Residue Amendment Research Articles

Seawater neutralization and gypsum amelioration of bauxite refining residue to produce a plant growth medium

Alumina production waste (bauxite refining residue) is highly alkaline, saline, and sodic, and hence cannot support plant growth for revegetation. Gypsum (CaSO4.2H2O) amendment of bauxite residue can lower alkalinity and improve the residue Ca status, but given the large gypsum requirement, efficient gypsum use is imperative. We investigated gypsum amelioration of residue sand (RS), examining changes in RS chemistry, and growth of Rhodes grass (Chloris gayana). Furthermore, we examined whether gypsum amelioration of RS should occur before or after seawater neutralization. We found that Ca from gypsum (20 t ha−1) was retained within the surface 0.2 m of RS, regardless of whether the gypsum was applied before or after seawater neutralization. This Ca was retained both as exchangeable Ca and as a precipitate (either calcite or hydrotalcite), with ca. 50% retained as exchangeable Ca in both approaches. Gypsum at 20 t ha−1, or even lower, provided sufficient Ca for maximum growth of Rhodes grass, in the surface, but higher rates would be required to allow Ca movement down the Na-dominated profile to ameliorate a larger rooting depth – this being important in environments where there are prolonged periods of water stress. The information presented will guide the efficient use of gypsum to ameliorate bauxite refining wastes.

Mitigation of CO2, CH4 and N2O from Acidic Clayey Soil Amended with Fertilizer Pellets Based on Alkaline Organic Residues

Alkaline organic residues, such as wood ash (WA), deinking paper sludge (DPS), and mixed paper sludge (MPS) could have a significant potential for mitigating greenhouse gases (GHG) when they are used for land application. The DPS was mixed and then granulated with MPS, WA and/or composted DPS to form pellets. A 56-d incubation study was carried out to investigate the effect of alkaline organic residue pellets on: (1) the biological and chemical properties of acidic clayey soil; (2) on carbon dioxide (CO2), on methane (CH4), and nitrous oxide (N2O) soil emissions. The experimental design included eight different treatments: unfertilized control (Control), fertilized control with mineral nitrogen (controlF), and six pelleted alkaline organic residue amendments (T1–T6) combined with mineral nitrogen fertilizer. The six amendments were: (T1) 100% DPS; (T2) 100% composted [50% poultry manure and 50% T1]; (T3) 50%WA + 50% T1; (T4) 50% WA + 50% T2; (T5) 50%T2 + 30%WA + 20% MPS; (T6) 50% T1 + 30%WA + 20% MPS. The results showed that alkaline residues significantly increased soil pH, the concentration of water-extractable organic carbon, and water-extractable nitrogen. Alkaline treatments had a positive effect on soil microbial activity. The highest mitigation efficiency of cumulative CO2 was obtained with T4, which released 10% less CO2 than other treatments. No significant effect on cumulative CH4 emissions was observed. Total cumulative N2O emissions were reduced by 37% with T5. Our study also showed that organic pellets based on alkaline residues improved the soil properties and can play a role in the mitigation of GHG in acidic clayey soil. Therefore, the co-application of alkaline organic residue pellets with chemical fertilizer might be considered as a sustainable approach in agriculture.

Soil macrofaunal activity, microbial catabolic limitations and nutrient cycling in cropping systems amended with woody residues and nitrogen inputs

Agroecological practices are emerging as efficient alternatives to address the challenge of sustainable agriculture. The objective of this study was to examine whether plant residue amendments from stems and leaves (SL) of an agroforestry shrub (Piliostigma reticulatum) enriched with nitrogen (N) sources improve nutrient cycling in Soudano-Sahelian cropping systems. The experimental design was organized into four replicates with six treatments consisting of two treatments of SL residue amendments (amended and non-amended) in combination with three treatments including additional N sources (natural soils, urea, and cowpea as intercrop). The results showed that the activity of termites (Nasutitermes torquatus) and ants (Messor galla and Pachycondyla rufipes) was 12–13 and 2–3 times higher in the SL amended soils than in non-amended soils, respectively. The activity of earthworms (Millsonia inermis) was highest in the SL amended soils associated with the cowpea intercrop, and was significantly lower in the urea enriched soils. SL amendments and N enrichments had no effect on soil basal respiration. The substrate-induced respiration with N substrates (L-alanine and L-argininel) was 25 and 52 % higher in the SL amended soils than in the natural soils without any N inputs, indicating N limitation of microbial activity. This corroborates the higher C/N ratio (14.3) observed in the SL amended soils compared to the natural soils without any inputs (10.3). The N enrichment decreased the C/N ratio of the SL amended soils but was not efficient to alleviate microbial catabolic limitations, likely by switching from N to C limitation. Overall, the SL amendments with or without N enrichments triggered temporarily the soil macrofaunal activity, increased the NH4-N availability compared to that of NO3-N, and improved crop performance.

Regulation of the product stoichiometry of denitrification in intensively managed soils

AbstractCrop residue amendment in conjunction with synthetic nitrogen (N) fertilization is a common agricultural practice that increases soil fertility and crop yield. However, such a practice may also change soil denitrification process. Here, we conducted an incubation experiment with a robotized continuous flow N2 free incubation system [using helium (He) and oxygen (O2)] and measured fluxes of N2O and N2 at a high resolution in an intensively managed soil to examine the interaction effect of straw amendment and N fertilization on soil denitrification. Four treatments were set consisting of (a) a nonamended treatment (Control); (b) a Straw treatment (2 g straw kg−1 dry soil); (c) a KNO3 treatment (KNO3, 15 mM KNO3); and (d) a Straw + KNO3 treatment (2 g straw kg−1 dry soil and 15 mM KNO3). During the oxic phase (80% He plus 20% O2) of the experiment (initial 2 days), flux rates of N2O were 0.54 and 0.38 kg N/ha day−1 in the Control and KNO3 treatments, respectively. Meanwhile, straw amendment triggered N2O fluxes immediately after the onset of treatments, which was more evident in the Straw + KNO3 treatment. During the anoxic phase (100% He), both N2O and N2 emissions increased in all treatments, with the effect being more pronounced in the Straw and Straw + KNO3 treatments. In line with the observed differences in gas fluxes, the abundances of nirK, nirS, and nosZ genes increased clearly in these treatments. Overall, the mean N2O/(N2O + N2) ratio (0.69 ± 0.03) in the Control treatment was significantly lower compared to the KNO3 treatment (18.8%) and higher than the straw‐amended soils (31.9% and 17.4% compared to the Straw and Straw + KNO3 treatments, respectively). Taken together, our results suggest straw amendment significantly altered N2O and N2 fluxes by decreasing the N2O/(N2O + N2) ratio; however, the effects of straw amendment depended on soil nitrate content.

Disentangling immobilization of nitrate by fungi and bacteria in soil to plant residue amendment

Plant residue incorporation improves soil microbial nitrate immobilization, which in turn alleviates nitrate accumulation, thereby improving N retention capacity and reducing N losses. However, how and why the respective nitrate immobilization by fungi and bacteria, which are dominant microorganisms in soil, responds to residue addition remains unknown. By adopting a novel amino sugar-based stable isotope probing approach, we show that both fungal and bacterial nitrate immobilization increased after Paspalum notatum residue addition. The increased proportion of the former was higher than that of the latter, and their difference became much larger with the increased residue addition rate. Furthermore, 70% and 32% of the variations in fungal and bacterial nitrate immobilization activities were explained by their respective biomass. The relative importance of fungal and bacterial nitrate immobilization shifted in a consistent manner with the relative abundance of fungi and bacteria, and the magnitude of these shifts was related to the residue addition rate. Our work demonstrates strong links between increased residue inputs, alterations in microbial community composition, and enhanced ecosystem functioning of nitrate immobilization and retention in soil.

Effect of biochars, biogenic, and inorganic amendments on dissolution and kinetic release of phytoavailable silicon in texturally different soils under submerged conditions

Extensive cropping leads to higher removal of silicon (Si) from the soils and makes it a limiting element for various crops. Application of silicic acid (H4SiO4) has limited scope due to high cost, low solubility, and high polymerization. The biogenic sources of Si are alternative to silicic acid (H4SiO4) and Si release from these sources is a function of different soil properties like pH, redox potential, texture etc. Kinetics release of plant available Si (PASi) from various organic and inorganic sources was evaluated in texturally different soils such as sandy loam (SL), sandy clay loam (SCL), and clay (CL) under a 60-day incubation study. Our findings suggest that the highest cumulative release of Si (cSi) was observed in SCL (47.6 mg/L) in control sets without any amendments. The highest cSi release among plant residue amendments was observed by bamboo leaves (340 mg/L) and rice husk (RH) (301 mg/L) in SL and SCL soils, respectively. Among biochar amendments, the rice husk biochar (RHB) released the maximum quantity (246.55 and 243.9 mg/L) of Si in SCL and CL soils respectively. Among the ashes, sugarcane bagasse ash had the highest release (316 mg/L) of Si in SCL and RHA which yielded 235.2 Si mg/L in CL soil for 60days. Silicon release kinetics for these sets of systems showed a diffusive behavior of Si being released from amendments primarily dependent on soil type.

Mushroom residue modification enhances phytoremediation potential of Paulownia fortunei to lead-zinc slag

Phytoremediation is an effective strategy for the remediation of lead-zinc slag, while the response of plant on lead and zinc was less concerned. In this study, mushroom residue was adding in lead-zinc slag to enhance the phytoremediation potential of P. fortunei, the effects of three treatments (lead-zinc slag, red soil, lead-zinc slag + 10% (m/m) mushroom residue) on the growth, physiology and microstructure of P. fortunei were determined. The results showed that the addition of mushroom residue increased the biomass, plant height and chlorophyll concentration of P. fortunei, indicating that the addition of mushroom residue can facilitate the growth of P. fortunei. Moreover, the proportions of oxalate-Pb forms and phosphate-Zn were dominant in leaves and stems of P. fortunei. With the addition of mushroom residue, Pb and Zn were transformed to the extraction state with weak migration activity, which can reduce the damage level of Pb and Zn to P. fortunei. The results from scanning transmission electron microscopy (STEM) showed that, the mushroom residue amendment could maintain the integrity of the cell structural of P. fortunei. The results from fourier transform infrared spectrometer (FTIR) analysis showed that the mushroom residue amendment could increase the contents of proteins and polysaccharides in P. fortunei, which can combine with the metals. Clearly, the mushroom residue amendment could promote the growth ability of P. fortunei in lead and zinc slag and strengthen the phytoremediation potential.

Soil respiration and nutrient availability after heating are influenced by salinity but not by prior drying and rewetting

Semi-arid and arid regions are characterised by drying and rewetting events, salinity as well as fires. The effects of these stresses on soils are all related to water availability and have been investigated extensively, but usually separately. To study the impact of two stresses, we combined a short heating event as it may occur in fast-moving grass fires with either a drying and rewetting event or salinity. In the first experiment, soils were incubated air-dried, moderately dried and constantly moist for 7 days after which the dried soils were rewetted. Seven days after rewetting, half of the replicates from each treatment were heated and then maintained at 60 °C for 30 min followed by rapid rewetting, while others remained unheated. The rewetting flush of respiration after 7 days was greater in previously air-dried soil than moderately dry soil. Regardless of prior water treatment, heating followed by rewetting compared to constantly moist soil increased respiration threefold and available N and P by about 20–30%. In the second experiment, NaCl was added to non-saline soil (EC1:5 0.01 dS m−1) to achieve EC1:5 1 and 4 ds m−1 (referred to as NS, S1 and S4). Soils were incubated moist for 1 month and then amended with pea residue at 10 g kg−1. Five days after residue amendment, half of the replicates from each treatment were heated and rewetted as in the first experiment. In unheated S4 compared to NS, cumulative respiration was 30% lower and available N and P were threefold and 30% higher. Heating reduced cumulative respiration by 10% in NS and S1 but by 30% in S4. Compared to unheated treatments, available N in heated NS was up to tenfold higher, but in S4, heating increased available N only up to threefold. In all salinity treatments, heating increased available P by about 15%. It can be concluded that the impact of short-term heating on nutrient availability and soil respiration was not affected by prior drying and rewetting. High salinity on the other hand reduced the impact on nutrient availability whereas the effect on soil respiration was exacerbated compared to non-saline soil.

Alkaline-thermally treated penicillin V mycelial residue amendment improved the soil properties without triggering antibiotic resistance

Penicillin V mycelial residue (PMR) is a byproduct of the pharmaceutical industry and may be disposed through land application after alkaline-thermal treatment. However, the efficacy of alkaline-thermally treated PMR in soil amelioration and the potential contamination risk caused by introduced penicillin V are poorly understood. In this study, soil pH, the contents of organic matter, available phosphorus, available potassium were measured to study the effect of alkaline-thermally treated PMR on soil fertility; the numbers of culturable microorganisms and the activities of enzymes, which not only reflect the decomposing ability of organic matter but also monitor the ecological suppression in soil ecosystem, were also investigated; moreover, the persistence of introduced penicillin V and the variation of antibiotic resistance genes (ARGs) in soil were examined to evaluate the resulting antibiotic resistance risk. The results indicated that the pH and the content of available potassium in amended soil with treated PMR profoundly improved. In addition, the culturable microorganisms and enzymes were not inhibited throughout the incubation of treated PMR in soil. The stability of treated PMR in soil relatively completed after 43 days. More importantly, the penicillin V derived by treated PMR rapidly depleted within 3 days, which suggested a relatively low environmental persistence. The treated PMR did not enrich the ARGs detected in soil, demonstrating that the addition of treated PMR might not trigger the antibiotic resistance risk in the short-term in soil. In conclusion, our results concluded that alkaline-thermally treated PMR is available for soil application.

The interactive effects of soil disturbance and residue quality on soil nitrogen mineralisation in a tropical sandy soil

Soil conservation practices, such as reduced and no tillage, have been found to enhance soil nitrogen (N) sequestration through decreasing the rate of N mineralisation of added organic materials. Nitrogen mineralisation is not only affected by tillage, but also by the quality (chemical composition) of the organic residues. This study evaluated the interaction of residue quality and soil disturbance on N mineralisation in a sandy soil. A 112-day incubation experiment was conducted with two levels of soil disturbance (undisturbed and disturbed conditions) and five plant residue amendments of contrasting quality. The contrasting quality (N, lignin (L), and polyphenols (Pp)) (in g kg–1) amendments follow: (i) unamended; (ii) Sesbania grandiflora (N 44, L 173, Pp 9.2); (iii) Indigofera hirsuta (N 41, L 177, Pp 30); (iv) Dipterocarpus tuberculatus (N 8.2, L 203, Pp 71); and (v) Eucalyptus camaldulensis (N 9.7, L 126, Pp 110). Residues (ii) and (iii) were fresh legume leaves, while (iv) and (v) were non-legume leaf litter. Disturbance only significantly increased N mineralisation rates in the legume-residue treated soils (increases of 18.8% for S. grandiflora and 27.1% for I. hirsuta) during the early stage of decomposition (first 14 days). In the legume treatment, disturbance significantly increased the ammonification, but decreased nitrification in soil relative to undisturbed soils. The difference in patterns of ammonification and nitrification was more pronounced in the early than in the later period of decomposition. This indicated an inhibitory effect of soil disturbance on nitrification, which was particularly pronounced in the legume-treated soils. The Pp content of residues was the major quality parameter regulating the soil ammonium-N and nitrate-N concentrations. Minimum soil disturbance should be adopted under legume soil organic amendment so that both ammonification and nitrification components of N mineralisation process can occur normally, and nitrate-loving crops can take up N in the form of nitrate-N which will enhance their yields. Moreover, undisturbed conditions under legume organic amendments reduced N mineralisation, resulting in enhancing soil N sequestration.

Earthworms offset straw-induced increase of greenhouse gas emission in upland rice production

Increasing water scarcity and rapid socio-economic development are driving farmers in Asia to transform traditionally flooded rice cropping systems into non-flooded crop production. The management of earthworms in non-flooded rice fields appears to be a promising strategy to support residue recycling and mitigate greenhouse gas (GHG) emissions triggered by residue amendment. We conducted a field experiment on non-flooded rainfed rice fields, with and without residue amendment. In-situ mesocosms were inoculated with endogeic earthworms (Metaphire sp.), with either low (ET1: 150 individuals m−2), or high density (ET2: 450 individuals m−2), and a control (ET0: no earthworms). We measured GHG emissions (methane (CH4); nitrous oxide (N2O); carbon dioxide (CO2)) twice a week during the cropping season with static chambers. Effects of earthworms on yield and root growth were additionally assessed. Earthworms offset the enormous increase of CH4 emissions induced by straw amendment (from 4.6 ± 5 to 75.3 ± 46 kg CH4-C ha−1 in ET0). Earthworm activity significantly reduced CH4 release, particularly at ET2, by more than one-third (to 22 ± 15 kg CH4-C ha−1). In contrast, earthworm inoculation did not affect N2O emission. Straw amendment more than doubled the global warming potential (GWP). Earthworms reduced GWP by 39% at low (ET1) and 55% at high densities (ET2). Earthworm activity reduced root mass density under conditions of straw amendment but did not affect yield. Earthworms can significantly reduce detrimental effects of rice crop residue amendment on GHG release under upland rice production. Organic carbon (C) might be preserved in earthworm casts and thereby limit C availability for CH4 production. At the same time, earthworm activity might increase methanotrophic CH4 consumption, due to improved soil aeration or less root exudates. Consequently, earthworms have a strong potential for regulating ecosystem functions related to rice straw decomposition, nutrient allocation and thus GHG reduction.

Short term effects of different green manure amendments on the composition of main microbial groups and microbial activity of a submerged rice cropping system

Green manuring is a feasible agricultural practice to mitigate soil degradation and loss of biodiversity caused by long term application of inorganic fertilizer. However, the effect of the types of green manure (legume vs non-legume) on soil microbial groups and activities are largely not known. Field experiments were conducted to investigate the effects of incorporating two green manures that originated from residues of barley (Hordeum vulgare) and hairy vetch (Vicia villosa), on microbial groups, biomass, enzyme activities, nutrient availability of soil, and crop yield in a mono-rice cropping system. Green manure biomasses were applied on an equal nitrogen biomass basis. We found that, compared to inorganic fertilizer, green manures amendment significantly increased composition of main microbial groups, microbial biomass C (MBC) and hydrolase activities of soil. Total PLFAs, Gm + bacteria, fungi and actinomycetes PLFAs were markedly increased by the barley residue amendment, whereas Gm- bacteria PLFA was mostly increased by the hairy vetch residue amendment. The higher hydrolase activities involved in C cycling were observed in the barley treatments, whereas soil enzyme activities involved in N and P cycling were higher in the hairy vetch treatments. Probably, differences between the two treatments dependent on different chemical composition of the green manures incorporated into the soil and their mineralization controlled by the soil C:N ratio. A decrease in oxidative enzyme activities and higher fungi: bacteria ratio as a result of the green manure amendment, in particular barley, suggested the potential of barley biomass incorporation to enhance C storage in submerged rice cropping systems.

13C-DNA-SIP Distinguishes the Prokaryotic Community That Metabolizes Soybean Residues Produced Under Different CO2 Concentrations.

The amendment of crop residues produced under elevated CO2 (eCO2) may alter soil microbial community structure and their functions on residue decomposition and carbon (C) cycling in soil. The key to understanding this process is to elucidate the structure of prokaryotic communities that metabolize crop residues derived from eCO2. A soil incubation experiment was conducted to explore the response of soil microbial community to the amendment of 13C-labeled soybean residues produced under ambient CO2 (aCO2) and eCO2. The residues were applied to a Mollisol, followed by 13C-DNA stable isotope probing (SIP) and Illumina sequencing on soil prokaryotic community over time. The structure of residue-metabolizing community differed in response to the amendment of eCO2- and aCO2-derived residues after 28 days of incubation. In particular, genera Actinomadura, Nocardia, Non-omuraea, and Shimazuella were the dominant members of the residue-metabolizing bacteria, which contributed to this difference. The relative abundances of genera Actinomadura, Nocardia and Shimazuella were 118–144%, 71–113%, and 2–4-fold higher in the Mollisol amended with aCO2-derived than eCO2-derived residue. In contrast, the relative abundance of Non-omuraea was 87–90% greater in the eCO2-residue treatment. However, during the incubation period, there was no difference between the two residue treatments in the community structure as a whole without SIP. These results implied that a pioneering prokaryotic community metabolized the residue initially prior to the entire community. Those bacteria genera being inhibited with the amendment of the eCO2-derived residue, compared to aCO2-derived residue, were likely preferential to metabolize recalcitrant C, which might be associated with changes of chemical composition of the residue under eCO2.

Effects of soil organic residue amendment on losses of dissolved organic carbon, P, Cu and Zn via surface runoff from arable soils

Dissolved organic carbon (DOC) constitutes the largest carbon pool in surface waters, with soil being its main source via surface and subsurface runoff. Amendment with organic residues can reduce soil erosion and surface runoff, but little is known how this affects the amount and composition of DOC losses via surface runoff and the associated transfer of nutrients and pollutants. In this study, artificial rainfall experiments were conducted on three pairs of soil runoff plots with contrasting organic matter management. A mixture of grass and wheat straw residues was incorporated into the topsoil of one plot in each pair (OI treatment) but not into the other (control). Artificial rainfall was applied onto both treatments at an intensity of 49.1 mm h−1, and surface runoff samples were collected at designated time steps for analysis of DOC, total dissolved phosphorus (TDP), copper (TDCu) and zinc (TDZn) concentrations, as well as for characterization of DOC by UV–vis absorbance (SUVA254 and E2:E3) and fluorescence spectroscopy (FI) indexes. The organic amendment reduced the loss rates of DOC, TDP, TDCu and TDZn by reducing surface runoff, although increasing the concentrations of DOC, TDP and TDCu. Regardless of the treatment, DOC, TDP and TDCu concentrations were always maximal at the onset of runoff and then continuously decreased after the initial flush. The observed relationships of TDP and TDCu concentrations with DOC indicate that the export of “dissolved” P and Cu primarily occurred in DOC-bound form, while the concentration of TDZn was not correlated with that of DOC. Surface runoff from the amended soils generally contained more hydrophilic and low molecular weight DOC (as indicated by low SUVA254 and high E2:E3 and FI values), particularly at high DOC concentrations. The ratio between TDCu and DOC concentration showed a positive relationship to DOC aromaticity (as indicated by SUVA254 values) in the OI treatment. The results indicate that organic amendment can reduce total rates of dissolved element losses with surface runoff, but attention should also be paid to the composition of lost DOC and the concentrations of DOC-associated solutes.

Implications of mycoremediated dry olive residue application and arbuscular mycorrhizal fungi inoculation on the microbial community composition and functionality in a metal-polluted soil

Metal-polluted soils represent hostile environments affecting the composition and functions of soil microbial communities. This study evaluated the implication of combining the mycoremediated dry olive residue (MDOR) amendment application with the inoculation of the arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae in restoring the quality, composition, and functionality of soil microbial communities. To achieve this aim, a mesocosms experiment was set up that included three variations: i) with and without application of Penicillium chrysogenum-10-transformed MDOR (MDOR_Pc), and Chondrosterum purpureum-transformed MDOR (MDOR_Cp) amendments; ii) with and without F. mosseae inoculation; and iii) 30-day and 60-day soil treatment time. As a result of this combined treatment, changes in the soil labile organic C and N fractions were observed throughout the experiment. Increases in the abundance of phospholipid fatty acids (PLFAs) for bacteria, actinobacteria, and Gram− and Gram+ bacteria were also recorded at the end of the experiment. The addition of MDOR amendments boosted fungal and AM fungi communities. AM fungi root and soil colonization was also enhanced as the result of improvement nutrient turnover and spatial conditions caused by adding MDOR in combination with an inoculation of F. mosseae. The composition and functionality of microbial communities seemed to be an important ecological attribute indicating an apparently fully functional restoration of this metal-polluted soil and therefore suggesting the suitability of the combined MDOR and AM fungus treatment as a reclamation practice.

Variations in soil bacterial taxonomic profiles and putative functions in response to straw incorporation combined with N fertilization during the maize growing season

Integrating nitrogen (N) fertilization with crop residue amendments is usually used to enhance soil nutrient levels and promote crop growth in regions with intensive agriculture. However, the interactive effects of straw incorporation and N fertilization on the abiotic and biological properties of soil are not fully understood, especially under field conditions at different crop growth stages. In this study, we estimated the dynamic changes in the soil physicochemical properties and bacterial communities in response to N fertilization, straw incorporation, and their combinations during the maize growing season in black soil region in Harbin, China. N fertilization increased the relative abundance of the typical copiotrophic bacterial taxa, Alphaproteobacteria, but reduced that of the oligotrophic group, Acidobacteria. The straw incorporation enhanced the relative abundance of Bacteroidetes and Gammaproteobacteria, within which a variety of cellulolysis-related species phylogenetically fell. Interestingly, the straw amendments changed the effects of N fertilization on the overall soil bacterial community composition, possibly by altering the soil total carbon, C/N ratio, fixed ammonium, and moisture level. N fertilization stimulated most of the carbon (C) transformation and N cycling processes, and the straw incorporation increased the cellulolysis, N fixation, ureolysis, ammonia oxidation and denitrification functions. There were no differences in the soil chemical properties, microbial taxa profiles or predicted functions between the conventional N fertilizer usage (high N level) and the optimized N fertilization management scheme (low N level), irrespective of straw incorporation, implying that moderately reducing the usage of N fertilizer will not change the ecosystem service and function in this organic matter-rich black soil region. The relative abundance of the copiotrophic bacterial taxa decreased at the mid-growing season, which might be caused by the low soil C and N availability. In contrast, the oligotrophic bacterial groups showed predominance at the mid-growing season, which might aim to mineralize soil organic matter to meet the growth needs of both the crops and the microbes. The nitrifiers (Nitrospirae) and nitrification process were sharply activated at the mid-growing season, especially under the straw amendment condition, inferring that the combination of straw application with N fertilizer could serve as an effective measure for improving soil fertility in Northeast China. The present study enhanced our knowledge on the dynamic changes in soil biotic and abiotic parameters in response to straw incorporation and N fertilization during the maize growing season. Still, this study provides a reference for designing an environmentally friendly fertilization strategy that both alleviates environmental stress and maintains a high crop yield in Northeast China.

Halophyte residue decomposition and microbial community structure in coastal soil

AbstractSaltmarshes are known for higher primary productivity and play a crucial role in carbon‐sequestration, nutrient‐cycling, and ecological services; however, scarce information are available on halophyte residue mineralization and microbial community structure during decomposition. Soil microcosms with residues (1% w/w) of three dominant halophytes (Aeluropus lagopoides, Arthrocnemum indicum, and Suaeda nudiflora) and one control were incubated under laboratory conditions and sampled at 1, 5, 10, 20, 40, and 90 days to link the microbial community structure and residues decomposition in degraded coastal soil. Samples were subjected to identification of active microbial groups and residue mineralization using fatty acid methyl ester (FAME) and CO2 evolution methods, respectively. Biochemical composition of residues was also analyzed. Cumulative CO2 evolution was elevated in residue‐amended soils compared with control, and it was highest in Arthrocnemum followed by Suaeda, Aeluropus, and control soil. The Aeluropus residue decomposed slower than others due to its high C/N ratio and low protein content. The contents of total FAME and biomarker FAMEs of microbial groups (bacterial, fungal, and actinomycetes) responded positively to the residue amendments compared with control, which indicate the improvement in soil microbial biomass. Soils amended with Suaeda had the highest amount of total (76.8 nmol/g) and fungal FAMEs (6.7 nmol/g), and bacterial (28.6 nmol/g) and actinomycete (3.0 nmol/g) FAMEs were elevated in Arthrocnemum amended soil. At the same time, soils amended with Suaeda (6.2%), Arthrocnemum (28.4%), and control (15.4%) had the greatest abundance of fungal, Gram‐negative and Gram‐positive FAME biomarkers, respectively. The present study suggests that residue of halophyte species affected the abundance of fungal and bacterial biomarkers, and the microbial community structure.

Short-term decomposition, turnover and retention of residue-derived carbon are influenced by the fertility level in a sandy loam soil

The straw residue amendment to soil is documented as an effective measure for integrated fertility management, and residue's decomposition dynamics are closely related to the physical, chemical and biological properties of soil. This paper aimed to investigate the effects of soil fertility on residue-derived carbon (C) decomposition, turnover and retention, and to identify the linkages between these processes and soil aggregation as well as microbial community. Arable soils following 27-year applications of compost and inorganic NPK along with a control (no fertilizer) were collected to divide into the corresponding high, medium and low fertility levels, and an in situ incubation was set up with these soils amended with and without 13C-labeled maize residues. During the whole incubation, the residue decomposition was significantly affected by the fertility level, and the retentions of residue-C in soils were ranked as high fertility soil > medium fertility soil > low fertility soil. Adding straw residue and improving the fertility level were favorable for the formation of water-stable macroaggregates. Following the addition of 13C-labeled residues, although the residue-C was preferentially incorporated into the large macroaggregate (>2000 μm) and then translocated to smaller aggregates, the large macroaggregate made the greatest contribution to the residue-C retention. The distinct microbial community dynamics determined their residue-derived 13C incorporations into microbial biomass. The increasing 13C incorporations into gram-positive (G+) bacteria, fungi and anaerobes and decreasing 13C incorporations into gram-negative (G−) bacteria, actinobacteria and aerobes corresponded to improving fertility levels. Consequently, soil aggregation and microbial community composition collectively explained 92% of the variation in residue-C retention, and their interaction exerted the largest effect. It can be concluded that residue return could effectively enhance soil fertility, which in turn contributes to residue-C retention by associating with macroaggregation and microbial community in a sandy loam soil.

Bioremediation of Petroleum Hydrocarbons in Crude Oil Contaminated Soil from Wonocolo Public Oilfields using Aerobic Composting with Yard Waste and Rumen Residue Amendments

Bioremediation of Petroleum Hydrocarbons in Crude Oil Contaminated Soil from Wonocolo Public Oilfields using Aerobic Composting with Yard Waste and Rumen Residue Amendments

Participatory agroecological research on climate change adaptation improves smallholder farmer household food security and dietary diversity in Malawi

This study examines whether agroecological farming practices, when employed by highly vulnerable households in sub-Saharan Africa, can improve food security and dietary diversity. The research involved a four-year study with 425 smallholder households, selected purposively based on high levels of food insecurity and/or positive HIV status. The households carried out agroecological experiments of their own choosing over a four-year period. Baseline (n = 306) and follow-up (n = 352) surveys were conducted in 2011 and 2013 respectively to assess changes in farming practices, food security, crop diversity and dietary diversity. Longitudinal mixed effects models were used with 203 matched households to estimate determinants of change in food security and dietary diversity at the population level. Qualitative interviews and focus groups were also conducted to provide depth to the survey findings. The findings show that participatory agroecology experimentation increased intercropping, legume diversification and the addition of compost, manure and crop residue amendments to the soil. Intercropping was associated with food security and the use of organic soil amendments was associated with gains in dietary diversity in bivariate analysis. Household food security and dietary diversity increased significantly over a 2-year period. Importantly, multivariate models showed that spousal discussion about farming was strongly associated with increased household food security and dietary diversity. Households who discussed farming with their spouse were 2.4 times more likely to be food secure and have diverse diets. Addition of compost or manure to the soil significantly influenced dietary diversity. These findings indicate that poor, vulnerable farmers can use agroecological methods to effectively improve food and nutritional security in sub-Saharan Africa. The study also highlights how linking agroecology to participatory research approaches that promote farmer experimentation and gender equity also lead to greater health and well-being. The study sheds light on how agroecological approaches can rapidly improve food security and dietary diversity, even under conditions of acute social, health or ecological stress. It draws attention to issues of equity and farmer-led approaches in addressing food security and nutrition.