Decreased Soil pH Research Articles

Long-term plastic film mulching altered soil physicochemical properties and microbial community composition in Shiyang River Basin, Northwest China

Plastic film mulching (PM) is used widely to improve crop water productivity in the arid regions of Northwest China. However, there are increasing concerns about the potential harm to soil health due to the presence of residue plastic film (RPF) mixed into the soil after long-term field mulching. In our study, we investigated the density of RPF in farmland topsoil (0 to 40 cm) (Exp. I) by analyzing 75 soil samples collected from 15 fields with varying durations of PM (ranging from 3 to 27 years). In addition, we examined the impact of long-term PM and PM + BM (BM, biodegradable film mulching) on soil health (Exp. II) based on an 8-year field experiment. The results illustrated that the weight of RPF ranged from 42.7 to 165.9 kg ha−1 after 3 to 27 years of mulching, with 10 out of 15 fields exceeded the national standard of China (75 kg ha−1). Compared with no film mulching treatment (NM), the long-term PM treatment significantly increased aggregate stability, while significantly decreased soil pH and the enzymatic activities of sucrase by 1.5 % and 33.4 %, respectively. Further, the Chao1, Shannon and Pielou's indices of bacteria significantly decreased after 8 years of PM. Compared with PM and NM, PM + BM treatment significantly improved the Chao1, Shannon and Pielou's indices of bacteria and altered the relative abundance of dominant bacterial and fungal phyla. The principal coordinates analysis (PCoA) revealed significant changes in the soil bacterial and fungal community structure under PM + BM, with the soil fungal community displaying higher sensitivity to PM + BM compared to PM. No significant differences were observed in soil organic matter (SOM), soil microbial biomass C (MBC), soil microbial biomass N (MBN) contents and the enzymatic activities of soils between PM + BM and PM treatments. Overall, BM could be a promising alternative to polyethylene plastic film for improving soil health and is recommended for farming practice in the arid regions of Northwest China.

Identification of cadmium phytoavailability in response to cadmium transformation and changes in soil pH and electrical conductivity

Owing to complex changes in the soil environment, determining cadmium (Cd) phytoavailability is challenging. We devised a soil-wheat system to monitor alterations in soil pH, electrical conductivity (EC), and Cd transformation under various rates of calcium chloride and/or low-molecular-weight organic acids (LMWOAs) addition. The findings indicate that decreasing soil pH value, increasing soil EC value, and Cd transformation affect the phytoextraction of Cd. The exchangeable Cd and transformation of Cd under shifts in soil pH and EC contribute differentially to the phytoextracted Cd. The level of potentially phytoavailable Cd was identified through complete wheat cultivation in which the soil pH decreased by 0.47 unit and soil EC increased by 600-1000 μS cm−1, resembling the concentration of 0.01 M LMWOAs extractable Cd, when transitioning from paddy to dryland soil. Based on considering the phytoextracted Cd as the phytoavailable Cd throughout a complete wheat growth term, the threshold for phytoavailable Cd in soil, ensuring the safety of wheat grain (limit: 0.1 mg kg−1), is determined to be 2.90 μg kg−1. Maintaining control over Cd phytoavailability in soil emerges as the key factor in ensuring the safety of wheat grain cultivation.

Evaluating the Long-Term Effect of Integrated Nutrients of Pome, Cow Dung and NPK on Soil Chemical Properties under a Garden-Egg Field

Soil amendments have been found to have a long-term effect on soil either positively or negatively, several soil management researches have been able to establish that sole application of inorganic fertilizer particularly nitrogen fertilizers can leave residual hydrogen ions in the soil which causes soil acidity over time. This study investigated the residual effects of different soil amendments of Palm Oil Mill Effluents (POME), cow dung, and NPK fertilizer, on soil chemical properties in two locations: Ekiti State University Teaching and Research Farm (EKSU) and Onu-Ijelu High School Agricultural Farm. The aim is to evaluate the long-term impact of these commonly used organic and inorganic nutrient sources on soil properties. The research utilizes a randomized complete block deign replicated three times to test the residual effect of the treatments. The research was divided into first and second trial, the result presented here is based on the outcome of the second trial. At the termination of the residual trial, it was found that organic matter contents of soils treated with cow-dung and POME increased while that of the NPK fertilizer reduced. There was a decrease in soil pH on soils treated with NPK fertilizer but found to increase on soils treated with POME and cow-dung. Other nutrient elements including exchangeable cations were also found to increase in soils with POME and Cow-dung. This phenomenon was attributed to mineralization process which made nutrients stored-up in these organic materials to be released slowly and at the same time reducing their loss from the soil. It was concluded that nutrients from organic sources have a longer residual advantage to soil and can be used in combination with inorganic fertilizer for better soil management. The findings from these result provides valuable insights into the long-term effect of these soil amendments and can help farmers and researchers make informed decisions about their appropriate and sustainable use in agriculture.

Investigation of Stability and Underlying Mechanism of Unstable Subgrades Loess Modified by Carbide Slag in Road Construction Projection

The repurposing of carbide slag (CS) coupled with the advancement of eco-friendly engineering methodologies promises a novel approach to addressing the technical challenges inherent in loess refinement. This inquiry delves into the feasibility of employing CS as an economically viable and ecologically sustainable remedy to amplify the engineering attributes of loess within the context of optimal preservation. In this investigation, assorted quantities of CS, spanning from 1% to 6%, were infused into the loess. The efficacy of CS as an additive was ascertained through a comprehensive array of tests administered across varied curing durations (0, 5, 10, 20, and 30 days), concentrating on its influence over the soil’s mechanical attributes. The study conducted various tests such as dual hydrometer, Attberg limit, specific gravity, compaction, unconfined compressive strength (UCS), consolidation, physico-chemical properties (pH, conductivity), and chemical analysis (sodium percentage and sodium adsorption rate). The study demonstrated that the incorporation of CS into loess resulted in an increase in hydraulic conductivity, UCS, and optimum water content while reducing maximum dry density, plasticity, and compressibility. Specifically, the application of 6% CS resulted in a significant 6.7-fold increase in UCS from 226.8 (kPa) to 1508.8 (kPa) over a 30-day curing period. It was also observed that the addition of CS and curing period resulted in a decrease in soil pH from 8.5 to 7.5 and an increase in electrical conductivity (EC) from 250 to 490 μs/cm. When the CS concentration was increased to 6%, the amount of Na+ ions, the total soluble salts, and the percentage of Na in the loess decreased. The phenomenon can be ascribed to the replacement of Ca2+ for Na+, leading to a more slender, diffuse double layer and heightened stability. The application of calcium silicate in loess subgrades enhances their stability and potency, concurrently providing an ecologically sound waste management resolution. Consequently, it emerges as a profoundly viable choice for ameliorating loess within the realm of the construction sector.

Diluted pyroligneous vinegar promoted Rhododendron growth by changing functional genes involved in N cycling in the rhizosphere

Excessive chemical fertilization in protected horticulture has caused nutrient accumulation, reduction of soil biodiversity, and subsequently soil degradation. Pyroligneous vinegar is a byproduct of pyrolysis for biochar production. While there has been an increase in interest in using pyroligneous vinegar as an amendment to improve soil quality, a paucity of data exists of its effect on the growth of acidophilous plants such as azalea (Rhododendron). To address this, we investigated the changes in the growth of azalea and soil microbial abundance, specifically those involved in nitrogen cycling in the rhizosphere with amendment of conventional inorganic NPK fertilizer (NPK) and four dilutions of pyroligneous vinegar each with matched NPK content. The results showed that the treatments of pyroligneous vinegar increased plant biomass (51%-99%), root length (29%-81%) and surface area (63%-151%), and nitrogen use efficiency (83%-299%) compared to NPK alone. The pyroligneous vinegar treatments decreased soil pH and increased the contents of rhizosphere soil dissolved organic carbon and nitrate, and changed potential denitrification activity. Compared with NPK, pyroligneous vinegar increased archaeal and bacterial amoA genes (AOA and AOB) abundances (45% − 79% and 39% − 75%, respectively) in nitrification, but inhibited the denitrification gene abundances (i.e. nirS and nirK abundance up to 21% lower). Pyroligneous vinegar increased the ratio of nosZ/(nirS + nirK), suggesting an increased potential to lower nitrous oxide emissions.Correlation analysis indicated that nitrogen use efficiency correlated positively with AOA and AOB, but negatively with nirS and nirK abundance. Therefore, our study suggests that pyroligneous vinegar could improve the growth of acidophilous plants and increase their nitrogen use efficiency by changing nitrogen cycling related functional genes, and could be a potential soil amendment in protected horticulture.

The Effects of Long-Term Application of Stabilized and Coated Urea on Soil Chemical Properties, Microbial Community Structure, and Functional Genes in Paddy Fields

The addition of fertilizers is indispensable in agricultural production, and currently, there is a wide variety of new types of fertilizers available. For example, commonly used are stabilized fertilizers with inhibitors and coated slow-release fertilizers, among others. However, the long-term effects of these fertilizers, when applied continuously are still uncertain. This study will provide scientific and theoretical support for the development and promotion of these fertilizers. A 16-year paddy field with brown soil treated with different urease and nitrification inhibitors, sulfur-coated urea (SCU), and resin-coated urea (PCU) was studied. The study showed that long-term use of conventional urea nitrogen fertilizer resulted in a significant reduction in soil total phosphorus (TP). Long-term application of NBPT and conventional urea significantly increased soil organic matter (SOM). Moreover, except for HQ and NBPT+DMPP, the prolonged application of new urea fertilizers also significantly enhanced soil total potassium (TK). Application of SCU fertilizer in brown soil type paddy fields resulted in a significant decrease in soil pH over time. However, changes in pH had no effect on the abundance of ammonia-oxidizing bacteria (AOB), as AOB was mainly affected by soil-available N. DMPP, HQ+DCD, NBPT+DMPP, SCU, and PCU significantly reduced the 16S rRNA gene copy number of soil bacteria, with the greatest effect of coated urea fertilizer (SCU and PCU). Long-term application of stable urea fertilizer with HQ significantly reduced the bacterial community in paddy soil. Conversely, HQ+DCD-stabilizede urea fertilizer significantly increased the population structure and abundance of Basidiomycota fungi while decreasing the population structure and abundance of Rozellomycota fungi. DMPP-stabilized urea fertilizer notably increased the population structure and abundance of Ascomycota fungi while decreasing the population structure and abundance of Rozellomycota and Chytridiomycota fungi. Furthermore, HQ-stabilized urea fertilizer significantly reduced the population structure and abundance of Chytridiomycota fungi.

Mechanisms underlying soil microbial regulation of available phosphorus in a temperate forest exposed to long-term nitrogen addition

With exogenous nitrogen (N) input into soil, phosphorus (P) could become a limiting nutrient for plant growth. Soil microbes play a crucial role in regulating soil P cycle and availability. P functional genes, further, regulate soil P availability. It is unclear how the addition of N in different chemical forms and rates influences the composition of soil microbes associated with P cycling and the abundance of P functional genes. A long-term experiment of N addition in three chemical forms with two levels in a temperate forest was performed to reveal the influences and the underlying mechanisms. We found that both chemical N forms and N rates selected for different P-solubilizing microbes. Ammonia form-N increased the abundances of P-solubilizing bacteria at low and high rates. Continuous N deposition included a significant decrease in soil pH and inhibited the viability and activity of bacterial communities in soil, especially the P-solubilizing bacteria. Thus, it restricted inorganic P mobilization and led to a decrease in soil available P. In addition, ammonium-N enhanced the relative abundance of most of the functional genes related to organic P mineralization, while nitrate-N presented a decrease trend. Ammonium-N significantly decreased most of the functional genes relevant to P transportation, whereas the other chemical N forms did not change them. Although N-addition consistently decreased the functional genes relevant to inorganic P solubilization, two of them (ppx and ppa) were the exceptions and showed an increase trend. N addition also decreased soil pH and altered soil properties, and indirectly contributed to the changes in community composition of P-solubilizing microbes and the abundances of multiple P functional genes. Our results provide a mechanistic explanation for the regulation of microbes on N-induced available P limitation via tuning the compositions of P-solubilizing microbes and the abundances of multiple P functional genes.

Maximizing trace metal phytoextraction through planting methods: Role of rhizosphere fertility and microbial activities

Brownfields are a widespread problem in the world. The poor quality of these soils and the potential presence of contaminants can pose a significant threat to plant establishment and growth. However, it may be possible to improve their establishment with an appropriate agricultural practice. In this paper, the effects of two common planting strategies, seeding and transplanting, on the establishment and growth of the hyperaccumulator species Noccaea caerulescens and on its phytoextraction capacity were investigated. A field experiment was conducted by direct sowing of N. caerulescens seeds on a plot of contaminated Technosols in Jeandelaincourt, France. At the same time, seeds were sown on potting soil under controlled conditions. One month later, the seedlings were transplanted to the field. One year later, the results showed that transplanting improved the establishment and growth of N. caerulescens. This was due to a decrease in soil pH in the rhizosphere, which subsequently increased nutrient availability. This change in rhizosphere properties also appeared to be the key that improved microbial activities in the rhizosphere soil of transplanted plants. The observed improvement in both rhizosphere nutrient availability and microbial activities, in turn, increased auxin concentrations in the rhizosphere and consequently a more developed root system was observed in the transplanted plants. Furthermore, the Cd and Zn phytoextraction yield of transplanted plants is 2.5 and 5 times higher, respectively, than that of sown plants. In conclusion, N. caerulescens transplantation on contaminated sites seems to be an adequate strategy to improve plant growth and enhance trace metal phytoextraction.

Phosphorus availability and fractions responses to chemodiversity of exogenous dissolved organic matter in lime concretion black soil

AbstractThe chemodiversity of exogenous dissolved organic matter (DOM) is significantly increased during the composting process, yet its influence on soil phosphorus (P) transformation is uncertain. A 60‐day incubation experiment was conducted to assess the availability and fractions of P in lime concretion black soil in response to exogenous DOM input, with three treatments: control (CK), soil with DOM from 30 days decomposed straw (DOM1) and soil with DOM from 90 days decomposed straw (DOM2). The results demonstrated that the addition of DOM caused an increase in the content of available P in the soil, particularly the addition of DOM1 with more protein‐like substances and a lower degree of humification. Compared to the control, DOM1 and DOM2 treatments showed an increase in available P content of 17.3%–54.3% and 0.6%–18.2%, respectively. However, the response of the soil's physicochemical and biological properties varied considerably. DOM1 treatment caused a marked decrease in soil pH compared to DOM2 treatment, which then led to the release of Ca2+ and Mg2+ and improved the solubility of inactive P. Moreover, DOM1 treatment was found to significantly raise the content of microbial biomass P (MBP), particularly at 60 days. The Mantel test and random forest analysis revealed that the strongest correlation was between MBP and available P. Furthermore, DOM1 treatment had a stimulating effect on the growth of phosphate‐solubilizing microorganisms, including Arthrobacter, Penicillium and Mortierella. This investigation could provide insights into how the chemodiversity of exogenous DOM affects the activation of legacy‐P in soil, thus enhancing the soil P supply capacity in agricultural systems.

Effects of alternate wetting and drying on oxyanion-forming and cationic trace elements in rice paddy soils: impacts on arsenic, cadmium, and micronutrients in rice.

Rice is a global dietary staple and its traditional cultivation under flooded soil conditions leads to accumulation of arsenic (As) in rice grains. Alternate wetting and drying (AWD) is a widely advocated water management practice to achieve lower As concentrations in rice, water savings, and decreased methane emissions. It is not yet clear whether AWD leads to tradeoffs between concentrations of As and micronutrient elements (e.g., zinc, manganese, molybdenum) in rice grain. We analyzed pore water chemistry and rice grain composition data from a field experiment conducted in Arkansas, USA, in 2017 and 2018 to test the hypothesis that AWD will have diverging effects on oxyanion-forming (arsenic, molybdenum) vs. cationic (cadmium, zinc, manganese, copper) trace elements. This was hypothesized to occur via decreases in soil pH and/or precipitation of iron oxide minerals during oxidizing conditions under AWD. Solubility of all trace elements, except zinc, increased in more reducing conditions. Consistent with our hypothesis, AWD tended to increase grain concentrations of cationic elements while decreasing grain concentrations of oxyanionic elements. Decreases in total As in rice grains under AWD were mainly driven by changes in dimethylarsinic concentrations, with negligible changes in inorganic As. Linear mixed-effects modeling showed that effects of AWD on grain composition were more significant in 2017 compared to 2018. These differences may be related to the timing of dry-downs in the developmental stage of rice plants, with dry-downs during the heading stage of rice development leading to larger impacts on grain composition of certain elements. We also observed significant interannual variability in grain elemental composition from continuously-flooded fields and postulate the warmer temperatures in 2018 may have played a role in these differences.

Linking plant traits to rhizosphere priming effects across six grassland species with and without nitrogen fertilization

The rhizosphere priming effect (RPE), i.e., the acceleration of soil organic matter decomposition (SOM) by plant roots, plays a key role in the soil carbon (C) cycle and its feedback to climate change. However, how plant traits regulate the RPE has rarely been investigated. Here we selected six grassland species with and without nitrogen (N) fertilization to examine the relationships between the RPE and plant traits, and also the interactive effect of plant traits and N fertilization on the RPE. All six species showed positive RPEs, ranging from 83% to 297% above the unplanted control. Among plant traits, specific rhizosphere respiration was the best predictor for the interspecific variation in the RPE, with the higher RPE related to higher specific rhizosphere respiration. The RPE was also positively linked to root N concentration across species. In contrast, leaf traits and root morphological or architectural traits could not explain the interspecific variation in the RPE. Nitrogen fertilization differentially affected the RPEs of six species through its interaction with plant traits and the effect on soil processes. Nitrogen fertilization increased leaf N concentration and specific rhizosphere respiration, causing higher photosynthesis and possibly root exudation. On the other hand, N fertilization increased mineral N, and decreased soil pH, β-glucosidase and β-cellobiohydrolase, causing lower microbial activities. The effect of N fertilization on the RPE was thus attributed to the balance between the changes in microbial activities and in plant traits. Overall, our results demonstrate that the variation of RPE across six species could be mainly explained by plant biomass and traits. It is promising that plant traits have important indicative functions in predicting the SOM decomposition through plant-soil interactions.

Decreased soil pH weakens the positive rhizosphere effect on denitrification capacity

The stimulating effect of rhizosphere on denitrification is considered to be an unavoidable loss of soil nitrogen (N) and detrimental to crop N use efficiency, which is regulated by crop growth and soil properties. Soil acidification, occurring rapidly in many intensive farming lands, affects both crop growth and soil properties, thereby altering rhizosphere effect on denitrification. However, the mechanism by which soil acidification regulates rhizosphere denitrification still remains unclear. Here, we determined the denitrification capacity (DC) and associated community compositions of nirK- and nirS-type denitrifiers in maize rhizosphere and bulk soils at four acidity gradients (pH = 6.8, 6.1, 5.2, and 4.2). Results showed that the stimulating effect of rhizosphere on DC strongly depended on soil pH. Compared to bulk soil, rhizosphere soil had significantly higher DC at pH ≥ 5.2, but not at pH of 4.2. With increasing soil acidity, the stimulation of rhizosphere on DC (calculated as the difference in DC between rhizosphere and bulk soils) decreased from 8.01 to 0.01 mg N kg-1 d-1. Moreover, soil acidification significantly reduced the differences in dissolved organic carbon (DOC) and abundance of key nirK-type denitrifier taxa between rhizosphere and bulk soils, both of which were positively related to the stimulation of rhizosphere on DC. These findings demonstrated that soil acidification could weaken the positive rhizosphere effect on denitrification via regulated C availability and associated nirK-type denitrifier community, potentially reducing N loss risk in rhizosphere soil. The independent role of soil pH should be fully considered when modelling N behaviour in plant-soil systems.

Effects of soil amendments and foliar selenium applications on soil cadmium immobilization and wheat accumulation

Wheat cadmium (Cd) contaminationis one of the environmental and agricultural concerns worldwide. Here, the effects of foliar selenium (Se) and soil amendments (lime, biofuel ash and sodium sulfide (DSO), iron mine tailing and alkali lignin (MX)) applications on the soil Cd fractions and wheat Cd accumulations were studied by incubation, greenhouse pot, and field plot experiments. The results showed that in soil incubation experiment, lime and MX applications significantly increased soil pH and DSO applications significantly decreased soil pH, while all the three amendments can significantly reduce the available Cd fractions by 16-21%. Foliar spraying can significantly increase the growth and yield of the high-Cd-accumulating-cultivar (Puxing5). In the greenhouse experiment, lime and MX applications considerably decreased grain Cd concentrations by 53-56% and 41-52% for Puxing5 and by 9-38% and 23-28% for Zhoumai30, respectively. In the field experiment, the Cd concentrations were significantly reduced by 67-69% and 69-74% in Puxing5 grain by lime and MX applications, respectively. DSO applications also significantly reduced Cd concentrations in grains by 56-59% for Puxing5 and by 22-27% for Zhoumai30 in the greenhouse experiment, but in contrast, increased Cd concentrations in field experiment by 20-23%. Our results implicate that the incubation and greenhouse experiments are necessary to be verified in the field and the foliar Se application is recommended when considered both the financial costs and production safety.

Acacia auriculiformis agroforestry fallows of different ages improve soil physico-chemical properties and carbon stocks on the Batéké plateau, Democratic Republic of Congo

Our study evaluated the effects of Acacia auriculiformis agroforestry fallows installed on impoverished sandy soils of the Bateke Plateau in the Democratic Republic of the Congo (DRC). We compared physico-chemical properties and carbon stocks of soils under 1 to 3, 3 to 5 and 5 to 7 yr-old Acacia auriculiformis fallows and 5 yr-old savanna fallows. Soils were collected at depths of 0–10 cm, 10–40 cm and 40–100 cm and analyzed for the following parameters: soil organic carbon (SOC), nitrogen (N), available phosphorus (P), exchangeable cations (Ca2+, Na+, K+, Mg2+), cation exchange capacity (CEC), pH (H2O and CaCl2), granulometry and bulk density. In general, results obtained showed that agroforestry fallows are superior to traditional fallows for most measured parameters. The presence of A. auriculiformis improves the chemical properties of the soils compared to savanna soils; soil C and N concentrations as well as cation exchange capacity (CEC) were higher (P < 0.0001) under agroforestry soils than under savanna soils, especially between 0 and 10 cm depth. Our results also showed that A. auriculiformis agroforestry fallows stored 1.5 times more soil carbon than savanna fallows between 0 and 100 cm depth with 75, 106, 114, and 106 Mg C ha−1 respectively for savanna, 1–3 years, 3–5 years, and 5–7 years fallow soils. However, establishment of A. auriculiformis agroforestry fallows resulted in a decrease in soil pH compared to savanna soils. Differences in age and depth of the agroforestry fallow soils did not influence the physico-chemical properties evaluated. Overall, our results show that the establishment of A. auriculiformis agroforestry fallow improves the physico-chemical properties and increases soil carbon stocks compared to traditional savanna fallow. Therefore, we suggest the scaling up of the A. auriculiformis agroforestry improved fallow as a soil regenerative agrotechnology in the tropics.

Features of growing garden strawberries in open ground conditions

The purpose of this study was to evaluate the effectiveness of strawberry cultivation in the use of PH regulators, synthetic and organic fertilisers, mulching practices, and the use of fungicides, insecticides, and herbicides. The pH of the soil was regulated by applying aluminium sulphate and limestone in the amount of 200 and 900 g per three square metres, respectively. Synthetic preparations with different macro- and microelements, as well as organic compost, were used to test the effect of fertilisers. The growth characteristics of the growing season, including flowering and fruiting indicators, were evaluated. The results showed that a decrease in soil pH has a positive effect on the efficiency of growing the plants under study. The use of fertilisers with a high potassium content increased the growth rate of the growing season, and preparations rich in phosphorus had a positive effect on the characteristics of the flowering period. The use of compost provided an increase in the productivity of strawberries, comparable to the use of synthetic fertilisers. Mulching has been shown to reduce the risk of fungal infections in plants and to increase growth indicators. The use of the herbicide was significantly effective in suppressing the growth of pest plants and improving the growth characteristics of strawberries. It was shown that the use of organic farming methods and reduced concentrations of herbicides and insecticides allows achieving high efficiency of strawberry cultivation

Influence mechanisms of N addition on the concentration of soil dissolved organic matter in China

AbstractSoil dissolved organic matter (DOM) plays a critical role in regulating the cycling of terrestrial biogeochemistry. However, the influence mechanisms of nitrogen (N) addition on soil DOM concentration are not well understood at the regional scale. We performed a meta‐analysis of 1004 paired observations from 115 literature to explore how N addition affected the soil DOM concentration, including dissolved organic carbon (DOC) and nitrogen (DON), in China. Overall, N addition markedly stimulated the soil DOC and DON concentrations by 5.2% and 33.1%, respectively. This implied that the stimulation by increased N availability than the suppression by decreased soil pH played a more important role in the soil DOM concentration under N addition. The N addition level showed a significantly positive correlation with the soil DOC and DON concentrations under N addition. The N addition influence on soil DOC concentration was decreased along with the increase in initial soil total nitrogen (TN). This demonstrated the microbial N mining theory in the low N soils and the stoichiometric decomposition theory in the high N soils at the regional scale. The mean annual precipitation (MAP) potentially facilitated the leaching out of soil DON and displayed a negative impact on the soil DON concentration under N addition. The increased soil depth and initial soil pH depressed the soil DOC concentration whereas stimulated the soil DON concentration under N addition. This indicated that DOC mostly accumulated in the top soil and DON largely leached to the deep soil. And the initial soil pH with high value perhaps promoted the uptake of DOC for microbes and the solubility of DON, and thus resulted in the opposite influences on the soil DOC and DON concentrations. Our study provided a mechanistic understanding on N addition influence on the C and N dynamics of terrestrial ecosystem at the regional scale.

Effects of microplastics and biochar on soil cadmium availability and wheat plant performance

AbstractBiochar is a promising amendment to promote cadmium (Cd) sorption and fixation in agricultural soil, where microplastics are emerging contaminants in soil. Herein, a greenhouse pot experiment was conducted to elucidate the effects on Cd availability in a soil–plant system by biochar and fresh/aged microplastics application. The fresh microplastics led to an obvious increase in soil Cd availability and Cd uptake by wheat plant, while the aged microplastics increased the available Cd in soil but had no effect on Cd uptake by wheat plant, which was likely attributed to the blocking effect of the aged microplastics on Cd transportation from the soil to the wheat plant. Unexpectedly, biochar had increased Cd availability and Cd uptake. The increased soil soluble Cd was because of both decreased soil pH and elevated dissolved organic matter (DOM) content resulted by biochar addition. Also, the unchanged Cd adsorption of the soil was likely responsible for the increased tested soil Cd availability. In addition, the combined effects of a greater decrease in soil pH, an increase in soil DOM content, and a reduction in Cd adsorption after the addition of microplastics to biochar‐amended soil resulted in a significant increase (ranging from 2.63% to 47.73%) in Cd availability compared to soil treated with biochar alone. Moreover, fresh microplastics inhibited wheat growth, and greater inhibition effect was observed for their aged ones. The biochar elevated the wheat biomass; however, the coexistence of microplastics and biochar decreased the wheat plant biomass compared with biochar alone, due to the negative influence of microplastics in plant growth.

Assessment of the effects of integrated rotation-tillage management on wheat productivity in the Loess Plateau region

The long-term use of conventional management practices coupled with the overapplication of synthetic fertilizers by smallholder family farms to meet food demand has negatively impacted the environment of farmland. Therefore, improved agronomic management practices are needed to enhance crop productivity. A 3-year (2016–2019) experiment was conducted to evaluate the effects of integrated rotation-tillage management [maize/soybean-wheat (MW/SW); chisel plow tillage (CPT), zero tillage (ZT), and plow tillage (PT)] on the farmland environment and wheat productivity in the Loess Plateau of China. The results indicated that SW and conservation tillage (CPT and ZT) increased soil nutrient levels and decreased soil pH and C/N values compared with conventional management practices (MW and PT); meanwhile, conservation tillage substantially increased soil moisture (SM, 3.56–16.06 %) compared with PT. Compared with MW and PT, SW and CPT increased aboveground biomass (0.26–4.45 % and 0.73–2.15 %, respectively) and nitrogen content (1.24–2.30 % and 0.26–2.73 %, respectively) during wheat development. Coincidentally, SW increased wheat actual yield (AY, 2.98 %) and maintained wheat theoretical yield (TY) and harvest index (HI) compared with MW; CPT increased wheat grain yield (AY, 6.72 %; TY, 3.28 %) and HI (2.26 %) compared with PT, while ZT caused significantly opposite results. CPT increased nitrogen fertilizer productivity (NfP, 3.28 %), nitrogen uptake efficiency (NupE, 1.19 %), and nitrogen use efficiency (NUE, 1.67 %) compared with PT regardless of crop rotations, while ZT significantly decreased NfP (9.69 %) and NupE (16.99 %) and increased NUE (8.18 %). Nevertheless, crop rotation did not substantially affect wheat nitrogen efficiency. Further correlation and partial least squares path modeling analysis revealed that elevated SM and nitrogen levels due to improved management practices had the potential to improve wheat productivity by regulating wheat growth characteristics. Overall, integrated SW-CPT management was more positive for improving farmland environment and enhancing wheat productivity in the Loess Plateau, which is suitable as a conservation strategy to adjust the cropping structure of smallholder family farms and promote sustainable agricultural development in arid and semiarid agricultural regions.

Ketersediaan N dan Fe-larut pada Tanah Ultisol yang diaplikasikan Lumpur Kolam Ikan

The use of fish pond mud in improving soil quality is generally still not widely used. This study used various doses of pond mud to determine the effect of pond mud doses on the availability of N and Fe-soluble in Ultisol soil planted with mustard greens. The research was conducted in the Greenhouse in April - May 2022 with a Completely Randomized Design (CRD), five doses of fish pond sludge namely at doses of 0; 0.5: 7.5: 10; and 12.5% applied to Ultisol soil. The results showed that applying fish pond sludge significantly affected soil pH, N-NO3-, N-NH4+ and Fe-soluble. Soil pH decreases due to a reaction between water and Fe compounds that bind OH- and release H+. Whereas N-NO3-, N-NH4+, and soluble-Fe significantly increased due to chemical reactions that produced soluble salts which reacted with water. As for the soil parameters, the effect of pond mud decreases soil pH at all doses of addition of mud and increases N-NO3-, N-NH4+, and soluble-Fe Ultisol, with the best doses of M3 (equivalent to 1 kg mud + 9 kg of soil). There is a relationship between the chemical properties of the soil and the fresh weight of the plants, as evidenced by the increase in the wet weight of the mustard plants.

Metagenomic analysis revealed the potential of lactic acid bacteria in improving natural saline-alkali land.

Management and improving saline-alkali land is necessary for sustainable agricultural development. We conducted a field experiment to investigate the effects of spraying lactic acid bacteria (LAB) on the cucumber and tomato plant soils. Three treatments were designed, including spraying of water, viable or sterilized LAB preparations to the soils of cucumber and tomato plants every 20days. Spraying sterilized or viable LAB could reduce the soil pH, with a more obvious effect by using viable LAB, particularly after multiple applications. Metagenomic sequencing revealed that the soil microbiota in LAB-treated groups had higher alpha-diversity and more nitrogen-fixing bacteria compared with the water-treated groups. Both viable and sterilized LAB, but not water application, increased the complexity of the soil microbiota interactive network. The LAB-treated subgroups were enriched in some KEGG pathways compared with water or sterilized LAB subgroups, such as environmental information processing-related pathways in cucumber plant; and metabolism-related pathways in tomato plant, respectively. Redundancy analysis revealed association between some soil physico-chemical parameters (namely soil pH and total nitrogen) and bacterial biomarkers (namely Rhodocyclaceae, Pseudomonadaceae, Gemmatimonadaceae, and Nitrosomonadales). Our study demonstrated that LAB is a suitable strategy for decreasing soil pH and improving the microbial communities in saline-alkali land.