High Soil Research Articles

Analytical and Experimental Evaluation of Two-Layered Unsaturated Sand Bearing Capacity

Pavement design methods based on principles of unsaturated soil mechanics take into account high soil shear strength due to matric suction resulting in more economical design especially in long roads. In this study, the bearing capacity of two-layer unsaturated sand was investigated using both analytical and experimental methods. At first, using the limit equilibrium method an analytical formula was proposed to determine the bearing capacity of two-layer unsaturated sand in which linear suction profile was considered in soil layers. It should be considered that the constant matric suction distribution assumed by the previous researchers doesn’t show the real profile of matric suction within the soil, sometimes resulting in miscalculated unsaturated bearing capacity. Also, the bearing capacity of two-layer unsaturated poorly graded sand was investigated experimentally in different suctions by a special unsaturated chamber apparatus (UCA) designed for this purpose. The results show more than double increase of unsaturated soil bearing capacity with Sr=25% compared to saturated soil. The formation of failure wedges in all experiments was investigated by image processing. An acceptable agreement was obtained between the theoretical and experimental bearing capacity results.

The Effect of Saltwater Stress on the Performance of Cherry Tomatoes

Rising sea levels and saltwater intrusion in aquifers pose significant challenges for South Florida agriculture, leading to increased groundwater salinity and potential crop losses. Utilizing salttolerant crop species presents a potential solution for saline soils and regions with active saltwater intrusion. However, the effects of soil salinization through groundwater alone remains less studied. This research investigates the impact of short-term, below-ground saltwater stress on the growth, survival, and overall health of commonly grown cherry tomatoes (Solanum lycopersicum). The objectives of the study are to: 1) determine the impact of saline groundwater on tomato plant health and 2) compare the nutrient content of soil and tomato plant tissue exposed to varying concentrations of saline water. Established cherry tomato plants were exposed to varying concentrations of NaCl solution, simulating saltwater intrusion into groundwater. Over 28 days, plant height, leaf chlorophyll levels, and disease occurrences were monitored. It was found that the NaCl treatments did not significantly affect cherry tomato performance under the parameters of height, chlorophyll levels, or leaf nutrition when compared to the control group. This study suggests that cherry tomatoes can tolerate short-term exposure to NaCl in groundwater. Further exploration of more intense salt stress conditions from groundwater could be beneficial for utilizing this crop in areas with saline soils or polluted groundwater. Identification of salt-tolerant cherry tomato varieties can provide alternative crop options for non-arable land affected by high soil salinity.

Wood Distillate Promotes the Tolerance of Lettuce in Extreme Salt Stress Conditions

Soil salinization is an adverse phenomenon in agriculture that severely affects crop growth and yield. The use of natural products, such as wood distillate (WD, derived from the pyrolysis of woody biomass), could be a sustainable approach to enhance the tolerance of plants cultivated in the saline soils. Hence, this study aimed to evaluate the potential of WD, a foliar sprayed at 0.2% (v/v), in lettuce plants subjected to grow under both moderate and high soil sodium chloride (NaCl) concentrations (ranging from 0 to 300 mM). The changes in the physiological and biochemical responses of these plants to the varying salt stress conditions allowed the identification of a maximum tolerance threshold (100 mM NaCl), specific to lettuce. Beyond this threshold, levels related to plant defense antioxidant power (antiradical activity) were lowered, while those indicative of oxidative stress (malondialdehyde content and electrolyte leakage) were raised, causing significant losses in leaf fresh biomass. On the other hand, WD significantly improved plant growth, enabling plants to survive high salt conditions >200 mM NaCl. Collectively, these observations highlight that treatments with WD could be of paramount importance in coping with current environmental challenges to have better yields under soil conditions of high salt concentrations.

Soil CO2 flux maps as tools to reduce the risk on soil diffuse degassing areas

Carbon dioxide released permanently from soils in diffuse degassing areas may constitute a permanent hazard for the population. Several villages in the Azores archipelago (Portugal) are placed in areas with anomalous soil CO2 degassing and lethal indoor CO2 concentration (>10 vol%) has been already recorded in some buildings. The 2021-2022 dislodgements of population at Vulcano (Italy) and La Palma (Spain) volcanic islands due to high soil CO2 degassing highlight the importance of defining criteria to produce human CO2 exposure risk maps, which are useful to mitigate the risk and should constitute valuable tools for land-use planners. Risk is assessed in the current study by combining susceptibility, exposure, and vulnerability maps. The defined criteria were applied to two villages in Furnas Volcano (São Miguel Island, Azores), showing that 58% and 98% of the buildings, respectively, at Furnas and Ribeira Quente villages are at high risk of CO2 exposure.

Distinguishing direct N2O emissions from 15N-labeled manure compost, urea, and maize roots in a field study

Nitrous oxide (N2O) emissions from agricultural activities are a significant contributor to global anthropogenic N2O emissions. Sustainable agriculture practices, including using manure compost to replace nitrogen (N) fertilizers, can reduce chemical fertilizer use and minimize negative impacts on soil health and water quality. However, the direct contributions of manure compost to N2O emissions have not been fully studied. We conducted a field study to distinguish the direct contributions of manure compost, urea, and residual maize roots to N2O emissions in an integrated crop-livestock agricultural system in Shandong Province, China. Using the 15N-labeling technique, we found that the majority (93.3%) of cumulative N2O emissions originated from the soil and other unaccounted sources. Notably, manure compost contributed 1.3%, while current-year urea, residual urea with root exudates, and maize root accounted for 3.4%, 1.9%, and 0.03% of cumulative N2O, respectively. Our results also demonstrated that applying manure compost in combination with urea resulted in lower seed yield-scaled N2O emissions (0.046 g N2O-N kg−1 seed) compared to applying urea alone, even when the total N input was identical, suggesting the potential of manure compost in a more sustainable agriculture model. The low emission factor of manure compost (0.005%) compared to urea (0.019%) supports this potential, indicating the slow-release nature of manure may mitigate N2O while maintaining crop yield. Additionally, the overall low emissions may be attributed to the relatively high soil pH (8.17), which influences the denitrification product ratio, favoring the conversion of N2O to N2. Our study provides valuable insights into the factors contributing to N2O emissions in integrated crop-livestock farming systems, and highlights the importance of distinguishing multiple sources of N2O emissions to develop effective strategies for reducing emissions while promoting sustainable agriculture.

Hydroponic Screening at Early Seedling Stage Identified Sources of Salinity Tolerance in Wheat (Triticum aestivum L.) Crop

Wheat is a vital crop globally, essential for agriculture, economics, and food security. However, in arid and semi-arid conditions, wheat production faces significant challenges due to low water availability, uneven rainfall distribution, and high soil salinity. The germination and early seedling stages are particularly vulnerable to these stresses. Therefore, this study assessed 15 wheat genotypes for their tolerance to salinity stress during early growth stages, using a hydroponic system with four salt stress levels (0, 50, 100, and 150 mM NaCl). Significant differences were observed for genotype and salinity main effects and their interaction on all investigated traits, indicating considerable variability in the response to salt stress among the investigated wheat cultivars. High NaCl concentrations led to substantial reductions in measured parameters across genotypes, with some showing resilience while others exhibited heightened sensitivity. Stress tolerance indices, such as mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HM), stress tolerance index (STI) and yield index (YI), were identified as reliable indicators for selecting salt-tolerant wheat cultivars. Consequently, Sidi Okba (G11), Ziad (G12), Tamezghida (G13) and Zidane (G14) emerged as the most promising, displaying acceptable performance under both non-stress and salt-stress conditions. These genotypes could serve as valuable genetic resources for breeding programs aimed at enhancing wheat’s salinity tolerance, particularly in arid and semi-arid regions.

Susceptibility of Zucchini Cultivars to Powdery Mildew (Podosphaera xanthii) under High and Low Nitrogen Regimes

Powdery mildew, primarily caused by Podosphaera xanthii, threatens cucurbit crop yield and longevity. Fungicides and resistant cultivars cannot fully manage or prevent the disease. Previous work has shown that powdery mildew incidence and severity can increase under high soil nitrogen. This study was conducted in Kentucky to determine disease severity and yield using a split plot design with nitrogen fertility (high: 140 kg/ha, low: 84 kg/ha) and zucchini cultivar (Cash Machine, Cue Ball, Desert, Dunja, Eight Ball, Emerald Delight, Golden Glory, Mexicana, and Spineless Perfection) as the main plot and subplot factors, respectively. In year one, powdery mildew severity was significantly higher in high soil nitrogen and varied significantly among cultivars. Yield was significantly lower in high soil nitrogen. Significant differences in fruit count, but not fruit weight, were observed among the cultivars. In year two, nitrogen did not significantly affect disease severity, but fruit weight and count were significantly lower in the high soil nitrogen treatment. ‘Golden Glory’ had significantly higher powdery mildew severity while ‘Mexicana’ and ‘Eight Ball’ had significantly lower severity compared to all other cultivars. Spineless Perfection had the highest fruit weight and was significantly higher than all other cultivars except for Cue Ball and Eight Ball. ‘Golden Glory’ had the highest fruit count and was significantly higher than all others except for ‘Dunja’. Nitrogen did not consistently affect disease severity throughout the study. The effects of powdery mildew on yield should be explored further, as heavily diseased plants did not always have low yield.

Evaluation of reanalysis soil moisture products using cosmic ray neutron sensor observations across the globe

Abstract. Reanalysis soil moisture products are valuable for diverse applications, but their quality assessment is limited due to scale discrepancies when compared to traditional in situ point-scale measurements. The emergence of cosmic ray neutron sensors (CRNSs) with field-scale soil moisture estimates (∼ 250 m radius, up to 0.7 m deep) is more suitable for the product evaluation owing to their larger footprint. In this study, we perform a comprehensive evaluation of eight widely used reanalysis soil moisture products (ERA5-Land, CFSv2, MERRA2, JRA55, GLDAS-Noah, CRA40, GLEAM and SMAP L4 datasets) against 135 CRNS sites from the COSMOS-UK, COSMOS-Europe, COSMOS USA and CosmOz Australia networks. We evaluate the products using six metrics capturing different aspects of soil moisture dynamics. Results show that all reanalysis products generally exhibit good temporal correlation with the measurements, with the median temporal correlation coefficient (R) values spanning 0.69 to 0.79, though large deviations are found at sites with seasonally varying vegetation cover. Poor performance is observed across products for soil moisture anomalies time series, with R values varying from 0.46 to 0.66. The performance of reanalysis products differs greatly across regions, climate, land covers and topographic conditions. In general, all products tend to overestimate data in arid climates and underestimate data in humid regions as well as grassland. Most reanalysis products perform poorly in steep terrain. Relatively low temporal correlation and high bias are detected in some sites from the west of the UK, which might be associated with relatively low bulk density and high soil organic carbon. Overall, ERA5-Land, CRA40, CFSv2, SMAP L4 and GLEAM exhibit superior performance compared to MERRA2, GLDAS-Noah and JRA55. We recommend that ERA5-Land and CFSv2 could be used in humid climates, whereas SMAP L4 and CRA40 perform better in arid regions. SMAP L4 has good performance for cropland, while GLEAM is more effective in shrubland regions. Our findings also provide insights into directions for improvement of soil moisture products for product developers.

Joint Impacts of Meloidogyne incognita and Soil Nutrition on Solanum lycopersicum var. cerasiforme.

Strategies for plant nutrient resource allocation under Meloidogyne spp. infection and different soil nutrient conditions are not well established. In response, the objectives of this research are to determine if increased vegetative growth of Solanum lycopersicon var. cerasiforme (cherry tomato) under high nutrition enhances resistance to M. incognita and whether adaptive strategies for growth, reproduction, and nutrient uptake by cherry tomato infected with M. incognita alter nutrient availability. The study was conducted under greenhouse conditions using high, medium, and low soil nutrient regimes. The research results indicate that the total biomass of cherry tomato was less in the presence of M. incognita infection under all three nutrient conditions, compared with plants grown in the absence of this nematode. However, the increase in the root/shoot ratio indicates that cherry tomato allocated more resources to belowground organs. Under the combined impacts of M. incognita infection and low or medium soil nutrition, the nitrogen content in root system tissues and the phosphorus content in shoot system tissues were increased to meet the nutrient requirements of galled root tissue and plant fruit production. It is suggested that plants increase the allocation of reproductive resources to fruits by improving phosphorus transportation to the aboveground reproductive tissues under low and medium nutrient conditions. Overall, the study highlights a significant impact of soil nutrient levels on the growth and resource allocation associated with M. incognita-infected cherry tomato. In response, soil nutrient management is another practice for reducing the impacts of plant-parasitic nematodes on crop production.

A longitudinal analysis of soil salinity changes using remotely sensed imageries

Soil salinization threatens agricultural productivity, leading to desertification and land degradation. Given the challenges of conducting labor-intensive and expensive field studies and laboratory analyses on a large scale, recent efforts have focused on leveraging remote sensing techniques to study soil salinity. This study assesses the importance of soil salinity indices’ derived from remotely sensed imagery. Indices derived from Landsat 8 (L8) and Sentinel 2 (S2) imagery are used in Random Forest (RF), eXtreme Gradient Boosting (XGBoost), Decision Tree (DT), and Support Vector Machine (SVR) are associated with the electrical (EC) conductivity of 280 soil samples across 24,000 hectares in Northeast Iran. The results indicated that the DT is the best-performing method (RMSE = 12.25, MAE = 2.15, R2 = 0.85 using L8 data and RMSE = 10.9, MAE = 2.12, and R2 = 0.86 using S2 data). Also, the results showed that Multi-resolution Valley Bottom Flatness (MrVBF), moisture index, Topographic Wetness Index (TWI), and Topographic Position Indicator (TPI) are the most important salinity indices. Subsequently, a time series analysis indicated a reduction in salinity and sodium levels in regions with installed drainage networks, underscoring the effectiveness of the drainage system. These findings can assist decision-making about land use and conservation efforts, particularly in regions with high soil salinity.

The coupling of sulfide and Fe-Mn mineral promotes the migration of lead and zinc in the redox cycle of high pH floodplain soils

In this study, we investigated the impact of fluctuating water levels on the distribution of lead (Pb) and zinc (Zn) in soil and sediments at a historical Pb-Zn smelting site along the Xiangjiang River. Despite the high pH levels (7 to 11) in the study area, which generally inhibits heavy metal solubility, we found that regular changes in water levels still affect Pb-Zn movement. Soil analysis revealed distinct redox zones within the unconfined aquifer, as shown by the variable Fe/Mn and Ce/Ce* ratios. Advanced techniques such as Mn K-edge XAFS, Mössbauer spectroscopy, and TOF-SIMS indicated persistent Fe-Mn redox cycling and highlighted the presence of Pb and Zn-rich manganese oxides near sulfur-bearing minerals. These findings suggest that acidic microzones produced by the oxidation of sulfur-bearing minerals become "refuges" for microbial and heavy metal activity. Considering that sulfur-containing minerals are widespread waste types in nonferrous metal smelting sites, these findings are instructive for a better understanding of the transformation mechanisms of heavy metal ions in nonferrous metal smelting-polluted environments and for guiding pollution remediation strategies.

Evaluation of aluminum tolerance diversity in Avena sativa L. from the VIR collection

Background. Oat is an important food and feed cereal crop in Russia. The area under oats is 10 million ha worldwide, and 3 million ha in Russia. Acid soils with excessive content of exchangeable aluminum occupy almost every third hectare in the exUSSR territory. Oats are relatively resistant to unfavorable soil factors. Among cereal crops, oat is second only to rye and triticale in terms of resistance to exchangeable Al forms. Despite the crop’s high environmental plasticity, an important condition for obtaining sustainable oat yields is the development of new cultivars with resistance to adverse environmental factors, including metal toxicity and high soil acidity.The objective of this work was to search for oat cultivars resistant to soil stressors (excess of Н+ and Al3+) for use in breeding for edaphic resistance.Materials and methods. The research material included 687 oat accessions from the VIR global plant genetic resources collection. The accessions underwent laboratory evaluation of their aluminum tolerance at the initial growth and development stages using the method of measuring radicle growth after the exposure to aluminum stress. Reproducibility of the used modification of the method was mathematically proved.Results and discussion. Significant variation in the resistance to the studied stressor was observed among the accessions. The regions acting as sources of valuable aluminum resistance genes were identified for the crop. The accessions selected for their high resistance to exchangeable aluminum can be used in breeding programs to develop high-yielding oat cultivars with edaphic resistance.

Relationship between nitrate, heavy metal, and sterols contents in Japanese agricultural soils with risk of groundwater pollution

In Japanese agricultural lands, nitrate-nitrogen contamination of soil and groundwater often occurs due to the application of livestock excrements and compost. Therefore, rural soils in Japan were sampled and analyzed for nitrate-nitrogen leaching, heavy metal content, and sterols associated with livestock excrement and compost to calculate contamination risk indicators. The results were analyzed using self-organizing maps and cluster analysis. Nitrate-nitrogen content using water extraction was detected in most of the sampled soils. In addition, many samples from areas that were already severely contaminated with nitrate-nitrogen showed particularly high concentrations. Coprostanol, an indicator of fecal contamination, was detected in more than half of the samples. The main source of nitrate-nitrogen contamination in these areas is livestock excrement and compost. Self-organization maps showed that areas with high nitrate-nitrogen contamination also corresponded to areas with high copper and zinc soil contents. The self-organization maps and cluster analysis resulted in five clusters: a nitrate-contaminated group mainly originating from livestock excrement and compost, a heavy metal-contaminated group, a general group, a nitrate-contaminated group mainly originating from chemical fertilizers, and a contaminated group with potentially hazardous substances requiring attention. Authorities and decision-makers can use the results to prioritize areas requiring remediation.

Morphological and Physiological Responses of Two Penstemon Species to Saline Water Irrigation

Penstemon, with more than 250 species native to North America, holds significant aesthetic and ecological value in Utah, supporting diverse pollinators. Despite their significance, the survival of penstemon is threatened by challenges such as habitat loss, climate change, and Utah’s naturally high soil salinity. To address these challenges and understand their adaptability, this study evaluated the salt tolerance of two penstemon species [Penstemon davidsonii (Davidson’s penstemon) and Penstemon heterophyllus (foothill penstemon)] under controlled greenhouse conditions. The aim was to develop baseline information for nursery production and landscape use that utilize reclaimed water for irrigation. Plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 1.0 dS·m−1 as control or a saline solution at an EC of 2.5, 5.0, 7.5, or 10.0 dS·m−1 for 8 weeks. Half of the plants were harvested after four irrigation events, and the remaining plants were harvested after eight irrigation events. At harvest, visual rating (0 = dead and 5 = excellent without foliage salt damage), plant width, number of shoots, leaf area, shoot dry weight, leaf greenness [Soil Plant Analysis Development (SPAD)], stomatal conductance, and canopy temperature were collected to assess the impact of salinity stress. In both species, salt damage was dependent on the salinity levels and length of exposure. After four irrigation events, both species exhibited foliage damage that increased in severity with rising EC. The most severe damage was observed in plants receiving saline solution at an EC of 10.0 dS·m−1. After eight irrigation events, P. davidsonii exposed to a saline solution with an EC of 10.0 dS·m−1 received a visual rating of 0, whereas P. heterophyllus had a visual rating of 0.4. Both species exhibited salinity-induced effects, with variations observed in the specific parameters and the degree of response. Penstemon davidsonii exhibited significant salinity stress, as indicated by reduced leaf area, shoot dry weight, SPAD reading, and stomatal conductance with increasing EC of the saline solution. In addition, in both species, at both harvests, canopy temperatures increased either linearly or quadratically by 8% to 36% as the EC levels of the saline solution increased. These results indicate that P. davidsonii was more sensitive to salinity stress than P. heterophyllus.

A new chronology of Cedrela fissilis (Meliaceae) for Southern Brazil: combining classical dendrochronology and radiocarbon dating

Cedrela fissilis is a tree species widely distributed in the tropical biomes of South America. This species has visible annual growth rings and can live for several centuries. The present study aims to (i) develop a chronology of C. fissilis to the Southern Brazilian Plateau using traditional dendrochronological methods, (ii) validate the dendrochronological dating using the radiocarbon (14C) bomb pulse method, and (iii) determine the influence of temperature and precipitation variations and their teleconnections with the tropical Pacific Ocean temperatures on the annual radial growth of this species. The ring width chronology was developed using 24C. fissilis trees. The Schulman years of 1957, 1962, 1963, 1966, 1969 and 1974 were independently dated using the 14C bomb pulse methodology by accelerator mass spectrometry (AMS). Tree-ring indices were compared with temperature and precipitation records from stations around the study forest. The chronology covers the period 1907-2018 (111 years) and is well replicated (> 10 trees) from 1941 onwards. Statistics commonly used in dendrochronology indicate that the chronology is highly reliable and of good quality (mean series intercorrelation r = 0.49; Rbar = 0.30; EPS = 0.86; MSI = 0.40). The 14C bomb pulse of selected calendar years showed that the trees were accurately dated using the classical cross-dating approach. Precipitation from November to December (wet period) is positively correlated with tree growth (r = 0.36, n = 49; p<0.05). In addition, variations in temperature from May to July are positively correlated with ring width (r = 0.39, n = 49; p<0.05), suggesting that C. fissilis growth is favored by abundant rainfall during the growing season and above-average winter temperatures. Interannual variation in the chronology is partially modulated by El Niño 3.4 (East Central Tropical Pacific Sea Surface Temperature) during Oct-Dec (r = 0.27, n = 68, p<0.05). The growth of C. fissilis trees is directly dependent on climate variability, suggesting that more abundant precipitation and higher winter temperatures, as projected for the future climate of southern Brazil, will have a positive effect on tree growth. However, prolonged droughts and high temperatures during the growing season will have a negative impact on tree growth, even in humid forests with high soil moisture content.

The impact on Cd bioavailability and accumulation in rice (Oryza sativa L.) induced by dry direct-seeding cultivation method in field-scale experiments

Dry direct-seeded rice cultivation has gained popularity and expanded its cultivated area due to reduced labor requirements and water consumption. However, the impact of this cultivation method on cadmium (Cd) bioavailability in soil and the accumulation levels in grains remains uncertain. Field experiments were conducted in acidic soils at two locations in southern China to compare rice varieties and evaluate the dry direct-seeding method alongside the wet direct-seeding and traditional transplanting methods. Dry direct-seeded rice reached significantly higher Cd concentrations in its tissues starting from the heading stage than transplanted rice. Cd accumulation levels by the maturation stage in the brown rice of dry direct-seeded rice were 18.33 %–150.69 % higher than those of wet direct-seeded and transplanted rice, with a considerable ability to translocate Cd into brown rice. Furthermore, dry direct seeding decreased iron plaque formation, particularly in the amorphous Fe form; it resulted in high soil temperature and low moisture content during tillering, elevating Cd availability in the soil. Additionally, the proportion of ions and more labile forms of Cd in the soil solution was high. Moreover, the soil under dry direct seeding had high urease and acid phosphatase enzyme activities. However, low richness and diversity in the bacterial community were characterized by a significant increase in the relative abundance of Actinobacteria and Gammaproteobacteria at the class level, while exhibiting decreased relative abundances of Alphaproteobacteria, Bacilli, and KD4-96, along with fewer biomarkers. Nonetheless, these differences are gradually reduced during the maturation stage. Overall, although dry direct seeding offers several advantages, it is crucial to implement additional measures to mitigate the increased health risks linked to rice cultivation through this approach in Cd-contaminated areas.

An effective strategy for biodegradation of high concentration phenol in soil via biochar-immobilized Rhodococcus pyridinivorans B403.

High concentration of phenol residues in soil are harmful to human health and ecological safety. However, limited information is available on the in-situ bioremediation of phenol-contaminated soil using biochar as a carrier for bacteria. In this study, bamboo -derived biochar was screened as a carrier to assemble microorganism-immobilized composite with Rhodococcus pyridinivorans B403. Then, SEM used to observe the micromorphology of composite and its bioactivity was detected in solution and soil. Finally, we investigated the effects of free B403 and biochar-immobilized B403 (BCJ) on phenol biodegradation in two types of soils and different initial phenol concentrations. Findings showed that bacterial cells were intensively distributed in/onto the carriers, showing high survival. Immobilisation increased the phenol degradation rate of strain B403 by 1.45 times (37.7mg/(L·h)). The phenol removed by BCJ in soil was 81% higher than free B403 on the first day. Moreover, the removal of BCJ remained above 51% even at phenol concentration of 1,500mg/kg, while it was only 15% for free B403. Compared with the other treatment groups, BCJ showed the best phenol removal effect in both tested soils. Our results indicate that the biochar-B403 composite has great potential in the remediation of high phenol-contaminated soil.

Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg−1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Feasibility and mechanism of high alumina cement-modified chlorine saline soil as subgrade material

Soil salinization is a serious problem during ground improvement and foundation construction around the coastal region. This study used high alumina cement (HAC) as a soil stabilisation agent to modify the coastal chlorine saline soil as roadbed backfilling materials. In addition, Ordinary Portland cement (OPC), slaked lime (SL) and fly ash (FA) were used to better the understanding of the chlorine fixation and roadbed performance. The microstructures of different hydration products were investigated through the utilization of the X-ray diffraction and scanning electron microscope equipped with an energy dispersion spectrometer. The HAC-SL-modified soil depicts that the aluminium and calcium phases are beneficial to the formation of Friedel’s salt and hydration products. The optimal chlorine fixation is approximately 20.5% at 6% HAC-SL incorporation (3% of HAC and 3% SL). At the early stage of curing, the strength of the HAC-treated soil is high. However, with a prolonged curing period, there is a slight decrease in the strength because the porosity will increase during the transformation of metastable CAH10 and C2AH8 into stable and dense C3AH6. This evolution can be prevented by incorporating SL to enrich calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). Furthermore, it is of key importance to mention that HAC reaction is quick, therefore, the compaction should be undertaken instantly to ensure the road performance.

Rapid estimation of soil Mn content by machine learning and soil spectra in large-scale

Manganese (Mn) is an essential element in both plants and the human body; however, traditional methods for monitoring Mn in soil are costly and inefficient. As such, it is necessary to establish a model for environmental research uses that can accurately predict soil Mn content over large areas. This study aims to develop a multilayer perceptron (MLP) model capable of accurately predicting Mn content in diverse soils based on visible and near-infrared (VNIR) spectroscopy. A dataset containing 18,675 soil samples compiled from the Land Use and Coverage Area Frame Survey was used to train and adjust the model, following which the optimal model was applied globally. The correlation coefficient, root mean square error, and mean absolute error values for the optimal model on the test set were 0.76, 140.52, and 97.30, respectively. Feature importance analysis revealed crucial spectral bands at approximately 1400, 2200, 2300, and 2400–2500 nm, which enabled the Mn content to be estimated. The presence of these spectral bands indicates that clay minerals, H2O, and OH− groups had significant influence on Mn content. The MLP model developed can effectively identify regions with potentially high or low soil Mn content. With improvement of the spectral database, this model can provide effective assistance in evaluating soil Mn distribution at the global scale.