Increased Soil Organic Carbon Research Articles

Multilevel driving mechanism of ecosystem multidimensional stability in the Yangtze River Economic Belt: A hierarchical linear model approach

Ecosystem stability is a multifaceted and complex concept. Understanding the distribution pattern of multidimensional ecosystem stability and its drivers is essential for sustainability. However, the understanding of both the scale dependence and the interaction among different levels of drivers is limited. In this study, the evaluation framework for the multidimensional stability of ecosystems in the Yangtze River Economic Belt (YREB) was constructed by fitting Normalized Difference Vegetation Index (NDVI) to temperature, precipitation, and other meteorological factors from the background characteristics and dynamic change process of ecosystems, and utilizing Auto-Regression (ARx) as well as correlation analysis. Consequently, a hierarchical linear model (HLM) was utilized to assess the impact of natural elements at the basin level and socioeconomic elements at the prefecture level on stability under scale effects and interactions. The results showed that the spatial stability of YREB was higher in the southeast and exhibited a discontinuous distribution in the southwest. The ecosystem multidimensional stability score was the first in the Qiantang River Basin (SI = 0.2586), and the lowest score was in the Taihu Lake Basin (SI = 0.14). In addition, natural and socio-economic factors promoted ecosystem stability to different degrees and along different directions, and the scale dependence of drivers at different levels must be considered. At the basin level, increased soil organic carbon content led to increased stability, while the expansion of farmland and built-up land led to a decrease in stability. At the prefecture level, the population dominated the decrease in stability. Nesting the two scales, demographic and economic factors mainly control stability through their influence on land use, particularly farmland and forestland. Overall, understanding multi-level, multi-scale, and multi-indicator drivers is crucial for strengthening ecological protection in the YREB and controlling the farmland expansion and the urbanization rate growth to maintain the ecosystem stability.

Response of maize yield to changes in soil organic matter in a Swedish long‐term experiment

AbstractAgricultural practices that lead to soil carbon sequestration may be a win–win strategy for mitigating global warming and improving soil fertility and resource use efficiency. The mechanisms through which soil organic carbon (SOC) concentration affects crop yields are numerous but difficult to separate. The objective of this study was to disentangle these processes and estimate to what extent the yield response to SOC is mainly driven by changes in physical or biochemical properties and processes. This was achieved by analysing the response of yields in continuous maize to SOC concentrations during 20 years (2000–2019), which had evolved in 14 experimental treatments in a Swedish long‐term field experiment at Ultuna since 1956, ranging from 0.94% to 3.65% in the topsoil (0–20 cm). Average maize yields during this period varied between 1.9 and 8.4 Mg dry mass per hectare in the different treatments. The treatments comprise applications of different mineral nitrogen (N) fertilizers and organic amendments and combinations thereof. Our analysis showed that maize yield in the treatments that were not severely limited by nitrogen supply or soil acidity increased by 16% for each percentage unit increase in SOC. We applied the widely used concept of critical N concentration in plant biomass to diagnose the N status in maize in the different treatments (N nutrition index [NNI]) and parameterized a response function between yield and pH (RpH). Dry soil bulk density (BD) was used as a proxy for soil physical properties. These three variables NNI, RpH and BD explained 95% of the variation in maize yields among treatments. Further analysis of the relationship between BD, SOC and plant available water capacity revealed that about two thirds of the yield increases in response to SOC change could be ascribed to associated changes in soil physical properties. Our analysis suggests that the extra storage capacity of water, which increased by up to 15 mm in the topsoil for each unit percentage increase in SOC, was the main driver for the observed yield responses. We conclude that measures for increasing SOC in soils most likely are an effective adaptation strategy for reducing the risk of crop damage during dry spells, which probably are becoming more frequent in the future due to climate change, even in relatively humid climates as in Sweden.

Microbes alter substrate from mineral‐associated carbon to litterfall with nitrogen additions and warming

AbstractNitrogen (N) additions often decrease soil respiration and increase soil organic carbon (C) stock. However, it is unclear how microbial substrates may shift with N additions and increasing temperature. Leveraging 12 years of N fertilization experiments and the associated shift in the dominant vegetation from C4 to C3, we explored the δ13C‐CO2 and temperature sensitivities of respired CO2 and extracellular enzyme activities in control and fertilized soils. N additions increased cellulose‐decaying extracellular enzyme activity while respiration remained similar between the control and fertilized soils. Temperature sensitivity of cellulose‐decaying extracellular enzyme activity decreased with the N additions. The δ13C‐CO2 data reveal that, as temperature increased, microbes in fertilized soils changed their dominant substrate from bulk soil organic C to plant litterfall. Our results suggest that long‐term N fertilization imposed C limitation on microbes, leading to enhanced microbial efforts to acquire C. This study highlights how long‐term N additions can promote the relative preservation of organic C in mineral soil while litterfall, the precursor to mineral‐associated C, is increasingly decayed as temperatures increase.

Crop sequence intensification: Meta‐analysis of soil organic carbon and aggregate stability in Argentina

AbstractIntensification of crop sequence (ICS) has been proposed as a key field practice to preserve soil health and achieve more sustainable agricultural systems. However, the effects of ICS are site‐specific and vary according to soil characteristics, climatic conditions, the duration of the crop sequencing and the types of crop involved. Soil aggregate stability (AS) and soil organic carbon (SOC) stock are useful indicators of soil health as they are closely linked to diverse soil services and functions and are sensitive to management practices. We performed a meta‐analysis of 33 studies to analyse the impact of ICS on SOC stock and AS in field experiments in the central‐eastern region of Argentina. Our results showed that ICS increased SOC stock and AS, with an overall mean change of 7% and 22%, respectively. Fine‐textured soils showed the greatest SOC stock increase (12%), comparable to the increase observed in coarse‐textured soils (11%); in medium‐textured soils this increase was less than half (5%). Coarse‐textured soils had the greatest increase in AS (32%), followed by medium‐textured and fine‐textured soils, which also showed notable improvements (25% and 19%, respectively). Greater diversity of crops resulted in larger increases in both AS and SOC. ICS generated a larger increase of SOC stock in the soil surface (0–10 cm) than in the subsurface (10–20 cm), whereas the opposite was found for AS. Long‐term studies (≥9 years) had the greatest effect on AS and SOC stock. Regression analysis revealed that the initial carbon stock influenced SOC stock results following ICS, increases being greater when initial carbon stock contents were smaller. Introducing gramineous species into the crop sequence was associated with a greater improvement of AS and SOC stock. Finally, the mean rate of carbon sequestration from ICS in all the studies amounted to 0.28 Mg ha−1 yr−1. Overall, ICS is a useful strategy for improving SOC storage and AS in this region, though results may vary according to soil characteristics and management practices.

Changes in soil hydraulic and physio-chemical properties under treated wastewater irrigation: A meta-analysis

Treated wastewater (TWW) is increasingly used for irrigation, but its higher salt content compared to conventional water sources can induce soil salinization and sodification. This, in turn, may result in structural degradation and deterioration of soil hydraulic properties. The practice of using TWW for irrigation is not new, and it has long been applied in arid countries, with limited other water resources, while in recent years it is also getting used elsewhere given the worldwide influence on water resources. However, comparing and extrapolating results from existing studies on the use of TWW for irrigation is challenging due to the heterogeneity between experimental setups in terms of water quality, irrigation techniques applied, and pedo-climatic conditions. To explore the effect of TWW quality on soil hydraulic and physio-chemical following TWW irrigation and to examine to what extent these effects are soil type dependent, we compiled a database with results from 24 peer-reviewed studies across different soil types containing information on the link between TWW irrigation, and hydraulic and physio-chemical properties through various measurements. The meta-analysis revealed that application of TWW significantly increases sodium adsorption ratio (on average 71 ± 6%) and electrical conductivity (on average 51 ± 5%) of soil as compared to the use of conventional water source. Overall, there were no significant effects on the soil pore space (bulk density, soil total porosity) or pH. Interestingly, the application of TWW significantly increased soil organic carbon and aggregate stability, potentially even benefiting soil structure. In addition, the organic compounds in TWW also might lead to hydrophobicity. Yet, the effects of TWW on soil hydraulic and physio-chemical properties are not consistent across different TWW types and soil classes. A larger number of studies is required to draw sound conclusions on this topic. Anyway, this analysis already indicated that different soil textures might react differently to TWW irrigation. While in medium-textured soils, salt accumulation was observed and TWW significantly increased soil organic carbon and saturated hydraulic conductivity, fine-textured soils are more prone to clogging and reduced in saturated hydraulic conductivity. We also noticed an impact of the type of TWW, since the degree of treatment has a big impact on the remaining components added to the soils together with the water. Primary TWW, from which settleable and floatable solids are removed, resulted in the highest accumulation of salts and significantly increased soil organic carbon and improved soil aggregate stability. However, the elevated biochemical oxygen demand or chemical oxygen demand in this type of TWW leads to an accumulation of organic materials in the soil, negatively affecting its permeability and reducing soil saturated hydraulic conductivity. This study stresses the need for more standardized experiments quantifying the effect of TWW not only in terms of transfer of contaminants and biosafety, but also an effect on soil quality, and more specifically soil physical quality, especially at the longer term.

Soil nitrogen availability mediates the positive effects of intercropping on soil organic carbon at global scales

Intercropping is an effective cultivation practice to develop sustainable agroecosystems and increase soil organic carbon (SOC) and nitrogen (N) with rich crop diversity. With increased duration, the changes in soil N availability might affect microbial and plant growth and consequently regulate the intercropping effects on SOC sequestration. However, the response of intercropping effects on SOC components to soil N availability has been poorly explored. In this study, we constructed a global database with 939 paired data (intercropping vs. monoculture) from 60 publications. We found that intercropping increased SOC (by 7.94%), microbial biomass carbon (MBC, by 23.73%), particulate organic carbon (POC, by 23.27%), and dissolved organic carbon (DOC, by 16.46%) compared to monoculture. The intercropping effects (percentage change, %) on SOC content strongly depends on soil N availability (soil C: N) and the interactions with duration and crop types. In N-limited soils (soil C: N > 15), intercropping increased SOC and POC contents by 14% and 31%, respectively, which were 2–3 times higher than those in N-rich soils (soil C: N < 15). It implies higher intercropping effects in more N-limited soils. In addition, intercropping increased MBC:SOC by 63% in N-limited but not in N-rich soils, indicating greater contributions of microbial-derived C to SOC storage in N-limited but not in N-rich soils. This might be attributed to that the stimulated microbial decomposition of soil organic matter counterbalanced the microbial-derived C accumulation in N-rich soils. Taken together, these results indicate that soil N availability regulates the intercropping effects on SOC content and the contributions of microbial-derived C to SOC storage. Overall, these findings highlight the importance of soil N availability on SOC content with intercropping, implying that intercropping is a suitable agricultural approach especially in N-limited soils and nutrient management should be carefully considered in long-term intercropping experiments.

Effect of intercropping with legumes at different rates on the yield and soil physicochemical properties of Cyperus esculentus L. in arid land.

Intercropping has the potential to enhance yields and nutrient availability in resource-limited agricultural systems. However, the effects on crop yield nutrients and soil properties can vary considerably depending on the specific plant combinations and intercropping ratios used. In this study, the advantages and impacts of intercropping C. esculentus with legumes were investigated by measuring their biomass, nutrient content, and soil properties. The experiment included five intercropping treatments: monoculture of C. esculentus (MC), intercropping of C. esculentus with Medicago sativa L. (alfalfa) at row spacing ratios of 4:4 (4:4CM) and 8:4 (8:4CM), and intercropping of C. esculentus with Glycine max (L.) Merr. (soybean), also at row spacing ratios of 4:4 (4:4CG) and 8:4 (8:4CG). Our results demonstrated that all four intercropping treatments (4:4CM, 4:4CG, 8:4CM, and 8:4CG) significantly increased the biomass of C. esculentus by approximately 41.05%, 41.73%, 16.08%, and 18.43%, respectively, compared with monoculture cultivation alone, among which the 4:4CG treatment was optimum. However, no significant differences were observed in alfalfa or soybean biomass across different intercropping ratios. A notable increase was found in the total nitrogen (TN) and total phosphorus (TP) contents in the leaves, roots, and tubers of C. esculentus under intercropping, along with increased soil organic carbon (SOC), alkaline-hydrolyzed nitrogen (AN), available phosphorus (AP), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and soil water content (SWC), and significantly reduced the soil pH. Among the intercropping treatments, the 4:4CG treatment also exhibited the most favorable soil properties. In particular, compared with MC, the 4:4CG treatment resulted in significant increases of 163.8%, 394.6%, and 716.8% in SOC, AN, and AP contents, respectively. The same treatment also led to significant increases of 48.34%, 46.40%, and 208.65% in MBC, MBN, and SWC, respectively. Overall, the findings suggest that the use of 4:4CG intercropping is an effective approach for sustainable farming management in Xinjiang.

Influence of woodchip size and nitrogen fertilization on carbon dioxide and nitrous oxide emissions from soils amended with orchard biomass

AbstractIncorporating large amounts of woody biomass into soil, such as in whole orchard recycling (WOR), can promote carbon sequestration, nutrient recycling, and ecosystem health in agricultural fields. Yet uncertainty regarding the effects of WOR on soil carbon (C) and nitrogen (N) dynamics influences management decisions. The objective of this research was to evaluate the effects of woodchip (WC) size and interaction with N fertilization on carbon dioxide (CO2) and nitrous oxide (N2O) emissions. An 8‐month incubation experiment incorporating WC (4% w/w, equivalent to ∼40 tons per acre) in four sieved sizes (0.2–1.6, 1.6–3.2, 3.2–6.4, and 6.4–12.7 mm) with and without N applications was conducted. All treatments with WC showed that CO2 emission peaked within the first week, then decreased drastically afterward. The CO2 peak delayed as the peak value decreased (WC size increased). The finest WC (&lt;1.6 mm) yielded the lowest total CO2 emissions and resulted in the greatest increase in soil C at the end of incubation. Nitrogen application reduced total CO2 emissions by 1% in the smallest WC size and by 8%–9% for those larger than 1.6 mm. The N2O emissions spiked following each fertilizer application with lowest total emissions from the smallest WC size, suggesting substantial N immobilization. The results imply that larger WC sizes can delay C mineralization and reduce initial N immobilization risks, but the smallest WC size may have stabilized and increased soil organic carbon. This research increased our understanding on WC mineralization that can be used in WOR management.

Effects of Organic Matter Addition on Soil Carbon Contents, CO2 Emissions, and Bacterial Compositions in a Paddy Field in South China

Increasing soil organic carbon (SOC) contents and reducing carbon dioxide (CO2) emissions in paddy soil fields can result in positive impacts on climate change mitigation and soil quality. However, SOC accumulation and its microbial driving factors under enhanced fertilization strategies (e.g., organic matter application) are still unclear. Therefore, we investigated the effects of organic matter addition on SOC variations, CO2 fluxes, and their relationships with soil bacterial compositions and functions through a 6-year fertilizer experiment in rice fields involving two fertilization types, namely chemical fertilizer (NPK) and chemical fertilizer combined with organic matter (NPK+OM). The results showed significantly higher and lower SOC contents (p &lt; 0.05) in the 10–20 cm soil layer under the NPK+OM treatment before rice transplanting and after rice harvest, respectively, than those under the NPK treatment. The lower SOC contents after rice harvest might be due to the great nutrient consumption, resulting in higher rice yields in the NPK+OM than those in the NPK treatment by 6.68 to 32.35%. Compared with NPK, NPK+OM reduced the in-situ CO2 fluxes by 38.70–118.59%. However, the ex-situ SOC mineralization rates were not affected by NPK+OM in the 0–10 and 10–20 cm soil layers. The 16S rRNA sequence indicated a significant increase in the abundance of non-singleton amplicon sequence variants (ASVs) in the NPK+OM treatment scenario compared to those in the NPK treatment scenario. The top three most important soil bacterial phylum influenced by NPK+OM were LCP-89, BRC1, and Rokubacteria in April, as well as Firmicutes, Nitrospinae, and BRC1 in July. Soil Actinobacteria was negatively correlated with the SOC contents in April and July. The results of the present study demonstrate the economic and ecological benefits of the organic matter addition in rice production, as well as the contribution of soil bacteria to SOC accumulation and CO2 emission reduction.

The Effect of Coffee Canopy Pruning and Fertilization on Coffee Growth and Soil Physical Properties

Arabica coffee is primarily cultivated in agroforestry systems in Indonesia, but limited local knowledge and technology adoption hinder its productivity due to insufficient practices in coffee pruning management. This study aims to analyze variations in coffee canopy pruning (Pruning+Bending) management and the impact on plant growth and soil physical characteristics.. The experiment employed a split-plot experimental design and utilized the Fisher test (5%) to assess the treatment effects. The primary plot focused on coffee canopy pruning using two management options: (1) Pruning (PR) and (2) Bending (BN). The subplots included various types and doses of fertilizer treatments: (1) Control (F0), (2) Chicken manure (F1), (3) Chicken manure+NPK fertilizer (F2), and (4) NPK fertilizer (F3). Each experimental plot covered an area of 20x20 m and contained 50 coffee plants. Bending techniques represent alternative pruning methods, and, in general, they have a significant impact on improving several coffee parameters compared to total pruning. Regarding the soil’s physical properties, the bending technique exhibited a higher infiltration rate than pruning. The management approach of Bending+Chicken manure: NPK fertilizer (BNF2) enhanced various coffee parameters, resulting in an increased stem diameter of 4.79 cm, new shoot length of 471.20 cm, and chlorophyll content of 6.83 mg/g. Furthermore, this treatment increased soil organic carbon content by 7.51% and reduced bulk density to 0.58 g/cm. In conclusion, the bending technique wasproven to be more advantageous than pruning, especially when combined with chicken manure and NPK fertilizer for enhancing coffee management among farmers.

Effects of Compound Fertilizer Decrement and Water-Soluble Humic Acid Fertilizer Application on Soil Properties, Bacterial Community Structure, and Shoot Yield in Lei Bamboo (Phyllostachys praecox) Plantations in Subtropical China

Lei bamboo (Phyllostachys praecox) is an economically viable bamboo species with rich nutrition, a good taste, and a high yield. However, heavy fertilization and covering cultivation are used to produce off-season bamboo shoots, resulting in soil degradation and a decline in site productivity. This study investigated how compound fertilizer decrement and water-soluble humic acid fertilizer application affects soil properties and shoot yield in Lei bamboo plantations of subtropical China. The soil nutrients, enzyme activities, and shoot yield were examined, the bacterial community structure was determined using the high-throughput sequencing method, and their relationships were evaluated under different fertilization treatments: single compound fertilizer and compound fertilizer decrement with water-soluble humic acid fertilizer applications. Compared with those after single compound fertilizer treatments (CF1, CF2), water-soluble humic acid fertilizer addition (CF2HA1, CF2HA2) increased soil organic carbon (SOC), available phosphorus (AP), microbial biomass nitrogen (MBN) contents, the ratio of SOC to total nitrogen (C/N), and sucrase and acid phosphatase (Acp) activities, and decreased alkali hydrolyzed nitrogen (AN) and microbial biomass carbon (MBC) contents. The bacterial community phyla comprised 83.62%–86.16% Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi. Water-soluble humic acid fertilizer application also significantly increased yields by over 30%. AP and MBN were important drivers affecting soil bacterial communities, whereas SOC, MBN, and Chloroflexi affected Lei bamboo shoots. Overall, compound fertilizer decrement and water-soluble humic acid fertilizer application shifted the available soil nutrients, sucrase and Acp activity, bacterial community diversity, and shoot yield. An improved understanding of humic acid and the application of humic acid water-soluble fertilizer are of great significance for soil improvement, ecological restoration, and the sustainable management of bamboo forests in the future.

Effects of Different Modifiers on Aggregates and Organic Carbon in Acidic Purple Soil

The aim of this study was to examine the effects of different modifiers on the changes in aggregates and organic carbon in acidic purple soil， providing a scientific basis for the remediation of acidic purple soil. Using purple soil as the research object， a total of six treatments were set up， including no fertilization （CK）， single fertilization （F）， fertilization with lime （SF）， fertilization with organic fertilizer （OM）， fertilization with biochar （BF）， and fertilization with distiller's grains ash （JZ）. We compared the composition of aggregates in acidic purple soil under the application of different modifiers， as well as the distribution pattern of organic carbon in aggregates of different particle sizes. Combined with the stability indicators of aggregates， we sought to clarify the impact of different modifiers on the structure of aggregates in acidic purple soil. The results showed that fertilization significantly increased the soil pH， with the JZ treatment being the most effective. Fertilization significantly increased soil organic matter content， with the OM treatment showing the largest increase. The BF and OM treatments significantly reduced soil bulk density， whereas the SF and BF treatments significantly increased soil moisture content （P &lt; 0.05）. All treatments used &lt; 0.25 mm aggregates as the dominant particle size. Fertilization could significantly increase the content of large aggregates （aggregate structure units with diameter &gt; 0.25 mm）. At the same time， fertilization treatments significantly increased the soil geometric mean diameter （GMD）， average weight diameter （MWD）， and R0.25 value （ &gt; 0.25 mm aggregate content） and reduced the fractal cone number （D） and aggregate destruction rate （PAD） values （P &lt; 0.05）. Fertilization also promoted the aggregation and stability of soil aggregates， with the OM treatment having the greatest effect. Compared with that in the CK treatment， fertilization could significantly increase soil organic carbon content by 31.71%-209.67%， with the OM treatment showing the most significant change. Different treatments of soil organic carbon were mainly distributed in large aggregates. Compared with that in the CK treatment， each treatment significantly increased the contribution rate of organic carbon in large aggregates by 19.34%-47.76%， with the OM treatment having the most significant effect （P &lt; 0.05）. In general， chemical fertilizer combined with organic fertilizer could promote the formation of large aggregates in acidic purple soil， improve the stability of soil aggregates， and increase the content of soil organic carbon， which is an effective measure to improve the soil structure and improve the quality of acidic purple soil.

An Assessment of Plant Growth and Soil Properties Using Coal Char and Biochar as a Soil Amendment

Soil degradation due to loss of soil organic carbon is a serious concern in semiarid agroecosystems. Biochar and other organic char products have long been known to increase soil organic carbon. In this study, three-year field observations were carried out on use of coal char (CC) and biochar (BC) as soil amendments in unirrigated semiarid rangeland soil. Coal was pyrolyzed at three different temperatures of 650, 750, and 800 °C to form CC650, CC750, and CC800, respectively, and BC was obtained from a local commercial producer. Manure, CC, and BC were incorporated in soil at 10% (v/v). Analyses of plant growth (aboveground biomass) and soil properties were performed and compared with the control treatment without char. In all three years, CC applied with manure (CC650M) produced significantly greater grass biomass, by 95, 42, 101%, and BC applied with manure (BCM) increased grass biomass by 89, 39, 52% in 2018, 2019, and 2020, than the controls in the respective years. Soil tests a year after application of char indicated significantly increased soil organic matter (OM) with CC and BC treatments (1.60–2.93%) compared with the control (1.37%). However, further detailed studies are required to investigate CC and BC interactions with soil in unirrigated semiarid rangelands.

Liming effects on microbial carbon use efficiency and its potential consequences for soil organic carbon stocks

Climate-smart agriculture aims amongst others at protecting and increasing soil organic carbon (SOC) stocks. The allocation of metabolised carbon (C) between soil microbial growth and respiration, i.e. C use efficiency (CUE) is crucial for SOC dynamics. We hypothesised that raising soil pH would alleviate CUE-limiting conditions and that liming could thus increase CUE, thereby supporting SOC accrual. This study investigated whether CUE can be manipulated by liming and how this might contribute to SOC stock changes. The effects of liming on CUE, microbial biomass C, abundance of microbial domains, SOC stocks and OC inputs were assessed for soils from three European long-term field experiments. Field control soils were additionally limed in the laboratory to assess immediate effects. The shift in soil pHH2O from 4.5 to 7.3 with long-term liming reduced CUE by 40 %, whereas the shift from 5.5 to 8.6 and from 6.5 to 7.8 was associated with increases in CUE by 16 % and 24 %, respectively. The overall relationship between CUE and soil pH followed a U-shaped (i.e. quadratic) curve, implying that in agricultural soils CUE may be lowest at pHH2O = 6.4. The immediate CUE response to liming followed the same trends. Changes in CUE with long-term liming contributed to the net effect of liming on SOC stocks. Our study confirms the value of liming as a management practice for climate-smart agriculture, but demonstrates that it remains difficult to predict the impact on SOC stocks due its complex effects on the C cycle.

Comparative efficacy of wheat-straw biochar and chicken-waste compost on cadmium contaminated soil remediation, reducing cadmium bioavailability and enhancing wheat performance under cadmium stress

Cadmium (Cd) pollution of soil and food crops is a widespread environmental issue caused by excessive industrialization, unsustainable urbanization, and intensive farming practices. Cd, a hazardous element, poses significant risks to agro-environmental sustainability, food safety, and human health. Using organic materials such as biochar and compost to stabilize Cd in contaminated soil is an environmentally benign and cost-effective strategy for remediating moderately to highly polluted soil. However, in response to the scarcity of comparative studies on biochar and compost efficacy, this research explores the impact of wheat-straw biochar and chicken waste compost on Cd-contaminated soil remediation. A greenhouse experiment using two application rates (1.5 % and 2.5 %) of biochar and compost in 10 mg kg−1 Cd-contaminated soil revealed significant (p≤0.05) effects. The 2.5 % compost application increased soil organic carbon (SOC) from 0.45 % to 0.85 %, while 2.5 % biochar enhanced soil pH from 7.1 to 7.7 and electrical conductivity (EC) from 0.33 to 0.44 dSm−1. Notably, 2.5 % biochar significantly reduced Cd bioavailability from 9.49 to 4.90 mg kg−1, root accumulation from 29.8 to 16.4 mg kg−1 and shoot translocation from 16.8 to 8.4 mg kg−1. This reduction was confirmed through translocation factor (51.5 %) and immobilization efficiency (48.4 %). Furthermore, 2.5 % biochar improved chlorophyll content (a, b, and total) and wheat morphological attributes under Cd stress in soil. Overall, higher rates of biochar (2.5 %) and compost (2.5 %) effectively mitigate Cd uptake, improve soil properties, and enhance physiological and morphological responses, suggesting their promise for sustainable soil management practices.

Enriched soil amendments influenced soil fertility, herbage yield and bioactive principle of medicinal plant (Cassia angustifolia Vahl.) grown in two different soils

High cost of chemical fertilizers and poor nutrient content in conventional organic sources (manure, compost, charcoal etc.) can be addressed through development of enriched organic amendments. However, there is a need to evaluate enriched organic amendments as a potential alternative of chemical fertilizers. Therefore, an effort was made to prepare enriched organic amendments through blending distillation waste of aromatic plant biomass (DWB) with naturally available low-grade rock phosphate (RP) and waste mica (WM). Enrich compost (ENC) was produced from DWB in a natural composting process, blended with mineral powder, whereas biochar fortified mineral (BFM) was prepared by blending biochar, derived from DWB through hydrothermal reaction, with mineral powder. The main aims of the present study were to investigate the impacts of ENC and BFM applications on soil properties, and herbage yield and quality of a medicinal herb Senna (Cassia angustifolia Vahl.). The performances of ENC and BFM at two different rates (2.5 and 5 t ha−1) were compared with the application of conventional farmyard manure (FYM, 5 t ha−1) and chemical fertilizers (CF, NPK 60-40-20 kg ha−1) in two different soils in a pot experiment. Both, ENC and EBC improved soil quality and fertility by increasing soil organic carbon, available nutrients, microbial biomass and enzyme activity. The ENC and BFM increased total herbage yields by 21 and 16.3 % compared to FYM. In both soils, the CF treatment produced the maximum dry herbage yields (32.7–37.4 g pot−1), which however were comparable to ENC (31.9–33.7 g pot−1) and BFM (30.7–35.1 g pot−1) treatments. Bioactive compound (sennoside) production in senna was significantly improved by ENC and BFM compared to CF. The present study indicates that ENC and BFM could not only help to overcome the limitation of conventional FYM, but also have the potentials to substitute costly chemical fertilizers, particularly in medicinal plant cultivation.

Optimizing nitrogen and phosphorus application to improve soil organic carbon and alfalfa hay yield in alfalfa fields.

Soil organic carbon (SOC) is the principal factor contributing to enhanced soil fertility and also functions as the major carbon sink within terrestrial ecosystems. Applying fertilizer is a crucial agricultural practice that enhances SOC and promotes crop yields. Nevertheless, the response of SOC, active organic carbon fraction and hay yield to nitrogen and phosphorus application is still unclear. The objective of this study was to investigate the impact of nitrogen-phosphorus interactions on SOC, active organic carbon fractions and hay yield in alfalfa fields. A two-factor randomized group design was employed in this study, with two nitrogen levels of 0 kg·ha-1 (N0) and 120 kg·ha-1 (N1) and four phosphorus levels of 0 kg·ha-1 (P0), 50 kg·ha-1 (P1), 100 kg·ha-1 (P2) and 150 kg·ha-1 (P3). The results showed that the nitrogen and phosphorus treatments increased SOC, easily oxidized organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC), microbial biomass carbon (MBC) and hay yield in alfalfa fields, and increased with the duration of fertilizer application, reaching a maximum under N1P2 or N1P3 treatments. The increases in SOC, EOC, DOC, POC, MBC content and hay yield in the 0-60 cm soil layer of the alfalfa field were 9.11%-21.85%, 1.07%-25.01%, 6.94%-22.03%, 10.36%-44.15%, 26.46%-62.61% and 5.51%-23.25% for the nitrogen and phosphorus treatments, respectively. The vertical distribution of SOC, EOC, DOC and POC contents under all nitrogen and phosphorus treatments was highest in the 0-20 cm soil layer and tended to decrease with increasing depth of the soil layer. The MBC content was highest in the 10-30 cm soil layer. DOC/SOC, MBC/SOC (excluding N0P1 treatment) and POC/SOC were all higher in the 0-40 cm soil layer of the alfalfa field compared to the N0P0 treatment, indicating that the nitrogen and phosphorus treatments effectively improved soil fertility, while EOC/SOC and DOC/SOC were both lower in the 40-60 cm soil layer than in the N0P0 treatment, indicating that the nitrogen and phosphorus treatments improved soil carbon sequestration potential. The soil layer between 0-30 cm exhibited the highest sensitivity index for MBC, whereas the soil layer between 30-60 cm had the highest sensitivity index for POC. This suggests that the indication for changes in SOC due to nitrogen and phosphorus treatment shifted from MBC to POC as the soil depth increased. Meanwhile, except the 20-30 cm layer of soil in the N0P1 treatment and the 20-50 cm layer in the N1P0 treatment, all fertilizers enhanced the soil Carbon management index (CMI) to varying degrees. Structural equation modeling shows that nitrogen and phosphorus indirectly affect SOC content by changing the content of the active organic carbon fraction, and that SOC is primarily impacted by POC and MBC. The comprehensive assessment indicated that the N1P2 treatment was the optimal fertilizer application pattern. In summary, the nitrogen and phosphorus treatments improved soil fertility in the 0-40 cm soil layer and soil carbon sequestration potential in the 40-60 cm soil layer of alfalfa fields. In agroecosystems, a recommended application rate of 120 kg·ha-1 for nitrogen and 100 kg·ha-1 for phosphorus is the most effective in increasing SOC content, soil carbon pool potential and alfalfa hay yield.

Interactive effects of long-term management of crop residue and phosphorus fertilization on wheat productivity and soil health in the rice–wheat

In the context of degradation of soil health, environmental pollution, and yield stagnation in the rice–wheat system in the Indo-Gangetic Plains of South Asia, an experiment was established in split plot design to assess the long-term effect of crop residue management on productivity and phosphorus requirement of wheat in rice–wheat system. The experiment comprised of six crop residue management practices as the main treatment factor with three levels (0, 30 and 60 kg P2O5 ha–1) of phosphorus fertilizer as sub-treatments. Significant improvement in soil aggregation, bulk density, and infiltration rate was observed under residue management (retention/incorporation) treatments compared to residue removal or residue burning. Soil organic carbon (SOC), available nutrient content (N, P, and K), microbial count, and enzyme activities were also significantly higher in conservation tillage and residue-treated plots than without residue/burning treatments. The residue derived from both crops when was either retained/incorporated improved the soil organic carbon (0.80%) and resulted in a significant increase in SOC (73.9%) in the topsoil layer as compared to the conventional practice. The mean effect studies revealed that crop residue management practices and phosphorus levels significantly influenced wheat yield attributes and productivity. The higher grain yield of wheat was recorded in two treatments, i.e. the basal application of 60 kg P2O5 ha–1 without residue incorporation and the other with half the P-fertilizer (30 kg P2O5 ha–1) with rice residue only. The grain yield of wheat where the rice and wheat residue were either retained/incorporated without phosphorus application was at par with 30 and 60 kg P2O5ha–1. Phosphorus levels also significantly affected wheat productivity and available P content in the soil. Therefore, results suggested that crop residue retention following the conservation tillage approach improved the yield of wheat cultivated in the rice–wheat cropping system.

Maximizing soil organic carbon stocks through optimal ploughing and renewal strategies in (Ley) grassland

Grassland management effects on soil organic carbon storage under future climate are unknown. Here we examine the impact of ley grassland durations in crop rotations on soil organic carbon in temperate climate from 2005 to 2100, considering two IPCC scenarios, RCP4.5 and RCP8.5, with and without atmospheric CO2 enhancements. We used the DailyDayCent model and a long-term experiment to show that ley grasslands increase soil organic carbon storage by approximately 10 Mg ha−1 over 96 years compared with continuous cropping. Surprisingly, extending ley duration from 3 to 6 years does not enhance soil organic carbon. Furthermore, in comparison with non-renewed grasslands, those renewed every three years demonstrated a notable increase in soil organic carbon storage, by 0.3 Mg ha−1 yr−1. We concluded that management of ploughing and renewal intervals is crucial for maximizing soil organic carbon stocks, through balancing biomass carbon inputs during regrowth and carbon losses through soil respiration.

High organic carbon content constricts the potential for stable organic carbon accrual in mineral agricultural soils in Finland

Sequestering carbon into agricultural soils is considered as a means of mitigating climate change. We used agronomic soil test results representing c. 95% of the farmed land area in Finland to estimate the potential of the uppermost 15 cm soil layer of mineral agricultural soils to sequester organic carbon (OC) and to contribute to the mitigation of climate change. The estimation of the maximum capacity of mineral matter to protect OC in stable mineral-associated form was based on the theory that clay and fine-sized (fines = clay + silt) particles have a limited capacity to protect OC. In addition, we used the clay/OC and fines/OC ratios to identify areas with a risk of erosion and reduced productivity, thus indicating priority areas potentially benefitting from the increased soil OC contents. We found that 32–40% of the mineral agricultural soils in Finland have the potential to further accumulate mineral-associated OC (MOC), while in the majority of soils, the current OC stock in the uppermost 15 cm exceeded the capacity of mineral matter to protect OC. The nationwide soil OC sequestration potential of the uppermost 15 cm in mineral agricultural soils ranged between 5 and 10 Tg, which corresponds to less than the annual greenhouse gas emissions in Finland. The fields with the highest potential for SOC accrual were found in the southern and southwestern parts of the country, including some of the most intensively cultivated high-clay soils. Although the nationwide potential for additional OC sequestration was estimated to be relatively small, the current OC storage in Finnish arable mineral soils (0-15 cm) is large, 128 Tg. Farming practices enabling maximum OC input into the soil play an important role as a tool for mitigating the loss of carbon from high-OC soils in the changing climate. Furthermore, especially in high-clay areas with potential for MOC accrual, efforts to increase soil OC could help improve soil structural stability and therefore reduce erosion and the loss of nutrients to the aquatic environments.