Water-stable Aggregates Research Articles

Soil management and seasonality impact on soil properties and soil erosion in steep vineyards of north-western Croatia

Abstract In order to mitigate vineyard degradation, we study different soil management to obtain the most suitable practices. To study the effects of water erosion on vineyards, a rainfall experiment (58 mm h-1 for 30 min) was applied on Anthrosols in humid conditions to assess the impact of treatment (Tilled, Straw and Grass) and season (Spring and Summer). Higher bulk density (BD) and soil water content (SWC) were on the Straw treatment in the Spring period. Also, the Tilled and Grass treatment noticed higher mean weight diameter (MWD) and water-stable aggregates (WSA). In the Summer, BD, SWC and MWD were significantly higher on the Grass treatment. Higher values of time to ponding (TP) and time to runoff (TR) in Spring were recorded on the Grass treatment, Runoff was higher on the Straw treatment. Higher sediment concentration (SC) and soil loss (SL) were noticed during the Tilled treatment. In the Summer period, TP was higher on the Straw treatment, while TR and Runoff were higher on the Straw, SC and SL on the Tilled treatment. This study confirms the positive effects of grass cover and straw mulching as a sustainable agricultural practice in sloped vineyards of north-western Croatia.

Long-term contrasting tillage in Cambisol: effect on water-stable aggregates, macropore network and soil chemical properties

Long-term contrasting tillage in Cambisol: effect on water-stable aggregates, macropore network and soil chemical properties

Soil-Available Nutrients Associated with Soil Chemical and Aggregate Properties following Vegetation Restoration in Western Sichuan, China

The status and drivers of soil-available nutrients in plant-recovered soils are not fully understood, limiting our ability to explore the role of soil-available nutrients in soil geochemical cycling and ecosystem sustainability. Here, we combined the spatial distribution of soil-available nutrients and chemical and aggregate properties from six soil types (subalpine meadow soil, meadow soil, dark brown soil, brown soil, yellow-brown soil, and cinnamon soil) and three horizons (a leaching horizon, sediment horizon, and parent material horizon) to study the status and drivers of soil-available nutrients. Our findings reveal that the soil-available nitrogen (AN) ranged from 72.33 to 169.67 mg/kg, the soil-available phosphorus (AP) ranged from 1.77 to 75.90 mg/kg, and the soil-available potassium (AK) ranged from 46.43 to 88.55 mg/kg in the six soil types. The subalpine meadow soil and the dark brown soil had the highest soil AN, with means of 169.67 and 139.35 mg/kg, respectively. The brown soil had the highest soil AP, with a mean of 75.9 mg/kg, and the dark brown soil and the brown soil had the highest soil AK, with means of 83.49 and 88.55 mg/kg, respectively. The results show that the soil types and soil depths had a significant impact on the status of AN, AP, and AK (p < 0.05). Moreover, a higher cation exchange capacity (CEC), the macro-aggregate contents (with 2–1 mm and 1–0.5 mm particle sizes) of the non-water-stable aggregates, and the macro-aggregate content and stability (2–1 mm particle size and geometric mean diameter (GMD) of the water-stable aggregates were deemed to facilitate soil-available nitrogen because of the positive correlations (p < 0.05). Lower exchangeable cations (ECs) and the micro-aggregate content (≤0.1 mm particle size) of the water-stable aggregates and higher soil cations helped in the accumulation of soil-available phosphorus and soil-available potassium, respectively. Moreover, the regulation of the soil chemical and aggregate properties was found to vary with soil type and horizon in a correlation analysis. Together, our results provide insights into the importance of chemical and aggregate properties in regulating soil nutrient availability across soil types, as well as providing strong support for the inclusion of soil resource utilization in regional forest restoration and management.

Synergistic effects of biochar and carboxymethyl cellulose sodium (CMC) applications on improving water retention and aggregate stability in desert soils

Making improvements to the water-holding characteristics and water-erosion resistance of desert soils, particularly in inland extremely arid areas, is vital for achieving both sustainable water resource utilisation and food security. The aim of this study is to evaluate the effects of the co-application of biochar and carboxymethyl cellulose sodium (CMC) on the physical properties of sandy desert soil, including infiltration rate, saturated water conductivity, field water-holding capacity and aggregate stability. Sandy desert soil samples were collected from jujube plantations on the southern edge of the Taklimakan Desert in the Hotan Prefecture, Xinjiang, China. Five CMC application ratios (C0:0, C1:0.01 g/kg, C2:0.02 g/kg, C3:0.04 g/kg and C4:0.08 g/kg) and five biochar application ratios (B0:0, B1:1.0 g/kg, B2:2.0 g/kg, B3:4.0 g/kg and B4:8.0 g/kg) were designed and a total of 11 experimental treatments were performed, which were labelled as CK (control group), B2C0, B2C1, B2C2, B2C3, B2C4, B4C4, B0C2, B1C2, B3C2 and B4C2. Compared with CK, the combined application of biochar and CMC reduced the soil bulk density (BD) by 1.29–9.41% and the saturated hydraulic conductivity (Ks) by 29.64–94.98%, and increased the soil saturated water content (SSWC) by 8.81–30.74% and the water holding capacity (WHC) by 13.91–36.87%. Similarly, the water-stable aggregates that were co-applied with biochar and CMC increased by 29.10–256.86%. This resulted in significant improvement in the stability of sandy desert soil against water erosion. The principal component analysis (PCA) results found B4C4 to have the best comprehensive improvement effect. Therefore, 0.08 g/kg of CMC and 8.0 g/kg of biochar were used as recommended for improving the hydraulic properties of desert soils. Generally, CMC and biochar have a mutually complementary effect on improving sandy desert soil, providing new ideas and approaches for the improvement of soil and the sustainable development of agriculture in desert areas.

Soil Aggregates Are Governed by Spacing Configurations in Alfalfa-Jujube Tree Intercropping Systems

Soil aggregates play an important role in affecting the structural stability of the soil, and it is important to understand the relationship between soil aggregate stability and crop yield in herbage-fruit tree intercropping systems. In this study, we determined the optimal spacing configurations for improving aggregate stability while increasing crop yields in alfalfa-jujube intercropping systems. The treatments included three intercropping patterns, i.e., the distances between alfalfa and jujube at 0.5 m (IP0.5m), 1 m (IP1m), and 1.45 m (IP1.45m), along with monoculture alfalfa (CKAL) and jujube (CKJU). The results showed that IP0.5m, IP1m, IP1.45m, and CKJU effectively improved soil aggregate structure compared to CKAL. The IP1m spacing significantly increased the amounts of macro-aggregates (8.2%), and improved soil mechanical properties and aggregate stability among the other treatments, which was partly attributable to increased mean weight diameter (13.6%) and decreased soil aggregate destruction rate of water-stable aggregates (2.9%). The results of the principal component analysis showed that IP1m treatments had a positive effect on PC1. The one-meter spacing of jujube-to-alfalfa intercropping optimized the soil structure while improving the yield (8.3%); thus, it can be considered the most suitable intercropping spacing configuration for growing alfalfa in jujube plantations.

Dynamic of Change in Soil Physical Properties and SoyBean Growth through The Application of Biochar on Lombok Vertisols

Vertisol is a type of soil whose mineral fraction is dominated by 2:1 type clay minerals (smectite) which have the property of swelling-shrinking periodically as the soil water content changes. However, these physical properties can be improved by the application of biochar so that it can support plant growth. The aim of this study was to evaluate the effect of biochar on changes in the physical characteristics of vertisols soils and growth performance of soybean plants. This research was conducted in Kawo Village, Pujut District, Central Lombok. This study was designed to test the application of two types of biochar, namely rice husk biochar (BS) and corn cob biochar (BJ) at several doses, namely 0, 15, 30 and 60 g/kg of vertisols soil and design using a randomized block design with 6 replications. The parameters measured were unit weight, soil density, porosity, soil tensile strength, available water capacity, aggregate stability, cole value, crack pattern and soybean growth test. The results showed that the application of biochar could improve the physical properties of vertisol soil and also has implications for improving the growth of soybean plants. Observational data showed that a dose of 60 g/kg of biochar, both rice husk and corn cob biochar, showed better changes in soil physical properties compared to biochar doses of 15 g/kg, 30 g/kg and without the addition of biochar. Besides that, the treatment of rice husk and corn cob biochar at a dose of 60 g/kg gave better vegetative growth of soybean plants.

Under-vine cover crops: Impact on physical and biological soil proprieties in an irrigated Mediterranean vineyard

Despite their potential benefits, cover crops in vineyards under to Mediterranean climate conditions are still not widespread, especially in the vine row. This under-vine space is normally kept weed-free through the application of herbicides and/or tillage. In this work, we evaluate the effect of a Trifolium fragiferum L. under-vine cover crop (UV) on soil quality, as reflected by a variety of physical, chemical, and biological soil indicators. 15 months after under-vine cover crop implementation, total (SOC) and particulate (POC) organic carbon storage, and soil aggregation (abundance (WSA) and mean weight diameter (MWD) of water stable aggregates) were compared with a control without cover (T) at 0–15 cm. In addition, for three consecutive years after under-vine cover crop implementation, the evolution of soil microbial communities was monitored through the determination of soil basal respiration, soil microbial biomass carbon and nitrogen (MBC and MBN), and community-level physiological profiles (CLPPs). The establishment of the under-vine cover crop resulted in higher values of SOC (27.78 Mg·ha−1 in UV vs. 20.71 Mg·ha−1 in T, +33%) and POC (4.75 Mg·ha−1 in UV vs. 2.73 Mg·ha−1 in T, +74%), as well as aggregation parameters (MWD: 1.82 µm in UV vs. 1.56 µm in T, +17% and WSA: 84.68% in UV vs. 71.58% in T, +18%). An evolution towards progressively greater values of biological activity (basal respiration) and microbial biomass was detected in under-vine cover crop soils as time elapsed. It was concluded that the Trifolium fragiferum L. under-vine cover crop led to soil quality improvement in our Mediterranean climate vineyard. Interestingly, this positive effect was noticed shortly after its implementation.

PHYSICO-CHEMICAL ASPECTS OF SOIL WATER STABILITY

The influence of contact with water of soil aggregates of chernozem, sod-podzolic and gray forest soils on their water stability has been studied. It is established that an increase in the contact time of soil aggregates with water leads to a gradual decrease in their water stability. The conducted verification of the effect of salt solutions on the water stability of soil aggregates showed that the loss of water stability of aggregates in contact with water is not directly proportional to the disjoining pressure. It was found that when soil aggregates come into contact with water, fractal clusters of humus particles (F-clusters) are isolated from them. It is suggested that F-clusters, which are the basis of soil gels, determine the physical basis of soil waterproofness.

РОЛЬ СЕВООБОРОТОВ В ПОДДЕРЖАНИИ АГРОФИЗИЧЕСКИХ СВОЙСТВ ЧЕРНОЗЕМОВ, ОРОШАЕМЫХ СЛАБОМИНЕРАЛИЗОВАННОЙ ВОДОЙ

Purpose: to determine effects of grain-fodder and vegetable crop rotation on the agrophysical properties of chernozems irrigated with low-mineralized water, in comparison with the non-irrigated counterpart. Materials and methods. The studies were carried out in Neklinovsky district Rostov region on ordinary chernozems in grain-fodder crop rotations, non-irrigated (without irrigation) and irrigated with annual irrigation rates of 1500–2500 cubic m/ha and in vegetable crop rotation with annual irrigation rates of 3000–4000 cubic m/ha. The source of irrigation is the Miussky estuary with low-mineralized water. Soil samples were taken in autumn after crop rotations, their granulometric texture, aggregate water stability and humus were determined. In profile pits - the soil bulk density. The selection of soil samples, their analysis and evaluation were carried out according to generally accepted methods. Results. The deterioration of water-physical properties was most clearly manifested during long-term irrigation with low-mineralized water on a plot with vegetable crop rotations, where irrigation rates were more than 3500 cubic m/ha. The arable land of such chernozem is highly compacted (1.41 t/cubic m), the bulk density 40 cm deeper is 1.45–1.47 t/cubic m. By granulometric texture, the upper soil layers acquired the properties of medium loamy soils due to the leaching of clay particles. There are practically no water-stable aggregates along the soil profile (about 10 %). Soil porosity deteriorated to excessively low values. Conclusions. Studies have shown that the higher the water load in crop rotations, the more the negative agrophysical properties of chernozems progress, especially when irrigated with low-mineralized waters.

Preliminary Study on the Effect of Different Ecological Cultivation Modes on the Water Stability of Soil Aggregates in Rubber Based Agroforestry Systems

Preliminary Study on the Effect of Different Ecological Cultivation Modes on the Water Stability of Soil Aggregates in Rubber Based Agroforestry Systems

Soil Aggregation and Aggregate-associated Carbon affected by Long-term Crop Residues Incorporation in Rice-Wheat Cropping System

Crop residue management is one of the options for enhancing soil organic carbon stabilization by improving soil aggregation in semi-tropical soil. We studied the influence of different levels crop residues incorporation on aggregation and carbon stabilization in different soil aggregates after 23 years of continuous rice- wheat cropping system on sandy loam calcareous soil. 100% residue incorporation caused a significant increment of 49.09 % in total water stable aggregates (>0.25 mm) in surface soil. Carbon content in both macro- and microaggregates was increased, but increment was greater in macroaggregates (33.47%) than microaggregates (16.23%). These results show that long-term application of organics in combination with inorganic fertilizers helped in carbon accumulation in macroaggregates, and thereby improving soil carbon status.

Effect of different biochar addition rates on Soil Physical Properties in rain-fed farmland

Biochar is extensively used for ameliorating soil structure. However, the evaluation of soil physical properties influenced by its large-scale use is still unclear. Moreover, research on biochar is mainly based on laboratory tests, lacking medium and long-term field positioning tests. In this study, a local field trial was conducted for 3 years on the Loess Plateau in central Gansu, China. Six levels of biochar treatment were set with application amounts of 0 t·ha-1, 10 t· ha-1, 20 t·ha-1, 30 t·ha-1, 40 t·ha-1, and 50 t·ha-1 (CK, T1, T2, T3, T4, and T5, respectively). The influence of various input levels of biochar on soil porosity, bulk density, aggregate stability, and soil saturated hydraulic conductivity from the 0 cm to 30 cm layer were studied during the three years of wheat field experiments. The experimental study indicates that the increase of biochar addition can significantly (p < 0.05) reduce soil bulk density and increase not only soil saturated hydraulic conductivity but also total soil porosity, content of soil mechanically stable aggregates, and its MWD from the 0 cm to 30 cm soil layer. Among them, T5 treatment is the most significant (p < 0.05). While its content determination of Water Stable aggregates and its MWD only have an obvious (p < 0.05) improvement effect from the 0 cm to 20 cm soil layer, and T5 is the most significant. Therefore, large-scale biochar application is conducive to the improvement of farmland soil physical properties in this region.

Key Soil Physicochemical Properties Regulating Microbial Community Structure under Vegetation Restoration in a Karst Region of China

Background: Vegetation restoration influences soil properties considerably, which in turn interact with microbial community structure and regulate ecosystem stability. However, the influence of soil physical properties on soil microbial community structure has been poorly characterized. Methods: We investigated changes in soil physicochemical properties and bacterial and fungal diversity and composition after natural restoration (grasslands (GL)) and afforestation (artificial forests (AF)) for more than 40 years in a karst faulted basin in China. Results: Compared with that in undamaged natural forests (NF), AF enhanced soil organic carbon and nutrient contents markedly, whereas GL improved soil water stable aggregate, bulk density, and pH. Alpha diversity analyses suggested that vegetation restoration had no significant effect on Chao 1 index and Shannon index of bacterial and fungal communities. However, according to the nonmetric multidimensional scaling analysis results, the dissimilarities in bacterial and fungal community composition between GL and NF were more distinct than those between AF and NF. Such diverse responses of bacterial community structure to vegetation restoration were largely explained by soil pH. Additionally, soil pH, porosity, bulk density, and field capacity were significantly correlated with fungal community structure ( P < 0.05). Conclusion: Vegetation restoration in ecologically fragile areas should focus on understanding interactions between microbial community structure and soil chemical properties as well as physical properties.

Corn straw return effectively improves the stability and increases the carbon and nitrogen contents of waterstable aggregates in northeastern China black soil

Corn straw return effectively improves the stability and increases the carbon and nitrogen contents of waterstable aggregates in northeastern China black soil

Karakteristike černozemolike karbonatne livadske crnice Oglednog polja za soju i šećernu repu u Starom Bečeju (Srbija)

In this study, Fluvisol from the area of Stari Beĉej (Serbia) was investigated with the aim of evaluating selected chemical and physical indicators of soil quality affter its long-term use in crop production. Ten bulk soil samples (soil depth: 0-210 cm) were collected to analyze soil chemical properties (humus, CaCO3, pH, P2O5, K2O), texture (six samples, soil depth: 0-130 cm), dry-stable aggregate distribution and stability of soil aggregates (four samples, soil depth: 0-80 cm). Additional undisturbed core samples (100 cm3 volume) were also collected to determine soil bulk density, total porosity, field air capacity, and field water capacity. Water infiltration capacity was also measured in the field using a double ring infiltrometer. The results indicated that the soil had a two-layer profile and a silty loam texture (with a physical clay content of 41-42% and a colloidal clay content of 27-28%). The humus horizon has quite favorable chemical properties up to a depth of 60 cm, and at a depth of 60-80 cm it is alkalized under the influence of saline groundwater. From an agronomic point of view, the structure of this soil is favorable. The results of determining the stabillity soil aggregates show that the soil structure in the Ahp and Ah horizons at depth (0-40 cm) with a content of 41% of water-stable aggregates < 0.25 mm is significantly worse (less favorable) than in the surface part of the AhBca horizon (40-60 cm) with a content of ~58% of waterstable aggregates < 0.25 mm. The main physical properties are not particularly favorable in the Ah and AhBca horizons to a depth of 80 cm. The Ah horizon is very compact (bulk density: 1.33-1.38 g/cm3 ), and the air-filled porosity is very low (less than 5%) and small (5-10%) at all depths up to 80 cm, and it is lowest in the surface 0-20 cm layer, only 3.8%. Infiltration capacity is low. The reserves of soil moisture available for plant growth in the soil layer 0-100 cm are very good (> 160 mm water depth). In summary, the results of this study show that perennial tillage can lead to a loss of soil productivity and serious soil degradation.

Impact of Landslides on Physicochemical and Biological Properties of Western Ghats Soils

Landslides cause major loss of natural forest ecosystem and it is negatively impact on forest land by depleting soil biological, physical and chemical properties to reduce crop productivity. The present study was conducted to assess the impact of landslides on soil quality of central Western Ghats regions of Karnataka. Soil samples were collected from Adlur, Kavalalli, Dongri, Artibail and Mastikatta to study the variation of soil biological physical and chemical properties in eroded and pristine soils. The results of the present investigation has revealed that the soil physicochemical properties such as water stable aggregates (60%), organic carbon (1.23%), organic matter (2.12%) and available N, P and K (323.41, 18.23 and 328.71 kg/ha respectively) were found to be higher in pristine ecosystem compared to eroded soils. Furthermore, soil biological properties like microbial biomass carbon, glomalin content and mycorrhizal spores and soil enzyme activity were found to be greater extent in the pristine ecosystem compared to eroded soils. The study highlights the impact of landslides on soil physicochemical and biological properties such that suitable remedies can be undertaken in order to prevent soil loss such that soil biological properties can be maintained which is pre-requisite for plant growth and development.

Deep vertical rotary tillage mitigates salinization hazards and shifts microbial community structure in salt-affected anthropogenic-alluvial soil

Soil tillage management is one of the major agricultural countermeasures to the ever-expanding soil salinization in arid and semiarid irrigated regions worldwide. However, how tillage implementations mitigate soil salinization hazard, improve soil quality and enhance microorganism function has not yet been clearly clarified. A two-consecutive-year field plot experiment with three tillage treatments, including CT (conventional rotary tillage, depth 25 cm), VRT (vertical rotary tillage, depth 25 cm) and DVRT (deep vertical rotary tillage, depth 50 cm), were conducted to examine the tillage effect on soil salinization and microbial communities. Dynamics of soil salinity (EC1:5), bulk density (ρb), saturated hydraulic conductivity (Ks), organic carbon (OC), water-stable aggregates (WSA), and bacterial and fungal community structures were measured. The results indicated that, compared with the CT and VRT treatments, the DVRT treatment had lower EC1:5 and ρb, but higher Ks at 0–40 cm soil layers. The promoted salt leaching was mostly attributable to the improved soil porosity and permeability under the DVRT treatment. The DVRT significantly increased soil total OC and percentage of > 2 mm (WSA1) and 2–0.25 mm (WSA2) aggregates, but decreased that of 0.053–0.01 mm (WSA4) aggregates. Soil bacterial richness and diversity was negatively responsive to the DVRT, whereas fungal richness and diversity showed positive responses to the DVRT. The DVRT did not alter the dominant microbial phyla but changed their relative abundance. At the genus level, the DVRT shifted bacterial community from Vicinamibacterales and Lysobacter -dominated to Vicinamibacterales, Geminicoccus and Marmoricola -dominanted, and transformed fungal community from Mortierella and Chaetomium -dominated to Mortierella and Aspergillus -dominated. Moreover, seasonal changes also showed significant direct and interactive influences on the above edaphic properties and microbial communities. Edaphic properties including EC1:5, OC, ρb and WSA1 explained the causal connection among tillage practices and microbial richness, diversity and community structure. It was concluded that the DVRT mitigated soil salinization hazards by promoting salt leaching and improving macro-aggregates and organic carbon, and shifted soil microbial communities by evolving the microbes better adaptable to the changed microhabitats.

State of water-stable soil structure in the Central Forest-Steppe under agrogenic and postagrogenic maintenance

Aim. To determine the regularities in the formation of water-stable structure and to obtain the objective integral information about the process of break-up and consolidation of the water-stable structure under agrogenic and postagrogenic load on the main soil types of the Central Forest-Steppe of Ukraine. Methods. The field method – the soils of chernozem type were investigated (seven chernozem-like soil types of different granulometric composition and humus content) in the central part of the Forest-Steppe of Ukraine, the laboratory analytical method (wet sieving of soil structure), the mathematical-statistical method (non-parametric statistics, factor, cluster, and fractal analyses). Results. The analysis of the water stability of the structure of chernozem-like soils in the Forest-Steppe demonstrates the perspectives of using modern statistical methods: fractal, factor, cluster methods, and the method of non-parametric statistics, which demonstrates their sensitivity to insignificant changes in the distribution of water-stable aggregates within the agronomically valuable interval. The soil types of postagrogenic maintenance form the distribution of water-stable aggregates, making up “prevailing” sizes of aggregates in the interval of sizes of 5–3 and 2–1 mm, which ensures the persistent state of the re-distribution where the index of Hurst has the values of H > 0.75. The agrogenic impact on soils changes the re-distribution of water-stable aggregates, destroying their natural distribution and ensuring the antipersistent state of the distribution with low stability (D > 1.43 and Н < 0.58). Under postagrogenic maintenance of soil types, there is a stable mutual connection between water-stable aggregates, structural units, and ESP (R = +0.78), and in the total of correlation relations, the direct and inverse correlation relations of R> ± 0.55 level are >30 % with the 1.5 to 1 ratio in favor of inverse proportion relations which ensures a high level of self-regulation for the hierarchical organization of the structural and water stable state. Conclusions. The determining index, characterizing the stability level of the water-stable structure, was found to be the content of water-stable aggregates of 3–1 mm and > 0.25 mm and the weighted average diameter of water-stable aggregates within the agronomically valuable interval of sizes that demonstrated a strong correlation (R = ± 0.76–0.96 ± 0.02) with fractal dimensionality (D > 1.4) and the index of Hurst (Н) which allowed for forming a gradation scale for the evaluation of the water-stable structure and the degree of agrogenesis manifestation of soils in the Forest-Steppe of Ukraine. In terms of the rate of agrogenesis manifestation via the formation of the degree of the water-stable structure, the soils of chernozem type were divided as follows: gray forest low-humus heavy-loamy light-clay soil on carbonate loess-like clay < typical low-humus heavy-loamy light-clay chernozem on loess-like clay < meadow-chernozem low-humus carbonate heavy- loamy soil on loess-like clay < typical medium-humus heavy-clay chernozem on loess.

Effect of Biochar on Soil Physiochemical Properties and Bacterial Diversity in Dry Direct-Seeded Rice Paddy Fields

The effects of biochar application on dry direct-seeded rice paddies remains unclear. Therefore, we applied biochar to dry direct-seeded rice paddy fields over 3 consecutive years to assess its effects on soil physicochemical properties and bacterial diversity (conventional fertilization [CK]; biochar + conventional fertilization [BC]). BC increased the content of 0.25–5 mm soil water-stable aggregate particles, but decreased that of <0.25 mm soil water-stable aggregates. At different soil depths, BC significantly reduced sand content and increased silt content. Compared to CK, BC significantly increased the available phosphorus and potassium content of the 0–10 and 10–20 cm soil layers. There were no significant differences in pH, organic matter, total nitrogen, total phosphorus, or total potassium content between the treatments at different soil depths. Compared to CK, BC significantly increased soil neutral phosphatase and catalase activities. Furthermore, BC significantly increased bacterial richness, but had no significant effect on bacterial diversity. According to Qualcomm sequencing analysis, BC increased the relative abundance of Verrucomicrobia, Chloroflexi, Bacteroidetes, Nitrospirae, Verrucomicrobiae, Blastocatellia_Subgroup_4, and Anaerolineae in soil compared to CK. The soil bacterial genera in BC had stronger interrelationships than those in CK. According to redundancy analysis, organic matter was the main environmental factor influencing bacterial community structure. Overall, biochar could promote soil nutrient conversion in dry direct-seeded rice paddies, improve soil effective nutrient content, change the composition of soil bacterial communities, and increase soil bacterial richness. Applying biochar in dry direct-seeded rice cultivation could help realize low-carbon agriculture.

Edaphic controls of soil organic carbon in tropical agricultural landscapes

Predicting soil organic carbon (SOC) is problematic in tropical soils because mechanisms of SOC (de)stabilization are not resolved. We aimed to identify such storage mechanisms in a tropical soil landscape constrained by 100 years of similar soil inputs and agricultural disturbance under the production of sugarcane, a C4 grass and bioenergy feedstock. We measured soil physicochemical parameters, SOC concentration, and SOC dynamics by soil horizon to one meter to identify soil parameters that can predict SOC outcomes. Applying correlative analyses, linear mixed model (LMM) regression, model selection by AICc, and hierarchical clustering we found that slow moving SOC was related to many soil parameters, while the fastest moving SOC was only related to soil surface charge. Our models explained 78–79%, 51–57%, 7–8% of variance in SOC concentration, slow pool decay, and fast pool decay, respectively. Top SOC predictors were roots, the ratio of organo-complexed iron (Fe) to aluminum (Al), water stable aggregates (WSagg), and cation exchange capacity (CEC). Using hierarchical clustering we also assessed SOC predictors across gradients of depth and rainfall with strong reductions in Roots, SOC, and slow pool decay associated with increasing depth, while increased rainfall was associated with increased Clay and WSagg and reduced CEC in surface soils. Increased negative surface charge, water stable aggregation, organo-Fe complexation, and root inputs were key SOC protection mechanisms despite high soil disturbance. Further development of these relationships is expected to improve understanding of SOC storage mechanisms and outcomes in similar tropical agricultural soils globally.