Soils Of Agroecosystems Research Articles

Copper in the soil of agroecosystems of vineyards: a modern view of the problem

The problem of copper in the soils of vineyards and other types of plantation and garden agroecosystems is not new, however, having loudly declared itself in scientific research in the second half of the 20th century, it has remained unresolved. In recent decades, the severity of this problem has not only not disappeared, but also acquired some new features. On the one hand, significant changes have taken place in Russia and the world in the socio-economic sphere, modern scientific and technological approaches have appeared that have changed the structure of the wine industry, formed new trends in supply and demand, contributed to the introduction of alternative types of land use, modernized agrotechnologies for growing grapes and processing. On the other hand, old environmental challenges have worsened and new ones have appeared, such as global climate change, which has a significant impact on the sustainability of the production of high-quality viticulture and winemaking products, to mitigate the consequences of which comprehensive adaptation approaches and innovative agrotechnological solutions are required. In this review, we discussed the results of research over the past 25 years, mainly by foreign authors, which allow us to look at the problem of copper in the soil of vineyards, based on modern ideas about the ways and scales of its accumulation, physico-chemical transformations and migration in the soil of ampelocenoses. The most relevant and discussed issues in the scientific literature regarding the influence of certain natural and agrogenic factors on the amount of copper accumulation in ampelocenosis soils are presented. The article considers already implemented and potential ways to mitigate the negative effects of soil pollution with copper, aimed at limiting and optimizing the use of copper-containing drugs, the introduction of soil-saving agrotechnologies in viticulture, the reclamation of copper-contaminated soils, as well as the replacement of copper-based fungicides with alternative drugs to implement sustainable plant protection strategies that are safe for the environment.

Towards a national model of humus (carbon) budget management in soils of agroecosystems in the Russian Federation

The prospect of adapting two methods for monitoring the fertility of agricultural soils (humus balance, HB) under spring and winter wheat crops (hereinafter referred to as grain crops) developed in the Russian Federation (RF) for the purposes of climate projects has been studied. It was revealed that the RosNIIzemproekt method (1998) underestimates the HB average value to -7.7 c/ha for RF. The RosNIIzemproekt method (1998) has logical errors in the calculation model and is not recommended for use. The TsINAO method (2000) has a more logical calculation model. According to this method, the average value of HB in soils for RF is generally positive and amounts to 3.3 c/ha (0.71 tCO2-eq/ha carbon units). This value constitutes ≈0.3% of average humus reserves in arable soils of the RF (108 tС/ha). The annual value of change in humus content under spring and winter wheat is incommensurably less than the total humus reserves in the soil. Statistically reliable assessment of changes in humus content requires a huge number of soil samples. This makes the verification procedure economically inexpedient. Another option is proposed to increase the time of humus accumulation. It is considered (IPCC, 2003) that a 20-year accumulation period is sufficient, which corresponds to the duration of soil climate projects. A coefficient (0.216) has been proposed for converting humus reserves (c/ha) to the value of a carbon unit (tCO2-eq/ha). The total sequestration of carbon by soils under grain crops in 2022 was about 11 million 914 thousand tCO2-eq. HB accounting significantly compensates for calculated emissions from agricultural production and reduces them by almost 10% (from 116 to 105 million tons CO2-eq in 2022). For both models of fertility monitoring, an assessment was made of the quality of the regression dependence of HB on the total biomass of photosynthesis (TBP) in soils under grain crops. It is shown that according to Fisher's t-test at a 5% significance level, the studied relationship is significant and characterized by the squares of the correlation coefficient (R2) equal to 0.554 and 0.998. In accordance with the Chaddock scale, the closeness of the correlative relationship between HB and TPB for winter wheat is assessed as high, and for spring wheat as very high.

Climate change and greenhouse gas emissions from soils under the winter wheat agroecosystem in Ukraine

The issue of global climate change is one of the most important challenges for modern environmental science. In this regard, assessment of greenhouse gas emissions from soils under agroecosystems is an extremely important task. The main purpose of the study was to assess the potential emissions of greenhouse gases (CO2 and N2O) from the soils under the winter wheat agroecosystem during its spring-summer growing season under the climate change in Ukraine. A comprehensive model of greenhouse gas emissions from agroecosystem soils was used as a theoretical basis. The study considered the main agroclimatic regions of Ukraine, such as Polissia, Forest-Steppe, Northern Steppe, and Southern Steppe. The modelling was performed for average long-term conditions of 1981–2020 and under scenario conditions (using the RCP4.5 climate scenario) for the decades of 2021–2030, 2031–2040, and 2041–2050. Estimates of CO2 emissions were obtained for the agroclimatic regions of Ukraine. According to the results, the largest CO2 emissions (0.886-0.940 t C-CO2/ha) will be expected when the average productive moisture supplies in the arable soil layer for the spring-summer period of winter wheat vegetation are 20–40 mm and the air temperature is 12–15 °C. Rise in the level of moisture reserves, averaged for the period, for more than 40 mm and the air temperature of 11–12 °C is accompanied by decrease in the level of CO2 emission (0.645–0.658 t C-CO2/ha). In arid conditions, with a decrease in the period-average moisture supplies in the arable soil layer to less than 20 mm and heightened average air temperatures (14.5–15.2 °C), a decrease in CO2 emissions is expected (0.755–0.770 t C-CO2/ha). The study showed that the highest N2O emission (1.087–1.703 kg N-N2O/ha) is expected at a high level of moistening (Md being equal to 0.474–0.713 relative units and air temperature – 11.3–13.0 °C) with a high intensity of nitrification and denitrification processes. Conditions characterizing the average level of N2O emission (0.657–0.890 kg N-N2O/ha) are formed under the moistening at a level of Md equaling 0.296–0.447 relative units and air temperature of 13.4–14.7 °C. There is a slowdown in denitrification processes and an increase in the share of emissions owing to nitrification. It has been found that the lowest N2O emission (0.508–0.537 kg N–N2O/ha) is expected under conditions of severe and very severe drought (according to the Md criterion), with a heightened temperature averaged at the level of 14.5–15.2 °C during the spring-summer period of winter wheat vegetation.

Spatial distribution and factors influencing the accumulation of toxic metals in soils in mountain agroecosystems, Rio De Janeiro, Brazil.

The concentrations of toxic metals (TM) were analyzed in 498 samples of agricultural soils used for intensive vegetable cultivation in the watershed of Barracão dos Mendes, Brazil. The goal of this study was to characterize the distribution of these elements and the main natural and anthropogenic factors affecting their accumulation. In general, the average concentrations of TM were higher than the reference quality values for cultivated soils in the region, with the exception of Cr, Co, Ni and Mn, and the average concentration of Cd was ten times greater. Three sources of variation in the distribution of TM concentrations were identified: one related to topographic relief, another related to lithology, and one related to the massive use of agrochemicals. These factors contributed to TM accumulation in the soil; moreover, the transport of toxic metal-enriched clay by runoff resulted in higher concentrations of these elements in the lower parts of the slope. The long-term application of massive amounts of fertilizers and pesticides resulted in the accumulation of Cr, Cu, Zn, Ni, Pb and Cd in the vegetable cultivation soils and promoted the enrichment of macronutrients, mainly P and K. Moreover, the spatial distribution of TM in the agricultural soils of this mountain agroecosystem was affected by intensive vegetable cultivation, which altered the natural TM distribution dynamics determined by variations in topographic relief and lithology. In intensive cultivation areas, the TM distribution was also influenced by soil management practices such as tillage along the slope direction and massive mineral and organic fertilization.

The impact of land-use changes and management intensification on bacterial communities in the last decade: a review.

In the last decade, advances in soil bacterial ecology have contributed to increasing agricultural production. Brazil is the world leading agriculture producer and leading soil biodiversity reservoir. Meanwhile, there is still a significant gap in the knowledge regarding the soil microscopic life and its interactions with agricultural practices, and the replacement of natural vegetation by agroecosystems is yet to be unfolded. Through high throughput DNA sequencing, scientists are now exploring the complexity of soil bacterial communities and their relationship with soil and environmental characteristics. This study aimed to investigate the progress of bacterial ecology studies in Brazil over the last 10 years, seeking to understand the effect of the conversion of natural vegetation in agricultural systems on the diversity and structure of the soil microbial communities. We conducted a systematic search for scientific publication databases. Our systematic search has matched 62 scientific articles from three different databases. Most of the studies were placed in southeastern and northern Brazil, with no records of studies about microbial ecology in 17 out of 27 Brazilian states. Out of the 26 studies that examined the effects of replacing natural vegetation with agroecosystems, most authors concluded that changes in soil pH and vegetation cover replacement were the primary drivers of shifts in microbial communities. Understanding the ecology of the bacteria inhabiting Brazilian soils in agroecosystems is paramount for developing more efficient soil management strategies and cleaner agricultural technologies.

Wheat cover crop has minimal effect on physical soil properties in the North Carolina Piedmont

AbstractEnvironmental awareness about soil and water conservation in agroecosystems has shifted behaviors toward favoring conservation practices in agricultural management. Interest in conservation tillage and cover cropping has increased, but some regions encounter major challenges with adjusting management to accommodate these practices while optimizing crop production. In an Ultisol in the North Carolina Piedmont, a long‐term corn (Zea mays) and soybean (Glycine max) rotation with tillage intensities ranging from no‐till to moldboard plowing in a randomized complete block design was used to assess changes in physical soil properties after introducing wheat (Triticum aestivum) as a winter cover crop. Cover crop biomass was measured along with volumetric water content (VWC) and bulk density (BD) at 0–15 cm, water retention (WR), water‐stable aggregation (WSA), and soil organic carbon (SOC) at 0–7.5 cm, and penetration resistance (PR) at 0–45 cm. No differences in VWC or WR could be solely attributed to cover cropping, but no‐till with cover cropping had the highest macroporosity where there was no vehicle traffic. Vehicle traffic had a stronger effect on soil compaction (BD and PR) than cover cropping regardless of tillage. Conservation tillage increased WSA and SOC when compared to plow tillage, but three seasons of a wheat cover crop did not significantly change these properties, possibly because wheat produced low biomass each year (750–1900 kg ha−1). Wheat had minimal effect on physical soil properties in the short term, and potential for improvement with long‐term optimal cover crop management in this region requires further assessment.

Traversing the prevalence of microplastics in soil-agro ecosystems: Origin, occurrence, and pollutants synergies

The ubiquity of plastics in modern life has made them a significant environmental concern and a marker of the Anthropocene era. The degradation of plastics results in the formation of microplastics (MPs), which measure 5 mm or less. The coexistence of MPs with other pollutants found in sludge, water treatment plant effluents, surface water, and groundwater, shapes the environmental landscape together. Despite extensive investigation, the long-term implications of MPs in soils remain uncertain, underscoring the importance of delving into their transportation and interactions with soil biota and other contaminants. The present article provides a comprehensive overview of MPs contamination in soil, encompassing its sources, prevalence, features, and interactions with soil flora and fauna, heavy metals, and organic compounds. The sources of MPs in soil agroecosystems are mulching, composting, littering, sewage sludge, irrigation water, and fertilizer application. The concentration of MPs reported in plastic mulch, littering, and sewage sludge is 503 ± 2760 items per kg−1, 4483 ± 2315 MPs/kg, and 11,100 ± 570 per/kg. The transport of MPs in soil agroecosystems is due to their horizontal and vertical migration including biotic and abiotic mobility. The article also highlighted the analytical process, which includes sampling planning, collection, purification, extraction, and identification techniques of MPs in soil agroecosystems. The mechanism in the interaction of MPs and organic pollutants includes surface adsorption or adhesion cation bridging, hydrogen bonding, charge transfer, ligand exchange, van der Waals interactions, and ion exchange.

Changing Drip Fertigation Strategy to Decrease Greenhouse Agroecosystem Soil Nitrate Residue and Improve Tomato Production in Northwest of China

Changing Drip Fertigation Strategy to Decrease Greenhouse Agroecosystem Soil Nitrate Residue and Improve Tomato Production in Northwest of China

Interference of microplastics on autotrophic microbiome in paddy soils: Shifts in carbon fixation rate, structure, abundance, co-occurrence, and assembly process

Autotrophic microorganisms play a crucial role in soil CO2 assimilation. Although microplastic pollution is recognized as a significant global concern, its precise impact on carbon sequestration by autotrophic microorganisms in agroecosystem soil remains poorly understood. This study conducted microcosm experiments to explore how conventional polystyrene (PS) and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microplastics affect carbon fixation rates (CFRs) and the community characteristics of soil autotrophic microorganisms in paddy agroecosystems. The results showed that compared with the control groups, 0.5 % and 1 % microplastic treatments significantly reduced soil CFRs by 11.8 − 24.5 % and 18.7 − 32.3 %, respectively. PS microplastics exerted a stronger inhibition effect on CFRs than PHBV microplastics in bulk soil. However, no significant difference was observed in the inhibition of CFRs by both types of microplastics in rhizosphere soils. Additionally, PS and PHBV microplastics altered the structure of autotrophic microbial communities, resulting in more stochastically dominated assembly and looser, more fragile coexistence networks compared to control groups. Moreover, microplastics drove the changes in autotrophic microbial carbon fixation primarily through their direct interference and the indirect effect by increasing soil organic carbon levels. Our findings enhance the understanding and predictive capabilities regarding the impacts of microplastic pollution on carbon sinks in agricultural soils.

Assessing the long‐term effects of conservation agriculture on cotton production in Northeast Louisiana using the denitrification–decomposition model

AbstractConservation agriculture (CA) aims to sustain agricultural production, soil, and environmental health in agroecosystems and has been promoted throughout the United States. The adoption of CA in cotton (Gossypium hirsutum) systems provides both agronomic and environmental benefits. Yet, there is limited information on the long‐term effects of CA practices on crop yield and adaptation strategies. An integrated CA system, that is, cover crops with no‐tillage (NT) instead of conventional agriculture, was implemented in the long‐term field experiments and assessed with an integrated biogeochemical model. Using the denitrification–decomposition model, this study estimated the effects of four different cover crops, for example, native grass (NG), hairy vetch (Vicia villosa), winter wheat (Triticum aestivum L.), and crimson clover (Trifolium incarnatum), on cotton yield under four different nitrogen (N) levels (e.g., 0, 50, 100, and 150 kg N/ha) and estimated responses on carbon (C) sequestration, and ecosystem functionality over a 10‐year study. The NT‐NG 50 N was used as a calibration dataset to accurately estimate the cotton lint yield with a normalized root mean square error (NRMSE) of 21% and model efficiency of 0.3. The calibration data validated the effects of hairy vetch, winter wheat, and crimson clover under the NT‐50 N with NRMSE of 24%, 21%, and 25%, respectively. According to the scenario analysis, the 50 kg N/ha application with a single‐irrigation event (10‐cm depth) was most beneficial for maximizing the cotton yield with cover crop incorporation at the NT system over the long term. The effects of increasing cover crop biomass (i.e., double seed rate) on C content, regardless of N application rates, varied based on the relationship between the main and cover crop species. Besides, the furrow plow tillage system provided efficient C sequestration. The proposed approach stands to provide agricultural and environmental sustainability with the implementation of cover crop or crop residue incorporation instead of increased N application, seed rates, and irrigation events under NT practices.

Chemical attributes, bacterial community, and antibiotic resistance genes are affected by intensive use of soil in agro-ecosystems of the Atlantic Forest, Southeastern Brazil.

Soil is one of the largest reservoirs of microbial diversity in nature. Although soil management is vital for agricultural purposes, intensive practices can have a significant impact on fertility, microbial community, and resistome. Thus, the aim of this study was to evaluate the effects of an intensive soil management system on the chemical attributes, composition and structure of prevalent bacterial communities, and presence and abundance of antimicrobial resistance genes (ARGs). The chemical characterization, bacterial diversity and relative abundance of ARGs were evaluated in soils from areas of intensive vegetable cultivation and forests. Results indicate that levels of nutrients and heavy metals were higher in soil samples from cultivated areas. Similarly, greater enrichment and diversity of bacterial genera was detected in agricultural areas. Of the 18 target ARGs evaluated, seven were detected in studied soils. The oprD gene exhibited the highest abundance among the studied genes and was the only one that showed a significantly different prevalence between areas. The oprD gene was identified only from soil of the cultivated areas. The blaSFO, erm(36), oprD and van genes, in addition to the pH, showed greater correlation with in soil of cultivated areas, which in turn exhibited higher contents of nutrients. Thus, in addition to changes in chemical attributes and in the microbial community of the soil, intensive agricultural cultivation systems cause a modification of its resistome, reinforcing the importance of the study of antimicrobial resistance in a One Health approach.

Fertilization enhances rice productivity by promoting phosphorus uptake and altering soil microbiota

Fertilization can enhance crop yield and improve soil health. However, its effects on nutrient uptake, soil microbiota, and rice yield remain unclear. Herein, we designed a double-cropping system with different fertilization treatments to determine their contributions to paddy soil agroecosystem and rice yield. Soil samples were collected before planting the early rice, after harvesting early rice, and after harvesting the late rice. Soil physicochemical properties, and rice yield, and rice nutrient (total nitrogen, phosphorus, and potassium contents) were determined. Variation of soil microbiota were also determined by high-throughput sequencing. We found that soil potassium content significantly improved during the planting process (P < 0.05), while rice phosphorus displayed significant variation under fertilization (P < 0.05). Notably, late rice yield was significantly higher than early rice yield (P < 0.001) after fertilization treatment. Furthermore, rice yield was positively correlated with available soil phosphorus (P < 0.05), indicating that fertilization promoted phosphorus uptake. Organic fertilizer altered the soil microbiota and increased Chloroflexi phyla abundance, while organic fertilizer combined with a compound microbial agent increased the diversity of soil microbial communities. A partial least squares path model revealed that fertilizer treatment directly positively affected rice yield by influencing phosphorus uptake and Shannon index (P < 0.01). Collectively, this study demonstrates that organic fertilization with compound microbial agents can stabilize soil nutrients, increase soil microbial diversity, and improve rice yield, thereby offering a guide for enhancing fertilizer utilization and improving agroecosystems.

Uptake of biocrust nitrogen by tree crops in a sandy soil agroecosystem

Biological soil crusts (biocrusts) are widespread in dryland ecosystems worldwide and were only recently discovered in agroecosystems. As agroecosystem biocrusts complete biological nitrogen (N) fixation, this research investigated if biocrust N could be released to biocrust subsoil and assimilated by a perennial tree crop. Biocrust was pulse labeled with 15NH4Cl (15N) in the greenhouse for eight weeks prior to application in a citrus (Citrus spp.) orchard in Southwest Florida, USA. Patches of labeled biocrust were applied to twelve citrus trees in September, with twelve trees in the same orchard not receiving biocrust (controls). The 15N in the biocrust, subsoil, crop fibrous roots, and crop leaves was quantified at seven dates leading up to fruit harvest 158 days after application. Sampling dates overlapped with citrus root (September–October) and shoot (March) flush periods. Isotopically labeled biocrust N was present in subsoil and crop roots one day after biocrust application and in leaves after three days. Results revealed that N was released from biocrust at a rate of 0.63% 15N released per day leading up to fruit harvest when 91.7% of 15N had been released. The amount of biocrust 15N in the fibrous roots increased during a root flush period (September–October) until 28 days after biocrust application and then decreased leading up to a leaf flush period and fruit harvest. Approximately 23.8% of total biocrust 15N was in the crop tissue at fruit harvest. Overall, these results indicate agroecosystem biocrusts have the potential to support tree crop growth during N demanding growth stages.

ПИЛОТНЫЙ КАРБОНОВЫЙ ПОЛИГОН: АНАЛИЗ ЗАПАСОВ УГЛЕРОДА В ПОЧВАХ СЕЛЬХОЗУГОДИЙ

The carbon cycle in agroecosystems is determined by the balance between the absorption of carbon dioxide by terrestrial vegetation of agricultural crops to create organic matter and its release during soil respiration. The soil cover is a powerful source of carbon dioxide and serves as a reservoir accumulating soil organic carbon. Organic carbon accumulating in the humus of soils serves as a drain of carbon dioxide, methane into the atmosphere for hundreds of years. The research was carried out in order to analyze the reserves of organic carbon in the soils of agroecosystems and assess the emission of CO2 and CH4 gases. The work was carried out in 2022-2023 at the site of a pilot carbon landfill (arable land) in the Republic of Bashkortostan. In field and laboratory experiments, technologies for controlling carbon dioxide emissions on agricultural lands were developed and tested. In the field, full-profile soil sections and digs were laid in accordance with GOST R58595-2019 with the determination of morphological properties and the selection of soil samples for laboratory analysis. Agrochemical analysis of the soil for the content of organic matter, the density of addition, the content of mobile phosphorus and potassium, the pH value allowed us to estimate the carbon stock of the soil of the carbon landfill according to the methodology of the Ministry of Natural Resources of the Russian Federation. The total reserves of organic carbon of the arable horizon at the carbon-new landfill amount to 503.8 t/ha, which vary and depend on the employment of the field and the characteristics of the agricultural crop. Measurement of the destructive part of the carbon cycle using a portable LI-COR 7810 camera showed that the fields occupied by crops differ in the intensity of the release of soil carbon dioxide ‒ in the field under pure steam, CO2 emissions were 2.18 times lower than under perennial grasses. The availability of data on the spatial distribution of organic soil carbon makes it possible to introduce carbon-dependent crop rotations with a set of crops that contribute to the maximum absorption of atmospheric CO2 and other greenhouse gases into the practice of agriculture.

Ecological problems of soil science and farming

The article noted the importance of respect for the natural environment in agricultural land use. Separate directions of human impact on the soil, plants and other objects of agroecosystems are considered. The negative role of soil erosion, which has become widespread, is indicated. Soil loses in some fields reaches 20 t/ha. In the Kursk region the 23% of arable land is eroded. Erosion leads to a decrease in the content of humus and nutrients in the soil. Measures to eliminate it are hydraulic structures, anti-erosion organization of the territory, the system of contour-reclamation agriculture, forest reclamation measures, soil protection tillage, crop rotation and others. In order to increase the soil-protective properties of the vegetation cover in crop rotations, the areas of winter crops and perennial grasses are increased. A seeded fallow is used instead of an unoccupied one. The article gives examples of creating an anti-erosion agro-environment. The reasons for the acquisition of toxic properties by the soil are considered. The main sources of toxicants entering to the soil are pesticides, mineral fertilizers and other agrochemicals. Under certain conditions crop rotation and tillage can increase toxicity. Our studies showed that the toxicity of soil under winter wheat, which was preceded by green manure fallow, was lower than when it was grown in black and seeded fallow. The positive role of both organic and mineral fertilizers in increasing the biological activity of the soil and reducing its toxicity has been established. Drawn attention to the problem of ensuring product quality and food safety. The biologization of agriculture is indicated as a necessary direction for improving the ecological state of agricultural landscapes. The biologization factors are named - crop rotation, intermediate crops, perennial grasses, the use of organic fertilizers (manure, composts, green manure, straw). A reserve for the cultivated plants protection against weeds and a possible alternative to chemical measures (the phytocenotic method) have been identified. The importance of an integrated approach in solving the environmental problems of soil science and agriculture is noted.

Characterization and Classification of Soils in Agroecosystems in a Moist Enclave in Northeastern Brazil

Modern times have required studies that take into account the main soil features, aligning the use of land with the protection of more sensitive environments. From this perspective, this study aimed to perform a morphological description and determine the physical and chemical attributes for soil classification in the community of Poção, located in the municipality of Martins/RN, by highlighting the more sensitive attributes in the differentiation of environments through multivariate analysis. Nine soil profiles were identified to perform the morphological description and collect samples for physical and chemical analyses. The study updates the soil classes found in the study area: Acrisols, Planosols, and Cambisols, with the relief being the main factor responsible for the difference between soil attributes. The influence of organic matter on the soil attributes highlights the importance of its maintenance. Aluminum and the clay fraction are responsible for the distinction of the Acrisol class, whereas silt, potassium sodium, total organic carbon, the electrical conductivity of the saturation extract, and the cation exchange capacity allow the differentiation of Fluvisols.

Soil potassium regulation by initial K level and acidification degree when subjected to liming: A meta-analysis and long-term field experiment

Potassium (K) is the most commonly neglected macronutrient in global change, especially in acidified areas. Lime is a typical management to eliminate soil acidification in agroecosystem soils; however, its impact on soil K dynamics remains inconsistent under different acidic environments. Here, we combine a meta-analysis based on 407 observations from 89 papers and a long-term experiment to investigate the effect and main driving factors of liming on soil K change. The meta-analysis showed that lime application significantly reduced topsoil exchangeable K (EK) content by an average of 4.8% globally. The decrease in topsoil EK content due to liming depended on various soil properties, crop types, fertilizer regimes, and experiment types. Boosted regression tree analysis showed that initial soil exchangeable K (IEK) and pH were the main factors affecting soil EK change under the lime application. The field experiment results further evidence that the decrease of soil EK after the lime application was mainly due to increased K uptake by the crop, and EK transformed to non-exchangeable K (NEK). The application of lime has a greater impact on reducing subsoil EK content at a higher IEK thresholds. Soil EK showed a significant negative relationship with exchangeable calcium (Ca) and a significant positive relationship with exchangeable aluminum (Al). Redundancy analysis revealed that K input (KI), IEK, lime, Ca, Al, pH, and exchangeable magnesium significantly affected the K in soil and crops. The partial least squares path model showed that lime application and IEK levels combined indirectly influence soil K (EK and NEK) by directly affecting soil Ca and Al, K uptake, and K balances. The findings highlight the importance of the lime effect on K management in globally adverse environmental agroecosystems and indicate the key role of initial soil EK levels and acidification degree for regulating crops to excavate the subsoil potassium when subjected to liming.

Intercropping efficiency of Pteris vittata with two legume plants: Impacts of soil arsenic concentrations

Intercropping of hyperaccumulators with crops has emerged as a promising method for remediating arsenic (As)-contaminated soil in agroecosystems. However, the response of intercropping hyperaccumulators with different types of legume plants to diverse gradients of As-contaminated soil remains poorly understood. In this study, we assessed the response of plant growth and accumulation of an As hyperaccumulator (Pteris vittata L.) intercropped with two legume plants to three gradients of As-contaminated soil. Results indicated that soil As concentration had a substantial effect on the As uptake by plants. P. vittata growing in slightly As-contaminated soil (80 mg kg−1) exhibited higher As accumulation (1.52–5.49 folds) than those in higher As-contaminated soil (117 and 148 mg kg−1), owing to the lower soil pH in high As-contaminated soil. Intercropping with Sesbania cannabina L. increased As accumulation in P. vittata by 19.3%− 53.9% but decreased in intercropping with Cassia tora L. This finding was attributed to S. cannabina providing more NO3--N to P. vittata to support its growth, and higher resistance to As. The decreased rhizosphere pH in the intercropping treatment also resulted in the increased As accumulation in P. vittata. Meanwhile, the As concentrations in the seeds of the two legume plants met the national food standards(<0.5 mg kg−1). Therefore, the intercropping P. vittata with S. cannabina is a highly effective intercropping system in slightly As-contaminated soil and provides a potent method for As phytoremediation.

DETERMINATION OF HEAVY METALS AND ENVIRONMENTAL HEALTH STATUS OF AGRO SOILS IN IKOT ABASI, NIGER DELTA, NIGERIA

Heavy metal pollution of soils is a worldwide concern due to the security of the agricultural products derivable from the heavy metal contaminated soils. The toxic metals enter the soil-agro ecosystem through natural processes derived from anthropogenic activities and geological weathered materials. This study is aimed at investigating the contamination status of soils from Ikot Abasi, Akwa Ibom State, being an area of intense agricultural and industrial activities. Twelve locations were demarcated for soil sampling, whereby top (0- 15 cm ) and sub-surface ( 15 – 30cm ) soil samples were obtained. The soil samples were air-dried and subjected to heavy metal determination (iron, Fe; cadmium, Cd; lead, Pb; zinc, Zn; copper, Cu; vanadium, V; nickel , Ni; chromium, Cr ; mercury, Hg ) by inductively coupled plasma– optical emission spectrometer (AGILENT 720 ICP-OES). The mean concentrations of heavy metals during the dry and wet seasons followed the order: Fe &gt; Zn &gt; Cu &gt; Cr &gt; Ni &gt; Pb &gt; V &gt; Cd &gt; Hg. The geo-accumulation index (Igeo) determined for all the metals studied were less than one , which falls in the Class zero , implying that the soils of the study area is practically unpolluted ; the potential ecological risk ( RI) were less than one , which was in the class of no potential ecological risk : modified degree of contamination ( mCd) calculated for both seasons falls in the category of less than 1.5 , which is nil to very low degree of contamination of the soils of the study area; pollution load index ( PLI), falls in the category of PLI of zero, which is excellence with no metal pollutant contamination. The public concern in respect of the security of the agricultural products derivable from the heavy metal contaminated soil, seem not to be applicable in the soils of Ikot Abasi, however, regular monitoring, is recommended to check possible future contamination.

Linkages of microbial community structure and root exudates: Evidence from microbial nitrogen limitation in soils of crop families

Rhizosphere microorganisms are critical for crop nutrient cycling and soil ecological functions in agroecosystem soils; however, there is limited information regarding the role of root exudates in determining soil microbial communities and functions in plant–soil systems, especially for microbial nutrient limitations. In the present study, rhizosphere soil samples were collected from the main food crop families, including maize, soybean, potato, and buckwheat, representing the cereals, Leguminosae, Solanaceae, and Polygonaceae families, in the northern Loess Plateau, China, to investigate soil microbial co–occurrences and assembly processes and the relationship between soil microbes and root exudates. The results showed that the crop families greatly regulated the soil microbial community composition and assembly, and all microorganisms of the four species were subjected to N limitation via the vector analysis. The topological properties of the soil microbial networks varied with the crop family, demonstrating that the ecological relationships of bacterial taxa are more complex than those of fungi. Stochastic processes were more important in stimulating assembly across the four crop families; the non–dominated process governed >60 % of the critical ecological turnover in community assembly, whereas dispersal limitation was the key factor influencing fungal community assembly. Furthermore, the metabolic profiles of root exudates in response to microbial N limitation varied by family. Microbial function and metabolic limitations were strongly associated with variations in root exudates, especially amino acids and organic acids, which were directly facilitated by crop families. Our results highlight the key roles of root exudates in stimulating microbial community structure and ecological functions from the perspective of microbial nutrient limitation and improve our understanding of plant–microbe interactions in agricultural ecosystems.