Total Nitrogen Stocks Research Articles

Soil dissolved carbon and nitrogen dynamics along a revegetation chronosequence of Caragana korshinskii plantations in the Loess hilly region of China

Widespread vegetation restoration is an effective measure used to control soil erosion and improve soil organic carbon (SOC) and total nitrogen (TN) storage; however, knowledge of soil dissolved carbon and nitrogen has not been well characterized. Caragana korshinskii plantations are valued for their critical role in soil and water conservation in the Loess Hilly Region. This study aimed to estimate the levels of soil carbon and nitrogen and their dissolved fractions in one farmland (Zea mays L.) and three C. korshinskii plantations at 15, 30 and 40 years; additionally, the distribution of soil carbon and nitrogen stocks among various soil depths were estimated. The results showed that afforestation with C. korshinskii resulted in a significant increase in the contents and stocks of SOC and TN and their dissolved fractions. At a depth of 0–10 cm, the 30-year-old C. korshinskii had the highest stocks of SOC and TN, but at depths of 40–100 and 100–200 cm, the highest SOC and TN stocks were found in the soil of 15-year-old C. korshinskii. The 15-year-old C. korshinskii had the highest stocks of SOC and TN at depths of 0–200 cm and the highest stocks of dissolved nitrogen across almost all soil layers. The soil at 100–200 cm contained 34%–54% of the total percentages of the cumulative stocks of SOC and TN and their fractions. The SOC stock was the most important factor affecting the variation in soil nitrogen fractions and contributed to more than 80% of the total variation; additionally, the nitrate (NO3-N) content and stock were the most important factors affecting the soil carbon fractions, contributing to 78% of the total variation. This study demonstrates that revegetation age and soil depth play important roles in determining carbon and nitrogen levels. The results also suggest that C. korshinskii plantations should be harvested and revegetated during the rapid growth period (∼15 years) during which they show the largest accumulations of soil carbon and nitrogen.

Does the duration of no-till implementation influence depth distribution of soil organic carbon, hydro-physical properties, and computed tomography-derived macropore characteristics?

No-till (NT) is a sustainable alternative to conventional-till (CT), however, the impacts of NT and its duration on the depth distribution of soil organic carbon (SOC), physical and hydrological parameters are less studied. Therefore, the objective of this study was to evaluate the changes in soil hydro-physical properties and X-ray computed tomography (XCT)-derived macropore characteristics to a depth of 40 cm as influenced by the duration [short-(5-yr) and long-(30 yr) term] of NT practice on a previously conventionally-tilled (CT) soil. The treatments included: CT, initiated in 1991; long-term NT (LTNT),1991; and short-term NT (STNT), 2016 established on silty clay loam soil (Udic Haplustolls). Four replicated intact soil cores were collected from each treatment at 0–10, 10–20, 20–30, and 30–40 cm depths. Data showed that the LTNT stored 23% more SOC stock in the 0–40 cm depth as compared to the CT. The LTNT also increased the total nitrogen (TN) stock, soil water retention (SWR), plant available water (PAW) content, and saturated hydraulic conductivity (Ksat) to the depth of 40 cm as compared to the CT. The LTNT increased the XCT-derived soil macroporosity [pores with > 500 µm equivalent cylindrical diameter (ECD)] and pore connectivity up to 20 cm than the CT. However, the STNT implementation increased the SWR at − 0.6, − 5, and − 30 kPa, pore connectivity, and Ksat only for the 0–10 cm depth than the CT. In addition, PAW showed a high correlation with SOC content [Pearson correlation coefficient (δ) = 0.71], and Ksat was highly correlated with the modulus of XCT-derived Euler-Poincaré characteristic (a measure of local connectivity; δ = 0.61). The study highlighted that pore connectivity and Ksat in surface soil (0–10 cm) were most responsive to the implementation of NT on a previously tilled soil. Data suggest that a longer duration of NT implementation was required to improve the SOC and soil hydro-physical parameters to a deeper soil profile (0–40 cm). Therefore, we conclude that the conversion of tilled soil to NT practice has beneficial effects, depending upon the duration of NT implementation, in enhancing the SOC and hydro-physical conditions, which may help in storing more water in deeper soil for enhanced production.

The vertical distribution of soil organic carbon and nitrogen in a permafrost‐affected wetland on the Qinghai–Tibet Plateau: Implications for Holocene development and environmental change

AbstractCurrently, we know little about accumulation of soil carbon and nitrogen in permafrost‐affected wetlands on the Qinghai–Tibet Plateau (QTP). In this study, we analyze the vertical distribution of concentrations, stocks, and apparent accumulation rates of soil organic carbon (SOC) and total nitrogen (TN) in a wetland underlain by ice‐rich permafrost in the Headwater Area of the Yellow River (HAYR) on the northeastern QTP in the context of Holocene environmental change. SOC and TN stocks at depths of 0–216 cm were 80.0 kg C m−2 and 6.7 kg N m−2, respectively. During the past 7.3 kyr, the general regional climate trend in the HAYR was cooling and drying, as indicated by the decline in chemical weathering in the soil profile. Overall, SOC and TN concentrations increased during this period. Meanwhile, an intense period of SOC and TN accumulation occurred at 1,110–720 yr BP, in contrast to much lower apparent accumulation rates of SOC and TN for the other periods during the past 7.3 kyr. This suggests that the accumulation of SOC and TN in permafrost‐affected wetlands was also affected by local environmental factors, such as soil material deposition rate, in addition to climatic controls as exerted mainly by temperature and precipitation. This study may help integrate relevant studies on plateau wetlands into global models and estimates to better simulate and predict interactions between the carbon cycle and climate changes on a global scale.

Evaluation of soil physico-chemical properties as affected by canopies of scattered agroforestry trees on croplands

Agroforestry tree species play an important role in improving soil fertility. Though studies have confirmed that different species show different potentials to improve soil fertility, it is difficult to compare them as the studies were conducted in different areas. The potential for different tree species to improve soil fertility on croplands in northern Ethiopia is not known. The objectives of this paper are to determine the effects of presence or absence of agroforestry tree species on soil physico-chemical properties and the effect of distance from the tree trunk on the same soil physico-chemical properties. Sixty composite and undisturbed soil samples from beneath canopies and outside canopies and 90 composite and undisturbed soil samples from three different distances from tree trunks were collected. The results revealed that soil bulk density, soil moisture, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Av.P), exchangeable potassium (Exch.K) and soil organic carbon stock (SOCS) were significantly (p < 0.05) different between soils beneath canopies and outside canopies as well as at different distances from the tree trunk. Soils around these agroforestry tree species have increased SOC, TN, Av.P, Exch.K and SOCS by 11.9 to 91.5%, 22.2 to 125.0%, 31 to 71%, 32 to 151.6% and 15.2 to 90.9%, respectively, compared to soils outside tree canopies. Faidherbia albida (Delile) A.Chev. has the highest potential for soil fertility compared to Balanites aegyptiaca (L.) Delile, Cordia africana Lam., Ziziphus spina-christi (L.) Desf., Acacia sieberiana DC and Croton macrostachyus Hochst. ex Delile. This study could provide useful information for soil fertility management and farmers’ decision-making when selecting tree species. The findings of this study imply that scattered trees on croplands significantly improve soil fertility and reduce the need for external fertiliser inputs.

The first national scale evaluation of total nitrogen stocks and burial rates of intertidal sediments along the entire coast of South Korea

The regulating ecosystem services, such as water purification, that tidal flats provide by nitrogen (N) burial are being increasingly recognized; yet, quantitative estimates remain limited. Here, we first present nationwide evaluation of total N stocks and burial rates in the Korean tidal flats, based on a 3 year long monitoring assessment combined with remote sensing approach. A total of 20 intertidal flats representing 7 provinces of South Korea were extensively surveyed in 2018–20. The sediment textural type (sand, mixed, and mud) classified from remotely sensed imagery was significantly correlated to that identified from field data (p < 0.01), warranting a nationwide estimate of total N stocks. The estimated total N stocks and burial rates in the tidal flats of Korea were 1.5 Tg N and 8,192 Mg N yr‐1, respectively. Total N stocks significantly varied by region, province, morphology, salinity, and land use type adjacent to the corresponding tidal flats. In general, the N stocks of tidal flats were influenced by the degree of terrestrial N inputs to the ocean. The N stocks were significantly correlated with several physical parameters, such as precipitation (p < 0.05) and tide (p < 0.01). Among the sediment properties, the mud content was found to be the key factor determining the total N stocks across the 20 intertidal flats (p < 0.01). Finally, by applying the environmental value for N removal (USD km‐2 yr‐1) to the tidal flat area (km2), the economic value of the total N removal was estimated as ~233 Million USD yr‐1 in Korea and ~15 Billion USD yr‐1 globally. Overall, the present work confirms the valuable ecosystem service of tidal flat's cost-efficient N removal capacity, highlighting marine ecosystem service.

Spatial Distribution and Regulating Factors of Soil Nutrient Stocks in Afforested Dump of Pingshuo Opencast Coalmine, China

Determining the regulating factors of soil nutrient variations can guide the implementation of land reclamation measures in opencast coalmine regions. In this study, 132 soil samples were collected at 22 sample sites in the South Dump of Pingshuo opencast coalmine, and soil physicochemical properties were separately measured to obtain the related soil information. Geostatistical analyses were employed to analyze the spatial distribution patterns of soil organic carbon stocks (SOCD), total nitrogen stocks (TND), available phosphorus stocks (APD), and available potassium stocks (AKD) at 0–60 cm. The results showed that the spatial distributions of these soil nutrient stocks were characterized by moderate (TND) to strong (SOCD, APD, and AKD) spatial dependence. Meanwhile, the values of SOCD (16.4–60.1 Mg ha−1) and TND (1.9–15.5 Mg ha−1) were much higher than those of APD (0.022–0.095 Mg ha−1) and AKD (0.31–1.40 Mg ha−1). The statistical analyses indicated that the influence of afforestation on SOCD, TND, APD, and AKD was not significant, and the dynamic variations of soil nutrient contents were mainly regulated by soil pH in the South Dump. The findings of this study can provide some scientific guidance for soil nutrient management in the opencast coalmine regions of similar ecosystems.

Land conversion from annual to perennial crops: A win-win strategy for biomass yield and soil organic carbon and total nitrogen sequestration

How much can we increase biomass yield by promoting land conversion from annual to perennial crops? Will increased biomass extraction for biorefineries reduce soil organic carbon (SOC) and total nitrogen (TN) stock? Which cropping system is more stable for biomass production over time? To our knowledge, no study has concurrently investigated the effects of land conversion from annual to perennial crops on biomass yield, yield stability, and changes in SOC and TN stock, which limits the understanding and application of sustainable agroecosystems producing biomass for biorefineries. Based on five-year continuous observations in central Jutland Denmark, our results showed that perennial crops significantly increased biomass yield by 19% and yield stability by 88% compared to annual crops. Perennial crops significantly increased SOC content by 4% and SOC stock by 11% at 0–100 cm depth across the five years. The opposite responses of SOC content and stock under annual and perennial crops led to even more significant differences between the crop types. Perennial crops had no effect on soil TN content and increased soil TN stock to one meter depth by 22%, whereas continuous annual crops had no effect on it. Neither annual nor perennial crops had effects on SOC and TN stock when estimated based on equivalent soil mass because the soil density increased under perennial crops. Our results showed that changes in SOC and TN stock between annual and perennial crops varied with the specific calculating methods (fixed depth/equivalent mass), thus the selected methods should be clearly defined in the future research. Increases in SOC content at one meter depth were positively correlated with biomass yield and yield stability, suggesting a win-win strategy for climate mitigation and food security. Altogether, our results highlight the potential to redesign the current cropping system for sustainable intensification by selecting proper perennial crops for green biorefineries.

Irrigated rice rotations affect yield and soil organic carbon sequestration in temperate South America

AbstractRice (Oryza sativa L.) systems rotated with perennial pastures have intensified in South America to increase annual grain productivity, but the effects on rice yield and soil quality remain poorly understood. We evaluated rice grain yield, crop and pasture biomass production, and soil organic carbon (SOC) and total nitrogen stocks (0–15‐cm depth) in three rice‐based rotations over 8 yr in Uruguay. Treatments were: (a) rice–pasture [a 5 yr rotation of rice–ryegrass (Lolium multiflorum Lam.)–rice, then 3.5 yr of a perennial mixture of tall fescue (Festuca arundinacea Schreb.), white clover (Trifolium repens L.), and birdsfoot trefoil (Lotus corniculatus L.)], (b) rice–soybean [a 2‐yr rotation of rice–ryegrass–soybean (Glycine max [L.] Merr.)–Egyptian clover (Trifolium alexandrinum L.)], and (c) rice–cover crop (an annual rotation of rice–Egyptian clover). Rice after soybean or pasture achieved the highest yield (9.8 Mg ha–1), 9% higher than rice after rice in the rice–pasture and rice–cover crop systems. Estimated belowground biomass under rice–pasture (2.7 Mg ha–1) was 12 and 42% greater than under rice–cover crop and rice–soybean rotations, respectively. Rice–pasture showed an increase of 0.6 Mg ha–1 yr–1 of SOC; no changes were observed in the intensified rotations replacing pasture with additional rice or soybean. All systems sustained soil total N. These results provide insights for implementing sustainable rice‐based rotations, with rice–pasture being the only system that increased SOC while achieving high rice yields and belowground biomass productivity.

Assessing soil organic carbon, N and P stocks and its relation to soil properties in artificial canopy gaps in a managed oriental beech (Fagus orientalis L.) forest#

AbstractBackgroundIn the Hyrcanian temperate forests, different canopy gaps sizes have been created by logging under silvicultural methods. Understanding the effects of gaps on forest ecosystems can help in the planning and decision‐making of forestry practices. Variations in ecological conditions caused by canopy gaps may have an impact on the forest stand, particularly soil nutrients.AimsThe purpose of the present research was to investigate the changes in soil organic carbon (SOC), total nitrogen (N) and phosphorus (P) stocks under different gap sizes in the Hyrcanian oriental beech forest.MethodsWe measured SOC, N and P stocks of soil at the depth of 0–20 cm among 15 artificial gaps along with adjacent closed stand which was created by single‐tree selection system in oriental beech stand, northern Iran. In the center and four cardinal positions of the edge of gaps as well as in the four adjacent closed canopy forests at the distance of 20 m from gaps, the soil sampling was performed.ResultsThe difference in C, N and P stocks among the artificial canopy gaps was statistically significant, and higher mean values were observed in large gaps. No significant difference was observed between gaps and adjacent closed stands with regard to soil C, N and P stocks. At artificial gaps and closed stands, the SOC stock was negatively correlated with clay and positively correlated with bulk density, sand, N and OC. With increasing bulk density, sand, N, P, and OC, N stock was increased in gaps. In gaps, SOC and P stocks were both positively related to soil microbial C and soil microbial P, respectively.ConclusionGenerally, it can be stated that there are similar relative ecological conditions between artificial gaps and closed stands, and the interaction among soil properties in gaps demonstrates gap dynamics in deciduous, broad‐leaved beech forest.

Estimating soil organic carbon and nitrogen stock based on high-resolution soil databases in a subtropical agricultural area of China

Quantifying soil organic carbon stock (SOCS) and total nitrogen stock (STNS) of the agriculture soils in China is crucial for predicting the future of global climate change and planning agricultural management practices. However, most of existing studies were based on relatively coarse soil databases, leading to large discrepancies in the SOC and STN estimates. The present study was conducted in Changting County of Fujian Province in China, covering an area of 29,375ha. A high-resolution soil database at a county-scale of 1:10,000 was employed to analyze the SOC density (SOCD) and STN density (STND) under different soil groups and land use types. Results indicated that the mean SOCD and SOCS for the surface layer (0–15 cm) were 2.93 ± 0.38 kg C m−2 and 861 Gg, respectively, and those for STND and STNS were 0.37 ± 0.06 kg N m−2 and 108 Gg, respectively. The SOCD and STND showed significant disparities among soil groups and land use types. We also compared the SOCD, SOCS, STND and STNS estimated from a coarser 1:1000,000 soil database, which was the most detailed soil database at the national scale, with the estimates in this study. The relative deviations in estimating SOCD and STND by soil groups from the coarser database were 8.1% and 60.6%, respectively, which could be primarily attributed to the assignment errors of soil attributes and polygon area variations in the coarse-scale soil database. Moreover, we found that the dominant factors determining SOCD were topographic and climatic factors (e.g. elevation and mean annual precipitation), while farming practices (e.g. N fertilizer application and irrigation conditions) as well as elevation were more important for STN estimates. Further, the deviations of STN estimates from the coarse- and fine-scale soil database were higher than those of the SOC estimates because: (1) The topographic and climatic factors had slight effects on STND from coarse- and fine-scale soil database while significantly affected SOCD; and (2) STN estimates tended to be more easily influenced by anthropic farming practices (e.g. significant irrigation conditions and N fertilization application) in the coarse-scale database than that in the fine-scale database. Therefore, a high-resolution soil database may improve the accuracy of SOC and STN assessment, especially for STN assessment, and the application of finer soil databases is a critical step for estimating SOCS and STNS at national and even global levels, and thus for accurately assessing regional C budget.

Coupling and decoupling of soil carbon, nitrogen and phosphorus stocks following grazing exclusion in temperate grasslands

Grazing exclusion is considered a crucial measure for improving ecosystem structure and function, including elements such as soil carbon and nutrients. However, little is known about the relationships of soil organic C (SOC), total nitrogen (TN), and total phosphorous (TP) stocks during long-term grazing exclusion. This study examined the SOC, TN, and TP stocks after 0–33 years of grazing exclusion in temperate grasslands on the Loess Plateau, China. The results showed that long-term grazing exclusion significantly increased SOC and TN stocks but declined TP stocks compared to those in grazing grasslands. In addition, grazing exclusion was more favorable for SOC and TN accumulations than TP accretion, and SOC and TN stocks were decoupled from TP stock. Overall, changes in SOC stock were determined by plant productivity, and TN stocks were also driven by soil microbial activities (i.e., N-acquiring enzymes). Nevertheless, plant and microbial characteristics had no effects on TP stocks following grazing exclusion. This study emphasizes the positive effect of grazing exclusion on SOC and TN accumulations, further, it is needed to explore soil phosphorus stabilization mechanisms during grassland restoration after grazing exclusion.

Soil Carbon and Nitrogen Stock and Their Spatial Variability Along an Exclosure Chronosequence at Kewet District, Central Dry Lowlands of Ethiopia

Empirical evidence and a better explanation of the effect of exclosures on soil properties are needed to rehabilitate degraded land and properly utilize the restored ecosystem. This study was conducted to determine soil organic carbon (SOC) and total nitrogen (TN) stocks and to map their spatial distribution and aggregate stability along open grazing land, 5, 15, and 20 years exclosure, and three slope positions. To map the spatial distribution of SOC and TN stocks an ordinary kriging interpolation method was applied. The results showed that the age of exclosure had significantly ( p &lt; .05) affected SOC and TN stock. Soil organic carbon stock was the highest in the 15-year-old (18.43 Mg ha−1) and lowest (14.22 Mg ha−1) in the 5-year-old exclosures. Similarly, the 15-year-old (1.81 Mg ha−1) and 5-year-old (1.41 Mg ha−1) exclosures had the highest and the lowest TN stock, respectively. Soil organic carbon associated with macroaggregates (&gt;250 µm) and microaggregates (&lt;250 µm) varied significantly ( p &lt; .05) between ages of exclosures and adjacent open grazing land. Significantly ( p &lt; .05) higher SOC stock (16.99 Mg ha−1) and macroaggregate associated SOC (3.05%) were recorded in the upper slope position as compared to the middle and lower slope positions. Due to the variation in vegetation cover and density and topography of the area, both SOC and TN stock showed high spatial variability across all ages of exclosure and adjacent open grazing land. Despite its inconsistency, the age of exclosure had affected SOC and TN stock, mean weight diameter, water-stable aggregates, and aggregate associated SOC. It is suggested that exclosure as a restoration measure of degraded landscapes can sequester and stock a significant amount of atmospheric CO2. Further study on soil organisms and litterfall is suggested to understand the dynamics of SOC and TN stocks in these exclosures.

Short-term soil physical responses to grazing and cover crops in an integrated crop-livestock agroecosystem

Cover crops (CCs) and grazing play critical roles in the successful implementation of integrated crop-livestock systems (ICLSs) because they can have a direct impact on soil functions. The present study was conducted to assess the short-term impacts of CCs and grazing on soil physical and hydrological properties. Two sites (Northern-Brookings and Northwestern-Brookings) were established in 2016 and 2017, respectively, in South Dakota, United States. The specific objective was to evaluate the impact of CCs and grazed CCs under oat (<i>Avena sativa</i> L.)/CCs–corn (<i>Zea mays</i> L.) rotation on soil physical and hydrological properties. Study treatments included (1) legume-dominated CC (LdC), (2) cattle-grazed LdC (LdC+G), (3) grass-dominated CC (GdC), (4) cattle-grazed GdC (GdC+G), and (5) no CC and no grazing (NC). After two to three years of management, CCs and grazing did not impact soil organic carbon (SOC) and total nitrogen (TN) stocks, and their values at approximate depth of 0 to 20 cm ranged from 50.9 to 60.6 Mg C ha⁻¹ and 3.65 to 4.92 Mg N ha⁻¹, respectively, among the treatments at each site. Cover crops decreased soil bulk density (ρ_b) at 0 to 10 cm and 10 to 20 cm depths and, in general, increased soil water retention (SWR), total porosity, and quasi-steady infiltration rate (Northern-Brookings only) compared to the NC. Cattle grazing of CC generally increased ρ_b and reduced SWR and porosity compared with the ungrazed CC but not to the often-perceived detrimental levels. Our findings showed that CCs can improve some aspects of soil physical health in the short term and that grazing of CCs and crop residue did not cause substantial physical damage to the soil under the conditions of these experiments.

The Effects of Windthrow Damage on Soil Properties in Scots Pine, Black Pine and Kazdağı Fir Stands in the Northwest Turkey

Aim of study: The short-term effects of windthrow damage on soil properties were investigated in Kazdağı fir (Abies nordmanniana subsp. equi-trojani), Scots pine (Pinus sylvestris L.) and black pine (Pinus nigra Arnold.) stand in northwest Turkey. Area of study: The study was carried out in Kastamonu and Sinop regions. Material and methods: In order to understand the effects of windthrow damage occurred in 2013, soil samples were collected at a depth of 0-30 cm from the disturbed and undisturbed sites in 2018 (5 year later), and analyzed for soil physical and chemical properties. Main results: The increases in temperature, wind speed and heavy rainfall in the study sites seemed to result in the windthrows. There were significant differences in soil physical and chemical properties among the three tree species, and also between the disturbed and the undisturbed sites. Highlights: After the windthrows, increased SOC and TN stocks, P and K could be related to the accumulation of organic matter. However, we were not able to identify a single mechanism to explain this observed relationship. Thus, the root-soil interactions of the three tree species should be conclusively examined in future studies in order to define the relationships between soil chemical properties and root features.

Do tree species affect decadal changes in soil organic carbon and total nitrogen stocks in Danish common garden experiments?

AbstractTemperate forest soils are often considered as an important sink for atmospheric carbon (C), thereby buffering anthropogenic CO2 emissions. However, the effect of tree species composition on the magnitude of this sink is unclear. We resampled a tree species common garden experiment (six sites) a decade after initial sampling to evaluate whether forest floor (FF) and topsoil organic carbon (Corg) and total nitrogen (Nt) stocks changed in dependence of tree species (Norway spruce—Picea abies L., European beech—Fagus sylvatica L., pedunculate oak—Quercus robur L., sycamore maple—Acer pseudoplatanus L., European ash—Fraxinus excelsior L. and small‐leaved lime—Tilia cordata L.). Two groups of species were identified in terms of Corg and Nt distribution: (1) Spruce with high Corg and Nt stocks in the FF developed as a mor humus layer which tended to have smaller Corg and Nt stocks and a wider Corg:Nt ratio in the mineral topsoil, and (2) the broadleaved species, of which ash and maple distinguished most clearly from spruce by very low Corg and Nt stocks in the FF developed as mull humus layer, had greater Corg and Nt stocks, and narrow Corg:Nt ratios in the mineral topsoil. Over 11 years, FF Corg and Nt stocks increased most under spruce, while small decreases in bulk mineral soil (esp. in 0–15 cm and 0–30 cm depth) Corg and Nt stocks dominated irrespective of species. Observed decadal changes were associated with site‐related and tree species‐mediated soil properties in a way that hinted towards short‐term accumulation and mineralisation dynamics of easily available organic substances. We found no indication for Corg stabilisation. However, results indicated increasing Nt stabilisation with increasing biomass of burrowing earthworms, which were highest under ash, lime and maple and lowest under spruce.Highlights We studied if tree species differences in topsoil Corg and Nt stocks substantiate after a decade. The study is unique in its repeated soil sampling in a multisite common garden experiment. Forest floors increased under spruce, but topsoil stocks decreased irrespective of species. Changes were of short‐term nature. Nitrogen was most stable under arbuscular mycorrhizal species.

Carbon and nitrogen stocks through time in abandoned croplands of the Comarca Lagunera, Mexico

Croplands in the Comarca Lagunera region of Mexico are undergoing abandonment due to water scarcity. The effects of vegetation succession following cropland abandonment on soil organic carbon (SOC) and total nitrogen (STN) stocks have been poorly studied although such effects have important implications for terrestrial carbon pools and the global carbon cycle. This study sought to determine the organic carbon and total nitrogen content in soil at two depths (0–30 cm and 30–60 cm) and the successional biomass with a chronosequence of 2, 15, 25, and 35 years of restoration after cropland abandonment, as well as uncultivated areas of native microphyllous desert scrub vegetation used as reference (Ref). Results revealed that the ecological succession 35 years after cropland abandonment resulted in high dominance by the species Prosopis glandulosa. Because of that, the latest stage since cropland abandonment (35 years) contained about three times more carbon and nitrogen (2.64 Mg C ha−1 and 0.62 Mg N ha−1, respectively) in aboveground biomass than reference areas (0.94 Mg C ha−1 and 0.21 Mg N ha−1, respectively). In contrast, soil carbon tended to decrease as years of abandonment increased. Thus, areas with 35 years of abandonment, although having high aerial carbon content, had the lowest soil carbon accumulation. Soil organic carbon and total nitrogen content showed no significant differences between the sampling depths in the investigated sites during the restoration time. These findings suggest that soil carbon accumulation after cropland abandonment through unmanaged ecological succession is difficult to achieve in this area.

Grassland management strategies influence soil C, N, and P sequestration through shifting plant community composition in a semi-arid grasslands of northern China

Current studies regarding the effects of grassland management strategies on the soil nutrient cycle have mostly focused on soil organic carbon (SOC). Less is known about the responses of SOC, total nitrogen (TN), and total phosphorous (TP) stocks to grassland management strategies at different soil depths. We therefore quantified vertical variations in SOC, TN, and TP stocks as well as controlling factors under three grassland management strategies (i.e., enclosure control, grazing twice a year, grazing combined with mowing) in 2014 and 2017 in a semi-arid grassland of northern China. We found that grazing twice a year and grazing combined with mowing led to an increase in plant production as well as soil C and N sequestration during 2014 to 2017. Changes in plant aboveground biomass (AGB), belowground biomass (BGB), and root-to-shoot ratio (R:S) all exerted significant positive effects on changes in soil C and N sequestration in the surface soil layer (0–30 cm), while changes in AGB and plant community composition played a more important role in mediating soil C, N, and P sequestration in response to grassland management strategies in the subsoil layer (30–100 cm). Specifically, grassland management strategies influence soil C, N, and P sequestration capacity by altering plant community composition. The results of this study provide new insights into the response mechanisms of plants and soils to grassland management practices and offer a range of new possible strategies that might be applied to the effective management of semi-arid grasslands.

Effects of different continuous fertilizer managements on soil total nitrogen stocks in China: A meta-analysis

Soil total nitrogen is critical for crop productivity and related to agricultural managements. However, the effects of different fertilizer applications on soil total nitrogen storage are not well understood. To quantify soil total nitrogen storage under different fertilizer management practices and explore the effects of climate, soil texture, experimental duration, and cropping system on soil total nitrogen storage in China, we conducted a meta-analysis of 67 fertilizer management strategies from experiments conducted over a period of at least three years. This meta-analysis included 854 observations of changes in soil total nitrogen stock (TNS) under no fertilizer application (control, CK), chemical fertilization with nitrogen, phosphorus, and potassium (CF), CF plus straw retention (CFS), and CF plus manure addition (CFM) relative to initial soil TNS. The CFM and CFS treatments increased soil TNS, and the CFM treatments increased soil C/N ratio the most. The longer the experimental duration, the greater the increase in soil TNS in the CF, CFS, and CFM treatments. Soil texture and crop type significantly affected the changes in soil TNS. The experimental duration, initial soil TNS, soil C/N ratio, and cropping system had significant linear correlations with the change in soil TNS. Temperature and precipitation were not correlated with soil TNS. Results of random forest modeling indicated that the most important factor affecting changes in soil TNS was experimental duration (positive correlation), followed by initial soil TNS (negative correlation). The CFM treatments had the largest increase in soil TNS under various conditions. We recommend promoting CFM to improve soil fertility in farmlands globally.

A progressive simulation method to estimate the stocks of surface soil organic carbon and total nitrogen in an estuarine archipelago

Simulating the soil organic carbon (SOC) and total nitrogen (TN) stocks in estuarine areas is important for the development of digital soil mapping and the regional inventory of carbon and nitrogen, and simulation accuracy is the key issue. In this study, a progressive simulation method was proposed to further improve accuracy through the adequate utilization of the correlations among soil parameters and their relations with the comprehensive land surface factor system. Three soil parameters, namely, SOC, TN, and bulk density (BD), were simulated using the method for estimating SOC and TN stocks. The simulations were progressively conducted in three levels (Levels 1–3) by using partial least squares regression (PLSR) and cokriging. Each of the parameters was simulated separately in Level 1, one parameter was simulated based on each of the two other parameters in Level 2, and one parameter was simulated based on the two other parameters in Level 3. A typical estuarine archipelago in southern China was selected to demonstrate the performance of the method in surface soil (0–20 cm). Results showed the effectiveness of the progressive simulation in improving accuracy when the PLSR was used. The simulation results in Level 3 had the highest accuracy among the results in all levels, increasing the accuracies for SOC, TN, and BD by 54.35%, 57.24%, and 5.61%, respectively, compared with those in Level 1 and achieving high accuracies compared with those in similar studies. The SOC and TN stocks amounted to 270.66 and 26.96 Gg, respectively, and the mean values of SOC and TN densities were 2.65 and 0.26 kg/m2, respectively, which are lower than global values and those for China. The SOC and TN densities exhibited distinct spatial heterogeneities, which were fundamentally driven by different types of island exploitations and large-scale sea reclamation activities.

Spatial and temporal dynamics of soil organic carbon stock and carbon sequestration affected by major land-use conversions in Northwestern highlands of Ethiopia

Soil organic carbon (SOC) is the major component of the terrestrial carbon (C) budget, a key indicator of environmental sustainability. So, estimating SOC stock and soil carbon (C) sequestration dynamics is important for evidence-based and carbon-conscious decisions. Quantification of SOC stock and soil C sequestration affected by land-use changes (LUCs) have received much attention in addressing food and climate security. This study aims to estimate the dynamics of SOC stock, soil C sequestration and associated soil parameters affected by major LUCs from 2012 to 2021 in Awi highlands of Amhara Regional State of Ethiopia. The study area has experienced dramatic LUC, particularly plantation and growing of Acacia decurrens (J.C. Wendl.) tree followed by recurrent deforestation and then cropping and back to the plantation. The study quantified spatial and temporal dynamics of SOC stock, soil C sequestration and associated changes affected by the LUCs. A total of 22 topsoil (0–20 cm) legacy data was obtained from the Ethiopian Soil Information System (EthiSIS) database of 2012. The same number of samples were collected at the same locations in 2021 by using the same sampling procedure as that of 2012. In addition, the same number of core samples were collected in 2021 for bulk density analysis. To estimate the unmeasured bulk density of legacy data, we applied a pedotransfer function. We used empirical equations and basic statistics to assess changes in SOC stock and C sequestration rate between the two periods. Statistically significant variation (P < 0.01) in SOC stock and C sequestration was observed between the two periods. LUC from acacia plantation to croplands caused a decline of SOC stock by −30.16%, and it also caused the decline of total nitrogen stock, available phosphorus, cation exchange capacity (CEC). However, the reverse LUC caused an increase in SOC by 27.74% and the abovementioned soil parameters. LUC from plantation forest to cropland caused emission of 8.3 tons of CO2 year−1. Generally, overall LUCs caused the net negative change in SOC stock by (−2.42 %) and associated soil parameters in the last ten years. Our study provides evidence that overall LUCs in the current study site caused a decline in SOC stock, along with associated soil parameters with carbon emitted to the atmosphere. Hence, sustainable land-use management options which can offset losses in SOC stock should be implemented soon.