Higher Soil Organic Matter Research Articles

Droplet size and physicochemical property effects on herbicide efficacy of pre-emergence herbicides in soybean (Glycine max (L.) Merr).

Unlike post-emergence herbicides (POSTs), little is known about droplet size effect on pre-emergence herbicide (PRE) efficacy. Four nozzle types were used to apply different PRE herbicides on eight soybean fields in Missouri and Mississippi in 2017 and 2018, respectively. Pendimethalin, metribuzin, clomazone, imazethapyr and pyroxasulfone were selected based on their physicochemical characteristics (adsorption, volatility and solubility) and were sprayed using XR11002, ULD12002, TTI6011002, and TTI11002 nozzles. The XR nozzle produced the smallest droplet size (DV0.5 ), 204 μm, followed by the ULD, TTI60 and TTI with DV0.5 of 468, 646, and 794 μm, respectively. Droplet size, spray coverage, nozzle type or physicochemical characteristics showed no effect on PRE herbicide efficacy, except in the Monroe County, MS, field, with pendimethalin. The TTI60 twin fan nozzle enhanced pendimethalin weed control (up to 91%) in comparison with pendimethalin sprayed with the TTI nozzle (64%), in a high organic matter (OM) soil composed of large soil clods and high weed pressure. It was hypothesized that improved herbicide penetration assisted by the TTI60 dual fan pattern increased herbicide-moisture contact and clod coverage by the herbicide. Under soils with higher OM content (>2%) pendimethalin weed control was reduced. In soils with low OM (<0.7%), low cation exchange capacity (CEC) (<13.1%) and rainfall of 12.2mm within 3days after application, metribuzin also resulted in reduced weed control. The results indicate that droplet size does not affect PRE herbicide efficacy regardless of physicochemical herbicide properties including adsorption, volatility and solubility. © 2019 Society of Chemical Industry.

Impacts of low-level liming on soil respiration and forage production in a fertilized upland grassland in Central France

Liming is a common agricultural practice for improving acidic soils, but the addition of liming materials may also promote soil carbon dioxide (CO2) emissions, with adverse effects for climate regulation. In grasslands, current understanding of liming impacts on greenhouse gas emissions is limited by a lack of field data on liming and soil respiration. Here we used a two-year field trial and in situ chamber measurements to evaluate the effects of repeated, low-level liming on soil CO2 emissions from an acidic managed grassland with high soil organic matter content. Soil pH, temperature and moisture were measured during the experiment, as well as microbial and plant biomass, in order to assess possible liming-induced changes to drivers of grassland carbon cycling. Soil CO2 emissions showed significant variation during the two-year study, driven primarily by fluctuations in soil temperature. Soil respiration rates were unaffected by liming treatment, despite significant lime-induced increases in soil pH. Liming was associated with a decrease in biomass produced per gram nitrogen, as well as a decrease in forage C:N in the second year and transient decreases in microbial C:N, but neither plant nor microbial biomass showed significant responses to liming addition. Collectively, our results suggest that positive effects of low-level liming on plants and soil are not offset by increases in soil CO2 emissions in situ, highlighting the potential for sustainable liming practices in fertilized grasslands.

Sorption and Desorption Characteristics of Tylosin in Three Louisiana Soils.

The macrolide antibiotic tylosin is widely used in animal production, but its environmental fate is not fully understood. Objectives of this study were to determine the effect of pH on tylosin A sorption and desorption in three sandy loam soils from Louisiana, USA, that had long histories of poultry waste application, to model sorption and desorption, and to estimate the effect of high soil organic matter on sorption. Twenty-four-hour sorption isotherms (5 to 200 mg L in 0.01 M CaCl) at pH 4.5, 6.0, and pH 7.5 were described by the Freundlich model. Desorption from the 200-mg L set at constant pH by 10 24-h extractions with 0.01 M CaCl recovered 43 to 98% of the added tylosin A, and further desorption with methanol increased recovery from 66 to 100%. Single-point distribution coefficient, as a function of pH from 4 to 9 in 0.01 M CaCl exhibited maxima from pH 6 to 7, reflecting increasing sorption of the positively charged form with increasing pH up to about the pKa. The data were well described, modeling pH-dependent negative charge according to Henderson-Hasselbalch along with tylosin speciation. Using soil from which organic matter had been removed by HO gave three to six times greater K at pH 6 to 7, but without or with reduced maxima. The data could be approximately described without invoking pH-dependent surface charge. Further study is needed to confirm whether an increase in soil organic matter with poultry waste application decreases tylosin sorption, thus increasing environmental risk.

Spatio-vertical characterization of the BTEXS group of VOCs in Chinese agricultural soils

Ubiquitous contamination of the BTEXS (benzene, toluene, ethylbenzene, xylene, and styrene) group in soils is a significant concern for ecological safety. However, comprehensive spatio-vertical survey of the BTEXS group on a national scale is rare to date. Using a static headspace gas chromatography–mass spectrometry method (HS-GCMS), this study performed a quantitative analysis of BTEXS levels in soils from Chinese rural areas in 2013 and 2016. The median ∑BTEXS concentrations in surface soils in 2013 and 2016 were 37.5 and 34.4 ng g−1 dry weight, respectively. Toluene was the dominant pollutant, accounting for approximately 41.6% and 32.1% of the total levels. BTEXS contamination was higher in Shanxi province, Northeast China, and Yunnan-Guizhou Plateau compared to the other regions. Vertically, toluene, m,p′-xylene and o′-xylene concentrations were significantly higher in the top soil layer (0–15 cm) and decreased significantly with increasing soil depth (p < 0.05). Higher soil organic matter was significantly associated with higher BTEXS concentrations of sampling site. BTEXS was also enhanced at sites with higher elevations and lower temperature due to global distillation effects. The findings of this study could help decision-makers to protect against BTEXS contamination in rural areas. These findings provide a basis for further study of the mechanism of BTEXS migration and transport in large-scale environment. CapsuleSpatio-vertical distribution, influence factors, exposure risks of BTEXS in soils from Chinese agricultural region was studied.

Effects of Biostimulant and Organic Amendment on Soil Properties and Nutrient Status of Lactuca Sativa in a Calcareous Saline-Sodic Soil

Many studies have reported the advantages of alternative agricultural practices using more environmentally-friendly products to ameliorate the negative impacts of salinity and sodicity, but few have examined the effects of these products in saline-sodic soils with high soil organic matter (SOM) content. The objective of this research was to examine the effect of biostimulant (Actiwave) and organic amendment (Corresal Plus) product on soil properties and on the nutrient content of lettuce (Lactuca sativa L.). A pot study with a calcareous saline-sodic soil was conducted using a completely randomized design with six treatments: Two rates of the biostimulant (ActA: 10 l ha−1 and ActB: 15 l ha−1), three rates of the amendment (CorA: 10 l ha−1, CorB: 15 l ha−1 and CorC: 50 l ha−1) and a control treatment. The application of Actiwave reduced soil electrical conductivity (E.C.), soil exchangeable Na and soluble Cl. It also increased leaf N and Zn content. On the other hand, the higher dose of Corresal Plus reduced soil pH and soil exchangeable Na and increased soil NO3-N. Additionally, CorC treatment decreased leaf Cl and increased leaf N content enhancing lettuce growth.. However, in most cases, the two products did not provoke significant changes indicating that their positive effects were probably masked by the high SOM content and the calcareous nature of the studied soil.

Effect of different rotation systems on mercury methylation in paddy fields

Rice (Oryza sativa) paddy is the hotspot of mercury (Hg) methylation. Given distinct influences of rotation systems on the physicochemical properties of paddy soils, we hypothesized different rotation systems in rice paddies inducing a large difference in Hg methylation. Here, we investigated Hg species distribution, dissolved organic matter (DOM) features, and Hg methylation in five rotation systems (Other farmland newly reclaim into paddy field, i.e., NR-R; Drain the water in winter, i.e., DW-R; Flooding in winter, i.e., FW-R; Rape-Rice rotation, i.e., Ra-R; Wheat-Rice rotation, i.e., Wh-R) of paddy fields to identify such hypothesis. Results shown that FW-R had the strongest Hg methylation, followed by Ra-R and Wh-R, then DW-R, and finally NR-R. We further found that much higher soil organic matter (SOM) and organo-chelated Hg (Hg-o) from straw residues and root exudates were the main cause for the greater Hg methylation in FW-R, Ra-R and Wh-R. This was because the protein-like fraction of SOM facilitated the net production of methyl Hg (MeHg), meanwhile the humin-like fraction had a strong affinity to MeHg in paddy soils. Therefore, it can be concluded that paddy soil under DW-R was the optimum pattern in order to reduce the occurrence of Hg methylation. However, paddy soils under Ra-R and Wh-R were the recommendable patterns if the productivity of paddy fields was considered.

Do Grass and Legume Cover Crops Improve Soil Properties in the Long Term?

Cover crops (CCs) are generally perceived to improve soil properties, yet available research suggests that CC impacts, particularly on physical properties, can be inconsistent. Length of time after CC adoption and CC species such as grass and legume CCs could differently influence CC effects, but experimental data are few. This study quantified 12‐yr cumulative impacts of grass CCs including cereal rye (Secale cereale L.) and grain sorghum [(Sorghum bicolor (L.) Moench] and legume CCs including Austrian winter peas (Pisum sativum L.) and soybean (Glycine max L.) CCs on soil physical and fertility properties under long‐term (∼30 yr) continuous no‐till corn (Zea mays L.)–soybean–winter wheat (Triticum aestivum L.) rotation on a silty clay loam in the western Corn Belt. Legume CCs did not alter soil properties, but grass CCs improved soil aggregation and increased organic matter concentration although water infiltration, water retention, plant available water, and most soil fertility properties were unaffected. Grass CCs increased the proportion of large water‐stable aggregates (2–8.0 mm) by 31 to 45% in the 0‐ to 15‐cm depth. Grass CCs also increased mean weight diameter of water‐stable aggregates by 34% and organic matter concentration by 11% in the upper 7.5‐cm depth. Results indicate that grass CCs improved some soil properties unlike legume CCs. Long‐term (15 yr) no‐till use before CC adoption, fine texture, and high organic matter level of the soil may explain the small grass CC and no legume CC effects. Overall, grass CCs impacted some soil properties but legume CCs had no effects in this silty clay loam after 12 yr.Core Ideas Legume cover crops (CCs) had no effects on soil properties after 12 yr. Grass CCs increased aggregation and organic matter but did not affect water infiltration, retention, and availability. Grass CCs had more impact on soil properties than legume CCs. Long‐term (15 yr) no‐till before CC adoption, fine texture, and relatively high soil organic matter may explain the small CC effects.

Extraction Method Development for Quantitative Detection of Silver Nanoparticles in Environmental Soils and Sediments by Single Particle Inductively Coupled Plasma Mass Spectrometry.

For understanding the environmental behavior and toxicity of Ag nanoparticles (Ag-NPs), a quantitative method for characterizing the AgNPs in soils and sediments is urgently needed. In this study, we validated a previously developed extraction method by optimizing the extraction of silver nanoparticles from soil and sediment samples to which engineered AgNPs had been added. The samples were analyzed by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Initially, different extraction conditions were evaluated to validate the optimal extraction procedure. Then the optimal extraction procedure was applied to environmental soil and sediment samples spiked with AgNPs. The extraction data for Ag-NPs with sizes below 30 nm was not shown due to the particle size detection limit of the SP-ICP-MS method (∼20 nm). The number concentrations of Ag particles extracted from different environmental soils and sediments matrices were in the range of (12 ± 1-23 ± 1) × 107 particles/g soil. Similarly, 53.4-100.0% of the particulate Ag mass was recovered. For the relatively low Ag mass recovery of Guiyu agricultural soil, the Ag mass recovery shows great improvement (from 53.4 to 105.8%) by the soil dilution using SiO2. The optimal method was validated to be feasible for extracting Ag-NPs from environmental soils and sediments, except for the soil with high soil organic matter (SOM) content. The SiO2 dilution of soil provides a promising way to promote the extraction of Ag-NPs in soil (or sediment) with high SOM content, which could further promote the study on the environmental behavior and toxicity of Ag-NPs in soil and sediment environment.

Role of Nutrient-Enriched Biochar as a Soil Amendment during Maize Growth: Exploring Practical Alternatives to Recycle Agricultural Residuals and to Reduce Chemical Fertilizer Demand

Recycling and value-added utilization of agricultural residues through combining technologies such as anaerobic digestion and pyrolysis could double the recoverable energy, close the nutrient recycle loop, and ensure cleaner agricultural production. This study assessed the beneficial application of biochar to soil to recycle digestate nutrients, improve soil quality, and reduce conventional chemical fertilizer. The addition of digestate-enriched biochar improved soil quality as it provided higher soil organic matter (232%–514%) and macronutrients (110%–230%) as opposed to the unenriched biochar and control treatments. Maize grown in soil amended with digestate-enriched biochar showed a significantly higher biomass yield compared to the control and non-enriched biochar treatments but was slightly lower than yields from chemical fertilizer treatments. The slightly lower yield (20%–25%) achieved from digestate-enriched biochar was attributed to slower mineralization and release of the adsorbed nutrients in the short term. However, digestate-enriched biochar could in the long term become more beneficial in sustaining soil fertility through maintaining high soil organic matter and the gradual release of micronutrients compared to conventional chemical fertilizer. Positive effects on soil micronutrients, macronutrients, organic matter, and biomass yield indicates that enriched biochar could partly replace chemical fertilizers and promote organic farming in a circular economy concept.

Evaluation on activation energy of deposited clay based on thermo-gravimetric analysis (TGA) and four kinetics models

In order to evaluate and compare the accurate activation energy variations of two kinds of deposited clays (i.e. non-organic clay and organic clay), thermo-gravimetric analysis (TGA) was firstly conducted to study the reaction characteristics of the two clay samples. Two periods of weight losses were observed according to each TGA curve for both clay samples. The first period happened due to water evaporation, while the second period was mainly caused by the composition reactions of clay minerals, especially influenced by the de-hydroxylation of kaolinite. An obvious phenomenon is that the organic clay with a high soil organic matter (SOM) has a higher activity energy. Then, four common kinetics models [i.e. the Coats-Redfern method, the Doyle integral method, the maximum rate method, and the distributed activation energy model (DAEM)] were used to calculate and compare the activation energy values. And the Doyle integral method and the DAEM method are considered as two recommended models to analyze the activation energy performance during thermal treatment. Some interesting conclusions can be summarized as: (1) The multi-period reactions of deposited clays during the heating process are common, especially for organic clay. It would be beneficial knowing its biomass resource feasibility concerning the second weight loss; (2) The high SOM has a significant influence on the potential energy unitization of deposited clays, while the variations of activity energy for deposited clays are influenced by the mineral compositions and microstructure features; (3) It is possible to evaluate the accurate activity energy of deposited clays combined with TGA tests and two recommended models (i.e. the Doyle integral method and DAEM method).

Dynamics of pH, Ferrum and Mangan, and Phosphorus on Newly Opened Paddy Soil having High Soil Organic Matter on Rice Growth

Research had been carried out at the Research and Soil Testing Laboratory and Greenhouse of Soil Research Institute, Bogor using newly opened paddy soil from Pesisir Selatan districts, West Sumatra (one year old). Total treatments tested were 12 which were combination of farmer rate, NPK recommendation (½×; ¾×; 1½×), straw compost (½×; ¾×; 1½×), and dolomite. The trial was conducted using a completely randomized design with three replications. This research had been prepared in two units, one unit for observing plant response to nutrient management and another unit for incubation trial with the same treatment placed in the greenhouse. Rice cultivar used was IR-42 in accordance to the preferred varieties of local farmers. The sampling method for measuring the solubility of Fe2+ and Mn2+, as well as the availability of PO43- was by centrifuge 50 g mud samples from the incubation pots then separated clear extract using filter paper. The observation results on dynamics of pH, Fe2+, Mn2+ and PO4-3 mainly occured in 1 to 14 days after submerging (incubation). After 14 days soil reaction had reached thermodynamic sequence of oxidation-reduction processes, the PO43- more available and pH of the soil reached the peak. The optimum dose of NPK fertilizer obtained 0.875 NPK or equal to 175 kg of urea, 87.5 kg of SP-36 and 87.5 kg KCl ha-1. The highest number of hills achieved from straw compost treatment 1½ organic matter (OM) or 3 tons with an increase of 20%. Application of ameliorant dolomite increased the number of tillers about 2-3%, but insignificantly different with no dolomite treatment.

Placing human landscape legacies in a dynamic systems framework.

Placing human landscape legacies in a dynamic systems framework.

Long-term effects of different planting patterns on greenhouse soil micromorphological features in the North China Plain

Soil structure represents a basis for soil water retention and fertiliser availability. Here, we performed a micromorphological analysis of thin soil sections to evaluate the effects of 10 years of organic planting (OPP), pollution-free planting (PFP), and conventional planting (CPP) on greenhouse soil structure in the North China Plain. We also analysed soil bulk density, soil organic matter (SOM), and wet aggregate stability. The CPP soil microstructure included weakly separated angular block or plate forms and weak development of soil pores (fissured or simply accumulated pores) with the highest bulk density (1.33 g cm−3) and lowest SOM (26.76 g kg−1). Unlike CPP, the OPP soil microstructure was characterised by highly separated granular and aggregated structures and an abundance of plant and animal remains. OPP was associated with the highest total porosity (55.4%), lowest bulk density (1.17 g cm−3), and highest SOM (54.81 g kg−1) in the soil surface layer. OPP also improved the ventilation pore content (proportion of pores >0.1 mm, 44.09%). OPP aggregates showed different hierarchies of crumb microstructure and higher mean weight diameter and geometric mean diameter values than did CPP. These results confirm the benefits of long-term OPP for soil structure and quality in the greenhouse.

Impact of Long-Term Reclaimed Water Irrigation on the Distribution of Potentially Toxic Elements in Soil: An In-Situ Experiment Study in the North China Plain.

The widespread use of reclaimed water has alleviated the water resource crisis worldwide, but long-term use of reclaimed water for irrigation, especially in agricultural countries, might threaten the soil environment and further affect groundwater quality. An in-situ experiment had been carried out in the North China Plain, which aimed to reveal the impact of long-term reclaimed water irrigation on soil properties and distribution of potentially toxic elements (As, Cd, Cr, Hg, Zn and Pb) in the soil profile as well as shallow groundwater. Four land plots were irrigated with different quantity of reclaimed water to represent 0, 13, 22 and 35 years’ irrigation duration. Pollution Load Index (PLI) values of each soil layer were calculated to further assess the pollution status of irrigated soils by potentially toxic elements (PTEs). Results showed that long-term reclaimed water irrigation caused appreciable increase of organic matter content, and might improve the soil quality. High soil organic matter concentrations conduced to high adsorption and retention capacity of the soils toward PTEs, which could reduce the risk of PTEs leaching into deep layers or shallow groundwater. Highest levels of Cr, Pb and Zn were observed at 200–240 cm and 460–500 cm horizons in plots. Longer irrigation time (35 years and 22 years) resulted in a decreasing trend of As, Cd, Hg, Pb and Zn in lower part of soil profiles (>540 cm) compared with that with 13-years’ irrigation years. Long-term reclaimed water irrigation still brought about increases in concentrations of some elements in deep soil layer although their content in soils and shallow groundwater was below the national standard. Totally speaking, proper management for reclaimed water irrigation, such as reduction of irrigation volume and rate of reclaimed water, was still needed when a very long irrigation period was performed.

Perennial crop legacy effects on nematode community structure in semi-arid wheat systems

The effects of diversifying wheat-based cropping systems in the Northern Great Plains (NGP) on soil chemical and physical properties is well documented: better soil tilth, improved water infiltration, and higher soil organic matter with crop rotations. However, the impact of crop rotations on soil biology is not as well understood. Nematode communities reflect soil quality and are directly observable, readily quantifiable, and occupy most of the consumer trophic levels in the soil food web. Within more humid climates, the community structure is better characterized to make associations with soil health and crop management strategies, but little is known about their community structure in semiarid regions such as the NGP. For this study, soils under contrasting cropping systems were sampled in the 15th year of a long-term study to quantify and assess the nematode community. Prior to planting, wheat-chemical fallow had a higher total nematode population than that of wheat-tilled fallow (P < 0.05). A wheat-pulse system with a history of crop perennation had a greater abundance of uncommon, omnivorous nematodes than a wheat-pulse system without a prior history of crop perennation. However, plant parasitic nematodes also were higher in abundance under the converted perennial system. Our results suggest that reducing soil disturbance and including a perennial component to cropping systems will foster a more diverse and balanced nematode community under semiarid dryland conditions, but potentially at the expense of increased plant parasitic nematode pressure.

Soil Chemical Analysis of Kazi and Kazi Organic Tea Garden and Compared to Ordinary Tea Gardens of Bangladesh

Tea is grown in Bangladesh under marginal climatic and soil conditions. Its production is greatly influenced by many physical, chemical, biological and natural factors. The increasing land use intensity without adequate and balanced use of chemical fertilizers and with little or no use of organic manure has caused severe fertility deterioration of our soils resulting in stagnating or even declining of crop productivity. The need of the hour is to achieve substantially higher crop yield than the present yield levels from our limited land resources on a sustainable basis. A feasibility study was carried out of one and only organic tea garden namely Kazi & Kazi Tea Estate at Panchaghar and compared to ordinary tea gardens located at Sylhet namely Zareen Tea Estate, Nurjahan Tea Estate and Malnichara Tea Estate as secondary data to investigate the fertility status of soil. Results of the present study showed that soil solutions were acidic in nature in all seasons. Medium to high soil organic matter, medium to high available iron and phosphorous, and low availability of potash showed that soils were not sufficiently fertile for crop production. Student t-test values of all the parameters with control sample showed statistically significant results for SOM and available P. The critical values have been fixed at 0.1% for N and 1% for OM, 10 μg/g for P, 80 μg/g for K, 25 μg/g for Mg, 90 μg/g for Ca, 2 μg/g for Zn and 20 μg/g for S. The nutrient status is much higher in Kazi & Kazi organic tea estate in compared to other ordinary tea estates in Bangladesh.

Relationship Between Soil Properties and Nitrogen Mineralization in Undisturbed Soil Cores from California Agroecosystems

ABSTRACTSoil nitrogen (N) mineralization rates from different agricultural regions in California were determined and related to soil properties. Undisturbed soil cores were sampled in spring from 57 fields under annual crop rotations and incubated at 25℃ for 10 weeks. Soil properties varied across and within regions, most notably those related to soil organic matter (SOM), with total soil carbon ranging from 6 to 198 g kg−1. Multivariate linear regression was used to select soil properties that best predicted N mineralization rates. Regression models with a good fit differed between soils with high and low SOM contents, but generally included a measure of SOM quantity, its quality as well as soil texture or mineralogy. Adjusted R2 values were 0.95 and 0.60 for high and low SOM soils, respectively. This study has shown that information on soil properties can contribute to better estimates of N mineralization in soils of contrasting characteristics.

Effects of fertiliser on phosphorus pools in soils with contrasting organic matter content: A fractionation and path analysis study

With the intensification of agricultural production in many European countries, more marginal soils with elevated organic matter (OM) content are being brought into cultivation. However, little is known about the transformations in the constituent phosphorus (P) pools of organic soils receiving applications of P fertiliser. Soil P fractions were measured before and after receiving fertiliser in a controlled experiment to determine the change in the soil pools and path analysis was used to evaluate the relationships between P pools. In this study, P deficient soils ranging in OM content from 8 to 76%, were placed in large pots, planted with ryegrass and subjected to P fertiliser applications ranging from 10 to 145 kg ha−1, and monitored over an eight-month study period. High OM soils had a diminished ability to build-up the labile pool from freshly applied P, with relatively low increases up to 200% of the initial value, compared to mineral soils in which the labile pool increased to >2500% of the initial concentration. Additionally, organic soils had higher P uptakes in the grass yield than mineral soils, indicating a higher availability of added P in the soil solution than mineral soils due to their limited sorption ability. In general, there was a reduction in the organic P pool over applications from 0 to 55 kg ha−1, which was indicative of partial mineralization, but was followed by an accumulation of added P over applications from 55 to 145 kg P ha−1. The residual P pools did not build-up with P additions, but data indicated the occurrence of mineralization in most of the soils with decreases of around 40% of the initial concentrations. Organic and residual pools therefore displayed potential to supply P to more labile P pools across all soils of this study. Path analysis indicated that applied P was the only source of labile P in the soil with the highest OM content, leaving it dependent on continuous P applications to supply P for productivity, whereas in the rest of the soils there were interrelations between the non-labile and labile pools. Low pH strongly immobilised the applied P and should be corrected before the initiation of any fertilisation program, even in soils deficient in plant available P. The results demonstrated that P added as fertiliser to organic soils does not accumulate as in mineral soils, which may leave them susceptible to P losses in surface runoff. Therefore, organic soils under agricultural production located in high status catchments should receive low P applications and only during periods with low probability of precipitation to minimise the possibility of P exports to receiving waters.

Mechanisms of Interaction between Persulfate and Soil Constituents: Activation, Free Radical Formation, Conversion, and Identification.

Persulfate-based in situ chemical oxidation (ISCO) for soil remediation has received great attention in recent years. However, the mechanisms of interaction between persulfate (PS) and soil constituents are not fully understood. In this study, PS decomposition, activation, free radical formation and conversion processes in 10 different soils were examined. The results showed that soil organic matter (SOM) was the dominant factor affecting PS decomposition in soil, but Fe/Mn-oxides were mainly responsible for PS decomposition when SOM was removed. Electron paramagnetic resonance (EPR) spectroscopy analysis showed that sulfate radicals (SO4•-) and hydroxyl radicals (•OH) generated from PS decomposition subsequently react with SOM to produce alkyl-like radicals (R•), and this process is dependent on SOM content. R• and SO4•-/•OH radicals predominated in soil with high and low SOM, respectively, and all three radicals coexist in soil with medium SOM. Chemical probe analysis further identified the types of radicals, and R• can reductively degrade hexachloroethane in high SOM soil, while SO4•- and •OH oxidatively degrade phenol in low SOM soil. These findings provide valuable information for PS-ISCO, and new insight into the role of SOM in the remediation of contaminated soil.

English

Biochar incorporation as a soil amendment has been shown to enhance soil quality. However, there has been conflicting reports on its short term effects on C and N mineralization and microbial biomass. An incubation experiment was conducted to determine the effects of three different levels (0.5, 1 and 2%) of biochar on carbon mineralization, soil organic carbon, nitrogen mineralization, microbial biomass and total nitrogen from mollisols of two different organic matter (high organic matter soil and low organic matter soil) levels. The experiment consisted of four treatments (Soil, Soil + 0.5% biochar, Soil + 1% biochar and Soil + 2% biochar) and each was replicated three times. Overall, soil respiration rate was reduced by biochar additions over a 100-day period. Two percent biochar application rate showed greatest CO2-C reduction. Soil respiration in high organic matter soil was higher than low organic matter soil. NO3--N level was reduced by biochar addition in both high and low organic matter soils. Control (Soil) of the high organic matter soil showed the highest NO3--N (33.79 mg kg-1) and NH4+-N (7.23 mg kg-1) values at 70 days. The total nitrogen was increased by biochar additions; 1 and 2% application rates showed the highest total nitrogen values. Biochar additions also increased soil microbial biomass carbon and soil microbial biomass nitrogen of both soils. Key words: Biochar, C mineralization, N mineralization, microbial biomass.