Increasing Soil Carbon Content Research Articles

Response mechanism of soil microorganisms to simulated precipitation in the source wetland of Qinghai Lake

BackgroundChanges in precipitation patterns crucially impact soil microbial communities, and the ecosystem in Qinghai-Tibet Plateau (QTP) is highly vulnerable to climate change. However, we do not fully understand how soil microbial communities in the source wetlands of QTP respond to changes in precipitation. In this study, we employed advanced techniques such as high-throughput sequencing and metabolomics to investigate how soil microbial communities in a source wetland of Qinghai Lake respond to changes in precipitation after quadrennial precipitation treatment.ResultsOur findings showed that the predominant microbiota in the source wetland was Proteobacteria. Interestingly, alterations in precipitation levels, whether increased or reduced, did not significantly impact the diversity or functional groups of the microbial community. However, the structure of the microbial community did respond notably to changes in precipitation, leading to shifts in the relative abundance of Spirochaetes and Treponema. A notable finding was that reduced precipitation levels (– 25% and − 50%) and mild increases in precipitation (25%) within the region contributed to increased soil carbon content. However, this effect ceased to manifest when precipitation increased by 50%. Additionally, the reduction in precipitation prompted the release of soil metabolites like syringic acid and aldosterone, while enhanced precipitation resulted in a decrease in aldosterone content.ConclusionsPrecipitation changes altered the relative abundance of soil microbial communities and metabolites, which was conducive to increasing carbon storage in this alpine wetland.

Biochar combined with different nitrogen fertilization rates increased crop yield and greenhouse gas emissions in a rapeseed-soybean rotation system

Biochar as agricultural soil amendment has been extensively investigated for its potential to sequester carbon, to mitigate greenhouse gases (GHGs) emissions, to enhance soil fertility and enhance crop yields. In this study, we investigated the impact of varying N fertilization rates in conjunction with biochar on soil properties, crop yield, and GHGs emissions in a rapeseed (Brassica napus L.)-soybean (Glycine max (L.) Merrill) rotation system for one year. Biochar and N fertilizer were applied following a factorial combination design of three biochar (B0: 0 t hm−2, B1: 15 t hm−2, and B2: 60 t hm−2) and three N fertilizer application rates (H: 100%, M: 75%, and L: 50% of the conventional application rates). In general, there was no significant effect of N fertilizer and its interaction with biochar application on soil water content, pH, and total carbon content, but the addition of biochar significantly increased these parameters (P < 0.05). The yield of both crops were significantly augmented by biochar up to 75% compared to using N fertilization alone, potentially due to enhanced N use efficiency. However, biochar significantly increased the cumulative N2O and CH4 emissions by as much as 2.2 times and 19 times, respectively, during the rapeseed season, thereby elevating the global warming potential (GWP) and the yield-scaled GWP. Nevertheless, the significantly increased soil carbon content following biochar addition might boost soil carbon sequestration, which could counterbalance the escalating GWP induced by GHGs. Therefore, we recommend a comprehensive and long-term evaluation of biochar's impact by considering crop yield, GHGs emissions, and carbon sequestration in agricultural systems to ensure sustainable agricultural management.

Soil organic carbon, aggregation and fungi community after 44years of no-till and cropping systems in the Central Great Plains, USA.

Implementing sustainable agricultural land management practices such as no-till (NT) and diversified crops are important for maintaining soil health properties. This study focuses on the soil health of three long-term (44years) tillage systems, NT, reduced tillage (RT), and conventional tillage (CT), in monoculture winter wheat-fallow (W-F) (Triticum aestivum L.) and wheat-soybean (W-S) (Glycine max (L.) Merrill) rotation. Soil organic carbon (C) was higher in NT than CT in the surface 0-5cm, but not different in the 5-15cm, demonstrating SOC stratification on the soil profile. The soil water content was higher in NT followed by RT and CT in the top 0-5cm. We found an association between increased carbon, aggregation, and AMF biomass. Greater soil aggregation, carbon and AMF were observed in NT at 0-5cm soil depth. The W-S cropping system had greater soil microbial community composition based on fungi biomass, AMF and fungal to bacteria ratio from phospholipid fatty acid analysis (PLFA). Large macroaggregates were positively correlated with total C and N, microbial biomass, Gram + , and AMF. Soil water content was positively correlated with macroaggregates, total C and N, and AC. No-till increased soil carbon content even after 44years of cultivation. By implementing conservation tillage systems and diversified crop rotation, soil quality can be improved through greater soil organic C, water content, greater soil structure, and higher AMF biomass than CT practice in the Central Great Plains.

Recycling fertilizers from human excreta exhibit high nitrogen fertilizer value and result in low uptake of pharmaceutical compounds

Recycling nutrients is essential for closing nutrient loops within a circular economy. Using locally available resources such as human excreta to produce bio-based recycling fertilizers can substitute mineral fertilizers and thereby promote environmentally friendly food production. To better understand the fertilizer potential and nitrogen value of human excreta, three novel and safe recycling products were evaluated in a field experiment. Two nitrified urine fertilizers (NUFs) and one fecal compost were applied alone or in combination, and compared against the commercial organic fertilizer vinasse. In addition, the uptake of pharmaceuticals was assessed for treatments with compost application. White cabbage (Brassica oleracea var. capitata f. alba) was cultivated in plots in three different soil types (sand, loam or silt) treated with the fertilizers according to plant needs and mineral soil nitrogen content. The two NUFs resulted in marketable yields similar to those of vinasse in all soil types. Combining fecal compost with a NUF led to increased marketable yield compared to compost alone. The highest yield was recorded from the sandy soil, where vinasse and NUF treatments led to comparable yields, as expected in organic productions systems (up to 72 t ha−1). The cabbage yield and total aboveground fresh biomass followed the following trend in all soils: NUFs ∼ vinasse ≥ compost + NUF ≥ compost. Nitrogen uptake in the cabbage heads and total biomass was significantly higher in sand (69.5–144 kg ha−1) than loam (71.4–95.8 kg ha−1). All compost treatments alleviated the effect of soil type and resulted in comparable nitrogen uptake and yield in all soil types. Plant uptake of pharmaceuticals (Carbamazepin) was higher in sand than in loam, and concentration in the edible part was lower than in the outer leaves. In conclusion, NUF alone appears to be a promising successful fertilizer substitute in horticultural food production. The combined application of NUF and compost led to slightly lower crop yields, but may increase soil carbon content in the long term, promoting climate-friendly food production.

Biochar changed the distribution of imidacloprid in a plant–soil–groundwater system

The use of biochar has increased, as its physicochemical properties reduce the adverse effects of pesticides. However, few studies have comprehensively investigated the effects of biochar on the distribution of pesticides in a plant–soil–groundwater system. In this study, a biochar produced from rice straw at 550 °C was chosen, and column experiments with five rated of biochar application (application rates = 0.0, 1.0, 2.0, 3.0, and 4.0% w/w for B0–B4, respectively) were conducted to investigate the capacity of biochar to immobilize imidacloprid (IMI) in soil, thereby decreasing its uptake by plants and leaching from soil into groundwater. Our results showed that IMI in plants, leached from soil, and detected in soil accounted for 3.78, 1.76, and 36.4% of the total IMI input, respectively, and the biochar treatments dramatically decreased the IMI distribution to 0.57, 0.11, and 13.4%, respectively. By contrast, the percentage of undetected IMI increased from 58.1% in the B0 treatment to an average of 86.0% in the biochar treatments. Biochar treatments increased IMI immobilization in soil, which could be related to the increased soil carbon content, surface area, cation exchange capacity. This study indicates that biochar with characters of high surface area and porosity can stabilize IMI and reduce its potential to harm plants and groundwater.

Biochar-induced changes in the soil diazotroph community abundance and structure in a peanut field trial

Biological nitrogen fixation (BNF) can help replenish available nitrogen (N) in cropland and reduce the use of chemical N fertilizers, with diazotrophs playing an important role. However, the response of diazotroph community and BNF activity in biochar amendment soil, especially in the deep soil horizon, are poorly understood. In this study, soil samples were collected from topsoil (0–20 cm) and subsoil (20–40 cm) in the field experiment (established in 2013) comprising treatments with no chemical fertilizer (CK), chemical fertilizer (NPK), biochar (BC), and biochar plus chemical fertilizers (BNPK). Here, we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene, and assessed the soil N2 fixation rate (RNfix) using acetylene reduction assay (ARA). Results showed that in the topsoil, the treatments with biochar significantly increased nifH gene copies and RNfix, which was consistent with the increased soil organic matter (SOM), total carbon-to-nitrogen ratio (C/N), dissolved organic carbon (DOC) and pH. In the subsoil, applying chemical fertilizers (NPK) strongly decreased RNfix, but had no effect on diazotroph abundance; in contrast, biochar application (BC) had no effect on RNfix, but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order. Diazotroph and bacterial gene copies were significantly and positively correlated in both top- and sub-soil, and they were mainly influenced by SOM and total nitrogen (TN). In addition, soil nitrate nitrogen (NO3−–N) was the major factor in shaping the vertical stratification of diazotroph community structure. Although nifH gene abundance was significantly correlated with RNfix in the topsoil, the structure equation modeling (SEM) showed the highest correlation between diazotroph community structure and RNfix. Hence, we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance. Biochar induced the dominant diazotroph community succession and increased soil carbon content and pH, which contributed to the BNF activity. Changes in the BNF activity were driven by the variation in diazotroph community structure.

Biochemical composition and function of subalpine shrubland and meadow soil microbiomes in the Qilian Mountains, Qinghai-Tibetan plateau, China.

Microorganisms participate in the soil biogeochemical cycle. Therefore, investigating variations in microbial biomass, composition, and functions can provide a reference for improving soil ecological quality due to the sensitivity of microorganisms to vegetation coverage changes. However, the differences in soil microorganisms between shrubland and meadow have not been investigated in ecologically vulnerable subalpine areas. This study aimed to investigate the biochemical composition and functions of the soil microbial community under two shrublands and a meadow at high altitudes (3,400–3,550 m). Three sites under two shrublands, Rhododendron thymifolium (RHO) and Potentilla fruticosa (POT), and one meadow dominated by Kobresia myosuroides (MEA), were selected on the southern slope of the Qilian Mountains on the northeastern edge of the Qinghai–Tibetan Plateau, China. Soil physicochemical properties, the microbial community composition expressed by the phospholipid fatty acid (PLFA) biomarker, and enzyme activities were analyzed as well as their relationships. The results showed that water holding capacity and the soil carbon, nitrogen, and potassium content in RHO and POT were higher than those in the MEA. Moreover, the soil active carbon, dissolved organic carbon, total nitrogen, and dissolved total nitrogen content in RHO were higher than those in POT. The abundance of total PLFAs, bacteria, and fungi beneath the shrublands was considerably higher than that in the MEA. The PLFA abundance in RHO was significantly higher than that in POT. The fungal-to-bacterial ratio of RHO and POT was significantly higher than that in the MEA. The activities of β-glucosidase, cellobiohydrolase, and leucine aminopeptidase were the highest in RHO among the three vegetation types, followed by POT and MEA. The redundancy analysis indicated that the biochemical composition of the soil microorganisms and enzyme activities were driven by total nitrogen, dissolved organic carbon, water holding capacity, and soil organic carbon. Therefore, shrublands, which have higher biomass, can improve soil moisture status, increase soil carbon and nitrogen content (especially active carbon and active nitrogen), and further increase the abundance of total PLFAs, bacteria, and fungi. The increase of microbial biomass indirectly enhances the activity of relevant soil enzymes. The variations in PLFA abundance and enzyme activities can be attributed to shrub species, especially evergreen shrubs, which create more favorable conditions for soil microorganisms. This study provides a theoretical basis for investigating the soil biogeochemical cycle and a scientific basis for soil management and vegetation restoration in the subalpine regions.

Above-and-Belowground Carbon Stocks in Two Contrasting Peatlands in the Philippines

Although tropical peatlands are huge carbon reservoirs, they are threatened by climate change and anthropogenic disturbances. Here, we assessed two contrasting peatland sites in the Philippines in terms of aboveground biomass and carbon content, soil carbon stock, and CO2 fluxes in the soils. The Caimpugan peatland in Agusan del Sur was considered the ‘undisturbed’ site, while the Bambanin peatland in Mindoro Oriental was the ‘disturbed’ site. The aboveground biomass at the undisturbed site was 35.8 ± 30.0 Mg ha−1) while at the disturbed site, it was 2.0 Mg ha−1 ± 1.9 Mg ha−1. The aboveground C content at the undisturbed site varied from 1.29 Mg C ha−1 to 37.2 Mg C ha−1, while the disturbed site only ranged from 0.1 Mg C ha−1 to 2.1 Mg C ha−1. A trend of increasing soil carbon content as the soil gets deeper was observed in both sites. At the undisturbed site, the average soil carbon content was 750 ± 710 Mg ha−1 and 595 ± 406 Mg ha−1 at the disturbed site. In terms of soil carbon emission, the undisturbed site had 3.6 ± 3.0 g C m−2d−1 and was only one-third the emission rate at the disturbed site (11.2 ± 6.4 g C m−2d−1). Our study highlights the dire condition of a disturbed peatland in terms of vegetation/soil carbon dynamics. We underscored the need to address the pressing issues on peatland drainage, agricultural activities, and human settlement within the peatland sites geared towards effectively managing this important carbon reservoir in the Philippines.

The effects of long-term application of organic and inorganic fertilizers on soil and plant Nitrogen-Carbon contents

Soil and crop management such as chemical fertilizer applications hurt the soil’s biological quality and productivity. The most well-known organic fertilizer such as animal manure, compost and mycorrhizal fungi are significantly contributing to soil organic carbon sink and consequently, organic fertilizers have a positive effect on the soil biological diversity and productivity. To increase soil carbon content, long-term organic fertilizer applications increase soil carbon budget hypothesis was tested under field conditions. The aim is to investigate the effects of different organic and inorganic fertilizer applications on the soil and wheat plant carbon and nitrogen content. A long-term field experiment was established in 1996 until the present time. In 2018, before cultivation control, Mineral fertilizer (NPK), Animal manure (25 ton ha-1), Compost (25 ton ha-1) and Compost+Mycorrhiza (10 ton ha-1) were applied. Adana-99 varieties of wheat seeds were sown. After harvest, soil and plant samples were taken and soil-plant carbon-nitrogen analyses were made. Results show that C % and N % contents of the plant seed, shoot, and root have higher concentrations than that of the control treatment. When the TC %, OC %, and N % contents of the soil at different depths (0-15 cm and 15-30 cm) and in the rhizosphere (R) and no rhizosphere (NR) area were examined, compost and animal manure treatments have higher content. At the rhizosphere area 0-15 cm depth the soil % OC, and % IC contents were statistically significant. The highest values of soil OC %, C: N and IC % contents at Rhizosphere 0-15 cm depth were obtained in animal manure with 2.94 %, 10.06, and 3.90 % respectively. Organic fertilizers application increased soil TC %, OC % and N% contents as well as contribute to the carbon and nitrogen budget. The results found support our hypothesis.

Response of Soil Organic Carbon Content in Different Slope Positions to Fertilization Management in Purple Soil Sloping Fields

The purple soil sloping field is the main cultivated land type in the Three Gorges area, and the soil fertility directly determines crop yield. In order to explore the effects of different fertilization treatments on the soil organic carbon content at different slope positions, field experiments were carried out at the Three Gorges Reservoir Test Station of Chengdu Institute of Mountain and Disasters, Chinese Academy of Sciences. A total of five treatments were set up:no fertilization(CK), conventional fertilization(T1), optimum fertilization(T2), biochar combined with 85% of T2(T3), and straw combined with 85% of T2(T4), to study the differences in soil aggregate composition, soil total organic carbon, soluble organic carbon, and microbial carbon content at different slope positions under different fertilization treatments. The results showed that:①Fertilization increased the content of soil mass and improved the organic carbon content of soil, especially with T3 and T4 treatments. ②The sequence of distribution of soil organic carbon content with CK, T1, and T2 treatments in different slope positions was downslope position>middle slope position>upslope position, while the soil organic carbon content of T3 and T4 treatments was the highest at the middle slope position. ③With the decrease of slope, the soluble organic carbon content of CK, T1, T2, and T3 treated soil showed an increasing trend; the carbon content of CK, T1, T2, and T4 treated soil microorganisms increased; while the distribution of T3 treated soil microbial carbon on the slope was highest at the middle slope followed by the lower slope. In general, both biochar and straw treatments can significantly increase soil carbon content and delay the migration of soil carbon on slopes, which provides guidance for improving the soil quality and reducing water pollution of purple soil dry slopes in the Three Gorges reservoir area.

Mixed plantations of Metasequoia glyptostroboides and Bischofia polycarpa change soil fungal and archaeal communities and enhance soil phosphorus availability in Shanghai, China.

Soil degradation has been found in urban forests in Shanghai, especially in the pure plantations. Mixed plantations are considered to improve soil quality because they can stimulate organic matter cycling and increase soil carbon and nutrient content. Although soil microbes play crucial roles in regulating soil biogeochemical processes, little is known about how mixed plantations affect soil microbial communities, including bacteria, archaea, and fungi. Here, we evaluated soil chemical properties, abundances and compositions of soil bacterial, archaeal, and fungal communities, and enzyme activities in pure and mixed Metasequoia glyptostroboides and Bischofia polycarpa plantations, located in Shanghai, China. The results showed that soil available phosphorus content in the mixed plantation of M. glyptostroboides and B. polycarpa was significantly higher than that in pure plantations, while no significant difference was observed in the content of soil organic carbon, total and available nitrogen, total and available potassium among the three studied plantations. We found higher fungal abundance in the mixed plantation, when compared to both pure plantations. Moreover, fungal abundance was positively correlated with the content of soil available phosphorus. No significant difference was found in the abundance and diversity of bacterial and archaeal community among the three studied plantations. A similarity analysis (ANOSIM) showed that mixed plantation significantly altered the community composition of archaea and fungi, accompanied with an increase of alkaline phosphatase activity. However, ANOSIM analysis of bacterial communities showed that there was no significant group separation among different plantations. Overall, results from this study indicated that fungal and archaeal communities were more sensitive to aboveground tree species than bacterial community. Moreover, mixed plantations significantly increased the activity of alkaline phosphatase and the content of soil available phosphorus, suggesting that afforestation with M. glyptostroboides and B. polycarpa is an effective way to alleviate phosphorus deficiency in urban forests in Shanghai, China.

The role of hydrology on enhanced weathering for carbon sequestration II. From hydroclimatic scenarios to carbon-sequestration efficiencies

Enhanced weathering (EW) scenarios are analyzed using the model presented in Cipolla et al. (2020). We explore the role of different hydroclimatic forcing on carbon-sequestration efficiencies. We also investigate whether increasing soil carbon content improves weathering conditions. We link olivine weathering rates to pH variations and quantify the suitability of hydroclimatic regimes to EW, based on rainfall intensity and frequency. The results show that the amount of CO2 reacting with olivine and ending up in solution in the form of HCO3− and CO32− increases with mean annual precipitation (MAP) up to 2000 mm, but then tapers off for higher MAPs. On the contrary, the sequestered CO2 continues to grow with MAP in a more significant way. We also quantify the increase of nutrients availability, especially when MAP exceeds 2000 mm. Lastly, the results suggest that organic matter amendments are more effective in humid environments (MAP higher than 2000 mm), confirming the central role of hydrologic processes on EW.

Effect of increasing soil carbon content on tobacco aroma and soil microorganisms

Soil carbon pool, the largest carbon pool in any terrestrial ecosystems, has been disrupted owing to high rates of fertilization and intensive crop rotation. Reduction of soil carbon caused decreases of tobacco quality. Firstly, the correlations between soil types (purple soil and paddy soil from the tobacco region in southern China) and tobacco aroma compounds were analyzed in this research. It was showed that the soil carbon pool is closely correlated with tobacco aroma. Secondly, effect of the soil carbon content on soil microorganisms were analyzed. The results indicated that improvement of the soil carbon increased the tobacco aroma and the abundance of Lactobacillales and Oceanospirillales. The present study revealed the correlations between the soil carbon, microbial community structure and tobacco quality, demonstrating the importance of improving the soil carbon for increasing tobacco quality.

Increasing soil carbon content with declining soil manganese in temperate rainforests: is there a link to fungal Mn?

Forest floor carbon (C) sequestration has been negatively correlated with manganese (Mn) availability, possibly due to reduced efficacy of Mn-peridoxase enzymes produced by Agaricomycete fungi. I examined a soil C and Mn dataset from a podzolization gradient, along with fungal sporocarp Mn concentrations, to potentially corroborate this finding. An inverse power relationship between soil C and soil Mn content across temperate rainforests was confirmed, which provides further evidence of a Mn bottleneck in C turnover. Average Mn concentrations of saprotrophic sporocarps were greater than those of ectomycorrhizal fungi, and displayed a similar inverse correlation with increasing soil C. The absence or limited effectiveness of select saprotrophic fungi across Mn-depleted forest soils may be one mechanism behind impeded turnover of recalcitrant organic matter.

Effectiveness of Bamboo Biochar Combined with Compost and NPK Fertilizer to Improved Soil Quality and Corn Yield

Biochar is a carbon-rich material produced from incomplete combustion of agricultural biomass through pyrolysis process. Bamboo biochar can increase soil carbon content, improve soil fertility and restore the degraded soil. Previously we found that bamboo-biochar was effective to improve maize yield with an optimum dosage 10.52 t ha-1 biochar. Here, we examined the effectiveness of bamboo-biochar combined with compost and NPK fertilizer to improved soil quality and crop yield. In this experiment, we used a randomized block design (RBD) with two factors, three replications. The first factor was biochar dosage (four levels), namely without biochar, biochar dosage 5.26 t ha-1, biochar dosage 10.52 t ha-1, biochar dosage 15.78 t ha-1. The second factor is the type of fertilizer with four types, namely: without fertilizer, compost, NPK, and compost+NPK. The results showed that biochar dosage 10.52 t ha-1 combined with compost+NPK could increase P and K availability, increase total soil microbes, and improved soil quality to be very good with soil quality rating value 18. The biochar dosage 10.52 t ha-1 combined with compost+NPK gave the dry weight seed-corn highest of 12.84 tons per hectare that increased 38.61% when compared with without biochar and with compost+NPK. The highest yield 12.84 tons of the dry weight of seed-corn per hectare provides the highest effectiveness-agronomic value 119.69% and feasibility of corn crop farming in drylands value 1.27.

Soil microbial response following wildfires in thermic oak-pine forests

The ecosystem response to wildfire is often linked to fire severity, with potentially large consequences for belowground biogeochemistry and microbial processes. While the impacts of wildfire on belowground processes are generally well documented, it remains unclear how fire affects the fine-scale composition of microbial communities. Here, we investigate the composition of soil bacterial and fungal communities in burned and unburned forests in an attempt to better understand how these diverse communities respond to wildfire. We explored the belowground responses to three wildfires in Linville Gorge, NC, USA. Wildfires generally increased soil carbon content while simultaneously reducing soil respiration. We employed amplicon sequencing to describe soil microbial communities and found that fires decreased both bacterial and fungal diversity. In addition, wildfires resulted in significant shifts in both bacterial and fungal community composition. Bacterial phylum-level distributions in response to fire were mixed without clear patterns, with members of Acidobacteria being representative of both burned and unburned sites. Fungal communities showed consistent increases in Ascomycota dominance and concurrent decreases in Basidiomycota and Zygomycota dominance in response to burning. Indicator species analysis confirmed shift to Ascomycota in burned sites. These shifts in microbial communities may reflect differences in the quality and quantity of soil organic matter following wildfires.

English

The soil is the most important carbon reservoir, but agricultural practices involved in tillage systems decrease the soil carbon stock. This study aims to evaluate the effect of no-tillage (NT) on carbon and microbiological attributes of the soil in corn plantations in Manaus-AM, Brazil. Soil was sampled in a secondary forest (SF) and in corn grown under different tillage systems, including conventional tillage (CT), which makes use of plowing and harrowing operations, and no-tillage (NT). Soil variables studied included, carbon content, soil microbial carbon and basal respiration, metabolic and microbial quotients. The data were analyzed by analysis of variance and Tukey's test. The results demonstrated that NT resulted higher carbon, lower basal respiration, and lower metabolic quotient than CT and SF. However, soil microbial carbon was similar in all tillage systems studied. We conclude that NT corn cropping increased soil carbon content more than CT, while it decreased basal respiration and metabolic quotient when compared to NT and SF. Moreover, soil microbial biomass in corn was similar in all tillage systems studied. This research demonstrated the importance of NT to soil carbon conservation and soil management in corn cropping. Key words: Tillage systems, land use, microbial soil biomass, basal respiration.

Effects of digestate fertilization on Sida hermaphrodita: Boosting biomass yields on marginal soils by increasing soil fertility

Perennial non-food energy crops are currently discussed as a more sustainable alternative to conventional energy crops like maize. As they can be cultivated on marginal soils, they reduce the risk of land use and food vs. fuel conflicts. In this study, we evaluated the perennial energy crop Sida hermaphrodita for its potential to be cultivated on marginal substrate and conventional agricultural soils over a three-year field and mesocosm experiment at agricultural conditions. Furthermore, we aimed for a closed nutrient loop by fertilizing plants with biogas digestate and using the carbon fraction of the digestate as soil amendment to ameliorate the overall soil fertility. As controls, plants were either untreated or fertilized with an equivalent amount of mineral NPK fertilizer. We found S. hermaphrodita to give highest DM yields of up to 28 t ha−1 under favorable soil conditions when fertilized with mineral NPK. However, on marginal substrate digestate fertilization resulted in a clear biomass yield advantage over NPK fertilization. An increased soil carbon content, water holding capacity and basal soil respiration indicated improved soil fertility in the marginal substrate. These results demonstrate the great potential of S. hermaphrodita to be cultivated on marginal soil in combination with organic fertilization via biogas digestate.

Long-term livestock exclosure did not affect soil carbon in southern Ethiopian rangelands

Controlled grazing management is considered as an effective strategy to enhance soil carbon sequestration, but empirical evidences are scarce. Particularly, the role of livestock exclusion related to soil carbon sequestration is not well understood in arid and semiarid savannas of Africa. We investigated the effectiveness of long-term (14–36years old) exclosures in enhancing soil carbon in the semiarid savanna, southern Ethiopia. We tested for differences in soil carbon content between exclosures and adjacent open-grazed rangelands, while accounting for effects of age of exclosures and soil depths. We collected soil samples at two soil depths (0–20cm and 20–50cm depths) from 96 plots from 12 exclosure and adjacent open grazing sites. We found no significant differences (P>0.05) between exclosures and adjacent open-grazed rangelands in soil carbon content in both soil depths. The age chronosequence further suggested a weak non-linear trend in increasing soil carbon content with increasing duration of exclosures. These results thus challenge the opinion that controlled grazing enhances soil carbon sequestration in semiarid savannas. However, we remain cautious in regard to the conclusiveness of these findings given the paucity of information regarding other confounding factors which may disentangle the effects of the exclosure, and most importantly in the absence of soil data prior to exclosures.

Fertilization alters microbial community composition and functional patterns by changing the chemical nature of soil organic carbon: A field study in a Halosol

Insight into the effects of fertilization on soil organic carbon (C) content and composition, and on microbial community and functions related to C decomposition are being gained, although the linkage between them remains elusive. To address this knowledge gap, a field experiment was conducted under different fertilization regimes, no fertilization (CL), chemical fertilization for 11years (CF), organic fertilization for 6years (OF6) and organic fertilization for 11years (OF11) in an alkaline sandy loam soil. Changes in soil C chemistry using 13C nuclear magnetic resonance (NMR) spectroscopy, microbial community using phospholipid fatty acid (PLFA) analysis and microbial functions using six hydrolase and three oxidoreductase enzyme activities were assessed. Fertilization significantly increased soil carbon contents, microbial biomass, and the abundance of fungi and bacteria. Nevertheless, CF induced a higher fungal-to-bacterial ratio due to a lower response in bacterial than fungal growth. In contrast, OF11 increased bacterial abundance, hydrolase activity, and consequently depleted labile C, resulting in higher alkyl-C contents and alkyl C/O-alkyl C ratios compared to other fertilizer treatments. Changes in microbial community composition and enzyme activity were tightly linked to soil C forms. Alkyl-C, carbonyl-C and ketone-C explained most of the variation (>89%) in soil microbial community, while alkyl-C and ketone-C explained most of the variation (>91%) in enzyme activity. Our results indicate that C composition rather than C quantity shaped soil microbial community composition and enzyme activity, restricting soil C decomposition. The practice of long-term organic fertilizer use is suggested to increase the quantity and recalcitrance of soil organic C.