary layer solutions for parameter estimation.[Result] The accuracy of boundary layer solutions for predicting solute concentration profile increased first and then decreased with time. Comparison of different boundary layer solutions indicated that the cubic polynomial solution was optimal at the beginning while the exponential solution turned to be better afterwards for most cases. Importantly, the boundary layer methods performed better in estimating retardation factor than dispersion coefficient. The retardation factor obtained from boundary layer solutions was almost the same but with an exception of the small flux solution. The dispersion coefficient was greater than the breakthrough curve fitting method and varied between boundary layer solutions. The cubic polynomial and logarithmic solutions had a minimum error in the determination of the dispersion coefficient.[Conclusion] Boundary layer solutions can be used to accurately predict solute profile distribution for the early stage of solute transport processes. Cubic and exponential solutions had better performance than other solutions. Neverthless, cubic and logarithmic solutions can be the first choice for estimating parameters.

Abstract:[Objective] Iron oxides are sensitive to the pedogenic environment and an important cement of soil aggregates. The differentiation of iron oxide phases occurs at multiple scales in natural systems, which may affect the formation and stability of soil aggregates. This study aimed to explore the differentiation of iron phases, including total iron (Fe_t), free Fe-oxide (Fe_d), amorphous Fe-oxide (Fe_o), hematite (Hm), and goethite (Gt) at the hillslope, profile and aggregate scales and evaluate their effects on the stability of soil aggregates.[Method] A topo-sequence of Ferrisol, derived from granite in the hilly area of central Fujian Province, was fractionated into aggregates using wet-sieving and pipette methods. Fe_d and Fe_o in bulk soils and different aggregates were extracted with the citrate-bicarbonate-dithionite (CBD) solution and the acid ammonium oxalate (AAO) solution, respectively. Diffuse reflectance spectroscopy (DRS) was applied to determine Hm and Gt content. The percentage of water-stable aggregate (WSA) and the mean weight diameter (MWD) were evaluated.[Result] At the hillslope scale, the Fe_d and Fe_d/Fe_t in bulk soils decreased, while the Fe_o and Fe_o/Fe_d increased downslope. Meanwhile, the Hm and Hm/(Hm+Gt) significantly declined, while the Gt kept a little variation downslope. At the profile scale, the upper layers generally possessed higher contents of Fe_d and Gt, as well as lower levels of Fe_o and Hm in contrast to the deeper layers. At the aggregate scale, Fe_d, Fe_o and Gt were enriched in micro-aggregates. The contents of Hm were comparable in the micro- and macro-aggregates, while Hm/(Hm+Gt) increased with the aggregate size. Micro-aggregates were the main components, but the >0.25 mm macro-aggregates dominated the aggregate stability along the hillslope. The WSA of 0.5~0.25 mm and 1~0.5 mm aggregates were significantly positively correlated with Fe_o and Fe_o/Fe_d respectively, and the WSA of 2~1 mm macro-aggregate was significantly positively correlated with the Hm and Hm/(Hm+Gt).[Conclusion] The iron oxides demonstrated significant differentiation from hillslope scale to aggregate scale. The soil aggregate stability in the top-slope and bottom-slope profiles were higher than those in the transitional profiles due to the upslope enrichment of Hm and downslope enrichment of Fe_o along the hillslope.

Abstract:[Objective] In order to explore magnetic characteristics of the yellow-red soil in the subtropical region and transformation of the magnetic minerals in the soil under relatively humid and cold climate conditions, the author selected a profile of yellow-red soil (Profile ZN) derived from granite weathering crust in Zhouning County, northeast of Fujian Province. Under a mid-subtropical monsoon mountain climate, this area had an average annual temperature of 15℃, an average annual rainfall of 2 049.3 mm, and an elevation of 906.4 m counted from the bottom of the profile. The profile was about 1.9 m thick. With the floating soil on the surface removed, a total of 20 samples were collected at 10 cm intervals from the soil and weathering crust layers of the profile.[Method] In this study, room temperature magnetic parameters of the samples were measured, and thermomagnetic analysis conducted of representative samples, in combination of chroma, major geochemical elements and diffuse reflectance spectrum analyses.[Result] Results show:The profile was low in magnetic susceptibility, and relatively low in content of magnetic minerals, the upper part of the profile contained relatively more superparamagnetic particles, while the lower part did relatively more multi-domain particles. a^*, b^* and Ca^*b^* varied in the same trend, being the highest in Horizon B and the lowest in Horizon C, while b^*/a^* was high in the profile surface. The content of Fe₂O₃ increased with the degree of pedogenesis, indicating that during the soil forming process, other elements were leached while iron accumulated relatively. Iron content was not a major factor limiting magnitude of magnetic susceptibility. The profile was lower than those in the humid and hot low altitude tropical and subtropical regions in CIA (chemical index of alteration).[Conclusion] By comparing this profile with the three (NPN, PC-GL, PC-SY) in the adjacent area, the following conclusions were drawn:(1) Profile ZN contains relatively less magnetic minerals, which are composed of mainly ferrimagnetic mineral and small portions of maghemite, antiferromagnetic minerals hematite and goethite as well as paramagnetic minerals. Moreover, its content of goethite is higher than that of hematite. The magnetic particles in the lower part of the profile are coarser, and mainly multi-domain particles. And the particles get finer, and the portions of single-domain and superparamagnetic particles increase with decreasing soil depth. (2) Parent material and climatic conditions are two important factors contributing to the difference in magnetic characteristics between different profiles, and the climate conditions are the main ones controlling the content of secondary magnetic minerals (especially hematite and goethite). Chroma index b^*/a^* can be used to measure the content of goethite/hematite. (3) Under a relatively humid and cold climate the transformation of magnetic minerals in the soil is dominated by the transformation of strong magnetic minerals (magnetite and maghemite) into weak magnetic minerals (hematite and goethite). (4) Temperature, instead of precipitation, is the dominant factor influencing the content and relative proportion of goethite and hematite in the soil derived from granite weathering crust in humid subtropical regions.

Abstract:[Objective] Characterizing spatial and temporal variability of soil salinity at field and landscape scales is important for a variety of agronomic and environmental concerns. In arid regios, soil salt content and its distribution position in the profile are important factors for the calculation of the irrigation quota of salinized soil. Due to the strong spatial variability of soil salinity content, the guiding value of soil surface salinization information for quota irrigation is very limited. A three-dimensional visualization study of the distribution and content of salinity in the soil profile is of great significance to the fixed irrigation of saline soil. The objective of this study was to evaluate apparent electrical conductivity (ECa) directed soil sampling as a basis for monitoring management-induced Spatio-temporal change in soil salinity.[Method] A soil salinity assessment study was conducted on an 18 hm² saline-sodic field in Alar's Agricultural Science and Technology Park from March to November 2018. The study evaluated the three-dimensional spatio-temporal change that had occurred as a result of irrigation with drainage water over that period. Using geospatial electromagnetic induction (EMI) measurements of ECa and a spatial response surface sampling design 18 soil profile sites were selected and they reflected the ECa measurements every time. At each site soil profile samples were taken at 0.2 m intervals to a depth of 1 m and analyzed for electrical conductivity of the saturation extract (ECe). Also, the soil apparent conductivity data of four different periods and the electrical conductivity data of soil profile samples collected synchronously were analyzed. The inversion model between measured and apparent conductivity of different soil layers in the soil profile was constructed by the multiple linear regression method. Furthermore, the 3D visualization of soil salinity was realized by using 3D-IDW and the spatial and temporal changes of soil salinity in cotton field under mulch drip irrigation of Xinjiang were studied.[Result] The results showed that there was a good correlation between the apparent conductivity and the measured conductivity. The determination coefficient (R²) of the measured conductivity inversion model based on the apparent conductivity data was between 0.82 and 0.99. The results of 3D-dimensional data statistics of soil electrical conductivity showed that the distribution characteristics and content of soil salinity in different periods are quite different. These differences were attributed to human factors such as irrigation, film mulching and uncovering, and natural factors such as air temperature, evaporation and groundwater level. Also, the distribution type of soil salinity in March was uniform and the electrical conductivity range of the 0-100cm soil profile was 0.78 to 0.88 dS·m^–1. The salinity in June and October was mainly concentrated in 0~20 cm and the electrical conductivity was 3.32 to 5.28 dS·m^–1, respectively. Also, the electrical conductivity of 20~100 cm was 0.99~1.36 to 0.95~1.70 dS·m^–1, respectively. In July, the salinity was mainly concentrated in 0~40 cm, and the conductivity in 0-40cm was 2.25~2.45 dS·m^–1while the conductivity of 40~100 cm was 0.87~0.93 dS·m^–1.[Conclusion] An assessment of three- dimensional spatio–temporal changes in soil salinity was conducted to provide a preliminary evaluation of the sustainability of irrigation quota on the Agricultural Science and Technology Park to ascertain its potential as an alternative for drainage water disposal. The results of this study can be used as guidance for accurate irrigation application in cotton fields.

Abstract:[Objective] The problems of high salinity, low nutrient and poor soil structure in the coastal saline-alkali area of Shandong province seriously affect the development of agricultural production. Therefore, the effective development and utilization of the soils in this region are of great importance to its agricultural production and income.[Method] In this study, the four land-use types (wasteland, grassland, cultivated land and forest land) in Kenli County of Dongying City were taken as the research objects, and the effects of different land-use types on the basic physical and chemical properties and aggregate stability of coastal saline-alkali soils were evaluated.[Result] The results showed that (i) the electrical conductivity (EC) and water-soluble K⁺ and Na⁺ contents in wasteland > cultivated land > grassland > forest land, with EC and Na⁺ content of wasteland being significantly higher than those from other sampling plots; (ii) the total nitrogen (N) and total organic carbon content (SOC) of the soils in forest land > grassland > cultivated land > wasteland, with SOC in the 0.25~2 mm water-stable aggregates being the highest; (iii) the mechanical stability mean weight diameter (MWD) and the mechanical stability aggregate content of > 0.25 mm particle diameter (R_0.25) were significantly lower in forest land than those of other sampling plots; (iv) the water stability mean weight diameter (WMWD) and the water stability aggregate content of > 0.25 mm particle size (WR_0.25) in wasteland were significantly lower than those in other sampling plots; and (v) the percentage of aggregate destruction (PAD) in wasteland > cultivated land > grassland > forest land. Additionally, results of the surface and internal scanning electron microscopy (SEM) of the 2 mm water-stable aggregates in grassland, cultivated land and forest land showed relatively obvious particles, pores, and adhesive materials. Furthermore, the Pearson correlation analysis showed that mechanical composition was significantly correlated with MWD and R_0.25 while PAD was significantly correlated with soil water soluble Na⁺ content and SOC of 0.25~2 mm water-stable aggregate soil.[Conclusion] Different land-use types have different effects on soil physical, chemical, and mechanical properties. The grassland and forest land use types have significant ameliorating effects on the physical and chemical properties of coastal saline soil while forest land use has higher carbon reserves and aggregate water stability, but lower mechanical stability. The results of this study can provide references for the rational planning and sustainable development of land use in the coastal saline-alkali area.

Abstract:[Objective] Grasslands in Songnen plain are propitious to the develop the mechanized-graziery due to its flat terrain and the climatic conditions, which influences by temperate continental monsoon climate. Moreover, influenced by the high plant coverage and diversity, black soil was developed, and the high quality forage species was dominated by Leymus chinensis in the past decades. However, the fragile eco-environment of Songnen grasslands could be impacted by the special topography, high salinity and shallow groundwater, and the parent material. Soil parameters are typically used to quantify the relationship between soil properties and forage yield and to identify the limiting factors of grassland productivity. Because of overgrazing and overdevelopment, the Songnen grasslands were degraded and salinized significantly. The husbandry was remarkable hindered by the low grassland productivity. The objectives of this study were:1) to investigate the spatial variation characteristics of soil physical and chemical properties; 2) to estimate the spatial variation characteristics of vegetation community; 3) to explore the potential linkages between dry yield of alfalfa and soil physical and chemical properties.[Method] The artificial grassland locates at the Xinfawopeng village of Baicheng City, which covers an area of 600 m×450 m. The soil sample points were set by grid method, with the spacing of each neighbor sample points was 50 m. The soil samples were collected from alfalfa artificial grassland from by cutting rings and soil auger in October 2017 and May 2018 for detecting the soil physico-chemical properties, meanwhile, the forage samples were collected in a quadrat of 1 m² (1 m×1 m). All the soil samples were air-dried, ground and then passed through a 2-mm sieve for chemical properties. The 1:5 of soil-water extracts were used to determining soil pH, EC, Na⁺, Ca²⁺, Mg²⁺, HCO₃^–, and CO₃^2–. The spatial variations of soil properties, including soil mass water content (MWC), soil pH, EC, and total alkalinity (TA) were determined by classical statistics and geostatistics. Furthermore, the spatial variations of biological characteristics of artificial grassland, such as the Shannon-Wiener Index (SWI), dry yield (DY), shoot height (SH), and cover degree (CD) in the study area, were analyzed with classical statistics and geostatistics.[Result] At the depth of 0~30 cm, very high spatial variability of the EC and TA were found, however, the pH and MWC showed moderate spatial variations; The biological properties of the grassland community showed high spatial variations. Results of multiple linear regression (MLR-step wise) suggested that the alfalfa dry biomass (DM) could be predicted by (DM)=2699.73–276.496 pH (7.17< pH <9.76), which indicated that the soil pH influenced the alfalfa yield more than other soil properties.[Conclusion] The above results indicated that the soil physico-chemical properties of artificial grasslands in western Songnen pain were high and moderate spatial variations, and the alfalfa could not tolerance the pH higher than 9.76.

Abstract:[Objective] Farmland pollution affects national food safety and public health. From the perspective of soil pollution, clarifying the scale and spatial layout of fallow land at the national scale is of great importance. To restore heavy metal-contaminated farmland soils and ensure green development of agriculture, an urgent scientific solution is needed for soil pollution. In recent years, fallow has been pioneered as a means of recuperation and management of polluted farmland. However, some important management issues such as how much farmland should be fallowed, location of the fallow area, and how to fallow are yet to be defined at the national scale.[Method] In this study, we constructed a database of heavy metal pollution in Chinese farmland soils which comprised of 6 490 sample data from 2 343 farmland locations. These data were extracted from 569 published papers on the topic of farmland heavy metal pollution (Including combined pollution and single heavy metal pollution, such as Ni, Hg, As, etc.), published from 2000 to 2018 on Web of Science and China National Knowledge Infrastructure (CNKI). We assessed heavy metal pollution, the influence index of soil comprehensive quality, and the potential ecological risk to identify the spatial distribution of fallow priority grades, including urgent-fallow zone (I), regular-fallow zone (II), controlled-rotation zone (III), and general-rotation zone (IV).[Result] The results showed that the excessive concentration rates of heavy metals was Cd (18.03%)>As (2.95%)>Ni (2.26%)>Hg (1.55%)>Zn (1.42%)>Pb (1.34%)>Cu (0.49%)>Cr (0.10%). The proportions of soil environmental quality index such as severely, moderately and slightly exceeded were 1.71%, 3.89% and 23.84%, respectively. Also, the ratio of extremely strong and very strong potential ecological risk accounted for 0.29% and 2.89%. The ratio of the fallow area in China due to soil heavy metal pollution is 15.58%, of which the proportions of level I, II and III are 0.77%, 1.53% and 3.26%, respectively. Level I fallow areas are mainly distributed in 8 provinces of China including Henan, Hunan, Yunnan, Anhui etc. Additionally, fallow areas are mainly distributed in Henan and Hunan province, followed by Liaoning and Shandong province.[Conclusion] To promote the remediation of heavy metal pollution in Chinese surface soils, the implementation of differentiated fallow strategies for farmland areas with different pollution levels is recommended. This study shows the status of heavy metal pollution in farmland soils and spatially identified the urgency of fallowing areas in China. It also provides theoretical support for controlling farmland soil pollution and fallow space-time allocation in China.

Abstract:[Objective] Desorption of antibiotics in soils in the presence of microplastics is key to its migration, transformation, and bioavailability. The objective of this study was to reveal the desorption characteristics of sulfamethoxazole in an artificial antibiotic contaminated soil in the presence of five different microplastics.[Method] Batch equilibrium desorption experiments were carried out using an acid paddy soil that was spiked with 33.4 mg·kg^–1 sulfamethoxazole and was aged for 5 days before use. Five polymeric microplastics including polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET) (1.67% and 3.33%). The microplastics were added to the soil individually and a soil:solution ratio of 1:10 was maintained in the experiment. The supernate was sampled for the sulfamethoxazole analysis using high-performance liquid chromatography (HPLC) from 0.25 to 96 h during the desorption kinetic experiment. Also, different concentration of NaCl and fulvic acid were added into the soil-microplastics mixture system to study the effect of salinity and dissolved organic matter (DOC) on sulfamethoxazole desorption, respectively.[Result] The results indicated that the desorption rate of sulfamethoxazole declined significantly and a slow desorption phase was observed from 10 h to 48 h after the addition of polyethylene and polystyrene microplastics. The equilibrium desorbed concentration of sulfamethoxazole declined significantly (P < 0.05) in the presence of polyethylene and polyvinyl chloride microplastics. The influence of sodium and calcium ions on sulfamethoxazole desorption from the soil was not affected by the addition of microplastics. However, the influence of fulvic acid on sulfamethoxazole desorption was mitigated after the addition of microplastics in general. Importantly, with an elevated concentration of fulvic acid, the decline of sulfamethoxazole desorption was negligible.[Conclusion] Generally, the desorption of sulfamethoxazole from soils was altered in the presence of microplastics. In soils with a relatively high concentration of DOC, elevated sulfamethoxazole desorption was observed. Therefore, this study highlights the migration and bioavailability of sulfamethoxazole in soils contaminated with microplastics and how different solvents influenced its desorption.

Abstract:[Objective] Increases in atmospheric CO₂ concentration have certain direct or indirect impacts on CH₄ emission from rice paddy fields. So it is of great significance to have an in-depth study on impacts of long-term elevated atmospheric CO₂ concentration on CH₄ emission and related microorganisms for assessing and managing CH₄ emissions from rice paddy fields in the context of future climate.[Method] To investigate effects of long-term elevated atmospheric CO₂ concentration on CH₄ emission and its mechanism, CH₄ emission fluxes and abundance of the methanogens and methanotrophs under ambient CO₂ (ACO₂) and elevated CO₂ conditions (ECO₂) in rice paddy fields were monitored during the 2016-2017 season, with the aid of the Chinese rice FACE platform that has been operating for more than 10 years. Moreover, meta-analysis was conducted to determine quantitatively effects of elevated CO₂ relative to duration on CH₄ emission from and the abundances of methanogens and methanotrophs in rice paddy fields.[Result] Results show that compared with ACO₂, long-term ECO₂ significantly reduced CH₄ emission and the abundance of methanogens by 28% and 39%, respectively (P<0.05), but increased the abundance of methanotrophs by 21% (P>0.05). Meta-analysis shows that with the increase in duration of CO₂ elevation, the effect of elevated atmospheric CO₂ concentration promoting CH₄ emission and the abundance of methanogens gradually decreased, while the effect on the abundance of methanotrophs gradually increased.[Conclusion] Therefore, it could be concluded that under future climate conditions, long-term elevated CO₂ will reduce CH₄ emission from rice fields, which is of great significance for mitigating the greenhouse effect brought about by rice cultivation.

Abstract:[Objective] Ammonia volatilization from solar greenhouses driven by excessive nitrogen input has received widespread attention in recent years. However, the ammonia volatilization emission of greenhouse system is mainly determined by soil surface ammonia volatilization. Greenhouses are semi-closed structures, as a result, a part of NH₃ emitted from soil can be absorbed again by the plant canopy or dissolved in the greenhouse membrane water and returned to the soil. The volatilization of ammonia from soil surface can not accurately reflect the amount of ammonia discharged into the atmosphere by solar greenhouse. Therefore, ammonia volatilization from soil surface is difficult to accurately reflect the amount of ammonia emitted into the atmosphere by solar greenhouse.[Method] Experiment comprised four treatments:(i) no nitrogen input with conventional irrigation (N0+FI), (ii) conventional nitrogen input with conventional irrigation (FT+FI), (iii) optimum nitrogen input with conventional irrigation (OPT+FI), and (iv) optimum nitrogen input with optimum irrigation (OPT+OI). Ammonia volatilization losses were measured in three vegetables seasons (tomato-watermelon-tomato) using intermittent closed chamber ventilation method. The air volume mask (Kanomax 6570) was used to measure the gas flow at the vent, and the ammonia concentration at the vent was continuously monitored by pumping method. In this way, the loss rate and amount of ammonia volatilization were measured from the whole greenhouse, and losses were compared with the soil surface.[Result] The results showed that the ammonia volatilization rate peaked on the same day after greenhouse fertilization, and there was no significant difference between fertilized and unfertilized (control) after 7 days. During the three planting seasons, the ammonia volatilization under different nitrogen treatments were:2.82-4.97 kg·hm^–2, 6.59-9.97 kg·hm^–2and 15.77-21.83·kg hm^–2, respectively, and the corresponding ammonia volatilization emission factors were 0.64%-1.50%, 3.11%-4.21% and 2.59%-3.90%, respectively. The trend of ammonia volatilization rate of the whole shed was basically consistent with that of the soil surface. The ammonia volatilization rate of the whole shed was N 2.22 kg·hm^–2 in the second quarter and N 2.92 kg·hm^–2 in the third quarter, which accounted for 13.38%-33.69% of the ammonia volatilization from the soil surface, and the ammonia volatilization coefficient was only 0.46%-1.48%, which was much lower than the ammonia volatilization from the soil surface.[Conclusion] Thus, it is concluded that the ammonia volatilization from solar greenhouse will be overestimated when only taking the soil surface ammonia volatilization into consideration. Measuring ammonia volatilization based on the whole solar greenhouse system is thus recommended in future studies.

Abstract:[Objective] Citrus production is one of the main income of farmers in the Three Gorges Reservoir area. The loss of nitrogen and phosphorus caused by excessive fertilizer in the Three Gorges Reservoir area present negative impacts on the aquatic environment.[Methods] In this study, sandy soil citrus orchard with natural grass mulching was chosen. The amount of nitrogen and phosphorus loss from surface runoff and leaching was observed for two consecutive years by plot experiment at six levels of fertilization. The pathways of nitrogen and phosphorus losses in the citrus orchard and the effects of different fertilization levels on nitrogen and phosphorus losses were investigated. Seven treatments were set in the experimental plot, with an average row and plant spacing of 4.7 m × 3.4 m; with no fertilizer application (T1) as the control, the application rates of nitrogen, phosphorus and potassium fertilizer for the T3, T4, T5, T6 and T7 treatments were 1.67, 2.33, 3.00, 3.67 and 4.33 times those of T2, respectively. During the growth season of navel orange in 2016—2017, rainfall and atmospheric deposition of nitrogen and phosphorus were monitored. Surface runoff water, sediment, and infiltration water were sampled for total nitrogen (TN) and total phosphorus (TP) content.[Results] Under the ecological protection mode of grass mulching, the surface runoff and soil erosion were effectively controlled. The main pathway of water loss in the rain-fed citrus orchard was leaching with a low coefficient of surface runoff and weak soil erosion. During the study period, the rainfall loss by seepage accounted for 48.9% of the rainfall, and the surface runoff only accounted for 1.73% of the rainfall. The amount of fertilization applied in deep furrow had no effect on the amount of nitrogen and phosphorus loss from the surface runoff. Leaching was the main pathway of nitrogen and phosphorus loss. The average leaching loss of total nitrogen and total phosphorus accounted for 99.0% and 76.9% of the total loss of nitrogen and total phosphorus respectively. Also, the amount of nitrogen loss (y) by seepage increased with the increase of application rates (x), and there was a significant linear correlation between them (y =0.35x–5.77, P<0.01). However, no significant correlation existed between the amount of phosphorus loss and application rates (P =0.05). Also, only a small amount of phosphorus can be leached to the bottom of the soil after the roots uptake and soil particles adsorption in up layers. Moreover, the residual phosphorus in the deep soil; after deep plough before citrus planting, had an impact on the leakage of phosphorus.[Conclusion] The problem of nutrient loss; leaching nitrogen loss in citrus orchards, in particular, should be given more attention. To reduce nutrient loss and achieve efficient utilization, nutrient management should be further optimized.

Abstract:[Objective] Priming effect (PE) plays a critical role in the storage and turnover of soil organic carbon (SOC) in forest ecosystems. The intensity and direction of the priming effect, induced by litters, usually depend on the availability of limited nutrient (e.g., phosphorus, P), especially in subtropical highly weathered forest soils. However, how P and litters addition affect the soil priming effect in this region is not clear. This study aimed to investigate the effects of litter and phosphorus addition on SOC mineralization and priming effects in subtropical low-phosphorus soils and to provide a theoretical basis for the study of the carbon cycle in forest ecosystems in this region.[Method] Three kinds of ¹³C-labeled litters (Pinus massoniana, Michelia macclurei and Liquidambar formosana) and P (KH₂PO₄) were added to P. massoniana forest soil. The incubation of treated and control soils was conducted for 35 days in the laboratory. The physical and chemical properties, microbial properties and priming effect of the soils were determined after incubation.[Result] The results showed that the addition of the three kinds of litters significantly increased the soil native SOC mineralization, and produced a positive priming effect. The intensity of priming effect performance for P. massoniana > M. macclurei > L. formosana. In addition, litters addition decreased the content of soil inorganic nitrogen (nitrate and ammonium nitrogen, IN), but increased microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and β-glucosidase (βG) and acid phosphatase (ACP) activities. P addition alone significantly enhanced SOC mineralization, and the available phosphorus (AP), dissolved organic carbon (DOC), microbial biomass carbon (MBC), MBN, and MBP were also increased. Compared with the addition of litters alone treatment, the M. macclurei and L. formosana litters combined with P addition significantly reduced the priming effect and ACP activity. Linear regression analysis revealed that the cumulative priming effect was correlated negatively with soil AP, MBN and MBP content, whereas it was positively correlated with ACP activities.[Conclusion] The addition of litters stimulated microbial growth and as such promoted SOC mineralization and produced a positive priming effect. Also, the intensity of priming was mainly related to the quality of litters. Although P addition alone increased SOC mineralization, the influence of P added with litters on soil priming effect was dependent on the litter types; with low-quality litter having a lower soil priming effect.

Abstract:[Objective] The utilization efficiency of phosphorus fertilizer is generally low in agro-ecosystems as phosphorus is readily co-precipitated with iron and manganese oxyhydroxides, iron aluminides, or directly adsorbed to the soil minerals, particularly in the red soil ecosystem. Thus, understanding the subsequent effects of phosphorus retained in the soil on soil ecological function and crop nutrient supply is of significance to guide the management of phosphorus fertilization.[Method] Based on a long-term fertilization experiment in red upland soil, this study investigated the effect of the conventional fertilization (CK) and short-term phosphorus fertilizer input (at rates of 0, 50, 100, 150 and 1 000 kg·hm^–2, P₂O₅) on soil nutrients, soil nitrogen cycle process and crop yields after 27 years. We evaluated the relationship between these factors and the residual effect of phosphorus using the multivariate statistical analysis method.[Result] Short-term P fertilizer addition at a high rate (1 000 kg·hm^–2, P1000) had no significant effects on soil total carbon (TC), total nitrogen (TN) and microbial biomass (MBC) compared to the conventional fertilization treatment (CK). Also, it significantly increased soil pH, nitrogen mineralization rate (N_min), soil nitrogenase activity (SNA), and potential nitrification rate (PNR) (P < 0.05), while it significantly decreased the net N₂O emission potential (N_N2O) (P < 0.05). Compared with the low phosphorus dosage treatments (50, 100, 150 kg·hm^–2), P1000 significantly increased soil available phosphorus (AP), N_min, SNA, PNR and potential N₂O production rate (P_N2O) by 33.3%-76.4%, 88.2%-388.1%, 111.4%-4 826.3%, 22.6%-152.4% and 13.8%-78.9%, respectively (P < 0.05), but significantly decreased the net N₂O emission potential by 64.6%-78.9% (P< 0.05). These results suggest that the application of a high dosage of phosphorus fertilizer has a strong residual effect on soil microbial activity and nitrogen processes even after 27 years. Spearman correlation analysis and redundancy analysis showed that AP and pH were the most important factors affecting soil microbial activities. Maize yield in the recent three years showed no significant difference among all treatments but was significantly positively correlated with TP, AP and pH. In comparison to low phosphorus treatments, P1000 treatments showed a promotion effect of 3%-23% on maize yield based on the historical yield data during 1991—2019.[Conclusion] Our results reveal that the short-term application of a large amount of phosphorus fertilizer has significant positive effects on maintaining soil fertility, microbial activity, soil nitrogen cycle function activity and crop yield even after 27 years, owing to the promotion of soil pH and slow release of available phosphorus.

Abstract:[Objective] The area of coastal saline soil is recognized as an important land resource with utilization value for agriculture. However, coastal mudflat area is usually characterized by poor plant growth and low microbial activity due to its high salinity suppressing most crops via the high osmotic stress, nutrient deficiency, toxicity and poor physical soil conditions. Soil microbes like Trichoderma spp. play a significant role in assisting plants to tolerate salinity stress. The present study aimed to investigate the effect of two Trichoderma-enriched bio-organic fertilizers on the yield and quality of cabbages (Brassica oleracea L.) grown in coastal saline soil as well as their effect on soil nutrient availabilities.[Method] Field and pot experiments were carried out with eight treatments:100% chemical fertilizer (CF), 30% bio-organic fertilizer plus 70% chemical fertilizer, 60% bio-organic fertilizer plus 40% chemical fertilizer, 100% bio-organic fertilizer (without chemical fertilizers), and using the non-fertilization treatment as the control (CON). The two bio-organic fertilizers were respectively prepared with strains of Trichoderma guizhouense NJAU 4742 (which is commercially available in China as a plant-growth-promoting agent) and T. arenarium 1A131 (which was previously isolated from saline mudflat of Dafeng, Jiangsu). The nutrient load of the seven fertilization treatments was set up to equal in the aspect of the contents of total N, P and K.[Result] Results obtained from both the field and pot experiments demonstrated that there was no significant difference in the effect of the two bio-organic fertilizers. Compared to the non-fertilized control (CON) and the full chemical fertilization (CF), 30% or 60% bio-organic fertilizer significantly increased the contents of nitrate N and available P in soil. The treatment of 60% bio-organic fertilizer plus 40% chemical fertilizer influenced the cabbage growth by significantly (P< 0.05) promoting the biomass of shoot and roots, and the chlorophyll content (shown by the SPAD values) in leaves. Among the fertilization treatments, application of 60% bio-organic fertilizer plus 40% chemical fertilizer resulted in the significantly highest yield and best quality of cabbage heads (with increased sugar and vitamin C contents, and less nitrate accumulation, P < 0.05). Moreover, principal component analysis (PCA) demonstrated that the significantly better plant growth effect did not correspond to the variation of soil nutrients. Rather, it may be related to the loaded microbes which were previously reported to be able to promote plant growth via producing phytohormones and activating the local microbiome.[Conclusion] Application of 60% bio-organic fertilizer combined with 40% chemical fertilizer, which allows the roots to develop to the maximum in such a saline ecosystem, is the optimized fertilization regime to cultivate cabbages in saline agriculture in coastal mud flats. Besides, compared to the nutrient load from the fertilizers, the function of the Trichoderma strains was found to be more directly linked to the plant-beneficial effect of this fertilization regime. The biological effect from the applied strains did not significantly rely on the origination of a specific strain. Moreover, the requirement of applying a local saline soil strain to the saline agriculture was not fully addressed here at least not in this study, and thus, needs further investigations.

Abstract:[Objective] Microorganisms in the rhizosphere play an important role in the process of plants resistance to soil-borne diseases. This study investigated the characteristics of rhizosphere microbial community and the mechanism of microbial community assembly in disease-conductive soil and disease-suppressive soil in a tomato-cultivated field.[Method] Real-time quantitative PCR was applied to detect the pathogen density in disease-conductive rhizosphere soil and disease-suppressive rhizosphere soil. Also, the distinction of tomato rhizosphere soil microbial community diversity, composition, structure, and assembly processes based on zero model were analyzed through high-throughput sequencing of 16S rRNA gene amplicon.[Result] Results show that, compared to disease-conductive soil, there was a significantly lower disease index of tomato bacterial wilt in disease-suppressive soils (disease index in disease-conductive soil and disease-suppressive soil were 47.5 and 22.5, respectively). The rhizosphere bacterial communities in disease-suppressive soils were characterized with higher alpha diversity, more abundant beneficial microorganisms, such as Actinobacteria, Firmicutes, Bacillaceae, and Streptomycetaceae, lower abundance of Ralstonia solanacearum (abundance of pathogenic bacteria decreased by 12.22 times) and accompanied with more stochastic processes. This shows that the adaptability of disease-suppressive soil to pathogenic disease stress was stronger than that of disease-conductive soil. The disease-conductive soil and disease-suppressive soil were mixed in a certain proportion to form three treatments; disease-conductive soil alone (D10H0), a mixture of disease-conductive soil and disease-suppressive soil with a mass ratio of 1︰1 (D5H5), and disease-suppressive soil alone (D0H10) to test the transmitability of inhibition properties of disease-suppressive soil. It was observed that with the increase in the proportion of disease-suppressive soil, the disease index of tomato bacterial wilt gradually decreased (the disease index in D10H0, D5H5, and D0H10 were 41.67, 29.17, and 16.67, respectively). While the diversity of bacterial alpha gradually increases, the abundance of Firmicutes, Streptomyces, and Bacillaceae increase significantly. Also, the dominant role of the stochastic and random processes is strengthened.[Conclusion] Disease stress had a significant effect on the alpha diversity, composition, structure, and community assembly process of the tomato rhizosphere microbial community. The disease-suppressive soil can recruit more beneficial microorganisms through plant roots to resist pathogenic disease stress.

Abstract:[Objective] Ammonia-oxidizing archaea (AOA) is considered the main microbial group catalyzing the nitrification process in acidic soils. However, how AOA adapts to acid stress remains largely uncertain, and we hypothesize that the gene encoding ATPase for microbial energy metabolism may likely play a key role in the adaption of AOA to acidic stress in these soils.[Method] In this study, 736 billion base pairs were obtained by ultra-deep metagenomics sequencing of acidic soils of Masson pine plantations with five different planting years (15 a, 24 a, 45 a, 55 a, 63 a). The phylogenetic congruency between the AOA amoA gene and ATPase subunit A gene was reconstructed to study the molecular mechanism that may enable the acidophilic lifestyle of AOA.[Result] The habitat expansion of AOA to the acidic environment cannot be explained by the phylogenetic evolutionary trajectory of canonic amoA genes encoding ammonia monooxygenase. The dominant AOA taxa from all 5 forest soils were phylogenetically affiliated with Nitrososphaerales and Ca. Nitrosotaleales based on amoA gene phylogeny. Even though Nitrososphaerales is more distantly related to Ca. Nitrosotaleales, it is more closely related to neutral AOA in alkaline soils. Therefore, the phylogenetic law based on the amoA gene cannot explain the successful colonization of Nitrososphaerales in acidic soils. The phylogeny of ATPase subunit A genes indicated a single clade of AOA in all acidic forest soils. These results thus suggest that during the habitat expansion and evolution of AOA, the amoA and ATPase genes could have experienced different selection pressures to cope with acid stress, and the V-ATPase gene may be obtained through horizontal gene transfer to adapt to acid stress. With the increase in forest age, the abundance of Ca. Nitrosotaleales group first decreased and then increased, while the abundance of Nitrososphaerales group first increased and then decreased. Also, it was observed that soil bioavailable potassium is an important environmental factor that significantly affects the structure of the AOA community.[Conclusion] These results indicate that the AOA populations in acid plantation soils under different planting years were clearly differentiated, and the horizontal transfer of V-ATPase gene may be an important mechanism that enables AOA to survive acidic stress for the habitat expansion.

Abstract:[Objective] Conservation tillage has attracted increasing attention over recent decades due to its benefits in improving soil quality. A 12-year fixed field experiment was conducted to assess the effects of long-term straw mulching on yields of rice and wheat, soil nitrogen fractions and microbial community with soil layers under a no-till system in Southwestern China.[Method] Two treatments, no-till without straw mulch (NT) and no-till with straw mulch (NTS), were used for the experiment. The soil was sampled at 0-5, 5-10, 10-20, and 20-30 cm soil layers. Soil total nitrogen (TN) and labile nitrogen fractions, including particulate organic nitrogen (PON), microbial biomass nitrogen (MBN), NH₄⁺-N, NO₃^–-N, and dissolved organic nitrogen (DON) were analyzed. Soil microbial community was determined using phospholipid fatty acid (PLFA) analyses. Crop yields were measured from September in 2013 to May in 2018.[Result] The results showed that compared to the NT treatment, the NTS treatment significantly increased wheat yield by 6.49%, with negligible effects on rice yield. The NTS treatment increased the contents of soil TN at 0-5 cm soil layer, NH₄⁺-N and NO₃^–-N at 0-5 cm layer, PON at 0-5 and 5-10 cm layers, and DON at 0-5 and 10-20 cm layers but not MBN content. Also, the NTS increased the DON/TN ratio at 0-5 and 10-20 cm layers rather than the ratios of other labile nitrogen fractions to TN. Soil total microbial PLFA and bacterial PLFA were higher in the NTS than in the NT treatment. Additionally, fungal and actinobacterial PLFA were comparable between the two treatments, leading to a lower fungal/bacterial ratio in the NTS. Principal component analysis revealed that the soil microbial community at 20–30 cm layer was separated from the other three soil layers, and soil microbial communities of NTS treatments were generally separated from NT treatments along the first principal component axis. Furthermore, redundancy analysis demonstrated that soil MBN, TN, and ratio of particulate organic carbon to PON were key factors in shaping soil microbial community. Soil TN, labile nitrogen fractions, and microbial PLFA fractions decreased with increased soil layers, irrespective of straw mulching status.[Conclusion] Straw mulching should be recommended to no-till systems in Sichuan province, Southwestern China because it leads to effective improvements in soil nitrogen contents, wheat yields, and soil total microbial PLFA.

Abstract:[Objective] Red soil is one of the important soil types in China. Its low fertility is a problem for agricultural output. Exploring the effect of different improvement measures on soil fertility is integral for realizing sustainable use of middle and low yield fields.[Method] In this study, dryland red soils derived from Quaternary red earth were collected from a field experiment in Yueyang, Hunan Province and used to measure the changes in soil pH and nutrient contents across different soil layers and years of different treatments. These treatments included fallow (F), no fertilizer control (CK), a single application of inorganic fertilizer of nitrogen, phosphate, and kalium (NPK), inorganic fertilizer combined with straw-return (NPKS), inorganic fertilizer combined with lime (NPKL), inorganic fertilizer combined with amendments of organic crushed-bones (NPKA), and inorganic fertilizer combined with commercial bio-organic fertilizer (NPKC). We also compared the activity of enzymes related to carbon, nitrogen, and phosphorus cycles in this soil using the microplate fluorescence method.[Result] Some treatments significantly affected soil nutrients and enzyme activities. Soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) in the 0-20 cm soil layer treated with NPKC in 2020 increased by 73%, 29%, 61%, and 1 847%, respectively, relative to the control. This treatment also significantly increased the enzyme activities of the enzymes that participate in the carbon cycle, including α-1, 4-glucosidase (αG), β-1, 4-glucosidase (βG), β-1, 4-xylosidase (βX), and cellobiohydrolase (CBH). Also, the activity of β-1, 4-N-acetylglucosamine (NAG), which is involved in the nitrogen cycle, was increased. Correlation analysis showed that SOM was significantly positively correlated with enzyme activities of αG, βG, βX, CBH, and NAG (P < 0.01). Additionally, the pH value was significantly negatively correlated with acid phosphatase (ACP) activity (P < 0.01). The effect of improvement measures on the enzyme activity of 0-20 cm soil layer was greater than on deeper layers. In 2019, compared with the control, NPKA treatment increased CBH enzyme activity in the 0-20 cm soil layer by 352%, but only by 2% in the 20-40 cm soil layer. Besides, ACP enzyme activity in the soil also showed a trend of increasing with years of treatment.[Conclusion] The combination of inorganic fertilizer and organic materials can significantly improve the nutrient status and soil enzyme activity in red soils. This can be used to efficiently improve the fertility of barren red soil.