Unamended Ones Research Articles

Remediation of Agricultural Soils with Long-Term Contamination of Arsenic and Copper in Two Chilean Mediterranean Areas

Soil amendments may decrease trace element accumulation in vegetables, improving food security and allowing the recovery of contaminated farmlands. Despite some promising results in the laboratory, validation of soil amendments in field conditions are scarce, especially in aerobic soils. Here, we assessed the effect of different potential soil amendments on arsenic (As) accumulation in lettuces. Then, we compared them in terms of food security and the associated investment (efficacy and efficiency, respectively). We also hypothesized that the soil amendments do not lead to side effects, such as yield decrease, phytotoxicity of Cu, or undesired changes in soil properties. Thereby, we assessed lettuces grown on untreated contaminated soils (C+), treated contaminated soils, and untreated uncontaminated soils (C−) in two contrasting soil types (sandy and loamy soils). The treated contaminated soils consisted of multiple soil amendments. Soil amendments were: diammonium phosphate (DP), iron sulfate (IS), ferrous phosphate (FP), calcium peroxide (CP), and organic matter (OM). We found that phosphate amendments (DP and FP) reduced the As in edible tissues of lettuce in both areas, while CP only reduced As accumulation in the sandy soils area. The As intake through lettuces grown on these amended soils was about 30% lower than on the unamended ones. Cu concentrations in lettuces above 25 mg kg−1 grown in contaminated soils without reducing growth were found, a result that differed from non-field studies.

Effect of sodium bisulfate amendments on bacterial populations in broiler litter

The accumulation of ammonia in poultry houses is of concern to bird and human health. Acidification of the litter by application of acidifying amendments such as sodium bisulfate (SBS) retains ammonia generated by microbial degradation of uric acid as harmless ammonium in the litter. Although some studies on the effects of litter amendments on specific bacteria and groups of bacteria have been carried out previously, wide gaps in knowledge remain. In the present study, 2 types of samples were prepared and either left unamended or amended with 2.5 or 10% SBS. One set of samples consisted of a 1:1 mixture of built-up litter and fresh poultry manure (L/M); the other of fresh wood shavings and fresh poultry manure (S/M). The samples were kept in the laboratory at room temperature for 35 d. The pH of unamended mixtures increased to 7.3 and 6.9 for L/M and S/M, respectively. A pH of 6.7 and 3.9 on day 35 was observed for L/M and SM with 2.5% SBS, respectively. The corresponding values for LM and SM amended with 10% SBS were 3.5 and 2.5, respectively. Plating data indicated that coliforms became less numerous in the unamended samples than the SBS-amended samples. This difference was also seen in data obtained by high-throughput sequencing of 16S rDNA. The sequencing data also indicated that sequences from the genus Oceanisphaera accounted for as much as 80% of the sequences from L/M and about 40% of those from S/M samples early on. Sequences from members of the order Clostridiales were enriched in L/M and S/M amended with 10% SBS as were sequences from the genus Turicibacter. Weisella species sequences were more prevalent in SBS-amended samples than in unamended ones. Sequences from the genus Corynebacterium, Brachybacterium, and Arthrobacter were more common in L/M samples than in S/M samples regardless of the SBS content. The data indicate that litter amendments affect some bacteria populations and not others. Further studies are required to determine if the observed population changes such as increased survival of coliforms warrant actions to improve the microbial quality of litter to be reused.

Mid‐term effects on ecosystem services of quarry restoration with Technosols under Mediterranean conditions: 10‐year impacts on soil organic carbon and vegetation development

The use of Technosols for the restoration of limestone quarries overcomes the usual “in situ” scarcity of soil and/or its poor quality. The use of mine spoils, improved with mineral and/or organic amendments, could be an efficient and environmentally friendly option. Properly treated sewage sludge from urban wastewater treatment plants could be a suitable organic amendment and fertilizer (rich in N and P) whenever its pollutant burden is low (heavy metals and/or organic pollutants). Its appropriate use could improve essential soil physical and chemical properties and, therefore, promote key ecosystem services of restored areas, such as biomass production and carbon sequestration, as well as biodiversity and landscape recovery. However, the mid‐term impacts of these restoration practices on soil functioning and their services have rarely been reported in the available literature. In this study we assess the mid‐term effects (10 years) of the use of sewage sludge as a Technosol amendment on soil organic carbon (SOC), nutrient status, and plant development in several restored quarries. Soils restored using sewage sludge showed a threefold increase in SOC compared to the corresponding unamended ones, despite the moderate sludge dosage applied (below 50 tonnes/ha). Plant cover was also higher in amended soils, and recruitment was not affected by sludge amendment at these doses. This study demonstrates that, used at an appropriate rate, sewage sludge is a good alternative for the valorization of mine spoils in quarry restoration, improving some important regulatory ecosystem services such as carbon sequestration, without compromising woody plant encroachment.

Assessment of 14C-prosulfocarb dissipation mechanism in soil after amendment and its impact on the microbial community

Adding organic amendments to soil could modify the bioavailability of herbicides and lead to changes in the microbial community’s activity and structure. The objective here was to study the dissipation and total mass balance of 14C-labeled prosulfocarb applied at two rates (4 and 10 mg kg-1) in unamended and green compost (GC)-amended soil. Soil dehydrogenase activity (DHA) and phospholipid fatty acid (PLFA) profile analysis were determined to evaluate the effect of herbicide residues on microbial community's activity and structure over the dissipation period. The dissipation rate of prosulfocarb decreased after soil amendment due to higher herbicide adsorption by the amended soil. The 50% dissipation time (DT50) increased 1.7 times in the unamended soil when the concentration of prosulfocarb increased 2.5 times. The mass balance results indicate that the sum of water and organic extractable fractions represented the highest amounts up to the dissipation of 50% 14C-prosulfocarb. The 14C-herbicide was then mainly mineralized (up to 11%-31%) or formed non-extractable residues (up to 35%-44%). The amount of 14C-prosulfocarb residues extracted with methanol was slightly higher in amended soils than in unamended ones. 14C-prosulfocarb mineralization was higher in unamended soils than in amended ones. The formation of non-extractable residues was continuous, and increased over time. Soil DHA decreased in the unamended soil and was maintained in the GC-amended soil at the end of the assay. The microbial structure was barely disturbed over the prosulfocarb degradation process, although it was clearly influenced by the application of GC. The results obtained reveal the influence organic amendment has on herbicide bioavailability to decrease its biodegradation and buffer its impact on the soil microbial structure.

Rehabilitation of a highly saline-sodic soil using a rubble barrier and organic amendments

The application of biochar and compost is a promising alternative to recover salt-degraded soils. However, in areas where the main source of salinity comes from the groundwater, it is also necessary to restrict the capillary rise of salts by means of a barrier. In this study, we show results of a field experiment, in which we tested the effect of a rubble barrier and the addition of biochar and compost on the establishment of a salt-tolerant grass (Distichlis spicata) in a highly saline-sodic soil. Our results showed that the capillary barrier: i) diminished the electrical conductivity and the CO2 fluxes by about one third to one half the values without barrier for both variables, ii) decreased the topsoil moisture (without barrier ca. 25–35%; barrier-zone ca. 15–25%), and iii) promoted the plant growth. Organic amendments did not show any effect. However, high-dose treatments had lower moisture content than the unamended ones (ca. 3–6% less water). Arrival of new plant species occurred preferably in the barrier-zone. We conclude that the barrier is an effective tool to decrease the soil salinity, but irrigation is needed to overcome smaller soil moisture during the dry season. Pyrochar was the most recommendable amendment to be used. However, biochar and compost doses were insufficient for the rehabilitation of this highly saline-sodic soil. The natural emergence of plant species (Suaeda torreyana, Kochia scoparia and Sonchus oleraceus) can improve the rehabilitation activities in an effective and inexpensive way. Urban residues can effectively be used to establish a plant cover in saline-sodic soils.

Simultaneous application of two herbicides and green compost in a field experiment: Implications on soil microbial community

The simultaneous use of herbicides and organic amendments is a common agricultural practice that may modify the behavior of the herbicides themselves and affect the microbial community in soils. There is little information about the changes in the soil microbial community by this agricultural practice under real field conditions. The aim of this work was to assess the effects on the soil microbial community (abundance, activity, and structure) of the following two herbicides triasulfuron (TSF) and prosulfocarb (PSC) applied as individual or combined formulations in an unamended soil (Soil) and in a soil amended with green compost (Soil + GC) at field scale. Herbicide dissipation, soil biomass, respiration, dehydrogenase activity (DHA), and the profile of phospholipid fatty acids (PLFA) were monitored for 100 days. Triasulfuron recorded a slower dissipation rate than PSC. The dissipation rate of TSF decreased in the GC-amended soils compared to the unamended ones. Furthermore, the Soil + GC recorded a higher soil biomass and respiration than the unamended ones. In the GC-amended soil, biomass values decreased with individual or combined TSF application compared to the Soil + GC control, while biomass values in the unamended soil increased with the application of combined herbicides after 100 days. In general, soil respiration values decreased with the application of herbicides in both the unamended and GC-amended soils. This negative effect was higher for the combined TSF + PSC application. DHA values decreased over time in the unamended soils treated with herbicides, but this decrease was not observed in the GC-amended soil. The microbial structure clearly changed throughout the experiment under the different conditions assayed. After 100 days of simultaneous TSF + PSC application, there was a significant increase in Gram-positive bacteria and a significant decrease in Gram-negative bacteria and Actinobacteria in the unamended soil. The GC-amended soil minimized the effects of TSF + PSC, and only the relative abundance of Actinobacteria increased at 100 days. The microbial community in the unamended and GC-amended soils behaved differently with herbicide application; however, the combined application of TSF and PSC altered soil microbial activity and structure compared to their individual application or non-application. The application of GC to soil buffered the impact of TSF and PSC on microbial biomass and activity, and reduced the shift in the soil microbial structure.

Application of mesotrione at different doses in an amended soil: Dissipation and effect on the soil microbial biomass and activity

The aim of this work was to estimate the dissipation of mesotrione applied at three doses (2, 10 and 50mgkg−1 dw) in an unamended agricultural soil, and this same soil amended with two organic residues (green compost (C) and sewage sludge (SS)). The effects of herbicide and organic residue on the abundance and activity of soil microbial communities were also assessed by determining soil microbial parameters such as biomass, dehydrogenase activity (DHA), and respiration. Lower dissipation rates were observed for a higher herbicide dose. The highest half-life (DT50) values were observed in the SS-amended soil for the three herbicide doses applied. Biomass values increased in the amended soils compared to the unamended one in all the cases studied, and increased over the incubation period in the SS-amended soil. DHA mean values significantly decreased in the SS-amended soil, and increased in the C-amended soil compared to the unamended ones, under all conditions. At time 0days, respiration values were significantly higher in SS-amended soils (untreated and treated with mesotrione) than in the unamended and C-amended soils. The effect of mesotrione on soil biomass, DHA and respiration was different depending on incubation time and soil amendment and herbicide dose applied. The results support the need to consider the possible non-target effects of pesticides and organic amendments simultaneously applied on soil microbial communities to prevent negative impacts on soil quality.

Long‐term effect of biochar on the stabilization of recent carbon: soils with historical inputs of charcoal

AbstractThis study was set up to identify the long‐term effect of biochar on soil C sequestration of recent carbon inputs. Arable fields (n = 5) were found in Belgium with charcoal‐enriched black spots (>50 m2; n = 14) dating >150 years ago from historical charcoal production mound kilns. Topsoils from these ‘black spots’ had a higher organic C concentration [3.6 ± 0.9% organic carbon (OC)] than adjacent soils outside these black spots (2.1 ± 0.2% OC). The soils had been cropped with maize for at least 12 years which provided a continuous input of C with a C isotope signature (δ13C) −13.1, distinct from the δ13C of soil organic carbon (−27.4 ‰) and charcoal (−25.7 ‰) collected in the surrounding area. The isotope signatures in the soil revealed that maize‐derived C concentration was significantly higher in charcoal‐amended samples (‘black spots’) than in adjacent unamended ones (0.44% vs. 0.31%; P = 0.02). Topsoils were subsequently collected as a gradient across two ‘black spots’ along with corresponding adjacent soils outside these black spots and soil respiration, and physical soil fractionation was conducted. Total soil respiration (130 days) was unaffected by charcoal, but the maize‐derived C respiration per unit maize‐derived OC in soil significantly decreased about half (P < 0.02) with increasing charcoal‐derived C in soil. Maize‐derived C was proportionally present more in protected soil aggregates in the presence of charcoal. The lower specific mineralization and increased C sequestration of recent C with charcoal are attributed to a combination of physical protection, C saturation of microbial communities and, potentially, slightly higher annual primary production. Overall, this study provides evidence of the capacity of biochar to enhance C sequestration in soils through reduced C turnover on the long term.

Boosting the electrocatalytic activity of Desulfovibrio paquesii biocathodes with magnetite nanoparticles

The production of reduced value-added chemicals and fuels using microorganisms as cheap cathodic electrocatalysts is recently attracting considerable attention. A robust and sustainable production is, however, still greatly hampered by a poor understanding of electron transfer mechanisms to microorganisms and the lack of strategies to improve and manipulate thereof. Here, we investigated the use of electrically-conductive magnetite (Fe3O4) nanoparticles to improve the electrocatalytic activity of a H2-producing Desulfovibrio paquesii biocathode. Microbial biocathodes supplemented with a suspension of nanoparticles displayed increased H2 production rates and enhanced stability compared to unamended ones. Cyclic voltammetry confirmed that Faradaic currents involved in microbially-catalyzed H2 evolution were enhanced by the addition of the nanoparticles. Possibly, nanoparticles improve the extracellular electron path to the microorganisms by creating composite networks comprising of mineral particles and microbial cells.

Effects of Wood Amendments on the Degradation of Terbuthylazine and on Soil Microbial Community Activity in a Clay Loam Soil

The herbicide terbuthylazine is widely used within the EU; however, its frequent detection in surface and groundwater, together with its intrinsic toxicological properties, may pose a risk both for human and environmental health. Organic amendments have recently been proposed as a possible herbicide sorbent in soil, in order to limit herbicide movement from soil to water. The environmental fate of terbuthylazine depends not only in its mobility but also in its persistence. The latter is directly dependent on microbial degradation. For this reason, the effects of pine and oak residues on terbuthylazine soil microbial community functioning and on the potential of this community for terbuthylazine degradation were studied. For this purpose, degradation kinetics, soil dehydrogenase activity and the number of live bacteria were assessed in a clay loam soil treated with terbuthylazine and either amended with pine or oak wood or unamended (sterilised and non-sterilised). At day 65, 85 % of the herbicide applied still persisted in the sterile soil, 73 % in the pine-amended one and 63 % in the oak-amended and unamended ones. Pine residues increased the sorption of terbuthylazine to soil and hampered microbial degradation owing to its high terbuthylazine sorption capacity and a decrease in the bioavailability of the herbicide. On the contrary, in the presence of oak residues, the herbicide sorption did not increase significantly. The overall results confirm the active role of the soil microbial community in terbuthylazine degradation in amended and unamended soils and in a liquid enrichment culture performed using an aliquot of the same soil as the inoculum. In this clay loam soil, in the absence of amendments, the herbicide was found to be quite persistent (t 1/2 > 95 days), while in the enrichment culture, the same natural soil bacterial community was able to halve terbuthylazine in 24 days. The high terbuthylazine persistence in this soil was presumably ascribable to its texture and in particular to the mineralogy of the clay fraction.

Changes in the microbial activity in a soil amended with oak and pine residues and treated with linuron herbicide

This work studies the effects of wood amendments on soil microbial community functioning and on the potential of this community for linuron degradation. For this purpose, soil dehydrogenase activity and the number of live bacteria, which represent broad scale measurements of the activity and viability of soil organisms, were assessed in soil treated with linuron and either amended with pine or oak wood or unamended (sterilized and non-sterilized). The overall results show that the microbial community had a significant role in linuron degradation. The linuron half-life values indicated a slower degradation rate in pine and oak amended soils than in unamended ones. This is attributed both to the higher sorption of linuron by these soils compared to the unamended ones and a consequent lower bioavailability of the herbicide for microbial degradation, and to the use of the pine and oak as an alternative carbon source by degrading microorganisms. Linuron did not affect the microbial community in terms of dehydrogenase activity and number of live bacteria, presumably because it had adapted to the herbicide. However, the dehydrogenase activity was significantly higher in the soils amended with pine or oak than in the non-amended ones, indicating that the presence of a carbon source favoured the overall bacterial community.

A hot-spot approach applied to nitrification in tropical acid soils

Several authors have reported that nitrification in acid soils may be restricted to microsites having a more favorable pH. The aim of this study was to propose a conceptual model of the functioning of nitrification in hot-spots, and to test it with the experimental data obtained in laboratory conditions using twelve tropical unamended and NH 4 + -amended soils with a wide range of pH (from 4.2 to 6.9). Nitrification was also measured in two selected soils where the pH was adjusted from 3.5 to 6.2. The model characterizes the relationship between the nitrification rates in unamended and NH 4 + -amended soils as a function of pH. It is based upon the assumption that nitrification of the NH 4 + coming from N mineralization occurs in the hot-spot (RN h), and the nitrification of the added NH 4 + occurs in the hot-spot and also in its adjacent surrounding region (RN s). The experimental design was chosen to be able to estimate both nitrification rates. Soil acidity limited nitrification more in NH 4 + -amended soils than in unamended ones. From our approach, this is due to less favorable conditions for nitrification in the region surrounding the hot-spot. The effect of self-induced acidity on nitrification was not noticeable neither in unamended nor in NH 4 + -amended treatments. The model described well three observations made in the experiments: (i) the minimum pH for nitrification to occur was lower for RN h (pH<4.2) than for RN s (pH<4.7), (ii) the RN h/RN s ratio increased with the decrease of pH (from 1.5 at pH 6 to 8.5 at pH 4), and (iii) for a given pH, the RN h/RN s ratio increased with the decrease of the initial pH of the soil. Among the soil parameters determined in this study (i.e. exchangeable Al, EDTA-extractable Cu and Zn, total C and N), only pH was related to nitrification. However, for a given pH, nitrification varied 3-fold among soils, depending upon their initial pH. This suggests that soil pH as determined on bulk soil is not suitable to predict nitrification in each individual soil, because it is not representative of the acidity level within the hot-spot.

Alleviation of verticillium wilt in pepper ( Capsicum annuum L.) by using the organic amendment COA H of natural origin

Pepper seedlings cv. “Piquillo” were grown for 3 months in unamended medium with organic growing medium COA H (containing salicylic acid (SA), soluble ammonium salts and sea weed extract from Ascophyllum nodosum) inoculated or not inoculated with Verticillium dahliae Kleb. and in amended growing medium with COA H inoculated or not inoculated with V. dahliae. Seedling growth parameters, leaf content of relative water and chlorophyll, leaf gas exchange and resistance as well as total phenolics in stems were determined on days 0, 7, 21, 28 and 33 after inoculation with V. dahliae. SA in stems was measured on days 0, 21 and 33 and leaf nutrient content was analysed on day 33. Results indicate that the organic amendment COA H delayed senescence in Verticillium-inoculated seedlings. In fact, inoculated seedlings that received COA H always exhibited similar leaf resistance to water vapour as well as leaf content of chlorophyll, relative water and nutrients to their relative healthy controls. By contrast, the content of chlorophyll a and relative water in leaves from unamended seedlings significantly decreased on days 21 and 28, respectively, reaching values 30 and 20% lower than those found in the unamended healthy controls. Likewise, the content of chlorophyll b, potassium (K) and magnesium (Mg) in leaves from unamended seedlings inoculated with V. dahliae had declined 35, 40 and 50%, respectively, of the control values by day 33 after pathogen inoculation. On the other hand, while Verticillium-inoculated seedlings grown in amended medium with COA H maintained control photosynthetic rates for 21 days after inoculation, CO 2 exchange rates decreased from day 21 in unamended ones and the leaf resistance in these seedlings enhanced 50% 1 week after inoculation. In addition, Verticillium-inoculated seedlings supplied with COA H delayed the appearance of disease symptoms and their disease index on day 33 was about 40% lower than that measured in unamended pepper. The early accumulation of phenolics (from day 7 after inoculation) in pepper grown in amended medium with COA H could be involved in the greater disease resistance and/or tolerance exhibited by these seedlings.

Increase of Bradyrhizobium japonicum numbers in soils and enhanced nodulation of soybean ( Glycine max (L) merr.) using granular inoculants amended with nutrients

Mineral microgranules, amended with nutrients and inoculated with either peat or liquid Bradyrhizobium japonicum inoculants, increased the growth and recovery of the bacterium during laboratory incubation in unsterilized soil. Increases in the range of 1 log unit per g or ml inoculant used were observed in different soil types. B. japonicum showed better survival with nutrient-amended granules than in unamended ones, in soil undergoing desiccation. In a growth chamber experiment, the number of nodules per plant were significantly increased by nutrient-amendment of the granules, but only under suboptimal conditions for nodulation. Nutrient-amended granules significantly enhanced early nodulation of soybean and increased N content of the grain at harvest in four field trials. All these effects were obtained using an average of 10 kg granules amended with 1.14 kg glycerol and 0.16 kg sodium glutamate per hectare. The possible use of nutrient-amended granules to improve efficacy and reliability of microbial inoculation is discussed.

Increase of Bradyrhizobium japonicum numbers in soils and enhanced nodulation of soybean (Glycine max (L) merr.) using granular inoculants amended with nutrients

Mineral microgranules, amended with nutrients and inoculated with either peat or liquid Bradyrhizobium japonicum inoculants, increased the growth and recovery of the bacterium during laboratory incubation in unsterilized soil. Increases in the range of 1 log unit per g or ml inoculant used were observed in different soil types. B. japonicum showed better survival with nutrient-amended granules than in unamended ones, in soil undergoing desiccation. In a growth chamber experiment, the number of nodules per plant were significantly increased by nutrient-amendment of the granules, but only under suboptimal conditions for nodulation. Nutrient-amended granules significantly enhanced early nodulation of soybean and increased N content of the grain at harvest in four field trials. All these effects were obtained using an average of 10 kg granules amended with 1.14 kg glycerol and 0.16 kg sodium glutamate per hectare. The possible use of nutrient-amended granules to improve efficacy and reliability of microbial inoculation is discussed.

Soil Amendments and the Rhizosphere Effect

Occurrence of bacteria ammonifiers, and nitrifiers in rhizosphere and non-rhizosphere soils of wheat and soybean, grown in unamended soil, soil amended with root exudates, urea or ammonium sulphate was studied. In unamended soil, both plants stimulated bacteria and ammonifiers in their rhizospheres on the 10th, 20th, and 30th day after sowing. In amended soils, the R/S values were lower than in the unamended ones. The different soil amendments resulted in different rhizosphere effects for each plant and during the certain growth phase. Soil amendments seemed to have less effect on the numbers of micro-organisms in the rhizosphere than in the root-free soil. The positive and negative rhizosphere effects in the occurrence of the autotrophic nitrifying bacteria, found in either the unamended or amended soils, seemed to be a characteristic of the rhizosphere environment. In der Rhizosphäre sowie im wurzelfreien Bereich unter Weizen und Sojabohne wurden die Gesamtkeimzahl, die Anzahl der Ammonifikanten sowie Nitrifikanten bestimmt, und zwar in Abhängigkeit von der Verabreichung von Wurzelausscheidungen (Weizen), Harnstoff oder Ammonsulfat. Im unbehandelten Boden stimulierten beide Pflanzen am 10., 20. und 30. Tag nach der Aussaat die Mikroorganismen der Rhizosphäre. In den behandelten Böden hingegen waren die R/S Werte niedriger. Die verschiedenen Behandlungen (Wurzelexsudate, Harnstoff oder Ammonsulfat) ergaben unterschiedliche Rhizosphäreneffekte bei jeder der beiden Pflanzen und auch zu den verschiedenen Untersuchungsterminen, wobei die Wirkung im Rhizosphäre-Bereich geringer war als im wurzelfreien Boden.