Soil Respiration Activity Research Articles

Use of biochar with immobilized free-living N-fixers as mineral fertilizer

It is known that biochar application as soil fertilizer lead to reduce N loss. At the same time because of its porosity biochar is high quality substrate for immobilization microorganisms. The practice of using free-living N fixing bacteria (FLNFB) in organic farming is widely used to increase the nitrogen content in the soil. In this study immobilisation FLNFB on two types of biochar (made of chicken manure and sewage sludge) was applied to increase soil quality and crop productivity. The effectiveness of immobilization has been proven using SEM method: biofilms of FLNFB on the porous surface of both types of biochars are visible in the SEM images. The effectiveness of application 1% by mass biochar with FLNFB was estimated during 30 days vegetation experiment in greenhouse conditions by estimating the chemical composition of the soil (pH, CEC, OM, Corg, Ntot), by estimating change the functional activity of the soil microbial community (soil respiration activity, leucine aminopeptidase enzyme activity), by estimating change the structure of the microbial community (qPCR were used to analyze nifH and 16S rRNA genes in order to study the total count of bacterial and fungi), by estimating change the plants characteristics (chlorophyll content, germination, root and shoot length, biomass). It was found that application biochar with FLNFB lead to higher content of Ntot (0.11-0.19%) in soil in the end of the experiment as comparing than that for soil samples with mineral fertilizer ( 0.09%) and control soil (0.08%). The application biochar with FLNFB lead to significantly increase nifH-genes in soil. The soil leucine aminopeptidase and respiration activity have a similar trend for samples with and without biochar. The use of biochar as fertilizer led to increase chlorophyll content (13-22%) and barley biomass (10-84%) and decrease the length of the root (3-33%) in comparison with the control soil.

Biochemical activity and microbial biomass in wetlands (Vereda) and well-drained soils under native vegetation types in Brazilian Cerrado

The Cerrado is the second largest Brazilian biome, a world biodiversity hotspot and home to important hydrographic basins. In this biome, native vegetation types play crucial environmental roles as natural repositories of carbon, water and biodiversity. However, the Cerrado is threatened by deforestation and land degradation. The soil microbiology knowledge of these areas would provide a better understanding of how this threatened environment functions and a basis for monitoring and conservation. This study investigates soil respiration, microbial biomass and enzymes activity of the native wetlands (veredas), and well-drained soils under native cerrado sensu stricto and semi-deciduous dry forest. Vereda soils produced the highest levels of soil biological attributes, while the semi-deciduous dry forest produced intermediate values and the Cerrado, the lowest values. Regardless of season, differences in soil activity were best correlated with five biological attributes: basal respiration, FDA, urease, β-glucosidase and acid phosphatase activity. Partial redundancy analysis indicated that variance in soil microbial and biochemical attributes was better correlated with soil physicochemical attributes than with vegetation type. Redundancy analysis and a Pearson correlation showed that the differentiating biological variables were best correlated with nitrogen concentration. Vereda soils have a far greater biochemical potential for metabolizing organic carbon under standard (i.e. aerobic) conditions, suggesting that draining vereda soils may lead to losses of organic matter and increased greenhouse gas emissions. The findings of this study provide a basis of ecological information on native Cerrado soils that can be used to manage and monitor the quality of this threatened biome.

Impact of oil contamination on ecological functions of peat soils from West Siberia of Russia.

For more than a century, the need for energy has exerted high demand on oil production and led to significant negative impacts on soil and water resources. The aim of our work was to assess such impacts on the ecological functions of oil-contaminated soils in West Siberia of Russia. The total petroleum hydrocarbons (PHC) content in contaminated soils varied between 3.7 and 390g kg-1 . Although peat had the ability to absorb some PHC, excess oil migrated in soil both downward and laterally. Catalase activity, soil respiration activity (basal respiration [BR], microbial biomass carbon [Cmic], and specific respiration activity [qCO2 ]), and Enchytraeus albidus survival and reproduction rates showed significant negative correlations with PHC concentrations, and thus they can be used as guides for establishing acceptable PHC limits in peat soils. Based on the Logit model, the concentration of PHC in peat soil that corresponds to ∼20% reduction on functions (worm reproduction, catalase activity, and basal respiration) is about 40-50g kg-1 . The concentrations of PHC that will result in 80% functional reductions (i.e., near-complete loss on functional activities) are worm production (177g kg-1 ), catalase activity (123g kg-1 ), and basal respiration (311g kg-1 ). This study provides quantitative understanding of the ecological impact of PHC contamination on peat soils and thus helps to establish science-based guidelines for the protection of ecological functions and services of peatland soils.

Differential effects of press vs. pulse seawater intrusion on microbial communities of a tidal freshwater marsh

AbstractTidal freshwater marshes (TFMs) are threatened by seawater intrusion, which can affect microbial communities and alter biogeochemical processes. Here, we report on a long‐term, large‐scale manipulative field experiment that investigated continuous (press) and episodic (pulse, 2 months/yr) inputs of brackish water on microbial communities in a TFM. After 2.5 yr, microbial diversity was lower in press treatments than in control (untreated) plots whereas diversity in pulse plots was unaffected by brackish water additions. Sulfate reducer abundance increased in response to both press and pulse treatments whereas methanogens did not differ among treatments. Our results, along with other lab and field measurements that show reduced soil respiration and extracellular enzyme activity suggest that continuous seawater intrusion will decrease macrophyte C inputs that reduce bacterial diversity in ways that also diminish ecosystem carbon cycling.

Application of biochar in estrogen hormone-contaminated and manure-affected soils: Impact on soil respiration, microbial community and enzyme activity

Biochar as a soil amendment has been proposed for enhancing carbon sequestration and manure-borne hormone contaminant remediation. However, little is known about the ecological risk of biochar application in the soil with hormone contamination. This study investigated the influence of biochar in three manure-impacted soils contaminated with estrogen hormones, natural estrogen 17β-estradiol and synthesized estrogen 17α-ethinylestradiol in a microcosm experiment. Specifically, microbial respiration was periodically determined during microcosm incubation while microbial community phospholipid fatty acids and activities of nutrient (C, N, P, S) cycling related enzymes (β-glucosidase, urease, phosphodiesterase, arylsulfatase) were characterized after the incubation. Results showed that the manure-impacted soils with high SOC generally had greater total microbial biomass, ratios of fungi/bacteria and Gram-positive bacteria/Gram-negative bacteria, and phosphodiesterase activity, but lower urease activity. Additionally, hormones stimulated microbial respiration and biomass, while had little impact on activity of the enzymes. On the other hand, biochar showed negative priming effect by significantly decreasing total microbial biomass by 8.7%–26.4%, CO2 production by 16.6%–33.5%, and glucosidase activity by 27.1%–41.0% in the three soils. Biochar significantly increased the activity of phosphodiesterase, showed no impact on arylsulfatase, while decreased the activity of urease. Overall, the study suggests that when used in hormone remediation in manure-impact soils, biochar could improve phosphodiesterase activity, but may decrease soil microbial activity and the activity of soil glucosidase and urease.

Long-term impact of grain legumes and nutrient management practices on soil microbial activity and biochemical properties

ABSTRACT Sustainability of rice-wheat rotation is questioned with soil degradation and depleting natural resources. The study aimed to assess the long-term impact of four crop rotations [rice-wheat, rice-wheat-mungbean, rice-chickpea, rice-wheat-rice-chickpea (2-year rotation)], each consisted of three nutrient treatments [control, integrated nutrient management (INM), and chemical fertilizers (RDF)] on soil carbon pools, soil microbial, and biochemical properties. Mungbean inclusion in rice-wheat rotation increased soil organic carbon (SOC) and microbial biomass carbon (MBC) by 17% and 27%. Rice-wheat-mungbean rotation increased soil enzymes activities over rice-wheat rotation, prominent on arylsulfatase (41%), dehydrogenase (38%), and phosphatases (32%). Rice-chickpea rotation had higher alkaline phosphatase (10%), β-glucosidase (13%), and protease (6%) activities over rice-wheat rotation. Rice-wheat-mungbean rotation increased the MBC/SOC and reduced MBC/MBN ratio over rice-wheat rotation, which indicates increased lability of soil carbon and enhanced nitrogen cycling rate. The INM treatment increased SOC (20%), MBC (53%), soil respiration (9%), and enzymes activities over RDF treatment, which was primarily attributed to higher organic matter input through farmyard manure and residues recycling. The higher SOC and microbial activity in legume-inclusive rotations influenced the base-crop (rice) productivity. Thus, the inclusion of grain legume and INM could improve microbial activity and biochemical functions in tropical rice soils.

Two potential equilibrium states in long-term soil respiration activity of dry grasslands are maintained by local topographic features

Soil respiration of grasslands is spatio-temporally variable reflecting the changing biological activities of the soil. In our study we analysed how the long-term soil respiration activities of dry grasslands would perform in terms of resistance and resilience. We also investigated how terrain features are responsible for response stability. We conducted a 7-year-long spatial study in a Hungarian dry grassland, measuring soil respiration (Rs), soil temperature (Ts) and soil water content (SWC) along 15 measuring campaigns in 80 × 60 m grids and soil organic carbon content in 6 of the occasions. Two proxy variables were introduced to grasp the overall Rs activity, as well as its temporal stability: average rankRs, the temporal average Rs rank of a measuring position from the campaigns revealed the persistent spatial pattern of Rs, while rangeRs, the range of ranks of the positions from the campaigns described the amplitude of the Rs response in time, referring to the response stability in terms of resistance or resilience. We formulated a hypothetic concept of a two-state equilibrium to describe the performance of the long-term Rs activity: Rs activity with smaller rangeRs, that is both the lower elevation positions with larger rankRs (“state I”) and the higher elevation positions with smaller rankRs (“state II”) correspond to an equilibrium state with several terrain attributes being responsible for the equilibrium responses. Majority of the measuring positions was belonging to none of these equilibrium states. These positions showed higher rangeRs for medium rankRs, suggesting resilience (not resistance) as a major strategy for this ecosystem.

Toxic effects of Red-S3B dye on soil microbial activities, wheat yield, and their alleviation by pressmud application

This study examined the effect of Red-S3B textile dye on soil microbial activities, uptake of the dye by wheat plants and growth on the dye-contaminated soil. Moreover, pressmud (PM) application was investigated for its alleviative effect on wheat yield and dye uptake by plants. Preliminarily, soil was spiked with a wide concentration range (0, 100, 250, 500, 750 and 1000 mg kg−1 soil) of Red-S3B dye and wheat was grown for 42-days. The dye did not suppress the activities of soil enzymes and growth of wheat seedlings at 100 mg kg−1; however, beyond this level the dye had a linear negative effect on these attributes. With 1000 mg dye kg−1 soil, wheat seedling biomass, viable microbial count, soil respiration, dehydrogenase, phosphatase, and urease activities decreased by 84%, 33%, 45%, 69%, 24%, and 11%, respectively as compared to uncontaminated soil. Moreover, phosphorus and potassium content in wheat shoot decreased, while the nitrogen content increased in Red-S3B contaminated soil. In the subsequent pot experiment, PM application (12.5 g kg−1 soil) was assessed to alleviate the adverse effect of moderately toxic level of Red-S3B dye (500 mg kg−1 soil) on wheat growth and yield. Root and straw biomass, and grain yield of wheat decreased by 13, 19 and 12%, respectively in Red-S3B contaminated soil as compared to uncontaminated soil. However, PM application to dye-contaminated soil retrieved the dye-induced reduction in root and straw biomass and grain yield to become statistically (p ≤ 0.05) at par with control plants. The color of Red-S3B was clearly visible in spikes depicting that plants absorbed Red-S3B but probably could not metabolize it. Amending the dye-contaminated soil with PM decreased Red-S3B content in awns from 78 to 37 mg kg−1. Hence, it is concluded that Red-S3B textile dye is highly toxic to soil microbes and wheat plants at levels exceeding 100 mg kg−1 soil. Soil application of PM alleviates the adverse effect of Red-S3B dye on wheat growth through reducing its uptake by plants.

Endophytic Fungus Alleviates Soil Sickness in Peanut Crops by Improving the Carbon Metabolism and Rhizosphere Bacterial Diversity

Endophytic fungi can profoundly affect host productivity, but the underlying mechanisms of these effects are only partly understood. As the most important regulators of plant-soil feedback, root exudates can easily cause soil sickness in continuous monoculture systems by reducing certain microbes in the rhizosphere. In this study, exudates from roots colonized by the endophytic fungus Phomopsis liquidambaris significantly increased rhizosphere bacterial abundance, soil respiration, microbial biomass and enzyme activities in a long-term continuously cropped peanut soil. Further analysis revealed that P. liquidambaris-colonized root exudates clearly altered the carbon metabolism and rhizosphere bacterial diversity, which were closely correlated with changes in soil chemical properties caused by the exudates from the colonized roots. Finally, a synthetic root exudate experiment further confirmed that the root exudates derived from P. liquidambaris colonization can indeed play an important role in promoting peanut growth. Therefore, these results show that this endophytic fungus could improve the carbon metabolism and rhizosphere bacterial community in long-term monoculture soils via exudates from colonized roots, which contribute to the alleviation of soil sickness.

Disentangling the direct and indirect effects of cropland abandonment on soil microbial activity in grassland soil at different depths

Cropland abandonment strongly affects plant-soil interactions. However, knowledge remains limited about how the production and diversity of plants and soil physicochemical parameters drive changes in soil microbial activity (such as microbial biomass, respiration, and enzyme activity) after cropland abandonment. Here, we investigated a grassland restoration chronosequence (0–30 years) to determine the dynamics of soil microbial biomass, respiration, and enzyme activity in the Loess Hilly, Region (China). Overall, cropland abandonment caused an increase in soil microbial activity primarily in the 0–20 cm soil layers. The metabolic quotient in the 0–10 cm layer decreased linearly with time since abandonment (recovery years). Structural equation models showed that recovery years directly and indirectly affected changes to soil microbial activity. Plant species richness, aboveground biomass, and soil organic carbon explained a large proportion of the variability in soil microbial activity in the 0–20 cm layer. However, the variability in soil microbial activity was mostly explained by plant species richness, belowground biomass, and soil total nitrogen in the 20–50 cm layers. Our results indicate that during recovery after cropland abandonment, changes in soil microbial activity are driven by plant characteristics and soil physicochemical parameters, with different drivers at different soil depths.

BIOLOGICAL ACTIVITY OF GREY FOREST SOILS OF THE STARODUB AND BRYANSK OPOLIE AGROECOSYSTEMS

The main indicators of biological activity of grey forest soils of the Starodub and Bryansk Opolie in natural ecosystems, regular and intensive agroecosystems, including radioactively contaminated ones, were determined year by year. It is established that the radioactivity of the soils in the natural ecosystem catena of the Starodub Opolie is practically identical. In agroecosystems the radionuclides in soil catenas are redistributed. They are accumulated in the agrohorizons of soil cavities. In the natural ecosystem the total number of invertebrates and the absolute number of earthworms are higher in grey forest soils, having the second humus horizon cavities, than in the grey forest soils of the neighboring low ridge. In both soils of opolie the earthworms predominate among invertebrates, accounting for about 81 % of their total number. Radioactive contamination reduces the number of earthworms less than the intensification of crop cultivation technologies. In the grey forest soil of the regular agroecosystem, this figure is reduced by 56%, and in the grey forest soil with the second humus horizon by 76 %. In intensive agroecosystems the number of earthworms is reduced less, by 39 and 23 %, respectively. The biomass of the microbiota is significantly greater in the grey forest soils with the second humus horizon of the soil cavities than in the grey forest soils of the neighboring low ridge. Radioactive contamination of these soils reduces microbiota biomass less than intensification of crop cultivation technologies. In the grey forest soils of the agroecosystem, this figure is reduced by 50%, and in the grey forest soil with the second humus horizon by 61 %. In the intensive agroecosystem the biomass of microbiota decreases less intensively, by 30 and 46 %, respectively. In the incubation experiment on the grey forest soils of the Bryansk Opolje it is marked that soil enrichment with organic matter activates the soil microbiota more than 2 times. To a lesser extent, soil respiration increases with NPK application. This figure rises more than 5 times with the combined use of straw and NPK. In the field experiment, the cultivation of winter wheat in the crop rotation after annual grasses and mineral fertilization at the rate of NeoPeoKm+Neo activated the soil microbiota by 75-76 %. The biological cultivation technology on the background of the aftereffect of dung, straw and green manure without mineral fertilization causes a decrease in soil respiration and cellulolytic activity, as compared with the intensive technology.

Integrating Amendment and Liquid Fertilizer for Aided-Phytostabilization and Its Impacts on Soil Microbiological Properties in Arsenic-Contaminated Soil

Indiscriminate overuse of liquid fertilizer and arsenic (As) contaminated soil by abandoned mines is one of the important environmental issues in Korea. This study was carried out to solve these two problems. Amendments (limestone, red mud and acid mine drainage sludge), liquid fertilizer and plant vegetation (Hairy vetch; Vicia villosa Roth) were simultaneously treated. Some soil chemical properties (pH, dissolved organic carbon, inorganic nitrogen content, and bioavailable As), soil respiration and enzyme activity (urease activity and dehydrogenase activity) were determined for chemical and biological assessment. Amendments decreased bioavailable As in soil, and acid mine drainage sludge had the best reduction efficiency in alkali soil. Liquid fertilizer affects not only soil chemical properties but also biological properties. Through multiple regression analysis, the rhizosphere effect through plant cultivation using specific root length index was reflected in the result of soil microbial and enzyme activity. In the reclamation of As-contaminated soil, the synergistic effect of multiple treatments could be confirmed. In particular, biological assessment indicators could be useful when evaluating the complex treatment of various restoration techniques, including the phytoremediation method. Based on these results, a long-term follow-up study on the field scale will be possible.

Effect of nano-fertilizers on soil microflora

Nano fertilizers are one of the recent advancement tools in agriculture that are developed with an aim to increase nutrient use efficiency, reduce wastage of fertilizers and indirectly the cost of cultivation. Besides this they improve the growth and yield of crop and the quality parameters. Nano-fertilizers are very effective for precise nutrient management in precision agriculture with matching the crop growth stage for nutrient and may provide nutrient throughout the crop growth period. However, it has also been speculated that nano-fertilizers can increase the crop growth up to certain optimum concentrations, further increase in concentration may cause nutrient toxicity thereby inhibiting the crop growth. It is also necessary to assess the effect of slow release nano-fertilizer on the soil enzyme activity and soil microbial population. The introduction of nano-fertilizers into the natural environment may pose threat to beneficial microbial communities. The impact of nano-fertilizers on microbial activity could be determined through measurement of soil respiration and enzymatic activities. This review would therefore focus on the effect of nano-fertilizers on the activity of soil microorganisms including both their beneficial and deleterious effects.

Microbial activity was greater in soils added with herb residue vermicompost than chemical fertilizer

Herb residue vermicompost is thought to have high agriculture value, while its effects on soil microbial activities have not been fully understood. Here, soil microbial biomass, respiration and enzyme activities in soil planted with maize were compared among treatments amended with herb residue vermicompost at rates of 25, 50, 75 and 100 g kg−1, chemical NPK fertilizer and no fertilizer (the control). Our results showed that soil microbial biomass carbon, respiration, and alkaline phosphatase, urease, and invertase activities were greater in soil amended with herb residue vermicompost than the unfertilized control (P <0.05). Compared with chemical fertilizer, herb residue vermicompost increased soil urease and alkaline phosphatase activities at each application rate, promoted soil respiration and microbial biomass carbon at the application rates of 50, 75 and 100 g kg−1, and increased soil inverse activity at the application rates of 75 and 100 g kg−1. In conclusion, herb residue vermicompost supported greater soil microbial biomass, respiration and enzyme activities than conventional NPK fertilizer, and the effect was larger when higher rates of herb residue vermicompost were added.

Responses of soil microbial biomass and enzyme activity to herbicides imazethapyr and flumioxazin

The use of herbicides is important for controlling weeds in crops. However, they can present impacts on soil properties, such as biological properties. In this study, we evaluated the responses of soil microbial biomass and enzymes activity to the application of the herbicides imazethapyr and flumioxazin and their mixture in an experiment under laboratory conditions, using soils with a different history of use. Soil microbial biomass C (MBC) decreased, while microbial biomass N (MBN) was not affected after the application of the herbicides as compared to the control. Soil respiration, respiratory quotient, and dehydrogenase (DHA) activity increased significantly after the application of the herbicides compared to the control. The hydrolysis of fluorescein diacetate (FDA) was not significantly different between the control and the herbicide treatments. The principal response curve showed the largest initial effects for the flumioxazin, followed by imazethapyr and their mixture. Flumioxazin had a different influence on soil respiration and respiratory quotient than imazethapyr and their mixture. Finally, the effects of herbicides on soil microbial biomass and enzymes are short-term as we observed recovery in the biological parameters over time.

Similar but Not Identical Resuscitation Trajectories of the Soil Microbial Community Based on Either DNA or RNA after Flooding

Both drought and flooding are unfavorable for soil microorganisms, but nevertheless, are highly relevant to the extreme weather events that have been predicted to increase in the future. The switch of soil water status from drought to flooding can happen rapidly and microbial activity might be either stimulated or further inhibited, but we have insufficient understanding of the underlying microbial processes. Here, we tracked the changes in soil bacterial and fungal abundance and their community structures, assaying the total (DNA-based) and potentially active (RNA-based) communities in response to abrupt flooding of dry soil. Also, rates of soil respiration and enzyme activity were measured after flooding. Results showed that the bacterial community was found to be more responsive than the fungal community to flooding. The bacterial community responses were clearly classified into three distinct patterns in which the intermediate pattern displayed highly phylogenetic clustering. A transient flourish of Bacilli which belongs to Firmicutes was detected at 8–48 h of flooding, suggesting its potential importance in the microbial assemblage and subsequent ecosystem functioning. Finally, the accumulative amount of CO2 released was more closely related than enzyme activity to the change in structure of the bacterial community after flooding. In conclusion, these findings extended our understanding of the underlying soil microbial processes following abrupt water condition changes.

Seasonal CH4 and CO2 effluxes in a final covered landfill site in Beijing, China

As the main solid waste disposal method in China, landfill sites are considerable sources of methane (CH4) and carbon dioxide (CO2). This study characterized the seasonal variation of CH4 and CO2 effluxes at a large and well-managed final covered landfill site in China. A three-year monitoring program was conducted. There were two different seasonal variation patterns for hotspot and non-hotspot’ CH4 and CO2 effluxes. For non-hotspots, the CH4 and CO2 effluxes' seasonal variations were mainly affected by the seasonal change of the landfill's cover soil respiration activity, particularly the CH4 oxidation capability. CH4 had a higher efflux in winter; in other seasons, the CH4 efflux fluctuated around 0; the CO2 effluxes were (1) increased in spring and peaked in summer or early autumn; (2) then, they decreased to a minimum value in late autumn or early winter; and (3) fluctuated with the CH4 efflux in winter. The CH4 emissions in winter account for 60.4–84.4% of the all year outputs. For the hotspots', the CH4 and CO2 effluxes seasonal variations were mainly determined by the seasonal change of the landfill cover's soil gas permeability. The ratio of CH4 emissions in winter to the all year outputs range from 17.4 to 68.7%.

Forest soil respiration and exoenzyme activity in western North America following thinning, residue removal for biofuel production, and compensatory soil amendments

AbstractCellulosic biofuel from forest thinning operations is a potential renewable energy source in regions with overstocked forests such as those in western United States. However, it is possible that biomass removal can deplete nutrients from soil, which can alter soil respiration (Rs) and exoenzyme properties, and potentially impact tree growth. This study evaluates the impact of biomass removal on Rs and exoenzyme properties and the capacity of soil amendments to counteract any potential effects. At two study locations, we created four post‐thinning biomass retention levels: full biomass removal (0×), full biomass retention (1×), double biomass retention (2×), and a no‐thin treatment. Four soil amendment treatments were applied to each biomass retention level: N fertilizer (F), biochar (B), fertilizer plus biochar (FB), and an untreated control (C). We evaluated treatment effects on Rs and activity of four exoenzymes to represent C‐cycling, N‐release, and P‐release processes. Biomass retention levels had no effect on Rs (p = .42) or exoenzyme activities (p &gt; .29). Variation in exoenzyme activity was explained by location, season, soil organic matter, soil moisture content, and temperature. Variation in Rs was explained by the same variables, in addition to C‐cycling exoenzyme activity and soil pH. Soil amendments had no effect on exoenzyme activities (p &gt; .49), and no main effect on Rs (p = .48), though amendments influenced Rs differently at each location (p = .02). Short‐term findings suggest small‐diameter biomass removal for cellulosic biofuel production will not impact Rs and exoenzyme properties, and paired with our tree growth study, provide evidence that biofuel systems are a feasible renewable energy source in the western North America.

Medium-term impact of tillage and residue retention on soil physical and biological properties in dry-seeded rice–wheat system in north-west India

Repeated puddling for rice cultivation and extensive tillage during wheat cultivation in the north-west of India has adversely affected soil health. Adoption of resource conservation technologies (RCTs) is required for long-term sustainability of conventional rice–wheat systems. However, the behaviour of these technologies is site-specific. A field study was conducted in 2016 to evaluate the medium-term impact of tillage and residue retention on soil physical and biological characteristics. Four treatments were imposed during 2011: conventionally-tilled (CT) rice followed by CT wheat all without residue retention (–M); zero-tilled (ZT) rice followed by ZT wheat and –M; CT rice followed by CT wheat and all with residue retention (+M); and ZT direct-seeded rice followed by ZT wheat and +M. In the surface layer (0–15 cm) of ZT, soil organic carbon (SOC) stock was higher by 15%, mean weight diameter (MWD) by 31.8% and bulk density (BD) by 4% compared to CT averaged across residue treatments. Irrespective of tillage, SOC stock was increased by 19% and MWD by 39% and BD decreased by 1.8% in +M compared with –M in the 0–15 cm soil layer. Infiltration rate was higher in +M than –M irrespective of tillage. Microbial biomass carbon, basal soil respiration and soil enzymatic activities were higher in ZT and +M than CT and –M respectively. Thus, medium-term adoption of RCTs such as ZT and residue retention enhanced soil physical and biological properties in this dry-seeded rice–wheat system. However, whether retaining wheat residue improves soil physical and biological properties requires further investigation.

Effects of ZnO nanoparticles on microbial biomass and enzyme activity in soils containing cellulose and lignin

In order to investigate the effect of ZnO nanoparticles (ZnONPs) on soil ecosystem in soil with added cellulose and lignin, five treatments were set up: cellulose, cellulose + ZnONPs, lignin, lignin + ZnONPs, and no addition. The soil respiration, microbial biomass, and the activities of soil enzymes were explored during a 56-day incubation time after the addition of ZnONPs. The results showed that when cellulose and lignin were added to the soil, the CO2 efflux increased by 90.9% and 18.2%, respectively, compared with the control soil. The microbial biomass carbon and the activity of peroxidase, polyphenol oxidase, β-glucosidase and cellulase were increased. Compared with the treatment with the addition of cellulose and lignin only, the exposure of ZnONPs increased the CO2 efflux, microbial biomass carbon, β-glucosidase and cellulase activities, but decreased the peroxidase and polyphenol oxidase activities. We concluded that the addition of cellulose and lignin to farmland soil increased respiration, microbial biomass and soil enzyme activity, but the degradation degree of cellulose was higher than lignin. The ZnONPs promote soil respiration, microbial biomass, and hydrolase activity throughout the culture period, but inhibited the activity of redox enzymes.