Soil Total C Research Articles

Coastal conversion alters topsoil carbon, nitrogen and phosphorus stocks and stoichiometric balances in subtropical coastal wetlands

The extensive conversion of coastal wetlands into agricultural and aquaculture areas has significant repercussions on soil nutrient balance. However, how coastal conversion specifically influences the dynamics and stoichiometry of topsoil carbon (C), nitrogen (N), and phosphorus (P) remains limited due to the considerable spatial variability and a lack of comprehensive field data. Here, we investigated the concentration and distribution of total C (TC), N (TN) and P (TP), along with their stoichiometric balance in four distinct coastal landscapes, including natural marshes and tidal flats, as well as converted agricultural croplands and ponds. The results revealed that converted croplands and ponds exhibited significantly higher concentrations of soil C, N and P, particularly in comparison to tidal flats. Furthermore, croplands and ponds have higher topsoil C stocks than tidal flats, but little difference or even lose stored C compared to marshes. Cropland soils showed considerably higher levels of available N (NH4+-N and NO3−-N) and available P compared to those in natural marshes and tidal flats. The distribution of soil TC, TN, and TP demonstrated greater spatial heterogeneity in natural marshes and tidal flats, while the converted areas were more uniform and became hotspots for N and P accumulation. Coastal conversion altered soil C:N:P stoichiometry, with cropland soils exhibiting a lower N:P ratio (2.9 ± 1.1), indicating that long-term application of N and P fertilizers could decrease the N:P ratio, as P is more retained in the soil than N. Furthermore, it was observed that the dynamics of C, N and P, as well as their stoichiometry, are closely linked to soil physicochemical properties, especially soil organic matter and texture. These findings highlight that coastal conversion and associated management practices markedly affected soil C, N and P dynamics in a representative wetland area of the subtropical regions, leading to a reshaping of their stoichiometric balances, particularly in the topsoil layer.

Soil total carbon and nitrogen under long‐term perennial bioenergy crops receiving various nitrogen fertilization rates

AbstractPerennial crops may sequester greater soil carbon (C) and nitrogen (N) than annual crops due to higher root biomass production, but the potential of long‐term cultivation of perennial bioenergy crops receiving various N fertilization rates in sequestering C and N needs further exploration. Soil samples (0–120 cm) collected from 2009 to 2019 under perennial bioenergy crops receiving various N fertilization rates and an annual crop were analyzed for soil total C (STC) and N (STN) in the US northern Great Plains. Perennial bioenergy crops were intermediate wheatgrass (IW, Thinopyrum intermedium [Host] Barkworth and Dewey), smooth bromegrass (SB, Bromus inermis L.), and switchgrass (SG, Panicum virgatum L.); N fertilization rates were 0, 28, 56, and 84 kg N ha−1, and annual crop was spring wheat (WH, Triticum aestivum, L.). The STC increased, but STN decreased by soil depth, regardless of treatments and years. At 0–120 cm, IW sequestered C at 10.6 Mg C ha−1 year−1 compared with 5.4–6.8 Mg C ha−1 year−1 for SB and SG from 2009 to 2019. Nitrogen fertilization rate had limited effect on STC and STN. At 0–30 cm, STC was 2.0–5.4 Mg C ha−1 greater and STN 0.10–0.24 Mg N ha−1 greater with perennial bioenergy crops than WH. Long‐term cultivation of IW can sequester more C in the soil to a greater depth than SB and SG and perennial bioenergy crops can sequester more C and N at the surface layer than an annual crop in the semiarid region of the US northern Great Plains.

Integration of pelleted biosolids with cover crops for improving soil properties

AbstractMeasuring and assessing soil properties is critical for understanding how changes in agronomic practices affect the capability of soil to support cropping systems. A field study was conducted on a Marietta silt loam soil at the Plant Science Center at Mississippi State University to determine the effects of pelleted biosolids (PBS) relative to poultry litter (PL) and inorganic N fertilizer applied to corn (Zea mays L.) and cotton (Gossypium hirsutum L.) in the presence of winter wheat (Triticum aestivum L.) cover crop (WCC) and winter fallow (WF) on soil properties. Experimental design was a split‐plot randomized complete block with three replications. The whole plots were WCC and WF and the subplots were fertilization. Fertilization treatments included PBS and PL at 11.2 Mg ha–1 and 6.7 Mg ha–1 applied to corn and cotton, a one‐time single application at 37 Mg PBS ha–1 to corn in 2016, inorganic N fertilizer at the recommended rate, and an unfertilized control. Soil cores were collected after harvest and analyzed for nutrient concentrations, water stable aggregate (WSA), and enzyme activities. The WCC reduced bulk density (ρb) and penetration resistance (PR) and increased soil total C (TC), WSA, and infiltration rate, as compared with winter fallow (WF). Relative to inorganic N fertilizer, application of PBS decreased soil ρb and PR by 3 and 20%, respectively, and increased soil TC, WSA, and infiltration by 19, 23, and 45%, respectively. A combination of PBS and WCC improved soil physical and chemical properties under southeast agroecosystems.

A comparative study of soil processes in depletion and accumulation zones of permafrost landslides in Siberia

Landslides are one of the main reasons for permafrost degradation in high latitudes. Any landslides consist of different top-down slope zones: removal, transit-depletion, and accumulation zones. These slope parts can demonstrate different successional behavior of plant community and carbon (C) cycling during post-sliding seral stages. To address this issue, soil respiration (SR), hydrothermal conditions (mineral soil temperature at a depth of 5 cm (ST5, °C), and gravimetric soil water content at a depth of 0–5 cm in mineral soil horizon (SWC5, %)), total soil C (TC) and nitrogen (TN) contents, and soil microbial activity at the middle (depletion zone) and lower (accumulation zone) slope parts of the landslides with different history have been studied. The most significant differences between the middle and lower slope positions were found at the ground microsites (or G-plots) of the L2001 landslide. Thus, here, a midslope part occurred to be a high source of C compared to the lower part. Midslope of L2001 was characterized by significantly higher SR at G-plots as well because of better hydrothermal conditions and more intensive vegetation regeneration. The accumulation zone of L2001 characterized by the lower SR despite significantly higher microbial activity due to the high nutrient level of the soil moved from the top, likely favored to promotion of the soil C stabilization processes. Despite the registered ST5 differences in the E-plots and the G-plots between middle and lower slope positions of the L1972 landslide, SR, TC, TN, and soil microbial activity did not differ significantly.

Soil Carbon Change Due to Land Conversion to Grassland in a Semi-Arid Environment

A 5-year study evaluated the change in the quantity of soil total C (STC), soil organic C (SOC), and soil inorganic C (SIC) stored in the surface 60 cm of the soil profile on two adjacent blocks of land with a long-term history of cropping (CH) or undisturbed grassland (NH) on similar soil types between 1999 and 2004. The NH area was tilled and a grass-legume species mix was seeded into plots on both the NH and the CH areas. Selected plots of restored grass were established so they could be grazed (GG) by livestock while other plots were left ungrazed (UG). Original undisturbed (and ungrazed) grassland plots within the NH area were used as a control treatment. Initially, STC and SOC in CH were lower than NH when compared under the semi-arid environmental conditions found in southwestern North Dakota. Over the study period, the undisturbed grass control plots had increases in STC and SOC levels in the soil profile of 3.90 kg·m−2 and 3.34 kg·m−2, respectively. Restored grass on the NH area with grazing showed increases in STC and SOC values of 2.11 and 1.26 kg·m−2, respectively, while without grazing, profile STC and SOC had values of 3.80 and 3.28 kg·m−2, respectively. Restored grass on the CH area showed increases in profile STC and SOC values of 0.55 and 1.96 kg·m−2, respectively, for the grazed plots and 0.78 and 2.11 kg·m−2, respectively, when left ungrazed. Soil inorganic C, though present in the soils, did not significantly change during the study. The lower C accumulation in the CH plots may be due to a lag time in the establishment of mycorrhizal associations with the seeded species, the inoculums of which were already present in the NH soils. Changes in STC were likely due to changes in water relationships in the soil profile where management changes affected water infiltration and its movement causing leaching of SIC below the 60 cm depth evaluated. Soils under undisturbed grassland continue to accumulate carbon while soils of the disturbed grassland or cropped prior to re-establishing grass showed losses that occurred due to either accumulating C at a lower rate or perhaps to C loss during the initial establishment period (1–2 years).

Sheep grazing to control weeds enhances soil carbon, not nitrogen

Sheep (Ovis aries L.) grazing on weeds and crop residue during the fallow period may enhance soil carbon (C) and nitrogen (N) through urine and faeces returned to the soil. We compared sheep grazing, tillage, and herbicide application as weed management practices on soil total C (STC), total N (STN), ammonium (NH4+)-N, and nitrate (NO3–)-N contents in a dryland 5-year crop rotation from 2012 to 2015 in the northern Great Plains, USA. The treatments were sheep grazing with no chemical input in organic crop production (GO), minimum tillage with chemical inputs (MT), and conventional tillage with no chemical input in organic crop production (TO). The 5-year crop rotation was safflower (Carthamus tinctorius L.)/sweet clover (Melilotus officinalis L.) cover crop–sweet clover cover crop–winter wheat (Triticum aestivum L.)–lentil (Lens culinaris L.)–winter wheat. At the 0–1.20 m depth, STC was 14–20 Mg C ha–1 greater in GO than MT and TO, but STN was 2.1–2.2 Mg N ha–1 greater in TO than GO and MT. The NH4+-N and NO3–-N contents were 5–21 kg N ha–1 greater in MT than GO and TO. While STC and STN tended to increase with year for all treatments, NH4+-N and NO3–-N contents varied with treatments and years. Sheep grazing enhanced soil C storage, but had a variable effect on N storage and residual N compared to tillage and herbicide application for weed control.

Effects of different management approaches on the stoichiometric characteristics of soil C, N, and P in a mature Chinese fir plantation

Carbon (C), nitrogen (N), and phosphorus (P) are commonly used to evaluate soil quality. However, still little is known about the effects of human activities on soil C, N, and P. In this study, we compared the stoichiometric characters of soil C, N, and P in a mature Chinese fir (C. lanceolata) plantation under four forest management approaches: uncut as a control (NC), clear-cutting (CC), controlled burning after clear-cutting (CCB) and conversion into a tea garden (TG). We measured the total C (TC), total N (TN), and total P (TP) contents and evaluated the ratios of C:N, C:P, N:P, and C:N:P in each treatment. The results showed that: (1) the contents of TC and TN in all management approaches decreased with increasing soil depth, while the TP content in NC, CC, and CCB decreased at first, then increased. More importantly, there was no significant difference in TP content under the four management approaches. (2) The ratios of C:N, C:P, N:P, and C:N:P decreased with increasing soil depth. Interestingly, the ratio of C:N was lower than that of C:P in every management approach. (3) Despite the different management approaches (NC, CC, CCB, and TG), the ratios of soil C:N:P were relatively stable, which were 24:4:1, 26:4:1, 21:3:1, and 21:3:1, respectively. CCB showed the greatest negative effect on soil TC, TN, and TP contents, suggesting it might be beneficial to avoid this approach for Chinese fir management.

Response of carbon and nitrogen to afforestation from 0 to 5 m depth on two semiarid cropland soils with contrasting inorganic carbon concentrations

Soil carbon (C) and nitrogen (N) combining with physical and chemical properties play important roles in terrestrial C and nutrient cycling; however, how C and N in deep soils respond to land-use change is less understood, hindering the precise evaluation of soil C dynamics and budgets. Here, we present results regarding soil C, N and related soil properties at 0–500 cm depth as affected by afforestation at two sites (Fufeng and Yongshou) with contrasting soil inorganic C (SIC) levels in China's Loess Plateau. The concentrations of SIC ranged from 12.94 to 20.17 g kg−1 in Fufeng and from 0.18 to 0.36 g kg−1 in Yongshou. The objectives of this study were to examine how soil C and N in deep soils are altered following afforestation and how these effects vary with soil depth and site. We found that the establishment of woodland on cropland increased soil porosity and saturated hydraulic conductivity but decreased the bulk density in the topsoils (0–20 cm). The conversion of cropland to woodland resulted in an increase of soil electric conductivity in the topsoils and a decrease in the deep soils in Fufeng but had an opposite influence with soil depth in Yongshou. This land-use change increased organic C and total N concentrations along the 0–500 cm soils at both sites but had divergent effects on the concentrations of SIC and soil total C (STC) between the two sites. Overall, the concentrations of SIC and STC increased in Yongshou but decreased in Fufeng after woodland establishment. The results from this study indicated the determination of the initial SIC concentration on the response of C to afforestation in semiarid soils, and such determination should be considered in biogeochemical models.

Soil C and N stocks of Alfisols under native tallgrass prairie in the mid-Southern, USA

The objective of this study was to evaluate the effects of soil moisture regime (i.e., aquic and udic) and physiographic region (i.e., Ozark Highlands of northwest Arkansas and Grand Prairie region of east-central Arkansas) on the change in soil carbon (C) and nitrogen (N) storage and other soil properties over a 15-year period. Soil samples were collected from the top 10 cm in 2001/2002 and again in 2016/2017 and the change over time was directly quantified for numerous soil properties. Averaged across soil moisture regime, TC content and concentration, C:N ratio, and TC fraction of soil organic matter all increased (P < 0.05) over time in the Ozark Highlands, as well as the Grand Prairie region, with the exception of total C (TC) content and concentration, which both decreased in the Grand Prairie. Despite the Grand Prairie region losing soil C at a rate of 0.23 Mg ha−1 yr−1 or 0.02% yr−1 over the 15-year duration of this study, soil C storage in 2016 did not differ between physiographic regions when averaged across soil moisture regime. The TC fraction of SOM changed more over time (P < 0.01) in the Ozark Highlands under aquic soil moisture conditions (1.3% yr−1) compared to the other three soil moisture regime/region combinations. This study demonstrates the value of direct measurements over time for assessing temporal changes in soil properties so that results can be used to guide expectations of the effects of physiographic region and soil moisture regime for future restoration activities to be as successful as possible.

Soil extractable organic C and N contents, methanotrophic activity under warming and degradation in a Tibetan alpine meadow

The Tibetan alpine meadow ecosystem is an important part of the Eurasian grasslands and is experiencing intense warming at approximately three times the global warming rate and rapid degradation. However, little is known about the effect of warming and degradation and their interactions on ecosystem functions like soil carbon (C) and nitrogen (N) pools and methane (CH4) uptake in this region. Here, we selected a long-term simulated warming site in a Tibetan alpine meadow with different degradation levels. After 4 years of warming, we analyzed soil total C (TC) and total N (TN) contents, extractable organic C (EOC) and extractable organic N (EON) contents as well as methanotrophic activity, abundance and community structure. Soil EOC and EON contents were measured through hot water extraction, whereas methanotrophic activity was measured along a gradient of CH4 concentrations in laboratory incubations. Michaelis–Menten kinetics analysis [maximal rate of velocity (Vmax) and half-saturation constant (Km)] was used to quantify changes in methanotrophic activity among the treatments. Active methanotrophic communities in the natural soils were measured via DNA-based stable isotope probing (SIP). The results showed that warming significantly increased soil EON contents, whereas degradation significantly decreased soil TC and TN contents, and EOC and EON contents. Methanotrophic activity was significantly lower at different levels of degradation but no significant effects were observed under warming. Changes in soil methanotrophic abundance among the treatments followed the same trend, but warming and degradation had no interactive effects on methanotrophic activity and abundance. Active methanotrophic communities in the natural meadow soils were dominated by Methylosinus (a Type II methanotroph). In conclusion, our results indicate that soil C and N pools and CH4 oxidation capability were influenced more strongly by degradation than warming. However, warming may have an additional effect on the stability of these important ecosystem processes, regardless of degradation in this region.

Short-Term Nitrogen Addition Does Not Significantly Alter the Effects of Seasonal Drought on Leaf Functional Traits in Machilus pauhoi Kanehira Seedlings

Research Highlights: Short-term nitrogen (N) addition did not significantly alter the effects of seasonal drought on the leaf functional traits in Machilus pauhoi Kanehira seedlings in N-rich subtropical China. Background and Objectives: Seasonal drought and N deposition are major drivers of global environmental change that affect plant growth and ecosystem function in subtropical China. However, no consensus has been reached on the interactive effects of these two drivers. Materials and Methods: We conducted a full-factorial experiment to analyze the single and combined effects of seasonal drought and short-term N addition on chemical, morphological and physiological traits of M. pauhoi seedlings. Results: Seasonal drought (40% of soil field capacity) had significant negative effects on the leaf N concentrations (LNC), phosphorus (P) concentrations (LPC), leaf thickness (LT), net photosynthetic rate (A), transpiration rate (E), stomatal conductance (Gs), and predawn leaf water potential (ψPD), and significant positive effects on the carbon:N (C:N) ratio and specific leaf area (SLA). Short-term N addition (50 kg N·hm−2·year−1 and 100 kg N·hm−2·year−1) tended to decrease the C:N ratio and enhance leaf nutrient, growth, and photosynthetic performance because of increased LNC, LPC, LT, leaf area (LA), SLA, A, E, and ψPD; however, it only had significant effects on LT and Gs. No significant interactive effects on leaf traits were detected. Seasonal drought, short-term N addition, and their interactions had significant effects on soil properties. The soil total C (STC), nitrate N (NO3−-N) and soil total N (STN) concentrations were the main factors that affected the leaf traits. Conclusions: Seasonal drought had a stronger effect on M. pauhoi seedling leaf traits than short-term N deposition, indicating that the interaction between seasonal drought and short-term N deposition may have an additive effecton M. pauhoi seedling growth in N-rich subtropical China.

Variations in Soil Bacterial Community Diversity and Structures Among Different Revegetation Types in the Baishilazi Nature Reserve.

We compared patterns of soil bacterial community diversity and structure in six secondary forests (JM, Juglans mandshurica; QM, Quercus mongolica; MB, mixed Broadleaf forest; BE, Betula ermanii; CB, conifer-broadleaf forest; PT, Pinus tabuliformis) and two plantation forests (LG, Larix gmelinii; PK, Pinus koraiensis) of the Baishilazi Nature Reserve, China, based on the 16S rRNA high-throughput Illumina sequencing data. The correlations between the bacterial community and soil environmental factors were also examined. The results showed that the broadleaf forests (JM, QM, MB) had higher levels of total C (TC), total N (TN), available N (AN), and available K (AK) compared to the coniferous forests (PT, LG, PK) and conifer-broadleaf forest (CB). Different revegetation pathways had different effects on the soil bacterial community diversity and structure. For the α-diversity, the highest Shannon index and Simpson index were found in JM. The Simpson index was significantly positively correlated with the available P (AP) (P < 0.05), and the Shannon index was significantly positively correlated with AK (P < 0.05). Compared with others, the increased ACE index and Chao1 index were observed in the CB and MB, and both of these α-diversity were significantly negative with AK (P < 0.05). The relative abundances of bacterial phyla and genera differed among different revegetation types. At the phylum level, the dominant phylum groups in all soils were Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia, Chloroflexi, Bacteroidetes, Gemmatimonadetes, and Planctomycetes. Significant differences in relative abundance of bacteria phyla were found for Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, and Proteobacteria. Correlation analysis showed that Soil pH, TC, TN, AP, and AK were the main abiotic factors structuring the bacterial communities. As revealed by the clear differentiation of bacterial communities and the clustering in the heatmap and in the PCA plots, broadleaf forests and coniferous forests harbored distinct bacterial communities, indicating a significant impact of the respective reforestation pathway on soil bacterial communities in the Baishilazi Nature Reserve.

Soil total carbon and nitrogen and crop yields after eight years of tillage, crop rotation, and cultural practice

Information on the long-term effect of management practices on soil C and N stocks is lacking. An experiment was conducted from 2004 to 2011 in the northern Great Plains, USA to examine the effects of tillage, crop rotation, and cultural practice on annualized crop residue (stems + leaves) returned to the soil and grain yield, and soil total C (STC) and total N (STN) stocks at the 0–120 cm depth. Tillage practices were no-tillage (NT) and conventional tillage (CT) and crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat-pea (Pisum sativum L.) (W-P), spring wheat-barley (Hordeum vulgaris L.) hay-pea (W-B-P), and spring wheat-barley hay-corn (Zea mays L.)-pea (W-B-C-P). Cultural practices were traditional (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and improved (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height). Crop residue and grain yield were greater with CW and W-P than W-B-P and grain yield was greater with the traditional than the improved practice. The STC at 10–20 and 90–120 cm was greater with CW or W-P than other crop rotations in CT and greater with CW than W-B-P in NT. The STN at 20–40 cm was greater with W-P than CW and W-B-P in CT. With NT and the improved cultural practice, STN at 0–5, 5–10, 20–40, and 60–90 cm was greater with W-P and W-B-C-P than other crop rotations. The STN at 0–10 cm correlated with annualized crop residue and grain yield (r = 0.94–0.97, P ≤ 0.05). Increased crop residue returned to the soil increased soil C stock with CW and W-P and N stock with W-P, but removal of aboveground crop biomass for hay decreased stocks with W-B-P. Increased soil N stock had a beneficial effect on crop grain yield.

Root and soil total carbon and nitrogen under bioenergy perennial grasses with various nitrogen rates

As aboveground biomass of perennial grasses is harvested for feedstock or bioenergy production, root biomass C and N become primary C and N inputs for enhancing soil C and N sequestration. Information is scanty about root biomass C and N and subsequent soil C and N stocks under bioenergy perennial grasses applied with various N fertilization rates in semiarid regions. We evaluated the effect of perennial grass species and N rates on root biomass C and N and soil total C (STC) and total N (STN) stocks at the 0–120 cm depth from 2011 to 2013, 2–4 yr after grass establishment, in the northern Great Plains, USA. Perennial grasses were intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth and Dewey), smooth bromegrass (Bromus inermis L.), and switchgrass (Panicum virgatum L.), and N fertilization rates were 0, 28, 56, and 84 kg N ha−1. Root biomass C and N at 0–15 and 0–120 cm were greater with intermediate wheatgrass and switchgrass than smooth bromegrass in 2011, but the trend reversed for root biomass C at 0–15 cm in 2012. Root biomass C at both depths among N rates and years. The STC at 0–15, 30–60, and 0–120 cm also varied among grass species and years. At 30–60 cm, STC increased with increased N rates under intermediate wheatgrass and switchgrass, but decreased under smooth bromegrass. At 60–90 cm, the trend for STC reversed. The STN at 15–30 cm was greater under intermediate wheatgrass than smooth bromegrass and switchgrass and at most depths was greater in 2012 than 2013. Overall root biomass C and N at 0–120 cm were 12–16 times greater and STC and STN 8–9% greater under perennial grasses than adjacent annual spring wheat. Although intermediate wheatgrass returned more root C and N to the soil than other grasses, both STC and STN varied among grass species and N rates. Increased root C and N inputs, however, increased STC and STN under perennial grasses compared with annual spring wheat.

Assessment of carbon pools in Inceptisol under potato (Solanum tuberosum) based cropping systems in Indo-Gangetic plains

Soil carbon pools play a major role in sustaining agro-ecosystems and maintaining environmental quality as they act as a major source and sink of atmospheric carbon. The long-term effect of manuring and fertilization on accessibility of carbon pools of soil in high intensity rice (Oryza sativa L.)−potato (Solanum tuberosum L.)−wheat (Triticum aestivum L.) and maize (Zea mays L.) −potato−onion (Allium cepa L.) cropping systems in Inceptisol of semi-arid sub-tropical India continuing for 10 years was studied. Soil samples were collected (0-15 and 15-30 cm soil depth) from the treatments comprising control (T1), 100% NPK-Fertilizer (T2), 100% N-Vermicompost (VC) (T3), 50% NPK-Fertilizer + 50% N-Vermicompost (VC) (T4), 100% NPK-Fertilizer + crop residue (CR) (T5), 100% N-Vermicompost + CR (T6). Assessment of carbon pools was done by estimating total soil C (TSC), total soil nitrogen (TSN), C:N ratio, carbon mineralization (Cmin), total polysaccharide (TP) and relationship between these pools. The results showed that the application of 100% N-VC (T3) and 100% N-VC + CR (T6) increased the TSC by 94% and 80%, respectively, over 100% NPK in rice-potato-wheat cropping system, while in maize-potato-onion system, 100% N-VC (T3) increased TSC by 48% over 100% NPK (T2) at 0-15 cm soil depth. The soil C:N ratios were generally wider in case of treatments receiving organic sources. In both the soil depths, the T6 treatment (100% N-VC + CR) had resulted higher C mineralization than the other treatments throughout the incubation period. The stable C was lower in maize–potato–onion system than that in the rice–potato–wheat system. The total polysaccharides was higher in organic amended treatments (T6, T3) over chemical fertilizer treatments in improving the TP content in soil which was related to greater C input.

Impact of fertilization on soil polyphenol dynamics and carbon accumulation in a tea plantation, Southern China

The strong role that soil polyphenols play in soil organic matter (SOM) formation affects soil carbon sequestration. N deposition, which comes from man-made fertilizer, influences plant growth and soil biochemical properties therefore greatly regulates soil polyphenol metabolism. The objective of this experiment was to understand the effect of fertilizer form and rate on soil polyphenol dynamics as well as to understand the potential relationship between soil phenols and C accumulation. Urea, rapeseed cake, and chicken manure, respectively, referred as N, B, and F in the text, were applied at three rates (low N, medium N, and high N, referred as 1, 2, and 3 in the text, respectively); plots without fertilization were set as control (CK, for short). Seasonal dynamics of soil total polyphenol (Tp) and bound polyphenol (Bp) concentrations were monitored. Polyphenol oxidase (PPO), peroxidase (POD), and soil fluorescein diacetate (FDA) hydrolysis activities, all factors relevant to polyphenol metabolism, were measured simultaneously. The relationship between soil polyphenols and soil C concentration was also determined. N-fertilization altered the seasonal change pattern and the accumulation level of soil Tp and Bp, which possibly resulted from the enhancement of soil microbial activities and the change of soil nutrient status. Positive linear correlation was observed between soil Tp and TC (total C) contents, which means fertilization could influence C accumulation through affecting the metabolism of soil polyphenols. Soil chemical characteristics and enzyme activities that relate to soil polyphenol metabolism were influenced by fertilization as well. Mitigated TC increment was observed in most fertilization treatments mainly due to the increased SOM decomposition rate. Our findings reveal the important role of soil phenols played in C accumulation in a tea plantation due to the significant, positive linear relationship between soil Tp and TC. Long-term studies, combined with soil microorganism community structure, soil humification, and tea leaf litter decomposition experiments, are necessary for fully understanding the role that polyphenols play in soil C cycle.

Effect of Mixed Liquid Fertilization on Growth Responses of Red peppers and Soil Chemical Properties

We evaluated the effect of mixed liquid fertilizer (MLF) on growth responses of plants and soil chemical properties. A pot experiment with red pepper (Capsicum annuum L.) using loam soil was conducted for 81 days in a temperature-controlled glasshouse, and four N fertilization treatments were laid out in a completely randomized design with three replicates: control (C), chemical fertilizer treatment (CF), and two rates (MLF-0.5 and MLF-1.0) of MLF treatment. Soils were periodically sampled and analyzed for pH, EC(Electrical Conductivity), total N, inorganic N and total C, and some growth characteristics of red peppers were measured. During the experimental periods, the pH of MLF soils was higher than that of CF soils. Soil EC increased right after application of CF or MLF, and the intial increase persisted in CF and MLF soils at the end of experiment. Soil total-N increased right after application of CF or MLF, and this initial increase persisted only in MLF-1.0 soils. Soil inorganic N content initially increased in CF or MLF-1.0 soils, but the initial increase disappeared in 56 days after transplanting. Soil total-C was maintained higher in MLF-1.0 soils and lower in CF soils than in control soils, and the intial increase in MLF-1.0 soils finally disappeared to the level of control soils. Plant height, dry weight of plant organs (shoots, roots and fruit), and the number, diameter and length of red pepper fruits were greatest in CF plants. On the other hand, the effect of MLF-application was different depending on the rate of application. However, no consistent effect of N treatments on some major elements of the organs of red peppers was observed. The amounts of N taken up by plants were 1.3 g for CF, 0.8 g for MLF-1.0, 0.5 g for MLF-0.5 and 0.4 g for control treatments. The results of this study showed that mixed liquid fertilizer (MLF) could appropriately serve as an alternative to chemical N fertilizer in red pepper cultivation.

Comparison of Three Methods for Measurement of Soil Organic Carbon

Quantification of soil organic carbon (SOC) is an important element in the assessment of the carbon sequestration potential of soils in tree-based intercropping (TBI) systems. The organic carbon (OC) concentrations of soils in TBI systems often differ from those in conventional agricultural systems due to the additional C inputs from litter fall and roots. However, the presence of soil inorganic carbon (SIC) can confound the measurements of SOC. This study compared three methods of measuring SOC: (i) measurement of the total soil C (TC) in one subsample and, after treatment in a muffle furnace (575 °C) for 24 h, measurement of SIC in another subsample; (ii) SOC measured after fumigation with 12 M hydrochloric acid (HCl) to remove SIC; and (iii) SOC measured after digestion with 0.73 M H2SO3 to remove SIC. The TC, SOC, and SIC concentrations were determined by combustion. A correction factor was applied to express SIC and SOC concentrations on an original, untreated soil basis. Measurement of SOC by the muffle furnace method resulted in the greatest SOC concentrations for Populus spp. (hybrid poplar) for samples from two of the three depths (0–10 and 20–40 cm). Measurement of SOC by the HCl fumigation and H2SO3 digestion methods were highly correlated, suggesting complete removal of SIC with minimal oxidation of SOC. These results have implications for the method of measuring SOC in calcareous soils under coniferous and deciduous tree species to a depth of 40 cm.

The impact of mulch type on soil organic carbon and nitrogen pools in a sloping site

Three mulch treatments were tested for their ability to control erosion on a sloping site. Additionally, the choice of mulch can also enhance revegetation success and improve soil organic matter input. This study aimed to investigate the effects of three mulching treatments, hydro-seeding, granite mulch and forest mulch, on soil C and N pools at different positions on highly erodible slope with approximately 30 % gradient. Soil moisture, total C (TC), total N (TN), hot water-extractable organic C (HWEOC), hot water-extractable total N (HWETN), microbial biomass C and N (MBC and MBN), inorganic N and potentially mineralisable N were measured. All variables were significantly higher in soils amended with forest mulch than those with hydro-seeding and granite mulch, for the same slope positions. Soil moisture was significantly higher in the lower slope position than middle and upper slope positions in hydro-seeding and granite mulch treatments, whereas no slope effect was observed on soil moisture under the forest mulch application. In the forest mulch treatment, the upper slope position had higher soil TC, TN, HWEOC, HWETN, MBC, MBN, NO3−-N and total inorganic N than the middle and lower slope positions. Five years following mulch application, forest mulch still exerted a significant influence on soil fertility compared to the other treatments and the influence on soil moisture suggests that this treatment would be the most effective in the control of water-driven soil erosion on this steep site.

Effects of the Long-Term Application of Anaerobically-Digested Cattle Manure on Growth, Yield and Nitrogen Uptake of Paddy Rice (Oryza sativa L.), and Soil Fertility in Warmer Region of Japan

The suitability of anaerobically-digested manure (ADM) from a biogas plant, as an alternative to chemical fertilizers for rice cultivation was evaluated by a long-term study. At the standard nitrogen (N) application rate (10 g m−2), the aboveground biomass, N uptake, and grain yield in rice plots with ADM application (MF) were not significantly different from those in the plots treated with chemical fertilizer (CF). Split application of ADM improved the apparent N efficiency. The N application rate corresponding to maximum grain yield was approximately 15 g m−2 by a split application, and more N application by using ADM saturated grain yield due to decrease in ripened grain ratio and individual grain weight. On the whole, the soil total-C, total-N and available N in the MF plot were not significantly different from those in the CF plot. The available phosphate (P) levels was lower in the MF plot than in either the CF plot or plot without N application (NF), mainly due to lower content of P in ADM. However, the P level remained much higher than the fatal threshold level for the growth of paddy rice. These findings suggest that under appropriate fertilization conditions, ADM is a valuable organic resource, and can be used continuously as an alternative to chemical fertilization for rice cultivation, without substantial changes in soil C and N fertility.