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Soil organic carbon (SOC) is the core component of terrestrial carbon (C) sink. Exploring the transformation and stabilization mechanism of SOC is key to understand the function of terrestrial C sink which copes with climate change. The traditional perspective is that plant residues are the initial source of SOC. The new concept of "soil microbial C pump" emphasizes that the synthesized products of soil microbial assimilation are important contributors to the stable SOC. This provides a new insight to the sequestration mechanism of SOC. Due to the complex and variable decomposition process of plant residues and the high heterogeneity of microbial residues, the transformation and stabilization mechanism of plant residues and microbial residues into SOC is still unclear. We reviewed research progress in plant and microbial residues, and introduced the characterization methods of quantification and transformation of plant residues and microbial residues, and also summarized the new findings on the transformation of plant and microbial residues into SOC. We further discussed the contribution and driving factors of microbial and plant-derived C to SOC. Finally, we prospected the future development direction and research focus in this field. This review would provide the scientific reference for the research of soil C sequestration in terrestrial ecosystem. [ABSTRACT FROM AUTHOR]

Abstract The increase in prices of fertilizers, energy and other materials necessary for the industry triggered a global economic crisis. Reason that was investigated on the biological and chemical characteristics in relation to the yield of radish nourished with humus from plant residue. The objective was to determine the appropriate dose of humus to obtain greater yield and its relationship with the chemical and biological characteristics of the radish. It is based on applied methodology with an experimental approach; Therefore, the Completely Random Block Design model was used, which consisted of 3 blocks and 5 treatments that were T1 with 0, T2 with 4, T3 with 6, T4 with 8 and T5 with 10 t/ha of humus and They applied 15 days after sowing. The physical characteristics of the radish were evaluated and processed using analysis of variance and Duncan. Concentration of elements in leaves and stomatal density were also analyzed. It was determined that T5 stood out in total plant length with 28.95 cm, plant weight with 76.87 g, equatorial diameter with 4,404 cm and commercial yield with 20,296 t/ha. Nitrogen consumption in relation to yield with 247.44 kg/ha. Stomatal density 459 stomata/mm2 and profitability with 150% and nutrient concentration in leaves highlighted T4 with N, K, Ca, Mg, Mo and Zn. It concludes that T5 stood out with 20,296 t/ha, which differed by 26.04% in relation to the control (T1) with 15,011 t/ha. Therefore, this dose added nutrients to the soil that improved the availability for plant absorption and this influenced the concentration of nutrients in leaves such as N, P and Fe and stomatal density with 459 stomata/mm2, which had a response in good development, strengthening against environmental stress and therefore greater performance.

At present, East Taihu Lake has been profoundly affected by human interventions. However, the earlier limnological conditions such as the occurrence of temporal nodes and the cause of eutrophication remain unclear due to the short temporal range covered by the instrumental record. The stable carbon isotope ratio of plant residue α-cellulose (δ13Ccellulose) is a sensitive proxy indicator of palaeoproductivity, but this proxy index is rarely used in Chinese lakes. In order to test whether δ13Ccellulose can be used as a lake ecological environment changes indicator, we investigated the relationship between the δ13Ccellulose and several geochemical proxies from a ∼ 30 cm core extending 100 years obtained from a shallow lake: East Taihu Lake, China. Here, the changes in δ13Ccellulose of plant residues in sediments from East Taihu Lake were coupled analysis with geochemistry indexes to identify the response of δ13Ccellulose from plant residues to the past environmental changes. Combined with the results of C/N ratios, δ13Ccellulose and other related studies, the big plant residues in the sediments of East Taihu Lake may be derived from autochthonous aquatic macrophytes. In addition, the δ13Ccellulose showed a significant negative correlation with total organic carbon, probably indicating the changes of primary productivity of the lake. The δ13Ccellulose and geochemical proxy records revealed that the environmental changes in East Taihu Lake have undergone three distinct periods. The first period (1900s-1960s) represented a natural state without intensive human disturbance. The acceleration of lake eutrophication from the middle period (1960s-1995s) was a consequence of intensive local human activities. The late stage (1995s-2010s) represented a minor decline in nutrient levels after the implementation of ecological protection and restoration. By comparing the results with historical documents and measurements from East Taihu Lake, we inferred that anthropogenic pressures were the primary cause of the changes in the aquatic macrophyte communities and environments. This study provides a unique approach to the ecological environment evolution of East Taihu Lake. At present, Taihu Lake still suffers from annual cyanobacterial blooms due to economic growth (urbanization and industrialization). There is an urgent need for interventions to reduce nutrient inputs in order to enhance ecosystem resilience. Finally, the results of study of East Taihu Lake in China reveal the potential of combining δ13Ccellulose and other geochemical proxies to study palaeoenvironmental change, which provides new perspectives for understanding lake ecological environmental change in lakes.

In this study, we explored the potential of a newly prepared nano-zero valent zinc (nZVZn), biochar (BC)/nZVZn and BC/hydroxyapatite-alginate (BC/HA-alginate) composites for the removal of inorganic As species from water. Relatively, higher percentage removal of As(III) and As(V) was obtained by nZVZn at pH 3.4 (96% and 94%, respectively) compared to BC/nZVZn (90% and 88%) and BC/HA-alginate (88% and 80%) at pH 7.2. Freundlich model provided the best fit (R2 = up to 0.98) for As(III) and As(V) sorption data of all the sorbents, notably for nZVZn. The pseudo-second order model well-described kinetics of As(III) and As(V) (R2 = 0.99) sorption on all the sorbents. The desorption experiments demonstrated that the As removal efficiency, up to the third sorption/desorption cycle, was in the order of nZVZn ∼ BC/HA-alginate (88%) > BC/nZVZn (84%). The Fourier transform infrared spectroscopy depicted that the –OH, –COOH, Zn–O and Zn–OH surface functional groups were responsible for the sorption of As(III) or As(V) on the sorbents investigated here. This study highlights that removal of As species from water by BC/nZVZn composite can be compared with nZVZn, suggesting that integrating BC with nZVZn could efficiently remove As from As-contaminated drinking water. This is the first study to explore the potential of a newly prepared sugarcane bagasse biochar/nano-zerovalent zinc (BC/nZVZn) based composite for the removal of inorganic arsenic (As) species from water. The results indicated high percentage removal of As(III) and As(V) from water by BC/nZVZn that were comparable to nZVZn alone. [ABSTRACT FROM AUTHOR]

Regular rice transplanting due to flooding, puddling and leveling has a negative impact on the soil structure, chemical properties and soil microbial activity. Therefore, the study was conducted on the effect of residues of pre-sowing some plants on quantitative and qualitative yield of rice in crop rotation. The experiment was conducted as split plots based on a randomized complete blocks design with four replications in Sari region during 2016 and 2017. Six crop rotation levels including fallow (control), faba bean, clover, perko, buko, and clover + ramtil + phaselia were used as main plots and four levels of nitrogen fertilizer including no consumption (control), 50% less than recommendation amount, recommendation amount based on soil test and 50% more than recommendation amount were 0, 50, 100 and 150 kg/ha of urea source as a sub plots, respectively According to the findings, the highest paddy yield (5147 kg/ha) was obtained for perko pre-sowing with 100 kg urea consumption per hectare, and pre-sowing of buko and multiple of clover + ramtil + phaselia was ranked next with 100 kg urea consumption per hectare. Totally, the highest paddy yield was achieved with pre-sowing of perko, buko, multiple of clover + ramtil + phaselia and clover and nitrogen consumption equals 100 kg urea per hectare. But, in pre-sowing of faba beans and fallow, the highest paddy yield was obtained with nitrogen consumption higher than recommendation amount (150 kg/ha). The highest protein yield was attributed to perko and buko pre-sowing. Moreover, the highest conversion efficiency, amylose content and gel consistency were obtained with perko pre-sowing, and these parameters got ranked next with pre-sowing of buko, clover + ramtil + phaselia, clover and faba bean, respectively.

Relay-cropping in saturated soil cultivation could increase land efficiency, but its effect on land use and nitrogen fertilizer efficiency is unclear. The research objective was to evaluate the land productivity of the relay-cropping system by calculating the land equivalent ratio (LER) and the effectiveness of nitrogen fertilizer, and by determining the effect of previous soybean biomass. The experiment was arranged in a three-factor randomized complete block design. The first factor was the cropping patterns of soybean and maize, i.e., relaycropping soybean-maize and maize monoculture. The second factor was the maize varieties, i.e., Pioneer 27 and Sukmaraga. The third factor was the application of N fertilizer with 4 doses: 0, 50, 100, and 150 kg ha-1. The results showed that the application of soybean biomass increased maize yield by 7.24%. Pioneer 27 produced a higher yield than Sukmaraga, and the dose of N fertilizer of 150 kg ha-1 resulted in the highest yield of 7.50 tons ha-1. The highest LER of 2.18% was achieved in the relay-cropping without applying follow-up N fertilizer (control). The experiment concludes relay-cropping after soybean save land by about 118% and save N fertilizer by 33.3%. The reduction of N fertilizer application by 33.3% (100 kg N ha-1) reduced corn cob productivity by 13.3%, and is not significantly different from 150 kg N ha-1. [ABSTRACT FROM AUTHOR]

Plant residues are often used as soil amendments in laboratory experiments, but they can reportedly release compounds interfering with soil DNA extraction and subsequent molecular biological analyses. Theoretically, for accurate comparison of microbial community composition in soils with and without added plant residues after a period of incubation, no significant difference at the beginning of the experiment is required between the amended and unamended control soils. We mixed plant residue into soil and immediately (within 10 min) commenced DNA extraction, and then performed 16S rRNA gene sequencing and quantitative PCR (qPCR) to determine bacterial community composition and abundance. Soil without plant residue addition served as a control. Five commonly used DNA extraction kits, 16S rRNA gene primer pairs, and soils, and two types (rice straw and alfalfa shoots) and three addition rates (2%, 4%, and 6%; w/w) of plant residue, were tested. In all cases, we found no significant difference in measured bacterial community composition or abundance between the treatments with and without added plant residue. [ABSTRACT FROM AUTHOR]

Regular rice transplanting due to flooding, puddling and leveling has a negative impact on the soil structure, chemical properties and soil microbial activity. Therefore, the study was conducted on the effect of residues of pre-sowing some plants on quantitative and qualitative yield of rice in crop rotation. The experiment was conducted as split plots based on a randomized complete blocks design with four replications in Sari region during 2016 and 2017. Six crop rotation levels including fallow (control), faba bean, clover, perko, buko, and clover + ramtil + phaselia were used as main plots and four levels of nitrogen fertilizer including no consumption (control), 50% less than recommendation amount, recommendation amount based on soil test and 50% more than recommendation amount were 0, 50, 100 and 150 kg/ha of urea source as a sub plots, respectively According to the findings, the highest paddy yield (5147 kg/ha) was obtained for perko pre-sowing with 100 kg urea consumption per hectare, and pre-sowing of buko and multiple of clover + ramtil + phaselia was ranked next with 100 kg urea consumption per hectare. Totally, the highest paddy yield was achieved with pre-sowing of perko, buko, multiple of clover + ramtil + phaselia and clover and nitrogen consumption equals 100 kg urea per hectare. But, in pre-sowing of faba beans and fallow, the highest paddy yield was obtained with nitrogen consumption higher than recommendation amount (150 kg/ha). The highest protein yield was attributed to perko and buko pre-sowing. Moreover, the highest conversion efficiency, amylose content and gel consistency were obtained with perko pre-sowing, and these parameters got ranked next with pre-sowing of buko, clover + ramtil + phaselia, clover and faba bean, respectively. [ABSTRACT FROM AUTHOR]

Nowadays, there are huge amounts of lignocellulosic materials left in agroforestry practice, which can be transformed into useful products. Biomass exploitation could be aiming not only at replacing conventional energy sources but also at preserving biodiversity and natural ecosystems. Five micromycetes were studied with goal to determine their potential to produce active cellulases as well as the ability to decompose pretreated wheat straw and oak sawdust after seven days of solid-state fermentation. Wheat straw was better lignocellulosic substrate than oak sawdust for the production of cellulases in all five micromycetes. Thus, Penicillium solitum BEOFB 1190m has shown to be the best producer of highly active forms of xylanases (7532.36 ± 89.37 U/L). The most active endo- and exocellulases (2299.70 ± 72.17 U/L and 195.66 ± 4.64 U/L, respectively) were produced by Trichoderma harzianum BEOFB 1230m, while the maximal value of β-glucosidase activity (215.69 ± 3.13 U/L) was detected after Fusarium graminearum BEOFB 820m cultivation. T. harzianum also showed high efficiency in wheat straw cellulose and hemicellulose depolymerization (23.90% and 33.00%, respectively), which resulted in the highest dry matter loss (36.25%). The results of the study showed great potential of tested micromycetes to synthesize cellulolytic enzymes and consequently transform abundant, low-cost plant residues such as wheat straw into useful products including biofuel.

Banana Fusarium wilt-suppressive soils are effective against pathogen invasion, yet soil physicochemical factors responsible for conducive or suppressive behavior have not been reported. Here, we investigated the changes in banana biomass, disease incidence (DI), soil culturable microbes and physicochemical properties by incorporating pepper and banana residues into conducive and suppressive soils. Before the incorporation of any residues, the suppressive soil significantly increased banana biomass and decreased DI compared to the conducive soil. The biomass of the suppressive soil was significantly higher than that of the conducive soil after the incorporation of either pepper or banana residues. Compared with the control (CK), the incorporation of pepper residues to both soils significantly reduced DI, while banana residues had the opposite effect. Additionally, both conducive and suppressive soils supplemented with pepper residues significantly reduced the amounts of culturable Fusarium oxysporum and increased the amounts of beneficial Pseudomonas and Bacillus. The pepper residue extracts significantly inhibited the growth of F. oxysporum mycelium. Soil alkali-hydrolyzable nitrogen (AN) responded most strongly to residue application to suppressive soil. The AN factor was significantly and positively correlated with banana biomass; however, there was no direct and significant negative correlation with DI. Further analysis of the results showed that elevated AN content could stimulate the amounts of culturable Bacillus in the soil, and Bacillus antagonized the proliferation of pathogen and thus indirectly and effectively reduced banana DI. In conclusion, soil AN content can indirectly improve the disease suppression ability of pepper-residue-mediated suppressive soil by manipulating the soil microbiome. [ABSTRACT FROM AUTHOR]

Input of plant residue carbon (C) stimulates microbial growth and activity, and thus may alter native soil organic matter (SOM) mineralization. The partition of plant residue C between microbial growth and respiration, and priming effect on soil organic C (SOC) are affected by initial SOM levels and plant residue types. However, how the interaction between SOM level and plant residue on microbial C use efficiency (CUE) and soil priming effect remains not very clear. Here, we quantified the ratio of plant residue C converted to microbial biomass production (as MBC) over that uptake by microorganism (MBC + respiration) and the priming effect on native SOC in two soils (with low and high initial SOM levels, abbreviated as LSOM and HSOM, respectively) added with 13C-labeled maize residues (root, stem and leaf) through a 180-day incubation. Microbial CUE of maize residue was the highest in the HSOM soil with leaf residue addition, and was the lowest in LSOM soil with stem and leaf residues addition. About 37% ~ 47% of maize residue C was remained in the soil after 180 days. At the end of incubation, the positive cumulative priming effects on native SOC mineralization induced by stem and leaf residues were 23% and 30% stronger (P < 0.05) in the HSOM soil than those of the LSOM soil, respectively. In contrast the root residue addition induced the negative priming effect on native SOC in the two SOM levels of soils. Overall, microbial CUE of maize residue was higher in soil with high initial SOM level, which is likely to promote SOM formation via microbial biomass, although there are many other factors that influence SOM formation. The interactive effect between initial SOM level and plant residue quality should be considered when understanding long-term SOM storage. [ABSTRACT FROM AUTHOR]

The decreasing number of farm households in Japan is beginning to affect soil carbon and nitrogen balance. At both cool and warm sites, the soil C level was the lowest in the second year of the experiment, and thereafter, it gradually increased. The change in soil C concentration was negative at the warmer site; however, the content reached 119 g C m−2 at the cooler site. Soil N showed a significant increase of 14.3 g N m−2 from the first year to over 4 years at the cooler site. At the cooler site, less soil decomposition contributed to the retention of soil C and N, and the dominant deciduous woody plants increased the supplemental C and N content. Land‐use management strategies involving conventional cultivation, abandonment and abandonment to recultivation did not affect the soil C and N balance for over 6 years. Fallow tillage to recultivation was less effective in retaining the C pool in the fifth year of the experiment, causing significantly lower soil C content (1.97 kg C m−2) than abandonment to recultivation (2.20 kg C m−2). Whereas the soil C content increased in the subsequent year (i.e. the sixth year), less productivity of recultivation crop (white mustard) contributed to a significant decrease in soil C, and abundant residue of winter wheat could recover the soil C and N in the subsequent year. The results suggest that agricultural abandonment can preserve soil C in cool regions and that the introduction of winter crops can maintain the C pool. [ABSTRACT FROM AUTHOR]

Abstract A continuous rise in the global demand for palm oil has resulted in the large‐scale expansion of oil palm plantations and generated environmental controversy. Efforts to increase the sustainability of oil palm cultivation include the recycling of oil mill and pruning residues in the field, but this may increase soil methane (CH4) emissions. This study reports the results of yearlong field‐based measurements of soil nitrous oxide (N2O) and CH4 emissions from commercial plantations in North Sumatra, Indonesia. One experiment investigated the effects of soil‐water saturation on N2O and CH4 emissions from inorganic fertilizers and organic amendments by simulating 25 mm rainfall per day for 21 days. Three additional experiments focused on emissions from (a) inorganic fertilizer (urea), (b) combination of enriched mulch with urea and (c) organic amendments (empty fruit bunches, enriched mulch and pruned oil palm fronds) applied in different doses and spatial layouts (placed in inter‐row zones, piles, patches or bands) for a full year. The higher dose of urea led to a significantly higher N2O emissions with the emission factors ranging from 2.4% to 2.7% in the long‐term experiment, which is considerably higher than the IPCC standard of 1%. Organic amendments were a significant source of both N2O and CH4 emissions, but N2O emissions from organic amendments were 66%–86% lower than those from inorganic fertilizers. Organic amendments applied in piles emitted 63% and 71% more N2O and CH4, respectively, than when spread out. With twice the dose of organic amendments, cumulative emissions were up to three times greater. The (simulated) rainwater experiment showed that the increase in precipitation led to a significant increase in N2O emissions significantly, suggesting that the time of fertilization is a critical management option for reducing emissions. The results from this study could therefore help guide residue and nutrient management practices to reduce emissions while ensuring better nutrient recycling for sustainable oil palm production systems.

Banana Fusarium wilt-suppressive soils are effective against pathogen invasion, yet soil physicochemical factors responsible for conducive or suppressive behavior have not been reported. Here, we investigated the changes in banana biomass, disease incidence (DI), soil culturable microbes and physicochemical properties by incorporating pepper and banana residues into conducive and suppressive soils. Before the incorporation of any residues, the suppressive soil significantly increased banana biomass and decreased DI compared to the conducive soil. The biomass of the suppressive soil was significantly higher than that of the conducive soil after the incorporation of either pepper or banana residues. Compared with the control (CK), the incorporation of pepper residues to both soils significantly reduced DI, while banana residues had the opposite effect. Additionally, both conducive and suppressive soils supplemented with pepper residues significantly reduced the amounts of culturable Fusarium oxysporum and increased the amounts of beneficial Pseudomonas and Bacillus. The pepper residue extracts significantly inhibited the growth of F. oxysporum mycelium. Soil alkali-hydrolyzable nitrogen (AN) responded most strongly to residue application to suppressive soil. The AN factor was significantly and positively correlated with banana biomass; however, there was no direct and significant negative correlation with DI. Further analysis of the results showed that elevated AN content could stimulate the amounts of culturable Bacillus in the soil, and Bacillus antagonized the proliferation of pathogen and thus indirectly and effectively reduced banana DI. In conclusion, soil AN content can indirectly improve the disease suppression ability of pepper-residue-mediated suppressive soil by manipulating the soil microbiome.

Within the domain of phytoremediation research, the proper disposal of harvestable plant parts, that remove pollutants from contaminated soil, has been attracted extensive attention. Here, the bioenergy generation capability of trace metals (Cu, Pb, Zn, Cd, Mn, and As) polluted plants was assessed. The biogas production potential of accumulators or hyperaccumulator plants, Elsholtzia haichowensis, Sedum alfredii, Solanum nigrum, Phytolacca americana and Pteris vittata were 259.2 ± 1.9, 238.7 ± 4.2, 135.9 ± 0.9, 129.5 ± 2.9 and 106.8 ± 2.1 mL/g, respectively. The presence of Cu (at approximately 1000 mg/kg) increased the cumulative biogas production, the daily methane production and the methane yield of E. haichowensis. For S. alfredii, the presence of Zn (≥500 mg/kg) showed a significant negative impact on the methane content in biogas, and the daily methane production, which decreased the biogas and methane yield. The biogas production potential increased when the content of Mn was at 5 000–10,000 mg/kg, subsequently, decreased when the value of Mn at 20,000 mg/kg. However, Cd (1–200 mg/kg), Pb (125–2000 mg/kg) and As (1250–10,000 mg/kg) showed no distinctive change in the cumulative biogas production of S. nigrum, S. alfredii and P. vittata, respectively. The methane yield showed a strong positive correlation (R2 =0.9704) with cumulative biogas production, and the energy potential of the plant residues were at 415–985 kWh/ton. Thus, the anaerobic digestion has bright potential for the disposal of trace metal contaminated plants, and has promising prospects for the use in energy production.

Flood increases due to an increase in river overflow which affects on abiotic and biotic factors. The preliminary study of flood-affected crops was carried out in flood-affected cropland of Koshi Tappu Region of Eastern Nepal. For the experiment the plant residues of Eichhornia crassipes and Sesbania rostrata and inorganic fertilizer were selected to examine the growth and yield in Vigna unguiculata. The appropriate treatments for the production of V. unguiculata were analyzed. Before applying treatments, soil was collected and analyzed for physicochemical, microbial biomass and available nitrogen. Soil texture, soil moisture, water holding capacity and bulk density (BD) were calculated. The parameters such as soil pH organic carbon, organic matter and total nitrogen were determined. Soil microbe increases the significance of organic carbon and soil nitrogen is correlated for growth and yield. The results showed that the combined urea and plant residue increases the highest yield. And the Eichhornia compost represents the highest leaf area index and biomass. The total pod production was found in the Echhhornia compost. The dry weight per single pod in Eichhornia fresh was 7.82 g and in Sesbania fresh was 7.42 g. It proves that the land pattern is significant for the soil organic compounds. The experiment showed that the use of plant residues enhanced the increase of physicochemical properties of soil by adding the nutrients. The combined Urea + Eichhornia supports the best growth and development of the plant. DOI: http://dx.doi.org/10.5281/zenodo.4338159

Flood increases due to an increase in river overflow which affects on abiotic and biotic factors. The preliminary study of flood-affected crops was carried out in flood-affected cropland of Koshi Tappu Region of Eastern Nepal. For the experiment the plant residues of Eichhornia crassipes and Sesbania rostrata and inorganic fertilizer were selected to examine the growth and yield in Vigna unguiculata. The appropriate treatments for the production of V. unguiculata were analyzed. Before applying treatments, soil was collected and analyzed for physicochemical, microbial biomass and available nitrogen. Soil texture, soil moisture, water holding capacity and bulk density (BD) were calculated. The parameters such as soil pH organic carbon, organic matter and total nitrogen were determined. Soil microbe increases the significance of organic carbon and soil nitrogen is correlated for growth and yield. The results showed that the combined urea and plant residue increases the highest yield. And the Eichhornia compost represents the highest leaf area index and biomass. The total pod production was found in the Echhhornia compost. The dry weight per single pod in Eichhornia fresh was 7.82 g and in Sesbania fresh was 7.42 g. It proves that the land pattern is significant for the soil organic compounds. The experiment showed that the use of plant residues enhanced the increase of physicochemical properties of soil by adding the nutrients. The combined Urea + Eichhornia supports the best growth and development of the plant. [ABSTRACT FROM AUTHOR]

Plant residues that remain in the soil of an integrated crop-livestock system constitute an important reserve of nutrients for crops in succession. The objective of this study was to evaluate the release of calcium (Ca), magnesium (Mg), and sulfur (S) from the decomposition of Urochloa brizantha cv. BRS Piatã pasture grass, fertilized with three different doses of nitrogen (N) and subjected to two different desiccation periods, prior to sowing a soybean crop. The experiment was conducted in Londrina, Paraná, between March 2016 and March 2018. Three different doses of N were applied to a pasture of U. brizantha cv. BRS Piatã (0, 150 and 300 kg N ha-1), forming three distinct paddocks. In each paddock, two different periods (60 and 15 days prior to sowing soybeans) for pasture desiccation were evaluated with four replications. Polynomial regression analysis was performed for the period after desiccation. Ca and S content in the U. brizantha straw did not vary over the course of decomposition, while magnesium content decreased, despite nitrogen fertilization and the desiccation periods. The amount of Ca released from U. brizantha straw by the end of the successive soybean cycle was approximately 15 kg ha-1, despite nitrogen fertilization and the desiccation periods. The amount of Mg released from U. brizantha straw by the end of the successive soybean cycle ranged from 10 to 15 kg ha-1, while the release of greater amounts tended to correspond with the presence of nitrogen fertilization in the pasture grass. The amount of S released from U. brizantha straw by the end of the successive soybean cycle ranged from 4 to 6 kg ha-1, while the release of lesser amounts tended to correspond with the presence of nitrogen fertilization in the pasture grass, despite the desiccation periods. [ABSTRACT FROM AUTHOR]

Energy worldwide crisis devotes the concern of the scientific forums to find better solutions for an efficient and economical energy source instead of the conventional Petro-fuels. Herein, this study addresses the utilization of plant waste-derived heterogeneous catalysts for efficient biodiesel (BD) production from waste frying oil (WFO). Hydrochar is fabricated from orange peels to valorize the waste-to-fuel approach through utilizing plant residue and WFO to make the whole process more economical and environmentally benign. Hydrothermal carbonization of orange peels is used for the fabrication of hydrochar. Then, a novel potassium carbonate/orange peel-derived activated hydrochar (KC/OAH) heterogeneous catalyst is employed for a competent methanolysis of WFO. Various characterization techniques are employed to elucidate the physicochemical properties of the proposed materials. The evaluated optimal mass ratio of the catalyst composition is 2:1 K 2 CO 3 : OAH (2-KC/1-OAH). Next, a central composite design (CCD) via response surface methodology (RSM) is utilized to disclose the optimum operational parameters at which the reaction is implemented. Optimum conditions of 4.4 wt %, 6.6:1 methanol to oil molar ratio, and 108 min reaction time at a fixed reaction temperature of 50 °C result in biodiesel conversion of c.a. 89.2 %. A low minimum selling price (MSP) of biodiesel of 1.12 $/kg is developed, which confirms the low cost of the overall process to produce the biodiesel. The significant leaching of K+ (2-KC/1-OAH) necessitates chemical regeneration via re-soaking of the spent catalyst in K 2 CO 3 , which restores the activity and provides the same high biodiesel conversion as the genuine catalyst. Ultimately, the physico-chemical properties of the produced biodiesel are found to be compatible with international limits, which elevates the safe usage of this fuel in automobile engines. [Display omitted] • Waste to fuel approach is achieved via utilizing catalyst waste precursor & WFO. • Hydrothermal carbonization is utilized for preparation of OAH from orange peels. • The low reaction conditions (6.6:1 M:O, 50 °C & 108 min) offer conversion of 89.2 %. • The minimum selling price of biodiesel production was estimated to be 1.12 $/kg. • The obtained biodiesel from WFO meets ASTM D-6751 and EN 14214 standards. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this work was to evaluate the effect of different amounts of black oat (Avena strigosa) straw covering soil surface on soil temperature at different depths. The treatments consisted of 0, 3, 6, and 9 Mg ha-1 straw. Soil temperature was measured hourly by a thermocouple inserted at different depths (0, 5, 15, 30, and 50 cm) and was used to adjust an equation correlating the temperature of covered soil with that of bare soil. With the correlations, it was possible to observe a point value of temperature (inversion temperature of straw effect), below which the presence of straw acts positively on the maintenance of soil temperature and above which the presence of straw acts negatively on soil heating.

Soil organic carbon (SOC) is the core component of terrestrial carbon (C) sink. Exploring the transformation and stabilization mechanism of SOC is key to understand the function of terrestrial C sink which copes with climate change. The traditional perspective is that plant residues are the initial source of SOC. The new concept of "soil microbial C pump" emphasizes that the synthesized products of soil microbial assimilation are important contributors to the stable SOC. This provides a new insight to the sequestration mechanism of SOC. Due to the complex and variable decomposition process of plant residues and the high heterogeneity of microbial residues, the transformation and stabilization mechanism of plant residues and microbial residues into SOC is still unclear. We reviewed research progress in plant and microbial residues, and introduced the characterization methods of quantification and transformation of plant residues and microbial residues, and also summarized the new findings on the transformation of plant and microbial residues into SOC. We further discussed the contribution and driving factors of microbial and plant-derived C to SOC. Finally, we prospected the future development direction and research focus in this field. This review would provide the scientific reference for the research of soil C sequestration in terrestrial ecosystem.

A continuous rise in the global demand for palm oil has resulted in the large‐scale expansion of oil palm plantations and generated environmental controversy. Efforts to increase the sustainability of oil palm cultivation include the recycling of oil mill and pruning residues in the field, but this may increase soil methane (CH4) emissions. This study reports the results of yearlong field‐based measurements of soil nitrous oxide (N2O) and CH4 emissions from commercial plantations in North Sumatra, Indonesia. One experiment investigated the effects of soil‐water saturation on N2O and CH4 emissions from inorganic fertilizers and organic amendments by simulating 25 mm rainfall per day for 21 days. Three additional experiments focused on emissions from (a) inorganic fertilizer (urea), (b) combination of enriched mulch with urea and (c) organic amendments (empty fruit bunches, enriched mulch and pruned oil palm fronds) applied in different doses and spatial layouts (placed in inter‐row zones, piles, patches or bands) for a full year. The higher dose of urea led to a significantly higher N2O emissions with the emission factors ranging from 2.4% to 2.7% in the long‐term experiment, which is considerably higher than the IPCC standard of 1%. Organic amendments were a significant source of both N2O and CH4 emissions, but N2O emissions from organic amendments were 66%–86% lower than those from inorganic fertilizers. Organic amendments applied in piles emitted 63% and 71% more N2O and CH4, respectively, than when spread out. With twice the dose of organic amendments, cumulative emissions were up to three times greater. The (simulated) rainwater experiment showed that the increase in precipitation led to a significant increase in N2O emissions significantly, suggesting that the time of fertilization is a critical management option for reducing emissions. The results from this study could therefore help guide residue and nutrient management practices to reduce emissions while ensuring better nutrient recycling for sustainable oil palm production systems. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the inhibition of weed growth by different plant parts, extraction methods and cultivars of Italian ryegrass (Lolium multiflorum Lam., IRG) and determine the levels of total phenol and flavonoid contents in shoots and roots of IRG. Shoot and root length of the five weeds were inhibited to a much greater degree by fermentation extract than water, boiling water and ethanol extracts. Shoot and root length were inhibited by 96 and 94% in Monochoria vaginalis, 72 and 95% in Aeschyoa indica L., 69 and 89% in Leptochloa chinensis L. and 61 and 99% in Echinochloa crus-galli L., respectively, in response to IRG shoot fermentation extracts at 5%. In response to the same extract, Ludwigia prostrata Roxb. shoot and root length were both 100% inhibited. Inhibition of shoot and root length of the aforementioned weeds was higher in response to fermentation extracts of IRG shoots than those of IRG roots. In addition, root length was inhibited to a greater degree than shoot length in response to the fermentation extracts. There were no differences between six cultivars (Greenfarm, Hwasan 101, Florida 80, Top 90, Corwinmaster and Corwinari) on inhibition of weed growth in response to IRG shoot extracts. Total phenol contents in the shoot of six IRG cultivars were almost 1.4-2 times higher than those of roots. Additionally, the total flavonoid contents in the shoot of six IRG cultivars were 8-19 times higher than those of roots. Standard phenol compounds such as hydrocinnamic acid, caffeic acid, p-coumaric acid and ferulic acid produced similar weed inhibition. Thus, it appears that the weed inhibiting effects of IRG can be attributed to their phenol contents. [ABSTRACT FROM AUTHOR]

In this work, residue powder of brown Rumex dentatus L. plant (R), after extracting most of its active components by 70% ethanol is used as an adsorbent for wastewater treatment. The biosorbent R before and after adsorption processes was investigated using Fourier-transform infrared spectroscopy and scanning electron microscopy. The factors affecting adsorption of Cd2+ and Cr3+ onto R such as biomass weight, initial concentration, contact time, temperature and pH were studied and the results showed that R had higher metal uptake percentage reaching 98.6% and 98.1 for Cd2+ and Cr3+, respectively, at pH, 50 mg of catalyst, 25°C and initial metal concentration of 100 mg L–1. The adsorption isotherm showed that Cd2+ adsorption follows Freundlich isotherms while Cr3+ fitted with Temkin isotherm and pseudo-second-order kinetics for both metal ions and the maximum amounts of metal ions adsorbed were found to be 81.76 and 31.5 mg g–1 for Cd2+ and Cr3+, respectively. Reusability test of R showed that R was effectively reusable adsorbent for both metal ions. [ABSTRACT FROM AUTHOR]

• The δ13C cellulose and geochemical proxies were analyzed in East Taihu Lake. • The δ13C cellulose probably indicates changes in the productivity of the lake. • There is an urgent need for action to reduce nutrient inputs to lakes. At present, East Taihu Lake has been profoundly affected by human interventions. However, the earlier limnological conditions such as the occurrence of temporal nodes and the cause of eutrophication remain unclear due to the short temporal range covered by the instrumental record. The stable carbon isotope ratio of plant residue α-cellulose (δ13C cellulose) is a sensitive proxy indicator of palaeoproductivity, but this proxy index is rarely used in Chinese lakes. In order to test whether δ13C cellulose can be used as a lake ecological environment changes indicator, we investigated the relationship between the δ13C cellulose and several geochemical proxies from a ∼ 30 cm core extending 100 years obtained from a shallow lake: East Taihu Lake, China. Here, the changes in δ13C cellulose of plant residues in sediments from East Taihu Lake were coupled analysis with geochemistry indexes to identify the response of δ13C cellulose from plant residues to the past environmental changes. Combined with the results of C/N ratios, δ13C cellulose and other related studies, the big plant residues in the sediments of East Taihu Lake may be derived from autochthonous aquatic macrophytes. In addition, the δ13C cellulose showed a significant negative correlation with total organic carbon, probably indicating the changes of primary productivity of the lake. The δ13C cellulose and geochemical proxy records revealed that the environmental changes in East Taihu Lake have undergone three distinct periods. The first period (1900s-1960s) represented a natural state without intensive human disturbance. The acceleration of lake eutrophication from the middle period (1960s-1995s) was a consequence of intensive local human activities. The late stage (1995s-2010s) represented a minor decline in nutrient levels after the implementation of ecological protection and restoration. By comparing the results with historical documents and measurements from East Taihu Lake, we inferred that anthropogenic pressures were the primary cause of the changes in the aquatic macrophyte communities and environments. This study provides a unique approach to the ecological environment evolution of East Taihu Lake. At present, Taihu Lake still suffers from annual cyanobacterial blooms due to economic growth (urbanization and industrialization). There is an urgent need for interventions to reduce nutrient inputs in order to enhance ecosystem resilience. Finally, the results of study of East Taihu Lake in China reveal the potential of combining δ13C cellulose and other geochemical proxies to study palaeoenvironmental change, which provides new perspectives for understanding lake ecological environmental change in lakes. [ABSTRACT FROM AUTHOR]

Organic matter has low N content; however, organic matter may be enriched by inoculation with selected diazotrophic bacteria. The aim of the paper was to evaluate the effects of biofertilizer produced by mixing different types and proportions of organic matter inoculated with the diazotrophic bacteria Beijerinckia indica. The experiment consisted of plastic trays (6 L) containing 5 kg of three different types of organic matter (filter mud cake, earthworm compost, and crop residue) applied in the following proportions (v:v:v): 1-(5:0:0), 2-(4:1:0), 3-(4:0:1), 4-(3:2:0), 5-(3:1:1), 6-(3:0:2), 7-(2:3:0), 8-(2:2:1), 9-(2:1:2), 10-(2:0:3), 11-(1:4:0), 12-(1:3:1), 13-(1:2:2), 14-(1:1:3), 15-(1:0:4), 16-(0:5:0), 17-(0:4:1), 18-(0:1:4), 19-(0:3:2), 20-(0:2:3), and 21-(0:0:5). Samples were collected following inoculation with B. indica at 0, 10, 20, 30, and 40 days of the maturation phase. The chemical analyses were: pH (H2O), total C and N, available P and K, and exchangeable Na+, Ca+2, Mg+2. The treatments with the best results showed significant effects following the maturation phase. The exceptions were C and N, which presented only individual effects. In general, the organic matter proportions (5:0:0), (3:2:0), and (2:3:0) resulted in a significant increase in the availability of nutrients. Biofertilizers with optimal organic matter proportions may be used to produce organic substrates that are more effective and have the potential to be applied as alternatives to soluble NPK fertilizers.

Oil incorporated plant residues are an important source of carbon inputs and its decomposition defines magnitudes of many soil processes. While soil properties, especially soil moisture levels, influence decomposition rates, the moisture level of plant residue itself can differ from that of the surrounding soil due to the so called “sponge effect”-water absorption by plant residue from the surrounding soil. Our study explored whether water absorption by plant residue varies depending on soil moisture and matric potential levels; and how soil characteristics and characteristics of the plant residue itself affect the magnitude of this effect. We examined water retention of two types of plant residue materials, namely, corn and soybean leaves, in soil materials with three contrasting particle size distributions (PSD); and analyzed water distribution patterns in the soil adjacent to the residue using X-ray computed micro-tomography. The results demonstrated that the sponge effect was especially pronounced when soil moisture levels ranged from 0.15 to 0.40 cm 3 cm − 3 (~ 30–80% water filled pore space). The leaves were fully saturated with gravimetric water content levels exceeding 2.0 g g − 1 even when the soil moisture level was only 0.15 cm 3 cm − 3 . Subsequent increase in residue moisture level was achieved due to vertical swelling of residue and reached 3.0–4.0 g g − 1 at soil moisture levels > 0.30 cm 3 cm − 3 . The sponge effect was greater in the coarse textured soil materials with lower soil water retention than in the fine textured soil material with high water retention; it was greater in soybean than in corn, possibly due to greater porosity of soybean leaves. Our results indicate that plant residue fragments incorporated into soil likely create moisture microenvironments for microbial decomposers that differ from those of the surrounding soil; and which, in relatively dry soil, can be more beneficial for plant decomposition than what can be inferred from the information on moisture levels of the soil itself. [ABSTRACT FROM AUTHOR]

Organic matter has low N content; however, organic matter may be enriched by inoculation with selected diazotrophic bacteria. The aim of the paper was to evaluate the effects of biofertilizer produced by mixing different types and proportions of organic matter inoculated with the diazotrophic bacteria Beijerinckia indica. The experiment consisted of plastic trays (6 L) containing 5 kg of three different types of organic matter (filter mud cake, earthworm compost, and crop residue) applied in the following proportions (v:v:v): 1-(5:0:0), 2- (4:1:0), 3-(4:0:1), 4-(3:2:0), 5-(3:1:1), 6-(3:0:2), 7-(2:3:0), 8-(2:2:1), 9-(2:1:2), 10-(2:0:3), 11-(1:4:0), 12-(1:3:1), 13-(1:2:2), 14-(1:1:3), 15-(1:0:4), 16-(0:5:0), 17-(0:4:1), 18-(0:1:4), 19-(0:3:2), 20-(0:2:3), and 21-(0:0:5). Samples were collected following inoculation with B. indica at 0, 10, 20, 30, and 40 days of the maturation phase. The chemical analyses were: pH (H2O), total C and N, available P and K, and exchangeable Na+, Ca+2, Mg+2. The treatments with the best results showed significant effects following the maturation phase. The exceptions were C and N, which presented only individual effects. In general, the organic matter proportions (5:0:0), (3:2:0), and (2:3:0) resulted in a significant increase in the availability of nutrients. Biofertilizers with optimal organic matter proportions may be used to produce organic substrates that are more effective and have the potential to be applied as alternatives to soluble NPK fertilizers. [ABSTRACT FROM AUTHOR]

Soil microbial communities and their related characteristics are an important agent for soil fertility, productivity, and sustainability. Also, they are useful indicators of soil quality and life index in agricultural systems. The objectives of this study were the effect of nanozeolite and plant residues on soil microbial communities and their characteristics and also, the assessment of incubation timing on soil microbial properties. Soil microorganisms are very important in the decomposition of plant residues. In this regard, the soil samples were treated by nanozeolite (0, 10 and 30% Weight), Alfalfa and wheat straw (0 and 5% Weight). The treated soil samples were incubated in lab condition for 90 days. The result of this study showed that Bacterial, Fungal, and Actinomycete populations increased by the addition of 30% of nanozeolite and 5% of plant residues, especially alfalfa straw. Also, the addition of nanozeolite and plant residues treatments improved MBC, BR, and SIR as microbial characteristics. These parameters increased after 30 days of starting incubation, then decreased until the 75th day and finally increased slightly on the 90th day. In fact, the addition of nanozeolite and plant residues into the soil had positive effects on improvement of carbon pools and increasing carbon sequestration in it. Applied nanozeolite and plant residues in soil, improved carbon pools and increased carbon sequestration in soil. Also the application of nanozeolite and plant residues especially alfalfa straw had positive effects on improvement of soil biological communities and characteristics. [ABSTRACT FROM AUTHOR]

Greenhouse gas emissions from paddy soils respond differently to different combinations of crop root residues and N forms. An incubation experiment was carried out to explore the effect of four crop residues (milk vetch, ryegrass, winter wheat, and rape) and four nitrogen treatments (without fertilizer, urea, (NH)SO, and KNO) on CH, CO, and NO emissions in a paddy soil. Except in KNO application treatments, CH emissions of milk vetch residue treatments were significantly higher than those of the rest residue treatments. In the presence of milk vetch and ryegrass residues, urea application significantly increased CH emissions in comparison to treatments without fertilizer. Urea significantly promoted CO emissions, whereas (NH)SO and KNO significantly inhibited CO emissions at all root residue treatments. Urea did not increase NO emissions, but (NH)SO and KNO promoted NO emissions at all residue treatments. In addition, KNO had more effects on the increase of NO emissions than (NH)SO in milk vetch-amended soils. Urea addition had no effect on global warming potentials, and (NH)SO and KNO addition significantly increased global warming potentials at all residue treatments except KNO + winter wheat residue combination. Our results indicated that urea application had no additive effect on global warming when root residues were left in paddy soils, whereas (NH)SO and KNO application could increase the risk of global warming. [ABSTRACT FROM AUTHOR]

Through field experiments and empirical analysis methods, this study determined the dependence of plant residue removal on the row cleaner’s settings in strip-tillage. The main research object of this study is row cleaners. By changing the slip angles (10, 15, and 22.5°), the gap between row cleaner discs in parallel (165, 180, and 195 mm), and the driving speed (1.3, 1.9, 2.5, and 3.1 m s−1), we determined what percentage of wheat residue was removed from the strip on the surface of the soil and what distance it was moved. The percentage of removed plant residue was determined by evaluating the differences between the masses of the plant residue taken from non-removed and removed strips. Empirical analysis of the results of the field experiments showed that both the amount of the removed plant residue and the distance it is moved to were the best when the slip angle was 15°, the gap between the discs of row cleaner was 180 mm, and the driving speed was 2.5 m s−1. With these parameters, up to three-quarters of the plant residue was removed from the soil surface of the strip, which was relocated 308 mm from the middle of the strip. If the slip angle and the driving speed are increased further, even more plant residue can be removed; however, if the plant residue is relocated too far away, it may fall into the zone of the adjacent strip.

Decomposition of the plant residue added to soil affects fate of native soil organic matter (SOM) via magnitude and direction of priming effect (PE). Soil pore characteristics, namely, pore size distribution (PSD), regulate air and liquid fluxes, as well as transport of solubilized decomposing residue to microorganisms. The goal of this study was to assess the effect of PSD on plant residue decomposition and PE as modulated by i) residue quality, ii) soil moisture status, and iii) long-term management history. We combined labeling and imaging approaches to visualize loss of decomposing residue and link it to PE in soils with two contrasting PSDs, dominated by small (5–10 μm) pores and by a combination of very small (<5 μm) and large (>30 μm) pores, respectively. The microcosms were incubated with 13 C-labeled corn and soybean leaves, in soils from long-term conventional and biologically based managements. X-ray computed micro-tomography scanning was utilized to visualize loss of intact leaves at early stages (7, 14, 24 d) of decomposition. We found that PSD of soil adjacent to the decomposing plant residue played a major role in the fate of the residue and of its decomposition products. In microcosms with prevalence of small (5–10 μm) pores decomposition of corn leaves was slower, movement of decomposition products into the adjacent soil was greater, and proportion of CO 2 that originated from the residue was lower than in the microcosms with prevalence of large pores. Greater positive PE took place in microcosms with small than with large pores. While these tendencies were observed in all studied soil moisture levels, management practices, and plant residue substrates, they were most pronounced in microcosms with more labile residue (soybean) in the soil from long-term biologically based management. Across treatments, the intensity of PE was greater for soils under conventional than biologically-based management. The findings emphasize importance of accounting for soil PSD when assessing processes of soil C accrual and priming. [ABSTRACT FROM AUTHOR]

The soil application of plant residues characterized by different carbon to nitrogen (C:N) ratios may lead to conditions more suitable to denitrifying and nitrite ammonifying bacteria. While the former microbial group fosters the loss of nitrogen (N) through the production of N 2 and nitrous oxide (N 2 O), the latter may retain N into the agroecosystems. At present time there is no evidence on the effect of plant residues application on ammonifying bacterial populations over the winter. Dynamics of denitrifiers and nitrite ammonifiers abundance, composition and gaseous emissions (i.e. N 2 O and CO 2 ) in soils following fall plough-down of barley (BRL) or red clover (RC) were evaluated at different time points for two consecutive winters in a humid temperate environment. Abundance of denitrifiers ( nirK and nirS ) and nitrite ammonifiers ( nrfA ) was greater in BRL-treated plots compared with RC, despite the higher C:N ratio of BRL. The present (DNA) and active (RNA) community structure of both denitrifiers and ammonifiers was different between BRL- and RC-treated plots and changed continuously during the two winters. The results suggested that both cold-induced edaphic conditions and crop residue application influenced and shaped the targeted functional communities. N 2 O and CO 2 emission rates did not respond to crop residue source, however the emissions were 5–8-times greater in coldest months (i.e. January/February) compared to other dates during both winters. Our findings showed that cold-adapted denitrifying and nitrite ammonifying bacteria had a very similar response to the crop residues in abundance and diversity, suggesting that the application of contrasting C:N ratio crop residues did not create different niches for the nitrite ammonifiers and denitrifiers during the winter. [ABSTRACT FROM AUTHOR]

Input and decomposition of plant-derived organic matter are key processes of the C and N cycling in the post-agricultural succession. This study compared three treatments in order to better understand the contribution of plant-derived organic matter to the C and N levels of the ecosystem in abandoned agrosystems. Mowing without plant residue removal can increase the addition of fresh plant residue and prevented the succession to Solidago altissima . In the fifth year of experimentation, the significantly higher floor litter C in the no mowing lead to a higher total C accumulation than that in the mowing treatments. Mowing reduced the floor litter C by 40% and 13%, in the third to fifth year of experimentation, respectively. Additionally, it rapidly changed the vegetation coverage, and decreased the total C in the early stages of post-agricultural succession. Therefore, mowing was less effective in retaining the C pool due to the addition of fresh plant residue and its decomposition, whereas no mowing can increase the addition of plant residue, leading to be relatively high total N. However, the N input might be insufficient to compensate for the mineral soil-N reduction in the early stages of post-agricultural succession. [ABSTRACT FROM AUTHOR]