Soil Urease Activity Research Articles

Effects of α-Fe2O3 modified chicken manure biochar on the availability of multiple heavy metals and soil biochemical properties

The problem of increasingly severe soil heavy metals contamination is of great concern worldwide. Herein, chicken manure and potassium ferrocyanide were used as raw materials to prepare a α-Fe2O3 loaded biochar (Fe2O3/BC) composite material through a simple calcination method. We found Fe2O3/BC obtained at 350 ℃ (Fe2O3/BC-350) exhibited excellent immobilization efficiency on multiple heavy metals in soil. And then density functional theory (DFT) calculations explained the reason of Fe2O3/BC-350 exhibited better remediation performance than the Fe2O3/BC-250 and Fe2O3/BC-550. When cultured for 90 days, the passivation effect of the 1% Fe2O3/BC-350 dosage treatment achieved the highest with the immobilization rates for Cu(II), Cd(II) and Pb(II) reaching 62.5%, 45.56% and 42.56%, respectively. The composite material increased soil pH and cation exchange capacity (CEC), and promoted the transformation of Cu(II), Cd(II) and Pb(II) ions from acid-soluble to more stable forms through ion exchange, precipitation and complexation. The soybean pot experiment further verified that Fe2O3/BC-350 could reduce the phytoavailable fractions of heavy metal soil remediation material. In addition, Fe2O3/BC-350 increased the activity of soil urease and sucrase. Meanwhile, the diversity and richness of the soil microbial community were improved. These results demonstrated that Fe2O3/BC-350 not only had an excellent immobilization effect on heavy metals in the soil, but also Fe2O3/BC-350 exhibited environmentally friendly in soil. As a result, Fe2O3/BC can serve as a promising remediation agent for multiple heavy metal polluted soils.

Effect of reclamation years on soil physical, chemical, bacterial, and fungal community compositions in an open‐pit coal mine dump in grassland area of Inner Mongolia, China

AbstractUnderstanding the process of changes in substrate physical, chemical, and biological properties is critical for vegetation ecosystem reconstruction of open‐pit coal mining dumps. However, the relationships of soil chemical, biological, bacterial, and fungal characteristics in open‐pit coal mining dumps in grassland area are still unclear. The purpose of this study is to understand the changes and relationships of soil physic‐chemical, bacterial, and fungal properties under the reclamation time series of open‐pit coal mining dumps. Soil samples were collected from the waste dump reclaimed after 2, 5, 10, and 15 years in Shengli West No. 2 open pit coal mine in Inner Mongolia, China, and the surrounding natural grassland was set as a control at 0–10 cm and 10–20 cm. Soil pH, electrical conductivity (EC), soil organic matter (SOM), nutrient properties, bacterial, and fungal community structures were measured in the waste dump reclaimed after 2, 5, 10, and 15 years. The results showed that soil pH was decreased at 0–20 cm in the waste dump while SOM was increased by 1.2 times in 0–10 cm reclaimed after 15 years than that after 2 years. Soil EC was decreased by 55.5% and 58.3%, respectively, in 0–10 cm and 10–20 cm, respectively, after 10 years than that after 2 years. Soil available nitrogen, available phosphorus, and available potassium were 97.8%, 13.2%, and 60.9% lower after 15 years' reclamation than those in control. The acid phosphatase in 0–10 cm and 10–20 cm was increased by 2.2 and 2.1 times, respectively, after 15 years compared with that after 2 years. Alkaline phosphatase was decreased by 16.8% reclaimed after 15 years than that after 2 years in 10–20 cm soil. The Shannon diversity index of fungi was increased by 42.0% and 43.8%, respectively, in 0–10 cm and 10–20 cm, in the waste dump reclaimed after 15 years than that after 2 years. Soil organic matter was positively correlated with soil urease activity. Soil pH, EC, and texture had different effects on bacterial and fungal communities. Therefore, appropriate measurements should be applied to the reclamation dumps to help the soil properties of reclamation areas to recover to the natural grassland.

Influence of Vegetation Types on the C, N, and P Stoichiometric Characteristics of Litter and Soil and Soil Enzyme Activity in Karst Ecosystems

Analyzing the ecological stoichiometric characteristics and soil enzyme activity of litter and soil in different vegetation types within karst areas can help to clarify the nutrient cycles and element abundance in those areas, in addition to providing basic data for vegetation restoration and reconstruction. In this study, the carbon (C), nitrogen (N), and phosphorus (P) contents of litter and soil and the alkaline phosphatase (ALP), sucrase (Suc), urease (Ure), and catalase (CAT) activity of soil were measured in grassland (GR), shrubland (SR), arbor and shrub compound forest (AS), and arbor forest (AR). The correlation between litter and soil stoichiometry and soil enzyme activity was analyzed to reveal the effects of different vegetation types on the C, N, and P stoichiometric characteristics of litter and soil, soil enzyme activity, and their driving mechanisms. The results showed that the C, N, and P contents of litter in the study area were 366.2–404.48 g/kg, 12.37–15.26 g/kg, and 0.76–1.05 g/kg, respectively. The C, N, and P contents of soil in the study area were 27.69–42.4 g/kg, 2.38–4.25 g/kg, and 0.56–0.68 g/kg, respectively. The litter N content and soil C and N contents were highest in the arbor forest (p < 0.05), while those in the grassland were the lowest (p < 0.05). The C:P and N:P ratios of the litter and soil in the arbor forest and arbor and shrub compound forest were higher than those in the other two vegetation types; however, the C:N ratio of the litter and soil in the arbor forest was lower than that in the other three vegetation types. The N element had a strong coupling relationship between litter and soil, while the P element had a weak relationship. The activity of the four soil enzymes in the four vegetation types were ranked as follows: arbor forest > arbor and shrub compound forest > shrubland > grassland. In general, the arbor forest communities were more conducive to nutrient cycling and accumulation. This information could help to guide the restoration and management of vegetation in karst areas.

Microplastics Alter Dehydrogenase, Urease, and Cellulase Activities in Soil

Microplastics Alter Dehydrogenase, Urease, and Cellulase Activities in Soil

Integrated 16S and metabolomics revealed the mechanism of drought resistance and nitrogen uptake in rice at the heading stage under different nitrogen levels.

The normal methods of agricultural production worldwide have been strongly affected by the frequent occurrence of drought. Rice rhizosphere microorganisms have been significantly affected by drought stress. To provide a hypothetical basis for improving the drought resistance and N utilization efficiency of rice, the study adopted a barrel planting method at the heading stage, treating rice with no drought or drought stress and three different nitrogen (N) levels. Untargeted metabolomics and 16S rRNA gene sequencing technology were used to study the changes in microorganisms in roots and the differential metabolites (DMs) in rhizosphere soil. The results showed that under the same N application rate, the dry matter mass, N content and N accumulation in rice plants increased to different degrees under drought stress. The root soluble protein, nitrate reductase and soil urease activities were improved over those of the no-drought treatment. Proteobacteria, Bacteroidota, Nitrospirota and Zixibacteria were the dominant flora related to N absorption. A total of 184 DMs (98 upregulated and 86 downregulated) were identified between low N with no drought (LN) and normal N with no drought (NN); 139 DMs (83 upregulated and 56 downregulated) were identified between high N with no drought (HN) and NN; 166 DMs (103 upregulated and 63 downregulated) were identified between low N with drought stress (LND) and normal N with drought stress (NND); and 124 DMs (71 upregulated and 53 downregulated) were identified between high N with drought stress (HND) and NND. Fatty acyl was the metabolite with the highest proportion. KEGG analysis showed that energy metabolism pathways, such as D-alanine metabolism and the phosphotransferase system (PTS), were enriched. We conclude that N-metabolism enzymes with higher activity and higher bacterial diversity have a significant effect on drought tolerance and nitrogen uptake in rice.

The effects of feeding with organic waste by terrestrial isopod Philoscia Muscorum on enzyme activities in an incubated soil

Soil fauna are important biological factors that affect litter decomposition and play an important role in the release of nutrients and improve soil enzyme activities. This study focused on the effects of isopods on enzymatic activities of soil. Lab experiments were conducted to assess the influence of terrestrial isopod Philoscia Muscorum on enzyme activities during the incubation. In Lab experimental food sources from wheat straw were prepared. Dehydrogenase, urease, alkaline phosphatase and arylsulphatase activity in soil treated with different number of isopods with wheat straw were determined in 28 days incubation. Results showed that the presence of isopods significantly increased (P

Effects of Urea Application on Soil Organic Nitrogen Mineralization and Nitrogen Fertilizer Availability in a Rice–Broad Bean Rotation System

Rice cultivation is facing a situation where rice production stagnates while nitrogen fertilizer (NF) application continues to increase. The effectiveness of the NF residues from the rice season on the growth of rotating broad beans is unclear. High NF use in rice cultivation also affects the nitrogen supply through soil organic nitrogen (SON) mineralization (SONM). However, the rules of SONM and the NF availability in the rice–broad bean rotation system (RBRS) are unknown. A field trial of the RBRS was conducted using 15N-labeled urea (CO(15NH2)2) as the partial NF source (15N accounted for 5.3% of the total pure nitrogen applied) for the rice and no NF for the broad bean. It was found that 33.0–38.1% of NF in the rice season was utilized. NF availability was low in the broad bean season (3.6–4.0%). SONM was the most important source, providing approximately 60% of the nitrogen for rice growth. The SONM into mineral nitrogen and the fixation of mineral nitrogen into SON occurred simultaneously, with SONM dominating in most cases. SON content decreased slowly in the rice season and dramatically in the broad bean’s podding stage with a 0.64 g kg−1 (24.1%) decrease. The high nitrogen application in rice season promoted SONM and aggravated groundwater pollution. Soil urease activity, rather than catalase, phosphatase, and invertase activities, can be the main monitoring object of SONM. Furthermore, fungal abundance (especially Aspergillaceae, Neuroceae, and unclassified_o__Helotiales), rather than bacteria, was the primary target for SONM monitoring. It is unreasonable to apply large amounts of NF in the rice season but not in the broad bean season in the RBRS. N1 (135 kg N ha−1) had the best comprehensive benefits regarding crop yield, nitrogen supply by SONM, NF utilization, and nitrogen loss on the environment in the RBRS.

Influence of Boron on Yield of Okra and Soil Microbial Activities in Inceptisols

Abstract: The study entitled “Influence of boron on yield of Okra and soil microbial activities inInceptisols” was carried out at E Block of Central Farm, Regional Research & Technology Transfer Station (RRTTS), OUAT, Bhubaneswar during January to April, 2021 with the objectives of studying the effect of foliar spray of boron on yield of Okra and the soil microbial activities. The experiment was laid out in RBD with ten treatments replicated thrice. The treatments included one on B control (only soil test dose NPK), NPK + 1.0 KgB/ha soil application and eight treatments of foliar application of B @ 0.25, 0.5, 0.75, and1.0% borax sprayed once or twice at 25 and/or 50 DAS. Plant and soil samples were collected one week after 1st and 2nd spraying for analysis of biometric and microbiological parameters including enzyme activities. The bacterial, fungal and actinomycetes population of soil in different treatments measured one week after 1stand 2 ndfoliar spray of Brecordeda significant increase in number of count in all treatments including the one applied with B as basal in soil over that in control. A reduction in population of fungus (2-16%) and actinomycetes (9-43%) measure done week after 2nd spray was observed over that recorded after 1st spray. In contrast, an increase in population of bacteria (0-28%) measured one week after 2nd spray was observed over that recorded after 1st spray. The urease activity of soil due to different boron treatments varied significantly among the treatments from 25.2 to 38.6 µg NH4+N݃ −1 soil/2h. The dehydrogenase activity of soil due to different boron treatments varied significantly among different treatments from 0.7 to 46.6 µg TPF݃ −1 soil /24h. The urease and dehydro genase activities of soil measured after 2nd foliar spray of B increased with application of B to okra irrespective of dose and application methods.

Influence of Companion Planting on Microbial Compositions and Their Symbiotic Network in Pepper Continuous Cropping Soil.

Continuous cropping obstacles have become a serious factor restricting sustainable development in modern agriculture, while companion planting is one of the most common and effective methods for solving this problem. Here, we monitored the effects of companion planting on soil fertility and the microbial community distribution pattern in pepper monoculture and companion plantings. Soil microbial communities were analyzed using high-throughput sequencing technology. Companion plants included garlic (T1), oat (T2), cabbage (T3), celery (T4), and white clover (T5). The results showed that compared with the monoculture system, companion planting significantly increased the activities of soil urease (except for T5) and sucrase, but decreased catalase activity. In addition, T2 significantly improved microbial diversity (Shannon index) while T1 resulted in a decrease of bacterial OTUs and an increase of fungal OTUs. Companion planting also significantly changed soil microbial community structures and compositions. Correlation analysis showed that soil enzyme activities were closely correlated with bacterial and fungal community structures. Moreover, the companion system weakened the complexity of microbial networks. These findings indicated that companion plants can provide nutrition to microbes and weaken the competition among them, which offers a theoretical basis and data for further research into methods for reducing continuous cropping obstacles in agriculture.

Biopriming with Bacillus subtilis Enhanced the Sulphur Use Efficiency of Indian Mustard under Graded Levels of Sulphur Fertilization

This study investigated the effect of bioinoculants (Bacillus subtilis and Pseudomonas fluorescens) as biopriming agents under varied sulphur (S) fertilizer levels (0, 20, 30, and 40 kg S ha−1) to enhance sulphur use efficiency (SUE) in Indian mustard. The experiment was conducted during the 2018–19 and 2019–20 winter seasons at the research farm of the Institute of Agricultural Sciences, Banaras Hindu University, Varanasi (25°26′ N, 82°99′ E). A randomized block design was employed to assess the combined effect of biopriming and S fertilization on the partitioning of S in different parts of mustard plants, S uptake, SUE, and soil urease, dehydrogenase, alkaline phosphatase, and arylsulphatase activity. Results showed that the application of S fertilizers along with biopriming significantly increased the S content, uptake, and SUE by plants and enzymes involved in the S mineralization process. Application of 40 kg S ha−1 + B. subtilis resulted in the highest S content in the root (0.12%), stover (0.30%), and seed (0.67%), and the highest total S uptake (2.97 g m−2 in the first year and 3.37 g m−2 in the second year), agronomic use efficiency (8.80 g g−1), apparent S recovery (22.37%), urease activity (156.68 µg NH4+ g−1 hr−1), dehydrogenase activity (42.80 µg TPF g−1 24 hr−1), and arylsulphatase activity (39.94 µg pNP g−1 hr−1). However, the highest alkaline phosphatase activity (129.17 µg pNP g−1 hr−1) was found in the treatment that received 40 kg S ha−1 + P. fluorescens. Further, the different indices of SUE revealed that the effect of biopriming was more prominent in apparent recovery efficiency than agronomic SUE and physiological SUE. Conclusively, the present study demonstrated that seed biopriming with B. subtilis along with S fertilization is more rewarding and can promote sustainable production of Indian mustard.

Analog soil organo–ferrihydrite composites as suitable amendments for cadmium and arsenic stabilization in co-contaminated soils

Remediation of CdAs co-contaminated soils has long been considered a difficult problem to solve, as Cd and As have distinctly different metallic characters. Amending contaminated soils with traditional single passivation materials may not always work well in the stabilization of both Cd and As. Here, we reported that analog soil organo–ferrihydrite composites made with either living or non-living organics (bacterial cells or humic acid) could achieve stabilization of both Cd and As in contaminated soils. BCR and Wenzel sequential extractions showed that organo–ferrihydrite, particularly at 1 wt% loading, shifted liable Cd and As to more stable phases. Organo–ferrihydrite amendments significantly (p < 0.05) increased soil urease, alkaline phosphatase and catalase enzyme activities. With organo–ferrihydrite amendments, the bioavailable fraction of Cd decreased to 35.3 % compared with the control (65.1 %), while the bioavailable As declined from 29.4 % to 12.4%. Soil pH, microbial community abundance and diversity were almost unaffected by organo–ferrihydrite. Ferrihydrite and organo fractions both contributed to direct Cd-binding, while the organo fraction probably maintained the Fe-bound As via lowering ferrihydrite phase transformation. Compared to pure ferrihydrite, organo–ferrihydrite composites performed better not only in reducing liable Cd and As, but also in maintaining soil quality and ecosystem functions. This study demonstrates the applications of organo–ferrihydrite composites in eco-friendly remediation of CdAs contaminated soils, and provides a new direction in selecting appropriate soil amendments.

Bacillus Thuringiensis Enhances the Ability of Ryegrass to Remediate Cadmium-Contaminated Soil

Phytoremediation technology has been widely used for the remediation of heavy metals in soil due to its favorable environmental and ecological effects, but establishing a single phytoremediation technology can result in bottlenecks, such as a long cycle, low biomass, and difficulty in root absorption. At present, inoculation with microorganisms that could assist plants in their remediation of contaminated soils is attracting increasing attention. Therefore, in this study we selected ryegrass and Bacillus thuringiensis (SY) and analyzed the effects of SY inoculation on the growth of ryegrass, including the accumulation of Cd in ryegrass, changes in heavy metal forms, and the heavy metal content in rhizosphere soil, using pot experiments. The results indicate that SY inoculation promotes root growth and development of the ryegrass and the accumulation of cadmium in the plants. In addition, SY inoculation increased the levels of soil nutrients and the activities of soil urease, sucrase, and alkaline phosphatase. This study reveals that the use of SY improves the remediation efficiency of ryegrass for cadmium-contaminated soil, and supports the application potential of microorganisms in soil remediation technology.

Reducing options of ammonia volatilization and improving nitrogen use efficiency via organic and inorganic amendments in wheat (Triticum aestivum L.).

This study investigates the effect of organic and inorganic supplements on the reduction of ammonia (NH3) volatilization, improvement in nitrogen use efficiency (NUE), and wheat yield. A field experiment was conducted following a randomized block design with 10 treatments i.e., T1-without nitrogen (control), T2-recommended dose of nitrogen (RDN), T3-(N-(n-butyl) thiophosphoric triamide) (NBPT @ 0.5% w/w of RDN), T4-hydroquinone (HQ @ 0.3% w/w of RDN), T5-calcium carbide (CaC2 @ 1% w/w of RDN), T6-vesicular arbuscular mycorrhiza (VAM @ 10 kg ha-1), T7-(azotobacter @ 50 g kg-1 seeds), T8-(garlic powder @ 0.8% w/w of RDN), T9-(linseed oil @ 0.06% w/w of RDN), T10-(pongamia oil @ 0.06% w/w of RDN). The highest NH3 volatilization losses were observed in T2 at about 20.4 kg ha-1 per season. Significant reduction in NH3 volatilization losses were observed in T3 by 40%, T4 by 27%, and T8 by 17% when compared to the control treatment. Soil urease activity was found to be decreased in plots receiving amendments, T3, T4, and T5. The highest grain yield was observed in the T7 treated plot with 5.09 t ha-1, and straw yield of 9.44 t ha-1 in T4. The shifting towards organic amendments is a feasible option to reduce NH3 volatilization from wheat cultivation and improves NUE.

Effects of Pruning on Vegetation Growth and Soil Properties in Poplar Plantations

Artificial pruning is an important silvicultural practice that can produce clear wood in poplar plantations. This study focused on the growth of poplar, understory vegetation diversity and soil properties in response to different pruning intensities in poplar plantations. We implemented three different pruning treatments based on the height-to-crown base (HCB) to tree height (H) ratio in Populus deltoides ‘Nanlin 3804′ plantations: CK (no pruning), a 1/3 pruning treatment and a 1/2 pruning treatment. The poplar growth conditions, understory vegetation biodiversity and soil properties were investigated for one year after pruning. Compared with CK, the 1/2 pruning treatment significantly decreased the increment of diameter at breast height (DBHi) and stem volume increment (Vi) by 16.4% and 12.8%, respectively. Meanwhile, pruning significantly promoted understory vegetation biomass and increased the Shannon–Weiner diversity index of understory vegetation, and these variables were positively correlated with pruning intensity. The 1/2 pruning treatment significantly reduced the contents of soil nitrate nitrogen (NO3-N), total inorganic nitrogen (IN) and microbial biomass nitrogen (MBN) by 21.9%, 13.9% and 22.4%, respectively. However, the 1/3 pruning treatment had no significant influence. Pruning mainlyaffectedthe soil enzyme activity in the surface (0–10 cm) layer. The 1/3 and 1/2 pruning treatments significantly decreased soil urease activity by 20.1% and 15.0%, respectively. Furthermore, nonmetric multidimensional scaling analysis showed that the seasonal variation in soil properties was significant, and significant differences among pruning treatments were mainly observed in July and October. Redundancy analysis showed that the growth of aboveground vegetation was significantly correlated with soil properties, particularly soil IN content and urease activity. Therefore, the results highlighted that pruning could promote the growth of understory vegetation and accelerate the transformation of soil nutrients. The 1/2 pruning treatment significantly inhibited the growth of poplar in terms of DBH and V, while the 1/3 pruning treatment promoted the growth of poplar in the short term. Overall, we think that the 1/3 pruning intensity is more suitable for pruning practice.

Effects of walnut/Rosa roxburghii compound planting on growth, fruit yield, quality of Rosa roxburghii and soil properties.

Walnut and Rosa roxburghii are important arbor and shrub fruit trees cultivated in the southwest mountainous area of China. Furthermore, those two species are compound cultivated in this area. In this study, we investigated the growth, yield, fruit quality, photosynthesis, and soil fertility of R. roxburghii in a 7-year typical 'Qianhe 7'/ 'Guinong 5' compound planting pattern in Guizhou. The results showed that compared with the monoculture, photosynthetic pigment content and photosynthetic rate of R. roxburghii leaves were significantly lower in the compound plantation. The growth and yield of R. roxburghii decreased significantly, with a 77.7% reduction of yield. Fruit quality of R. roxburghii was improved. The content of ascorbic acid (Vc), total phenol, carbohydrate, K, Ca, Mg, Fe, Mn, Zn, and other substances increased significantly. Fruit Vc and Mn content increased by 34.1% and 64.1%, respectively. The contents of total N, available N and K in the soil increased by 45.8%, 34.8% and 67.8%, respectively. The abundance of soil microorganisms and functional bacteria increased significantly, with the increase of bacteria and fungi being more than 36.0%. The increase of potassium bacteria and nitrogen fixing bacteria was 71.3% and 124.8%, respectively. However, the contents of organic matter, carbon-nitrogen ratio, total P, total K, available mineral nutrient (P, Ca, Mg, Fe, Mn, Cu, Zn) contents decreased. While the activities of soil urease and catalase were increased, the activities of other soil enzymes (sucrase, cellulase, protease, phosphatase) were significantly reduced. In summary, with continuous growth of walnuts in the walnut/R. roxburghii compound plantation, there was obvious shade and soil fertility competition for R. roxburghii, which affected its yield, but had a improvement effect on fruit quality.

Distribution Characteristics of Active Soil Substances along Elevation Gradients in the Southern of Taihang Mountain, China

Active soil substances, which can indicate environmental changes sensitively, have the fastest turnover rate. Vegetation diversity and soil bio-physicochemical properties according to five elevations classes (800 m, 1000 m, 1100 m, 1200 m, and 1500 m a.s.l.) in the Southern Taihang Mountain were investigated. Soil ammonium-N (NH4+—N), nitrate-N (NO3−—N), microbial biomass carbon (MBC), and nitrogen (MBN), as well as soil urease (URE) and sucrose (SUC) activities were determined. The results showed that elevation gradients, soil layers, and their interaction had significant effects on most of the active soil substances. With the rise of elevation, soil NO3−—N, inorganic N, MBC, and MBN contents, as well as SUC activity and SUC/MBC ratio basically showed an inverted V-shaped distribution trend and reached the peak value at 1100 m (p &lt; 0.05). Soil URE showed a fluctuating upward trend and reached the peak value at 1500 m (p &lt; 0.05), and the URE/MBC ratio showed a straight upward trend. With the depth of soil layer, the contents of active soil substances tended to decrease, showing a phenomenon of surface aggregation. Active soil substances were correlated with plant community diversity indexes, soil water content, pH, available N, and available phosphorus contents, and available N was the main factor affecting active soil substances, which could explain 34.4% of the variation. In summary, at the intermediate slope of 1100 m, soil moisture and tightness were suitable for soil microbial activity and plant growth, the highest contents of active soil substances, indicating a fast turnover of soil carbon and nitrogen. The present study enriched our understanding of soil carbon and nitrogen turnover mechanisms in the mountain ecosystem.

Moisture-dependent response of soil carbon mineralization to temperature increases in a karst wetland on the Yunnan-Guizhou Plateau.

Wetlands are facing gradual drying, leading to large carbon loss due to the transformation from anaerobic to aerobic conditions, but the temperature and drought effects from the temperature and moisture fluctuation on soil organic carbon (SOC) mineralization remain uncertain. An incubation study with three moisture levels (100%, 60%, and 40% WHC, marked as W100, W60, and W40, respectively) and four temperature levels (5, 10, 15, 20°C, marked as T5, T10, T15, and T20, respectively) was conducted to determine the effect of temperature and moisture interactions on SOC mineralization in the karst wetland of the Yunnan-Guizhou Plateau. Compared with T5, the cumulative mineralization CO2 in T20 increased by 83.18% (W40), 154.63% (W60), and 148.16% (W100), respectively. The mineralized CO2 at W60 and W40 significantly decreased compared to that at W100 at the four temperature levels. Temperature, moisture and their interactions had significant positive effects on SOC mineralization rates and cumulative mineralized CO2. The temperature sensitivity of SOC mineralization rates (Q10) under W40 and W60 increased by 22.03% and 24.52%, respectively, compared to that under W100. The cumulative mineralized CO2 was positively related to soil urease activity and negatively related to soil pH, N-NH4+, SOM, and catalase activity. Temperature and moisture fluctuation and soil properties explained 85.40% of the variation in SOC mineralization, among which temperature and moisture fluctuation, soil properties, and their interactions explained 19.71%, 4.81%, and 60.88%, respectively. Our results indicated that SOC mineralization is influenced by the joint effect of temperature and drought, as well as their induced changes in soil properties, in which higher temperatures can increase soil CO2 emissions by enhancing the SOC mineralization rate, but the positive effect may be weakened from the drying wetland.

Effects of Cinnamomum camphora coppice planting on soil fertility, microbial community structure and enzyme activity in subtropical China.

Cinnamomum camphora (C. camphora) is a broad-leaved evergreen tree cultivated in subtropical China. Currently, the use of C. camphora clonal cuttings for coppice management has become popular. However, the effects of C. camphora coppice planting on soil abiotic and biotic variances remained unclear. In this study, we collected soil from three points in the seven-year C. camphora coppice planting land: under the tree canopy (P15), between trees (P50), and abandoned land (Control) to investigate the effects of C. camphora coppice planting on soil fertility, microbial community structure and enzyme activity. The results revealed that C. camphora coppice planting significantly increased soil fertility in the point under the tree canopy (P15) and point between trees (P50), and P15 had more significant effects than P50. Meanwhile, in P15 and P50, soil bacterial, fungal alpha-diversity were improved and microbial community structures were also changed. And the changes of soil organic carbon and total nitrogen promote the transformation of soil bacterial, fungal community structures, respectively. In addition, C. camphora coppice planting significantly (p < 0.05) increased soil urease (UE), polyphenol oxidase, and peroxidase activities, while significantly decreased soil ACP activity. This study demonstrated that the C. camphora coppice planting could improve soil fertility in subtropical China, which promoted the transformation of soil microbial community from oligotrophs (K-strategist) to copiotrophs (r-strategist). Thus, this work can provide a theoretical basis for soil nutrient variation and productive management of C. camphora coppice plantation in subtropical China.

Inhibiting N2O emissions and improving environmental benefits by integrating garlic growing in grain production systems

The grain–economic cropping system combines grain production with economic benefits. Under this system, decreasing the N2O emissions from farmland soil will be more conducive to the development of green agriculture. Therefore, we determined the soil N2O emissions and ecological benefits of garlic–maize and wheat–maize cropping systems from 2019 to 2020. Compared with wheat–maize, garlic–maize significantly decreased the soil urease activity and dissolved inorganic nitrogen (DIN) content, which significantly decreased the N2O emission fluxes by 44.6% and 36.4% in the crop growing seasons during 2019–2020, respectively, thereby indicating that planting garlic could effectively inhibit the soil N2O emissions. Moreover, garlic enhanced the ecological benefits of the planting system by 2.1 times as an economic crop. Path analysis showed that the soil temperature, water-filled pore spaces, and DIN significantly promoted soil N2O emissions in the wheat–maize system but weakened them in the garlic–maize system. However, the urease activity significantly affected the DIN content, which indicates that garlic could significantly decrease DIN production by inhibiting the urease activity to reduce N2O emissions. Our findings demonstrate that garlic can be used as an environmentally friendly economic crop to optimize planting systems.

Effects of combined application of biochar and nitrogen fertilizer on soil quality of summer maize-winter wheat system

The effects of nitrogen fertilizer and biochar on topsoil quality in the drylands of northwest China were studied in field trials for two years. A split plot design with two factors was adopted, with five nitrogen rates (0, 75, 150, 225 and 300 kg N·hm-2) as main plots, and two rates of biochar (0 and 7.5 t·hm-2) as submain plots. We collected soil samples at 0-15 cm depth after two years of winter wheat-summer maize rotation and measured physical, chemical, and biological properties. The minimum data set (MDS) was established by using principal component analysis and correlation analysis to analyze the responses of soil quality to nitrogen fertilizer and biochar addition. The results showed that the combined application of nitrogen fertilizer and biochar could improve soil physical properties, increase macroaggregate content, reduce soil bulk density, and increase soil porosity. Both fertilizer application and biochar application had a significant effect on soil microbial biomass carbon and nitrogen. The application of biochar could improve soil urease activity and the contents of soil nutrients and organic carbon. Six out of 16 indicators (urease, microbial biomass carbon, total phosphorous, total nitrogen, pH, and available potassium) relating to soil quality were used to construct MDS, and soil quality index (SQI) was calculated. The variation range of SQI was 0.14-0.87, with that of 225 and 300 kg N·hm-2 nitrogen application combined with biochar application being significantly higher than other treatments. Soil quality could be significantly improved by application of nitrogen fertilizer and biochar. Interactive effect was observed, which was particularly stronger under high nitrogen application rate.