Increased Soil Organic Carbon Content Research Articles

Methods of evaluating soil bulk density: Impact on estimating large scale soil organic carbon storage

Bulk density (BD) is one of the most important parameters used to calculate soil organic carbon (SOC) storage. Differences in the methods available to substitute missing BD data, including mean, median, and pedo-transfer functions (PTFs), are considered the main reason for the high uncertainty in SOC storage estimations at large scales. In this study, we used the measured BD and SOC contents of 1007 soil profiles to evaluate the accuracy of six BD substitution methods (two mean methods, a median method, and three PTFs). The results showed that PTFs underestimated SOC storage by 8% in the 0–20cm soil layer, while mean and median methods overestimated SOC storage by 45% and 51%, respectively. Furthermore, the accuracy of PTFs estimates decreased with increasing soil depth. Relative to the measured values, and based on mean errors, root mean square errors, and method efficiency, the PFTs estimates were more accurate than those of the mean and median methods. Estimation bias increased with increasing SOC content for all methods, but differed among different soil types. The results of this study demonstrate that PTFs provide more accurate estimates of SOC storage when the extent of missing BD is substantial. Furthermore, the results provide new insights into establishing optimized PTFs, which contain more soil properties and piecewise functions of SOC content, in order to improve SOC storage estimates at large scales.

Occurrence and spatial pattern of water repellency in a beech forest subsoil

Abstract Most recent studies on soil water repellency (WR) were limited to the humous topsoil or to shallow subsoil layers slightly below the main root zone to approximately 0.5 m depth. Hence, the main objective of the present study was to investigate the wettability pattern of a forest soil including the deeper subsoil. The selected site was a 100 years old beech forest on a well-drained sandy Cambisol in northern Germany which showed moderate to partly extended acidification. Results obtained from three sampling transects (3 m length, 2 m depth; sampling grid 8 × 8 samples per transect; minimum distance of sampling locations to nearest tree about 0.5 m) show that contact angles (CA) were always in the subcritical WR range (0° < CA < 90°). Significant impact of the tree distance on WR was not observed for any of the transects. A prominent feature of two transects was the minimum WR level (CA < 10°) for samples with soil organic carbon (SOC) contents around 0.25–0.4%. For the topsoils it was observed that CA increased with SOC content from that minimum to a maximum CA of 60–75° for transects 1 and 2 with mean pH values < 3.5. For transect 3 with slightly higher average pH close to 4.0, average CA of samples were always < 10° and showed no trend to increase with increasing SOC content or other soil parameters like N content or C/N ratio. Subsoil samples, however, behave differently with respect to SOC: for these samples, generally low in SOC, the CA increase with decreasing SOC occurred at all transects for approximately 50% of the samples but did not show any clear tendencies with respect to further parameters like texture, pH or N content. We conclude that the SOC content is the most prominent parameter determining wettability, either positively correlated with WR for topsoils or negatively correlated for subsoil samples very low in SOC. We finally conclude for moderately acid beech forest stands that emerging WR starts in the A horizon after reaching a pH lower than 3.5, whereas subsoil WR might appear already at higher pH values. Even SOC contents of ~0.01–0.02% turned out to be very effective in increasing the CA up to 70°, which points out clearly the importance of small amounts of soil organic matter in affecting subsoil wettability. With respect to site hydrology we conclude that ongoing acidification as well as predicted higher frequencies of extended droughts due to climate change will promote the occurrence of WR with corresponding implications for site and catchment hydrology.

Effect of Mineral and Humic Substances on Tailing Soil Properties and Nutrient Uptake by Pennisetum purpureum Schumach

Tin mining produces a by-product sand tailing from soil leaching with characteristic low pH and total organic carbon, and can be reclaimed by providing a suitable ameliorant. When available in situ, ameliorant materials can be economically used as they are required in large amounts. Fortunately, Bangka Belitung has sample stock of such kaolinite-rich minerals that can be utilized for improving soil chemical properties. Extracted organic materials, such as humic substances, can also be utilized as they influence the complex soil reactions, and promote plant growth. Thus, this study aimed to assess the effects of mineral, humic materials and interaction of both material on soil chemical properties and nutrient uptake of Pennisetum purpureum Schumach. A completely randomized design with 2 factors and 3 replications each was employed. Factor 1 was mineral matter is 0; 420; 840; 1.260 Mg ha-1 while Factor 2 was humic material is 0; 0.46; 0.92; 1.38 kg C ha-1. Air-dried samples of tailing were applied with oil palm compost then mixed evenly with mineral and humic materials. Penissetum purpureum Schumach was planted after 4 weeks incubation, and maintained for another 4 weeks. The results demonstrated that the addition of mineral matter significantly increased soil organic carbon content, total N, exchangeable K, Fe, Mn and boosted nutrient - total Ca, Mg and Mn – uptake of the plant. But the application of humic material increased only soil organic carbon content. The interaction of both materials only lowered soil pH.

Long-term evaluation of productivity, stability and sustainability for cropping systems in Mediterranean rainfed conditions

Abstract Mediterranean cropping systems in rainfed conditions are generally based on rotations with a very high frequency of winter wheat and, therefore, they are at risk of declining trends for yield and soil health in the long-term. In order to quantify this risk, a long-term experiment was set-up in 1971 in central Italy, which is still running at present (2016). This experiment is based on 13 rotations, i.e. three continuous winter wheat systems with different N fertilization rates (W150, W200 and W250), five maize/winter wheat rotations with increasing wheat frequency (maize preceded by 1–5 years of wheat: i.e., WM, 2WM, 3WM, 4WM and 5WM) and five two-year rotations of winter wheat with either pea (WP), faba bean (WFB), grain sorghum (WGS), sugar beet (WSB) or sunflower (WSU). All these rotations are managed either with the removal of crop residues after harvest (REM), or with their burial into the soil at ploughing (BUR). For each rotation, all phases are simultaneously grown in each year, according to a split-plot design (with REM and BUR randomised to main plots), with three replicates in complete blocks and plots of 24.5 m2 each. The following data are considered: (1) total and marketable biomass yields from 1983 to 2012; (2) content of Organic carbon (OC) and total nitrogen (N) in soil, as determined in 2014. Considering the 30-year period, BUR resulted in an average positive effect on yield (+3.7%), increased OC (+13.8%) and total N content (+9.4%) in soil, while the C/N ratio was not significantly affected. Wheat in two-year rotations showed a significantly higher (+19.4%) average yield level than in continuous cropping or in 2WM, 3WM, 4WM and 5WM, mainly due to a drop in yield occurring in the first (−13%) and second (−19%) year of recropping. Increasing N fertilisation level from 150 to 250 kg N ha−1 with continuous cropping resulted in an increase (+3.7%) in long-term average yield and in a decrease in yield stability. All rotations heavily based on wheat (continuous cropping and 5WM) produced the highest amount of buried biomass (>175 t ha−1 in 30 years), with the highest increase in soil OC content (>16 t ha−1). All the other rotations produced a lower amount of residues and were less efficient in terms of carbon sequestration in soil, apart from WFB, which gave a high increase in soil organic carbon content (+18.9 t ha−1 in 30 years), in spite of a low amount of buried residues (158 t ha−1).

Mycorrhizal hyphal disruption induces changes in plant growth, glomalin-related soil protein and soil aggregation of trifoliate orange in a core system

By breaking up soil, tillage often disrupts mycorrhizal extraradical mycelium (ERM). In a core having four windows covered with 37-μm mesh in a perspex box, trifoliate orange (Poncirus trifoliata) seedlings were colonized with an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae. The core was rotated weekly at 180° around vertical axes, in order to simulate ERM disruption. After 13 such rotations, root mycorrhizal colonization, soil hyphal length inside and outside the core, and plant biomass were substantially reduced. On the other hand, mycorrhizal inoculation without disruption of ERM (static core) was associated with significant increase in biomass production, compared with disruption of ERM (rotating core). Disruption of ERM (rotating core) inhibited the production of easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) inside the core under mycorrhization, due to breakdown of ERM. Mycorrhization markedly increased soil organic carbon content, distribution of water-stable aggregate (WSA) at 0.5–4mm size and mean weight diameter (MWD), whereas core rotation showed a negative effect on MWD and the percentage of WSA within 1–4mm size under mycorrhization and within 0.25–2mm size under non-mycorrhization. It was proposed that soil tillage, in terms of the core rotation, strongly disrupted ERM network, which adversely influenced EE-GRSP and T-GRSP production and plant growth under mycorrhization, subsequently weakening the GRSP functioning on WSA stability.

Changes of soil microbial biomass carbon and their impact factors for Pinus tabuliformis plantations at different development stages on the Loess Plateau, China.

By taking an abandoned land as control and the young (13-15 year-old), middle-age (25-27 year-old) and mature (41-43 year-old) plantations of Pinus tabuliformis as research objects, the variation characteristics and impact factors of soil microbial biomass carbon (MBC) for the P. tabuliformis plantations in 0-60 cm soil layer were studied. Results showed that the average MBC at the young, middle-age and mature plantations was 93.08, 122.64 and 191.34 mg·kg-1, respectively, which showed a significant increase with growth stage and was significantly higher than the abandoned land (42.93 mg·kg-1). The average MBC contents gradually decreased with soil depth. Compared with the abandoned land, the average MBC at the young, middle-aged and mature plantations respectively increased by 134.2%, 221.7% and 375.7% in the 0-20 cm soil layer, 101.3%, 164.3% and 337.5% in the 20-40 cm soil layer, and 103.1%, 146.2% and 303.0% in 40-60 cm soil layer. The MBC for the whole soil layer of 60 cm had a highly significant correlation with the DBH, height and root biomass of the P. tabuliformis plantation, as well as the thickness, biomass and total nitrogen of litter. Meanwhile, the MBC also showed significant correlations with soil organic carbon (SOC), total nitrogen and moisture content. Principal component analysis showed that the root biomass, litter biomass and SOC were the principal factors affecting MBC. The P. tabuliformis plantation significantly increased SOC content mainly through litter of leaf and root and improved the MBC in the growth process.

A soil carbon proxy to predict CH4 and N2O emissions from rewetted agricultural peatlands

The temporal and spatial variations in greenhouse gas (GHG) emission estimates in wetlands impede our ability to predict and upscale total emissions; thus, a scalar parameter is needed to predict GHG emissions. We investigated the importance of soil organic carbon (SOC) in the prediction of methane (CH4) and nitrous oxide (N2O) emissions in rewetted agricultural peatlands, positing that both CH4 and N2O production are explained by the quantity and turnover of SOC. Field CH4 and N2O fluxes, along with other edaphic and environmental variables, were monitored in rewetted peatlands with a range of SOC (6%, 11%, and 23%) that were recently converted from row crops to flooded rice cultivation to reverse soil subsidence. Nitrogen (N) fertilization reduced annual CH4 emission by 77.2% in the 6% C field, but this effect was not found in other fields. Annual N2O emissions were not affected by N fertilization and averaged 8.9, 5.2, and 1.9kgN2O-Nha−1 for the 6%, 11%, and 23% C fields, respectively. SOC was the dominant factor controlling both CH4 and N2O emissions. The annual emission for both CH4 and N2O was accurately described by a decaying power regression with increasing SOC contents (R2>0.49). This relationship was also observed after splitting total annual emission of CH4 and N2O into growing and fallow seasons. Nitrogen fertilization and the seasonality in CH4 and N2O emissions did not change the relationships. The inverse correlation between SOC and CH4 and N2O emissions was likely caused by different chemical composition of SOC in various soils. Our results suggest that SOC can be a potential proxy to predict CH4 and N2O emissions in rewetted peatlands to better define GHG predictions of wetland restoration efforts.

Changes in soil organic matter composition after afforestation of arable farmland in northeast China

ABSTRACTSince the 1970s, a substantial area of arable farmland in a semi-humid area of northeast China has been planted as deciduous forests (Populus tomentosa Carr.). This study investigates the effects of afforestation on soil organic carbon (SOC) content and the chemical composition of the soil. Soil samples (Calcic chernozem) were collected from the upper 10 cm of paired arable land and secondary forests established 5 and 25 years previously. Carbon isotope analysis and pyrolysis–gas chromatography/mass spectrometry were used to determine SOC composition. The results show that (i) compared to the arable land, five years of afforestation caused a decrease in SOC and N concentration, while 25 years of afforestation resulted in an increase in SOC content; (ii) stable isotope δ13C analyses of the forest soils show gradual loss of crop-derived C and an accumulation of forest-derived C; and (iii) afforestation increased lignin abundance and decreased decompositional activity in the 25-year-old forest topsoil. Higher amounts of short-/mid-chain aliphatic compounds were observed in the 5-year-old forest (5–10 cm); and (iv) the arable soil contained substantially higher amounts of decomposed plant material and microbially derived substances. The results obtained suggest that long-term afforestation increases the SOC concentration, and alters the chemical composition of SOC.

Effects of Conservation Tillage on Topsoil Microbial Metabolic Characteristics and Organic Carbon within Aggregates under a Rice (Oryza sativa L.)-Wheat (Triticum aestivum L.) Cropping System in Central China.

Investigating microbial metabolic characteristics and soil organic carbon (SOC) within aggregates and their relationships under conservation tillage may be useful in revealing the mechanism of SOC sequestration in conservation tillage systems. However, limited studies have been conducted to investigate the relationship between SOC and microbial metabolic characteristics within aggregate fractions under conservation tillage. We hypothesized that close relationships can exist between SOC and microbial metabolic characteristics within aggregates under conservation tillage. In this study, a field experiment was conducted from June 2011 to June 2013 following a split-plot design of a randomized complete block with tillage practices [conventional intensive tillage (CT) and no tillage (NT)] as main plots and straw returning methods [preceding crop residue returning (S, 2100−2500 kg C ha−1) and removal (NS, 0 kg C ha-1)] as subplots with three replications. The objective of this study was to reveal the effects of tillage practices and residue-returning methods on topsoil microbial metabolic characteristics and organic carbon (SOC) fractions within aggregates and their relationships under a rice–wheat cropping system in central China. Microbial metabolic characteristics investigated using the Biolog system was examined within two aggregate fractions (>0.25 and <0.25 mm). NT treatments significantly increased SOC concentration of bulk soil, >0.25 aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer by 5.8%, 6.8% and 7.9% relative to CT treatments, respectively. S treatments had higher SOC concentration of bulk soil (12.9%), >0.25 mm aggregate (11.3%), and <0.25 mm aggregate (14.1%) than NS treatments. Compared with CT treatments, NT treatments increased MBC by 11.2%, 11.5%, and 20%, and dissolved organic carbon (DOC) concentration by 15.5%, 29.5%, and 14.1% of bulk soil, >0.25 mm aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer, respectively. Compared with NS treatments, S treatments significantly increased MBC by 29.8%, 30.2%, and 24.1%, and DOC concentration by 23.2%, 25.0%, and 37.5% of bulk soil, >0.25 mm aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer, respectively. Conservation tillage (NT and S) increased microbial metabolic activities and Shannon index in >0.25 and <0.25 mm aggregates in the 0−5 cm soil layer. Redundancy analysis showed that the SOC and its fractions (DOC and MBC) were closely correlated with microbial metabolic activities. Structural equation modelling showed that the increase in microbial metabolic activities directly improved SOC by promoting DOC in >0.25 mm aggregate in the upper (0−5 cm) soil layer under conservation tillage systems, as well as directly and indirectly by promoting DOC and MBC in <0.25 mm aggregate. Our results suggested that conservation tillage increased SOC in aggregates in the topsoil by improving microbial metabolic activities.

Influence of humic acid applications on modulus of rupture, aggregate stability, electrical conductivity, carbon and nitrogen content of a crusting problem soil

Abstract. Soil structure is often said to be the key to soil productivity since a fertile soil, with desirable soil structure and adequate moisture supply, constitutes a productive soil. Soil structure influences soil water movement and retention, erosion, crusting, nutrient recycling, root penetration and crop yield. The objective of this work is to study humic acid (HA) application on some physical and chemical properties in weakly structured soils. The approach involved establishing a plot experiment in laboratory conditions. Different rates of HA (control, 0.5, 1, 2 and 4 %) were applied to soil during three incubation periods (21, 42 and 62 days). At the end of the each incubation period, the changes in physicochemical properties were measured. Generally, HA addition increased electrical conductivity values during all incubation periods. HA applications decreased soil modulus of rupture. Application of HA at the rate of 4 % significantly increased soil organic carbon contents. HA applications at the rate of 4 % significantly increased both mean soil total nitrogen content and aggregate stability after three incubation periods (p &lt; 0.05). Therefore, HA has the potential to improve the structure of soil in the short term.

Influence of compost of sewage sludge and low-quality water on pesticide uptake by tomato plants grown in an iron mine soil

In mine soils, especially from arid or semiarid areas, the use of low-quality water for irrigation is a usual practice. Therefore to fill this gap, different experiments have been carried out to evaluate the effect of compost, pesticide and wastewater on the growth of tomato plants in a mine soil located at an iron extraction area. Soils proceeded from Alquife mine wastes whose most outstanding characteristics are alkaline conditions, low organic matter and electrical conductivity and high As concentration. The compost of sewage sludge (CSL) used to amend this soil had a slightly acid pH (6.8), EC 3.0 ± 0.07 dS m-1 (1/10 ratio, m/V) and 10 % organic carbon (OC) content. Irrigation was performed with distilled water (DW) or wastewater (WW) and two pesticides, the insecticide thiacloprid and the fungicide fenarimol, were applied to the soil. Tomato was grown directly from seeds on each pot. Four treatments with addition of pesticides were considered. For comparison purposes, two additional treatments without pesticides were also included. Addition of compost of sewage sludge led to a significant and sustained increase of soil OC content and dehydrogenase activity, while irrigation with wastewater had a slight or negligible effect on both properties. The plant species responded negatively to wastewater irrigation when this practice was undertaken with the application of both pesticides. No detectable amounts of thiacloprid, a relatively unstable and polar insecticide, were found in soil. The concentration of fenarimol in soil was higher after amendment with compost, but was not modified by irrigation with wastewater. In tomato shoots, the amounts of both pesticides were inversely correlated with final soil organic carbon, indicating that this soil property is relevant for their plant uptake. Besides, fenarimol concentrations in the soil and the tomato shoots were inversely related (r = −0.836). Tomato was not able to grow healthy in Alquife mine soil without compost addition. The irrigation with wastewater only reduced plant growth when used in combination with pesticides. Uptake of both pesticides by tomato plants was negligible according to the low bioaccumulation factor values, but was almost doubled for wastewater irrigation. Caution should be taken with the use of treated wastewater, because it may reduce plant growth in tomato that is a species sensitive to salinity.

Differences in fertilization impacts on organic carbon content and stability in a paddy and an upland soil in subtropical China

The stability of soil organic carbon (SOC) is of great importance in controlling long-term carbon (C) sequestration and feedbacks of soil C pools to climate change. It has been well documented that rice cropping and organic amendments could enhance SOC stocks, while the stability of the sequestered C has not been well understood yet. The objective of this study was to examine the difference in SOC content and stability between a paddy and an upland field under long-term fertilization and to explore the potential link between SOC chemical and biological stability. Soils were collected from two adjacent long-term paddy (annually double-rice cropping) and upland (annually double-corn cropping) experiments with the same soil parent material, where different fertilization regimes were initiated in 1981 and 1986, respectively. The chemical and biological stability of SOC were measured by acid hydrolysis and aerobic incubations, respectively. The C concentration was significantly higher in the paddy soil than in the upland soil, regardless of fertilization regimes. As compared to the initial level, long-term rice cropping without any fertilization (CK) significantly enhanced SOC concentration, whereas corn cropping led to a slight decline. Manure amendments combined with inorganic NPK fertilizers (NPKM) significantly increased SOC content relative to the inorganic NPK application alone treatment (NPK) in both the upland and paddy fields. The paddy soil had significantly greater cumulative C released per gram of soil C (i.e., the biological stability of SOC) than the upland soil. Cumulative C released per gram of soil C was significantly higher in NPKM than in NPK in both the paddy and upland soils, whereas no significant difference was observed between the CK and NPK treatments. Acid hydrolysis could reveal the difference in C stability between the paddy and upland soils, but could not characterize the effect of fertilization. Rice cropping facilitates SOC accumulation relative to upland cropping, whereas the inherent SOC stability is lower under the former than the latter in the site. The lower SOC turnover in the paddy than in the upland is mainly due to anaerobic conditions. Organic amendments significantly enhance SOC, but reduce its stability in both the paddy and upland fields. The sensitivity of acid hydrolysis is relatively low in determining SOC stability.

Adsorption of phosphate and organic matter on metal (hydr)oxides in arable and forest soil: a mechanistic modelling study

SummaryPhosphate (PO4) and organic matter (OM) compete for adsorption to metal (hydr)oxides. Our objective was to quantify the effect of OM on PO4 solubility in forest and arable soil by desorption experiments and surface complexation (SC) modelling. We sampled different types of soil along an age gradient (≈50–2500 years) and from different depths (0–80 cm). The soil types are calcareous and cover a range of soil organic carbon (SOC) contents (5.6–43.5 g kg−1), PO4 contents (0.2–5.9 mmol kg−1) and water‐soluble PO4 concentrations (0.03–13.4 µm). Assuming that PO4 concentrations are controlled by desorption, PO4 concentrations were expected to correlate with the PO4 loading on metal‐(hydr)oxide surfaces. However, we show that the PO4 loading alone is a poor predictor of PO4 solubility because its solubility increases with increasing SOC content. These data were explained by SC modelling, which shows a decrease in the apparent adsorption affinity of PO4 with increasing OM loading on to the metal (hydr)oxides. As a consequence, if the competition with OM is disregarded in SC modelling, it results in underestimation of the PO4 concentration by several orders of magnitude. For forest soil, predicted OM loadings increase slightly with increasing soil age. For arable soil, however, OM loadings were much smaller, which we explain by the replacement of PO4 with OM. Overall, adsorption interactions strongly affect PO4 solubility and levels of OM and PO4 stabilization in soil.

Fine-root distribution, production, decomposition, and effect on soil organic carbon of three revegetation shrub species in northwest China

Revegetation with xerophilous shrubs is an effective approach to combat desertification in northwestern China; however, evaluation studies on fine-root properties of shrubs and soil organic carbon are limited. To gain a better understanding of revegetation practices, we investigated the vertical distribution of fine-root biomass, necromass, production, and effect on soil organic carbon (SOC) content in three shrub species (Salix psammophila, Hedysarum mongolicum, and Artemisia ordosica). In addition, we also estimated the fine root decomposition rate with litterbag techniques. The results showed that revegetation practices resulted in a significant increase in SOC content. Over a 10year period of revegetation, the SOC content in S. psammophila, H. mongolicum, and A. ordosica plots increased by 0.87, 1.07, and 1.82 times, respectively, more than that in bare-land plot. Increase in total SOC content was mainly due to increase in light-fraction SOC, except for the A. ordosica plot. Variations in the short-term increase of SOC content after revegetations with the three shrubs on sand land might be explained by fine root decomposition rates, at least in part. A. ordosica may be a better species for SOC accumulation and sequestration in the study site. Additionally, fine-root biomass and production were not associated with more SOC content increase in shrub plots. The results suggest the mechanism of SOC accumulation and sequestration differed among shrub plots and highlight the effectiveness of different shrub species as revegetation materials in terms of SOC accumulation and sequestration.

The Effects of Long‐term Fertiliser Applications on Soil Organic Carbon and Hydraulic Properties of a Loess Soil in China

AbstractBased on a 28‐year in situ experiment, this paper investigated the impacts of organic and inorganic fertiliser applications on soil organic carbon (SOC) content and soil hydraulic properties of the silt loam (Eumorthic Anthrosols) soils derived from loess soil in the Guanzhong Plain of China. There were two crop (winter wheat and summer maize) rotations with conventional tillage. The treatments included control without fertiliser application, organic manure application (M), chemical fertiliser application (NP), and the application of organic manure with chemical fertiliser (MNP). The results showed that the 28‐year organic manure applications (M and MNP) significantly (p &lt; 0·05) increased SOC content at surface layer (0–10 cm), but the effect of chemical fertilisers alone on SOC was not significant. Organic manure treatments (M and MNP) apparently improved soil hydraulic properties. Compared with control, field capacity and total porosity significantly (p &lt; 0·05) increased while soil bulk density significantly (p &lt; 0·05) decreased for organic manure applications. The M and MNP treatments increased soil water retentions by 3·2–10·8%, which was dependent of suction tensions. However, the NP treatment had no significantly impact on soil water retention compared with control. Neither organic nor inorganic fertiliser applications significantly changed saturated hydraulic conductivity. However, a clear difference was observed for unsaturated hydraulic conductivity between the M and the control at 0–5 cm. Overall, long‐term applications of organic manuring increased SOC content and amended soil hydraulic properties. However, the effects of chemical fertilisers on these soil properties were limited. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Cropping System Impacts on Carbon Fractions and Accretion in Typic Ustochrept Soil of Punjab, India

Implementation of best management practices (BMPs) to increase crop productivity by intensive cultivation on marginal/fallow lands has positive impact on soil organic carbon (SOC). Because of difference in BMPs, impact of cropping system (CS) on SOC is not similar across soil types. Therefore, this study evaluated the relative influence of 10 different CSs on important SOC fractions and accretion in Typic Ustochrept of Punjab, India. Conversion of fallow lands to agricultural systems for eight years significantly increased SOC concentration in 0–15 cm layer. However, keeping the field fallow for the same period decreased SOC concentration by 24% from antecedent level of 3.8 to 2.8 g C kg−1. Among different CSs, significant differences in SOC concentration was recorded in crops amended with farmyard manure (FYM). All maize (Zea mays L.)-based CSs contained significantly higher SOC concentration as compared with that in rice (Oryza sativa), cotton (Gossypium hirsutum), and groundnut (Arachis hypogaea)-based CSs except for the groundnut-potato (Solanum tuberosum)-bajra (Pennisetum glaucum), which also received FYM. While comparing three important CSs of the region, maize-wheat cropping system had 5.6% higher labile carbon (LC) than for cotton-wheat, and was 7.3% higher in rice-wheat system. On an average, among different CSs, maize-based CSs had the maximum SOC pool, followed by that in groundnut, cotton, and the minimum in rice (31.3 Mg C ha−1)-based CS in 0–60 cm soil profile. The rice equivalent yield ranged between 6.9 Mg ha−1 to 38.6 Mg ha−1 under different CSs.

Assessing the impact of afforestation on soil organic C sequestration by means of sequential density fractionation.

Afforestation is a prevalent practice carried out for soil recovery and carbon sequestration. Improved understanding of the effects of afforestation on soil organic carbon (SOC) content and dynamics is necessary to identify the particular processes of soil organic matter (SOM) formation and/or decomposition that result from afforestation. To elucidate these mechanisms, we have used a sequential density fractionation technique to identify the transfer mechanisms of forest derived C to soil fractions and investigate the impact of afforestation on SOC sequestration. Surface soil samples from continuous maize crop land (C4) and forest land (C3), which had been established 5, 12 and 25 yr, respectively, on the Northeast China Plain were separated into five density fractions. SOC, nitrogen (N) concentration and δ13C data from the three forests and adjacent cropland were compared. Afforestation decreased SOC concentration in the < 2.5 g cm-3 fractions from 5 yr forest sites, but increased SOC content in the < 2.0 g cm-3 fractions from 25 yr forest sites. Afforestation did not affect soil mass distribution, SOC and N proportional weight distributions across the density fractions. The < 1.8 g cm-3 fractions from 12 and 25 yr forests showed higher C/N and lower δ13C as compared to other fractions. Incorporation of forest litter-derived C occurred from low density (< 1.8 g cm-3) fractions to aggregates of higher density (1.8-2.5 g cm-3) through aggregate recombination and C transport in the pore system of the aggregates. Some forest litter-derived C could transfer from the light fractions or directly diffuse and adsorb onto mineral particles. Results from this study indicate that microaggregate protection and association between organic material and minerals provide major contribution to the SOC sequestration in the afforested soil system.

Simulating the effects of chemical and non-chemical fertilization practices on carbon sequestration and nitrogen loss in subtropical paddy soils using the DNDC model

Understanding the long-term and quantitative effects of different fertilization practices on carbon sequestration and nitrogen loss is important when establishing the best fertilization regime. In this study, the DeNitrification–DeComposition (DNDC) model was validated first for the change of soil organic carbon (SOC) at the site mode and at the regional mode, and then it was used to simulate the effects of three fertilization practices including rice straw (RS) returning, chemical fertilizer application (CF), and green manure planting (GM) on C and N dynamics in paddy soils from a subtropical area of China. The prevailing fertilization practices in the study area were set as the baseline scenario, and alternative scenarios were assigned by varying only one of the three fertilization practices. All three fertilization practices increased SOC content but had different effects on rice yield, N2O emission, and nitrate leaching loss. Compared with a baseline RS rate of 15 %, the SOC contents less than RS rates of 30, 50, and 80 % were increased on average by 12.84, 29.48, and 53.50 %, respectively. SOC content also increased as the CF rate rose from 70 to 130 % of the baseline scenario and then leveled off from 130 to 160 %. SOC contents under GM were higher than that without GM by 35.74 %. Both the N2O emissions and the nitrate leaching were increased with the increasing CF rate, while they decreased under GM treatment. However, RS increased the N2O emissions but decreased the nitrate leaching. The polygon-based modeling method with the DNDC could accurately evaluate the general trend of SOC dynamics and nitrogen loss from paddy soils.

Effects of rice straw incorporation and tillage depth on soil puddlability and mechanical properties during rice growth period

Soil puddlability, a measure of susceptibility of soil to puddling, affects regeneration of soil structure during the rice growth period, but the intrinsic controlling factors are unclear. It was hypothesized that rice straw incorporation and tillage depth influence soil puddlability and soil mechanical and hydraulic properties during the rice growth period as they influence soil organic carbon (SOC) in the plough layer. Using a three-year experiment, the objectives of this study were (1) to determine the effects of rice straw incorporation and tillage depth on root growth traits, sinkage resistance after puddling, and tensile strength, shrinkage capacity, water retention curve and penetration resistance during the rice growth period, and (2) to determine whether mechanical properties from puddling tillage, through the rice growth period, to harvest are correlated with SOC concentration. Rice straw was incorporated partially (C1) and fully (C2) to different depths of plough layer by shallow tillage (ST) and deep tillage (DT). Compared with no rice straw incorporation (C0), rice straw incorporation decreased the sinkage resistance after puddling (C2<C1<C0) and increased SOC concentration and aggregate stability. Shallow tillage increased the penetration resistance more than deep tillage irrespective of rice straw incorporation. The difference in tensile strength and total porosity were small among the rice incorporation treatments at the 1st drainage (C2≥C1≥C0), but became more profound with increasing number of drainage because the tensile strength and total porosity decreased in C0, increased in C2, particularly under ST. The root weight was lower, and the root length was longer in C1 than in C2 particularly at the deeper depth of the plough layer under ST, suggesting the impedance of root growth due to higher sinkage and penetration resistances. SOC concentration was weakly correlated with the sinkage and penetration resistances and the tensile strength after the 1st drainage, but not with the tensile strength after the 2nd and 3rd drainages. In conclusion, rice straw incorporation is important to maintain SOC and then improve soil puddlability and the recovery of pore structure during the rice growth period.

Effects of long-term treatments of different organic fertilizers complemented with chemical N fertilizer on the chemical and biological properties of soils

Continuous cultivation has been known to decrease soil organic matter content. Application of organic matter to cultivated soil is an important practice from the point of view of maintaining an adequate amount of soil organic matter. Soil organic matter content significantly affects soil microbial activity, which is an important index of soil quality. In this study, a field experiment was conducted to examine the long-term effects of different kinds of organic matter in combination with inorganic nitrogen (N) fertilizer on chemical and biological properties of soils. There were seven treatments, namely (1) CK (without fertilization), (2) Chem-N (applying chemical N fertilizer only), (3) Comp (applying compost with the same rate of N as the Chem-N treatment), (4) Comp + l/3 N (applying compost complemented with 33% of the chemical N fertilizer of the Chem-N treatment), (5) Comp + 2/3 N (applying compost complemented with 66% of the chemical N fertilizer of the Chem-N treatment), (6) GM + 1/3 N (applying green manure complemented with 33% of the chemical N fertilizer of the Chem-N treatment) and (7) Peat + 1/3 N (applying peat complemented with 33% of the chemical N fertilizer of the Chem-N treatment). After continuous treatment for 12 years and with cultivation of 24 crops on the same area, soils were sampled for analyses of chemical and biological properties, enzymatic activities and phospholipid fatty acid (PLFA) profiles. The results showed that compared with CK and Chem-N treatments, applications of compost and peat increased soil organic carbon (SOC) content and altered microbial activities and microbial community structure. However, application of green manure for 12 years had no effect on SOC content. Both microbial activities and PLFA profiles were clearly dependent on the characteristics of the applied organic amendments. In summary, a peat application led to the highest increase in SOC content compared to compost and green manure; however, compost-treated soil had a higher microbial population and higher microbial and enzyme activities, while the effects of both green manure and chemical N fertilizer on soil properties were similar.