Decomposition Rate Of Residues Research Articles

Biodegradable plastics fragments induce positive effects on the decomposition of soil organic matter

The escalating accumulation of plastic waste in ecosystems poses a significant health concern to soil environment, yet the environmental effects of plastics remains largely unexplored. Biodegradable plastics could offer a viable alternative to conventional persistent plastics, but our understanding of their potential benefits or detrimental effects on the decomposition of plant debris by soil biomass is limited. In this study, we conducted a year-long field experiment to examine the environmental response and impact on plant debris decomposition in the presence of varying quantities of persistent versus biodegradable plastics. Our findings indicate that the decomposition rate decreased by 2.8–4.9% for persistent plastics, while it increased by 1.3–4.2% for biodegradable plastics. Persistent plastics primarily induced adverse effects, including a reduction in soil nutrients, microbial diversity, bioturbation, enzyme activity, easily decomposable carbon, and microbial biomass carbon in plant debris. In contrast, biodegradable plastics resulted in beneficial effects such as an increase in enzyme activity, microbial biomass carbon, and easily decomposable carbon. We also observed that the decomposition rate of plant residues and nutrient release are closely associated with changes in the organic carbon chemical structure induced by different plastic film fragments. A significant shift in alkoxy carbon content facilitated the release of nutrients and soluble carbon, while modifications in carboxyl and aromatic carbon content hindered their release. Overall, our study reveals over one year that biodegradable plastics primarily induce positive effects on the decomposition of soil organic matter.

Edaphic fauna and residue decomposition rate under different management of plant species in no-tillage system

Edaphic fauna and residue decomposition rate under different management of plant species in no-tillage system

Degradation of peat-forming plants at the first stages of decomposition in natural and post-pyrogenic peatlands of West Siberia

The aim of the study. Assessment of the phytomass stocks and decomposition rate of peat-forming plants’ residues in peat deposits of natural and post-pyrogenic peatlands at the initial stages of decomposition. Location and time of the study. The study was carried out in 2022 (May-September) at two oligotrophic bog sites: “Bakcharskoye” (field station “Vasyuganye”, IMCES SB RAS) and “Iksinskoye”, which are located in the north eastern spurs of the Great Vasyugan mire in the Bakcharsky and Shegarsky districts of the Tomsk region, Russia. Methods. The phytomass stocks were determined by the cutting method. The following fractions were separated: living phytomass (annual and perennial photosynthetic phytomass, i.e. green parts of grasses, shrubs leaves, mosses); perennial non-photosynthetic phytomass, i.e. shrubs stems, roots of grasses and shrubs; and dead phytomass (mortmass), i.e. litter, moss litter, standing dead phytomass. The decomposition rate of plant residues was determined by the method of litter bags placement in peat (Chamaedaphne calyculata, Sphagnum fuscum, Mixed sample consisting of 60% S. fuscum and 40% Ch. calyculata). In the initial and decomposed samples, the ash content was determined by the dry combustion method. The total carbon and nitrogen content, as well as the carbon and nitrogen isotopic composition, were determined using a DELTA V Advantage isotope ratio mass spectrometer. Results. This short-term study conducted during the growing season in conditions of undisturbed (Natural Ryam) and post-pyrogenic (Gar) phytocenoses showed that due to a significant amount of mortmass (2402 g/m2) Natural Ryam had organic matter stock exceeding that in the Gar by 1.7 times. On average, 59% of organic matter loss from the total losses during the growing season occurred in the first month. In both Gar and Natural Ryam conditions, minimal losses of organic matter were characteristic for Sphagnum fuscum (3.1 and 3.5% respectively). For the remaining samples the Gar conditions were more favorable for the degradation at the initial stages of decomposition. The Mixed sample occupied an intermediate position between its individual components in terms of mass losses. Carbon losses correlated well with mass losses both over 1 month of degradation (r=0.87) and over 4 months (r=0.96). In contrast to carbon, nitrogen accumulated in the Mixed sample at the initial stages of degradation, both after 1 month and 4 months. Conclusions. With smaller phytomass stocks in areas of post-pyrogenic succession, more active decay at the initial stages of organic matter decomposition occurs exactly under these conditions. The impact of post-pyrogenic succession on the rate of organic matter decomposition of Chamaedaphne calyculata plant residues and the Mixed sample was demonstrated. The most intensive decomposition of litter occured during the first month of degradation. Additionally, in the conditions of a burnt bog, a more intense release of nitrogen from all plant residues and accumulation of ash elements in Sphagnum fuscum samples were observed. The mixing of litter components influenced both the rate and dynamics of decomposition. The carbon and nitrogen isotopic composition began to change during the initial stages of decomposition, leading to enrichment with heavier isotopes 15N and 13C. This research emphasizes the importance of studying the processes of plant litter decomposition at the initial stages and considering the plant residue composition when studying the processes of organic matter transformation.

Impact of Temperature and Moisture on the Decomposition of Peat-Forming Plants: Results of a Two-Year Incubation Experiment

The decomposition rate of plant residues is determined by both abiotic (temperature, moisture) and biotic factors (biochemical composition). To separate the contribution of each factor to the decomposition process, long-term incubation experiments under controlled conditions are required. Two-year incubation experiments were conducted with various types of peat-forming plants (Sphagnum fuscum, Chamaedaphne calyculata, Eriophorum vaginatum, and a mixed sample consisting of 60% Sphagnum fuscum and 40% Chamaedaphne calyculata). The experiments were carried out at temperatures of 2, 12, and 22 °C, with varying moisture levels (W = 30, 60, and 90% of their water-holding capacity). In all plant samples, the highest rates of C(CO2) emission (DecR) were observed in the initial stages of decomposition. The cumulative carbon loss (Ccum) during the experiment ranged from 45 to 196 mgC/g of plant material at 22 °C and 23 to 156 mgC/g of plant material at 2 °C. The decay constant (k) for all plant samples increased with rising temperature. The results of the three-way ANOVA showed that the influence of the examined factors on the cumulative losses of C(CO2) decreased in the following order: the type of plant > temperature > moisture. Throughout the experiment, the influence of the type of plant and moisture on DecR increased, while the effect of temperature decreased. The highest temperature sensitivity (Q10 = 0.71–6.19) was observed in the low-temperature range (2–12 °C) during months 4 to 6 of incubation. These results are relevant for modeling and predicting the rate of transformation of peat organic matter under changing climatic conditions.

Residual biomass quality index: a tool for conservation agriculture

ABSTRACTOne of the pillars of a no-tillage system is the addition of adequate amounts of residue to keep the soil continuously covered. Cover crops are a tool for supplying the demand for the permanence of residues on the soil surface and releasing nutrients to the soil. However, there is no index that relates these two factors and can reconcile the maximum permanence of crop residues in the soil with the maximum N supply via N mineralization of such residues. This study aimed to assess the effect of different cover crops on the decomposition rate of residues and N release, using the residual biomass quality index (RBQI) to evaluate cover crop systems. The study was conducted in a long-term experiment in a Latossolo Vermelho (Ferralsol, Oxisol) under no-tillage in the two agricultural years 2017/18 and 2018/19. The experiment was in a split-plot factorial scheme with eight winter cover crops and three N rates in randomized blocks with three replications. The cover crop systems were black oat (O), common vetch (V), forage radish (R), white lupine, rye, annual ryegrass, oat + vetch (O+V), and oat + vetch + radish (O+V+R). The N rates applied to the corn in succession were 0, 90, and 180 kg ha-1. The decomposition rate, remaining dry mass (RDM) on the soil surface, N release rate, and N accumulated release (NAR) were assessed using litterbags. Considering NAR and RDM evaluated for up to 105 days, the N release index (NRI) and remaining dry mass index (RDMI) were determined, and the residual biomass quality index (RBQI) was obtained using the product of these variables. The consortia O+V+R and O+V resulted in a decomposition rate and N release rate closer to the rates observed for oats and rye. The NAR was similar to that observed for Fabaceae species, and the RDM was similar or superior to that found for black oat. With these characteristics, the systems in the O+V+R and O+V consortia presented the highest values of RBQI, ranging from 0.61 to 0.90, indicating that RBQI is a potential indicator for choosing cover crop systems that promote greater sustainability of the no-tillage system. The use of N fertilizer in corn did not change the rates of decomposition and N release from the residues of cover crops.

Harvest Residue Decomposition from Eucalyptus sp. Plantations in Temperate Climate: Indicators and Contribution to Nutrient Cycling

The sustainable management of forest plantations by keeping the harvest residues on site improves the soil’s chemical, physical and biological properties while constituting an important nutrient reserve. Our objectives were: (a) to identify and quantify the characteristics of Eucalyptus dunnii, Eucalyptus grandis and Eucalyptus globulus that affect the decomposition rates of harvest residues, as well as indicators that can explain the process and (b) to quantify the potential recycling of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) to the soil from residue decomposition and the quantitative and qualitative differences between the species. We analyzed the information of five commercial plantations of Uruguay. At the harvest, the biomass of leaves, thin and thick branches, bark and their respective N, P, K, Ca and Mg contents were quantified. At each site, bags with samples of the different residues were left to decompose and were periodically collected throughout 24 months. Eucalyptus dunnii presented the largest amounts of residues of all parts. The decomposition rates of the different residues depended on their chemical constitution, part size and the species. Eucalyptus dunnii leaves showed the shortest half-life (0.94 years), while the bark of the same species presented the longest (5.62 years). Total nitrogen and carbon (total and soluble) contents, which can be easily determined, emerged as good predictors for half-life estimation. The release patterns of nutrients depended more on their dynamics in the plant and their parts than on the species itself. The results highlight the importance of nutrient recycling to ensure the sustainability of the productive system in the medium and long term.

Changes in the nitrogen isotopic composition during the transformation of peat-forming plant litter at dried and post-pyrogenic sites of oligotrophic bogs

The aim of the study. Assessment of changes in the nitrogen isotopic composition (δ15N) during the decomposition of the main peat-forming plants’ litter in peat of oligotrophic bog ecosystems in the southern taiga subzone of West Siberia. Location and time of the study. The studies were carried out in 2019–2021 in two oligotrophic bogs: “Bakcharskoye” (field station “Vasyuganye” (IMCES SB RAS)) and “Iksinskoye”, which are the north-eastern spurs of the Great Vasyugan mire and located in the Bakcharsky district of the Tomsk region, Russia. Methods. The decomposition rate of peat-forming plants’ litter was determined by the method of partially isolated samples, which is widely used to study the transformation of plant material and peat. The nitrogen isotopic composition in the original and decomposed samples of the plant material was determined by isotope ratio mass spectrometry using a DELTA V Advantage mass spectrometer combined with a Flash 2000 elemental analyzer (EA-IRMS). Results. A three-year study of the decomposition of peat-forming plants (Sphagnum fuscum, Chamaedaphne calyculata, Eriophorum vaginatum and a Mixed sample) in four ecosystems (natural - VASnat, drained - VASdry, post-pyrogenic - Iksa1 and Iksa2) showed that melioration and fire influenced the litter decomposition rate, increasing the latter in the drained bog and slowing down Sph. fuscum and Mixed sample decomposition by 1.5–9.0% at the site with pyrogenic effects. During the plant litter transformation carbon and nitrogen were released as 24–62% and 21–46%, respectively. In all studied samples, except for Sph. fuscum, a relationship was revealed between the plant litter mass loss and changes in the nitrogen isotopic composition. Conclusions. The effect of peat fires is manifested by a decrease in the plant residue decomposition rate. The dynamics of changes in the isotopic composition during the transformation of the studied plant residues depended on the plant species, but does not depend on decomposition duration (1, 2, 3 years) and sample location. Key words: transformation of plant residues; nitrogen isotopes; biogeochemical cycle; pyrogenic peatlands; drained peatlands; West Siberia.

Produção de brócolis em plantio direto com diferentes coberturas vegetais e doses de nitrogênio

ABSTRACT No-till vegetable farming is a feasible alternative to reduce erosion-induced losses and to increase soil nutrient availability, because cover crop residue protects the soil and its decomposition promotes nutrient cycling, which can improve the yield of the subsequent crop. The present study assessed the production and decomposition of cover crops and the agronomic performance of broccoli grown on this residue using different nitrogen doses in a no-till system. A randomized block design was used, in a split-split plot arrangement of main plots (cover crops), sub-plots (N doses) and sub-sub plots (decomposition times), with four repetitions. Seven cover crops were studied, as follows: [1) signal grass (SG); 2) sunn hemp (SH); 3) pearl millet (PM): 4) SG+SH; 5) SG+PM; 6) SH+PM and 7) SG+SH+PM]; in addition to four doses of nitrogen topdressing [T1) no N application (control); T2) 60 kg/ha N; T3) 90 kg/ha N and T4) 120 kg/ha N]; and five cover crop residue decomposition times: zero (cutting), 15, 30, 60 and 90 days after transplanting (DAT) the broccoli seedlings. Cover crop dry weight (DW) production, residue decomposition, and the head fresh (HFW) and dry weight (HDW) and yield (YLD) of broccoli were assessed. Among the cover crops, sunn hemp and the intercropped SG+SH treatment exhibited the lowest DW production and, along with signal grass, the shortest half-life (T½) and highest residue decomposition rate. The best-performing broccoli plants were those grown using PM, SH and a combination of both as cover crops. The highest broccoli production was obtained using sunn hemp residue, regardless of nitrogen topdressing, with HFW of 788 g/plant and YLD of 30 t/ha.

Species evenness affects algae driven co-metabolism with aquatic plant residues

Understanding the mixed decomposition processes of aquatic plant residues is crucial for evaluating the carbon cycle of lakes. However, the complex effect of species evenness, and especially the algae driving co-metabolism effect in eutrophic lakes are still far from clear. In this study, three dominant aquatic plants (Phragmites australis, Nymphoides peltatum, and Potamogeton malaianus) and algae from the typical eutrophic and shallow Lake Taihu, China, were selected to simulate their mixed decomposition process. The addition of algae accelerated the mass loss of cellulose, hemicellulose, and lignin of aquatic plant residues and increased the total mass loss by 2.29~6.32% in mixed decomposition. The positive co-metabolism effect, with the intensity ranging from 10% to 17%, occurred during the mixed decomposition process. In addition, the positive co-metabolism effect was also found among plant residues during mixed decomposition and the co-metabolism intensity of species evenness mixed decomposition was more than twice as high as that of non-evenness mixed decomposition. The addition of algae during the decomposition of aquatic plant residues altered the stoichiometry of available nutrients and affected the microbial decomposition activity. The abundance of decomposition bacteria, especially Bacteroidetes, was increased and the community structure also changed, as evidenced by a 71% increase in the number of bacteria phylum. As a result, these biogeochemistry processes accelerated the decomposition rates of aquatic plant residues and thus produced the positive co-metabolism effect. Therefore, the co-metabolism effects of mixed decomposition described in this study are prevalent in eutrophication lakes and have important effects on the lake carbon cycle, which need to be considered in future lake management.Graphical

Wheat cover crop alters soil microbial community and increases cucumber yield under different potassium regimes

Cover crops can promote the subsequent plant growth and improve soil potassium (K) fertility. However, whether and how wheat cover crop benefits cucumber growth and yield under different K regimes and their functional roles are still unclear. In this study, a two-year greenhouse experiment from spring 2017 to autumn 2018 was conducted to evaluate the effects of wheat cover crop on cucumber plant growth, nutrition and yield. Moreover, a litterbag experiment was carried out in the greenhouse in spring 2018 to investigate the nutrient dynamics during decomposition of wheat shoot and root residues under the two K regimes. Soil bacterial and fungal communities during residues decomposition were analyzed by high-throughput amplicon sequencing, and the abundances of total bacterial, fungal, Bacillus and Pseudomonas spp. communities were also estimated by quantitative PCR. The responses of cucumber growth to changes in the soil microbial communities induced by wheat cover crop were assessed by plant-soil feedback experiment. Wheat cover crop increased cucumber yield except for in spring 2017 and plant growth and K concentration at 70 d in spring 2018, and reduced K application did not weaken the beneficial effects of wheat on cucumber growth and yield. Decomposition rate and nutrient release of wheat shoot residue differed from root residue, but no differences in shoot or root residue decomposition rate and nutrient release between the two K regimes. Wheat shoot and root residues differently changed the abundances, compositions and diversities of soil bacterial and fungal communities. Wheat shoot residue increased total bacteria, Bacillus and Pseudomonas spp. community abundances compared with root residue irrespective of K regimes, and Bacillus spp. community abundance was higher in shoot residue with reduced K application than that with normal K application from 220 to 240 d. Wheat shoot residue decreased the Shannon and inverse Simpson diversities of soil bacterial and fungal communities compared with root residue from 200 to 240 d. Moreover, there was significant difference in these diversities of soil fungal community of root residue between the two K regimes except for 240 d. In addition, wheat cover crop caused more stable co-occurrence network with more positive and negative total links and wheat shoot residue had higher these links than root residue, while reduced K application decreased these links of both shoot and root residues. Feedback effects of changes in soil microbial communities induced by wheat cover crop on cucumber growth were positive, and such effect was stronger in shoot residue than in root residue irrespective of K regimes. Overall, wheat cover crop can alter soil microbial communities and enhance cucumber productivity through positive plant-soil feedbacks mediated by soil biota, and reduced K application did not weaken such beneficial effects.

Modelling soil carbon stocks following reduced tillage intensity: A framework to estimate decomposition rate constant modifiers for RothC-26.3, demonstrated in north-west Europe

Simulating cropland soil carbon changes following a reduction in tillage intensity is necessary to determine the utility of this management practice in climate change mitigation. In instances where reduced or no tillage increases soil carbon stocks, this is typically due to reduced decomposition rates of plant residues. Although some soil carbon models contain a priori decomposition rate modifiers to account for tillage regime, these are typically not calibrated to specific climatic regions, and none are currently available for the Rothamsted Carbon Model (RothC). Here, we present a modelling framework to estimate a tillage rate modifier (TRM) for the decomposition rate constants in RothC-26.3 which determine decay between soil carbon pools. We demonstrate this for north-west Europe, using published data assembled through a recent systematic review with propagation of error from input parameters throughout the framework. The small magnitude of soil carbon change following a reduction in tillage intensity in this region is reflected in our TRM estimates for no-till of 0.95, with 95% Credible Intervals [0.91, 1.00], and reduced tillage of 0.93 [0.90, 0.97], relative to conventional high-intensity tillage with a default TRM of 1. These TRMs facilitate realistic simulation of soil carbon dynamics following a reduction of tillage intensity using RothC, and our simple, transparent, and repeatable modelling framework is suitable for application in other climatic regions using input data generalisable to the context of interest.

Absence of a home-field advantage within a short-rotation arable cropping system

AimsThe home-field advantage (HFA) hypothesis predicts faster decomposition of plant residues in home soil compared to soils with different plants (away), and has been demonstrated in forest and grassland ecosystems. It remains unclear if this legacy effect applies to crop residue decomposition in arable crop rotations. Such knowledge could improve our understanding of decomposition dynamics in arable soils and may allow optimisation of crop residue amendments in arable systems by cleverly combining crop-residue rotations with crop rotations to increase the amount of residue-derived C persisting in soil.MethodsWe tested the HFA hypothesis in a reciprocal transplant experiment with mesh bags containing wheat and oilseed rape residues in soils at three stages of a short-rotation cropping system. Subsets of mesh bags were retrieved monthly for six months to determine residue decomposition rates, concomitantly measuring soil available N, microbial community structure (phospholipid fatty acid analysis), and microbial activity (Tea Bag Index protocol) to assess how plants may influence litter decomposition rates via alterations to soil biochemical properties and microbial communities.ResultsThe residues decomposed at similar rates at all rotational stages. Thorough data investigation using several statistical approaches revealed no HFA within the crop rotation. Soil microbial community structures were similar at all rotational stages.ConclusionsWe attribute the absence of an HFA to the shortness of the rotation and soil disturbance involved in intensive agricultural practices. It is therefore unlikely that appreciable benefits could be obtained in short conventionally managed arable rotations by introducing a crop-residue rotation.

Conservation agriculture practices drive maize yield by regulating soil nutrient availability, arbuscular mycorrhizas, and plant nutrient uptake

Conservation agriculture (CA) can sustainably increase crop productivity through improved soil chemical, physical, and biological properties, among others. However, the implementation of all its three main components (i.e., no-tillage, organic soil cover/mulch, and crop diversification) in southern Africa is often challenging, resulting in variable yield responses. Disentangling the contributions of CA practices is necessary to understand the drivers of maize grain yield within the region. Here we analysed two 6-year long component omission experiments, one at a sandy soil location and the other at a clay soil location. In these two experiments, soil chemical parameters, total plant nutrient uptake, rate of crop residue decomposition, and arbuscular mycorrhizal fungi (AMF) colonization of maize roots were assessed. Soil chemical properties only differed across systems at the sandy soil location with the mulched systems under no-tillage (NT) resulting in increased soil organic carbon levels, total nitrogen, and soil available phosphorus as compared to conventional tillage with no mulch or rotation (CT). Conventional tillage-based systems resulted in fastest decomposition of maize residues, while systems with NT and rotation resulted in highest AM fungal root colonization rate of maize at the clay soil location. Total plant N uptake was almost 2-fold higher in tilled and no-tilled systems with both mulch (M) and rotations (R) (i.e., NT+M+R and CT+M+R) as compared to CT. Structural equation modeling was used to disentangle the links between cropping systems, soil chemical and biological properties, plant nutrient uptake, and maize grain yield. Cropping systems had direct and indirect influences on yield at both locations. At both locations, cropping systems influenced yield via plant N uptake, with the NT+M+R and CT+M+R systems having more beneficial effects compared to other systems, as shown by their higher path coefficients. In conclusion, we recommend a more holistic approach to cropping system assessment that includes a higher number of abiotic and biotic determinants. This would allow for a more rigorous evaluation of the drivers of yield and increase our understanding of the effects and performance of practices under the prevailing agro-ecological conditions. • Mulching under no-tillage increase soil organic carbon (SOC) and total nitrogen (N) • No-tillage plus rotation improve symbiosis of arbuscular mycorrhizal fungi & maize • Conventional tillage enhances stover decomposition but reduces SOC and N build-up • Conservation agriculture influences maize yield positively via nitrogen uptake

Sunlight and soil biota accelerate decomposition of crop residues in the Argentine Pampas

The benefits of maintaining soil organic matter in agroecosystems have long been recognized, although there are many open questions with respect to the controls on crop residue decomposition and the consequences for carbon and nutrient cycling. The large extension of intensively cropped agriculture in the Argentine Pampas of soybean, sunflower, wheat, and maize motivates the need for a broader understanding of these controls. In modern no-till agriculture, post-harvest crop residues may remain upright as standing or on the soil surface for extended periods of time; nevertheless, the effects of sunlight exposure and its interaction with soil biota on decomposition of crop residues have not been evaluated. We established a manipulative experiment using soybean, sunflower, wheat and maize crop residues with treatments of full or attenuated sunlight exposure and presence or absence of soil biota. Species identity was significant in determining rates of leaf residue decomposition with mass loss of soybean ≥ sunflower > wheat ≥ maize. Sunlight exposure significantly accelerated decomposition of leaf residues in the absence of soil biota, while soil biota significantly contributed to increased leaf residue decomposition with and without sunlight exposure. In contrast, stem residue decomposition was modest under all conditions and differences in decomposition were determined by species identity. Surface area for leaf and stem residues across species was the strongest litter quality predictor for the variation in crop residue decomposition. Our results suggest that sunlight exposure, duration of fallow period with or without rotation or cover crops, and the proportion of leaves vs. stems in crop residues interacting with soil biota may be fundamental elements in determining carbon turnover in these intensively cropped agroecosystems. There would be great value in incorporating the impacts of sunlight exposure and unexplored aspects of crop residue quality in models for sustainable agriculture in the region and globally.

Decomposition Rate of Organic Residues and Soil Organisms’ Abundance in a Subtropical Pyrus pyrifolia Field

The use of mulching, compost, and their interaction on organic residue (OR) decomposition rate (k), time of residue decay, primming effect, and soil organisms’ community composition was tested in a 16-year P. pyrifolia field experiment conducted from January 2020 to June 2021. A 2 × 2 factorial design was used with compost and mulching as the two factors within four blocks. OR decomposition was characterized by using litter bags with different mesh, and soil organisms were identified at family level. The half-decay rate (hd), total-decay rate (td), and remaining residue mass (Rm) varied among the organic residue management and mesh-type. The highest values of k and primming effect were found in litter bags with 15 mm2 size containing compost in the plots that received compost. For soil organisms’ abundance and richness, the highest values were found on plot that received both mulching and compost. The observed results suggested that the OR management determined organic matter decomposition, soil organisms’ abundance and richness in an Acrisols of the Southern Brazil. Soil organisms were the main factors contributing to the data variance (e.g., Acaridae, Blattidae, Chrysopidae, Halictophagidae, and Forficulidae).

Rice straw carbon mineralization is affected by the timing of exogenous glucose addition in flooded paddy soil

Crop straw amendment is a farm management approach for enhancing soil carbon sequestration. Moreover, crop straw residue decomposition rates are affected by irregular exogenous organic carbon secretion or metabolism such as that from root exudates or microbial metabolites. To quantify the mineralization rate of straw residue affected by exogenous organic carbon addition and elucidate the underlying mechanisms, in this study, a total of 0.5 g 13C- labeled dry rice straw was added into pre-incubated soil (equivalent to 200 g dry soil) and incubated for 20 days. Then,1mL of a solution with 50 mg glucose was added only once into the soil on day 21 (G(1a)) or day 35 (G(1b)), twice with 25 mg glucose every 14 days (G(2)) or four times with 12.5 mg glucose every 7 days (G(4)). Soil without glucose addition served as a control. The frequent addition of glucose induced higher soil respiration than that induced by only one addition, and stimulated the mineralization of rice straw carbon compared to that in the control in the following order: G(4) (14.6%) > G(1a) (12.7%) > G(2) (12.3%) > G(1b) (11.2%) = control (11.2%). In general, frequent addition of glucose decreased the soil redox potential (Eh) and fungi to bacteria ratio. Structural equation modeling analysis showed that the rice straw carbon mineralization rate was positively correlated with the 13C-dissolved organic carbon (13C-DOC) content and negatively regulated by Eh. Microbial bioactivity exerted indirect positive effects on rice straw carbon mineralization by influencing the 13C-DOC content. A decrease in the fungi to bacteria ratio induced by frequent addition of glucose improved the microbial bioactivity and enhanced rice straw carbon mineralization. Our results suggested that single exogenous organic carbon additions may underestimate residue or soil organic matter decomposition rates in the field.

Plant residue quality index and ecological potential approach for selective reincorporation of crop residues in soil.

Abstract Reintegration of agricultural residue into the soil is a sustainable approach for replenishment of soil nutrients. Plant physiology determines the quality of residue produced by a crop and its quality governs the process of decomposition in the soil. The present study attempts to establish formulated approach to select quality crop residues for re-usage in soil. Four major crops, rice, wheat, maize and sugarcane were selected to analyse their quality and quantitative potential to generate a quality index. Residue production ratio (RPR), agricultural ecological potential (AEP) and, gross residue potential (GRP) values were determined to correlate their decomposition pattern with nutrient release rate. The calculated gross residue potential showed the availability of residue generated by crop was highest in wheat. Agricultural ecological potential further implied that 48% of wheat and maize crop residue should be left on the field for maintaining ecological services. The results are studied in coherence to explain the ecological importance of retaining crop residues in the field. The chemical parameters integrated as plant residue quality index (PRQI) further confirms the high nutrient value of wheat and rice crop residues correlated with their higher decomposition rate. The present study implies that decomposition rate of crop residues can decide their retain value depending on nutrient release rate. This would facilitate in establishing the relationship between qualities of decomposing residue requirements with crop growth of a particular species.

Succession of fungal community and enzyme activity during the co-decomposition process of rice (Oryza sativa L.) straw and milk vetch (Astragalus sinicus L.).

The co-incorporation of rice straw (RS) and milk vetch (MV) into paddy fields has been increasingly applied as a sustainable farming practice in southern China. Our previous study revealed the contribution of bacteria to the co-decomposition of the RS and MV mixture, although additional underlying factors driving the co-decomposition process need to be clarified. The present study further determined the succession of fungal communities and enzyme activity in the co-decomposition process of the RS and MV mixture. The results showed that non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled RS and MV mixture during the co-decomposition process, stimulating mixture decomposition. Overall fungal abundance was 19.6-30.6% higher in the RS and MV mixture throughout the study than in the single residue. Fungal diversity and community structure were mainly affected by the sampling date rather than the type of residue. Specifically, mixing RS and MV significantly increased the abundance of Peziza sp. and Reticulascus tulasneorum (lignocellulose- and lignin-decomposing fungi) and exhibited higher activities of C- and N-related hydrolases than monospecific residues. Random forest (RF) models showed that bacteria contributed more to the residue decomposition and activities of C-related hydrolases, N-related hydrolases, and oxidases than fungi. However, both RF and partial least squares path models revealed that fungal abundance and community structure directly or indirectly affected the residue decomposition rate. These findings showed that mixing RS and MV could stimulate their decomposition by enhancing C-related hydrolase activity and Peziza sp. and Reticulascus tulasneorum abundance.

The combination of residue quality, residue placement and soil mineral N content drives C and N dynamics by modifying N availability to microbial decomposers

Crop residues are the main source of carbon (C) inputs to soils in cropping systems, and their subsequent decomposition is crucial for nutrient recycling. The interactive effects of residue chemical quality, residue placement and soil mineral nitrogen (N) availability on carbon and N mineralization dynamics were experimentally examined and interpreted using a modelling approach with the deterministic-functional, dynamic decomposition module of the Simulateur mulTIdisciplinaire pour les Cultures Standard (STICS) model. We performed a 120-day incubation at 25 °C to evaluate how the mineralization of C and N from residues would respond to residue type (residues of 10 crop species with C:N ratios varying from 13 to 105), placement (surface or incorporated) and initial soil mineral N content (9 or 77 mg N kg−1 dry soil). A reduced C mineralization rate was associated with N limitation, as observed for high-C:N ratio residues, and shaped by residue placement and initial soil mineral N content. This was not observed for low-C:N ratio residues. Overall, increased net N mineralization corresponded with reduced N availability. Using the optimization procedure in the STICS decomposition module to explain the C and N dynamics of surface-decomposing residues, we estimated that 24% of the total soil mineral N would be accessible to decomposers. The STICS decomposition module reproduced the C and N dynamics for each treatment well after five parameters were optimized. The optimized values of the biomass C:N (CNbio), residue decomposition rate (k), humification coefficient of microbial C (h), and microbial decomposition rate (λ) were significantly correlated with total N availability across all 40 treatments. Under low total N availability, CNbio increased, while k, h and λ decreased compared to their values under high N availability, suggesting functional changes in the microbial community of decomposers. Our results show that an N availability approach could be used to estimate residue C dynamics and net N mineralization in the field in response to crop residue quality and placement and demonstrate the potential to improve decomposition models by considering the effects of N availability on C dynamics.

Cover crop residue moisture content controls diurnal variations in surface residue decomposition

The effect of cover crop (CC) surface residues on water, carbon, and nitrogen cycling in no-till systems depends in part on the water retention properties of decomposing residues and the extent of decomposition. This study (1) examined the effect of decomposition on residue water retention properties; (2) characterized diurnal variations in residue decomposition rates in response to changes in soil-residue-air environmental conditions; and (3) examined the diurnal relationships between cover crop surface residue decomposition and residue environment (moisture and temperature). Maximum gravimetric water content (θg) and characteristic water release curves were determined for red clover (Trifolium pratense L.) and cereal rye (Secale cereale L.) residues collected at 0, 4, 10, and 16 weeks after termination for red clover, and at 2, 5, and 18 weeks for cereal rye. In addition, residue carbon dioxide (CO2-C) flux, along with soil-residue-air environmental conditions, were measured diurnally for red clover at 4, 10, and 16 weeks after termination, and for cereal rye at 5 weeks after termination. Maximum residue θg decreased as decomposition progressed. Cover crop residue decomposition also influenced water release curves such that the water retained at any given water potential (ψresidue) declined with increasing decomposition. These decomposition-associated changes in residue water retention properties were strongly related to residue lignin concentrations. Cover crop surface residue CO2-C flux showed distinct diurnal patterns that were strongly related to ψresidue or residue θg. At a diurnal scale, residue CO2-C flux increased during the nighttime from 18:00 to 06:00 h when residues gain moisture from the atmosphere and soil, and decreased during the daytime from 06:00 to 18:00 h when residues lost moisture via evaporation. Increase in temperature decreased residue CO2-C flux due to moisture limitations. Therefore, CC surface residue decomposition models must address both diurnal changes in ψresidue and the changes in water retention properties as residues decompose.