Higher Microbial Biomass Carbon Research Articles

Long-Term Cropping Management Practices Affect the Biochemical Properties of an Alabama Ultisol

Interest in improving the long-term sustainability of agricultural production systems has focused on identifying management practices that promote soil health. No tillage, cover cropping, and amending soils with broiler (Gallus gallus domesticus L.) litter are commonly adopted conservation practices that have been shown to improve soil fertility and crop yield. However, the overall influence of these conservation practices on soil health in the southeastern US are not well understood. Thus, a study was conducted to evaluate the influence of tillage, broiler litter (BL) applications, and cropping systems on soil biochemical properties. Soils were collected from field research plots under long-term management (>than 25 years of tillage, 15 years of broiler litter application, and 15 years of cropping system). Soil microbial biomass, C, N, and P, amidohydrolases, and dissolved organic matter (DOM) were evaluated as indicators of soil health. Adopting tillage and BL into the agricultural management system modified the biochemical parameters of the soils evaluated. Most of these modifications occurred in the 0–5 cm depth. Higher microbial biomass carbon (MBC; 85%) and nitrogen (MBN; 10%) and enzyme activities of asparaginase (65%) and glutaminase (70%) were observed in the 0–5 cm depth under no tillage (NT) compared to conventional tillage (CT), indicating greater biological activities were established in these soil ecosystems. Broiler litter applications increased microbial biomass N and activities of asparaginase and glutaminase in both soil depths. In addition, microbial biomass phosphorus (MBP) was increased following BL application in the 0–5 cm depth. The results suggest that long-term management of NT and BL additions can improve the health of eroded southeastern US soils by altering the soil biochemical parameters.

Biological and Chemical Vicissitudes in Soil Rhizosphere Arbitrated under Different Tillage, Residues Recycling and Oilseed Brassica-Based Cropping Systems

In this study, the impacts of long-term soil and crop management practices on crop productivity and soil health in oilseed brassica-based production systems were examined. Different tillage, crop residue recycling and cropping systems (fallow–mustard, cluster bean–mustard, green gram–mustard, maize–mustard, pearl millet–mustard and sesame–mustard) were studied for 5 years at two soil depths (0–15 and 15–30 cm) in a split-plot design with three replications. No-till permanent beds with crop residue (PB + R) noticeably improved soil organic carbon (SOC), microbial biomass carbon (MBC), enzymes (dehydrogenase (DHA) and alkaline phosphatase (AlP)), nitrogen fractions (available and total nitrate) and available phosphorus and potassium content in both soil layers compared to conventional tillage without crop residues. However, the plough soil layer (0–15 cm) showed higher concentrations of soil carbon, enzymes, N fractions and available P than in the subsoil (15–30 cm). The dynamic soil biological and chemical properties also varied with the crop stage, and higher MBC at 30 days, SOC and enzymatic activities at 60 days, and N fractions and available P and K during the harvesting of mustard crop were recorded. Green gram–mustard rotation showed higher values in terms of biological and chemical parameters. Thus, the legume-based mustard crop rotation following no-till permanent beds and residue recycling was found to be holistic in terms of improving soil health and nutrient cycling.

The impact of stand composition and tree density on topsoil characteristics and soil microbial activities

The assessment of long-term effects of forest management practices, particularly species mixing and stand density, provides valuable information for the forestry sectors. This study evaluated and compared the effect of stand composition and density on organic horizon (i.e., OL, OF, OH) and organo-mineral horizon characteristics of nine stands in the Orleans State Forest (France), seven years after the first thinning treatments. To this end, three triplets of stands of pure Quercus petraea Matt., pure Pinus sylvestris L. and a mixture of both species were selected. Each stand consisted of two plots with different tree densities: low and normal. Physicochemical variables were measured on the organic humus horizon (OH), while microbial biomass carbon (MBC) and nitrogen (MBN), and soil microbial metabolic profile were evaluated on the organo-mineral horizon; the abundance of soil microbial populations (i.e., bacteria, fungi and archaea) in each plot was also assessed by qPCR. The OH thickness consistently increased under pure pine stands (25–35 mm), while other OH characteristics showed no variation based on stand composition and tree density. Low-density plots exhibited changes in microbial biomass, with a significant decrease in both MBC and MBN. Moreover, the highest MBC was recorded under pure pine stands (1241 mg C.kg−1 DW soil), and the highest MBN under pure oak stands (24–39 mg N.kg−1 DW soil). The highest C assimilation rates were recorded in the mixed stands, especially under low tree density. Bacteria and archea were similarly abundant across stand compositions and tree densities, while fungi tended to be more abundant in the mixed coniferous-broadleaf stands. Our findings should be considered by the forestry sectors of European countries where these two species are distributed, and suggest that EU forestry strategies should promote biodiversity in the context of tree plantations.

Biochar particle size coupled with biofertilizer enhances soil carbon-nitrogen microbial pools and CO2 sequestration in lentil

Introduction: Biochar and biofertilizer have emerged as sustainable soil amendments to improve soil fertility and quality. However, it is necessary to determine how biochar’s various particle sizes and biofertilizers affect soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and CO2 sequestration.Methods: This research examined two rhizobia inoculum products—Biozote-N and Rhizogold—along with three biochar particle sizes (<2, 2–5, and 5–10 mm) under incubation intervals of 3, 6, and 10 days.Results: The MBC (µg g−1 soil) and MBN (µg g−1 soil) increased significantly (p < 0.05), however, a significant (p < 0.05) decrease in the organic C and mineralizable C within the <2 mm biochar treatment was observed. With biochar size of 2 mm on day 3, the CO2 evolution was 25% lower, but it increased 4%–19% from day 6–10 compared to the other biochar sizes and the biochar control. Sizes 2 and 2–5 mm were 43% lower in MBN, whereas 5–10 mm was 70% lower (µg g−1 OC). Biozote-N outperformed Rhizogold and no-biofertilizer on days 6 and 10, registering 6% and 20% higher MBC (g g−1 soil/OC), respectively. No biofertilizer increased CO2 production by 14% and 23% on days 3 and 6, respectively. On day 10, however, CO2 production inside Biozote and Rhizogold plots increased by 67% and 45% relative to the control, respectively. Biofertilizers enhanced MBN (µg g−1 OC) by 37%, with the contribution of Biozote-N being 18% more than that of Rhizogold. The Biozote-N and Rhizogold plots had a 13 and 28% increase in mineralizable N compared to the control. After the spring (lentil) crop, there was a 5%–18% higher MBC (g g−1 soil), 6%–17% higher MBC (g g−1 OC), 2%–10% greater CO2 evolution, 23% higher MBN, and 77% higher mineralizable N than after the fall (maize) crop.Discussion: The results demonstrated the usefulness of Biozote-N for enhanced MBC and MBN, as they decreased C mineralization at the small biochar size (2 mm) even after 1 year of their combined application to lentil crop, showing that biochar-Biozote-N were more successful at boosting soil organic fertility and C sequestration.

Microbial responses to soil cooling might explain increases in microbial biomass in winter

In temperate, boreal and arctic soil systems, microbial biomass often increases during winter and decreases again in spring. This build-up and release of microbial carbon could potentially lead to a stabilization of soil carbon during winter times. Whether this increase is caused by changes in microbial physiology, in community composition, or by changed substrate allocation within microbes or communities is unclear. In a laboratory incubation study, we looked into microbial respiration and growth, as well as microbial glucose uptake and carbon resource partitioning in response to cooling. Soils taken from a temperate beech forest and temperate cropland system in October 2020, were cooled down from field temperature of 11 °C to 1 °C. We determined microbial growth using 18O-incorporation into DNA after the first two days of cooling and after an acclimation phase of 9 days; in addition, we traced 13C-labelled glucose into microbial biomass, CO2 respired from the soil, and into microbial phospholipid fatty acids (PLFAs). Our results show that the studied soil microbial communities responded strongly to soil cooling. The 18O data showed that growth and cell division were reduced when soils were cooled from 11 to 1 °C. Total respiration was also reduced but glucose uptake and glucose-derived respiration were unchanged. We found that microbes increased the investment of glucose-derived carbon in unsaturated phospholipid fatty acids at colder temperatures. Since unsaturated fatty acids retain fluidity at lower temperatures compared to saturated fatty acids, this could be interpreted as a precaution to reduced temperatures. Together with the maintained glucose uptake and reduced cell division, our findings show an immediate response of soil microorganisms to soil cooling, potentially to prepare for freezing events. The discrepancy between C uptake and cell division could explain previously observed high microbial biomass carbon in temperate soils in winter.

Soil organic carbon fraction accumulation and bacterial characteristics in curtilage soil: Effects of land conversion and land use.

Conversion of curtilage land into cropland or grassland can have substantial effects on soil nutrition and microbial activities; however, these effects remain ambiguous. This is the first study to compare the soil organic carbon (SOC) fractions and bacterial communities in rural curtilage, converted cropland, and grassland compared with cropland and grassland. This study determined the light fraction (LF) and heavy fraction (HF) of organic carbon (OC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and the microbial community structure by conducting a high-throughput analysis. Curtilage soil had significantly lower OC content, the DOC, MBC, LFOC and HFOC of grassland and cropland soils were 104.11%, 55.58%, 264.17%, and 51.04% higher than curtilage soil averagely. Cropland showed notably high bacterial richness and diversity, with Proteobacteria (35.18%), Actinobacteria (31.48%), and Chloroflexi (17.39%) predominating in cropland, grassland, and curtilage soil, respectively. Moreover, DOC and LFOC contents of converted cropland and grassland soils were 47.17% and 148.65% higher than curtilage soil while MBC content was 46.24% lower than curtilage soil averagely. Land conversion showed more significant effects on microbial composition than land-use differences. The abundant Actinobacteria and Micrococcaceae population and the low MBC contents indicated a "hungry" bacterial state in the converted soil, whereas the high MBC content, Acidobacteria proportion, and relative abundance of functional genes in the fatty acid and lipid biosynthesis indicated a "fat" bacterial state in cropland. This study contributes to the improvement of soil fertility and the comprehension and efficient use of curtilage soil.

Tradeoffs of microbial life history strategies drive the turnover of microbial-derived organic carbon in coastal saline soils.

Stable soil organic carbon (SOC) formation in coastal saline soils is important to improve arable land quality and mitigate greenhouse gas emissions. However, how microbial life-history strategies and metabolic traits regulate SOC turnover in coastal saline soils remains unknown. Here, we investigated the effects of microbial life history strategy tradeoffs on microbial carbon use efficiency (CUE) and microbial-derived SOC formation using metagenomic sequencing technology in different salinity soils. The results showed that high-salinity is detrimental to microbial CUE and microbial-derived SOC formation. Moreover, the regulation of nutrients stoichiometry could not mitigate adverse effects of salt stress on microbial CUE, which indicated that microbial-derived SOC formation is independent of stoichiometry in high-salinity soil. Low-salinity soil is dominated by a high growth yield (Y) strategy, such as higher microbial biomass carbon and metabolic traits which are related to amino acid metabolism, carbohydrate metabolism, and cell processes. However, high-salinity soil is dominated by stress tolerance (S) (e.g., higher metabolic functions of homologous recombination, base excision repair, biofilm formation, extracellular polysaccharide biosynthesis, and osmolytes production) and resource acquisition (A) strategies (e.g., higher alkaline phosphatase activity, transporters, and flagellar assembly). These trade-offs of strategies implied that resource reallocation took place. The high-salinity soil microbes diverted investments away from growth yield to microbial survival and resource capture, thereby decreasing biomass turnover efficiency and impeding microbial-derived SOC formation. Moreover, altering the stoichiometry in low-salinity soil caused more investment in the A-strategy, such as the production of more β-glucosidase and β-N-acetyl-glucosaminidase, and increasing bacterial chemotaxis, which thereby reduced microbial-derived SOC formation. Our research reveals that shift the microbial community from S- and A- strategies to the Y-strategy is important to increase the microbial CUE, and thus enhance SOC turnover in coastal saline soils.

Grazing Regulates Changes in Soil Microbial Communities in Plant-Soil Systems

Soil microorganisms promote material transformation and energy flow in the entire ecological environment and play a key role in the stability and development of grassland ecosystems. Studies on the impacts of grazing on the soil microbial community and the establishment of a reasonable grazing intensity are crucial to improve our knowledge of the mechanisms underlying grassland degradation and to accurately assess the influence of grazing management on grassland functions and the nutrient cycle. Based on the grassland grazing control experimental platform, we compared the structure and diversity characteristics of soil microbial communities under six grazing intensities (0.00, 0.23, 0.34, 0.46, 0.69, and 0.92 AU ha−1) (1 AU = 500 kg of adult cattle) on the Hulunbuir Leymus chinensis meadow steppe. The results showed that soil microbial biomass carbon (MBC) and nitrogen (MBN) decreased with increasing soil depth. The 0–10 cm soil layer of G0.34 had the highest MBC and MBN, and the G0.92 treatment had the lowest MBC and MBN. Heavy grazing significantly decreased the MBC and MBN contents in the soil surface layer. The soil bacterial diversity under light grazing treatment (0.23 AU ha−1) was higher than that under heavy grazing, and the fungal diversity under the no-grazing treatment was higher than that under the grazing treatment. Overgrazing reduced the bacterial species in the soil. The plant belowground biomass significantly (p = 0.039) influenced the bacterial community structure, and the soil pH (p = 0.032), total nitrogen (p = 0.011), and litter (p = 0.007) significantly influenced the fungal community. The effects of grazing on microbial communities were primarily driven by vegetation productivity, litter mass, and soil geophysical and chemical characteristics. This study deepened our understanding of the impacts of grazing practices on soil microbial communities on the meadow steppe, suggesting that moderate-disturbance grazing can promote the sustainable development of grassland vegetation-soil microorganisms.

Keeping thinning-derived deadwood logs on forest floor improves soil organic carbon, microbial biomass, and enzyme activity in a temperate spruce forest

Deadwood is a key component of forest ecosystems, but there is limited information on how it influences forest soils. Moreover, studies on the effect of thinning-derived deadwood logs on forest soil properties are lacking. This study aimed to investigate the impact of thinning-derived deadwood logs on the soil chemical and microbial properties of a managed spruce forest on a loamy sand Podzol in Bavaria, Germany, after about 15 years. Deadwood increased the soil organic carbon contents by 59% and 56% at 0–4 cm and 8–12 cm depths, respectively. Under deadwood, the soil dissolved organic carbon and carbon to nitrogen ratio increased by 66% and 15% at 0–4 cm depth and by 55% and 28% at 8–12 cm depth, respectively. Deadwood also induced 71% and 92% higher microbial biomass carbon, 106% and 125% higher microbial biomass nitrogen, and 136% and 44% higher β-glucosidase activity in the soil at 0–4 cm and 8–12 cm depths, respectively. Many of the measured variables significantly correlated with soil organic carbon suggesting that deadwood modified the soil biochemical processes by altering soil carbon storage. Our results indicate the potential of thinned spruce deadwood logs to sequester carbon and improve the fertility of Podzol soils. This could be associated with the slow decay rate of spruce deadwood logs and low biological activity of Podzols that promote the accumulation of soil carbon. We propose that leaving thinning-derived deadwood on the forest floor can support soil and forest sustainability as well as carbon sequestration.

Phosphorus and potassium supplementing bio-mineral fertilizer augments soil fertility and improves fruit yield and quality of pomegranate

• A bio-mineral fertilizer (BMF) was developed to replace chemical fertilizer. • The BMF was developed from low-grade minerals combined with P and K mobilizer. • The BMF was found as effective as P and K chemical fertilizers in pomegranate cultivation. • BMF application remarkably improves fruit yield and quality of as well as soil fertility. Large-scale use of chemical fertilizers has brought about environmental pollution and raised food safety issues besides increasing the cost of production. The present study focused on using natural minerals inoculated with nutrient mobilizing microorganism so - called bio - mineral fertilizer to partially substitute chemical fertilizers dose. Two years of field trials and a pot culture experiment were carried out with pomegranate to look into the possibility of bio-mineral fertilizer use in saving phosphorus (P) and potassium (K) chemical fertilizers application and in improving soil fertility, tree nutrition, and fruit quality. Results manifested that application of bio-mineral fertilizer significantly enhanced available nitrogen (N), P, and K content of soil and also improved concentration of P, K, magnesium (Mg) and sulphur (S) in the tree foliage. As a consequence, higher fruit yield with perceptible improvement in quality attributes viz. aril percent, 100 arils test weight, juice acidity, ascorbic acid, total phenolics, anthocyanin concentration was observed in bio-mineral treated trees. The highest yield (73.97% increase over control) was recorded with the application of 150 g tree −1 bio-mineral fertilizer which was equivalent to the yield obtained with the recommended dose of P and K chemical fertilizers. In addition, the application of bio-mineral fertilizer led to improvement in the nutritional quality of fruit and also soil microbial environment as indicated by higher microbial biomass carbon and enzymes activities. So, the results indicate that Penicillium pinophilum based bio-mineral fertilizer may be recommended to supplement P and K requirement of pomegranate tree and get maximum benefits in terms of yield, quality, and production cost savings.

Legume cover crop type and termination method effects on labile soil carbon and nitrogen and aggregation

AbstractGrowers use cover crops to provide nutrients for crops and build soil organic matter (SOM). Termination methods may alter the effects of cover crops on soil labile C and N. We examined how two cover crops and three termination methods affected soil microbes, soil aggregates, and C and N pools in an organic grain system. We compared crimson clover (Trifolium incarnatum L.) (CC), hairy vetch (Vicia villosa Roth) (HV), and a control together with disking, mowing, or a roller‐crimper for effects on hot‐water‐extractable carbohydrates, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), potentially mineralizable C and N, and aggregation (quantified by mean weight diameter [MWD]). Disking comprised flail mowing plots and then cultivating. Roller‐crimping occurred via a roller with blades. Vetch soil contained 14% higher MBC than no cover crop pretermination, possibly because of enhanced rhizodeposition. Planting CC resulted in 44% higher MBC than no cover crop a week after termination, likely due to its higher biomass C/N ratio. Disking decreased MWD relative to flail mowing in no cover crop soils at 4 wk after termination across both years at 0‐to‐5‐cm depth. In addition, MWD was lower under CC than under no cover crop for both the flail mowed and roller‐crimped treatments at 4 wk after termination across both years from 0 to 5 cm. This is possibly due to enhanced desiccation of the soil in bare plots after termination. Our results indicate that quantity and quality of biomass of different legume species, rather than termination methods, dominated effects on labile C.

Animal manures promoted soil phosphorus transformation via affecting soil microbial community in paddy soil

Animal manures are reported as good substitutes for chemical fertilizers to mobilize soil phosphorus (P). However, the mechanisms on how different types of manures regulate microbial biomass involved in P mobilization remain unclear. In this study, we conducted a two-year field experiment to investigate variations in soil microbial biomass carbon (MBC) and P (MBP) and P fractions after 30% animal manures substitution (pig manure (PM), chicken manure (CM), and dairy manure (DM)) in paddy soil. Furthermore, a 30-day incubation experiment was used to explore the mechanisms of soil P transformation induced by 100% manures addition. Two-year field experiment results showed that, compared to the chemical NPK fertilizer, 30% manure substitution didn't influence rice and wheat yields significantly but decreased soil total P loss from runoff by 3.2%. However, 30% manure substitution significantly enhanced MBC and MBP by 11.3–18.4% and 57.1–81.2%, respectively, which also promoted the transformation of moderately labile P (M-P) to labile P (L-P). Moreover, the incubation experiment also convinced that all manures caused higher MBC than chemical P fertilizer. Meanwhile, compared to the no P fertilizer, manures increased L-P and organic P by 2.7%–14.7% and 6.4%–20.0%, respectively. Redundancy analysis indicated that soil MBC/MBP ratio was the main factor to soil L-P and M-P, indicating that animal manures can improve soil microbial abundance and thus promote M-P to L-P in soil. Among three animal manures, PM could improve the mobilization potential of P mostly, due to the highest C source activity by 13C NMR analysis. Our study indicated that animal manures especially PM can be considered as a good candidate for agricultural P management in paddy soils because of their capacity to promote soil P transformation.

Intercropping of Leguminous and Non-Leguminous Desert Plant Species Does Not Facilitate Phosphorus Mineralization and Plant Nutrition.

More efficient use of soil resources, such as nitrogen (N) and phosphorus (P), can improve plant community resistance and resilience against drought in arid and semi-arid lands. Intercropping of legume and non-legumes can be an effective practice for enhancing P mineralization uptake, and plant nutrient status. However, it remains unclear how intercropping systems using desert plant species impact soil-plant P fractions and how they affect N and water uptake capacity. Alhagi sparsifolia (a legume) and Karelinia caspia (a non-legume) are dominant plant species in the Taklamakan Desert in Xinjiang Province, China. However, there is a lack of knowledge of whether these species, when intercropped, can trigger synergistic processes and mechanisms that drive more efficient use of soil resources. Thus, in a field experiment over two years, we investigated the impact of monoculture and intercropping of these plant species on soil-plant P fractions and soil-plant nutrients. Both plant species’ foliar nutrient (N, P, and K) concentrations were higher under monoculture than intercropping (except K in K. caspia). Nucleic acid P was higher in the monoculture plots of A. sparsifolia, consistent with higher soil labile P, while metabolic P was higher in monoculture K. caspia, associated with higher soil moderately labile Pi. However, both species had a higher residual P percentage in the intercropping system. Soils from monoculture and intercropped plots contained similar microbial biomass carbon (MBC), but lower microbial biomass N:microbial biomass phosphorus (MBN:MBP) ratio associated with reduced N-acetylglucosaminidase (NAG) activity in the intercropped soils. This, together with the high MBC:MBN ratio in intercropping and the lack of apparent general effects of intercropping on MBC:MBP, strongly suggest that intercropping improved microbe N- but not P-use efficiency. Interestingly, while EC and SWC were higher in the soil of the K. caspia monoculture plots, EC was significantly lower in the intercropped plots. Plants obtained better foliar nutrition and soil P mineralization in monocultures than in intercropping systems. The possible positive implications of intercropping for reducing soil salinization and improving soil water uptake and microbial N-use efficiency could have advantages in the long term and its utilization should be explored further in future studies.

Equivalent incorporation of Chinese milk vetch and rice straw enhanced nutrient mineralization and reduced greenhouse gas emissions

ABSTRACT Incorporation of crop residues into the soil provides essential nutrients and increases carbon stocks, which also increases greenhouse gas emissions from the soil. The present study was conducted to determine the effect of co-incorporation of Chinese milk vetch (CMV) and rice straw (RS) at different mixing rations on the dynamics of nutrient mineralization and the emissions of CO2 and CH4. The Fluvo-aquic paddy soil was collected and mixed with crop residues at 20 g kg−1 soil and incubated for 187 days. The CMV and RS were incorporated with the ratios of 100%:0% (M100), 75%:25% (M75S25), 50%:50% (M50S50), 25%:75% (M25S75), and 0%:100% (S100), respectively. Results showed soil total nitrogen (N) concentrations were higher with the higher proportion of CMV in the mixing residues. At 8 days of incubation (DOI), both soil available phosphorus (P) and potassium (K) concentrations were greater in treatments with the higher ratio of RS, but there were no significant differences among M75S25, M50S50, M25S75, and S100 at and after 37 DOI. The CO2 emission rate of M100 was significantly higher than that of other treatments at 8 and 12 DOI. Even though the CH4 emission rate of M50S50 was significantly higher than that of other treatments at 8 DOI, S100 resulted in the significantly higher cumulative production of CH4 after 22 DOI. Predicted from the exponential regression models, S100 had the highest CO2-C and CH4-C mineralization potentials. Additionally, the M50S50 treatment resulted in 3.7%-54.7% higher microbial biomass carbon (MBC) concentration than other treatments at the end of the incubation. In summary, the mixing ratio of 1:1 was recommended for the co-incorporation of CMV and RS by considering both the nutrients availability and the greenhouse gas emissions.

Assessing the potential of biochar aged by humic substances to enhance plant growth and soil biological activity

BackgroundSoil carbon-rich organic amendments (biochar, humic substances) may improve the quality and fertility of arable soil. Their co-application can additively enhance the beneficial effect on soil. Hypothetically, the pre-treatment of biochar, by aging via soaking in a solution of commercially available humic substances, could result in synergism, which may exceed the benefit from simple co-application of both amendments to the soil. Therefore, the aim of this study was to investigate the impact of biochar, humic substances, the combination of both, and the impact of biochar aged by humic substances solution on soil microbial activities and plant growth in a short-term pot experiment with lettuce.ResultsThe aging of biochar decreased the C:N ratio as compared to non-activated biochar. The co-application of biochar and humic substances into the soil resulted in the highest microbial biomass carbon and respiration activity. The majority of enzyme activities (β-glucosidase, arylsulfatase, N-acetyl-β-d-glucosaminidase, phosphatase) were the highest in humic substances-amended soil. The application of humic substances and biochar with humic substances seemed to stimulate microbial growth and activity followed by the competition of microflora for nutrients with plants, whereas the aged biochar behaved differently. The plants treated by aged biochar achieved the highest values of dry aboveground and root biomass of all variants. However, the assumed rapid uptake of nutrients by plants resulted in lower nutrient availability for microflora, and a decline in microbial viability.ConclusionsBased on this study, the positive effect of co-applied humic substances and biochar on soil fertility, quality, and health can be concluded. The usability of biochar aging by humic solution requires further study.Graphic abstract

Nutrient Dynamics in Sandy Soil and Leaf Lettuce Following the Application of Urea and Urea-Hydrogen Peroxide Impregnated Co-Pyrolyzed Animal Manure and Bone Meal

There is a paucity of data regarding the effect of nutrient-enriched biochar amendments on nutrient dynamics in both soil and crops. This is important because unlike pristine biochar, nutrient-enriched biochar is applied to the soil in minute quantities as large amounts may led to over application of the nutrients loaded in it. The current study examined the effects of both phosphorus- and nitrogen-enriched biochars on the dynamics of both macro and micronutrients in the sandy soil and leaf lettuce grown thereon. The phosphorus enrichment followed co-pyrolysis of animal manure (cow dung) with 25% and 50% bone meal (w/w), while the nitrogen enrichment was achieved by soaking the co-pyrolyzed biochar into urea and urea-hydrogen peroxide. The performances of the nutrient-enriched biochar were compared with the conventional amendment of urea and triple superphosphate (TSP) in the production of leaf lettuce over a period of two seasons in a pot experiment. The nutrient-enriched biochar amendments resulted into higher microbial biomass carbon and carbon to nitrogen ratios than the conventional amendment. The conventional amendment caused more phosphorus, potassium, and magnesium accumulations in the leaf lettuce than the nutrient-enriched biochar amendments. The nutrient-enriched biochar amendments led to more accumulations of nitrogen, calcium, and micronutrient elements in the leaf lettuce and availabilities of all the nutrient elements in the soil and thus, nutrient-enriched biochar acted as a reservoir that could provide nutrients to the growing lettuce beyond a single growing season.

Aboveground litter addition for five years changes the chemical composition of soil organic matter in a temperate deciduous forest

Global climate change has been found to affect plant net primary production and thereby could modify the quantity and quality of aboveground litter, which may consequently affect soil organic carbon (SOC). Whether those changes have influenced the chemical components of SOC is still unclear, especially for the soil beneath the surface soil. This study examined the changes in biopolymers (lignin, substituted fatty acids, amino sugars) in 0–10 cm and 10–20 cm soil depth in a temperate forest after five years of aboveground litter addition or removal treatments. The results showed that although SOC and soil nitrogen contents were not influenced by litter manipulation, the lignin phenols and substituted fatty acids contents in SOC of 10–20 cm soil were significantly higher in litter addition treatment compared to litter removal treatment, suggesting a selective accumulation pathway for these plant biopolymers in the 10–20 cm soil under litter manipulation. Soil amino sugar content, however, was not influenced by litter manipulation, although microbial biomass carbon (MBC) and nitrogen in 0–10 cm soil were significantly higher in litter addition plots due to the significantly higher substrate availability (dissolved organic carbon) and nutrient availability (total dissolved nitrogen) than those in the control. Although higher MBC could increase decomposition of SOC, this effect did not counterbalance the effect of higher aboveground litter input in litter addition plots, but rather changed the composition of SOC toward compounds of a purportedly more stable composition. The effects of aboveground litter removal were not entirely in contrast to the effects of aboveground litter addition on SOC, hinting that belowground inputs could sustain the storage of SOC for at least five years under aboveground litter removal treatment. The changes in the chemical composition of SOC under litter manipulation for five years suggested the potential changes in SOC stability and pool size in the future, especially in the 10–20 cm soil, to which more attention should be paid in future litter manipulation studies.

Effects of biochar and TUAT-1 bio-inoculant on grain yield and nitrogen efficiency of forage rice ‘Monster rice 1’ under different N application modes

ABSTRACT The application of bio-inoculant and biochar can be an effective strategy for stimulating crop growth, while improving soil fertility in an environmentally friendly manner. A greenhouse experiment was conducted to study the effects of biochar and TUAT-1 bio-inoculant under two N fertilization modes (basal and split) on the yield of forage rice and nutrient distribution in the soil rhizosphere. Positive effects of the biochar and bio-inoculant, either alone or in combination, on growth, photosynthesis rate, and yield components were depended on the mode of N application. There was no change in either microbial biomass carbon (MBC) or microbial biomass nitrogen (MBN) with the treatments of biochar and bio-inoculant with split N fertilization, whereas both these treatments, either alone or in combination, resulted in higher MBC and MBN with basal N fertilization. The NO3 −–N concentration of surface floodwater under biochar treatment was significantly reduced immediately after soil N fertilization, whereas biochar addition did not reduce the NH4 +–N concentration of surface floodwater at each of our monitoring points. The findings indicate that biochar and the mode of N fertilization have the potential to improve forage rice productivity and soil nutrient availability, while minimizing the potential of nitrate (NO3 −–N) leaching.

Effects of different tillage and fertilization management practices on soil organic carbon and aggregates under the rice–wheat rotation system

Studying the impact of tillage and fertilization on soil organic carbon (SOC) content and aggregate is essential to define better strategies for improving soil structure and SOC sequestration. A field experiment was conducted for 9 years to investigate effects of different tillage and fertilization management practices on SOC and its active fractions [labile organic carbon (LOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC)] within the bulk soil and in soil aggregates under rice (Oryza sativa L.)–wheat (Triticum aestivum L.)-based cropping systems. Five treatments were included: conventional tillage with no fertilizer (CT), conventional tillage with chemical fertilizer (CTFR), reduced tillage with chemical fertilizer (RTFR), conventional tillage with organic manure (CTOM), and reduced tillage with organic manure (RTOM). The results showed that the organic manured plots (CTOM and RTOM) significantly increased the concentrations of SOC and active carbon fractions (LOC, DOC and MBC) within the bulk soil and soil macroaggregates, and increased the mass proportion of macroaggregates (>250 μm) compared with chemical fertilizer treatments (CTFR and RTFR) or CT. The highest SOC concentration and macroaggregates (>250 μm) were observed in CTOM. The increased SOC, especially active carbon fractions, was mainly concentrated in soil macroaggregates (>250 μm). Soil aggregates were dominated by macroaggregates (>250 μm), which had higher MBC and lower PAOC (the percentage of slow plus passive carbon fractions) after 9 years of RTOM treatment than after CT or CRFR treatment. The results indicated that RTOM played a positive role in promoting the formation of the soil macroaggregate structure. By studying the responses of SOC and water-stable aggregate contents to different tillage and fertilization managements, the continual application of organic manure may be feasible and the periodic organic manure addition may be combined with reduced tillage practice to produce an integrated soil management strategy for the paddy–upland rotation region in Middle China.

Characteristics of Paddy Soil Organic Carbon Mineralization and Influencing Factors Under Different Water Conditions and Microbial Biomass Levels

Paddy soil often undergoes frequent dry-wet alternation. The change in water status not only affects the physical and chemical properties of the soil, but also changes the structure and diversity of the soil microbial communities, which in turn determines the rate of soil organic carbon mineralization. However, the effects of different water conditions and soil microbial biomass levels on the process of soil organic carbon mineralization and its mechanisms are still unclear. Therefore, this study took typical subtropical paddy soil as the research object, applied a laboratory incubation experiment with two water treatments of dry-wet and continuous flooding, and reduced the soil microbial biomass through chloroform fumigation, thereby obtaining high and low soil microbial biomass carbon contents, to elucidate the influencing mechanisms of microbial biomass and water conditions on organic carbon mineralization in paddy soil. The results showed that during the first 30 d of incubation, the dry-wet treatment was in a non-flooded stage and its cumulative CO2 emissions were significantly lower than those of the continuous flooded treatment. After 30 d, the dry-wet treatment entered the flooded stage. The difference in the cumulative CO2 emissions of the soils with a high microbial biomass carbon content between the dry-wet and continuous flooding treatments gradually decreased, and there was no significant difference on day 78. In the soil with a low microbial biomass carbon content, the cumulative CO2 emissions of the dry-wet treatment on day 78 was still significantly lower than that of the continuous flooded treatment. The soils with a low microbial biomass carbon content showed a faster CO2 emission rate at the beginning of the incubation period (first 20 d), which was 1.1-6.1 times greater than that of the high microbial biomass carbon soils owing to their high soil dissolved organic carbon (DOC) content, and the CO2 emission rate then gradually decreased until it was below that of the soil with a high microbial biomass carbon content. The soil organic carbon mineralization rate became stable later in the incubation period (days 45-78). The stable mineralization rate of the high microbial biomass carbon soil was 20%-30% higher than that of the low microbial biomass carbon soil. The multiple regression analysis results showed that the decrease in the soil DOC content (ΔDOC) and the increase in the Fe2+ content (ΔFe2+) significantly affected the change in cumulative CO2 emissions (ΔCO2) under continuous flooding conditions, but had no effect on ΔCO2 during the flooding stage of the dry-wet treatment. The correlation analysis showed that the daily CO2 emission rate of soils with high microbial biomass carbon was significantly positively correlated with glucosidase activity under dry-wet treatment and significantly negatively correlated with acetylglucosaminidase (NAG) and peroxidase activities under continuous flooding treatment. In the low microbial biomass carbon soils, the daily CO2 emission rate of the continuous flooding treatment was negatively correlated with the NAG activity, but showed no correlation with enzyme activities under dry-wet management. In summary, the cumulative CO2 emissions of dry-wet treatment were lower than those of continuous flooding treatment, and the difference was significant in soils with low microbial biomass carbon. The size of the soil microbial biomass determined the level of the stable soil organic carbon mineralization rate. The amount of soluble organic carbon and iron reduction affected the soil CO2 emissions under continuous flooding conditions, and the soil water conditions affected the daily CO2 emission rate and its key influencing enzymes. This study provides data and theoretical support for the carbon cycle and carbon sequestration potential in paddy soil.