Increased Soil Organic Matter Research Articles

Pinpointing the distinctive impacts of ten cover crop species on the resident and active fractions of the soil microbiome

Cover crops are used in agriculture to minimize soil erosion, prevent nutrient leaching and increase soil organic matter content. Cover crops can also be grown to stimulate the soil microbial community to improve soil biological conditions. Despite their widespread use, little is known about the impact of different cover crop species on the composition and activity of the soil microbiome. Here we investigate the effect of distinct cover crop species on the rhizosphere microbiome and characterize both the resident (ribosomal (r)DNA-based) and the potentially active (rRNA-based) fractions of the bacterial, fungal, protist and metazoan communities in the cover crops rhizosphere. We conducted a field experiment using 70-l bottomless containers in which we grew ten monocultures of commonly used cover crop species belonging to five plant families, and an unplanted control treatment (fallow). The total DNA and RNA were extracted from soil and the bacterial, fungal, protistan and metazoan communities were characterized using Illumina MiSeq sequencing. We found that all cover crop species significantly impacted the resident and the potentially active microbial communities in their rhizospheres. Cover crops exerted distinct selection strengths on the native microbial communities. For individual cover crops, the impacts on the resident and the potentially active microbial communities differed while showing similar overall tendencies. Oilseed radish (Brassicaceae) was shown to provoke the strongest microbial shifts, in part attributable to a promotion of the bacterial family Pseudomonadaceae and a repression of Microascaceae in the rhizosphere. Lentil (Fabaceae) induced a widespread stimulation of fungal taxa, including Trichocomaceae and fungal members of the Glomerales order, whereas black oat and hybrid ryegrass (both Poaceae) gave rise to relatively mild changes in the soil microbial communities. Analyses of rRNA-based rhizobiome data revealed that, except for phacelia, all cover crops induced an increase in microbial network complexity as compared to the fallow control. Data presented here provide a broad baseline for the effects of cover crops on four organismal groups, which may facilitate future cover crop selection to advance soil health.

Vapor-phase biodegradation and natural attenuation of petroleum VOCs in the unsaturated zone: A microcosm study

Traditional natural attenuation studies focus on aqueous process in the saturated zone while vapor-phase biodegradation and natural attenuation in the unsaturated zone received much less attention. This study used microcosm experiments to explore the vapor-phase biodegradation and natural attenuation of 23 petroleum VOCs in the unsaturated zone including 7 monoaromatic hydrocarbons, 6 n-alkanes, 4 cycloalkanes, 3 alkylcycloalkanes and 3 fuel ethers. We found that monoaromatic hydrocarbon vapors were easily attenuated with significantly high first-order attenuation rates (9.48 d−1-43.20 d−1) in live yellow earth, of which toluene and benzene had the highest rates (43.20 d−1 and 28.32 d−1, respectively). The 13 aliphatic hydrocarbons and 3 fuel ethers all have relatively low attenuation rates (<0.54 d−1) in live soil and negligible biodegradation contribution. We explored the effects of soil types (black soil, yellow earth, lateritic red earth and quartz sand), soil moisture (2, 5, 10, and 17 wt%) contents and temperatures (4, 15, 25, 35 and 45 °C) on the vapor attenuation. Results showed that increasing soil organic matter (SOM) content, silt content, porosity and soil microorganism numbers enhanced contaminant attenuation and remediation efficiency. Increasing moisture content reduced the apparent first-order biodegradation rates of monoaromatic hydrocarbon vapors. The vapor-phase biodegradation had optimal temperature (∼25 °C in yellow earth) and increasing or decreasing temperature slowed down biodegradation rate. Overall, this study enhanced our understanding of vapor-phase biodegradation and natural attenuation of petroleum VOCs in the unsaturated zone, which is critical for the long-term management and remediation of petroleum contaminated site.

Effects of fermented and supplemented chicken manure on the nutrient management aspects of an apple orchard

AIt is a huge challenge for farmers worldwide to successfully increase the organic matter content of their soils and improve their water balance at the same time. Therefore, the main aim of the study is to develop and test organic-based nutrient composite materials that can be successfully used by farmers to increase soil organic matter content, improve water management parameters and implement water-efficient technologies. The study was performed in the orchard of the Institute of Horticultural Science of the University of Debrecen in Hungary (Debrecen-Pallag). The experiment was set up in a ten-year-old apple (Malus domestica ‘Pinova’) orchard. In the trial, fermented poultry manure and superabsorbent polymers (SAP) were used at different doses to study their effects on soil properties and fruit quality. Applied composite materials increased the nitrate and organic nitrogen content of the soil. Treatments did not affect the sugar content of the fruits but significantly and positively affected the individual fruit weight and the titratable acidity of the fruits.

Accumulation, migration and health risk of trace metals in a soil-strawberry-human system of the Yangtze River Delta region, China

Growing concern has been paid to metals in soil-strawberry system. In contrast, few attempts have been made to investigate bioaccessible metals in strawberries and further assess health risk based on bioaccessible metals. Moreover, the connections between soil parameters (e.g. soil pH, organic matter (OM), total and bioavailable metals) and metal transfer in soil-strawberry-human system still need to be systematically investigated as well. Considering that strawberries are extensively grown under plastic-shed conditions in China, a total of 18 paired plastic-shed soil (PSS) and strawberry samples were taken from the strawberry bases located in the Yangtze River Delta of China as a case study to assess accumulation status, migration and health risk of Cd, Cr, Cu, Ni, Pb, and Zn in the PSS-strawberry-human system. Overall, heavy application of organic fertilizers induced accumulation and contamination of Cd and Zn in PSS. In particular, 55.6% and 44.4% of PSS samples had considerable and moderate ecological risk caused by Cd, respectively. Despite no metal pollution in strawberry, PSS acidification mainly caused by high nitrogen input promoted Cd and Zn uptake by strawberry and enhanced bioaccessible concentrations of Cd, Cu, and Ni. In contrast, the increased soil OM caused by organic fertilizer application decreased Zn migration in PSS-strawberry-human system. Additionally, bioaccessible metals in strawberries induced limited non-cancer and cancer risk. To mitigate accumulation of Cd and Zn in PSS and metal transfer in the food chain, feasible fertilization strategies should be developed and carried out.

Differential Responses of Soil Microbial N-Cycling Functional Genes to 35 yr Applications of Chemical Fertilizer and Organic Manure in Wheat Field Soil on Loess Plateau

Fertilization changes nitrogen (N)-cycling processes and associated microbial communities in agricultural ecosystems. However, the long-term responses of N-cycling potential and microbial functional genes to different fertilization sources remain unclear. Soil samples were collected to a depth of 20 cm under winter wheat applied annually with N fertilizer (NF), organic manure (OM), N fertilizer plus organic manure (NM), and a control without fertilization (CK) for 35 yr, and they were analyzed for microbial functional genes involved in soil N cycling using metagenome sequencing in the Loess Plateau of China. Soil N fractions were greater with OM and NM than NF and CK. The total abundances of N-cycling genes were 9.3% (p &lt; 0.05) greater with NM than CK, and 8.2% (p &lt; 0.05) and 12.2% (p &lt; 0.01) higher with OM and NM than NF, respectively. Compared to CK, OM and NM increased the abundance of genes associated with nitrification, denitrification, dissimilatory nitrate reduction, and assimilatory nitrate reduction, but decreased the abundance of genes related to organic N metabolism. However, NF increased the abundance of genes involved in nitrification. Both OM and NM also enhanced the relative abundance of Proteobacteria carrying N-cycling genes but reduced those of Firmicutes and Cyanobacteria. Soil organic carbon, total N, and potential carbon mineralization were the dominant factors affecting the abundances of N-cycling genes. Long-term application of OM and NM can promote N cycling by enhancing gene abundance due to increased soil organic matter and microbial biomass compared to NF and CK.

Effect of Chicken Manure Fermentation Extract as an Alternative to Chemical Fertilizer on Cucumber Growth and Soil Microbiome Environment

ABSTRACT In recent years, the destruction of the soil environment caused by excessive application of chemical fertilizers has attracted attention to using organic fertilizers to replace chemical fertilizers. Previous studies have shown that chicken manure fermentation extract (CMFE) as an organic fertilizer may also directly influence soil nutrient availability from the soil native pool and fertilizer application. However, it is unclear whether application CMFE can partially replacing chemical fertilizer to reduce the amount of chemical fertilizer without reducing cucumber yield. Therefore, an experiment was conducted in Yantai Agricultural Science Academy of Shandong Province in 2018 and 2019. In 2018, five fertilization combinations were set up, namely CK (900 kg·ha−1 chemical fertilizer), T1 (750 kg·ha−1 chemical fertilizer +150 L·ha−1 CMFE), T2 (675 kg·ha−1 chemical fertilizer +225 L·ha−1 CMFE), T3 (600 kg·ha−1 chemical fertilizer +300 L·ha−1 CMFE) and T4 (525 kg·ha−1 chemical fertilizer +375 L·ha−1 CMFE). Selected the optimal combination T3 for testing in 2019. The yield, quality, photosynthesis and growth indicators of cucumber, as well as soil nutrients and microbial content were determined. The results showed that the fertilization combination of 600 kg·ha−1 chemical fertilizer +300 L·ha−1 CMFE (T3) can minimize the amount of chemical fertilizer used without reducing yield. Compared with conventional fertilizer application, CMFE partially replacing chemical fertilizer did not reduce cucumber yield, but significantly increased cucumber vitamin C and protein content. CMFE partially replacing chemical fertilizer increased the root to shoot ratio as well as the fresh and dry weight of vegetative organs in cucumber, optimizing the growth and development of cucumber. Compared with conventional fertilizer application, CMFE partially replacing chemical fertilizer increased the content of soil organic matter, improved the composition structure of soil microbial community, increased the relative abundance of Actinomycete and Acinetobacter, and reduced the relative abundance of Bacteroides, Ascomycota, and Basidiomycetes. Overall, CMFE partially replacing chemical fertilizer optimized the growth and development of cucumbers, increased the root to shoot ratio, increased soil organic matter content, increased microbial abundance and diversity, and improved the composition structure of soil microbial communities. Therefore, in order to reduce the use of fertilizers, it is recommended to partially replacing chemical fertilizers with CMFE, with the optimal combination of 600 kg·ha−1 chemical fertilizer +300 L·ha−1 CMFE (T3).

Arbuscular mycorrhizae influence raspberry growth and soil fertility under conventional and organic fertilization.

Introducing beneficial soil biota such as arbuscular mycorrhizal fungi (AMF) to agricultural systems may improve plant performance and soil fertility. However, whether bioinocula species composition affects plant growth and soil fertility, and whether fertilizer source influences AMF colonization have not been well characterized. The objectives of this research were to: (1) assess if AMF bioinocula of different species compositions improve raspberry (Rubus idaeus L.) performance and characteristics of soil fertility and (2) evaluate the impact of fertilizer source on AMF colonization. Five bioinocula with different AMF species compositions and three fertilizer sources were applied to tissue culture raspberry transplants in a randomized complete block design with eight replicates. Plants were grown in a greenhouse for 14 weeks and plant growth, tissue nutrient concentrations, soil fertility, and AMF root colonization were measured. Shoot K and Zn concentrations as well as soil pH and K concentration increased in the Commercial Mix 1 treatment (Glomus, Gigaspora, and Paraglomus AMF species) compared to the non-inoculated control. RFI (raspberry field bioinoculum; uncharacterized AMF and other microbiota) increased soil organic matter (SOM), estimated nitrogen release (ENR), and soil copper (Cu) concentration compared to the non-inoculated control. Furthermore, plants receiving the Mix 1 or RFI treatments, which include more AMF species, had greater AMF root colonization than the remaining treatments. Plants receiving organic fertilizer had significantly greater AMF colonization than conventionally fertilized plants. Taken together, our data indicate that coupling organic fertilizers and bioinocula that include diverse AMF species may enhance raspberry growth and soil fertility.

Utilization of Livestock Waste as Biochar and Poschar to Increase Soil Organic Matter and Red Chili Yields

&#x0D; &#x0D; &#x0D; &#x0D; This study examines the impact of biochar and poschar fertilisers derived from livestock manure on red chilli yields and soil organic matter variations. The results demonstrated that the interaction between biochar and poschar substantially affected the fresh chilli pod weight per plant and organic matter content. Applying biochar and poschar organic fertilisers derived from animal manure substantially influenced plant height, fresh fruit weight per plant, and soil organic matter. The interaction between cow manure and poschar from poultry manure produced the highest yield of chilli fruit weight per plant, or an increase of 323.88% compared to the absence of biochar and poschar. The organic matter content of the soil underwent a significant change, with the highest organic matter content resulting from the interaction between chicken biochar and chicken poschar, which increased by 143,00% compared to the control group.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D;

Cover crop and biofuel crop effects on hydraulic properties for claypan soils

AbstractPerennial biofuel and cover crops systems are important for enhancing soil health and can provide numerous soil, agricultural, and environmental benefits. The study objective was to investigate the effects of cover crops and biofuel crops on soil hydraulic properties relative to traditional management for claypan soils. The study site included selected management practices: cover crop (CC) and no cover crop (NC) with corn/soybean rotation, switchgrass (SW), and miscanthus (MI). The CC mixture consisted of cereal rye, hairy vetch, and Austrian winter pea. The research site was located at Bradford Research Center in Missouri, USA, and was implemented on a Mexico silt loam. Intact soil cores (76‐mm diam. by 76‐mm long) were taken from the 0–10, 10–20, 20–30, and 30–40 cm depths with three plot replicates and two sub‐samples per plot replicate per depth. Soil hydraulic properties evaluated for each sample included: saturated hydraulic conductivity (Ksat), water retention, bulk density, and pore size distributions. Results showed with the test of Duncan's least significant differences that treatments of MI (1.18 Mg m−3) and SW (1.21 Mg m−3) had lower values of bulk density averaging across soil depth than CC (1.27 Mg m−3) and NC (1.31 Mg m−3). Management systems significantly increased Ksat with the biofuel treatments at 0–10 cm compared to NC system. The MI management showed a significant increase in macroporosity and fine mesoporosity as compared to other management systems. Slight changes have occurred in the measured soil physical properties for CC system compared to NC plots. Overall, increasing soil organic matter from more plant roots from long‐term biofuel cropping systems can improve soil water storage and crop productivity.

Ecosystem services of organic versus inorganic ground cover in peach orchards: A meta‐analysis

AbstractSeveral organic (e.g., compost, hay, straw, grass) and inorganic (e.g., plastic film) ground cover (GC) forms are used in peach orchards worldwide. Yet, there is a lack of quantitative studies on peach orchard ecosystem services comprising fruit yields and quality, soil health indicators, and biological pest control. To fill this knowledge gap, we performed a meta‐analysis of 55 peer‐reviewed research. Overall, inorganic GC increased peach yields by 7.7 ± 1.8%, while organic GC reduced it, though not statistically significant (p &gt; 0.05), by 1.7 ± 3%. Both forms of GC have enhanced single fruit mass, with a greater increase in inorganic (4.2 ± 1.7%) than in organic GC (1.2 ± 1.2%), and soluble solids content by 5.9 ± 0.9% and 3.2 ± 0.7%, respectively. Inorganic GC did not significantly affect titratable acid and fruit hardness, while organic GC reduced titratable acid (13.7 ± 2.1%), and fruit hardness (89 ± 2.9%). Soil temperature has increased in orchards with inorganic GC (2.8 ± 2.9%) and reduced with organic GC (8.3 ± 2.4%). Inorganic GC marginally increased soil water storage, while organic GC increased it by 9.3 ± 2.1%. Both organic and inorganic GC increased soil water content by 13.1 ± 2.4% and 26.1 ± 3.4%, respectively. Unlike inorganic GC, organic GC increased soil organic matter, available nitrogen, available phosphorus, and available potassium by 28.3 ± 3.3%, 25.1 ± 2.7%, 23.5 ± 4.6%, and 30.9 ± 3.3%, respectively. Equally significantly, organic GC increased predator abundance (47.5 ± 5.9%) and reduced pest incidence (2.4 ± 1.8%). Overall, inorganic GC systems slightly increased peach yield but are not sustainable due to their negative soil health and environmental impacts. In contrast, organic GC systems delivered an acceptable yield level while providing numerous ecosystem services, enabling sustainable long‐term peach production.

Community assembly processes of soil bacteria and fungi along a chronosequence of rice paddies cultivated on saline‐sodic land

AbstractSaline‐alkali soils cover an area of more than 900 million ha and pose an acute threat to global food security. Rice cultivation is an effective method of saline‐sodic soil amelioration in the Songnen Plain in northeastern China. However, the changes in soil microbial communities that follow rice cultivation are largely unknown. In this study, soil bacterial and fungal communities were investigated using high‐throughput sequencing along a chronosequence of rice paddies cultivated in saline‐sodic soils. The results showed that soil fungi and bacteria become more diverse and abundant after rice cultivation compared with uncultivated saline‐sodic soil, in combination with the decreased pH and increased soil organic matter, indicating the amelioration of saline‐sodic soil. The processes of microbial succession following rice cultivation can be divided into two stages: shorter than and longer than 10 years. Moreover, soil fungi and bacteria exhibited distinct variation patterns as they were dominated by different influential factors. The results indicated that bacteria were more strongly dominated by soil properties than fungi, while the latter were more dependent on vegetation. As rice cultivation continued, fungi exhibited better adaptation and faster succession than bacteria in response to environmental shifts after rice cultivation. Therefore, measures that can enhance plant–microbe interactions may be a viable approach for promoting saline‐sodic soil amelioration. This study provided novel insights into the microbial assembly processes following rice cultivation on saline‐sodic lands.

EFFECT OF MUNICIPAL SOLID WASTE TREATMENT TECHNIQUES ON SOIL CHEMICAL PROPERTIES IN SUDAN SAVANNAH, KANO STATE, NORTHERN NIGERIA

The objective of this study was to determine the impact of municipal solid waste (MSW) treatment techniques on the soil Chemical properties of Sudan Savannah, Nigeria. MSW was collected from multiple metropolitan sites and mixed together. The composite sample was used to produce biochar and compost treatments. The effect of MSW treatment techniques on the qualities of soil was assessed by applying treatments and controls (untreated MSW) to soil at various rates. Soil samples were collected four weeks after treatment application, processed and analyzed in the laboratory. Results showed significant difference (*P≤0.05) in soil Mg and Zn, as well as highly significant difference at (**P≤0.01) in soil EC and K values. Biochar is recommended for acidic soil to improve soil pH, whereas compost is suggested for increasing soil organic matter and microbial activity. The use of untreated MSW is primarily advised for long-term soil deterioration solutions.

Assessment of the agronomic value of solar-dried sludge and heavy metals bioavailability based on the bioaccumulation factor and translocation index

This study aimed to assess the agronomic value of solar-dried sludge (SDS) and the transfer of Cr, Ni, Pb, and Cu to wheat (Triticum aestivum) and faba bean (Vicia faba). A greenhouse experiment was performed involving two rates of SDS (15 t/ha and 30 t/ha) from an activated sludge-based wastewater treatment plant. In addition to the single use of an SDS amendment, co-application of SDS and mineral fertilizers was also included to determine the best scenario resulting in high yields and less negative implications on the environment. Data for both wheat and faba bean showed that applying SDS at 30 t/ha led to competitive yields compared to the ones obtained previously, while 15 t/ha of SDS and mineral fertilizers were co-applied. The use of SDS increased soil organic matter, slightly decreased the pH value, and increased soil salinity. The contents of Ni, Cu, and Pb were not significantly affected by the application of SDS. Only Cr showed high soil concentrations in proportion to the increasing rates of SDS. The bioaccumulation of heavy metals in roots was more important in 30 t/ha than that in 15 t/ha amended soil. In the case of wheat, the bioconcentration factor (BCF) root values correspond to the following order: Cr (0.89) &amp;gt;Cu (0.85)&amp;gt; Ni (0.28)&amp;gt; Pb (0.22). In the case of faba bean, BCF roots were observed as follows: Cu (1.04 &amp;gt; Ni (0.37)&amp;gt; Cr (0.16)&amp;gt; Pb (0.15). Wheat excluded Cr, Ni, and Pb from the uptake by shoots, and Cu was translocated from roots to shoots with a percentage of 11% at 30 t/ha of applied SDS. Faba beans demonstrated more important values of HM’s translocation by respecting this order (Ni (37.7%) &amp;gt; cu (30.24%)&amp;gt; Cr (17.59%), while Pb was excluded from the translocation. No significant difference was observed regarding the translocation index when the sludge rate has been duplicated from 15 t/ha to 30 t/ha. Based on these outcomes, SDS used at the rate of 30 t/ha is the best scenario to amend the soil and provide nutrients to plants. Wheat is translocating less heavy metal to the edible part; it is, thus, the most suitable crop to be involved in the current context.

Effects of Phosphogypsum and Suaeda salsa on the Soil Moisture, Salt, and Bacterial Community Structure of Salinized Soil

The improvement of saline soil is an important issue that cannot be ignored in the farmland soil environment. The change in soil salinity will inevitably affect the soil bacterial community. This experiment was based on moderately saline soil in the Hetao Irrigation Area, conducted by applying phosphogypsum (LSG), interplanting Suaeda salsa with Lycium barbarum (JP) and applying phosphogypsum and interplanting S. salsa with L. barbarum (LSG+JP),and the local unimproved soil of a L. barbarum orchard was used as the control (CK), to explore the effects of different improvement methods on soil moisture, salinity, nutrients, and bacterial community structure diversity during the growth period of L. barbarum. The results showed that compared with that under CK, the LSG+JP treatment significantly decreased the soil EC value and pH value from the flowering stage to the deciduous stage (P<0.05), with an average decrease of 39.96% and 7.25%, respectively; the LSG+JP treatment significantly increased soil organic matter (OM) and available phosphorus (AP) content during the whole growth period (P<0.05), with an average annual increase of 81.85% and 203.50%, respectively. The total nitrogen (TN) content was significantly increased in the flowering and deciduous stages (P<0.05), with an annual average increase of 48.91%. The Shannon index of LSG+JP in the early stage of improvement was increased by 3.31% and 6.54% compared with that of CK, and the Chao1 index was increased by 24.95% and 43.26% compared with that of CK, respectively. The dominant bacteria in the soil were Proteobacteria, Bacteroidetes, Actinobacteria, and Acidobacteria, and the dominant genus was Sphingomonas. Compared with that in CK, the relative abundance of Proteobacteria in the improved treatment increased by 0.50%-16.27% from the flowering stage to the deciduous stage, and the relative abundance of Actinobacteria in the improved treatment increased by 1.91%-4.98% compared with that in CK in the flowering and full-fruit stages. Redundancy analysis (RDA) results showed that pH, water content (WT), and AP were important factors affecting bacterial community composition, and the correlation heatmap showed that Proteobacteria, Bacteroidetes, and EC values were significantly negatively correlated (P<0.001); Actinobacteria and Nitrospirillum were significantly negatively correlated with EC values (P<0.01). In conclusion, the application of phosphogypsum and interplanting S. salsa with L. barbarum (LSG+JP) could significantly reduce soil salinity, increase nutrients, and improve the diversity of soil bacterial community structure, which is beneficial to the long-term improvement of saline soil in the Hetao Irrigation Area and the maintenance of soil ecological health.

Potential of Medicago sativa and Perilla frutescens for overcoming the soil sickness caused by ginseng cultivation.

There are serious soil sickness in ginseng cultivation. Crop rotation is an effective agricultural management to improve soil sustainability and reduce soil sickness. To explore an appropriate ginseng rotation system, Medicago sativa (alfalfa) and Perilla frutescens (perilla) were planted on ginseng cultivation soil for 1 year to evaluate the improvement effect of both. Through chemical analysis and high-throughput sequencing technology, we found that after alfalfa and perilla cultivation for one-year, various nutrients and enzyme activities in ginseng cultivation soil were significantly improved. In addition, perilla significantly increased the diversity and richness of soil fungal communities. Cultivation of alfalfa and perilla significantly changed the composition of soil bacterial and fungal communities and significantly reduced the abundance of the potentially pathogenic fungi Ilyonectria. Further pot experiments also showed that the improved soil could significantly increase root activity of ginseng plant after two plants were planted. It should be noted that, unlike alfalfa, perilla decreased soil electrical conductivity, increased soil organic matter, soil urease, and may significantly improve the diversity and richness of soil fungal community. Moreover, in the pot experiment, the root fresh weight of ginseng cultured in perilla treated soil increased significantly. This study highlights that perilla may have better soil improvement effect than alfalfa and it has the potential to be used in the soil improvement of ginseng cultivation.

Role of microbial iron reduction in arsenic metabolism from soil particle size fractions in simulated human gastrointestinal tract

Gut microbiota provides protection against arsenic (As) induced toxicity, and As metabolism is considered an important part of risk assessment associated with soil As exposures. However, little is known about microbial iron(III) reduction and its role in metabolism of soil-bound As in the human gut. Here, we determined the dissolution and transformation of As and Fe from incidental ingestion of contaminated soils as a function of particle size (<250 μm, 100–250 μm, 50–100 μm and < 50 μm). Colon incubation with human gut microbiota yielded a high degree of As reduction and methylation of up to 53.4 and 0.074 μg/(log CFU/mL)/hr, respectively; methylation percentage increased with increasing soil organic matter and decreasing soil pore size. We also found significant microbial Fe(III) reduction and high levels of Fe(II) (48 %−100 % of total soluble Fe) may promote the capacity of As methylation. Although no statistical change in Fe phases was observed with low Fe dissolution and high molar Fe/As ratios, higher As bioaccessibility of colon phase (avg. 29.4 %) was mainly contributed from reductive dissolution of As(V)-bearing Fe(III) (oxy)hydroxides. Our results suggest that As mobility and biotransformation by human gut microbiota (carrying arrA and arsC genes) are strongly controlled by microbial Fe(III) reduction coupled with soil particle size. This will expand our knowledge on oral bioavailability of soil As and health risks from exposure to contaminated soils.

Effects of N fertilizer reduction combined with straw biochar application on the yield, Si, and N nutrition of double-cropping rice.

Nitrogen (N) and silicon (Si) are important nutritional elements for rice. However, excessive N fertili-zer application and the ignorance of Si fertilizer are common in practice. Straw biochar is rich in Si, which can be used as a potential Si fertilizer. In this study, we conducted a consecutive 3-year field experiment to explore the effects of N fertilizer reduction combined with straw biochar application on rice yield, Si and N nutrition. There were five treatments: conventional N application (180 kg·hm-2, N100), 20% N reduction (N80), 20% N reduction with 15 t·hm-2 biochar (N80+BC), 40% N reduction (N60), and 40% N reduction with 15 t·hm-2 biochar (N60+BC). The results showed that compared with N100, 20% N reduction did not affect the accumulation of Si and N in rice; 40% N reduction reduced foliar N absorption, but significantly increased foliar Si concentration by 14.0%-18.8%; while combined application of biochar significantly increased foliar Si accumulation, with an increase of Si concentration by 38.0%-63.3% and Si absorption by 32.3%-49.9%, but further reduced foliar N concentration. There was a significant negative correlation between Si and N concentration in mature rice leaves, but no correlation between Si and N absorption. Compared with N100, N reduction or combined application of biochar did not affect soil ammonium N and nitrate N, but increased soil pH. Nitrogen reduction combined application of biochar significantly increased soil organic matter by 28.8%-41.9% and available Si content by 21.1%-26.9%, with a significant positive correlation between them. Compared with N100, 40% N reduction reduced rice yield and grain setting rate, while 20% N reduction and combined application of biochar did not influence rice yield and yield components. In summary, appropriate N reduction and combined with straw biochar can not only reduce N fertilizer input, but also improve soil fertility and Si supply, which is a promising fertilization method in double-cropping rice fields.

Effect of Long-Term Semiarid Pasture Management on Soil Hydraulic and Thermal Properties

Semiarid pasture management strategies can affect soil hydraulic and thermal properties that determine water fluxes and storage, and heat flow in unsaturated soils. We evaluated long-term (>10 years) perennial and annual semiarid pasture system effects on saturated hydraulic conductivity (ks), soil water retention curves (SWRCs), soil water thresholds (i.e., volumetric water content (θv) at saturation, field capacity (FC), and permanent wilting point (PWP); plant available water (PAW)), thermal conductivity (λ), and diffusivity (Dt) within the 0-20 cm soil depth. Forage systems included: Old World bluestem (Bothriochloa bladhii) + legumes (predominantly alfalfa (Medicago sativa)) (OWB-legume), native grass-mix (native), alfalfa + tall wheatgrass (Thinopyrum ponticum) (alfalfa-TW), and annual grass-mix (annual) pastures on a clay loam soil; and native, teff (Eragrostis tef), OWB-grazed, and OWB-ungrazed pastures on a sandy clay loam soil. The perennial OWB-legume and native pastures had increased soil organic matter (SOM) and reduced bulk density (ρb), improving ks, soil water thresholds, λ, and Dt, compared to annual teff and alfalfa-TW (P < 0.05). Soil λ, but not Dt, increased with increasing θv. Grazed pastures decreased ks and water retention compared to other treatments (P < 0.05), yet did not affect λ and Dt (P > 0.05), likely due to higher ρb and contact between particles. Greater λ and Dt at saturation and PWP in perennial versus annual pastures may be attributed to differing SOM and ρb, and some a priori differences in soil texture. Overall, our results suggest that perennial pasture systems are more beneficial than annual systems for soil water storage and heat movement in semiarid regions.

Exploring options for increasing maize yields and grain Zn concentrations in sub-Saharan Africa

BackgroundIncreasing zinc (Zn) concentrations in maize grains could contribute to alleviating widespread human Zn deficiency in sub-Saharan Africa (SSA). However, trade-offs between grain Zn concentrations and maize yields have been observed.ScopeUsing data from researcher-managed, on-farm and on-station field trials in Kenya, Zambia and Zimbabwe, we aimed (i) to confirm whether this trade-off is found in current farming systems in SSA and (ii) to explore whether genotypic and management options, relevant for the African context, can increase both yields and grain Zn concentrations across several environments.ResultsAn overall negative, but weak relation between maize yields and grain Zn concentrations was found. High yields and high grain Zn concentrations did not co-occur. The negative relation between grain Zn concentrations and yields cannot be bypassed by selecting one of the commercially available varieties used in this study. Nitrogen application increased yields, but had contrasting effects on grain Zn concentrations depending on variety and site. Grain Zn concentrations were positively related with soil organic carbon and P and K availability.ConclusionsAttaining grain Zn concentrations above the HarvestPlus target of 38 mg kg−1, considered adequate for reducing human Zn deficiency, with current commercially available maize varieties and presented management options, is not possible without compromising yield levels. Increasing soil organic matter content and balanced application of N, P and K fertilisers could increase grain Zn concentrations. These practices likely will also increase yields and could be a viable option to bypass the trade-off between maize yields and grain Zn concentrations.

Combined Utilization of Chinese Milk Vetch, Rice Straw, and Lime Reduces Soil Available Cd and Cd Accumulation in Rice Grains

Cadmium (Cd) pollution poses a growing threat to rice production in acidic paddies. In south China, a common agricultural practice involves the combined utilization of Chinese milk vetch (M) and rice straw (R). However, it is unclear how the addition of lime to these amendments affects Cd bioavailability and accumulation in soil. Control (CK), chemical fertilizer (F), Chinese milk vetch + rice straw + chemical fertilizer (MRF), and Chinese milk vetch + rice straw + chemical fertilizer + lime (MRFL) treatments were applied to develop a kind of green, efficient, and practical amendment for acidic paddies. We conducted a microplot experiment to explore Cd immobilization in paddy soil and the Cd content in rice grains with these treatments. The results showed that compared with F, the rice Cd in the MRF and MRFL treatments were significantly decreased by 51.7% and 65.2% in early rice and 23.0% and 43.3% in late rice, respectively. Both the MRF and MRFL treatments significantly reduced soil available Cd and weak acid-extractable cadmium (Aci-Cd) concentrations and increased soil organic matter (SOM), exchangeable cation concentrations, and pH, which converted Cd into a stable form in soil. In addition, the MRF and MRFL treatments increased soil pH value by reducing soil exchangeable hydrogen ion concentration (E-H). Additionally, recombination of Cd forms was the primary factor in the reduction in available Cd concentration according to partial least squares path modeling (PLS-PM) analysis. The Cd concentration of rice grains was primarily associated with soil available Cd, soil pH value, and SOM. Overall, these results provide useful data and novel insights into reducing rice grain Cd in south China.