<Emphasis Type="Italic">Trichoderma</Emphasis> improves the growth of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Bio-fertilizer application has been proposed as a strategy for enhancing soil fertility, regulating soil microflora composition, and improving crop yields, and it has been widely applied in the agricultural yields. However, the application of bio-fertilizer in grassland has been poorly studied. We conducted in situ and pot experiments to investigate the practical effects of different fertilization regimes on Leymus chinensis growth, with a focus on the potential microecological mechanisms underlying the responses of soil microbial composition. L. chinensis biomass was significantly (P?<?0.05) increased by treatment with 6000 kg ha^?1 of Trichoderma bio-fertilizer compared with other treatments. We found a positive (R² =?0.6274, P <?0.001) correlation between bacterial alpha diversity and L. chinensis biomass. Hierarchical cluster analysis and nonmetric multidimensional scaling (NMDS) revealed that soil bacterial and fungal community compositions were all separated according to the fertilization regime used. The relative abundance of the most beneficial genera in bio-fertilizer (BOF) (6000 kg ha^?1Trichoderma bio-fertilizer) was significantly higher than in organic fertilizer (OF) (6000 kg ha^?1 organic fertilizer) or in CK (non-amend fertilizer), there the potential pathogenic genera were reduced. There were significant negative (P?<?0.05) correlations between L. chinensis biomass and the relative abundance of several potential pathogenic genera. However, the relative abundance of most beneficial genera were significantly (P?<?0.05) positively correlated with L. chinensis biomass. Soil properties had different effects on these beneficial and on these pathogenic genera, further influencing L. chinensis biomass.     

Combined biochar and nitrogen fertilizer reduces soil acidity and promotes nutrient use efficiency by soybean crop

Purpose

Soil acidification is universal in soybean-growing fields. The aim of our research was to evaluate the effects of soil additives (N fertilizers and biochar) on crop performance and soil quality with specific emphasis on ameliorating soil acidity.

Materials and methods

Four nitrogen treatments were applied as follows: no nitrogen (N0), urea (N1), potassium nitrate (N2), and ammonium sulfate (N3), each providing 30 kg N ha^?1. Half plot area of the N1, N2, and N3 treatments was also treated with biochar (19.5 t ha^?1) to form N-biochar treatments (N1C, N2C, N3C). Both bulk and rhizosphere soils were sampled separately for the following analyses: pH, exchangeable base cations (EBC), exchangeable acidity (EA), total inorganic N (IN), total N (TN), and microbial phospholipid fatty acids (PLFAs). Soybean biomass and nutrient contents were also determined. Correlation analysis was applied to analyze the relationships between soil chemical properties and soybean plant parameters.

Results and discussion

With N-biochar additions (N1C, N2C, N3C), soil chemical properties changed as follows: pH increased by 0.6–1.2 units, EBC, IN, and TN increased by 175–419, 38.5–54.7, and 136–452 mg kg^?1, respectively, and PLFAs increased by 23.6–40.9 nmol g^?1 compared to the N0 in the rhizosphere. Microbial PLFAs had positive correlations with soil pH; EBC; exchangeable K, Ca, Na, and Mg; TN; IN; NH₄ ⁺; and NO₃ ^? (r?=?0.66–0.84, p?<?0.01). There were negative correlations between PLFAs and EA or exchangeable Al (r?=??0.64, ?0.66, p?<?0.01), which indicated that the additives increased microbial biomass by providing a suitable environment with less acid stress and more nutrients. The additives increased soil NH₄ ⁺ and NO₃ ^? by promoting soil organic N mineralization and reducing NH₄ ⁺ and NO₃ ^? leaching. Moreover, the soybean seed biomass and the nutrient contents in seeds increased with N-biochar additions, especially in the N3C treatment.

Conclusions

N-biochar additions were effective in ameliorating soil acidity, which improved the microenvironment for more microbial survival. N-biochars influenced N transformations at the plant–soil interface by increasing organic N mineralization, reducing N leaching, and promoting N uptake by soybeans. The soil additive ammonium and biochar (N3C) were best in promoting soybean growth.

     

Concentrations and Exports of Fecal Indicator Bacteria in Watersheds with Varying Densities of Onsite Wastewater Systems

The research goal was to determine if onsite wastewater system (OWS) density had an influence on the concentrations and watershed exports of Escherichia coli and enterococci in urbanizing watersheds. Eight watersheds with OWS densities ranging from <?0.1 to 1.88 systems ha^?1 plus a watershed served by sewer (Sewer) and a mostly forested, natural watershed (Natural) in the Piedmont of North Carolina served as the study locations. Stream samples were collected approximately monthly during baseflow conditions between January 2015 and December 2016 (n?=?21). Median concentrations of E. coli (2014 most probable number (MPN) 100 mL^?1) and enterococci (168 MPN 100 mL^?1) were elevated in streams draining watersheds with a high density of OWS (>?0.77 system ha^?1) relative to watersheds with a low (<?0.77 system ha^?1) density (E. coli: 204 MPN 100 mL^?1 and enterococci: 88 MPN 100 mL^?1) and control watersheds (Natural: E. coli: 355 MPN 100 mL^?1 and enterococci: 62 MPN 100 mL^?1; Sewer: 177 MPN 100 mL^?1 and 130 MPN 100 mL^?1). Samples collected from watersheds with a high density of OWS had E. coli and enterococci concentrations that exceeded recommended thresholds 88 and 57% of times sampled, respectively. Results show that stream E. coli and enterococci concentrations and exports are influenced by the density of OWS in urbanizing watersheds. Cost share programs to help finance OWS repairs and maintenance are suggested to help improve water quality in watersheds with OWS.     

<Emphasis Type="Italic">Lotus ornithopodioides</Emphasis> L. a potential annual pasture legume species for Mediterranean dryland farming systems

Twenty-three populations of Lotus ornithopodioides L., collected from different regions of the Mediterranean basin, were investigated for their ecological and agronomic traits in Western Australia. Great variability was found between and within populations for flowering time, forage and seed yield. Flowering time ranged between 75 and 120 days, dry matter production from 2.8 to 4.3 t ha^?1 and seed yield from 284 to 684 kg ha^?1. Other important traits such as non-shattering pods and hard seed were taken into account during the selection to assure an easy seed harvesting and legume persistence in the targeted environments. The high level of hard seed recorded in early winter, associated to the low seedling regeneration, indicates that L. ornithopodioides is best suited to ley cropping systems. Elite lines of L. ornithopodioides characterized by early flowering time, high seed yield and non-shattering pods were selected. Two of them, LOR02.1 and LOR03.2, showed dry matter higher than 4.0 t ha^?1 and seed yield around 700 kg ha^?1 resulting the lines with most potential for Mediterranean farming systems. The results encourage the exploitation of L. ornithopodioides germplasm to develop a new annual self-reseeding legume resource for Mediterranean farming systems for both forage production and crop rotation uses.     

Predicting soil loss in central and south Italy with a single USLE-MM model

Purpose

The USLE-MM estimates event normalized plot soil loss, A_e,N, by an erosivity term given by the runoff coefficient, Q_R, times the single-storm erosion index, EI₃₀, raised to an exponent b₁?>?1. This modeling scheme is based on an expected power relationship, with an exponent greater than one, between event sediment concentration, C_e, and the EI₃₀/P_e (P_e = rainfall depth) term. In this investigation, carried out at the three experimental sites of Bagnara, Masse, and Sparacia, in Italy; the soundness of the USLE-MM scheme was tested.

Materials and methods

A total of 1192 (A_e,N, Q_REI₃₀) data pairs were used to parameterize the model both locally and considering all sites simultaneously. The performances of the fitted models were established by considering all erosive events and also by distinguishing between events of different severity.

Results and discussion

The b₁ exponent varied widely among the three sites (1.05–1.44) but using a common exponent (1.18) for these sites was possible. The A_e,N prediction accuracy increased in the passage from the smallest erosion events (A_e,N?≤?1 Mg ha^?1, median error =?3.35) to the largest ones (A_e,N?>?10 Mg ha^?1, median error =?1.72). The Q_REI₃₀ term was found to be usable to predict both A_e,N and the expected maximum uncertainty of this prediction. Soil erodibility was found to be mainly controlled by the largest erosion events.

Conclusions

Development of a single USLE-MM model appears possible. Sampling other sites is advisable to develop a single USLE-MM model for a general use.

     

Spatial variation of soil respiration in a coastal protection forest in southeastern China

Purpose

Forest soil respiration is an important component of global carbon budgets, but its spatial variation is inadequately understood. This research aimed to measure soil respiration (R _s), soil water content (M _s-5), soil temperature (T), and carbon dioxide (M _co2) in a coastal protection forest (CPF), which is one kind of man-made forests designed for coastal protection primarily along the coast in China, to determine the relationships among them, and to analyze their spatial distributions in a small scale.

Materials and methods

We measured R _s, M _s-5, T, and M _co2 of 100 plots in an approximately flat grid (totally 4 hm²) by LI-8100A in a Casuarina equisetifolia L. forest on a state-owned forest farm of 326 hm² in SE China. Traditional statistics and geo-statistics including semivariance, Moran’s I index, and fractal dimension were used to analyze data.

Results and discussion

Key findings were that (1) the spatial mean of R _s, M _s-5, T, and M _co2 were 1.194 μmol m^?2 s^?1, 11.387 mmol mol^?1, 14.153 °C, and 407.716 ppm, respectively, in the forest; (2) the relationship between soil respiration and the other three factors was weak, while M _s-5, T, and M _co2 have strong relationships with each other; and (3) the four factors, especially soil respiration, had strong autocorrelation within given limits and showed great heterogeneity with 95 % confidence intervals around the means in the study area, all of which can provide important value for the study of carbon cycling and for the sustainable management of coastal protection forests.

Conclusions

According to geo-statistical analysis and field investigations, soil respiration in the coastal forest is less than in some broad-leaf forests but higher than in some conifers. Strong heterogeneity and autocorrelation are clear; however, its relation with other three factors is weak. CPF is a considerable potential forest for carbon conservation if it is well managed.

     

An overlooked nitrogen loss linked to anaerobic ammonium oxidation in estuarine sediments in China

Purpose

Despite its importance, anammox (anaerobic ammonium oxidation) in estuarine sediment systems remains poorly understood, particularly at the continental scale. This study aimed to understand the abundance, diversity, and activity of anammox bacteria and to determine the main factors influencing the anammox process in estuarine sediments in China.

Materials and methods

Estuarine sediments were collected from 18 estuaries spanning over 4000 km. Experiments using an ¹⁵ N–tracer, quantitative PCR, and clone library construction were used to determine the activity, abundance, and diversity of anammox bacteria. The impact of environmental factors on anammox processes was also determined.

Results and discussion

The abundance of the anammox-specific hydrazine synthase (hzsB) gene ranged from 1.8 × 10⁵ ± 3.4 × 10⁴ to 3.6 × 10⁸ ± 7.5 × 10⁷ copies g^?1 dw. Candidatus Scalindua, Brocadia, Kuenenia, Jettenia, and two novel unidentified clusters were detected, with Scalindua dominating the anammox population. Additionally, the abundances of Scalindua, Kuenenia, and Brocadia were found to be significantly correlated with latitude. The anammox rates ranged from 0.29 ± 0.15 to 13.68 ± 3.98 nmol N g^?1 dw h^?1 and contributed to 2.39–82.61% of total N₂ production. Pearson correlation analysis revealed that the anammox rate was positively correlated with total nitrogen, total carbon, and temperature, and was negatively correlated with dissolved oxygen (DO). The key factors influencing the hzsB gene abundance were ammonium concentration, salinity, and DO. Ammonium concentration, pH, temperature, and latitude were main variables shaping the anammox-associated bacterial community.

Conclusions

Our results suggested that anammox bacteria are ubiquitous in coastal estuaries in China and underline the importance of anammox resulting in N loss at a continental scale.

     

Effect of Metals on Decolorization of Reactive Blue HERD by <Emphasis Type="Italic">Comamonas</Emphasis> sp. UVS

Comamonas sp. UVS was able to decolorize Reactive Blue HERD (RBHERD) dye (50 mg L^?1) within 6 h under static condition. The maximum dye concentration degraded was 1,200 mg L^?1 within 210 h. A numerical simulation with the model gives an optimal value of 35.71?±?0.696 mg dye g^?1 cell h^?1 for maximum rate (V_max) and 112.35?±?0.34 mg L^?1 for the Michaelis constant (K_m). Comamonas sp. UVS has capability of decolorization of RBHERD in the presence of Mg²⁺, Ca²⁺, Cd²⁺, and Zn²⁺, whereas decolorization was completely inhibited by Cu²⁺. Metal ions also affected the levels of biotransformation enzymes during decolorization of RBHERD. Comamonas sp. UVS was also able to decolorize textile effluent with significant reduction in COD. The biodegradation of RBHERD dye was monitored by UV–vis spectroscopy, FTIR spectroscopy, and HPLC.     

Tillage system affects fertilizer-induced nitrous oxide emissions

Since the development of effective N₂O mitigation options is a key challenge for future agricultural practice, we studied the interactive effect of tillage systems on fertilizer-derived N₂O emissions and the abundance of microbial communities involved in N₂O production and reduction. Soil samples from 0–10 cm and 10–20 cm depth of reduced tillage and ploughed plots were incubated with dairy slurry (SL) and manure compost (MC) in comparison with calcium ammonium nitrate (CAN) and an unfertilized control (ZERO) for 42 days. N₂O and CO₂ fluxes, ammonium, nitrate, dissolved organic C, and functional gene abundances (16S rRNA gene, nirK, nirS, nosZ, bacterial and archaeal amoA) were regularly monitored. Averaged across all soil samples, N₂O emissions decreased in the order CAN and SL (CAN?=?748.8?±?206.3, SL?=?489.4?±?107.2 μg kg^?1) followed by MC (284.2?±?67.3 μg kg^?1) and ZERO (29.1?±?5.9 μg kg^?1). Highest cumulative N₂O emissions were found in 10–20 cm of the reduced tilled soil in CAN and SL. N₂O fluxes were assigned to ammonium as source in CAN and SL and correlated positively to bacterial amoA abundances. Additionally, nosZ abundances correlated negatively to N₂O fluxes in the organic fertilizer treatments. Soils showed a gradient in soil organic C, 16S rRNA, nirK, and nosZ with greater amounts in the 0–10 than 10–20 cm layer. Abundances of bacterial and archaeal amoA were higher in reduced tilled soil compared to ploughed soils. The study highlights that tillage system induced biophysicochemical stratification impacts net N₂O emissions within the soil profile according to N and C species added during fertilization.     

Effects of biogas slurry application on peanut yield,soil nutrients,carbon storage,and microbial activity in an Ultisol soil in southern China

Purpose

Biogas slurry (BS) was known to influence soil–plant ecosystems when applied as a fertilizer, especially in combination with a chemical fertilizer (CF). Limited information was available regarding how this combination of BS–CF actually affected the soil–plant ecosystems. The purpose of this study was to evaluate the effects of BS–CF combinations on peanut yield, soil properties, and carbon (C) storage in a red soil (Ultisol) in southern China.

Materials and methods

The soil was fertilized with five treatments, including a control (T1), CF-only (T2) treatment, and three treatments with different BS–CF combinations (T3–T5). The final quantities of N/P₂O₅/K₂O applied in T2–T5 were 120:90:135 kg ha^?1. In T3–T5, 15 % (18 kg ha^?1), 30 % (36 kg ha^?1), and 45 % (54 kg ha^?1) of total N (TN), respectively, were applied with BS and the remaining TN was applied with CF. Crop yield, soil nutrients, C storage, and microbial activity were determined through field and laboratory experiments.

Results and discussion

In the field experiment, peanut grain yields of T3–T5 were higher than those of T1 (44.5–55.7 %) and T2 (10.8–19.4 %), with the highest yield from T4 (3588 kg ha^?1). The relationship between BS–TN inputs and peanut grain yield conformed to the linear-quadratic equation: y?=??1.14x ²?+?59.1x?+?2988 (R ²?=?0.98). The biomasses of peanut plants, at the flowering, pod production, and harvesting stages, were higher in T4 compared with those in T1 and T2. Moreover, T4 produced higher soil N and P (total and available) concentrations at the pod production and harvesting stages relative to other treatments, with increased soil microbial biomass C and N, and enhanced dehydrogenase and urease activities, at the flowering, pod production, and harvesting stages. Data from the incubation experiment were fitted to a first-order kinetic model, which showed that although the application of BS increased potentially mineralizable C, the additional C seemed to slowly degrade, and so would be retained in the soil for a longer period.

Conclusions

A BS–CF combination increased peanut grain yield and biomass, due to increases in soil N and P availability, microbial biomass C and N concentrations, and urease and dehydrogenase activities. Moreover, the organic C retention time in the red soil was extended. Combined application of BS–CF at a suitable ratio (36 kg BS–TN ha^?1), together with proper management practices, could be effective to improve the quality and nutrient balance of amended soils.

     

Taxon-specific responses of soil microbial communities to different soil priming effects induced by addition of plant residues and their biochars

Purpose

This work investigated changes in priming effects and the taxonomy of soil microbial communities after being amended with plant feedstock and its corresponding biochar.

Materials and methods

A soil incubation was conducted for 180 days to monitor the mineralization and evolution of soil-primed C after addition of maize and its biochar pyrolysed at 450 °C. Responses of individual microbial taxa were identified and compared using the next-generation sequencing method.

Results and discussion

Cumulative CO₂ showed similar trends but different magnitudes in soil supplied with feedstock and its biochar. Feedstock addition resulted in a positive priming effect of 1999 mg C kg^?1 soil (+253.7 %) while biochar gave negative primed C of ?872.1 mg C kg^?1 soil (?254.3 %). Linear relationships between mineralized material and mineralized soil C were detected. Most priming occurred in the first 15 days, indicating co-metabolism. Differences in priming may be explained by differences in properties of plant material, especially the water-extractable organic C. Predominant phyla were affiliated to Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Firmicutes, Planctomycetes, Proteobacteria, Verrucomicrobia, Ascomycota, Basidiomycota, Blastocladiomycota, Chytridiomycota, Zygomycota, Euryarchaeota, and Thaumarchaeota during decomposition. Cluster analysis resulted in separate phylogenetic grouping of feedstock and biochar. Bacteria (Acidobacteria, Firmicutes, Gemmatimonadetes, Planctomycetes), fungi (Ascomycota), and archaea (Euryarchaeota) were closely correlated to primed soil C (R ²?=??0.98, ?0.99, 0.84, 0.81, 0.91, and 0.91, respectively).

Conclusions

Quality of plant materials (especially labile C) shifted microbial community (specific microbial taxa) responses, resulting in a distinctive priming intensity, giving a better understanding of the functional role of soil microbial community as an important driver of priming effect.

     

Effects of saline water irrigation and fertilization regimes on soil microbial metabolic activity

Purpose

Irrigation and fertilization can change soil environment, which thereby influence soil microbial metabolic activity (MMA). How to alleviate the adverse effects by taking judicious saline water irrigation and fertilization regimes is mainly concerned in this research.

Materials and methods

Here, we conducted a field orthogonal designed test under different saline water irrigation amount, water salinity, and nitrogen fertilizer application. The metabolic profiles of soil microbial communities were analyzed by using the Biolog method.

Results and discussion

The results demonstrated that irrigation amount and fertilizer application could significantly change MMA while irrigation water salinity had no significant effect on it. Medium irrigation amount (30 mm), least (50 kg ha^?1) or medium (350 kg ha^?1) N fertilizer application, and whatever irrigation water salinity could obtain the optimal MMA. Different utilization rates of carbohydrates, amino acids, carboxylic acids, and polymers by soil microbial communities caused the differences of the effects, and D-galactonic acid γ-lactone, L-arginine, L-asparagine, D-glucosaminic acid, Tween 80, L-threonine, and D-galacturonic acid were the indicator for distinguishing the effects.

Conclusions

The results presented here demonstrated that by regulating irrigation water amount and fertilizer application, the effects of irrigation salinity on MMA could be alleviated, which offered an efficient approach for guiding saline water irrigation.

     

Spatial patterns of microbial denitrification genes change in response to poultry litter placement and cover crop species in an agricultural soil

Subsurface-banding manure and winter cover cropping are farming techniques designed to reduce N loss. Little is known, however, about the effects of these management tools on denitrifying microbial communities and the greenhouse gases they produce. Abundances of bacterial (16S), fungal (ITS), and denitrification genes (nirK, nirS, nosZ-I, and nosZ-II) were measured in soil samples collected from a field experiment testing the combination of cereal rye and hairy vetch cover cropping with either surface-broadcasted or subsurface-banded poultry litter. The spatial distribution of genes was mapped to identify potential denitrifier hotspots. Spatial distribution maps showed increased 16S rRNA genes around the manure band, but no denitrifier hotspots. Soil depth and nitrate concentration were the strongest drivers of gene abundance, but bacterial gene abundance also differed by gene, soil characteristics, and management methods. Gene copy number of nirK was higher under cereal rye than hairy vetch and positively associated with soil moisture, while nirS gene copies did not differ between cover crop species. The nirS gene copies increased when manure was surface broadcasted compared to subsurface banded and was positively associated with pH. Soil moisture and pH were positively correlated to nosZ-II but not to nosZ-I gene copy numbers. We observed stronger correlations between nosZ-I and nirS, and nosZ-II and nirK gene copies compared to the reverse pairings. Agricultural management practices differentially affect spatial distributions of genes coding for denitrification enzymes, leading to changes in the composition of the denitrifying community.     

Grasses and legumes facilitate phytoremediation of metalliferous soils in the vicinity of an abandoned chromite–asbestos mine

Purpose

The present study was carried out in Roro region, Chaibasa, Jharkhand, India, to assess the impact of chromite–asbestos mine waste (CMW) on a nearby agroecosystem. The role of metal-accumulating grass–legume association in facilitating phytoremediation was investigated.

Materials and methods

Soil and plant samples were collected from (i) chromite–asbestos mine waste (CMW) with Cynodon dactylon, Sorghastrum nutans, and Acacia concinna; (ii) contaminated agricultural soil-1 (CAS1) from a foothill with Cajanus cajan; (iii) contaminated agricultural soil-2 (CAS2) distantly located from the hill, cultivated with Oryza sativa and Zea mays; and (iv) unpolluted control soil (CS). Total metal concentrations were quantified in both soils and plants by digesting the samples using HNO₃, HF, HClO₄ (5:1:1; v/v/v), and HNO₃ and HClO₄ (5:1; v/v), respectively, and analyzed under flame atomic absorption spectrophotometry. Metal grouping and site grouping cluster analysis was executed to group the metals and sampling sites. Translocation factor (TF) and bioconcentration factor (BCF) were calculated to determine the phytoremediation efficiency of grasses and legumes.

Results and discussion

Results indicate that total metal concentrations in the CMW were in the order of Cr?>?Ni?>?Mn?>?Cu?>?Pb?>?Co?>?Zn?>?Cd. High concentrations of Cr (1983 mg kg^?1) and Ni (1293 mg kg^?1) with a very strong contamination factor were found in the CAS, which exceeds the soil threshold limits. Further, metal and site grouping cluster analysis also revealed that Cr and Ni were closely linked with each other and the CMW was the main source of contamination. Among all the metals, Cr and Ni were mainly accumulated in grasses (C. dactylon and S. nutans) and legumes (A. concinna and C. cajan) as compared to cereals (Z. mays and O. sativa). The TF of Cr was >1 for grasses. Except for Zn, the BCF for all the metals were <1 in roots and shoots of all the plants and cereals.

Conclusions

The present study revealed that abandoned CMW is the source of contamination for agriculture lands. Phytoremediation relies on suitable plants with metal-scavenging properties. Grass–legume cover (C. dactylon, S. nutans, A. concinna, and C. cajan) has the ability to accumulate metals and act as a potential barrier for metal transport, which facilitate the phytoremediation of the CMW. Possibilities for enhancing the barrier function of the grass–legume cover need to be explored with other low-cost agronomic amendments and the role of rhizospheric organisms.

     

The potential of using alternative pastures,forage crops and gibberellic acid to mitigate nitrous oxide emissions

Purpose

In grazed pastures, nitrous oxide (N₂O), a powerful greenhouse gas and an ozone depletion substance, is mostly emitted from animal excreta, particularly animal urine-N returned to the soil during grazing. We conducted a series of four field lysimeter and plot experiments to assess the potential of using gibberellic acid (GA) and/or alternative pastures or forage crops to mitigate N₂O emissions from outdoor dairy farming systems.

Materials and methods

Pasture and forage plants assessed in the experiments included Italian ryegrass (Lolium multiflorum L.), lucerne (Medicago sativa L.), diverse pastures (including plantain (Plantago lanceolata L.), chicory (Cichorium intybus L.), perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.)), fodder beet (Beta vulgaris L.), kale (Brassica oleracea L.), as well as the standard perennial ryegrass and white clover (RG/WC) pastures. N₂O was determined using a standard static chamber method in the field either on top of lysimeters or field plots.

Results and discussion

The results showed that the application of GA to urine-treated lysimeters with Italian ryegrass, lucerne or RG/WC pastures did not result in lower N₂O emissions. However, the use of diverse pastures which included plantain with a lower urine-N loading rate at about 500 kg N ha^?1 significantly decreased N₂O emissions by 46 % compared with standard RG/WC with a urine-N loading rate at 700 kg N ha^?1. However, when urine-N was applied at the same rates (at 500 or 700 kg N ha^?1), the N₂O emissions were similar between the diverse and the standard RG/WC pastures. This would indicate that it is the N-loading rate in the urine from the different pastures that determines the N₂O emissions from different pastures or forages, rather than the plants per se. The N₂O emissions from cow urine from fodder beet were 39 % lower than from kale with the same urine-N application rate (300 kg N ha^?1).

Conclusions

These results suggest that N₂O emissions can potentially be reduced by incorporating diverse pastures and fodder beet into the grazed pasture farm system. Further studies on possible mechanisms for the lower N₂O emissions from the different pastures or forages would be useful.

     

Microbial pathways for nitrous oxide emissions from sheep urine and dung in a typical steppe grassland

The aim of this study was to determine the responses of nitrifiers and denitrifiers to understand microbial pathways of nitrous oxide (N₂O) emissions in grassland soils that received inputs of sheep excreta. Sheep dung and synthetic sheep urine were applied at three different rates, simulating a single, double, or triple overlapping of urine or dung depositions in the field. Quantitative PCR and high-throughput sequencing were combined with process-based modeling to understand effects of sheep excreta on microbial populations and on pathways for N₂O production. Results showed that emissions of N₂O from urine were significantly higher than from dung, ranging from 0.12 to 0.78 kg N₂O-N ha^?1 during the 3 months. The N₂O emissions were significantly related to the bacterial amoA (r?=?0.373, P?<?0.001) and nirK (r?=?0.614, P?<?0.001) gene abundances. It was autotrophic nitrification that dominated N₂O production in the low urine-N rate soils, whereas it was denitrification (including nitrifier denitrification and heterotrophic denitrification) that dominated N₂O production in the high urine-N rate soils. Nitrifier denitrification was responsible for most of the N₂O emissions in the dung-treated soils. This study suggests that nitrifier denitrification is indeed an important pathway for N₂O emissions in these low fertility and dry grazed grassland ecosystems.     

Response of CaCl<Subscript>2</Subscript>-extractable heavy metals,polychlorinated biphenyls,and microbial communities to biochar amendment in naturally contaminated soils

Purpose

Biochar can be used to reduce the bioavailability and leachability of heavy metals, as well as organic pollutants in soils through adsorption and other physicochemical reactions. The objective of the study was to determine the response of microbial communities to biochar amendment and its influence on heavy metal mobility and PCBs (PCB52, 44, 101, 149, 118, 153, 138, 180, 170, and 194) concentration in application of biochar as soil amendment.

Materials and methods

A pot (macrocosm) incubation experiment was carried out with different biochar amendment (0, 3, and 6 % w/w) for 112 days. The CaCl₂-extractable concentration of metals, microbial activities, and bacterial community were evaluated during the incubation period.

Results and discussion

The concentrations of 0.01 M CaCl₂-extractable metals decreased (p?>?0.05) by 12.7 and 20.5 % for Cu, 5.0 and 15.6 % for Zn, 0.2 and 0.5 % for Pb, and 1.1 and 8.9 % for Cd, in the presence of 3 and 6 % of biochar, respectively, following 1 day of incubation. Meanwhile, the total PCB concentrations decreased from 1.23 mg kg^?1 at 1 day to 0.24 mg kg^?1 at 112 days after 6 % biochar addition, representing a more than 60 % decrease relative to untreated soil. It was also found out that biochar addition increased the biological activities of catalase, phosphatase, and urease activity as compared with the controls at the same time point. Importantly, the Shannon diversity index of bacteria in control soils was 3.41, whereas it was 3.69 and 3.88 in soils treated with 3 and 6 % biochar soil. In particular, an increase in the number of populations with the putative ability to absorb PCB was noted in the biochar-amended soils.

Conclusions

The application of biochar to contaminated soils decreased the concentrations of heavy metals and PCBs. Application of biochar stimulated Proteobacteria and Bacteroides, which may function to absorb soil PCB and alleviate their toxicity.

     

For how long does the quality and quantity of residues in the soil affect the carbon compartments and CO<Subscript>2</Subscript>-C emissions?

Purpose

The mineralization/immobilization of nutrients from the crop residues is correlated with the quality of the plant material and carbon compartments in the recalcitrant and labile soil fractions. The objective of this study was to correlate the quality and quantity of crop residues incubated in the soil with carbon compartments and CO₂-C emission, using multivariate analysis.

Materials and methods

The experiment was conducted in factorial 4?+?2?+?5 with three replicates, referring to three types of residues (control, sugarcane, Brachiaria, and soybean), and two contributions of the crop residues in constant rate, CR (10 Mg ha^?1 residue), and agronomic rate, AR (20, 8, and 5 Mg ha^?1 residue, respectively, for sugarcane, soybean, and Brachiaria), evaluated five times (1, 3, 6, 12, and 48 days after incubation). At each time, we determined the CO₂-C emission, nitrogen and organic carbon in the soil, and the residues. In addition, the microbial biomass and water-soluble, labile, and humic substance carbons fractionated into fulvic acids, humic acids and humin were quantified.

Results and discussion

Higher CO₂-C emissions occurred in the soil with added residue ranging from 0.5 to 1.1 g CO₂-C m^?2 h^?1 in the first 6 days of incubation, and there was a positive correlation with the less labile organic soil fractions as well as residue type. In the final period, after 12 days of soil incubation, there was a higher relation of CO₂-C emission with carbon humin. The sugarcane and soybean residue (20 Mg ha^?1) promoted higher CO₂-C emission and the reduction of carbon residue. The addition of residue contributed to an 82.32 % increase in the emission of CO₂-C, being more significant in the residue with higher nitrogen availability.

Conclusions

This study shows that the quality and quantity of residue added to soil affects the carbon sequestration and CO₂-C emission. In the first 6 days of incubation, there was a higher CO₂-C emission ratio which correlates with the less stable soil carbon compartments as well as residue. In the final period of incubation, there is no effect of quality and quantity of residue added to soil on the CO₂-C emission.

     

Assessing the potential of using biochar in mine rehabilitation under elevated atmospheric CO<Subscript>2</Subscript> concentration

Purpose

Re-establishment of soil nitrogen (N) capital is a priority in mine rehabilitation. We aimed to evaluate the effects of biochar addition on improving mine spoil N pools and the influence of elevated CO₂ concentration on mine rehabilitation.

Materials and methods

We assessed the effects of pinewood biochar, produced at three temperatures (650, 750 and 850 °C, referred as B₆₅₀, B₇₅₀ and B₈₅₀, respectively), on mine spoil total N concentrations with five different plant species, including a tree species (Eucalyptus crebra), N-fixing shrubs (Acacia floribunda and Allocasuarina littoralis) and C₃ and C₄ grasses (Austrodanthonia tenuior and Themeda australis) incubated at ambient (400 μL L^?1) and elevated (700 μL L^?1) atmospheric CO₂ concentrations, as well as the effects of elevated CO₂ on mine rehabilitation.

Results and discussion

Soil total N significantly improved following biochar incorporation under all plant species (P < 0.05) except for T. Australis. E. crebra had the highest soil total N (0.197%, 0.198% and 0.212% for B₆₅₀, B₇₅₀ and B₈₅₀, respectively). Different from the negligible influence of elevated CO₂ on soil properties under the grasses and the N-fixing shrubs, elevated CO₂ significantly increased soil water and hot water extractable organic C (WEOC and HWEOC, respectively) and decreased total C under E. crebra, indicating that the nutrient demands were not met.

Conclusions

Biochar addition showed the potential in mine rehabilitation in terms of improving soil N pool, especially with E. crebra. However, it would be more difficulty to rehabilitate mine spoils in future with the rising atmospheric CO₂ concentration.