Coarse-textured Soils Research Articles

Unlocking the potential of conservation agriculture for soil carbon sequestration influenced by soil texture and climate: A worldwide systematic review

Conservation Agriculture (CA) systems have gained significant attention as a sustainable cropping approach that not only improves crop yields but also contributes to climate change adaptation and mitigation through enhanced soil organic carbon (SOC) sequestration. However, a comprehensive understanding of the influence of soil texture and climate conditions on SOC sequestration under CA remains limited. To address this knowledge gap, we conducted a systematic review using the PRISMA method, analyzing data from 35 peer-reviewed articles encompassing 71 field experiments and 451 observations worldwide. Our findings demonstrate the substantial positive impact of CA on SOC sequestration, with an overall increase of approximately 78%. Remarkably, only a mere 2% of observations reported neutral effects, while 20% indicated adverse outcomes. Notably, SOC sequestration rates were highest in tropical regions experiencing dry winters, reaching an impressive 2.50 Mg/ha/year in the topsoil layers. Moreover, fine and moderate textured soils, such as clay, clay loam, loam, and clay sandy, exhibited higher SOC sequestration rates (20-27%) compared to coarse-textured soils dominated by sandy proportions (9%). These findings emphasize the significance of climate conditions and soil texture in shaping the impact of CA on SOC sequestration.

Modification of the RothC model to evaluate the inconsistent effect of conservation tillage on SOC stock and a suggestion of a national-scale assessment framework

Simulation of conservation tillage effect on soil organic carbon (SOC) stock on the national scale is essential for Tier 3 level greenhouse gas inventory in the agricultural sector. However, the conservation tillage effects varied depending on different soil conditions, potentially leading to inaccurate national assessments. This study aimed to propose a framework for estimating the national scale impact of conservation tillage on SOC. As even in the most commonly used SOC dynamic model, the Rothamsted Carbon Model (RothC), does not reflect the conservation tillage effect in an explicit way, we modified it by developing the tillage rate modifiers (TRMs). First, we investigated the conditions for the inconsistent conservation tillage effects using the decision tree analysis based on 210 field experiment data from the mid-latitude region. The results highlighted that soil sand content and the existing SOC stock were the main factors driving the inconsistencies. After we categorized into four distinctive conditions, the TRMs for each condition were parameterized using a genetic algorithm. The average TRMs were 0.88 in the soils with sand content >37.6 % and 1.58 in the soils with sand content ≤37.6 %, indicating that conservation tillage is more effective in coarse-textured soil, and there is a risk of decreasing SOC stock in the latter condition. Using the modified RothC model, a three-step national-scale simulation framework was suggested: compiling country-specific data, establishing baseline and conservation tillage scenarios, and modeling conservation tillage effects with uncertainty analysis. Our approach also defined the maximum conservation tillage area, factoring in local cropping systems and soil conditions. Our refined RothC model with TRMs provides a nuanced understanding of conservation tillage effects, emphasizing the role of soil characteristics. The proposed national-scale simulation framework offers a reliable tool for evaluating conservation tillage impact on SOC, ensuring more accurate greenhouse gas inventories in agriculture.

Soil bacterial habitat generalists strengthen depth-dependent organic carbon accrual in coastal reclaimed lands after afforestation

The microbially driven soil organic carbon (SOC) turnover and accrual at the aggregate scale are crucial to reveal potential SOC sequestration and stabilization. However, information about how afforestation in reclaimed lands influences the bacterial contribution to SOC within soil aggregates remains unclear. Here, we investigated the bacterial taxonomic and functional composition and habitat associations of species (i.e., generalists and specialists) in different aggregates. Soil aggregates were isolated using an optimal soil moisture method. Bacterial taxonomic and functional composition were determined using high-throughput sequencing and PICRUSt2, respectively. We evaluated the effect of bacterial traits on SOC accrual within aggregates along the soil profile in unreclaimed tideland and two poplar plantations at different stages of reclamation (i.e., reclaimed 24 and 64 years prior to data collection) in East China. The bacterial traits and SOC concentration did not differ significantly among different-sized aggregates and that bacterial alpha diversity and SOC within aggregates increased with reclamation time, but this was only pronounced in surface soil. The relative abundance of generalists increased, specialists decreased in the soil profile with reclamation time, and the magnitude of variation declined with soil depth. The random forest model and variation partitioning analysis confirmed that generalists and specialists dominated the variation in SOC. Moreover, some subgroups from Proteobacteria, Acidobacteria, Actinobacteria, and Chloroflexi phyla were rich in generalists and may play crucial roles in SOC accrual. These findings suggest that the bacterial traits and SOC in coastal coarse-textured soil were not affected by aggregate sizes and might rely on other aggregate attributes (e.g., stability). Furthermore, SOC accrual was strongly affected by an increase in habitat generalists. We provide new insights into the variation pattern in SOC and bacterial traits at the aggregate scale and illustrate that bacterial generalists have the greatest impact on SOC accrual in coastal reclaimed lands after afforestation.

Excluding quartz content from the estimation of saturated soil thermal conductivity: Combined use of differential effective medium theory and geometric mean method

Saturated soil thermal conductivity (λsat) is the maximum soil thermal conductivity value of a given soil. Although it can be determined accurately with a heat pulse sensor, there are challenges to prepare fully saturated soil samples. Numerous models have been developed to estimate λsat, and among these, the geometric mean method (GMM) generally performs well. The GMM requires soil mineral composition or quartz content information, which is unavailable for most soils. Earlier studies commonly used assumed that quartz content (fquartz) was equal to sand content (fsand) or to 0.5 × fsand, which led to significant λsat estimation errors especially on coarse-textured soils. We derived a novel method to estimate λsat from soil porosity (ϕ) based on a combination of the GMM and differential effective medium theory (DEM). The new DEM-GMM approach has a single parameter, cementation exponent (m). Using a calibration dataset of 43 soils, we determined best fit m values for soils in three groups: 1.66 for Group I (fsand < 0.4), 1.62 for Group II (0.4 <= fsand < 1) and m = -1.34ϕ+1.70 for Group III (fsand = 1). Using best fit m values for different groups, the new model can estimate λsat values from ϕ. Independent validation results on another 46 soils showed that the new model outperformed the GMM method with the assumption that fquartz = fsand or fquartz = 0.5 × fsand. The mean RMSE, Bias and R2 values of the DEM-GMM approach were 0.202 W m−1 K−1, 0.013 W m−1 K−1 and 0.89, respectively, and corresponding values of the GMM with the two assumptions were 0.295 and 0.476 W m−1 K−1, 0.056 and -0.28 W m−1 K−1, 0.80 and 0.82, respectively. The robust performance of the DEM-GMM approach suggests that it can be incorporated into thermal conductivity models to accurately estimate the thermal conductivity of unsaturated soils.

Adding nitrification inhibitors to N fertilisers induces rhizosphere acidification and enhances P acquisition: A meta-analysis

Ammonium (NH4+) absorption by crops enhances inorganic phosphate (Pi) acquisition efficiency mediated by rhizosphere acidification. The application of nitrification inhibitors (NIs) prolong NH4+ retention in soil by inhibiting ammonia oxidation and facilitating ammonium uptake by crops which may promote crop P utilisation. However, the efficacy of NIs on enhanced P-utilisation efficiency has not been comprehensively evaluated, and the mechanism underlying these effects remains unclear. Here, a meta-analysis of 92 peer-reviewed articles (1217 paired observations) was conducted to investigate soil pH and crop P absorption changes under NIs amendment, and boosted regression tree model was adopted to identify the primary factor regulating enhanced P-efficiency. The results showed that the addition of NIs reduced the rhizosphere soil pH by 12.37% and increased bulk soil pH by 2.38%, increased plant N and P uptake by 16.09% and 8.49%, respectively, and shoot N and P concentrations by 4.38% and 6.73%, respectively. NIs significantly decreased the crop N/P ratio and alleviated P limitation for crop production. Fertiliser (N and P) application method, NI product type, and soil properties (soil organic carbon, available P, total N content and soil texture) are major factors affecting crop P uptake. Using dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP) as NIs combined with the application of ammonium-based fertiliser, adoption of subsurface or one-time N application, or application of these fertilisers to coarse-textured soils could significantly decrease rhizosphere soil pH while increasing crop P uptake. This study quantitatively demonstrated the positive impact of NIs on crop P acquisition using a meta-analysis approach, enhanced the knowledge on the incidental efficacy of N stabilisers and provide a strategy for the sustainable management of N and P in agriculture.

Root but not shoot litter fostered the formation of mineral-associated organic matter in eroded arable soils

Erosion leads to a decline in carbon (C) stocks in arable soils and negatively impacts soil functions worldwide. For soil restoration, it is critical to identify the factors that link crop residue quality to effective C sequestration in the soil, primarily through the formation of mineral-associated organic matter (MAOM) and through incorporation into aggregates (oPOM). The widely accepted concept links effective C stabilization with input of high-quality substrates, but studies of C-deficient soils do not support this assumption. Therefore, we aimed to determine the potential of eroded arable soils to stabilize C from barley shoot and root residues, which represent high- and low-quality inputs, respectively. In a year-long laboratory experiment, we added the residues to two soil pairs (eroded and non-eroded) with different soil textures, observed the formation of oPOM and MAOM and identified microbial groups important for substrate transformation. We found that eroded soils retained added residues very efficiently (35–65% bound residue C), making them a high-priority target for C sequestration. Root residues caused more efficient MAOM formation than shoot residues, primarily by direct binding of depolymerized root-C to mineral surfaces without subsequent microbial transformation. This root C stabilization in MAOM was more pronounced in eroded (highly C-undersaturated) soils than in non-eroded soils and in fine-textured soils, which provided more space for microbial colonization and C sorption, than in coarse-textured soils. Shoot residues were decomposed and metabolized by a microbiome rich in efficient bacterial decomposers (Actinobacteria, Xanthomonadales). This led to inevitably higher C losses related to their growth and biomass turnover, and probably also to an intense priming effect on pre-existing MAOM that lowered the efficiency of MAOM formation. Our results argue for crops with robust root systems, or for the inclusion of deep-rooted plants in crop rotations, which could help rapidly restore the C stocks in arable soils.

Combined influence of ash and poultry manure on soil reaction and performance of maize (&lt;i&gt;Zea mays&lt;/i&gt;) in a coarse-textured acid soil of South-East, Nigeria

Crop production can be limited by soil acidity. A two-factor factorial experiment involving three levels each of ash and poultry manure (PM) was conducted to determine the effects of ash and PM on soil reaction and performance of maize in an acid soil. The ash comprised of mixture of ash from wood, cocoa husk and palm bunch. The levels of ash (0.00, 3.00, 6.00 t ha–1 ) and PM (0.00, 4.00, 8.00 t ha–1 ) were combined to obtain nine treatment combinations (control, 3.00 ash and 0.00 PM, 3.00 ash and 4.00 PM, 3.00 ash and 8.00 PM, 0.00 ash and 4.00 PM, 3.00 ash and 0.00 PM) which were replicated thrice. The experiment was laid out in a randomized complete block design. Soil samples were collected at 3, 6, 9 and 12 weeks after planting (WAP), plant height measured at 3, 5, 7, and 9 WAP while cob oven-dry weight was measured after oven-drying harvested cobs at maturity. Analysis of variance was conducted on the data collected using GenStat version 14. The highest plant height of 132.50 cm at 12 WAP and the highest oven-dry cob weight of 7.15 t ha–1 were obtained from plots treated with 6.00 and 8.00 t ha-1 of ash and PM, respectively, and these were significantly (p ≤ 0.05) different from the other treatments. The lowest exchangeable acidity of 1.33 cmol kg–1 which varied significantly (p ≤ 0.05) from the other values observed at the other plots was obtained at the plot treated with the combination of 6.00 and 4.00 t ha–1 of ash and PM, respectively at 12 WAP. The combination of ash and PM at 3.00 and 8.00 t ha–1 gave the highest pH of 6.80, and this was significantly (p ≤ 0.05) different from the other treatments. Therefore, ash and PM at varying levels of combination can simultaneously ameliorate soil acidity and improve maize performance; however, the best combination of ash and PM application which showed the potential to produce optimum effect in simultaneously ameliorating soil acidity and increasing maize performance was the combination of 6.00 tonnes of ash and 8.00 tonnes of PM.

Assesment of Boron in Soil, Plant and Irrigation Water under Cotton-wheat Cropping System of Northern India

Background: The use of high yielding varieties, high analysis fertilizers and intensive cultivation has depleted the fertility of soils particularly with respect to micronutrients. The deficiency of B is expected to be high in coarse-textured soils having low organic matter, high CaCO3 and high pH. Methods: Geo-referenced surface (0-15 cm, n=155) soil samples, cotton leaves at pre flowering stage (n=75), wheat flag leaves (n=80) and tube well water (n=75) samples were collected from Bathinda, Mansa and Mukatsar districts of Punjab. Result: About 5, 18 and 20 per cent of soil, cotton and wheat samples were deficient in B, respectively. Hot water soluble B in soil was significantly positively correlated with pH (r= 0.230*), ESP (0.680**), B concentration in leaves of cotton (r=0.259*) and wheat (r=0.531**) but negatively with CaCO3 in soil (r= -0.210*). About 40 per cent of tubewell waters had greater than 2.0 mg B l-1. On an average, one cm ha of tube well water may add up to 93g B ha-1 to soil.

The short-term response of soil microbial communities to digestate application depends on the characteristics of the digestate and soil type

Anaerobic digestion of organic waste is a key process to produce renewable energy and meet the growing demand for sustainable energy. The residues of anaerobic digestion – called digestates – can be used as soil amendments to improve crop yields. However, the effect of digestates on the soil biota, especially on microorganisms, needs to be better documented before a large scale use of digestates in agriculture. In addition, how the quality and composition of the digestate may affect soil microbial communities has not been properly addressed yet. We designed a microcosm experiment under controlled experimental conditions to compare effects (42 days) of four digestates produced from varying intakes (cattle manure and/or energy crop and/or food residues and/or slurry) on soil microbial communities; a control microcosm made of undigested cattle manure was also used. Each digestate was applied on three contrasting soils representing contrasted pedo-climatic conditions (especially soil type and climate). These three soils presented different prokaryotic and fungal communities structures. The effect of digestate inputs on the soil microbial biomass and diversity was assessed using molecular DNA-based tools (quantification of extracted soil DNA and high-throughput sequencing, respectively) in comparison to the untreated cattle manure control condition. Our results show that 42 days after digestate application, significant differences of soil microbial communities were observed according to the digestate characteristics; these differences were soil-dependent. Thus, in the silty clay loam soil, no effect of digestates was observed on soil microbial biomass or diversity (P > 0.05), as compared to the undigested cattle manure. In the two other soil types (loam and sandy loam), soil microbial biomass decreased (around −40 %, P < 0.001) when digestates having a low total organic carbon content (from 0.61 to 3.3 g.100 g−1) were applied. None of the digestates affected the soil prokaryotic diversity whatever the soil type (P > 0.05). Digestate application resulted in higher fungal diversity (around +35 %; P < 0.001) in soils with low C/N ratio (9.14 in average). The microbial community structure of coarse-textured soil appeared more impacted by organic inputs than fine-textured soils. To conclude, our results show that different soil types, harboring distinct microbial community structures, responded differently to different digestates application. This response was also digestate-dependent.

Evaluation of Siderophore Production by Different Promising Microbial Isolates

Indian alkaline soils are deficient in iron due to high pH, high calcium carbonate, highly permeable coarse textured soils, and soils low in organic carbon content. This study is carried out to increase the iron use efficiency of soil by using promising microbial isolates. Production of siderophore by promising microbial isolates is a greatest invention which help in increasing uptake of iron. A short-term laboratory experiment was carried “To evaluate the siderophore productions by different promising microbial isolates using chrome azurol S assay technique”. Ten microbial isolates were inoculated on plate as well as in broth medium. Plates were observed for orange halo formation around the bacterial growth. The size of orange halo around the colony of each microbial isolates was measured. The broth cultures inoculated with inoculum, incubated at 28 ± 20C for 24-72 hr with constant shaking at 120 rpm. After the incubation, the culture broths were centrifuged at 10,000 rpm for 10 min. The cell free supernatants were subjected to quantitative estimation of siderophores by CAS-shuttle, absorbance was measured at 630 nm against a reference consisting of 0.5 ml of uninoculated broth and 0.5 ml of CAS reagent. Obtained results indicated that in both plate and broth assays medium inoculated with strain Pseudomonas fluorescens show significantly higher orange halo formation around the growth and maximum siderophore content in aliquot. Inoculation of this plant growth promoting microbial isolates will be the great achievement in replacing chemical fertilizers in agriculture.

A novel approximate solution to slope rainfall infiltration

Slope rainfall infiltration is a critical component of the Earth's hydrologic processes. Although various infiltration models have been proposed to simulate rainfall infiltration, simple and accurate ones are still scarce. This work developed a non-integral infiltration model for sloping surfaces, called modified approximate solutions under constant pressure conditions (MASCP). New expressions were proposed to improve slope infiltration simulation by introducing a developing saturated zone in soil water content (SWC) profile to quantify the role of ponding water during infiltration. The MASCP was then extended to simulate the infiltration with uniform and non-uniform initial SWC distributions under complex rainfall patterns. The model performance was evaluated by comparing with Hydrus-1D and the sloping Green-Ampt model for four distinct textured soils. The results demonstrated that the ponding time and infiltration rate simulated by the MASCP agreed well with those by Hydrus-1D at all given conditions. Besides, the MASCP yielded higher simulation accuracy than the sloping Green-Ampt model, especially for coarse-textured soils, low rainfall intensity, and long rainfall hiatus. In conclusion, the MASCP is a simple and accurate computation tool for slope rainfall infiltration modeling.

Gross nitrogen transformation rates in shifting cultivation systems in northern Thailand: Controlling factors and implications for inorganic nitrogen availability

Slash-and-burn practices and subsequent fallow periods affect soil nitrogen (N) availability. Although extensive studies have examined the global temporal patterns of inorganic N after fire, NO3− regulation remains unclear due to ecosystem-dependent responses. Despite inorganic N pool control by NH4+ and NO3− production and consumption, local-scale patterns and mechanisms of gross N transformations, particularly in tropical regions, remain insufficiently understood. Thus, we aimed to elucidate the controlling factors of inorganic N in the shifting cultivation cycle in Northern Thailand, using a 15N pool dilution method on soil samples at 0–10 cm depth collected across various post-burning stages (1, 4, 6, and 7 years after burning) and forest. We found that gross ammonification was enhanced by high soil organic matter and microbial biomass, while gross nitrification was enhanced by greater soil alkalinity. Ammonium immobilization increased with higher microbial biomass, while NO3− immobilization increased with lower NH4+ availability. With increasing fallow period, microbial biomass and consequently gross ammonification increased, boosting the NH4+ pool. Soil acidity, correlated with soil texture, influenced nitrification: coarser-textured soil intensified acidity and decreased gross nitrification, resulting in NH4+-dominance, while finer-textured soil alleviated acidity, promoting nitrification over NH4+ immobilization, leading to NO3−-dominance. Our findings confirm that the fallow stage, along with which microbial biomass increases, was an essential driving factor regulating ammonification, while soil acidity, unrelated to fallow but a function of sand/silt content, was an essential driving factor regulating nitrification under shifting cultivation in Northern Thailand.

Effect of soil and water salinity on dry season boro rice production in the south-central coastal area of Bangladesh

Salinity varies with location and time of the year. It can significantly impact crop production. The level of negative impacts depends on the salt concentration and time of its occurrence, which, however, has not been studied for many crops, especially for rice grown in the coastal area of Bangladesh. Our study explored the impact of spatio-temporal fluctuations in soil and water salinity on boro rice production in the south-central coast of Bangladesh. Here, we simulated the soil salinity from November 2020 to May 2021 for fourteen locations classes using the SWAP-WOFOST model. The model was calibrated and validated with measured secondary data. Next, the yield of two salt-tolerant boro rice varieties (BRRI dhan47 and BRRI dhan67) was simulated using the customized soil, weather, and crop data. We also simulated the yield by adopting agronomic management practices (i.e., changing planting time and using fresh irrigation water). Our results showed that salinity levels varied with different soil textural classes, soil depth, location, and time of the year, and that had a significant influence on boro rice production, giving spatial variability. Specifically, boro rice had a higher yield in coarse texture soil than in fine texture soil. Simulated yields in areas proximate to the sea ranged from 668 to 1239 kg ha−1, yields that are significantly lower than those simulated in moderate (2098–4843 kg ha−1) and low salinity zones (4213–4843 kg ha−1). Moreover, the simulation of yield with sowing/planting rice earlier by fifteen days provided a higher yield than the current planting practice since it could avoid salinity at later stages of growth. For a similar reason, growing rice inside the polder provided a higher yield than outside the polder. The insights gained from our study carry significant implications for contemporary crop-level adaptation strategies and policy-making in coastal districts.

Developing scoring functions based on soil texture to assess agricultural soil health in Quebec, Canada

Adoption of soil health indicators to assess physical, biological, and chemical properties involves adapting their interpretation for a specific region using scoring functions. Accordingly, we used data provided from 1166 soil samples distributed between fine-, medium-, and coarse-textured soils, collected in agricultural areas across the province of Quebec, Canada, and analyzed for 15 soil health indicators. Scoring functions were calculated according to the means and standard deviations obtained for each soil health indicator by textural group. Three scoring types were used: “more-is-better”, “less-is-better”, and “optimum-is-best”. The results showed that 12 indicators were significantly influenced by soil texture and need separate scoring functions, except for wet aggregate stability, penetration resistance of the surface hardness (0–15 cm), and pH. This led to the development of one to three scoring functions for each soil health indicator. Correlation analysis between soil health indicators was also investigated to better understand relationships between soil physical, biological, and chemical properties. We observed that soil biological indicators were moderately to strongly correlated with each other ( r = 0.59–0.74) and with soil physical indicators ( r = 0.60–0.76). Overall, the results of this study led to the development of new scoring functions based on soil texture to interpret soil health indicators objectively and accurately for the benefit of Quebec farmers and agricultural stakeholders. The findings of this study demonstrated the need to adapt scoring functions to better account for the impact of regional factors on agricultural soils for the interpretation of soil health indicators.

Improving coarse-textured mineral soils with pulp and paper mill sludges: Functional considerations at laboratory scale

Building up the organic matter content of coarse-textured soils with organic amendments seeks to ameliorate the productivity of these soils, which is limited by plant available water and nutrient supply. Wood fibre-based sludges from the pulp and paper industry have potential for soil conditioning. In this study, the effects of three different pulp and paper mill sludges at application rates of 10 and 20 vol-% on water retention, respiration, and nitrogen (N) dynamics were examined in a series of laboratory studies using coarse field soils. Water retention curves comprising 13 matric potentials revealed that the amendments increased total soil porosity and volumetric water content at matric potentials corresponding to macro- and mesopores size range with pore diameters of >30 μm and 30–0.2 μm, respectively. Volumetric water content at field capacity increased by c. 10–30%, depending on the type (fresh, lime-stabilised and fibre sludge) and application rate of the amendment, with no marked change in the water content at the permanent wilting point. This was reflected as a mean increase of 1.9–3.3 mm in the plant available water content relative to the non-amended soils (17 mm), which corresponds to 19–33 m3 per hectare. At most, an increase of 5.5 mm (55 m3 ha−1) in plant available water was achieved by the fibre sludge amendment at an application rate of 20 vol-%. During a 60-day laboratory incubation, c. 30–40% of the carbon (C) added to soil in the sludge materials was respired as carbon dioxide. Additional N accelerated decomposition without increasing total respired C. Decomposition of the amendments in the soil led to a net N immobilisation of roughly 5–10 mg min-N g−1 added C, which occurred mainly during the first two weeks after soil incorporation. Overall, pulp and paper mill sludge amendments may serve to alleviate water shortages during drought in coarse-textured soils, but may generate a transient plant-microbe competition in N uptake.

Divergent effects of intensified precipitation on primary production in global drylands

Amplification of hydrological cycle under warming climate is anticipated to result in intensified precipitation characterized by fewer, more intense events and correspondingly longer dry intervals between events, even without major changes in annual total precipitation. Vegetation gross primary production (GPP) in drylands is highly responsive to intensified precipitation, however, how intensified precipitation influences GPP in global drylands is not well understood. Based on multiple satellite datasets from 2001 to 2020 and in-situ measurements, we investigated the effects of intensified precipitation on global drylands GPP under diverse annual total precipitation along the bioclimate gradient. Dry, normal, and wet years were identified as years with annual precipitation anomalies below, within, and above the range of one standard deviation. Intensified precipitation led to increases or decreases of GPP during dry or normal years, respectively. However, such effects were largely weakened during wet years. The responses of GPP to intensified precipitation were mirrored by soil water availability, as intensified precipitation enhanced root zone soil moisture, and thus vegetation transpiration and precipitation use efficiency during dry years. During wet years, root zone soil moisture showed less response to changed precipitation intensity. Land cover types and soil texture regulated the magnitude of the effects along the bioclimate gradient. Under intensified precipitation, shrubland and grassland distributed in drier region with coarse soil texture showed greater increases of GPP during dry years. As global precipitation will likely further intensify, the impacts of intensified precipitation on dryland carbon uptake capacity will be highly diverse along the bioclimate gradients.

Influence of iron seed priming on seed germination, growth and iron content in rice seedlings

The area under direct-seeded aerobic rice (DSR) is increasing in Indo-gangetic plains due to labor and water scarcity. However, iron (Fe) deficiency is a severe problem in DSR under coarse-textured soils, resulting in poor germination, interveinal chlorosis, and poor seedling establishment. Fe seed priming is a better option to ensure higher seed germination and optimum supply of Fe at initial growth stages. Hence, the experiment was conducted with seven seed priming treatments i.e. Control (hydropriming), 0.5% Fe through ferrous sulfate (FeSO4 7H2O), 1.0% Fe through FeSO4 7H2O, 0.25% Fe through ethylene diamine tetra acetic acid chelated iron (Fe-EDTA), 0.5% Fe through Fe-EDTA, 0.025% Fe through iron oxide nanoparticle (FeO NPs) and 0.05% Fe through FeO NPs. The Fe seed priming showed a significant increase in Fe content of paddy seeds over the hydropriming treatment. Among different treatments, FeSO4.7H2O (1.0% Fe) showed highest germination percentage (91.3%), root length (8.4%) and shoot length (9.4%) followed by FeSO4.7H2O (0.5% Fe) which was significantly higher over the control. But, the treatment involving Fe-EDTA (0.5% Fe) showed adverse effects on germination and seedling growth. Ferrous (Fe2+) iron and total Fe content in rice seedlings showed similar trends to total Fe content in primed seeds treated with different Fe sources. Thus, Fe seed priming of rice with FeSO4.7H2O (1.0%Fe) for 12 h was effective for higher germination percentage, greater iron content at initial growth stages and ameliorated the Fe deficiency in direct seeded aerobic rice.

Effect of Changes in Throughfall on Soil Respiration in Global Forest Ecosystems: A Meta-Analysis

To date, there has been limited knowledge about how soil carbon dioxide (CO2) emissions from forest ecosystems at a global scale respond to the altered precipitation, and the key influencing mechanisms involved. Thirty-seven studies conducted under throughfall manipulation conditions in forest ecosystems around the globe were selected in this meta-analysis, with a total of 103 paired observations. Experimental categories such as climate types, forest types, soil texture, and the area size of changes in throughfall manipulation were included to qualify the responses of annual soil CO2 emissions to the altered throughfall. The responses of the annual soil CO2 emissions to the altered throughfall would be more sensitive in temperate forests than those in tropical and subtropical forests, probably due to the relatively long residence time of soil carbon (C) and the seasonal freeze–thaw events in temperate forests, as well as the relatively high concentration of non-structural carbohydrates in the belowground part of temperate terrestrial plants. A relatively large positive response of the soil CO2 emissions to the increased throughfall was observed in Mediterranean forests due to small precipitation during the growing season and mostly coarse-textured soils. Besides climate types, the sizes of the effect of the altered throughfall on the soil CO2 emissions (lnRCO2) varied with forest types and soil texture categories. Based on the regression analysis of the lnRCO2 values against the changes in throughfall, the annual soil CO2 emissions in forest ecosystems at a global scale would be increased by 6.9%, provided that the change in annual precipitation was increased by 10%. The results of structural equation modeling analysis indicate that fine root biomass and soil microbial biomass, along with the changes in annual precipitation, would substantially affect the altered throughfall-induced annual soil CO2 emissions in global forest ecosystems. The findings of this meta-analysis highlight that the measurement of soil respiration components, the priming effects of soil organic C decomposition, and C allocation between the aboveground and belowground parts of different tree species under the altered precipitation conditions, deserve more attention in the future.

Change in soil organic carbon storage as influenced by forestland and grassland conversion to cropland in Canada

Conversion of native grassland and forest to agricultural land results in significant losses of soil organic carbon (SOC). However, the quantity of SOC loss upon conversion of native grassland and forest varies with climate, soil texture and agricultural management practices. In this study, we quantified the change of SOC stock as influenced by native grassland and forest conversion to agricultural soils in Canada through a meta-analysis. We determined both the absolute and relative change of SOC from its native state upon the conversion to agriculture. In more humid and temperate region of Eastern Canada losses of SOC upon the conversion of forest to agricultural land varied with soil textures, on an absolute basis, 18 t C ha−1 for the coarse-textured soil, 43 t C ha−1 for the medium-textured soil, and 65 t C ha−1 for the fine-textured soil from its native vegetation; corresponding, on a relative basis, to 22%, 30% and 32%, respectively. On the Canadian prairies, forestland conversion to cropland resulted in losses of 27 t C ha−1 or 25% for the medium-textured soil whereas there was no change in SOC for the coarse-textured soil. On the Canadian prairies, the conversion of native grassland to agriculture resulted in losses of SOC, on average from 15, 26, and 5 t C ha−1 in coarse-, medium- and fine-textured soils, respectively. However, because of high inherent variation in SOC stocks among the various soil textures, losses of SOC upon grassland conversion, on a relative basis, were highly variable (14–26%), and no statistically significant differences were observed among soil texture classes. The results of this work clearly show that climate and soil texture are main drivers of SOC change after the conversion of native grassland and forest to agriculture and are key factors that must be considered in the development of either national or regional SOC models. The results of this study suggest that more detailed stratification of samples across soil textures and climates improve the accuracy of estimates of SOC loss associated with native grassland and forest conversion to agriculture.

Nutrient availability and microbial traits constrained by soil texture modulate the impact of forest fire on gross nitrogen mineralization

Wildfire is a primary disturbance of forests and has been expected to influence soil nitrogen (N) transformation. However, the effect of fire on soil gross N mineralization is still under debate. This study used the 15N dilution and Miseq sequencing techniques to examine the impact of fire history on soil nutrient availability, microbial traits, and gross N mineralization rates at five forest sites. Results showed that fire had both positive and negative effects on soil gross N mineralization, depending on sampling sites. Fire promoted gross N mineralization rates by 41–49% in fine-textured soils by increasing dissolved organic C and N concentrations, microbial abundances, and microbial interactions (connectance of microbial co-occurrence networks) in soil. In contrast, fire decreased the rates by 24–44% in coarse-textured soils by reducing the above measurements. The results suggest that the effect of fire on soil gross N mineralization is regulated by soil texture. This study provides insights into the complex mechanisms of how fire affects soil gross N mineralization in forest ecosystems.