Calcareous Soils Research Articles

Substantial contribution of inorganic carbon sources to CO2 emissions in calcareous vineyard soils in Germany

AbstractIn light of climate change and increasing global temperatures, it is important to equally prioritize the study of inorganic carbon dynamics in calcareous soils within temperate ecosystems, as has been done for arid or semiarid environments. A significant area of vineyards in Germany is established on calcareous soils. However, the potential influence of inorganic carbon on CO2 emissions in these vineyards has not been sufficiently explored when evaluating the carbon footprint of management practices in relation to carbon storage. Therefore, we aimed to differentiate between organic and inorganic sources of CO2 emissions from six vineyard soils located in the southwest of Germany that had previously received organic soil amendments (OA). Inorganic carbon content varied between 8 and 55 g kg−1 across different sites, with variations observed in the inorganic‐to‐organic carbon ratio. Soil samples were incubated under standard laboratory conditions for 48 h, and the source of emitted CO2 was determined using a two‐end‐member mixing model. The contribution of inorganic carbon to CO2 emissions was influenced by the quantity of inorganic carbon, with an increase in contribution with increasing inorganic‐to‐organic carbon ratio. On average, abiotic sources accounted for 5% to 40% of the emitted CO2 at the different sites, with one site showing no significant contribution of inorganic carbon. CO2 production from inorganic carbon was higher in the subsoil compared with the topsoil, likely related to the higher content of inorganic carbon in the subsoil. Notably, there was no discernible influence of OA on carbonate dissolution. This study emphasizes the significance of considering abiotic sources of CO2 emissions in addition to soil respiration in calcareous soils and highlights the need for further investigation to apply these findings at the field scale.

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

The influence of variations in salinity levels on the biocementing process on soil improvement of liquefaction potential

Abstract This article presents an innovative method of soil improvement cementing to increase the shearing strength of very loose sand with 10% relative density (Dr) in saline conditions. Salt in saline soils destroys the stability of stable soils. In contrast, the salt content reduces the level of homogenization of unstable soils, causes technical problems in calcareous soils, and affects their stability, especially if the salt content is more than 3.0%. The variations in salinity levels can determine the optimal percentage of salt levels in the stabilized soil. The application of biocementation to saline soil can drastically increase the shear strength of soil in soil with potential liquefaction in coastal areas due to earthquakes. Calcium carbonate deposition (MICP) in the microbial-induced biocementing process is a new method that utilizes the metabolic processes of microorganisms in this study using Bacillus sp. In the MICP process, microbes need Ca2+ ions obtained from fly ash, which can produce SiO2 and CaO to produce CaCO3 for binding between particles. Soil improvement was carried out by combining initial soil, fly ash, mycobacteria, and variations in salinity obtained from NaCl with varying percentages of 0%, 1%, 2%, and 3,4% after testing at curing times 7, 14, 21, and 28 days. The research samples from the UCS and direct shear tests showed that the shear and UC strength that were treated increased. The highest increase in shear strength was at 3,4% salinity at 28 days of 80.9°. CaCO3 production resulting from the binding between particles in the biocementing reaction can be seen from the results of SEM tests. Soil improvement using biocementing in this study resulted in an effective increase in the strength of loose sand soil in salinity condition.

The effects of Zn, FYM and their combine application on soil physical and biological parameters under long-term rice based cropping systems in calcareous soil

The effects of Zn, FYM and their combine application on soil physical and biological parameters under long-term rice based cropping systems in calcareous soil

Effect of six rootstocks on leaf content of micronutrients (Fe, Zn, Mn, and Cu) in ‘Valencia’ orange trees under a calcareous soil

Effect of six rootstocks on leaf content of micronutrients (Fe, Zn, Mn, and Cu) in ‘Valencia’ orange trees under a calcareous soil

The Effect of Bentonite, Poultry Manure and Elements on Some Chemical Properties of Sandy Calcareous Soil

The Effect of Bentonite, Poultry Manure and Elements on Some Chemical Properties of Sandy Calcareous Soil

Tomato yield and soil chemical properties influenced by low–molecular–weight organic acids in calcareous soil

<p>Calcareous soils have restrictive characteristics that limit and pose a challenge for crop production; in this environment, plants can exude low-molecular-weight organic acids (LMWOAs). This study aimed to verify the influence of exogenously applied LMWOAs in calcareous soils on tomato yield and the chemical characteristics of soil and leachate. <em>Solanum lycopersicum</em> L. seedlings were grown in pots containing calcareous soil in a greenhouse, fertilized by drip irrigation with Steiner nutrient solution in which the treatments 0.1 mM citric acid (CA), 0.1 mM oxalic acid (OA), 0.01 mM salicylic acid (SA) and a control without LMWOAs (T0) were prepared, applied during the whole growth cycle. The experiment was repeated four times, with twenty replicates per treatment, under a completely randomized design. The yield per plant was quantified, while pH and microbial respiration (RMS) were measured in the soil. The pH, electrical conductivity (EC), oxidation-reduction potential (ORP), carbonate (CO<sub>3</sub><sup>2–</sup>), and bicarbonate (HCO<sub>3</sub><sup>–</sup>) contents were quantified in the leachates. SA application reduced the soil pH (8.75). SA and CA improved the fruit yield per plant by 11% and 33%, respectively (p < 0.05). CA induced a 1.7% reduction in leachate pH (p < 0.05) and a 15.9% increase in HCO<sub>3</sub><sup>–</sup> content (p < 0.05). SA decreased EC and CO<sub>3</sub><sup>2–</sup> concentrations by 8.9 and 23.1% (p < 0.05), but increased HCO<sub>3</sub><sup>–</sup> content by 23.1 % (p < 0.05). The use of LMWOAs as a strategy in the management of calcareous soils can promote favorable conditions for tomato yield per plant.</p>

Effect of soil properties on phosphate desorption from some cultivated soils in arid region

<p><span lang="EN-US">Kinetics of soil chemical processes is one of the most important areas in environmental chemistry for metals availability in soils and mechanisms of desorption. Phosphorus (P) is one of the most important macronutrients that control plant growth and crop production. The present study aims to evaluate the influences of soil properties of Alluvial (<em>Typic torrerets</em>) and calcareous (<em>Typic calcids</em>) on the Kinetics of P desorption using batch and anion exchange resin techniques used for P adsorption, which is highly correlated with P uptake by growing plants. Results indicated that P desorption was best described by empirical modified Freundlich (power function) and Elovich equations and, to a lesser degree, by theoretical diffusion and first-order equations. The rate of P desorption from the alluvial soils was positively and highly correlated and largely controlled by clay content (r=0.96<sup>**</sup>) and surface area (r=0.87<sup>**</sup>), as indicated by the simple correlation coefficient and R<sup>2 </sup>in the multiple stepwise regression analysis. These soil properties largely controlled the variations in the kinetic parameters that describe the rate of P desorption and P intensity in the four tested kinetic models. On the other hand, calcium phosphate and active CaCO<sub>3</sub> contents in the calcareous soils were negatively correlated. They largely controlled the variations in the rate and intensity parameters of the kinetic models. These results suggest that surface precipitation on the CaCO<sub>3</sub> surface controls P desorption in calcareous soils, while reversibly, phosphate adsorption on the clay surface controls P desorption in the alluvial soils, which decreases in both cases, crop production.</span></p>

Optimal Plant Density Is Key for Maximizing Maize Yield in Calcareous Soil of the South Pannonian Basin.

Plant density, the number of plants per unit area, is an important factor in maize production. Plant density exhibits high variability and depends on a number of factors, i.e., the length of the growing period of the hybrid, the morphological characteristics of the plant, the amount and distribution of precipitation during the growing season, the reserve of winter moisture in the soil, the level of soil fertility, the time of sowing, agronomic management practices, and biomass and yield. The objective of this paper was to determine the agronomic optimal plant density for maize in calcareous soil in the semiarid conditions of the South Pannonian Basin. Field experiments were conducted at the experimental field-IFVCNS (two locations: Rimski Šančevi and Srbobran) to evaluate four plant densities (55,000; 65,000; 75,000; and 85,000 plants ha-1). The experimental sites "Rimski Šančevi" and "Srbobran" are located in the typical chernozem zone of the southern part of the Pannonian Basin. On average for all hybrids, the grain yield followed a second-degree polynomial model in response to the increasing planting density, with the highest value at plant density (PD2: 65,000 plants ha-1). To achieve maximum yield, the optimal planting density for corn hybrids of the FAO 200 group should be 57,600 plants ha-1, for the FAO 300 group 64,300 plants ha-1, for the FAO 400 group 68,700 plants ha-1, for the FAO 500 group 66,800 plants ha-1, and for the FAO 600 group 63,500 plants ha-1. "Which-Won-Where" biplot showed that the hybrid H24 from FAO 600 group was the highest yielding in all of the environments. Hybrid H17 from the same FAO group was the most stable across all of the environments. Selected hybrids may further be studied for planting density and nutritional requirements for getting maximum yield. By introducing new maize hybrids with higher genetic yield potential and better agronomic management practices, modern mechanization and agricultural techniques allowed to increase planting densities.

The Effect of Manganese and Sulfur Applications on the Rocket (Eruca vesicaria subsp. Sativa) Plant Grown in Lime Soils

Due to the high lime and pH in the soil, sulfur and micro element deficiencies are observed in green vegetable plants. Rocket, one of the green vegetables and a member of the Brassicaceae family, is widely produced in our country. It is noteworthy that rocket is grown by producers almost everywhere and that this plant grown in our region also has a deficiency of microelements. For this reason, in this study were investigated that the sulfur and manganese requirement of rocket, which is one of the vegetable plants grown in Konya calcareous soil, and the effect of the interaction between these two elements on plant growth and yield. In our study, sulfur (S) fertilizer was applied in three doses (0- 40- 80 kg S da-1) and manganese (Mn) fertilizer in three doses (0- 1- 2 kg Mn da-1) was applied to the rocket plant. The experiment was carried out in the greenhouse conditions according to the randomized plots factorial design. At the end of the experiment, the average leaf height, chlorophyll SPAD value, plant fresh weight, plant height and plant Mn concentration did not differ with different doses of fertilizer applications in the rocket plant. On the other hand, the sulfur concentration in the plant and soil increased significantly with sulfur fertilization (p

How far can the interactive effects of continuous deficit irrigation and foliar iron fertilization improve the physiological and agronomic status of soybeans grown in calcareous soils under arid climate conditions?

Water and iron are crucial elements for soybean growth and development, particularly in calcareous soils and arid climatic conditions. The aim of this study was to improve iron and water use efficiency and enhance soybean resilience to water scarcity and iron deficiency. So, the effect of 16 treatments; 4 deficit irrigation water regimes (25, 50, 75 and 100 % crop water requirements (CWR)) combined to 4 foliar iron gradual concentrations (F0=0, F1=1, F2=3 and F3=5 g/L of FeSO4) applied at 3–4 leaves, at the beginning of flowering and at the end of flowering; was investigated in this split plot experiment with 4 replicates. Our results showed that supplying iron and water to plants can improve chlorophyll florescence a, chlorophyll content, stomatal conductance, yield, iron uptake, and protein content. Determining the optimal combination of deficit irrigation treatment and gradual iron sulfate concentrations for soybean is an alternative to save water and improve growth parameters. In our manuscript, we can conclude that 75 % CWR × F2 is the best combination of the two factors that led to the same biological yield as 100 % CWR. Consequently, we can say that applying F2 as a foliar iron concentration led to an economy of 25 % of the soybean crop water requirement by ensuring an adequate supply of soluble iron, facilitating root uptake, promoting protein synthesis, enhancing chlorophyll formation, and supporting overall nutrient uptake and metabolism.

Phosphorus solubilizing Bacillus sp. strain MN-54 increased the yield and economic returns of pearl millet due to improved phosphorus use efficiency

Phosphorus (P) deficiency is a frequent problem in calcareous soils of Pakistan because of P-fixation, which poses significant threats to pearl millet productivity. The use of P-solubilizing bacteria (PSB) is regarded as a promising approach for improving P-availability in soil-plant systems. However, it needs optimization of P application into the soil. Therefore, this 2-year field study was conducted to optimize P doses in combination with PSB (Bacillus sp. MN54) inoculation to improve phosphorus use efficiency (PUE), yield, economic returns, and grain quality of pearl millet. Five P doses, i.e. 0 (native soil P only - control), 30, 60, 90, and 120 kg P2O5 ha−1 combined with and without PSB inoculated seeds were used in the study. The application of 90 kg P2O5 ha−1 + seed inoculation with PSB improved the grain yield by 36.8% and 36.0% during 1st and 2nd year, respectively. The same treatment significantly improved the PUE, grain protein, zinc (Zn), and total grain P contents compared to the control treatment. Furthermore, the highest economic returns (1053.3 and 1050.5 $ ha−1) and benefit:cost ratio were observed under 90 kg P2O5 ha−1 + seed inoculation with PSB during both years. In conclusion, application of 90 kg P2O5 ha−1 combined with PSB seed inoculation is a pragmatic option to improve P uptake, grain yield, PUE, grain quality and economic returns of pearl millet grown on calcareous soils.

Copper dynamics in vineyard topsoils as affected by the supply of aerated compost tea: Insights from a batch experiment

Aerated compost teas (ACTs) are rich in soluble humic substances (SHS) that have high affinity for metals, notably Cu. Using a batch experiment, we measured the extent to which two ACTs altered Cu dynamics in vineyard topsoils one day and 21 days after their addition. Soils were extracted with 0.01 M KCl, and total Cu concentration, free Cu ion fraction and size distribution of Cu ligands were measured in the extraction solution to assess the impact of ACT on the mobility of Cu. Diffusive gradient in thin film (DGT) measurements were carried out to assess the effect of ACT on Cu bioavailability, and the dissociation rate of Cu-SHS complexes was measured. The results revealed that ACT increased the mobility of Cu from a factor 1.2 to 5.8 depending on the soil, the ACT and the incubation time. Cu mobilization was associated with an increase in absorbance at 254 nm and a decrease in the free Cu ion fraction in the KCl extract. Associated with the strong agreement between the size distribution of SHS and that of Cu ligands in the KCl extract of soils treated with ACT, these results showed that Cu was mobilized through complexation by the SHS present in ACTs. A fraction of the SHS supplied with ACTs sorbed onto the soil constituents, notably in calcareous soils where this fraction reached 86% for ACT B. Between 15% and 50% of the SHS remaining in solution degraded between day one and day 21 under the presumed action of microflora. This explains why the Cu mobilization efficiency of ACTs was on average lower in calcareous soils than in non-calcareous soils, and decreased with time. Lastly, ACT increased the bioavailability of Cu in soils from a factor 1.3 to 4.2, due to the relatively high dissociation rate of Cu-SHS complexes.

Iron (Fe) and zinc (Zn) coated urea application enhances nitrogen (N) status and bulb yield of onion (A. cepa) through prolonged urea-N stay in alkaline calcareous soil

Onion (A. cepa) is an important horticulture crop which is sensitive to nutrient limitations worldwide. Urea hydrolysis to ammonia (NH3) and carbon dioxide (CO2), due to soil urease activity, causes urea-N loss. Comparative to several commercial products, the potential use of micronutrient coated urea to reduce urea hydrolysis based NH3-volatilization losses is novel to-date. In this study, boron (B), iron (Fe), zinc (Zn) and copper (Cu) were coated on urea at their full or half recommended rates as (B)-half, (Fe)-half, (Zn)-half, (Cu)-half, (B)-full, (Fe)-full, (Zn)-full, (Cu)-full, (B+Fe)-half, (B+Zn)-half, (B+Cu)-half, (Fe+Zn)-half, (Fe+Cu)-half, (Zn+Cu)-half, (B+Fe)-full, (B+Zn)-full, (B+Cu)-full, (Fe+Zn)-full, (Fe+Cu)-full and (Zn+Cu)-full having gum-only coated urea as an internal control. Parallel to these, p-Phenylenediamine (PPD-0.2 %, 0.4 %, 0.6 %, 0.8 % and 1.0 %) and hydroquinone (HQ-0.5 %, 1.0 % and 2 %) coated urea treatments were also used with acetone-only coated urea as an internal control. Whereas the uncoated urea treatment was taken as an overall control. In pot experiment, the soil residual urea concentrations were increased by 2, 0.5, 1.85, 2.69 and 3.15 folds at 8 days after incubation (DAI), by 5.6, 1.89, 5.97, 0.54 and 6.23 folds at 12 DAI and by 119, 123, 155, 84 and 87 folds at 16 DAI under (B)-full, (B+Zn)-full, (Fe+Zn)-full, PPD-0.8 % and PPD-1.0 % coated urea treatments, respectively, as compared to uncoated urea. Among these five coating combinations, 54.26 % and 44.82 % bulb yield increments were observed under (Fe+Zn)-full and PPD-1 % coated urea, respectively, in comparison to uncoated urea in field experiment. However, the 33.33 % increment in nitrogen agronomic efficiency (NAE) and subsequent economic gains proved (Fe+Zn)-full coated urea application as a solution to address N losses in alkaline calcareous soils.

Integrated use of phosphorus sources, phosphate solubilizing bacteria, and rhizobium enhanced growth, nitrogen, and phosphorus uptake in chickpea

Expensive phosphatic fertilizers and limited phosphorus (P) availability hamper chickpea production in calcareous soils. Using cheaper P sources could reduce production costs. A field experiment assessed the combined effect of single superphosphate (SSP) and rock phosphate (RP) ratios (RP: SSP; 0:100, 25:75, 50:50, 75:25, and 100:0), phosphate solubilizing bacteria (PSB; with and without), and rhizobium (with and without) on chickpea growth and N and P uptake. RP:SSP ratios of 0:100 and 25:75 yielded higher plant height, growth rate, branch number, N concentration in straw and seeds, crude protein content, and P concentration and uptake in both straw and seeds compared to the 100:0 ratio. PSB application significantly improved chickpea growth, seed and straw N concentration, seed crude protein, and P uptake. Rhizobium-inoculated seeds also enhanced growth, N and P concentration in straw and seed, and P uptake. PSB enhanced rhizobium efficiency by promoting chickpea growth and increasing N and P concentration and uptake through solubilizing low-availability P from RP and SSP. Using RP:SSP (25:75) with PSB and rhizobium is recommended for enhanced chickpea growth and nutrient uptake in calcareous soils.

Relationship between calcium forms and organic carbon content in aggregates of calcareous soils in northern China

The agricultural soil organic carbon (SOC) pool is one of the most active C pools in terrestrial ecosystems, and soil aggregates are the main site of SOC fixation. Mineral sorption plays a crucial role in SOC accumulation. Calcium (Ca) is a typical soil mineral element that plays a crucial role in SOC accumulation and is fundamental for the formation of soil aggregates. Although Ca has been shown to regulate the stability of SOC, the relationship between different forms of Ca and SOC within aggregates in northern China remains unclear. In this study, we selected five soils (black soil, light chernozem soil, fluvo-aquic soil, sierozem soil, and loess soil) with different calcium carbonate (CaCO3) contents as the target materials. Water-stable aggregates were separated using the wet-sieving method. Soil respiration was measured using the static alkali absorption method (carbon dioxide [CO2] absorption by NaOH solution). The CaCO3 content was quantified using the CO2 gas volume method, and the continuous leaching method was used to analyze the different forms of Ca (water soluble-Ca, exchangeable-Ca, acid soluble-Ca, and bound to organic-Ca). In-situ field sampling was used to reveal the associations between different forms of Ca and SOC within aggregates. The results showed that besides the CaCO3 form, exchangeable-Ca (20.06 %–57.86 %) and bound to organic-Ca (26.69 %–73.91 %) were major Ca forms in calcareous soils. There was a nonsignificant negative correlation between CaCO3, acid soluble-Ca, and exchangeable-Ca and SOC in the bulk soil. However, there was a significant negative correlation among CaCO3, acid soluble-Ca, and exchangeable-Ca with SOC in macro-aggregates (> 0.25 mm) and micro-aggregates (0.25–0.053 mm). A 90-day incubation experiment was conducted to verify the previous speculations, which revealed that CaCO3 increased SOC mineralization and reduced the content of SOC, while enhancing the acid soluble-Ca and bound to organic-Ca content. In the treatment with added CaCO3, there was a negative correlation between acid soluble-Ca and bound to organic-Ca and SOC in bulk soil and macro-aggregates (> 0.25 mm). The effect of Ca2+ on SOC should not be ignored. Excessive Ca2+ may be converted into different forms of Ca to occupy the bonding sites for SOC on the surface of soil particles with silt and clay particles, forming a pseudo-aggregate structure, and the SOC traveling between soil particles, which is not conducive to SOC stabilization and accumulation.

Incorporation of compost and biochar enhances yield and medicinal compounds in seeds of water-stressed Trigonella foenum-graecum L. plants cultivated in saline calcareous soils

BackgroundThe combination of compost and biochar (CB) plays an important role in soil restoration and mitigation strategies against drought stress in plants. In the current study, the impact of CB was determined on the characteristics of saline calcareous soil and the productivity of fenugreek (Trigonella foenum-graecum L.) plants. The field trials examined CB rates (CB0, CB10 and CB20 corresponding to 0, 10, and 20 t ha‒1, respectively) under deficit irrigation [DI0%, DI20%, and DI40% receiving 100, 80, and 60% crop evapotranspiration (ETc), respectively] conditions on growth, seed yield (SY), quality, and water productivity (WP) of fenugreek grown in saline calcareous soils.ResultsIn general, DI negatively affected the morpho-physio-biochemical responses in plants cultivated in saline calcareous soils. However, amendments of CB10 or CB20 improved soil structure under DI conditions. This was evidenced by the decreased pH, electrical conductivity of soil extract (ECe), and bulk density but increased organic matter, macronutrient (N, P, and K) availability, water retention, and total porosity; thus, maintaining better water and nutritional status. These soil modifications improved chlorophyll, tissue water contents, cell membrane stability, photosystem II photochemical efficiency, photosynthetic performance, and nutritional homeostasis of drought-stressed plants. This was also supported by increased osmolytes, non-enzymatic, and enzymatic activities under DI conditions. Regardless of DI regimes, SY was significantly (P ≤ 0.05) improved by 40.0 and 102.5% when plants were treated with CB10 and CB20, respectively, as similarly observed for seed alkaloids (87.0, and 39.1%), trigonelline content (43.8, and 16.7%) and WP (40.9, and 104.5%) over unamended control plants.ConclusionsOverall, the application of organic amendments of CB can be a promising sustainable solution for improving saline calcareous soil properties, mitigating the negative effects of DI stress, and enhancing crop productivity in arid and semi-arid agro-climates.

Bio-Efficacy Evaluation of Herbicides for Weed Management in Rabi Onion

A field experiment entitled “Bio-efficacy evaluation of herbicides for weed management in rabi onion” was conducted at Weed Control Research Farm, Department of Agronomy, College of Agriculture, Junagadh Agricultural University, Junagadh (Gujarat) during the rabi season of 2021-22 on medium black calcareous soil. The experiment comprising 14 treatments was laid out in a randomized block design with three replications. The results revealed that next to weed-free treatment, tank-mix pendimethalin 450 g/ha + oxyfluorfen 120 g/ha as pre-planting fb HW at 40 DATP, tank-mix pendimethalin 450 g/ha + oxyfluorfen 120 g/ha as pre-planting fb pre-mix propaquizafop + oxyfluorfen 43.75+105 g/ha at 40 DATP and tank-mix pendimethalin 450 g/ha + oxyfluorfen 120 g/ha as pre-planting fb pre-mix quizalofop + oxyfluorfen 100 g/ha at 40 DATP control of complex weed flora, reduced population and dry matter of weeds and having less reduction in yield due to better control of weeds, less crop-weed competition, higher weed control efficiency.

Effects of Different Proportions of Ammonium Sulfate Replacing Urea on Soil Nutrients and Rhizosphere Microbial Communities

In order to investigate the effects of ammonium sulfate, an industrial by-product, on soil nutrients and microbial community when applied in different proportions instead of using urea as nitrogen fertilizer, a pot corn experiment was conducted. A completely randomized block experimental design was used, with a total of five treatments:CK (no fertilization), U10S0 (100 % urea), U8S2 (80 % urea + 20 % ammonium sulfate), U6S4(60 % urea + 40 % ammonium sulfate), and U0S10 (100 % ammonium sulfate). The basic physical and chemical properties of soil and the dry weight of maize plants were determined by conventional methods, and microbial sequencing was performed using the Illumina NovaSeq platform. The experiment results showed that:① In each growth stage of maize, the pH of soil treated with fertilization (7.85-8.15) was decreased compared with that of CK (8.1-8.21), and the pH showed a decreasing trend with the increase in ammonium sulfate content. ② The soil available nitrogen content increased gradually with the increase in the ammonium sulfate ratio at each growth stage of maize. Compared with that in the CK and U10S0 treatments, the ratio in the U0S10 treatment increased 30.56 % to 63.68 % and 13.22 % to 38.43 %, respectively. The variation trend of organic carbon content was opposite to that of available nitrogen (U8S2 > U6S4 > U0S10), and the addition of ammonium sulfate was still higher than that of U10S0 at other growth stages except for the seedling stage. ③ The protease activity of all fertilization treatments was higher than that of the control, and the protease activity was gradually enhanced with the continuous growth of corn and the increase in the ammonium sulfate ratio. The protease activity of the U0S10 treatment was higher than that of the U10S0 treatment at each growth stage of corn, which increased by 10.54 %-100 %. Soil sucrase activity ranged from 0.04 to 0.24 mg·(g·24 h)-1, and those in the U0S10 treatments were significantly higher than those in the U10S0 and CK treatments at all growth stages, increasing by 20.32 % to 99.16 % and 24.31 % to 79.33 %, respectively. ④ The species abundance of bacteria and fungi in maize rhizosphere under all fertilization treatments were lower than those under the CK treatment, followed by those under the U10S0 treatment. The species diversity trend of the bacterial community in the three treatments with ammonium sulfate replacing urea were U8S2 > U0S10 > U6S4, and that of fungi were U6S4 > U8S2 > U0S10. ⑤ The maize dry weight of the U10S0 treatment and U0S10 treatment was the highest, which was 39.47 % and 36.16 % higher than that of the CK treatment, respectively, but the difference was not significant. The Pearson model showed that the species abundance and diversity of soil rhizosphere fungi and bacteria were affected by relevant environmental variables, among which pH value and soil available nitrogen content were the most important factors affecting microbial diversity. In conclusion, when corn planting in calcareous brown soil, replacing urea with a certain proportion of ammonium sulfate can improve soil nutrients more than urea alone, which affects the growth and rhizosphere microbial community of corn to a certain extent and has a greater yield.

Effects of Freeze-Thaw Cycles on Bioaccessibilities of Polycyclic Aromatic Hydrocarbons.

The bioaccessibility of particle-bound hydrophobic organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), and the factors influencing their re-release are crucial for assessing potential human health risks via inhalation and hand-mouth exposure. However, the mechanisms by which various factors affect the re-release of PAHs in body fluids, particularly in response to environmental changes like freeze-thaw cycles, remain unclear. To obtain a better understanding, an in vitro method was employed to investigate the re-release processes of PAHs from different soil types (ferrallitic soil and calcareous soil) in simulated body fluids (simulated lung fluid and simulated saliva) under varying freeze-thaw conditions (0, 15, and 30 cycles). The findings indicated that the bioaccessibilities of phenanthrene and pyrene decreased with the frequency of freeze-thaw cycles, which were constrained by soil nature and simulated body fluids compositions as well. Additionally, this study observed that the portion of reversible adsorption of PAHs declined after exposure to freeze-thaw cycles in a nonlinear manner, suggesting that the potential human health risk associated with PAHs could be mitigated due to the "aging effect" which occurred as PAHs became less bioaccessible over time. These results underscore the importance of considering the characteristics of pollutants, body fluids, and environmental media when conducting a precise assessment of the human health risks posed by such contaminants.