Non-cultivated Soils Research Articles

Using Pseudo-Color Maps and Machine Learning Methods to Estimate Long-Term Salinity of Soils

Soil salinity assessment methods based on remote sensing data are a common topic of scientific research. However, the developed methods, as a rule, estimate relatively small areas of the land surface at certain moments of the season, tied to the timing of ground surveys. Considerable variability of weather conditions and the state of the earth surface makes it difficult to assess the salinity level with the help of remote sensing data and to verify it within a year. At the same time, the assessment of salinity on the basis of multiyear data allows reducing the level of seasonal fluctuations to a considerable extent and revealing the statistically stable characteristics of cultivated areas of land surface. Such an approach allows, in our opinion, the processes of mapping the salinity of large areas of cultivated lands to be automated considerably. The authors propose an approach to assess the salinization of cultivated and non-cultivated soils of arid zones on the basis of long-term averaged values of vegetation indices and salinity indices. This approach allows revealing the consistent relationships between the characteristics of spectral indices and salinization parameters. Based on this approach, this paper presents a mapping method including the use of multiyear data and machine learning algorithms to classify soil salinity levels in one of the regions of South Kazakhstan. Verification of the method was carried out by comparing the obtained salinity assessment with the expert data and the results of laboratory tests of soil samples. The percentage of “gross” errors of the method, in other words, errors when the predicted salinity class differs by more than one position compared to the actual one, is 22–28% (accuracy is 0.78–0.72). The obtained results allow recommending the developed method for the assessment of long-term trends of secondary salinization of irrigated arable land in arid areas.

Imidacloprid Uptake and Accumulation in Lettuce Plant (Lactuca sativa L. var. longipolia) and Its Effects on Abundance of Microbial Communities in Cultivated and Non-Cultivated Arid Soil.

Systemic plant protection products, such as neonicotinoids (NIs), are capable of being translocated throughout a plant. Although NIs are less toxic to mammals, fish, and birds, their impact on microbial and non-target insects is of concern. This study investigates the uptake, translocation, and accumulation of the NI, imidacloprid (IMI), in romaine lettuce (Lactuca sativa L. var. longipolia). Exposing 15-day-old seedlings to "10 mg/L" of IMI, the effects on microbial communities in both cultivated (CS) and non-cultivated soil (NCS) were studied along with IMI translocation within plant tissues. The concentrations of IMI in soil varied temporally and between soil types after initial application, with a decrease from 2.0 and 7.7 mg/kg on the first day of sampling to 0.5 and 2.6 mg/kg on the final sampling day (day 35) for CS and NCS, respectively. The half-life of IMI soil was 10.7 and 72.5 days in CS and NCS, respectively, indicating that IMI degraded more quickly in CS, possibly due to smaller grain size, aeration, microbial degradation, and water flow. The accumulated concentrations of IMI in lettuce tissues ranged from 12.4 ± 0.2 and 18.7± 0.9 mg/kg in CS and NCS, respectively. The highest concentration of IMI was found in the shoots, followed by the roots, whereas the soil showed the lowest IMI residuals at the end of the trial. Soil bacteria and fungi were altered by the application of IMI, with a lower abundance index within the bacterial community, indicating a negative impact on the distribution of bacteria in the soil.

Protecting groundwater in intensive agricultural areas through irrigation with treated wastewater: focus on nitrate, salt, and Escherichia coli

A set of 4 soil column duplicates was irrigated with treated wastewater to study the possible leaching of nitrate, salt, and Escherichia coli to groundwater. The reclaimed water was a municipal secondary effluent, stored for 5 days to attenuate microbial contamination. It had nitrate concentration of 36.1±4.9 mgN/L, electrical conductivity of 1.6±0.1 mS/cm, and E. coli content between 36 and 918 MPN/100 mL (median value of 194 MPN/100 mL). Soil column tests were carried out over a period of 80 days, considering both the cultivation of a typical Mediterranean crop (pepper) and the edge case of non-cultivated soil. Nitrate and salt were up-taken by crops for around 90% and 50%, respectively, while they leached through non-cultivated soil according to linear relationships, with nitrate moving faster than salts. Due to its natural decay, E. coli never reached 66 cm depth. Crop irrigation with reclaimed water can be managed so as not to cause significant leaching of E. coli and nitrate, even though it may result in a small leaching of salt. Replacing groundwater with reclaimed water as an irrigation source should be considered as a possible action to protect aquifers, and especially those suffering from saline contamination, from the effects of overexploitation and overfertilization practices.

Response of the tomato rhizosphere bacterial community to water–oxygen coupling under micronanobubble oxygenated drip irrigation in mildly saline soil

AbstractThe deterioration of the soil water–air environment due to salinization can reduce soil bacterial activity and cause crop yield reduction. Micronanobubble oxygenated drip irrigation can significantly improve the nonsaline soil water–air environment and enhance bacterial activity, but its effect on salinized soil bacteria is unknown. In this study, we used a tomato cultivation experiment in mildly saline soil to evaluate the responses of the rhizosphere bacterial community to the soil microenvironment created by micronanobubble oxygenated drip irrigation. The results indicated that the soil environmental factors (including soil electrical conductivity, i.e., EC) (r = 0.46) and root length (r = −0.86) had important regulatory effects on bacterial community function, which had significant direct effects on tomato yield (r = 0.46). The moderate dissolved oxygen concentration treatment significantly reduced the EC by 63.22%–73.32% compared with CK (noncultivated soil treatment) and generally increased the root length; however, only the combination of a moderate dissolved oxygen concentration and excess irrigation (A15W1.2) significantly increased tomato yields by 190.90% compared with A0W0.8 (the combination of a low dissolved oxygen concentration and insufficient irrigation) because the irrigation water volume was the limiting condition affecting the benefits of the root length increase. The high dissolved oxygen concentration treatment significantly reduced the EC by 60.36%–92.31% and increased the bacterial community diversity by 4.08%–6.16% compared with CK; these aforementioned changes favored the increase in tomato yield. However, similar to the result of the moderate dissolved oxygen treatments, the tomato yields were significantly higher and among the highest of all treatments only when a high dissolved oxygen concentration was combined with sufficient irrigation or excess irrigation (A30W1 or A30W1.2) due to the limiting effect of the irrigation water volume. Therefore, accounting for the changes in EC, soil bacterial community, and tomato yields, A15W1.2, A30W1, and A30W1.2 are recommended for tomato production in mildly saline soils.

Passion fruit plants alter the soil microbial community with continuous cropping and improve plant disease resistance by recruiting beneficial microorganisms.

Passion fruit (Passiflora edulis) is widely grown in tropical and subtropical regions, showing high economic and ornamental value. Microorganisms are indicators for the stability and health of the soil ecosystem, which can affect the yield and quality of passion fruit under continuous cropping. High-throughput sequencing and interactive analysis were used to analyse the variation of microbial communities in the noncultivated soil (NCS), cultivated soil (CS), and the rhizosphere soil of purple passion fruit (Passiflora edulis f. edulis ×Passiflora edulis f. flavicarpa, RP) and yellow passion fruit (Passiflora edulis f. flavicarpa, RY). An average of 98,001 high-quality fungal internal transcribed spacer (ITS) sequences, mainly from Ascomycota, Basidiomycota, Mortierellomycota, Mucoromycota and Glomeromycota, as well as an average of 71,299 high-quality bacterial 16S rRNA sequences, mainly from Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes and Chloroflexi, were obtained per sample. It was found that the continuous cropping of passion fruit increased the richness but reduced the diversity of soil fungi, while it dramatically increased the richness and diversity of soil bacteria. In addition, during the continuous cropping, grafting different scions in the same rootstock contributed to the aggregation of differential rhizosphere microbial communities. Among fungal genera, Trichoderma showed higher abundance in RY than in RP and CS, while the opposite was observed in the pathogen Fusarium. Moreover, the co-occurrence network and potential function analyses also showed that the appearance of Trichoderma was related to Fusarium and its contribution to plant metabolism was significantly greater in RY than in RP and CS. In conclusion, the rhizosphere of yellow passion fruit may be beneficial for the enrichment of disease-resistant microbes, such as Trichoderma, which may be an important factor inducing stronger resistance to stem rot. It will help to form a potential strategy for overcoming the pathogen-mediated obstacles in passion fruit and improve its yield and quality.

Impact of Using Aldanfeeli Valley Water on the Pollution of Soils with Heavy Metals

The current study included collecting samples of water and soil from three main agricultural sites on Aldanfeeli Valley in Mosul city (North Iraq), where soil samples included two from each location, one for agricultural soil watered with untreated Valley water, and the second sample was from the adjacent uncultivated soils. A fourth site was chosen for the purpose of comparison at the end of Aldanfeeli Valley where the cultivated soil was watered with water of the Tigris River before the confluence of the River Valley. In addition to estimating the concentrations of heavy metals (Zn, Cd, Pb, Cu, Fe) in both water and soils, the present study aimed to identify some chemical and physical properties of the soils, namely: electrical conductivity, pH, organic matter, calcium carbonate, cations and anions, soil texture, and specific gravity. Despite the fact that the waters of Aldanfeeli Valley are poor for agricultural purposes in terms of salinity and total concentrations of both chloride and half of sulphate ions, the results showed that all soils do not suffer from the problems of salinity and alkalinity. Regarding the concentrations of heavy elements (Zn, Pb, Cd, Cu, Fe), their averages in the cultivated soils (23.86, 5.98, 75.14, 7.53 and 140.18) p.p.m. respectively, were higher than their counterparts in non-cultivated ones (18.70, 5.47, 36.82, 6.17 and 114.63) p.p.m. respectively. All soil samples especially the cultivated ones indicated higher concentrations than those of the irrigation waters (6.47, 4.87, 8.87, 2.27 and 7.07 p.p.m. respectively. The iron recorded at all sites higher means when compared to the rest elements. These were (140.18 and 114.63) p.p.m. in both the cultivated and noncultivated soils respectively. In both the second and the third sites of the cultivated soils; lead concentration averages of (114.25 and 91.06) μg g-1 respectively, have exceeded its standard limit (50 μg g-1); whereas, cadmium concentration averages in these two sites were (8.23 and 6.88) μg g-1 respectively, have exceeded its critical limit (5 μg g-1).
 

Assessment of soil redistribution in a typical karst catchment using 137Cs

An effective assessment of soil erosion and redistribution is a prerequisite for soil erosion control and is critical to achieving sustainable development goals. The most typical landscape in the karst region of Southwest China is found in the peak-cluster depression area, but little attention has been given to the soil redistribution here. A typical karst peak-cluster depression catchment water area in Southwest China was selected, and 137Cs technology was used to evaluate the soil redistribution rate and soil erosion process along a total transect (hillslope, depression and sinkhole) in the catchment. The results showed that the distribution of 137Cs had a high spatial variability on the total transect of the catchment (CV = 60.04%), the middle slope was the most severely eroded (highest erosion rate of 13.49 t ha−1 yr−1), and the area between the bottom slope and the depression was the primary sedimentary area on the surface in the catchment. The distribution of soil properties on the hillslope was affected by the process of soil redistribution. According to the distribution of the 137Cs soil profile, the soil profile of the hillslope was uniform, and signs of historical tillage activities were evident; the historical tillage activities of depressions were in the range of 0–20 cm depth, while the 137Cs in the sinkhole was mostly distributed in the shallow layers and decreased exponentially with depth, reflecting the depositional characteristics of noncultivated soil. In addition, this study found evidence of underground soil loss in sinkholes since the 1960s; the shallow sediment of these sinkholes mainly came from depressions, with an average deposition rate of 11.77 t ha−1 yr−1. Human disturbance and land-use change controlled recent changes in soil redistribution. The soil erosion rate of the hillslopes in catchments was extremely low (average erosion rate of 1.92 t ha−1 yr−1). The rocky desertification of hillslopes occurred before 1960; it was not a short-term contemporary process that occurred only during recent decades. This study showed that underground soil loss mainly occurred through sinkholes for a short period of time (100 years). These research results are of great significance for understanding the evolution of rocky desertification and the process of soil erosion.

EFFECT OF RICE PLANT ROOT TTC-REDUCING ACTIVITY ON THE CHEMICAL FORM OF IODINE IN CULTIVATED SOIL SOLUTIONS

Abstract This study aimed to evaluate the effect of rice plant root activity on the chemical form of stable iodine (I) in a cultivated soil solution. Concentrations of I−, IO3− and organic-I were analyzed 4 days after exposure I− or IO3− solutions to each of the cultivated soil surface. When exposed to I−, its concentration in the cultivated soil was approximately the same as that in the non-planted soil. When the rhizosphere was exposed to IO3−, the I− concentration in the soil increased under cultivation conditions. IO3− remained undetected in the soil solution. The organic-I concentration in the cultivated soil solution was higher than that in the non-cultivated soil. Concentrations of organic-I increased under IO3− addition compared to I− addition. A weak positive correlation was observed between the TTC-reducing activity of plant roots, and the total and organic-I concentrations in the soil solution. It was suggested that the amount of organic I formed from IO3− was determined by the reducing activity of the roots.

Soil Contamination by Phthalate Esters in Cultivated and Non-Cultivated Soils in North African Arid Regions: A Tunisian Case Study

Over the last decades, several studies showed that phthalic acid esters (PAEs) were ubiquitous environmental contaminants and became a major threat to human health. This study provided the first case study about the concentration and the potential sources of soil’s PAEs, both in Tunisia and North Africa. Soil samples were collected from four cultivated (CS) and two adjacent native soils (NS) at 0-10 cm and 10-30 cm layers in southeastern Tunisia. The PAEs concentrations were analyzed using a gas chromatography-mass spectrometry (GC-MS) system. Results showed that the total concentration of PAEs ranged from 2.40 to 11.05%. Higher values were detected in NS in the 0-10 cm layer contrary to CS which showed higher PAEs concentration in 10-30 cm depth. The di-n-butyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) were the most abundant PAEs. In the 0-10 cm layer, PAEs concentration was highly related to the age of the plastic film in CS. We observed a positive association between PAEs concentration and conductivity (EC) values. The PAEs concentrations were affected by the presence of soil organic matter (SOM) in CS. This decrease of PAEs in CS compared to the NS may be related to the microbial decomposition activity stimulated by the presence of fresh organic residues and fertilizers. These results showed that CS and adjacent NS in the studied regions were contaminated by PAEs which is probably a result of agricultural activities. More investigations on PAEs concentrations in various soil managements are needed to confirm these results.

Effects of Organic Agriculture in Structure and Organic Carbon Adsorption at Colloidal Scale in Marginal Olive Groves, Characterized by the Extended DLVO Model

Relationship between macroscopic and microscopic behavior of soils is a difficult issue, especially when dealing with complex properties such as structure or carbon sequestration, but it is necessary for a suitable understanding of the agricultural soil quality. In this work, we used the extended-DLVO theory to compute total energy of interaction between particles (kT), of three soils over granodiorites. This parameter allows predicting the tendency to aggregate formation at the colloidal scale, being the basis of soil structure. Furthermore, we characterized the mechanism and adsorption capacity of humic molecules on mineral surfaces, and its influence in the interaction energy, by means of the adsorption isotherms. The aim was to compare first the effects of organic farming on conventionally managed soils and, second, to compare these with a non-cultivated forest soil under Mediterranean climate. When total energies are negative (particle attraction), or positive (particle repulsion) but near 0 kT (<100 kT), then particle flocculation occurs and the structure at colloidal scale can be developed. Total energy was less in the forest sample and greater in the soil of conventional groves, with intermediate values in organic farming soil. This indicates a tendency toward particle flocculation and more stability of the structure at colloidal scale in less disturbed soils, agreeing with other soil physical properties such as the total porosity (50, 41 and 37% in forest, organic and conventional plots, respectively) or the aggregate stability index (0.94, 0.73 and 0.66, respectively), which followed the same trend. Of the three components of the total energy of interaction, the acid-base force was a key factor. This component, related with the electron-donor component of surface free energy, γ−, yielded a strong attractive force (−150 kT at 3 nm) when calcium solutions were analyzed for the forest soil. This indicates a clear hydrophobic character of this sample. Because the mineralogical composition of the samples is quite similar, hydrophobicity should be attributed to the organic carbon content of the forest soil, which is much higher than that of the cultivated ones (12.03 vs. 1.44% and 0.88% in organic and conventional farms, respectively), proving to be an essential element for the development of the structure at the colloidal level.

Short-Term Effects of Reclamation of Aquaculture Ponds to Paddy Fields on Soil Chemical Properties and Bacterial Communities in Eastern China Coastal Zone

Large areas of tidal flats were previously developed into aquaculture ponds and were recently encouraged to be converted into paddy fields to fulfill food and economic needs in China. However, the influences of short-term rice cultivation at the reclaimed aquaculture ponds on soil chemical properties and bacterial communities are poorly understood. To address this issue, we collected mineral soil samples at 0–20 and 20–40 cm depths from non-cultivated soils and paddy fields after being reclaimed from aquaculture ponds in Nantong, China, and identified soil bacterial communities using high-throughput sequencing. The results suggested that rice cultivation significantly increased the accumulation of total soil carbon (TC) and dissolved organic carbon (WSOC). The pH, ammonium (NH4+), nitrate (NO3−) and available phosphorus (AP) varied with the reclamation duration but did not show a unanimous tendency. Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi and Planctomycetes dominated the bacterial community in both non-cultivated and cultivated soils after reclamation regardless of cultivation ages and soil depth. The variations in the diversity and composition of the soil microbial community were mainly associated with electrical conductivity (EC), WSOC, TC, NH4+ and NO3− in non-cultivated and cultivated lands. Here, we found that short-term rice cultivation at the reclaimed aquaculture ponds strongly influenced soil bacterial communities and chemical properties, especially in the 0–20 cm depth, in the coastal regions.

Composition of Zingiber officinale Roscoe (Ginger), Soil Properties and Soil Enzyme Activities Grown in Different Concentration of Mineral Fertilizers

Ginger is rich in different chemical compounds such as phenolic compounds, terpenes, polysaccharides, lipids, organic acids, minerals, and vitamins. The present study investigated the effect of mineral fertilizers on the content of mineral elements in the rhizomes of Zingiber officinale Roscoe, soil enzymes activity, and soil properties in Surkhandarya Region, Uzbekistan. To the best of our knowledge, the present study is the first in Uzbekistan to investigate the mineral elements of ginger rhizome inhabiting Termez district, Surkhandarya region. A Field experiment was conducted at the Surkhandarya experimental station research Institute. Four treatments have been studied (Control with no fertilizers (T-1), N75P50K50 kg/ha (T-2), N125P100K100 kg/ha (T-3) and N100P75K75 + B3Zn6Fe6 kg/ha (T-4)). Results showed that T-4 treatment significantly increased ginger rhizome K, Ca, P, Mg, Fe, Na, Mn, Zn, Si, Li, and V content as compared to all other treatments and control. T-3 treatment significantly increased Mo, Ga, and Ag content in comparison to other treatments. Soil enzymes showed a significant increase for all treatments against control, while T-4 treatment has recorded the highest enzyme activity in comparison to all other treatments in urease, invertase, and catalase content. Soil chemical properties have significantly changed for all treatments against the non-cultivated soil and the zero fertilizers plantation with variation among different treatments. Results showed that ginger root is rich in minerals and can be used as a great potential for nutritional supplements and soil enrichment. This study suggest that combination of macro-microelements have the potential to increase the content of mineral elements in the rhizomes of ginger in field conditions.

Impact of human disturbances on soil cyanobacteria diversity and distribution in suburban arid area of Marrakesh, Morocco

BackgroundCyanobacteria are among the first photoautotrophic component of soil microorganism communities which play a key ecological role in nutrient cycles and soil productivity. However, the sustainability of these soil biodiversity ecosystem services is increasingly compromised, especially in urban and peri-urban areas where soils are heavily exploited and used for a wide range of human activities. The aim of this study is to assess the impact of different types of human disturbances on cyanobacteria diversity and distribution in suburban soils of Marrakesh. Soil and cyanobacteria sampling were carried out during two campaigns at six sites located along an anthropogenic gradient from the least urbanized suburbs of Marrakesh to the highly anthropized suburban area. In the laboratory, soil physicochemical characteristics were measured. The morphological identification of cyanobacteria species was based both on microscopic observation and on soil cultures in solid and liquid Z8 media.ResultsThe results showed a total of 25 cyanobacteria taxa belonging to ten genera, four families, and two orders (Oscillatoriales 88% and Chroococcales 12% of taxa). Among the taxa identified, seven strains were isolated in soil culture in nutrient media and purified in monoalgal culture. The highest cyanobacterial diversity was recorded in irrigated soil with treated wastewater compared to the non-cultivated control soil. In Principal Component and Cluster Analysis, suburban soils were subdivided into three groups depending on the chemical properties and cyanobacteria composition. Cyanobacteria diversity was significantly associated with the soil moisture, total organic carbon (TOC), PO4-P, NO3-N, and NH4-N contents.ConclusionsWhile diversity and microalgal biomass were significantly lower in the soils affected by municipal and mining solid wastes, the input of organic matter and nutrients from treated wastewater appears to be beneficial for the increasing of the biodiversity of soil cyanobacteria. This survey provides a first inventory of the soil cyanobacterial communities and shows their spatial variability and high sensitivity to the land-use practices and anthropogenic disturbances on urban soil in Moroccan drylands.

Evolutionary biology and interaction among the anastomosis groups of Rhizoctonia spp.

Rhizoctonia solani Kuhn and other Rhizoctonia spp. are the plant pathogenic fungi widespread in the world and in both cultivated and noncultivated soils. Rhizoctonia spp. are readily isolated from diseased plants and soils, which differ in their pathogenicity, cultural, morphological and physiological characteristics. Identification of species and intraspecific groups (ISGs) is sometimes very difficult, due to the absence of the authentic cultures, which hinders mycological and pathological studies. The genus Rhizoctonia can be identified using various techniques such as, sequence analysis of ITS regions, DNA fingerprinting and the rDNA coding sequence. The introduction of the concept of anastomosis groups (AGs) or intraspecific groups has also aided species and subspecies identification. There are 13 different anastomosis groups exists in Rhizoctonia solani of which AG 1-4 were strong pathogenic on many plants and AG 6-10 were orchid mycorrhizae. Analysis of restriction fragment length polymorphisms (RFLPs) and the sequences within ribosomal RNA genes (rDNA) among different anastomosis groups of R. solani isolates exhibited DNA base sequence homology and diverging evolutionary affinities for hyphal anastomosis. More recently, ribosomal DNA (rDNA) sequences have been used to study the genetic relationships between AG of R. solani. The ecology and epidemiology of each ISG of R. solani must be investigated in order to gain a better understanding of this important group of fungi.

<p class="Body"><strong>Gamasina mite communities (Acari: Mesostigmata) in grain production systems of the southwestern Brazilian Amazon</strong></p>

Emphasis has been given in the Brazilian state of Mato Grosso to the implementation of more sustainable production practices, including what has been termed agrosilvopastoral production system (ASPS), which involves the integration of different types of land use in a same area along time, seeking increased ecological stability. The Gamasina mite group (order Mesostigmata) is usually diverse and abundant in non-cultivated soils, where they can prey on arthropods and nematodes; some are commercialized for biological pest control. The objective of this study was to evaluate the diversity and abundance of edaphic Gamasina in plots of grain production managed under conventional (alternating cultivation) system and under ASPS, both with the adoption of no-tillage cultivation, in the municipality of Sinop, Mato Grosso state. In samples of soil and litter taken biweekly from August 2015 to May 2016, 762 Gamasina representing 32 species of 21 genera and nine families were collected. Considering both systems together, the dominant Gamasina were quite different from those of other parts of Brazil. Calculated ecological indexes showed no major differences between the two systems, possibly because of the relatively short time since the implementation of ASPS. In both systems, Rhodacaridae was one of the dominant families (37.5% of the Gamasina), followed by Macrochelidae (20.9%) and Laelapidae (18.8%). The most abundant species were Multidentirhodacarus squamosus Karg (Rhodacaridae), a new species of Holostaspella (Macrochelidae) and Cosmolaelaps barbatus Moreira, Klompen and Moraes (Laelapidae). Future studies are warranted, allowing more time for the adoption of ASPS to produce possible ecological changes.

Agriculture increases the bioavailability of silicon, a beneficial element for crop, in temperate soils

Crops may take benefits from silicon (Si) uptake in soil. Plant available Si (PAS) can be affected by natural weathering processes or by anthropogenic forces such as agriculture. The soil parameters that control the pool of PAS are still poorly documented, particularly in temperate climates. In this study, we documented PAS in France, based on statistical analysis of Si extracted by CaCl2 (SiCaCl2) and topsoil characteristics from an extensive dataset. We showed that cultivation increased SiCaCl2 for soils developed on sediments, that cover 73% of France. This increase is due to liming for non-carbonated soils on sediments that are slightly acidic to acidic when non-cultivated. The analysis performed on non-cultivated soils confirmed that SiCaCl2 increased with the < 2 µm fraction and pH but only for soils with a < 2 µm fraction ranging from 50 to 325 g kg−1. This increase may be explained by the < 2 µm fraction mineralogy, i.e. nature of the clay minerals and iron oxide content. Finally, we suggest that 4% of French soils used for wheat cultivation could be deficient in SiCaCl2.

Inoculation of arbuscular mycorrhizal fungi increases lettuce yield without altering natural soil communities

ABSTRACT Agricultural practices may lead to a decline in the presence and abundance of natural arbuscular mycorrhizal fungi (AMF). AMF inoculation can be an environmental friendly alternative or complement to chemical fertilizers in agriculture. Initially, through ribosomal DNA internal transcribed spacer (ITS) metabarcoding, we characterized the composition of fungal communities from three organic orchard soils, as well as from three adjacent non-cultivated soils. Organic orchard management had a negative impact on AMF community, leading to reduced alpha diversity and relative abundance of AMF taxa, compared to non-cultivated soil (e.g. 10 vs. 11 in richness and 2.1 vs. 2.6 in Shannon index). Using trap plants, we multiplied the AMF communities from the abovementioned orchard and non-cultivated soils. Afterward, a microcosm experiment was carried out to study the effect of inoculation with these AMF communities on (i) lettuce (Lactuca sativa L.) yield and nutritional quality (two consecutive crops), and (ii) root fungal communities. During the second crop cycle, AMF inoculants led to higher lettuce yields (by an average of 186%, irrespective of the origin of the inoculum), but resulted in no substantial modification of lettuce nutritional quality. Moreover, AMF inoculants did not exert a significant effect on fungal (including AMF) or AMF communities.

Carbon sequestration in aggregates from native and cultivated soils as affected by soil stoichiometry

Quantitative influence and underlying mechanisms of nutrient stoichiometry on mineralization of native Soil organic C (SOC) and straw C in different aggregate classes from cultivated and non-cultivated soils are still unclear. Soil samples (Mollisols) from a native woodlot and a farmland converted from woodlot were sieved into three aggregate classes (mega-aggregates (6.3-2 mm), macro-aggregates (2-0.25 mm), and micro-aggregates (< 0.25 mm)) and incubated (180 days) under different nutrient rates (nil, low, and high supplies of N and P) with or without 13C-enriched straw amendment. Significantly higher percentage of native SOC was mineralized from mega- and macro-aggregates (65.8-82.2%) compared with micro-aggregates (48.3-52.0%) in woodlot soil. Nutrient addition significantly increased aggregate-associated C in both soils with straw, and the increase was greater in farmland than in woodlot soil and in large-sized aggregates than in micro-aggregates. These results suggested that large aggregates serve as a C reservoir of labile C, while micro-aggregates that contained C was not easily mineralized even with abundant nutrients. Differences of C mineralization among aggregate size classes were significant in woodlot soil but not in farmland soil. Depletion of SOC was greater with increasing nutrient addition rates in farmland aggregates without straw, while the depletion in woodlot aggregates showed no difference among nutrient treatments, suggesting that microbial activity was nutrient-limited in farmland aggregates. The results improved our knowledge on SOC mineralization in response to residue-nutrient management in different aggregate classes from cultivated and non-cultivated soils, which have important implications for strategies to improve soil fertility or mitigate climate change via increased SOC.

FACULTATIVE EXTREMOPHILIC BACTERIA IN BRAZILIAN AGRICULTURAL SOILS

The objective was to study different groups of bacteria that can adapt to extreme conditions of temperature, pH and salinity, as well as to identify bacterial strains from cultivated (CS) and non-cultivated (US) soil samples collected in the city of Brazlândia, Brazil. 38 strains were collected and submitted to growth tests at 45, 55, 65 and 75oC, pH of 3, 4, 5, 9, 10 and 11 and salinity of 5, 10 and 15% of NaCl. Eleven strains were selected based on their biochemical characterization and identified based on their 16S rDNA sequences. Four groups of bacteria in the CS and US samples were identified and able to grow under the most extreme conditions. Eleven bacterial strains were considered Gram-negative and separated into three groups based on their positive reactions to biochemical characteristics. Based on the glucose oxidation / fermentation test, seven strains belonged to Enterobacter sp. In addition, two strains of Pseudomonas sp. and two strains, which were not economically related to Giesbergeria sp. and Chryseobacterium sp. They were found. This study showed that some bacteria found in agricultural soils in Brazil have the potential to be used to control phytopathogens under extreme environmental conditions.

Microwave assisted biocidal extraction is an alternative method to measure microbial biomass of carbon from cultivated and non-cultivated soils.

Developing simple and cost-effective methods for soil microbial biomass carbon (MBC) measurement eases routine laboratory analysis and enables large numbers of soil samples to be measured in a relatively short period of time. Thus, the objective of this study was to develop a microwave-assisted biocidal-extraction (MWE) method which does not employ CHCl3 as biocide and K2SO4 as C-extractor, to estimate MBC. First, the microorganisms of soil samples are killed using microwave (MW) irradiation at energy level of 800 J g-1 soil as biocide followed by microwave irradiation extraction (MWE) at 562 W (120 J g-1 soil for 1 min), using deionized water as solvent. Microbial biomass of carbon from two contrasting soils microwaved with 80, 100, and 140 J g-1 soil did not differ from those obtained by using the chloroform fumigation-extraction (CFE) method with 0.5 mol L-1 K2SO4 as extractant. To evaluate the robustness of the MWE method, twenty-six soil samples, from cultivated and non-cultivated areas, with clay contents from 70-690 g kg-1, organic carbon from 5.52 to 50.82 g C kg-1 and pH values from 3.9 to 6.8 were analyzed for MBC using MWE and CFE methods. There was a linear regression (MW = - 17.87 + 0.92*K2SO4; R2 = 0.705; p < 0.001) between MWE and CFE. The biocidal microwave-assisted extraction method using 120 J g-1 soil for 1 min is a cleaner method for evaluating MBC, because it does not require chloroform, potassium sulfate salt and takes a shorter time to extract a set of soil samples.