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Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control < KNO3 < rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification. [ABSTRACT FROM AUTHOR]

To improve the nutritional and commercial value of grape, and to meet the human body's requirement for selenium (Se), it is important to increase the absorption capacity of grapevine for Se. In this study, different straws of Solanum sect. Solanum (Solanaceae) plants (Solanum nigrum var. humile (Bernh. ex Willd.) C.Y. Wu & S.C. Huang, Solanum diphyllum L., Solanum nigrum L., and Solanum alatum Moench) were mixed into the Se-supplemented soil before planting the 'Summer Black' grape seedlings. Then, the physiological and Se accumulation characteristics of grapevine were studied after planting for two months in the pre-treated soil. The obtained results showed that the photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoid) content, the antioxidant enzymes (superoxide dismutase, peroxidase and catalase) activity, and the biomass of grapevine were increased by S. nigrum var. humile, S. diphyllum and S. nigrum straw amendments, while S. alatum straw amendment led to opposite results. Furthermore, grapevine Se concentration, soil pH and available soil Se concentration were also significantly improved by mixing with the straws of S. nigrum var. humile, S. diphyllum, and S. nigrum and the significant positive correlations between them were observed. In conclusion, S. nigrum var. humile, S. diphyllum, and S. nigrum straw amendments were beneficial for the growth and accumulation of Se in grapevine. In terms of Se concentration in the grapevine, the S. nigrum straw amendment had the best promoting effect. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control < KNO3 < rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification.

Inversion tillage with straw amendment is widely applied in northeastern China, and it can substantially increase the storage of carbon and improve multiple subsoil functions. Soil microorganisms are believed to be the key to this process, but research into their role in subsoil amelioration is limited. Therefore, a field experiment was conducted in 2018 in a region in northeastern China with Hapli-Udic Cambisol using four treatments: conventional tillage (CT, tillage to a depth of 15 cm with no straw incorporation), straw incorporation with conventional tillage (SCT, tillage to a depth of 15 cm), inversion tillage (IT, tillage to a depth of 35 cm) and straw incorporation with inversion tillage (SIT, tillage to a depth of 35 cm). The soils were managed by inversion to a depth of 15 or 35 cm every year after harvest. The results indicated that SIT improved soil multi-nutrient cycling variables and increased the availability of key nutrients such as soil organic carbon, total nitrogen, available nitrogen, available phosphorus and available potassium in both the topsoil and subsoil. In contrast to CT and SCT, SIT created a looser microbial network structure but with highly centralized clusters by reducing the topological properties of average connectivity and node number, and by increasing the average path length and the modularity. A Random Forest analysis found that the average path length and the clustering coefficient were the main determinants of soil multi-nutrient cycling. These findings suggested that SIT can be an effective option for improving soil multi-nutrient cycling and the structure of microbial networks, and they provide crucial information about the microbial strategies that drive the decomposition of straw in Hapli-Udic Cambisol.

Straw is widely incorporated into soil worldwide, but most studies have concentrated on the effects of straw mulching or incorporation with topsoil. To determine the effect of depth of straw incorporation on bacterial and fungal communities, we established a field experiment in a region in Northeast China with Haplic Chernozems using four treatments: conventional tillage (CT, tillage to a depth of 15 cm with no straw incorporation), straw incorporation with conventional tillage (SCT, tillage to a depth of 15 cm), inversion tillage (IT, tillage to a depth of 35 cm) and straw incorporation with inversion tillage (SIT, tillage to a depth of 35 cm). The soils were managed by inversion to a depth of 15 or 35 cm after harvest. The results show that soil organic carbon content was significantly higher and pH and bulk density were significantly lower in the 15–35 cm layer in IT and SIT than CT and SCT. Fungal abundance was higher with straw incorporation, but fungal diversity was lower in the 0–15 cm layer in SCT and SIT than in CT and IT. Path length in the bacterial network was shorter and connectivity was higher in CT + SCT than in IT + SIT, leading to a more complex ecosystem, and the fungal network had opposite patterns. The key taxa in the phylum Actinobacteriota and Ascomycota in the microbial networks changed dramatically at the genus level following inversion tillage with straw amendment, which may increase bacterial network resistance to environmental disturbances and unstable fungal networks, resulting in large changes in the fungal community involved in the decomposition of recalcitrant straw-derived C and the more efficient acquisition of limiting resources. [ABSTRACT FROM AUTHOR]

In order to test the short-term effects of straw amendment on soil organic C (SOC) stabilization, SOC protection mechanisms, and soil bacterial community, we examined which bacterial taxonomic groups were associated with protected C fractions via different soil depths. We conducted a 5-year field experiment including a total of four treatments: S0 (no straw amendment), S1 (0–20 cm straw-amended soil), S2 (0–40 cm straw-amended soil) and S3 (0–60 cm straw-amended soil). The core method was used for soil sampling, and 180 soil samples was collected. Our results showed that straw amendment significantly increased bulk soil C content, enhanced the constituents of physically separated fractions and their OC contents, and changed the soil bacterial community composition at different soil depths. SOC was more accelerated in macroaggregate-derived unprotected and microaggregate-derived physically protected fractions at soil depths of 0–20 cm. Physically protected and physico-biochemically protected fractions were the major C protection mechanisms at soil depths of 20–40 cm and 40–60 cm soil depths. Our study also provides evidence that straw amendment significantly increases the bacterial phyla abundance of Proteobacteria and Bacteroidetes at each soil depth. Moreover, straw amendment enhanced the relative abundances of Gemmatimonadetes and Nitrospirae at soil depths of 40–60 cm and have a positive correlation with physically and physico-biochemically protected C pools. These results indicate that straw amendment can regulate C sequestration processes by enhancing SOC physical protection and modulating bacterial community, especially in the deep soil. In addition, straw amendment in subsoil (0–40 cm or 0–60 cm) is more beneficial for C storage and stabilization. [ABSTRACT FROM AUTHOR]

In order to test the short-term effects of straw amendment on soil organic C (SOC) stabilization, SOC protection mechanisms, and soil bacterial community, we examined which bacterial taxonomic groups were associated with protected C fractions via different soil depths. We conducted a 5-year field experiment including a total of four treatments: S0 (no straw amendment), S1 (0–20 cm straw-amended soil), S2 (0–40 cm straw-amended soil) and S3 (0–60 cm straw-amended soil). The core method was used for soil sampling, and 180 soil samples was collected. Our results showed that straw amendment significantly increased bulk soil C content, enhanced the constituents of physically separated fractions and their OC contents, and changed the soil bacterial community composition at different soil depths. SOC was more accelerated in macroaggregate-derived unprotected and microaggregate-derived physically protected fractions at soil depths of 0–20 cm. Physically protected and physico-biochemically protected fractions were the major C protection mechanisms at soil depths of 20–40 cm and 40–60 cm soil depths. Our study also provides evidence that straw amendment significantly increases the bacterial phyla abundance of Proteobacteria and Bacteroidetes at each soil depth. Moreover, straw amendment enhanced the relative abundances of Gemmatimonadetes and Nitrospirae at soil depths of 40–60 cm and have a positive correlation with physically and physico-biochemically protected C pools. These results indicate that straw amendment can regulate C sequestration processes by enhancing SOC physical protection and modulating bacterial community, especially in the deep soil. In addition, straw amendment in subsoil (0–40 cm or 0–60 cm) is more beneficial for C storage and stabilization.

Freeze-thaw-cycles (FTCs) change the dynamics of soil physiochemical and biological processes, and could change the soil nitrogen (N) heterogeneity in sloping fields. In this study, both continuous cropping of corn (CC) and corn-soybean rotation (CS), with-straw-amendment (SA) and with-no-straw-amendment, were considered to investigate how FTCs change soil total N (TN) and available N (alkali-hydrolyzable N, AN) at different slope positions in the Mollisol region of Northeast China. When a large amount of snow fell, after FTCs: (1) TN decreased by 40–79% at all slope positions under CC and CS, mainly influenced by snowmelt-erosion, nitrification-denitrification and N-upward-movement, and (2) AN decreased at both the top slope (51–64%) and back slope (36–81%) positions, mainly influenced by snowmelt-erosion, nitrification-denitrification and N-upward-movement, but increased (2–65%) under CS at the bottom slope position, mainly due to deposition, N-upward-movement, nitrification-denitrification and previous crop. In contrast, when less snow fell, after FTCs: (1) N transformation changed both TN and AN on the slopes, mainly influenced by microorganisms, N-upward-movement, and previous crops, and (2) AN decreased by 20–26% at the bottom slope position under both CC and CS, mainly influenced by nitrification-denitrification and N-upward-movement, but increased by 111–116% at the back slope position under CS. SA did not change the TN distribution on the Mollisol farmland slope after FTCs in a short time period, but it helped sustain a high AN content (4.5–8.6%) in the soil. TN loss was usually severe after FTCs, and should be controlled urgently to increase soil fertility and reduce environmental pollution. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effects on chemical and microbiological properties of paddy soil of short-term biochar, straw, and chemical fertilizers compared with chemical fertilization alone. Five soil fertilization treatments were evaluated: regular chemical fertilizers (RF), straw+regular chemical fertilizers (SRF), straw biochar+regular chemical fertilizers (SCRF), bamboo biochar (BC)+regular chemical fertilizers (BCRF), and straw biochar+70% regular chemical fertilizers (SC+70%RF). Their effects were investigated after approximately 1.5 years. The soil pH and cation exchange capacity (CEC) were significantly higher in biochar-treated soils. The soil phosphorous (P) and potassium (K) contents increased with biochar application. The soil Colwell P content was significantly increased with the addition of straw biochar in the treatments of SCRF and SC+70%RF. The oxygen (0):carbon (C) ratio doubled in BC picked from the soil. This indicated that BC underwent a significant oxidation process in the soil. The denaturing gradient gel electrophoresis (DGGE) fingerprints of microbial communities differed among the treatments. Soils with added biochar had higher Shannon diversity and species richness indices than soils without biochars. The results suggest that biochar can improve soil fertility.

Long‐term no‐tillage management and crop residue amendments to soil were identified as an effective measure to increase soil organic carbon (SOC). The SOC content, SOC stock (SOCs), soil carbon sequestration rate (CSR), and carbon pool management index (CPMI) were measured. A stable isotopic approach was used to evaluate the contributions of wheat and maize residues to SOC at a long‐term experimental site. We hypothesized that under no‐tillage conditions, straw retention quantity would affect soil carbon sequestration differently in surface and deep soil, and the contribution of C3 and C4 crops to soil carbon sequestration would be different. This study involved four maize straw returning treatments, which included no maize straw returning (NT‐0), 0.5 m (from the soil surface) maize straw returning (NT‐0.5), 1 m maize straw returning (NT‐1), and whole maize straw returning (NT‐W). The results showed that in the 0–20 cm soil layer, the SOC content, SOCs, CSR and CPMI of the NT‐W were highest after 14 years of no‐tillage management, and there were obvious differences among the four treatments. However, the SOC, SOCs, and CSR of the NT‐0.5 and NT‐W were the highest and lowest in 20–100 cm, respectively. The value of δ13C showed an obviously vertical variability that ranged from –22.01‰ (NT‐1) in the 0–20 cm layer to –18.27‰ (NT‐0.5) in the 60–80 cm layer, with enriched δ13C in the 60–80 cm (NT‐0.5 and NT‐1) and 80–100 cm (NT‐0 and NT‐W) layers. The contributions of the wheat and maize‐derived SOC of the NT‐0.5, NT‐1 and NT‐W increased by 11.4, 29.5 and 56.3% and by 10.7, 15.1 and 40.1%, relative to those in the NT‐0 treatment in the 0–20 cm soil layer, respectively. In conclusion, there was no apparent difference in total SOC sequestration between the NT‐0.5, NT‐1, and NT‐W treatments in the 0–100 cm soil layer. The contribution of wheat‐derived SOC was higher than that of maize‐derived SOC. [ABSTRACT FROM AUTHOR]

Abstract Soil dissolved organic matter (DOM) alters heavy metal availability, but whether straw amendment can manipulate soil selenium (Se) speciation and availability through DOM mineralization remains unclear. In this study, allochthonous maize straw and selenate were incubated together in four different soils for 1 y. The transformation and availability of DOM associated Se (DOM-Se) was investigated during aging. Results indicated that soil solution and soil particle surfaces were dominated by hexavalent hydrophilic acid-bound Se (Hy-Se). The amount of fulvic acid bound Se in soil solution (SOL-FA-Se) was higher than humic acid bound Se in soil solution (SOL-HA-Se), except in krasnozems, and mainly existed as hexavalent Se (Se(VI)). Tetravalent Se (Se(IV)) was the main valence state of FA-Se adsorbed on soil particle surfaces (EX-FA-Se) after 5 w of aging. The proportion of soil-available Se (SOL + EX-Se) decreased with increasing straw rate. However, under an application rate of 7500 kg·hm−2, soluble Se fraction (SOL-Se) reduction was minimal in acidic soils (18.7%–34.7%), and the organic bound Se fraction (OM-Se) was maximally promoted in alkaline soils (18.2%–39.1%). FA and HON could enhance the availability of Se in the soil solution and on particle surfaces of acidic soil with high organic matter content. While Se incorporation with HA could accelerate the fixation of Se into the solid phase of soil. Three mechanisms were involved in DOM-Se aging: (1) Reduction, ligand adsorption, and inner/outer-sphere complexation associated with the functional groups of straw-derived DOM, including hydroxyls, carboxyl, methyl, and aromatic phenolic compounds; (2) interconnection of EX-FA-Se between non-residual and residual Se pools; and (3) promotion by soil electrical conductivity (EC), clay, OM, and straw application. The dual effect of DOM on Se aging was highly reliant on the characteristics of the materials and soil properties. In conclusion, straw amendment could return selenium in soil and reduce soluble Se loss. Graphical abstract Unlabelled Image Highlights • The dynamical changes of fractionation and speciation of DOM bound Se in soils were investigated. • Straw amendment accelerated selenium retention and the reduction of hydrophilic acid bound Se. • FA and HON bound Se fraction reserved available Se while HA fraction fixed Se into soil solid phase. • EX-FA-Se indicates the soil Se availability and maintains the balance of Se within soil pools. • The acidic and phenolic functional groups were involved in DOM and Se interaction. [ABSTRACT FROM AUTHOR]

Abstract Straw application in combination with synthetic N fertilizer could increase crop yield and improve soil fertility, however, contradictory observations have been reported on the effects of straw addition on soil N 2 O emission. Straw application can affect both denitrification rate and its product stoichiometry (N 2 O/(N 2 O + N 2) ratio), whereas the latter remains rather unclear since the ratio is strongly regulated by other soil parameters, e.g. nitrate and oxygen concentrations at denitrifying micro-sites. In this context, we conducted an incubation experiment with a robotized continuous flow incubation system using a He/O 2 atmosphere and measured N 2 O and direct N 2 fluxes over 22 days. Soil amended with and without rice straw (2.5 g kg−1 soil) in conjunction with nitrate fertilizer (10 mM KNO 3) and non-amended control soil were incubated under 85% water-filled pore space. To simulate a short soil anoxic period, three different O 2 partial pressures phases were set (20%, 5% and 10%). Additionally, N 2 O site preference signatures of soil-emitted N 2 O were analyzed to identify the processes contributing to N 2 O fluxes. Addition of nitrate increased cumulative N 2 O fluxes and decreased cumulative N 2 fluxes compared with non-fertilized control, while rice straw amendment increased both N 2 O and N 2 emissions drastically compared with the nitrate only treatment. The N 2 O SP values ranged from 0.4 to 2.7‰ among all treatments, indicating denitrification/nitrifier denitrification was the dominating source. The results suggest that straw amendment can trigger high denitrification rate, whereas the effect of straw amendment on the amount of emitted N 2 O and the N 2 O/(N 2 O + N 2) product ratio strongly depends on soil NO 3 − concentration. As a conclusion, the present study suggests that straw amendment in conjunction with nitrate-N can increase soil N 2 O emissions under conditions favoring denitrification, even though it may decrease the overall N 2 O/(N 2 O + N 2) product ratio. Highlights • Combined effect of straw addition and soil NO 3 − was shown on direct N 2 fluxes. • Decrease in soil NO 3 − caused a quick shift from N 2 O production to reduction. • Effect of straw addition on N 2 O and N 2 fluxes depends on soil NO 3 − content. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A laboratory study was conducted to investigate volatile organic compound (VOC) emissions from agricultural soil amended with wheat straw and their associations with bacterial communities for a period of 66 days under non-flooded and flooded conditions. The results indicated that ethene, propene, ethanol, i-propanol, 2-butanol, acetaldehyde, acetone, 2-butanone, 2-pentanone and acetophenone were the 10 most abundant VOCs, making up over 90% of the total VOCs released under the two water conditions. The mean emission of total VOCs from the amended soils under the non-flooded condition (5924 ng C/(kg·hr)) was significantly higher than that under the flooded condition (2211 ng C/(kg·hr)). One “peak emission window” appeared at days 0–44 or 4–44, and over 95% of the VOC emissions occurred during the first month under the two water conditions. Bacterial community analysis using denaturing gradient gel electrophoresis (DGGE) showed that a relative increase of Actinobacteria, Bacteroidetes, Firmicutes and γ-Proteobacteria but a relative decrease of Acidobacteria with time were observed after straw amendments under the two water conditions. Cluster analysis revealed that the soil bacterial communities changed greatly with incubation time, which was in line with the variation of the VOC emissions over the experimental period. Most of the above top 10 VOCs correlated positively with the predominant bacterial species of Bacteroidetes, Firmicutes and Verrucomicrobia but correlated negatively with the dominant bacterial species of Actinobacteria under the two water conditions. These results suggested that bacterial communities might play an important role in VOC emissions from straw-amended agricultural soils. [ABSTRACT FROM AUTHOR]

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO3-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N2O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO3-N decreased. When15NO3-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg−1only 1.1 ± 0.4 mg kg−1NO3-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N2O-N emissions were at levels of only micrograms kg−1soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N2O. [ABSTRACT FROM PUBLISHER]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil organic carbon (SOC) accumulation and its components are influenced by agricultural practices, which are interfered by soil microorganisms. A field experiment was conducted to investigate how straw amendment and soil tillage influenced SOC fractions and chemical components, and their interrelations with microbial communities evaluated through phospholipid fatty acids (PLFAs) in Mollisols. Density fractionation and Fourier-transform Infrared Spectroscopy were combined to characterize OC properties, including free and occluded light fractions (fLFC, oLFC), heavy fraction (HFC), aliphatic-C and aromatic-C functional groups. Compared with control soil, straw amendment caused surface SOC increased by 6.7%–12.4% (P < 0.05). The dissolved OC, microbial biomass carbon (SMBC), fLFC, oLFC, aliphatic-C, and total PLFAs also increased after straw amendment. Whereas the aromatic-C proportions in bulk soil, fLFC, and oLFC decreased. The OC components and microbial properties didn't obviously change in soil with straw ash amendment. Straw amendment to the subsurface layer only increased subsurface SOC and OC fractions (P < 0.05). Principal component analysis revealed that soil microbial community structure changed with the amounts of straw amendment, soil tillage further underpinned the separation. The separation via PC1 was associated with labile OC components, including SMBC, fLFC, oLFC, and aliphatic-C pointing to soils with higher amounts of straw amendment, and with recalcitrant aromatic-C and HFC pointing to soils without straw or straw ash. Higher amounts of straw amendment plus soil tillage affected soil microbial community structure, and consequently influenced OC sequestration by altering labile OC fractions and components in Mollisols. • Different forms of straw strongly affected OC chemical components in Mollisol. • Labile OC fractions were more sensitive to different forms of straw return. • Changes in OC fractions strongly affected microbial community structure. • Straw return improved OC fractions by regulating soil microbial community structure. • Straw amendment at moderate rate may be more feasible considering resource use efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Native grasslands around the word face increased threats from non-native species. Fescue prairie in North America, in good rangeland condition, is dominated by the perennial bunch grass, Festuca hallii, whereas disturbances are often colonized by Poa pratensis, an introduced perennial rhizomatous grass which is competitive in nitrogen rich soils. F. hallii thrives in typical low nitrogen grassland soils and recovers poorly once disturbed. Disturbance to soil caused by well site construction may decrease organic carbon and potassium, and increase nitrogen, phosphorus, pH and electrical conductivity, creating conditions conducive to invasion by P. pratensis. This research tested the hypothesis that F. hallii would tolerate nitrogen depleted soil, through addition of carbon as a straw amendment to newly reclaimed well sites, better than P. pratensis. Our second hypothesis was that F. hallii is negatively affected by disturbed soil and P. pratensis is not. We treated three sites with three straw amendment rates, seeded monocultures of F. hallii and P. pratensis, and monitored establishment over three years. F. hallii biomass, root biomass, leaf length and cover increased in response to straw treatments, whereas P. pratensis showed little response. F. hallii was positively affected by prior-year soil water, and current-year ammonium and potassium. P. pratensis was positively affected by current-year soil water, potassium and nitrate. P. pratensis responded positively to higher pH and electrical conductivity found in disturbed soil and F. hallii responded poorly. The positive relationship of P. pratensis to pH above 7 could explain why it can invade reclaimed disturbed grassland; whereas the negative reaction of F. hallii might explain its failure to recover. We concluded the addition of straw as a soil amendment is a possible solution to poor establishment of F. hallii. [Copyright &y& Elsevier]

The biochemical properties of soil have often been described as early and sensitive indicators of ecological changes in both natural soil and agroecosystem. In the current study, the impacts of the amendment of Bt-transgenic rice (KMD) straw on biological activities in water-flooded soil were investigated under laboratory conditions and compared with non-transgenic rice (Xiushui 11) straw. The results showed that there were some differences in protease, neutral phosphatase and cellulase activities between soil amended with Bt-transgenic rice straw and non-transgenic rice straw at the early stage of incubation, and none of these differences were persistent. However, differences in dehydrogenase activity, methanogenesis, hydrogen production and anaerobic respiration between soil supplemented with Bt-transgenic rice straw and non-transgenic rice straw were persistent over the course of incubation. Dehydrogenase activity, methanogenesis and anaerobic respiration were considerably lower from sample days 7 to 56, but higher after day 56 in soil amended with Bt-transgenic rice straw. In comparison, the H2-production in soil containing Bt-transgenic rice straw was significantly lower after day 56. The results demonstrated that the amendment of the Bt-transgenic rice straw altered some important biological properties in water-flooded soil, indicating a shift in microbial populations or a change in the metabolic abilities of the microbial community as a result of substrate availability in soil. [Copyright &y& Elsevier]

The impact of straw incorporation (6 Mg ha[sup -1] year[sup -1]) into agricultural soils compared with straw removal on organic matter mineralization and salinity was studied. The mineralization coefficient (CO[sub 2]-C evolved/organic C ratio) was obtained to evaluate organic matter mineralization. Soil salinity was measured as means of electrolytic conductivity of saturation paste extract. Both parameters were measured seasonally during two years in two salt-affected soils of the semiarid Central Ebro Valley (northeast Spain), a saline soil and a saline-sodic soil. The electrolytic conductivity (ranging from 2.5 dS m[sup -1] to 24.3 dS m[sup -1]) and the mineralization coefficient (ranging from 5.9 10[sup -4] day[sup -1] to 37.9 10[sup -4] day[sup -1]) varied widely during seasonal samplings of both soils. The lowest electrolytic conductivity values, coincided with the highest mineralization coefficient values. Straw mulching and burying decreased significantly the average seasonal electrolytic conductivity of both soils: 2.5 times in the saline soil, and 1.9 times in the saline-sodic soil. The EC reduction only increased significantly (P < 0.05) the mineralization coefficient on saline soil (1.6 times). Straw amendment, followed by rainy periods, allowed the soluble salts leaching but did not modify significantly sodium content. A logarithmic regression was found between mineralization coefficient and electrolytic conductivity (r[sup 2] = 0.41), considering both soils. Infiltration, water aggregate stability, and qCO[sub 2] were improved with the straw amendment, but only in saline soil. Soil differences showed the existence of a double effect: an osmotic and a specific ion effect. [ABSTRACT FROM AUTHOR]

Straw amendment and plant root exudates modify the quality and quantities of soil dissolved organic matter (DOM) and then manipulate the fractions of soil selenium (Se) and its bioavailability. Two typical soils with distinct pH were selected to investigate the effect of different contributors on DOM-Se in soil. The mechanisms relying on the variation in DOM characteristics (quality, quantity and composition) were explored by UV–Vis, ATR-FTIR and 3D-EEM. Straw amendment significantly (p < 0.05) suppressed the selenate bioavailability. The reduction in wheat Se content was greater in krasnozems than in Lou soil, as more HA fraction appeared in krasnozems. The root exudates of wheat mainly elevated the low molecular hydrophilic compounds (Hy) in soil, which contributed to the SOL-Hy-Se fractions and thus grain Se in soils (p < 0.01). However, straw amendment promoted DOM transforming from small molecules (Hy and FA) to aromatic large molecules (HA), when accompanied with the reduction and retention of Se associated with these molecules. As a result, selenium bioavailability and toxicity reduced with DOM amendment and DOM-Se transformation. Image 1 • Straw amendment significantly inhibited selenate bioavailability in Lou soil and krasnozems. • Root exudates stimulated more SOL-Hy-Se fraction and thus enhanced Se availability. • Formation of HA-Se from selenate resulted in the reduction and retention of Se in soil. The wheat root and straw amendment affect selenate bioavailability through the Hy and FA/HA components and their functional groups in soil DOM. [ABSTRACT FROM AUTHOR]

To investigate the effects of straw amendments on the yield and root spatial distribution of maize under water stress, an experiment with rainproof shelter was conducted in the field experimental station of Shenyang Agricultural University in 2016 and 2017. The drip irrigation facilities were used to perform water stress treatments. Straw burying (T 1 ) and straw incorporation (T 2 ) as two approaches of straw amendments were conducted combined with three depths of 15 cm (D 1 ), 30 cm (D 2 ), and 45 cm (D 3 ) for straw returning, ploughing tillage at above three depths without straw presence as control in this study. During seedling and silking stages of maize, drought and water logging stresses were introduced respectively to the plants. Our results showed that the yield of maize under S 1 T 1 D 2 treatment in 2016 was significantly increased by 5.7%-7.1%. Compared with all the rest treatments, the dry weights of lateral roots and deep roots under S 1 T 1 D 2 treatment were increased by 67.3%-149.9% and 17.9%-116.4%, respectively. The dry matter accumulation in shoot of maize observed from S 1 T 1 D 2 treatment was significantly lower than those under other treatments, with 2.1%-35.8% reduction. Our results indicated that S 1 T 1 D 2 could significantly promote the growth and spatial distribution of maize root, accounting to release water stress and keep yield stabilization or promotion. Therefore, 30 cm of straw burying could be used as a suitable approach of straw returning for maize production in northeastern China, where the climate is with a pattern of drought first and waterlogging in later stage.