Increasing Soil Organic Matter Content Research Articles

Fate of contaminants of emerging concern in the reclaimed wastewater-soil-plant continuum

Reclaimed wastewater irrigation, a common agricultural practice in water-scarce regions, chronically exposes the agricultural environment to a wide range of contaminants of emerging concern (CECs) including pharmaceuticals and personal care products. Here we provide new data and insights into the processes governing the translocation of CECs in the irrigation water-soil-plant continuum based on a comprehensive dataset from 445 commercial fields irrigated with reclaimed wastewater. We report on CEC exposures in irrigation water, soils, and edible produce (leafy greens, carrots, potatoes, bananas, tomatoes, avocados, and citrus fruits). Our data show that CEC concentrations in irrigation water and their physiochemical properties (mainly charge and lipophilicity) are the main factors governing their translocation and accumulation in the soil-plant continuum. CECs exhibiting the highest detection frequency in plants (lamotrigine, venlafaxine, and carbamazepine) showed a reduction in their leaf accumulation factor with increasing soil organic matter content. The higher soil organic matter likely reduced the available CEC concentration in the soil solution due to soil-CEC interactions, leading to reduced uptake. Interestingly, the concentration of carbamazepine in the leaves showed a saturation-like trend when plotted against its concentration in the soils. This probably resulted from steady-state conditions when uptake equals in-planta decomposition. Our data indicate that due to continuous reclaimed wastewater irrigation, the soil acts as a sink for CECs. CECs in the soil reservoir can be desorbed into the soil solution during the rainy season and be taken up by rain-fed crops.

Effects of Leonardite Amendments on Vineyard Calcareous Soil Fertility, Vine Nutrition and Grape Quality.

Vineyard calcareous soils are usually low in organic matter, which makes them prone to physical, chemical, and biological degradation. Besides, these soils are also usually poor in various nutrients in plant-available form, e.g., iron. To make up for this lack of soil fertility, on the one hand, manures, and on the other, iron chelates are usually used. However, the soil application of these materials is not free from problems, and other amendments based on leonardites could be advantageously used as an alternative. Therefore, two organic amendments, one leonardite alone (1 Mg/ha), and the other leonardite (1 Mg/ha) plus ferrous sulphate heptahydrate (0.5 Mg/ha), were tested for three years in a commercial vineyard calcareous plot under Mediterranean climate. The effects of these amendments on soil fertility, plant nutrient contents, and berry quality were studied against a control of bare soil by means of a fully randomized trial with three repetitions per treatment. Soil organic matter (SOM) increased as a consequence of both leonardite treatments, but much more than expected on the basis of a simple mass transfer from the amendments. With the ferrous-sulphate-heptahydrate-supplemented leonardite, the increase in SOM was noticeably higher. This is explained on the basis of nutrient quantity and intensity-pH-related effects, which increased soil nutrient plant-availability and presumably enhanced vine root growth. In response to the higher plant availability of nutrients, the petiole nutrient concentrations were observed to increase under the leonardite treatments. However, only a trend to increase potassium in petioles and in grape must, linked to a decrease of grape must pH, was observed in harvest quality under the leonardite treatments. Leonardite and adequately supplemented leonardite seem to have potential for increasing SOM contents and nutrient plant-availability, thus improving the soil fertility of vineyard calcareous soils.

Bio-Based Waste’ Substrates for Degraded Soil Improvement—Advantages and Challenges in European Context

The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be reversed by supporting remediation/reclamation processes. One of the possibilities is the introduction of biodegradable waste/biowaste substrates into the soil. The additives can be the waste itself or preformed substrates, such composts, mineral-organic fertilizers or biochar. In EU countries average value of compost used for land restoration and landfill cover was equal 4.9%. The transformation of waste in valuable products require the fulfillment of a number of conditions (waste quality, process conditions, law, local circumstances). Application on degraded land surface bio-based waste substrates has several advantages: increase soil organic matter (SOM) and nutrient content, biodiversity and activity of microbial soil communities and change of several others physical and chemical factors including degradation/immobilization of contaminants. The additives improve the water ratio and availability to plants and restore aboveground ecosystem. Due to organic additives degraded terrains are able to sequestrate carbon and climate mitigate. However, we identified some challenges. The application of waste to soil must comply with the legal requirements and meet the end of use criteria. Moreover, shorter or long-term use of bio-waste based substrate lead to even greater soil chemical or microbial contamination. Among pollutants, “emerging contaminants” appear more frequently, such microplastics, nanoparticles or active compounds of pharmaceuticals. That is why a holistic approach is necessary for use the bio-waste based substrate for rehabilitation of soil degraded ecosystems.

Estimation of crop residue cover in rice paddies by a dynamic-quadripartite pixel model based on Sentinel-2A data

Crop residues left on the field after harvest increase soil organic matter content and improve soil quality. Linear spectral mixture analysis (LSMA) is an important technique for calculating crop residue cover. Traditionally, farmland has been considered to be composed solely of soil and crop residue endmembers. But rice paddy fields are often more complex than other fields. In the decomposition of pixels reflectance, leaving out potential endmembers greatly increases the variability of existing endmember reflectance. The error is then transferred to the rice residue endmember. In this paper, a dynamic-quadripartite pixel model (DQPM) is proposed to adapt LSMA to calculate rice residue cover (RRC) in complex paddy fields. This method considers that pixels in paddy fields are composed of four endmembers: soil, rice residues, green moss and white moss. With the approach, soil moisture can be calculated to automatically correct the reflectance of the soil endmembers of each pixel. The calculation results of our model were verified with field data and compared with those from the static-quadripartite pixel model (SQPM) without considering soil moisture (SM) content and with the dynamic-dimidiate pixel model (DDPM). Results confirm the feasibility of DQPM. The results show that with four endmembers, RRC has a large range of improved computational accuracy with DQPM compared with SQPM and DDPM. DDPM has a large error under 1% < SM < 3% (gravimetric water content) and 60% < RRC < 70%. Only when SM is near 0.3, SQPM can achieve good accuracy. Among the three models, DQPM has the best robustness under different soil moisture and RRC scenarios. Therefore, our proposed method is useful for calculating RRC in complex paddy field scenarios.

Effects of different fertilizer application practices on newly reclaimed soil structure and its nutrient content

Effects of organic fertilizer practice (OF), organic fertilizer combined with chemical fertilizer practice (OC), and conventional fertilization practice (CF) on soil structure were evaluated by combining micro and macro analyses in newly reclaimed cultivated land. Soil organic matter (SOM), cation exchange capacity (CEC), soil bulk density (BD), soil moisture content (SMC), and aggregate stability were also analyzed. The CF soil structure was mainly composed of moderately separated block and angular structures with the minimum SOM (7.08 g/kg) and the highest BD (1.40 g/cm3), and the pore type was mainly simple surface cracks. Compared with CF, OF and OC significantly increased SOM content by 59.3 and 29.6% (p &lt; 0.05) and CEC by 13.5 and 5.2%, respectively. The newly reclaimed soil structure was improved to a moderately separated clump structure and a well-developed aggregated structure, and the number of composite accumulation pores gradually increased. Moreover, OF and OC were associated with higher mean weight diameter (MWD), geometric mean diameter (GMD) values, and lower BD and fractal dimension (D) values. The water-stable macroaggregates (R0.25) and the aggregate stability of newly reclaimed soil were significantly increased, with a stronger improvement observed under OF. These results confirm the benefits of OC and OF practices on the structural stability, water and fertilizer retention characteristics of newly reclaimed cultivated land, and will be conductive to improving the soil quality and achieving sustainable soil development. Bangladesh J. Bot. 50(3): 781-794, 2021 (September) Special

Potential role of organic matter in the transmission of antibiotic resistance genes in black soils

The degradation of black soil is a serious problem with the decrease in soil organic matter (SOM) content in northeast China, and animal manure as a reservoir of antibiotic resistance genes (ARGs) is commonly amended into soil to sustain or increase the SOM content. However, the potential effect of SOM content on soil resistome remains unclear. Here, a soil microcosm experiment was established to explore the temporal succession of antibiotic resistance genes (ARGs) and bacterial communities in three black soils with distinct difference in SOM contents following application of poultry manure using high-throughput qPCR (HT-qPCR) and MiSeq sequencing. A total of 151 ARGs and 8 mobile genetic elements (MGEs) were detected across all samples. Relative abundance of ARGs negatively correlated with SOM content. Manure-derived ARGs had much higher diversity and absolute abundance in the low SOM soils. The ARG composition and bacterial community structure were significantly different in three soils. A random forest model showed that SOM content was a better predictor of ARG pattern than bacterial diversity and abundance. Structural equation modeling indicated that the negative effects of SOM content on ARG patterns was accomplished by the shift of bacterial communities such as the bacterial diversity and abundance. Our study demonstrated that SOM content could play an important role in the dissemination of ARGs originated from animal manures, these findings provide a possible strategy for the suppression of the spread of ARGs in black soils by increasing SOM content.

Experimental Study on Thermal Conductivity of Organic-Rich Soils under Thawed and Frozen States

Thermal properties are important for featuring the water-heat transfer capacity of soil. They are also key to many processes in earth sciences, such as the land surface processes and ecological and geoenvironmental dynamics and their changes in permafrost regions. With loose and porous structures, the organic matter layer in soil strata substantially influences soil thermal conductivity. So far, thermal conductivity of mineral soils has been explored extensively and in depth, but there are only limited studies on that of organic soils. In this study, influences of soil temperature, soil moisture saturation (SMS), and soil organic matter (SOM) content on soil thermal conductivity were analyzed on the basis of laboratory experiments on the silt-organic soil mixtures of varied mixing ratios. Results show that soil thermal conductivity declines slowly with the lowering temperatures from 10 to 0°C; however, it increases and finally stabilizes when temperature further lowers from 0 to -10°C. It is important to note that thermal conductivity peaks in the temperature range of -2~0°C (silty and organic-poor soil) and -5~0°C (organic-rich soil), possibly due to phase changes of ice/water in warm permafrost. Under both thawed and frozen states, soil thermal conductivity is positively related with SMS. However, with rising SOM content, the growth rate of soil thermal conductivity with SMS slows gradually. Given the same SMS, soil thermal conductivity declines exponentially with increasing SOM content. Based on the experimental and theoretical analyses, a new empirical computational formula of soil thermal conductivity is established by taking into account of the SOM content, SMS, and soil temperature. The results may help better parameterize in simulating and predicting land surface processes and for optimizing frozen soil engineering designs and provide theoretical bases for exploring the dynamic mechanisms of environmental changes in cold regions under a changing climate.

Interrelation between harvester ant activity, soil fertility, and land management in the arid lands of the Negev Desert, Israel

Much of the open lands in arid areas are highly degraded reaching a state grazing or crop yields become low and non-profitable a state grazing or crop yields become low and non-profitable. Implementation of deep tilling and fertilization to enhance yields may cause destructive outcomes for the environment. An alternative approach may be conservation agriculture practices also involving the triangular interrelation among the harvester ant activity, soil fertility, and land management practices to maximize and increase the sustainable agricultural utilization of semi-arid farm land. In order to define this interrelation, a study was carried out at three sites in the northern Negev, Israel between 2014 and 2017. In each site, three different land management practices were carried out (cereal breeding, grazing, and conservation). The findings indicate that in the first three years, the harvester ants' foraging activity increased soil organic matter content by 0.25% per year, followed by an increase of 0.5 % year−1, caused by ants' nesting and foraging. In this state, partial grazing or rainfed crop breeding using a conservative tillage scheme can be carried out until sustainability. Cultivations such as fertilizing with organic matter and land management practices such as savanna trees or local perennials plantations may strengthen the interrelation among the harvester ant activity, soil fertility and biological productivity leading to an increased sustainable agriculture utilization.

Biochar Application Mitigates the Effect of Heat Stress on Rice (Oryza sativa L.) by Regulating the Root-Zone Environment.

Coping with global warming by developing effective agricultural strategies is critical to global rice (Oryza sativa L.) production and food security. In 2020, we observed that the effect of heat stress on rice plants was mitigated by biochar application (40 g kg−1 soil) in a pot experiment with six consecutive days (6–11 days after transplanting) of daily mean temperatures beyond the critical high temperature (33°C) for tillering in rice. To further determine the eco-physiological processes underlying the effect of biochar on resistance to heat stress in rice plants, we compared root-zone soil properties as well as some plant growth and physiological traits related to nitrogen (N) utilization between rice plants grown with and without biochar in the pot experiment. The results showed that the application of biochar improved the root-zone environment of rice plants by reducing soil bulk density, increasing soil organic matter content, and altering soil bacterial community structure by increasing the ratio of Proteobacteria to Acidobacteria, for example. As a consequence, root morphology, architecture, and physiological traits, such as N assimilation and transport proteins, as well as shoot N uptake and utilization (e.g., photosystems I and II proteins), were improved or up-modulated, while the heat-shock and related proteins in roots and leaves were down-modulated in rice plants grown with biochar compared to those without biochar. These results not only expand our understanding of the basic eco-physiological mechanisms controlling increased heat-stress tolerance in rice plants by the application of biochar, but also imply that improving the root-zone environment by optimizing management practices is an effective strategy to mitigate heat stress effects on rice production.

Effects of Application of Recycled Chicken Manure and Spent Mushroom Substrate on Organic Matter, Acidity, and Hydraulic Properties of Sandy Soils.

Soil organic matter is a key resource base for agriculture. However, its content in cultivated soils is low and often decreases. This study aimed at examining the effects of long-term application of chicken manure (CM) and spent mushroom substrate (SMS) on organic matter accumulation, acidity, and hydraulic properties of soil. Two podzol soils with sandy texture in Podlasie Region (Poland) were enriched with recycled CM (10 Mg ha−1) and SMS (20 Mg ha−1), respectively, every 1–2 years for 20 years. The application of CM and SMS increased soil organic matter content at the depths of 0–20, 20–40, and 40–60 cm, especially at 0–20 cm (by 102–201%). The initial soil pH increased in the CM- and SMS-amended soil by 1.7–2.0 units and 1.0–1.2 units, respectively. Soil bulk density at comparable depths increased and decreased following the addition of CM and SMS, respectively. The addition of CM increased field water capacity (at –100 hPa) in the range from 45.8 to 117.8% depending on the depth within the 0–60 cm layer. In the case of the SMS addition, the value of the parameter was in the range of 42.4–48.5% at two depths within 0–40 cm. Depending on the depth, CM reduced the content of transmission pores (>50 µm) in the range from 46.3 to 82.3% and increased the level of residual pores (<0.5 µm) by 91.0–198.6%. SMS increased the content of residual pores at the successive depths by 121.8, 251.0, and 30.3% and decreased or increased the content of transmission and storage pores. Additionally, it significantly reduced the saturated hydraulic conductivity at two depths within 0–40 cm. The fitted unsaturated hydraulic conductivity at two depths within the 0–40 cm layer increased and decreased in the CM- and SMS-amended soils, respectively. The results provide a novel insight into the application of recycled organic materials to sequester soil organic matter and improve crop productivity by increasing soil water retention capacity and decreasing acidity. This is of particular importance in the case of the studied low-productivity sandy acidic soils that have to be used in agriculture due to limited global land resources and rising food demand.

Effects of conventional versus no-tillage systems on the population dynamics of elaterid pests and the associated damage at establishment of maize crops

No-till agriculture, combined with the practices of continuous soil cover by retaining crop residues and of crop rotation, including cover crops, represents a relatively widely adopted management system that aims to increase soil organic matter content as well as long-term sustainability. However, its impacts on wireworm populations in the soil and risk of damage to crops are uncertain, and current recommendations may unjustifiably limit grower options. Consequently, this study examined the effects of no-tillage soil management on the population dynamics of Agriotes wireworm pests (Coleoptera: Elateridae) by bait sampling, maize plant damage assessments, and pheromone trapping (adults) within three farms in northeastern Italy, from 2011 through 2016, as compared to conventional tillage. The four-year cropping rotation consisted of winter wheat (Triticum aestivum), oilseed rape (Brassica napus), maize (Zea mays), and soybean (Glycine max) under both tillage treatments. The nature and intensity of damage caused by wireworms to maize early stages was assessed each year. Wireworms and beetles comprised of four different species (A. brevis, A. sordidus, A. ustulatus, and A. litigiosus) were captured, with the numerically dominant species (A. sordidus) accounting for over 90% of all captures. All species responded similarly to tillage practices. No effects of tillage operations were associated with beetle captures (P > 0.28) and larval densities (P > 0.45). No differences were observed between tillage treatments in wireworm feeding maize damage scores (P > 0.17; means for no-till and conventional tillage maize were 3.82 and 4.14 percent damage, respectively). These results suggest that switching from a conventional tillage system to a no-till maize production may not cause an increase of wireworm damage to maize, even though no-till conditions have been historically associated with increased wireworm damage risk. Possible causes of these results are discussed.

Quantitative assessment of the potential for soil improvement by planting Miscanthus on saline‐alkaline soil and the underlying microbial mechanism

AbstractPhytoremediation using Miscanthus is a valuable technique for the restoration of saline‐alkaline soil, but the potential is not quantified. To assess this potential, a 5 years field experiment was conducted on saline‐alkaline soils with three genotypes of Miscanthus and an unplanted control. The bulk soil (0–20‐cm depth) physicochemical properties were measured annually from 2015 to 2018, while the bacterial and fungal community structures of the rhizosphere soil were investigated by high‐throughput sequencing after 5 years under Miscanthus (2018). The results showed that Miscanthus cultivation on saline‐alkaline soil reduced soil salinization and improved soil fertility on this site. Specifically, compared with the blank control, the five‐years Miscanthus cultivation (mean of three different genotypes pooled) decreased the soil pH by 0.33 units (8.78–8.45) and electrical conductivity by 23.4 μS/cm (226.7–203.3 μS/cm), as well as increasing soil organic matter content from 18.9 to 34.9 g/kg and total potassium content from 15.2 to 18.0 g/kg. In addition, the soil improvement was more pronounced with a longer duration of growth. Miscanthus remediates saline‐alkaline soils by altering the microbial community compositional abundance rather than its diversity. The improvement is due to enrichment of beneficial bacteria leading to soil desalinization (e.g., by Gemmatimonadaceae), litter decomposition (e.g., by Chitinophagaceae), plant growth promotion (e.g., by Micrococcaceae), and the reduction of harmful fungi (e.g., Pleosporales and Chitinophagaceae). Soil pH, electrical conductivity, organic matter, and total potassium were the main physicochemical properties affecting bacterial and fungal communities. Our results quantify the soil improvement potential of Miscanthus and clarify the underlying microbial mechanisms, laying a solid foundation for further implementation of saline‐alkaline soil phytoremediation using Miscanthus. In the future, more extensive multi‐location trials are required to assess if these improvements are seen across a wide diversity of environments.

SOIL ORGANIC MATTER (SOM): STATUS, TARGET AND CHALLENGES IN NEPAL

Changes in soil organic matter (SOM) are slow and difficult to monitor, usually apparent after few decades. Recent changes in the agriculture had its influence on soil, including the soil organic matter content. About 60% of soil in Nepal now have low organic matter content. Agriculture Perspective Plan (APP) was focused more on the concept of green revolution to increase the chemical fertilizer inputs, however, the scenario is changing. Use of organic fertilizers is promoted extensively by government and different organizations with a target of increasing SOM content from 1.92% in 2015 to 4% by 2035. This paper aims at analysing the current status, targeted goal and the challenges faced in the augmentation of the soil organic matter using data available. Achieving this target requires an addition of extra 2.244 ton/ha of organic matter on a yearly basis for 20 years. The average amount of organic matter (2.5-3 ton/ha) applied is lesser than a single season grain harvest. 4.69% of sites had high soil organic matter in fiscal year 075/76 which slipped to 2.64% in 2076/77. The sites with low soil organic matter increased from 12.73% to 15.31%. The causes behind the SOM decline varies according to different agro-ecological zones like soil erosion, residue burning, imbalanced fertilizer use, defective FYM production etc. Findings suggest precise technologies required to be adopted to tackle with the different niche specific causes of soil fertility decline. Despite the complete nutrient content, bulky nature of organic fertilizers sets a major drawback regarding their transportation, distribution and commercialization. Government of Nepal is promoting organic fertilizer use by subsidizing their production cost by 50%. Following integrated nutrient management (INM) techniques, sustainable soil management practices (SSMP) and promotion of use of locally available resources can play a huge role in making the technology sustainable to the farmers.

Effects of Rice Husk Compost on Some Soil Properties, Water Use Efficiency and Tomato (Solanum lycopersicum L.) Yield under Greenhouse and Field Conditions

ABSTRACT The effect of rice husk compost (RHC) on some soil properties, evapotranspiration (ETa), yield (Y) and water use efficiency (WUE) of tomato (Solanum lycopersicum L.) plant under the field and greenhouse conditions was investigated. In the experiments carried out at the experimental field and the greenhouse of Agricultural Faculty in Ondokuz Mayıs University, Samsun, Turkey. The RHC was applied to surface soil (0–20 cm) at 0%, 3%, 6% and 9% (0 – 6 – 12 – 18 Mg ha−1) doses with three replications according to the randomized plots experimental design. RHC application generally improved the soil quality parameters according to the control treatment during the experiment carried out with growing tomato plant in the field and greenhouse conditions. RHC treatments increased electrical conductivity, field capacity and permanent wilting point, available water content with increasing soil organic matter content, reduced soil pH and bulk density (Db) over the control treatment. Db values of the soils in the field and greenhouse decreased according to the control treatment with 3% > 6% > 9% doses of RHC. Field capacity, permanent wilting point and available water capacity (AWC) values of the soils generally increased according to the control with 9% > 6% > 3% doses of RHC application. While 92-day ETa values in field ranged from 426 mm in control to 314 mm in 9% RHC application, 112-day ETa values in greenhouse ranged from 547 mm in control to 375 mm in 3% RHC application. According to the control treatment, the highest reduction in ETa values was 26.3% with 9% RHC in the field and 31.5% with 3% RHC application in the greenhouse. Soil organic matter values of the soils had significant correlations with Db (−0.868**), AWC (0.667*), yield (0.593*) and WUE (0.722**) in the greenhouse conditions and with Db (−0.628**), AWC (0.427*), yield (0.468*) in the field conditions. While there were negative relationships between WUE and ETa in field (−0.818**) and greenhouse (−0.365) conditions, the positive relationships between yield and WUE were determined in field (0.280) and greenhouse (0.887**). When comparing the control treatments, RHC applications in field and greenhouse conditions helped to water saving as 118 mm (1181 ton ha−1) and 216 mm (2160 ton ha−1), respectively. According to the results, the applications of 6% RHC in field and 9% RHC in greenhouse conditions were suggested to reduce ETa values, and to improve the soil quality parameters, WUE and tomato yield.

Impacts of Relative Elevation on Soil Nutrients and Apple Quality in the Hilly-Gully Region of the Loess Plateau, China

Relative elevation, as one of the decisive factors to the redistribution of soil water, nutrients, sunshine, and temperature in a region influences apple yield and quality by adjusting soil water and nutrients. To explore the impact of relative elevation on apple quality, this research investigated the conditions of soil moisture and nutrients at different elevations of terrace apple orchards in the hilly-gully region of the Loess Plateau. The results showed that soil water content decreases when the elevation increased, whereas soil nutrients fluctuated significantly at different elevations of terrace orchards and the contents were lower than the standard level of the Loess Plateau, especially soil organic matter, but total potassium was higher. The apple firmness increased when the elevation increased and had a good linear relationship with elevation. Apple vitamin C content in weed-covered orchards was higher than in the ploughing and weeding management orchards. The impact of soil nutrients, including soil water, nitrogen, phosphorus, and potassium on apple quality were concentrated in soluble solid and total acid. Irrational irrigation or partial use of nutrients, such as more use of nitrogen and less use of phosphorus and potassium, may deteriorate the apple quality. Therefore, we suggested that the amount of irrigation be increased appropriately with the raising of elevation. Moreover, part of the weed should be kept to cover the orchard, as well as mowing regularly and covering the surface. This would not only improve water use efficiency and increase soil organic matter content, it would also maintain apple quality and ensure sustainable development of the apple orchards.

The importance of initial application and reapplication of biochar in the context of soil structure improvement

Abstract It was shown that the use of biochar provides many benefits to agriculture by improving the whole complex of soil properties, including soil structure. However, the diverse range of biochar effects depends on its physicochemical properties, its application rates, soil initial properties etc. The impacts of biochar, mainly its reapplication to soils and its interaction with nitrogen in relation to water-stable aggregates (WSA) did not receive much attention to date. The aims of the study were: (1) to evaluate the effect of initial application (in spring 2014) and reapplication (in spring 2018) of different biochar rates (B0, B10 and B20 t ha−1) as well as application of biochar with N-fertilizer (40 to 240 kg N ha−1 depending on the requirement of the cultivated crop) on the content of WSA as one of the most important indicators of soil structure quality, (2) to assess the interrelationships between the contents of soil organic matter (SOM) and WSA. The study was conducted in 2017–2019 as part of the field experiment with biochar on Haplic Luvisol at the experimental station of SUA in Nitra, Slovakia. Results showed that initial application as well as reapplication of biochar improved soil structure. The most favorable changes in soil structure were found in N0B20B treatment (with biochar reapplication) at which a significantly higher content of water-stable macro-aggregates (WSAma) (+15%) as well as content of WSAma size fractions of &gt; 5 mm, 5–3 mm, 3–2 mm and 2–1 mm (+72%, +65%, +57% and +64%, respectively) was observed compared to the control. An increase in SOM content, due to both, initial biochar application and its reapplication, significantly supported the stability of soil aggregates, while organic matter including humic substances composition did not.

Effects of mercapto-palygorskite on Cd distribution in soil aggregates and Cd accumulation by wheat in Cd contaminated alkaline soil

Cadmium (Cd) contamination in alkaline soils is a serious issue in China. As the basic structural units of soil, soil aggregates play an important role in the migration and transformation of heavy metal. However, there are few studies on the effects of adding amendments on Cd distribution in soil aggregates in alkaline soils. In this study, pot experiments were conducted to assess the effects of mercapto-palygorskite (MPAL) on soil aggregates and Cd accumulation in wheat. The results showed that MPAL application had no effect on wheat yield but significantly reduced the Cd uptake by the roots and the Cd transport to the adjacent internode. Application of 0.1% MPAL reduced the Cd concentration in two wheat grains (0.57 and 0.44 mg/kg, control) to 0.10 and 0.09 mg/kg in moderately Cd-contaminated soil, which are below the China national standard limit of 0.1 mg/kg (GB 2762-2017). MPAL application had no effect on soil pH, cation exchange capacity, mass proportion and mean weight diameter of soil aggregates, but increased soil organic matter content. Importantly, MPAL application promoted the migration of Cd from large particles (>0.25 mm) to small particles (<0.048 mm), reduced the unstable Cd fractions in >0.25 mm soil particles of clay soil and in >0.075 mm soil particles of sandy soil, and increased the stable Cd fractions in bulk soils and soil aggregates. The effects of MPAL addition on soil aggregates (grain size fraction metals loading and accumulation factor) of sandy soil were more prominent than on those of clay soil. Under MPAL treatments, wheat grains Cd concentration was significantly positively correlated with the available Cd in >0.075 mm soil particles and the total Cd in >0.25 mm soil particles. These results indicated that MPAL application in alkaline soils promoted the migration of Cd to micro-aggregates and inhibited the uptake and transport of Cd by wheat roots, thus reducing the Cd concentration in wheat grains.

LIBS and FTIR–ATR spectroscopy studies of mineral–organic associations in saline soil

AbstractDirect characterization of the spatial distribution of elements and compound binding of salt–organic associations in soil is imperative for understanding the mechanisms of organic matter decomposition and nutrient release involved in soil degradation and development processes. However, traditional chemical methods would damage the chemical bonds in salt–organic associations, and modern spectroscopic techniques provide alternative options for resolving this problem. In this study, mid‐infrared‐attenuated total reflectance spectroscopy (FTIR–ATR) was used to obtain molecular group information; laser‐induced breakdown spectroscopy (LIBS) was applied to obtain microlevel distribution of elements, and two‐dimensional correlation spectroscopy (2DCOS) analysis was conducted to illustrate the binding combination features of mineral–organic associations in saline soil from the Hetao Irrigation District in China. The results showed that the distributions of Mg, Ca, Na, and K were heterogeneous at the microlevel; the spatial distributions of Mg and Ca showed a significant correlation (r = 0.90***), while K displayed a negative correlation with the soil organic matter (SOM) contents. In the soil with lower SOM contents, the elements were distributed at the top of the ablation area and enhanced with the increasing SOM content, which reflected the trends of the SOM layer thickness outside the mineral–organic associations at the microlevel. Furthermore, 2DCOS analysis suggested that the hydrogen bonds in silicate groups were stronger than those of organic functional groups, such as C=O/C=C, when combined with salt‐related compounds, and Mg, Ca, Na, and K did not originate from clay mineral compounds in saline soil but partially originated from deposited organic associations.

Facultative-anaerobic microbial digestion of coal preparation waste and use of effluent solids to enhance plant growth in a sandy soil

Coal preparation solid waste, which is a major environmental issue for coal-producing areas in China, may be microbiologically digested and transformed into a product suitable as a soil amendment to increase soil organic matter content and prevent and enhance plant/crop growth. Coal preparation waste collected from a coal sorting plant in Inner Mongolia, China was digested in bioreactors inoculated with microbial enrichments prepared from activated sludge and cow manure. The effluent solids from the coal preparation waste bioreactors were analyzed for their suitability as organic soil amendments, which complied with China standards. Plant growth tests were conducted in sandy soil from a semi-arid region in Colorado, which was amended with the effluent solids. Kentucky bluegrass (Poa pratensis L.) and chives (Allium schoenoprasum) were used as the representative plants for the growth tests, where results indicated substantially higher yields of Kentucky bluegrass and chives for the sandy soils amended with the effluent solids when compared to a commercial organic fertilizer. The number and average length of Kentucky bluegrass shoots were 10 and 5.1 times higher, respectively, in soils amended with the effluent solids. Similarly, the number and average length of chives shoots were 10 and 1.7 times higher, respectively, in soils amended with the effluent solids. Overall, the microbial digestion of coal preparation waste for application as an organic soil amendment is a viable alternative and beneficial use of coal preparation solid waste.

Enhancement of no-tillage, crop straw return and manure application on field organic matter content overweigh the adverse effects of climate change in the arid and semi-arid Northwest China

Soil organic matter (SOM) is important for sustainable agricultural production. Agricultural management can directly or indirectly affect SOM content and associated soil organic carbon (SOC) stocks. The SOM content and crop productivity are generally low in the farmlands in the arid and semi-arid regions of China, and are highly sensitive to climate changes. An improvement in SOM content may greatly enhance the efficiency of fertilizer and water use, thereby increasing the resilience of agricultural systems to climate change. However, little information is available on the response of SOM to the interactions of cultivation measures and changing climate in the regions. Here we analyzed the effects of climate and long-term management practices on SOM content at three sites in the arid and semi-arid regions of China using the SOM data monitored under a range of management practices. We showed that the manure application, crop residue return and no-tillage had significantly increased SOM content from 12.1% to 127.5% in the long-term experiment at three sites. We also used the DayCent model to simulate the effects of these management practices in combination with future climate changes on the SOM content, and found that climate changes in the near future would not increase SOM content, and even decrease SOM content under conventional agronomic management, but the possible adverse impact of climate change on SOM can be outweighed by the enhancement of agronomic management. Our results provide important information for improving management to maintain SOM content and sustainable production under future climate changes.