Soil Carbon Content Research Articles

Plant Growth and Soil Water Content Changes under Different Inter-Row Soil Management Methods in a Sloping Vineyard.

The main objective of this study was to investigate soil-plant-water interactions based on field measurements of plant reflectance and soil water content (SWC) in different inter-row managed sloping vineyards. The following three different soil management applications were studied: tilled (T), cover crops (CC), and permanent grass (NT) inter-rows. We measured SWCs within the row and between rows of vines. Each investigated row utilized 7 to 10 measurement points along the slope. Topsoil SWC and temperature, leaf NDVI and chlorophyll concentrations and leaf area index (LAI) were measured every two weeks over the vegetation period (May to November) using handheld instruments. We found that management method and slope position can significantly affect the soil's physical and chemical properties, such as clay or soil organic carbon contents. Cover crops in the inter-row significantly reduced average SWC. The in-row average topsoil SWCs and temperatures were lower in all study sites compared to the values measured in between rows. Significantly higher SWCs were observed for the upper points compared to the lower ones for CC and T treatments (58.0 and 60.9%, respectively), while the opposite was noted for NT. Grassed inter-row grapevines had significantly lower leaf chlorophyll content than the other inter-row managed sites (p < 0.001). The highest average leaf chlorophyll contents were observed in the T vineyard (16.89 CCI). Based on slope positions, the most distinguishable difference was observed for the CC: 27.7% higher chlorophyll values were observed at the top of the slope compared to the grapevine leaves at the bottom of the slope (p < 0.01). The leaf NDVI values were not as profoundly influenced by slope position in the vineyard as the chlorophyll values were. For overall LAI values, the T treatment had significantly lower values compared to NT and CC (p < 0.001). Moderate correlations were observed between NDVI and LAI and soil nitrogen and carbon content. In general, we found that both inter-row management and slope position can significantly influence soil parameters and affect plant growth, and consequently can accelerate plant stress under sub-optimal environmental conditions such as prolonged drought.

Wild boar (Sus scrofa) has minor effects on soil nutrient and carbon dynamics

ABSTRACT Wild boar populations have increased worldwide, but the consequences of their disturbances on boreal forest ecosystems are largely unknown. We investigated how wild boars affect soil processes in a Swedish boreal forest. We estimated effects on ecosystem functioning using phospholipid fatty acid analyses (PLFA) to characterise microbial groups, and by measuring soil respiration, soil carbon (C), nitrogen (N) and phosphorus (P) concentrations, as well as the availability of NO3 − and NH4 +. We compared samples collected inside wild boar enclosures with adjacent reference areas without wild boar disturbance. We found no difference in soil microbial composition, except for a consistently higher fungi:bacteria ratio in the enclosures. These results are contrary to our hypothesis that rooting raises nitrogen levels, which in turn result in more bacteria. Soil nutrient levels showed inconsistent patterns, suggesting that substrate changes – as opposed to nutrient changes – stimulated fungal growth. Soil respiration was lower in the enclosures, contradicting earlier findings suggesting increased soil CO2 emissions from wild boar rooting. Overall, our study suggests that increased wild boar abundance has a minor impact on soil processes in boreal forests. Future studies should determine if the modest impacts remain across time and boreal forests.

Variations in the soil micro-food web structure and its relationship with soil C and N mineralization during secondary succession of subalpine forests

The soil micro-food web is an important network of belowground trophic relationships and it participates directly and indirectly in soil ecological processes. In recent decades, the roles of the soil micro-food web in regulating ecosystem functions in grasslands and agroecosystems have received much attention. However, the variations in the soil micro-food web structure and its relationship with ecosystem functions during forest secondary succession remain unclear. In this study, we investigated how forest secondary succession affected the soil micro-food web (including soil microbes and nematodes) and soil carbon and nitrogen mineralization across a successional sequence of “grasslands – shrublands – broadleaf forests – coniferous forests” in a subalpine region of southwestern China. With forest successional development, the total soil microbial biomass and the biomass of each microbial group generally increased. The significant influences of forest succession on soil nematodes were mainly reflected in several trophic groups with high colonizer-persister values (particularly bacterivore3, herbivore5 and omnivore-predator5) that are sensitive to environmental disturbance. The increases in the connectance and nematode genus richness, diversity, and maturity index indicated an increasingly stable and complex soil micro-food web with forest succession, which was closely related to soil nutrients, particularly the soil carbon contents. Additionally, we found that the soil carbon and nitrogen mineralization rates also exhibited generally increasing trends during forest succession, which had significant positive correlations with the soil micro-food web composition and structure. The path analysis results indicated that the variances in ecosystem functions induced by forest succession were significantly determined by soil nutrients and soil microbial and nematode communities. Overall, these results suggested that forest succession enriched and stabilized the soil micro-food web and promoted ecosystem functions via the increase in soil nutrients, and the soil micro-food web played an important role in regulating ecosystem functions during forest succession.

Effects of the construction of fertile and cultivated soil layer on soil fertility and maize yield in Albic soil.

We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm-2·a-1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

Micromorphological soil assessment in abandoned quarry dumps of the Central Caucasus, Russia

This study compared the micromorphological and agrochemical metrics in soils from the quarry dumps and zonal soils, the Central Caucasus. Soil micromorphological investigations are important tool for evaluation of soil dynamics after anthropogenic impacts on terrestrial ecosystems. The results showed that the carbon content in the primary soil of the sand and gravel quarries was lower than that in the reference soil. The differences detected were statistically significant for both the Urvan plot soils (t = 11.95; p = 0.000) and the Progress plot soils (t = 18.73; p = 0.000). In contrast, in the quarry with clay bottom substrate (Gerpegezh), no significant difference was found between the reference and postmine soils. The reference soil around the sand and gravel quarries was slightly more acidic than the primary soil. In the clay quarry, the primary soil was more acidic with a strong acidic value, while the reference soil was neutral. The difference of nutrients (P, K, NH4+, NO3-) between the primary and reference soils were negligible. The only exception was the NO3- content in the reference soil of Progress settlement, where it was significantly higher (t = 4.19; p = 0.002) than in the original soil of the site. No difference was observed for the mineral component of the primary soil. Investigation of key zonal soils of the region. Zonal Caucasus soils: Phaeozem Gleiyc, Phaeozem and Umbric Retisol are different in terms of micro texture. Thus, Phaeozem Gleiyc characterizes by microstructure composed by primary angular mineral forms. Phaeozem and Retisol demonstrated formation of biogenic structure with alteration of mineral particles. Data obtained show that rapid self revegetation of the quarries results in initialization of primary soil formation and transformation of the soil microstructure and organization on the micro level.

Effect of Different Soil Organic Carbon Content in Different Soils on Water Holding Capacity and Soil Health

An experiment was carried out to study the effect of soil organic carbon (SOC) and soil texture on the distance of the wetting front, cumulative water infiltration (I), infiltration rate (IR), saturated water conductivity (Ks), and water holding capacity (WHC). Three levels ( 0, 10, 20, and 30 g OC kg-1 ) from organic carbon (OC) were mixed with different soil materials sandy, loam, and clay texture soils. Field capacity (FC) and permanent wilting point (PWP) were estimated. Soil materials were placed in transparent plastic columns(12 cm soil column ), and water infiltration(I) was measured as a function of time, the distance of the wetting front and Ks. Results showed that advance wetting front as a function of time for soil column was 6 minutes and with no differences between OC levels for sandy soils, while it ranged between 90 minutes (0% OC) - 130 minutes (3% OC) for loam soils, and between 470 minutes (0 %OC) and 590 minutes (1%OC) for clay soils, at the same time cumulative water infiltration(I) increases at the beginning of infiltration and decreases with time and levels of OC. The highest infiltration values were in sandy soils, giving data of 0.05 and 0.12 cm min-1, with no significant differences with OC rates. IR values decreased when OC increased in loam soils, and IR increased exponentially in clay soils with increasing OC levels. The values of Ks decrease with increasing OC for sandy and loam soils, and increase when OC increases above 3% for clay soils. FC and WP values were increased for sandy, loam and clay soils when OC was increased. The AW values decreased for both sandy and clay soils compared to loam soils. It can be concluded that AW can be estimated from FC values regardless of texture and OC by the linear function: AW=0.51(FC)+0.005.

Baseline high-resolution maps of organic carbon content in Australian soils

We introduce a new dataset of high-resolution gridded total soil organic carbon content data produced at 30 m × 30 m and 90 m × 90 m resolutions across Australia. For each product resolution, the dataset consists of six maps of soil organic carbon content along with an estimate of the uncertainty represented by the 90% prediction interval. Soil organic carbon maps were produced up to a depth of 200 cm, for six intervals: 0–5 cm, 5–15 cm, 15–30 cm, 30–60 cm, 60–100 cm and 100–200 cm. The maps were obtained through interpolation of 90,025 depth-harmonized organic carbon measurements using quantile regression forest and a large set of environmental covariates. Validation with 10-fold cross-validation showed that all six maps had relatively small errors and that prediction uncertainty was adequately estimated. The soil carbon maps provide a new baseline from which change in future carbon stocks can be monitored and the influence of climate change, land management, and greenhouse gas offset can be assessed.

Changes in soil carbon, nitrogen, and phosphorus in Pinus massoniana forest along altitudinal gradients of subtropical karst mountains.

Changes in altitude have a long-term and profound impact on mountain forest ecosystems. However, there have been few reports on changes in soil carbon, nitrogen, and phosphorus contents (SCNPC) along altitudinal gradients in subtropical karst mountain forests, as well as on the factors influencing such changes. We selected five Pinus massoniana forests with an altitudinal gradient in the karst mountain area of Southwest China as research objects and analyzed the changes in SCNPC along the altitudinal gradient, as well as the influencing factors behind these changes. Soil organic carbon, total nitrogen, and available nitrogen contents first increased and then decreased with increasing altitude, whereas the contents of total phosphorus and available phosphorus showed no obvious trend. In the karst mountain P. massoniana forest, SCNPC in the topsoil is most significantly affected by total glomalin-related soil protein (TG) and soil moisture content (SMC) (cumulative explanatory rate was 45.28-77.33%), indicating that TG and SMC are important factors that affect SCNPC in the karst mountain P. massoniana forest. In addition, the main environmental factors that affect SCNPC in the subsoil showed significant differences. These results may provide a better scientific reference for the sustainable management of the subtropical mountain P. massoniana forest.

Methods for determining the organic carbon content in soils (critical review)

The paper presents theoretical basis of the methods for determining the content of soil organic carbon (SOC) both by direct dry combustion using automated analyzers and indirectly – by I.V. Tyurin and Walkley–Black oxidation. Author's and literature experimental data of SOC analyses in various soils by these methods are presented. Comparative analysis of the above data showed that in some cases the content of SOC determined by oxidability is lower than the one obtained by dry combustion (in most cases), while in others, on the contrary, the content of SOC is higher. This conclusion fully complies with the theoretical views of I.V. Tyurin on the chemical nature of soil organic matter (SOM). A schematic description of determining the content of total (organic) carbon in non-carbonate soils by dry combustion method using automated analyzers Leco (USA) and AH-7529 (Gomel, Belarus) is given. It was pointed out that it is difficult to determine SOC content by dry combustion method with automated analyzers in carbonate soils. For these soils it is recommended to determine the content of inorganic carbon by decomposition of carbonates with HClO4 solution using express analyzer AN-7529. The direct method of determining the content of SOC has the best metrological characteristics compared to ones of the indirect method, which convincingly confirms the authoritative opinions of Schollenberg and Tyurin about the inaccuracy of the latter. It is concluded that the indicators determined by the methods of Tyurin and Walkley–Black and dry combustion are chemically independent, characterizing, respectively, the oxidability and organic carbon content of SOM. It is recommended to use dry combustion method with automated analyzers when monitoring the content and stocks of organic carbon in soils.

Vegetation restoration effects on soil carbon and nutrient concentrations and enzymatic activities in post-mining lands are mediated by mine type, climate, and former soil properties

Vegetation restoration is a widely used, effective, and sustainable method to improve soil quality in post-mining lands. Here we aimed to assess global patterns and driving factors of potential vegetation restoration effects on soil carbon, nutrients, and enzymatic activities. We synthesized 4838 paired observations extracted from 175 publications to evaluate the effects that vegetation restoration might have on the concentrations of soil carbon, nitrogen, and phosphorus, as well as enzymatic activities. We found that (1) vegetation restoration had consistent positive effects on the concentrations of soil organic carbon, total nitrogen, available nitrogen, ammonia, nitrate, total phosphorus, and available phosphorus on average by 85.4, 70.3, 75.7, 54.6, 58.6, 34.7, and 60.4 %, respectively. Restoration also increased the activities of catalase, alkaline phosphatase, sucrase, and urease by 63.3, 104.8, 125.5, and 124.6 %, respectively; (2) restoration effects did not vary among different vegetation types (i.e., grass, tree, shrub and their combinations) or leaf type (broadleaved, coniferous, and mixed), but were affected by mine type; and (3) latitude, climate, vegetation species richness, restoration year, and initial soil properties are important moderator variables, but their effects varied among different soil variables. Our global scale study shows how vegetation restoration can improve soil quality in post-mining lands by increasing soil carbon, nutrients, and enzymatic activities. This information is crucial to better understand the role of vegetation cover in promoting the ecological restoration of degraded mining lands.

Littoral enchytraeids and Eisenia fetida earthworms facilitate utilization of marine macroalgae as biofertilizers

Marine macroalgae are often used as biofertilizers in the coastal regions across the world. However, the effects of soil fauna in macroalgae decomposition are not fully understood. We conducted a microcosm experiment to assess the possibility of using a mixture of native Enchytraeidae and the model earthworm species Eisenia fetida to accelerate decomposition of dominant algae taxa from White Sea (Fucus spp.) and Black Sea (Cystoseira spp.) after their amendment to soil with simultaneous mitigation of the associated carbon dioxide (CO2) emissions. During 45 days of the microcosm experiment, we measured CO2 emission from the soil and evaluated changes in macroalgal biomass, δ13C and δ15N isotopic signatures of soil, macroalgae, earthworm faeces and enchytraeid tissues as well as bulk carbon and nitrogen content in soil. The mass of Cystoseira spp. residues, unlike that of Fucus spp., significantly decreased during the experiment (by approximately 73 % of the initial level). This effect was amplified by the co-action of E. fetida and Enchytraeidae (by 65 % of the initial). The addition of Enchytraeidae into microcosms led to the more than two-fold reduction of CO2 emission in all treatments. Differential enrichment of soil and earthworm casts with macroalgae-derived carbon and nitrogen, as suggested by stable isotope analysis, indicated that macroalgae-originating carbon pathway is rather driven by a synergistic activity of enchytraeids and earthworms (δ13C enrichment up to 4.8 ‰). Nitrogen transfer was dependent on the microbial activity and could be modulated and channelized by enchytraeids, whose δ15N values strictly corresponded to algal taxa. This highlights the importance of annelids in increasing the value of macroalgae as biofertilizers.

Patterns of Needle Nutrient Resorption and Ecological Stoichiometry Homeostasis along a Chronosequence of Pinus massoniana Plantations

Nutrient resorption and stoichiometry ratios are vital indicators to explore nutrient transfer and use efficiency for plants, particularly under the condition of nutrient limitation. However, the changing rules about nutrient resorption and ecological stoichiometry homeostasis are still unclear with the development of plantations. We determined carbon (C), nitrogen (N), and phosphorus (P) concentrations in soil and in fresh and senesced needles along a chronosequence of Pinus massoniana plantations (10, 20, 30, and 36 years old) in Guizhou Province, China. We also calculated the N and P resorption efficiency (NRE and PRE, respectively) and the homeostasis coefficient. The results showed that fresh and senesced needles’ C and N concentrations maintained an increasing trend, whereas their P concentrations decreased initially and subsequently increased as the plantations’ ages increased. Fresh needles’ N:P ratios indicated that N limitation existed before 20 years old, while P limitation appeared in the 30-year-old plantations. The NRE and PRE showed patterns of increasing initially and decreasing subsequently along the chronosequence of P. massoniana plantations, which was coupled with weak stoichiometric homeostasis to reduce nutrient deficiency. Therefore, the appropriate nutrient management measurements should be induced to promote tree growth and the sustainable development of P. massoniana plantations.

Optimizing Sampling Strategies for Near-Surface Soil Carbon Inventory: One Size Doesn’t Fit All

Soils comprise the largest pool of terrestrial carbon yet have lost significant stocks due to human activity. Changes to land management in cropland and grazing systems present opportunities to sequester carbon in soils at large scales. Uncertainty in the magnitude of this potential impact is largely driven by the difficulties and costs associated with measuring near-surface (0–30 cm) soil carbon concentrations; a key component of soil carbon stock assessments. Many techniques exist to optimize sampling, yet few studies have compared these techniques at varying sample intensities. In this study, we performed ex-ante, high-intensity sampling for soil carbon concentrations at four farms in the eastern United States. We used post hoc Monte-Carlo bootstrapping to investigate the most efficient sampling approaches for soil carbon inventory: K-means stratification, Conditioned Latin Hypercube Sampling (cLHS), simple random, and regular grid. No two study sites displayed similar patterns across all sampling techniques, although cLHS and grid emerged as the most efficient sampling schemes across all sites and strata sizes. The number of strata chosen when using K-means stratification can have a significant impact on sample efficiency, and we caution future inventories from using small strata n, while avoiding even allocation of sample between strata. Our findings reinforce the need for adaptive sampling methodologies where initial site inventory can inform primary, robust inventory with site-specific sampling techniques.

How do land use and land cover changes after farmland abandonment affect soil properties and soil nutrients in Mediterranean mountain agroecosystems?

Mediterranean mountains are sensitive agroecosystems that have suffered intense land use and land cover changes (LULCC) during the last century. From the middle of the twentieth century, most of the cultivated lands in Mediterranean mountains were abandoned, allowing the recovery of vegetation (through natural revegetation and afforestation programmes). To examine the effects of farmland abandonment, secondary succession (natural revegetation) and afforestation, an intensive soil sampling was carried out in the Araguás catchment (Central Spanish Pyrenees) including sparsely vegetated areas (badlands), grasslands, shrublands and afforested sites. LULCC were mapped, and soil physico-chemical properties were analysed in reference sites (unaltered areas during the last centuries) and in the different land uses. Likewise, the soil organic carbon (SOC) content in the bulk soils and in the fractions separated by density fractionation have been studied. This study evidenced that farmland abandonment led to a mosaic landscape with different land use and land covers. Results show that LULCC significantly affect soil physico-chemical properties (soil texture, stoniness, pH, SOC, total carbon, CorgN ratio, bulk density and field capacity). Significant differences were observed between secondary and afforested sites following farmland abandonment. Afforestation triggered higher SOC than shrubland sites (natural revegetation) (1.4 and 1.1% respectively), suggesting a slower process of organic matter accumulation after farmland abandonment in the natural revegetation compared to afforestation. The significant role of grassland sites for enhancing the accumulation of SOC has been also confirmed. The results showed also significant differences in the relative contribution of each organic fraction to the bulk SOC: the amount of labile fraction (free and occluded labile fractions) is significantly higher in afforested and shrubland sites (58.1 and 51.2% respectively) than in grassland sites (36.8%). Understanding the effects of LULCC on soil properties and SOC dynamics is essential when planning post-land management practices after farmland abandonment.

Rainfall partitioning and its influence on dissolved carbon and nitrogen fluxes through plant-soil system of a xerophytic shrub in northern China

Dissolved carbon (DC) and dissolved nitrogen (DN) driven by rainfall partitioning are critical components of carbon and nitrogen cycles in terrestrial ecosystems, especially in vegetation restoration areas. However, the variations of DC and DN fluxes in the input (throughfall and stemflow) and output (infiltration and surface runoff) water pathways of shrub ecosystem in drylands were poorly understood. In this study, the rainfall partitioning, dissolved organic and inorganic carbon (DOC and DIC) and DN fluxes in 52 rainfall events affecting a xerophytic shrub ecosystem on the heavily eroded Chinese Loess Plateau were measured over the 2019–2021 rainy seasons. The contributions of plants and topsoil (0–5 cm) to the variations in DC and DN fluxes along water pathways were quantified. We found that the DC and DN fluxes in throughfall accounted for more than 80% of net input flux, and the topsoil infiltration of DC and DN fluxes into soil layer below 5 cm depth were the most important output flux (contribution more than 98%). The mean event plant-derived DC and DN fluxes were 52.2 and 5.3 mg m−2, respectively, accounting for 45.4% and 12.2% of net DC and DN input fluxes (115.2 and 43 mg m−2). The soil-buffered DC and DN fluxes (455.6 and 29.5 mg m−2) were 3.95 and 0.69 times greater than the net input fluxes, respectively. The DC and DN fluxes in infiltration had the best correlation and increased most quickly with rainfall depth in the four different water pathways. Furthermore, the soil carbon content in 0–50 cm depth and soil nitrogen content in 0–10 cm depth in shrub-covered land was significantly higher than those in bare land (p < 0.05). This study highlights the important roles of rainfall partitioning in plant-sourced and soil-buffered DC and DN fluxes, which should be considered in soil carbon and nitrogen accumulation in drylands.

Annual burying of straw after pelletizing: A novel and feasible way to improve soil fertility and productivity in Northeast China

Increasing the amount of straw returning has the potential to improve soil fertility, but is not widely accepted due to yield reductions in regions with low temperatures and precipitation. Thus, annual straw burying with large amounts after pelletizing was established considering soil fertility, crop yield and economic income. A three-year field trial with a large amount (75 Mg ha−1 year−1) of pelletized straw (PS75) and chopped straw (CS75), normal amount (15 Mg ha−1 year−1) of chopped straw (CS15), and no straw returning (CK) was conducted for spring maize. PS75 increased the soil total carbon content by 8–17 % and 29–51 % as compared to the other treatments between 0–20 and 20–40 cm respectively. PS75 also had a higher total nitrogen content, moderate soil C/N ratio, lower bulk density, and comparable soil pH in the third year. Specifically, PS75 increased grain yield by 5–7 % relative to CK, and 6–21 % relative to CS15 in the second and third years. PS75 also increased grain yield by 5–28 % than CS75 in the three years with higher kernel number and 100-kernel weight. This was partly attributed to a longer grain filling period due to higher soil carbon and nitrogen contents for PS75 than others. Notably, PS75 exhibited increased trends in grain yield and economic income with experimental year compared to CK. Overall, annual pelletized straw burying with a large amount is a feasible pathway for improving the soil fertility and crop yield in Northeast China.

Biochar Blended with Nitrogen Fertilizer Promotes Maize Yield by Altering Soil Enzyme Activities and Organic Carbon Content in Black Soil

Biochar and nitrogen fertilizers are known to increase soil carbon storage and reduce soil nitrogen loss as amendments, suggesting a promising strategy for highly effectively increasing soil productivity. However, few studies have explored the mechanisms of their effects on crop yield in terms of active carbon fraction and enzyme activity, which ultimately limits the potential for the application of biochar in combination with nitrogen fertilizers. To evaluate the effect of biochar and nitrogen fertilizer on the improvement of black soils in northeast China, a field experiment was conducted in the black soil to compare and analyze the application methods on total organic carbon (TOC), total nitrogen (TN), enzyme activities, and maize yields. Biochar rates: CK, C1, C2, and C3 (0, 9.8, 19.6, and 29.4 Mg·ha-1); N fertilizer rates: N1/2 and N (30 and 60 kg·ha-1). Results indicated that biochar and N fertilizer amendments significantly ameliorated soil fertility, such as TOC and TN, compared to the unamended soil. The TOC levels in the C3 treatment increased by 35.18% and the TN levels by 23.95%. The improvement in TN is more significant when biochar is blended with N fertilizer. Biochar blended with N fertilizer increased maize cellulase, urease, and invertase activities by an average of 53.12%, 58.13%, and 16.54%, respectively. Redundancy analysis showed that TOC, TN, and MBN contributed 42%, 16.2%, and 22.2%, respectively, to the maize yield indicator. Principal component analysis showed that reduced N fertilizer was more effective in improving yields, with a maximum yield increase of 50.74%. Biochar blended with N fertilizer is an effective strategy to improve the fertility and productivity of black soils in northeast China, while nitrogen fertilizer reduction is feasible and necessary for maintaining grain yield.

Elevated methylmercury production in mercury-contaminated paddy soil resulted from the favorable dissolved organic matter variation created by algal decomposition

Algae-derived organic matter (AOM) may considerably regulate methylmercury (MeHg) production and accumulation in the paddy fields by changing the soil-dissolved OM (SDOM) properties. In this study, a 25-day microcosm experiment was performed to compare the responding mechanisms of MeHg production in the Hg-contaminated paddy soil-water system to the input of algae-, rice-, and rape-derived OMs. Results showed that algal decomposition could release much more cysteine and sulfate than crop straws. Compared with crop straw-derived OMs, AOM input greatly increased the dissolved organic carbon concentrations in soil but resulted in a greater decrease in tryptophan-like fractions while accelerated the formation of high-molecular-weight fractions in soil DOM. Moreover, AOM input significantly increased MeHg concentrations in the pore water by 19.43%–3427.66% and 52.81%–5846.57% compared to rape- and rice-derived OMs, respectively (P < 0.05). And, a similar MeHg changing pattern was also observed in the overlying water (10–25 d) and the soil solid-phase particles (15–25 d) (P < 0.05). Correlation analysis revealed that MeHg concentrations in the AOM-added soil-water system had significantly negative and positive relationships with the tryptophan-like C4 fraction and molecular weight (E2/E3 ratio) of soil DOM, respectively (P < 0.01). These findings suggest that AOM has a higher capacity than crop straw-derived OMs to promote MeHg production and accumulation in the Hg-contaminated paddy soils by creating a favorable soil DOM variation and providing more microbial electron donors and receptors.

COMPARATIVE EFFECT OF INTEGRATED FERTILIZATION APPROACHES ON SOIL HEALTH AND CROP PRODUCTIVITY OF WHEAT (TRITICUM AESTIVUM L.) UNDER DIFFERENT TILLAGE SYSTEMS

The study was conducted at Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan to monitor the impact assessment of tillage systems on soil health indicators by integrating organic and inorganic resources to sustain wheat production in arid and semi-arid conditions i.e. high temperature and low rainfall. The field experiment was conducted in 2019-20 and carried out in alkaline soil (pH 8.2) with low organic matter (0.45%) to grow wheat after rice and treatments were arranged in randomized complete block design. Farmyard manure (FYM 20.5 Mg/ha), rice crop residues application (CRA 100%) and chemical fertilizers (CF) N-P-K 100-80-60 kg/ha, respectively were used under conventional and conservation tillage systems. During this research different growth and yield parameters were noted and evaluated the level of N, P, K and organic matter contents from soil and plant at the harvest. The results indicated that the combined application of FYM and CRA with CF improved the chlorophyll contents (20% in conventional tillage and 39% in conservation tillage) which helped in nutrient translocation (N, P, K) and increased growth, biological and grain yield by improving soil organic carbon (SOC) and organic matter contents in soil. Growth parameter i.e. germination percentage upto 64%, plant height 27% and spike length upto 35% were increased by T7 . The conservation tillage method was the best where we used T7 i.e. CF + 25% FYM + 50% CRA, and CF + 50% FYM + 25% CRA by conserving moisture and built OM (0.90%), soil organic carbon (0.49%) and mineral nutrition in soil as well as in wheat leaves. It is concluded that the integrated use of organic and inorganic resources are helpful for sustainable wheat production by enhancing fertilizer use efficiency (FUE) to improve soil health especially in arid to semi-arid climate conditions in alkaline soil.

Potential methane production in oligohaline wetlands undergoing erosion and accretion in the Mississippi River Delta Plain, Louisiana, USA

Methane (CH4) is steadily increasing in the atmosphere from different sources including wetlands. However, there is limited landscape level CH4 flux data in deltaic coastal systems where the availability of freshwater is impacted by the combined effect of climate change and anthropogenic impacts. Here we determine potential CH4 fluxes in oligohaline wetlands and benthic sediments in the Mississippi River Delta Plain (MRDP), which is undergoing the highest rate of wetland loss and most extensive hydrological wetland restoration in North America. We evaluate potential CH4 fluxes in two contrasting deltaic systems, one undergoing sediment accretion as result of a freshwater and sediment diversions (Wax Lake Delta, WLD), and one experiencing net land loss (Barataria-Lake Cataouatche, BLC). Short- (<4 days) and long-term (36 days) incubations using soil and sediment intact cores and slurries were performed at different temperatures representing seasonal differences (10, 20, 30 °C). Our study revealed that all habitats were net sources of atmospheric CH4 in all seasons, and CH4 fluxes were generally the highest for the 20 °C incubation. The CH4 flux was higher in the marsh habitat of the recently formed delta system (WLD) with total carbon content of 5–24 mg C cm−3 compared to the marsh habitat in BLC, which had high soil carbon content of 67–213 mg C cm−3. This suggests that the quantity of soil organic matter might not be a determining factor in CH4 flux. Overall, benthic habitats were found to have the lowest CH4 fluxes indicating that projected future conversions of marshes to open water in this region will impact the total wetland CH4 emission, although the overall contribution of such conversions to the regional and global carbon budgets is still unknown. Further research is needed to expand the CH4 flux studies by simultaneously using several methods across different wetland habitats.