Soil Aggregate Distribution Research Articles

Response of carbon and nitrogen dynamics in soil water‐stable aggregates to wheat straw incorporation in the Yangtze River Delta of China#

AbstractBackgroundResearch on the changes of organic carbon (OC) and total nitrogen (TN) contents in soil aggregates is crucial for better evaluating C and N dynamics in paddy soil.AimsWe investigated the effects of wheat straw incorporation on soil aggregate distributions and stability, the contents of OC and TN in bulk soil, and aggregates as well as their relationships.MethodsA rice paddy field experiment in China with four treatments: (1) unfertilized control (CK), (2) mineral NPK fertilizer (NPK), (3) NPK plus medium‐rate wheat straw incorporation (MSNPK), and (4) NPK plus high‐rate wheat straw incorporation (HSNPK). Soil samples were collected from four soil layers (0–5, 5–10, 10–20, and 20–30 cm, respectively) after the rice harvest, and the samples were separated into four classes of aggregates with different sizes (>5, 5–2, 2–0.25, and <0.25 mm).ResultsThe >5 mm fraction dominated aggregate size distribution, but the 2–0.25 mm fraction had the highest OC and TN contents throughout soil profile among treatments. The proportions of >5 and 5–2 mm aggregates, mean weight diameter (MWD), geometric mean diameter (GMD), the proportion of aggregates greater than 0.25 mm (R0.25), bulk soil organic carbon (SOC) and TN contents, and OC and TN contents in aggregates were highest in HSNPK and lowest in CK at either depth. Both bulk SOC and TN contents positively correlated withR0.25, MWD, GMD, and OC and TN contents in aggregates, and positively and negatively correlated with all aggregates (p< 0.05), except between bulk TN and the proportion of 5–2 mm aggregates. The OC content in the 5–2 mm aggregates (increase in MSE = 23.87%) and the TN content in the 2–0.25 mm aggregates (increase in MSE = 13.89%) were more important than other driving factors for bulk SOC and TN, respectively.ConclusionIn conclusion, these results confirmed that the application of HSNPK increased bulk SOC and TN contents, soil aggregates distributions (i.e. >5 mm and 5–2 mm fractions) and stability, and the OC and TN contents in all aggregates at both depths in rice paddy fields of China, which might improve soil C and N sinks in agricultural ecosystems.

Decreased soil aggregation and reduced soil organic carbon activity in conventional vegetable fields converted from paddy fields

AbstractSoil structure and organic carbon are key factors that reflect soil quality in sustainable agricultural production. Many studies have concentrated on soil aeration under intensive anthropogenic agricultural practices, but the relationship between soil aggregate stability and soil organic carbon (SOC) functional groups is poorly understood, particularly in degraded greenhouse vegetable fields converted from paddy fields. To solve this problem, soil samples were collected from local vegetable fields and adjacent paddy fields. Conventional open‐air vegetable fields and greenhouse vegetable fields, both with a 6–8‐year cultivation history following conversion from paddy fields, were considered. SOC functional groups were characterised by 13C cross‐polarisation magic‐angle‐spinning nuclear magnetic resonance (13C CPMAS NMR). The results showed that the mean weight diameter (MWD) values of water‐stable soil aggregates in the open‐air vegetable fields and greenhouse vegetable fields decreased by 64.6% and 66.7%, respectively, compared with those in the paddy fields. Similar results were obtained for the soil aggregate distribution, and soil aggregates in the greenhouse vegetable fields and open‐air vegetable fields were mainly in the 0.25–2 mm size classes. Among all SOC functional groups, O‐alkyl C exhibited the greatest decrease after the conversion of paddy fields to vegetable fields, no matter whether greenhouse vegetable fields or open‐air vegetable fields. The degradation of soil structure decreased the physical protection of SOC functional groups by soil aggregates, and therefore, decreased the total SOC content and labile C functional group fractions in bulk soil. At the soil aggregate scale, the decrease of O‐alkyl C mainly occurred in microaggregates (0.053–0.25 mm), while aromatic C decreased significantly in macroaggregates (>0.25 mm) in the greenhouse vegetable fields converted from paddy fields. Correlation analysis showed that O‐alkyl C was significantly positively related to MWD and the proportion of large soil macroaggregate (>2 mm). This result suggested that soil aggregates become fragile in long‐term vegetable cultivation after conversion from paddy fields, and a large loss of O‐alkyl C might be the main reason for this phenomenon.Highlights Soil aggregation was significantly decreased in conventional vegetable fields converted from paddy fields. SOC accumulation was closely positively related to soil macroaggregate formation. O‐alkyl C mainly decreased in microaggregates, with the opposite observed for aromatic C, in soil of greenhouse vegetable fields. The large loss of O‐alkyl C may explain the degradation of soil aggregates.

Caragana korshinskii Kom. plantation reduced soil aggregate stability and aggregate-associated organic carbon on desert steppe.

BackgroundAfter implementing of the “Grain-for-Green” project, Caragana korshinskii Kom. has been widely planted in China’s arid regions. Although natural restoration grassland and artificial Caragana plantations measures have long been focuses in carbon research, the combined influence of natural restoration grassland and artificial Caragana plantation measures on aggregate stability and the aggregate-associated organic carbon (OC) remains unclear.MethodWe selected natural grassland (NG) and three different densities of Caragana plantations (high planting density, HG; middle planting density, MD; low planting density, LD) on desert steppe. The soil aggregate distribution and stability index such as fractal dimension (D), mean weight diameter (MWD), geometric mean diameter (GMD), percentage of aggregation destruction (PAD), as well as aggregate-associated OC concentration and stock were measured.ResultsResults shows that the soil aggregates were primarily macroaggregates (>2 mm) and mesoaggregates (0.25–2 mm) under dry sieving while microaggregates (<0.25 mm) were preponderant under wet sieving (more than 57%). Overall, compared with Caragana plantations, the MWD (4.43 and 4.51 mm) and GMD (1.72 and 1.83 mm) were both highest in two soil layers under the NG and the D (2.77 and 2.71) was lowest. Compared with the NG, the aggregate-associated OC stocks in the 0–40 cm depths in the LD, MD, and HD decreased by 41.54%, 46.93%, and 42.03%, respectively. SOC stock was mainly concentrated in the soil aggregate with sizes of >2 mm and <0.25 mm. These results suggested that natural grassland restoration measures could improve the soil aggregate stability and aggregate-associated OC concentration better than Caragana plantation restoration measures, which NG may be optimal for increasing carbon sequestration and stabilizing soil aggregates on desert steppe.

Effects of different concentrations of super-absorbent polymers on soil structure and hydro-physical properties following continuous wetting and drying cycles

Super-absorbent polymers (SAPs) are widely used chemical water-saving materials, which play an active role in the accumulation of soil water and the improvement of soil structure. Little is known about their performance with repeated usage or about factors influencing their efficiency under alternate wetting and drying cycles. In this study, various concentrations of SAP (0, 0.1, 0.2 and 0.3%) in soil following three continuous wetting and drying cycles (T1, T2 and T3), were studied to determine effects on soil structure stability and hydro-physical properties. The results indicated that the SAP improved soil water supply capacity under conditions of mild drought (T2) and sufficient irrigation (T3) at concentrations of 0.2 and 0.3%, but a reduction was observed under severe drought conditions (T1), which was negatively correlated with the SAP concentration. The physical adsorption of the SAP by soil and the chemical connection between the SAP and soil mineral colloids as Si-O-Si bonds, -OH bonds and different crystalline silica were the important factors that directly lead to the reduction of water retention capacities of the SAP with alternating wet and dry conditions. Compared with the control, the soil liquid phase ratios of the SAP treatments were increased by 8.8–202.7% in the T1 and T2 cycles, which would have led to a decrease in the soil air phase ratios. After repeated wetting and drying cycles, the SAP treatments increased the amount of >0.25 mm soil aggregates and the contents of water-stable macro-aggregate (R0.25), and decreased the amount of <0.053 mm soil aggregates, especially with higher concentrations of the SAP. Increases in mean weight diameter (MWD) and geometric mean diameter (GMD), and declines in fractal dimension (D) and unstable aggregates index (ELT) were all observed with the SAP treatments, which indicated an improvement in soil stability and structure. It was concluded that the distribution and stability of soil aggregates and soil water supply capacity was closely related to SAP concentration, soil moisture condition and the interaction between the SAP and soil particles.

秦岭天然林凋落物去除对土壤团聚体稳定性及细根分布的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 秦岭天然林凋落物去除对土壤团聚体稳定性及细根分布的影响 DOI: 10.5846/stxb201912272807 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 农业部农业环境重点实验室开放基金(K4030217149);国家林业公益性行业科研专项(201304307) Effects of litter removal on soil aggregate stability and distribution of fine roots in natural forests of Qinling Mountains Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:研究凋落物去除对秦岭天然林土壤团聚体稳定性及细根分布特征的影响机制,为森林生态治理提供理论依据。结果表明:(1)凋落物去除导致云杉林10-40 cm土层土壤中粒径大于0.25 mm水稳性团聚体含量(WR0.25)较对照显著降低(P<0.05);混交林10-40 cm土层的大于0.25 mm机械稳定性团聚体含量(DR0.25)显著降低(P<0.05);红桦林表层0-10 cm土壤团聚体的平均质量直径(MWD)显著降低(P<0.05);(2)凋落物去除导致三种天然林0-20 cm土层的细根生物量密度(FRBD)较对照显著降低44.18%-57.24%,细根体积(FRV)显著降低24.64%-60.41%;三种天然林中红桦林0-40 cm各土层的FRV最高;(3)凋落物去除导致云杉林0-40 cm土层的土壤容重较对照显著增加5.24%-13.04%,三种天然林0-40 cm土层的土壤有机碳含量显著降低7.92%-25.21%,全氮含量显著降低10.17%-18.10%;(4)相关分析表明,云杉林土壤的团聚体破坏率(PAD)和土壤不稳定团粒指数(ELT)与FRBD、细根根长密度(FRLD)和FRV均呈极显著负相关,混交林土壤的PAD与FRBD呈极显著负相关关系(r=-0.814),红桦林土壤团聚体MWD与FRBD、FRLD和细根比根长(FSRL)均呈显著负相关关系(r=-0.777、-0.771和-0.786)。综上,凋落物去除在总体上降低了天然林土壤团聚体的稳定性及有机碳和全氮含量,并且不利于林木细根的生长。 Abstract:The objective of this study is to investigate the effects of litter removal on the characteristics of soil aggregates stability and fine root distribution so as to provide theoretical bases for vegetation restoration and ecological protection in Qinling Mountains. Results indicated that (1) the litter removal significantly decreased the percentages of >0.25 mm water-stable aggregates (WR0.25) in 10-40 cm soil layer (P<0.05). The percentage of >0.25 mm mechanical-stable aggregates (DR0.25) in 10-40 cm soil layer of mixed forest was also decreased significantly (P<0.05). The mean weight diameter (MWD) of aggregates in 0-10 cm soil layer of Betula albosinensis forest was decreased (P<0.05) by litter removal. (2) By litter removal, the fine root biomass density (FRBD) in 0-20 cm soil layer of the three forests significantly decreased by 44.18%-57.24%; the fine root volume (FRV) significantly decreased by 24.64% to 60.41%. The FRV in 0-40 cm soil layer of Betula albosinensis forest was the highest among the three forests. (3) After 3-year litter removal, the soil bulk density in 0-40 cm soil layer of Picea asperata forest significantly decreased by 5.24%-13.04%. The soil organic carbon contents in 0-40 cm soil layer of the three forests significantly decreased by 7.92%-25.21%, and the contents of total nitrogen significantly decreased by 10.17%-18.10%. (4) The results of correlation analysis showed that percentage of aggregate destruction (PAD) and unstable soil aggregate index (ELT) of Picea asperata forest soil had significantly negative correlations (P<0.01) with FRBD, fine root length density (FRLD), and FRV. The PAD of mixed forest soil showed a significantly negative correlation (P < 0.01) with FRBD (r=-0.814). The aggregate MWD of Betula albosinensis forest soil had significantly negative correlations (P < 0.01) with FRBD, FRLD and fine specific root length (FSRL) (r=-0.777, -0.771 and -0.786). Overall, the litter removal decreased the stability of soil aggregates, the contents of soil organic carbon and total nitrogen in soils of natural forests, which also inhibited the growth of fine roots. 参考文献 相似文献 引证文献

Vertical distribution of soil aggregates and associated organic carbon fractions under conventional vegetable- and rice-based tillage operations

Context Vegetable- and rice-based cropping systems are the dominant agricultural practices across South Asia, but the conventional tillage method associated with their cultivation is responsible for soil degradation in terms of aggregates and organic carbon in the surface layer. However, knowledge of its impact on the deeper layers is needed because the aggregate and organic carbon dynamics in deeper soils are little understood. Aims This study analysed the effects of conventional rice-based tillage (RBT) and vegetable-based tillage (VBT) operations on the vertical distribution of aggregates and aggregate-associated organic carbon fractions. Methods Soil samples were collected from 10 vegetable and rice fields, where conventional tillage systems were applied, and analysed for the vertical distribution of aggregates, soil carbon stock, aggregate-associated total organic carbon (AATOC), the relationship between mean weight diameter (MWD) and AATOC, and intra-aggregate particulate organic carbon (iPOC). Key results Soil macroaggregates, MWD, AATOC, and iPOC for the surface soils under RBT were less than for soils under VBT, indicating that soils under RBT had weaker aggregate stability compared to soils under VBT. The relationship between MWD and AATOC was significant (P &lt; 0.01) for the top layers of VBT, but this relationship was non-significant for RBT. Conclusions The study suggests that wet rice cultivation has an adverse effect on soil aggregate stability and its associated organic carbon fractions. Implications Alternative tillage operations for rice-based cultivation are necessary to avoid soil degradation in rice fields.

Effects of long-term (70 years) nitrogen fertilization and liming on carbon storage in water-stable aggregates of a semi-arid grassland soil

Grasslands cover up to 40.5% of the world's landmass and store 30% terrestrial carbon (C). Various practices, including mineral fertilization and liming, are used to manage these ecosystems with potential long-term effects on the size and distribution of soil aggregates and inevitably carbon dynamics. The objective of this study was to examine the long-term effects of nitrogen fertilization and liming on soil carbon storage and its dynamics in water-stable aggregates of a semi-arid grassland. Soil samples (0–10 cm) were collected from Ukulinga long-term grassland trial in Pietermaritzburg, South Africa where nitrogen fertilizers have been applied annually and lime every five years for 70 years. Ten treatments were studied: the control (0 kgN/ha and unlimited), lime at 2250 kg/ha (L), ammonium sulphate at 70 kg/ha (AS70) and 211 kg/ha (AS211); ammonium nitrate at 70 kg/ha (AN70) and 211 kg/ha (AN211); AS70 + lime (AS70L); AS211 + lime (AS211L); AN70 + lime (AN70L) and AN211 + lime (AN211L).Nitrogen fertilizers significantly reduced soil pH and increased total soil N. Liming increased soil pH with no effect on total soil N. Lime and lime + N fertilizer treatments had no effect on mean weight diameter (MWD) while separate N application decreased MWD and large macro-aggregates (LMA). Lime only treatment had no effect on water stable aggregate (WSA) fractions. Nitrogen fertilization and liming (separately or in combination) did not affect total C concentration and stocks. Overall, soils had very high total soil organic carbon ranging from 49.7 – 57.6 g/kg across treatments. Nitrogen fertilization decreased organic carbon in LMA in AS70 (1.52%) and AN211 (1.67%) treatments compared to the control (3.40%) which was in concert with increases in C associated with small macro-aggregates (SMA) and micro-aggregates (MiA and SCA). Organic carbon in SMA was 2.67 % (AS70); AS211 (2.62 %); AN70 (2.02 %); AN211 (2.49 %) compared to 1.26 % in the control. Lime + N fertilizer treatments increased C storage in all aggregate fractions compared to N fertilizer only treatments. The lack of response in total SOC to 70 years of N fertilization and liming suggests possible C saturation given the high soil C concentration. Changes in C associated with WSA fractions suggests their importance as diagnostic indicators of N fertilization and liming induced changes in SOC. Findings also show that ammonium-based N fertilization is associated with soil acidification, dispersion of LMA resulting in an increase of microaggregates and C stored in them. Liming can counteracts acidifying and the dispersive effect on NH4+ associated with ammonium-based fertilizers thus restoring macro-aggregation in N fertilized grasslands. These findings suggests that long-term N addition may result in poor soil physical condition and possible stabilization of C in stable fractions.

Organic fertilization promotes crop productivity through changes in soil aggregation

Soil aggregates are the key functional units of soil ecosystems which are essential to biogeochemical cycling and plant growth. However, it remains unclear how fertilization regimes influence soil aggregation, associated resources, and microbial distribution among aggregates, as well as the potential subsequent impacts for other abiotic and biotic processes. For this, a long-term maize cropping field experiment was conducted in the subtropical region of China under four fertilization treatments: no fertilizer, chemical fertilization, organic fertilization, and chemical plus organic fertilization. Additionally, we classified soil aggregates into large macro-aggregates (>2 mm), small macro-aggregates (0.25–2 mm), and micro-aggregates (<0.25 mm) and compared soil nutrients, enzyme activities, and microbial communities of each aggregate fraction and bulk soil as well as crop productivity and plant carbon (C), nitrogen (N), and phosphorus (P). Results showed that long-term organic fertilization (1) increased soil C, N, and P contents within macro-aggregates, while increased bacterial and fungal biomass within all three aggregate size fractions, (2) increased N-acquiring enzyme activity, C:P, and N:P enzyme ratios but decreased phosphatase activity and C:N enzyme ratio regardless of aggregate fractions, and (3) promoted crop productivity but decreased plant C:N, C:P, and N:P ratios compared with chemical fertilization. Additionally, the fungi:bacteria ratio and phosphatase activity decreased, but the gram-positive to gram-negative bacterial ratio, C-acquiring enzyme activity, C:N and C:P enzyme ratios increased with decreasing aggregate size. The partial least squares models confirmed that macro-aggregates had strong effects on crop performance while micro-aggregates was the main determinant of microbial community. Taken together, long-term organic fertilization promotes soil functioning and crop productivity via increasing the proportion of soil macro-aggregates.

The Development and Utilization of Saline–Alkali Land in Western Jilin Province Promoted the Sequestration of Organic Carbon Fractions in Soil Aggregates

Soil samples from T (0~20 cm) and S (20~40 cm) layers of four saline–alkali rice fields (R5, R15, R20, and R35) with different reclamation years were selected to study the distribution of soil aggregates and the contents of readily oxidizable organic carbon (ROC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), potentially mineralizable carbon (PMC), and soil organic carbon (SOC). The effects of large macroaggregate (&gt;2 mm, LMA), small macroaggregate (0.25 to 2 mm, SMA), and microaggregate (&lt;0.25 mm, MA) particle size, soil layer, and soil physicochemical properties on SOC fractions were also analyzed. The results showed that the LMA size in saline–alkali paddy fields were easily decomposed and was unstable due to the influence of the external environment. With the increase in reclamation years, the proportion of LMA in the S layer decreased gradually. The ROC, DOC, MBC and TOC contents of aggregates in the T and S layers gradually increased with the increase in reclamation years, and SOC fractions contents of aggregates in different grain sizes were SMA &gt; LMA &gt; MA. An effective way to increase carbon sink and improve the ecological environment in western Jilin Province is to change the soil environment by planting rice in saline–alkali land.

Pedoclimatic factors and management determine soil organic carbon and aggregation in farmer fields at a regional scale

The degradation of soil from agricultural land is a major threat to food security and a driver of global changes. Soil conservation systems are thus being promoted and/or adopted worldwide. In this on-farm study conducted in Switzerland, we compared the effect of three cropping systems – conventional with tillage, conventional without tillage (i.e. no-till) and organic farming with tillage – on soil quality. Samples from 60 winter wheat fields belonging to these three systems were analysed for soil carbon concentration, soil aggregate distribution and soil biological properties (microbial carbon and mycorrhizal biomarkers), at three different depths (0–5 cm, 5–20 cm and 20–50 cm). Information about cropping practices was collected through surveys. The main differences in soil properties between systems occurred for the surface layer (0–5 cm depth), with increased soil organic carbon concentration and stock under no-till compared to the conventionally tilled fields. No-till and organic fields showed a higher mean aggregate size and proportion of macroaggregates in the surface layer compared to tilled conventional fields, with a greater amount of carbon in the large macroaggregates. However, large within-system variability was also observed, which tended to override differences between systems. Across systems, clay content, microbial carbon, and the mycorrhizal PFLA biomarkers were the major drivers of soil organic carbon concentration, clay to carbon ratio and carbon accumulation in the large macroaggregate fraction. Aggregation at 0–5 cm was mostly related to tillage depth, while climate variables and especially clay content played a major role for deeper layers. Our results demonstrate that within the constraints set by soil texture and climate, organic agriculture and no-till can contribute to improved soil carbon and aggregation properties. Thus, we advocate for the identification of the main drivers of soil quality in order to inform management and improve soil functioning in agricultural fields in the long term.

Trade-off between soil aggregate stability and carbon decomposition under 44 years long-term integrated nutrient management in rice-wheat-jute system

ABSTRACT Soil stability, yield decline and higher carbon decomposition are the key issues in intensive agriculture. Long-term integrated nutrient management (INM) influences carbon (C) dynamics and maintains the soil aggregate stability, which driven by the type of cropping system and climatic zone. Therefore, the specific effects of rice-wheat-jute cropping system on soil aggregate distribution, C-stability, and trade-off between C-storage and decomposition rate were studied of a long-term INM trial in the sub-tropical zone. We investigated the effect of four long-term nutrient management practices that include, control, N (nitrogen (N) and no phosphorus (P), and potassium (K)), NPK (N, P and K) and INM (N, P, K + farmyard manure (FYM)). Results showed that the addition of FYM with NPK improved macro-aggregates by 71%, and associated C-pools by 30%. The INM enhanced C-storage (20%), however, the decomposition rate was also higher (28%) over control at 35 °C at field capacity. A trade-off exists between the soil-aggregate stabilization and C-decomposition rate. The proportion of C-storage was higher than decomposition in INM. Further, the C-sequestration varied (0.17 to 0.26 t ha−1 y−1) under different treatments and were found highest in INM, indicating long-term soil stability and yield sustainability in the rice-wheat-jute system.

Soil and organic carbon redistribution in a recently burned Mediterranean hillslope affected by water erosion processes

Forest fires cause many changes in the physical, chemical and biological soil properties such as aggregation and soil organic carbon contents (SOC) as well as on soil hydrology and erosion processes. Most studies on post-fire soil erosion in Mediterranean environments have been plot-based and research at hillslope or broader scale is scarce. Understanding SOC nature, distribution and modifications, as produced by forest fires and erosion, has become crucial to model and define the role of soil erosion as source or sink of C, and to sustainably manage ecosystem services related to the soil resource. This research provides data about the loss and redistribution of soil and SOC in a Mediterranean forest hillslope burned with high severity, at the Natural Park of Sierra de Espadán, Spain. Soil was sampled in coupled hillslopes (ca. 0.25 ha) (BU: burned, CO: control) at bottom (depositional), middle (transport) and top positions (eroding) at two depths (0–2 cm, 2–5 cm), and under two environments (UC: under canopy soil, BS: bare soil). Sediments were collected after each erosive event along one year, and yields were calculated. Samples were analysed to assess aggregate stability (AS), size and density fractionations, SOC contents and stocks. The main hypothesis is that fire affects soil characteristics related to aggregation and SOC stabilization and, together with erosion processes, may modify SOC distribution within aggregates and the burned hillslope.Soils were in general very stable, but some differences in the results of the methods used were observed. Significant differences were found for the environment (under canopy vs bare) and soil depth but not for slope position. SOC content was high both at BU and CO with no significant differences. In the BU hillslope, a homogenization of SOC contents was observed along the hillslope, while in the CO, a higher SOC content was measured in the depositional and transport sites than in the eroding one. Similar trends were observed for SOC stocks. Only four erosive rain events were registered in this study, which generated no sediment yields in CO hillslope. In the BU one, sediment yields were measured (0.05–0.58 Mg ha−1, total 0.925 Mg ha y−1), which mobilised OC amounts ranging between 0.005 and 0.04 MgC ha−1. When samples were fractioned, changes were observed in the mass distribution of soil and sediment aggregates by size and density, and in the OC content between density fractions of BU soils with regard to sediment and CO soils.According to the results, effective post-fire management should be oriented to control and reduce the erosion of aggregates < 2 mm, which present the highest SOC content and are very prone to be transported off-site. This fraction should include all the partially burned biomass (free light material), which acts as a first mulching and contains high amounts of OC that should be kept within the burned hillslope to increase soil fertility, promote vegetation recovery and act as a C sink. In the BU hillslope, eroded free light material might be buried at the depositional site and if the conditions are favourable for its conservation, SOC accumulation would be promoted, which may have implications for its stabilization, and the role of soil erosion as a C sink.

Adsorption-Release Characteristics of Phosphorus and the Community of Phosphorus Accumulating Organisms of Sediments in a Shallow Lake

One of the most challenging issues for developing countries in modern times is the care and management of clean, potable drinking water sources. Accordingly, this study singled out potential contributing factors to harmful algae blooms with a particular focus on phosphorus (P) release. The potential risks of P release for the drinking water from a lake in Fujian were assessed by investigating the spatial-temporal distribution of P, its exchange capacity, and its discharge capacity in sediment, including the community composition of phosphorus accumulating organisms (PAOs) and the phosphate’s initial migration effects on sediments. Different mixed materials, including soil aggregate distributions, sorbent, fractions, adsorption-desorption of P, and the community composition of PAOs were assessed. Total phosphorus (TP) content was measured at 24.4 ± 1.2 to 563.9 ± 38.2 mg/kg, but contents displayed some spatial differences. The dominant Ps found in the sample sediments were organic phosphorus and inorganic phosphorus associated with hydroxide Fe/Al-P, which accounted for 48.6% and 43.6%, respectively, of the TP content in the lake’s central waters. The TP concentration in vertical sediment ranged from 436.2 ± 21.3 to 602.9 ± 31.4 mg/kg. The TP spatio-temporal distribution inputs varied with rainfall (p &lt; 0.05). P deposition occurred throughout most water bodies (p &lt; 0.05), covering extensive areas and also decreasing at lower depths. Forty-four operational taxonomic unit (OTU) phosphorus-accumulating organism types from 11 phyla were detected in the sediment samples obtained from the Sanshiliujiao Lakes region. Proteobacteria also dominated compared to the organisms with the strongest PAOs. The diversity of PAOs in summer samples was significantly higher than that of the autumn samples. These findings provide a scientific foundation for determining the future discovery of the microbial mechanisms involved in the phosphorus metabolic cycle found in reservoir sediments. Various forms of phosphorus influenced the PAO diversity, especially Fe/Al-P. Thus, the abundance of PAOs in the sediment proved to be an essential component of the P cycle and may even play a key role in regional material circulation and in causing other environmental issues.

In‒situ immobilization remediation, soil aggregate distribution, and microbial community composition in weakly alkaline Cd‒contaminated soils: A field study

Biochar has advantages of a large specific surface area and micropore structure, which is beneficial for immobilization remediation of heavy metal‒contaminated soils. A field experiment was conducted to investigate the effects of rice husk biochar (BC) (7.5, 15, and 15 t hm−2) on Cd availability in soils and accumulation in maize (Zea mays L), soil aggregate structure, and microbial community abundance. The results show that BC treatment promoted the formation of large aggregates (5–8 and 2–5 mm) and enhanced aggregate stability, whereas it decreased the proportion of ≤0.25 mm soil aggregates. The geometric mean diameter and mean weight diameter under BC‒treated soils increased by 9.9%–40.5% and 3.6%–32.7%, respectively, indicating that the stability of soil aggregates increased. Moreover, BC facilitated the migration of Cd from large particles (>0.5 mm aggregates) to small particles (<0.25 mm aggregates). The application of BC decreased diethylenetriamine pentaacetic acid ‒extractable Cd by 17.6%–32.12% in contrast with the control. The amount of Cd in maize was reduced by 56.7%–81.1% for zhengdan958, 52.4%–85.9% for Sanbei218, and 73.7%–90.4% for Liyu16. When compared with the control groups, BC addition significantly (P < 0.05) increased the number of Ace observed, Shannon diversity indices, and the relative abundances of Proteobacteria, Acidobacteria, and Bacteroidetes. Therefore, rice husk BC exhibited a certain feasibility in immobilizing remediation of weakly alkaline Cd‒contaminated soils.

Long-term grass mulching waste recycling and evaluation activation of dissolved organic carbon

This study aimed to clarify that long-term leguminous grass mulching (crown vetch (CV) and white clover (WC)) and gramineous grass (orchardgrass (OG)) drive the distribution of soil aggregates and are associated with dissolved organic matter (DOM) components. Excitation emission spectroscopy and parallel factor analysis (EEM-PARAFAC) were used to evaluate the influence of different grass mulches among aggregates. The results indicated that legumes had a more significant impact on the distribution of aggregates and DOM content than gramineae grass mulching. Leguminous grass mulching significantly increased the proportion of macroaggregates >250 μm (74.65%–83.50%) and aggregates associated with dissolved organic carbon (DOC), especially in microaggregates <250 μm (172.27 mg kg−1 to 391.55 mg kg−1). In addition, leguminous grass mulching (CV and WC) contributed more to the increase in soil total nitrogen (TN) and three identified fluorescent components (UVC humic-like, UVA humic-like and protein-like). The component of UVC humic-like relative abundance decreased (48.66%–36.57%), and the protein-like component increased (21.88%–36.50%) as the aggregate size decreased, but the DOM three compositions did not change. The DOM of macroaggregates had higher aromaticity and lower molecular weight than microaggregates, and the highest abundance of UVC humic-like component (54.52%) was found in the gramineous (OG) large macroaggregates, while the higher abundance of protein-like components (31.07%–36.50%) occurs in leguminous mulching (CV and WC) microaggregates. The results contribute to a further understanding of the dynamic process by which grass mulching mediates aggregate formation and DOM component transformation in semiarid apple orchards under grass waste management.

Influence of Tillage on the Mollisols Physicochemical Properties, Seed Emergence and Yield of Maize in Northeast China

Tillage practices are critical for sustaining soil quality necessary for successful crop growth and productivity, but there are only few studies for strip tillage (ST) in the Mollisols region of Northeast China at present. A long-term (≥10-year) study was carried out to investigate the influence of within the tilled row (IR) and between rows (BR) in ST (10-year), conventional tillage (CT, 14-year) and no tillage (NT, 14-year) treatments on soil physicochemical properties. Soil samples were taken in May of 2019 at 0–5, 5–10, 10–20 and 20–30 cm depths and used to analyze bulk density (BD), soil aggregate distribution and stability, and soil organic carbon (SOC). Meanwhile, our study also explored the differences in seed emergence, soil moisture, and temperature during the seed emergence period, and yield of maize (Zea mays L.) among the different treatments. Similar soil properties were observed between ST-BR and NT, which showed they had a significantly greater BD, &gt;0.25 mm water stable aggregate content (WR0.25) (especially in the amount of &gt;2 mm and 1–2 mm size proportion), aggregate stability, and SOC than ST-IR and CT-IR at a depth of 0–20 cm. By improving soil conditions of seedbed, ST-IR and CT-IR increased soil temperature above NT by 1.64 °C and 1.80 °C, respectively, and ST-IR had a slight greater soil moisture than CT-IR in the top 10 cm layer during the seed emergence period. Late maize seed emergence was observed NT in than ST-IR and CT-IR and the average annual yields in ST were slightly greater than NT and CT, but the differences were not significant. Our results also showed that CT-BR had a poor soil structure and lower SOC than other treatments at 0–30 cm depth. We conclude from these long-term experimental results that ST could improve soil water-heat conditions to promote seed germination, maintain soil structure, and increase the maize yield and it should be applied in the Mollisols region of Northeast China.

Global meta-analysis suggests that no-tillage favourably changes soil structure and porosity

Role of soil to meet global food security, sustainable intensification and food nutritional quality has got renewed attention with a larger focus on soil physical condition. No-tillage (NT) practice can essentially contribute to develop a sustainable, low carbon and resource efficient agriculture, and encourage the use of crop residues for added soil benefits. Soil aggregation and pore size distribution, two most important soil physical factors controlling the mass and energy transport processes within the soil and between soil and environment, were evaluated under the NT through a global meta-analysis of 5065 pairs of data points from 419 peer-reviewed studies. Compared to conventional tillage (CT), NT increased mean weight diameter of aggregates, water stable aggregates, and macroaggregates by averages (0–30 cm) of 25, 10 and 22%, respectively, although predominantly in 0–10 and/or 10–20 cm layers, with an accompanying reduction in microaggregates. A small but significant 3% decrease in total porosity, a large reduction (20–32%) in macroporosity and a moderate increase (4–7%) in microporosity were realized under NT up to 20 cm soil depth. Bulk density remained stable, although a very large decrease (70% change over CT) in saturated hydraulic conductivity was recorded in 10–20 and >30 cm soil layers. Years of adoption of NT had an additive effect on mean weight diameter and macroaggregates, and the total and macroporosity. Increase in latitudes favoured soil aggregation and micropore volume under NT, while clay content was unfavourable to macro- and water stable aggregate contents. Improvement in structure and water retention properties relate to long-term sustainable development of soils by following no-till practice, which has far-reaching implications beyond the boundaries of agronomy.

Stability of Soil Aggregates at Different Altitudes in Qinling Mountains and Its Coupling Relationship with Soil Enzyme Activities

To explore changes in soil aggregate stability along an elevation gradient, and its regulating factors, soil samples were taken from the 0-10 cm surface layer at 3 different elevations on Taibai Mountain. We measured and analyzed the distribution of soil aggregates, physical and chemical properties, microbial biomass, and extracellular enzymes. The results showed that: ① the soil aggregates from the 3 elevations had mean weight diameters (MWD) of 2.17 mm, 1.83 mm, and 1.82 mm (increasing elevation), and geometric mean diameters (GMD) of 1.66 mm, 1.39 mm, and 1.32 mm, respectively. ② The change in soil aggregate stability along an elevation gradient was regulated by extracellular enzymes in the soil, in particular, the LAP in soil meso-aggregate and the BG in soil micro-aggregate. ③ Microorganisms can alleviate the N limitation at high elevations by adjusting the relative production of extracellular enzymes and altering nutrient utilization efficiency, which also changes soil aggregate stability along an elevation gradient. The results of this study have important scientific significance for soil quality evaluation and ecological environment protection in Taibai Mountain.

Optimizing interaction between crop residues and inorganic N under zero tillage systems in sub-humid region of Kenya

Conservation agriculture practices involving zero tillage and residue retention are promising nutrient management strategies for soil health restoration. Despite their potential positive impact on soil fertility, improved crop yields and increased revenues for smallholder farmers; their effect on nitrogen inputs and crop growth is not clearly understood. This may limit their potential as a nutrient management strategy that may remedy soil degradation and boost crop yields for farmers. This study investigated how different tillage practices, crop residues and inorganic nitrogen (N) options affect maize production, soil fertility and economics of smallholder farming systems. The study was conducted in a short-term (2 years) on-station trial, under randomized complete block design with three replications in a maize monocrop system. Six treatments, involving three different rates of maize stover residue (0, 3 and 5 t ha−1) and inorganic N (0, 3 and 5 t ha−1) inputs, respectively, were assessed under conventional and zero tillage systems. Mineral N and organic C were assessed at four depths (0–10 cm, 10–30 cm, 30–60 cm and 60–90 cm) whereas soil aggregate distribution was assessed at 0–5 cm, 5–10 cm, 10–15 cm and 15–20 cm depths. Application of inorganic N as the only input increased (p ≤ 0.05) grain yield (with the yields doubling in the short rains (SR) of 2015 and increasing by 1.4 times in long rains (LR) of 2016) compared to unfertilized control treatment. Treatment, soil depth and the time of sampling significantly affected soil mineral N concentration (p ≤ 0.05). Soil organic C reduced significantly (p ≤ 0.05) with sampling depths, but no differences were observed across treatments. At 0–5 cm depth, the proportion of large macroaggregates in zero tillage increased (48%; p ≤ 0.05) after application of crop residues at 5 t ha−1 relative to 3 t ha−1. Zero tillage treatment with application of 5 t ha−1 of residue and 80 kg N ha−1 was the most dominant and most profitable compared to the other treatments. This treatment had a benefit cost ratio (BCR) of 2.9 (in the short rains season of 2015) and 3.0 (long rains of 2016 seasons). Its marginal rate of return (MRR) was 368% (in the 2015 short rains season) and 416% (in the 2016 long rains season). This makes it a good nutrient management strategy with potential of optimizing maize yields.

Winter nocturnal warming affects the freeze-thaw frequency, soil aggregate distribution, and the contents and decomposability of C and N in paddy fields

Climate warming is expected to cause greater increases in nocturnal temperatures than daytime temperatures, thereby altering freeze-thaw cycles. Although the importance of freeze-thaw cycles in regulating soil aggregate stability and nutrient availability has attracted increasing attention, little is known about how winter nocturnal warming modulates freeze-thaw frequency, soil aggregate distribution, or the contents and mineralization of soil organic carbon (SOC) and total nitrogen (TN) in paddy fields. The nocturnal soil temperature in the upper 0–2 cm layer in a paddy field was elevated by approximately 2 °C using a passive nocturnal warming method during winter. An anaerobic experiment with a first-order reaction model was conducted to measure the C decomposition (C0) and N mineralization (N0) potentials in bulk soil and four soil aggregate fractions. Winter nocturnal warming significantly decreased freeze-thaw frequency and affected soil aggregate distribution and SOC and TN contents in <0.25 mm aggregate. Both SOC and TN fractions were significantly increased in the 0.25–1 mm aggregate but decreased in the >2 mm aggregate due to winter nocturnal warming. Winter nocturnal warming did not affect C0, N0, C0/SOC, and N0/TN in bulk soil. However, it decreased C0 and C0/SOC in all aggregates except the 0.25–1 mm aggregate, and increased N0 and N0/TN in all aggregates except the >2 mm aggregate. In the nocturnal warming treatment, the highest C0 and N0 values were found in the <0.25 mm aggregate, but only the N0 in the <0.25 mm aggregate was significantly larger than that in the other three soil aggregates. Our study indicated that winter nocturnal warming would reduce the freeze-thaw frequency and change C and N distributions in soil aggregates, resulting in increased soil N availability in the subsequent rice growth season.