Soil Biological Degradation Research Articles

Bacteroidota structure in the face of varying agricultural practices as an important indicator of soil quality – a culture independent approach

The choice of appropriate agricultural practices has a major impact on soil quality, crop productivity, and bacterial community structure. The aim of our study was to gain insight into Bacteroidota structure, including the phylum, family, and genus in the context of the application of different agricultural practices (crop rotation, intercropping mixture, long-term maize monoculture) across changing seasons (spring, summer, autumn), which is undoubtedly novel among previous reports on different cropping systems. Additionally, the Spearman correlation test as well as ANOVA and RDA statistical analyses were conducted to expand the information on chemical factors directly affecting Bacteroidota abundance in the soil environment. Bacteroidota were shown to be present with varying abundance depending on the agricultural practice and the season. The highest abundance of Bacteroidota occurred when crop rotation was the main agricultural practice, where the highest average yield was also recorded. Thus, our study identified crop rotation as the best of the three agricultural practices compared. The reduction in the relative abundance of Bacteroidota, in particular Flavobacterium sp. in fields K20 (intercropping) and K21 (monoculture), and the achievement of almost twice the lower average yield in field K21 than in field K3, indicated the poorer quality of these soils. We therefore concluded that the increased abundance of Bacteroidota could indicate good quality agricultural soils. It was also proved that the genera Mucilaginibacter and Edaphobaculum are the most sensitive to soil chemistry over the changing seasons, while the genus Flavobacterium is sensitive to agricultural practices and its presence may indicate good quality of agricultural soils. Statistical analyses indicated that chemical properties have a strong influence on Bacteroidota structure formation in agricultural soils. Overall, our results have evidenced that the Bacteroidota community can be an important indicator of soil quality in studies of soil biological degradation processes, since a decrease in the abundance of these beneficial microorganisms potentially could be connected with reduction of the soil quality, fertility and ultimately affects crop yield. They have also shown that the community of this group of bacteria varies between seasons of the year.

Aggregate distribution and substrate-induced respiration under different tillage and mulching management systems in organic farming

ABSTRACT In organic farming, intensive tillage for weed eliminating may cause physical and biological soil degradation. Weed residue mulch can be used to stabilize the organic carbon in the soil by improving soil aggregation and increasing microbial activity. However, the effectiveness of weed mulch in no-tillage (NT) and conventional tillage (CT) systems remains unclear. Therefore, we studied the influence of clipped weed mulch (CM) and no mulch (NM), in combination with NT and CT on the water-stable aggregates, and carbon stabilization in different-sized soil aggregates as well as on substrate-induced respiration (SIR) and the fungal-to-bacterial activity ratio at a soil depth of 0–5 cm. Macroaggregates (>4 mm water- stable aggregates) were 46.8% higher in NT than in CT in June and October 2014 and 52.4% higher with NT in 2015. Microaggregates (0.5- and 0.25-mm aggregates) were higher in CT than NT in both years. The use of CM also increased water-stable aggregates in both years. In 2014, >4-mm aggregate fraction was 6.5% higher with CM than with NM. In 2015, the same parameters were even more effective, with >4-mm and 2-mm aggregate fractions were 23.9% and 34.9% higher with CM respectively. MWD was higher in NT than in CT in both years and CM had slightly increased (but not significantly) this in October. In both years, soil organic carbon (SOC) and nitrogen were significantly higher in NT than in CT, and in October CM further increased these in both tillage systems. In both tillage systems, the highest amounts of SOC was measured in >4-mm aggregate fraction than microaggregates. In both years, microbial SIR was higher in NT than in CT. Further, research is needed to find out long term effect of weed residue mulch in these changes in both tillage systems.

Effectiveness of Arachis pintoi Karp. and Greg. as Biomulch to Control Weeds on Maize Cultivation

Weeds is one of the limiting factors in crop production that has significant effects, both economically and ecologically. Continuous use of herbicides increased the resistance of weeds to herbicides and causes chemical and biological soil degradation. The use of cover crops can be an alternative to environmentally friendly weed management. The objective of this research was to study the effectiveness of Arachis pintoi as biomulch in suppressing the growth and development of weeds. This experiment used nested-randomized block design with the first factor was the slope of land with 2 levels (flat and sloping lands) and the second factor was the types of mulch with 5 levels (without mulch without weeding, without mulch with weeding, plastic mulch, straw mulch and A. pintoi biomulch). The types of mulch factor nested on the slope of the land factor. The results showed that the use of A. pintoi biomulch suppressed the growth of weed more than 58% compared to the without mulch without weeding treatment. The study also showed that A. pintoi was effective in suppressing broadleaf and sedge weeds but not effective to suppress grass weeds. The use of A. pintoi biomulch by allowing the coverage of the entire soil surface suppressed the growth and yield of maize compared to the without mulch with weeding and straw mulch treatments.

The cover crop determines the AMF community composition in soil and in roots of maize after a ten-year continuous crop rotation

Intensive agricultural practices are responsible for soil biological degradation. By stimulating indigenous arbuscular mycorrhizal fungi (AMF), cover cropping enhances soil health and promotes agroecosystem sustainability. Still, the legacy effects of cover crops (CCs) and the major factors driving the AM fungal community are not well known; neither is the influence of the specific CC. This work describes a field experiment established in Central Spain to test the effect of replacing winter fallow by barley (Hordeum vulgare L.) or vetch (Vicia sativa L.) during the intercropping of maize (Zea mays L.). We examined the community composition of the AMF in the roots and rhizosphere soil associated with the subsequent cash crop after 10 years of cover cropping, using Illumina technology. The multivariate analysis showed that the AMF communities under the barley treatment differed significantly from those under fallow, whereas no legacy effect of the vetch CC was detected. Soil organic carbon, electrical conductivity, pH, Ca and microbial biomass carbon were identified as major factors shaping soil AMF communities. Specific AMF taxa were found to play a role in plant uptake of P, Fe, Zn, Mn, and Cd, which may shed light on the functionality of these taxa. In our conditions, the use of barley as a winter CC appears to be an appropriate choice with respect to promotion of AMF populations and biological activity in agricultural soils with intercropping systems. However, more research on CC species and their legacy effect on the microbial community composition and functionality are needed to guide decisions in knowledge-based agriculture.

Bt rice cultivation does not cause soil biological degradation in terms of C, N, and P cycles

Preventing soil biological degradation under the cultivation of Bacillus thuringiensis (Bt) crops is crucial to soil health. Despite studies concerning environmental risks of Bt crops, we surprisingly know little about whether soil biological degradation occurs under Bt crop cultivations. To fill this gap, we calculated the index of resistance (IR) and resilience (IR′) of 13 soil properties (the activities of enzymes, the rates of ecosystem processes, soil microbial biomass, and soil carbon and nutrients) using soil samples collected from an 8‐year Bt rice cultivation experiment, including three treatments, that is, continual cultivation of Bt rice (GM) and non‐Bt rice (non‐GM), and rotation between Bt and non‐Bt rice every 2 years (GM/non‐GM rotation). In GM and GM/non‐GM rotation, the IR of the activities of dehydrogenase, acid phosphatase, methane production rates was significantly greater than that in non‐GM. Further, the IR of denitrification, methane oxidation, microbial carbon, and microbial nitrogen was significantly lowered in GM, and the IR of microbial carbon in GM/non‐GM rotation was significantly decreased compared with that in non‐GM. However, the results of IR′ showed no significant differences in these soil properties between treatments, except for methane oxidation and urease in GM and microbial nitrogen in GM/non‐GM rotation. Taking into consideration of soil resistance and resilience, the most soil properties remained relatively stable. These findings suggest that the Bt rice cultivations have not significantly resulted in soil biological degradation.

Easily degradable carbon – an indicator of microbial hotspots and soil degradation

AbstractThe effect of arable soil was quantified against non-cultivated soil on easily degradable carbon and other selected microbiological factors,i.e.soil microbial biomass, respiration activity, and dehydrogenase activity. The intent was to ascertain whether easily degradable carbo can be useful as a sensitive indicator of both soil biological degradation and microbial hot-spots indication. As a result, it was found that soil respiration activity was significantly higher (p <0.0001) in all controls, ranging between 30-60vs.11.5-23.7 μmol CO2kg d.m.−1 h−1for the arable soils. Dehydrogenase activity was significantly lower in the arable soil (down to 35-40% of the control values, p <0.001) varying depending on the soil type. The microbial biomass was also significantly higher at the non-cultivated soil (512-2807vs. 416-1429 µg g−1d.m., p <0.001), while easily degradable carbon ranged between 620-1209 mg kg−1non-cultivated soil and 497-877 mg kg−1arable soil (p <0.0001). It was demonstrated that agricultural practices affected soil properties by significantly reducing the levels of the studied parameters in relation to the control soils. The significant correlations of easily degradable carbon-respiration activity (ρ= 0.77*), easily degradable carbon-dehydrogenase activity (ρ= 0.42*), and easily degradable carbon-microbial biomass (ρ= 0.53*) reveal that easily degradable carbon is a novel, suitable factor indicative of soil biological degradation. It, therefore, could be used for evaluating the degree of soil degradation and for choosing a proper management procedure.

Atividade microbiana e enzimática em solo após a aplicação de xisto retortado

O objetivo deste trabalho foi avaliar o efeito da aplicação de doses crescentes de xisto retortado (XR) sobre características biológicas indicadoras da qualidade do solo. Foram realizados experimentos, em Argissolo Vermelho distrófico arênico, em condições de laboratório e de campo. Em laboratório, os tratamentos consistiram da aplicação ao solo de sete diferentes doses de XR (0, 300, 450, 600, 750, 1.500 e 3.000 kg ha-1). Em campo, os tratamentos foram compostos por quatro diferentes doses de XR (0, 750, 1.500, 3.000 kg ha-1) combinadas à adubação mineral recomendada, avaliados em dois cultivos de feijão (Phaseolus vulgaris L.), no sistema plantio direto. Avaliaram-se: a evolução de CO2, o carbono da biomassa microbiana (CBM), a atividade enzimática do solo e o teste de ecotoxicidade. A aplicação de doses crescentes de XR melhorou a atividade microbiológica do solo, por reduzir a emissão de CO2 sem causar variação no CBM e sem provocar impactos negativos sobre a atividade enzimática do solo. Os resultados obtidos com as enzimas em condições de campo, após duas aplicações de XR, aliados aos de CBM, do quociente metabólico (qCO2) e do teste ecotoxicológico, em condições de laboratório, indicam que o uso do XR não provoca a degradação biológica do solo.

Assessment of soil biological degradation using mesofauna

The aim of this work was to assess soil degradation by means of simple and relatively easy to measure biological indicators derived from mesofauna, and to provide criteria to derive threshold values from benchmark sites. We hypothesized (1) that simple biological attributes may be derived from soil mesofauna to be used as soil biological degradation indicators and (2) that this would be best attained by contrasting the deviation of the indicators from natural and managed benchmark sites. The study was conducted on Typic Hapludolls from Córdoba, Argentina. Soil biological degradation was assessed by comparing the deviation of one multivariate and two univariate indicators in intensively managed arable sites from benchmark sites. Three bioindicators were useful to assess soil biological degradation. Specifically, the OM/PA ([Oribatida + Mesostigmata]/[Prostigmata + Astigmata]) index and the multivariate indicator were effective in discriminating between the benchmark and the intensively managed sites and in distinguishing soil degradation levels among intensively managed sites; this finding confirmed our hypothesis. The indicators analyzed were robust and sensitive not only to tillage but also to a combination of management variables. The combined use of Principal Component Analysis and Minimum Spanning Trees techniques also proved to be an effective tool to evaluate the distance between intensively managed sites and between each intensively managed site and the three benchmarks. The bioindicators proposed are simple and easy to measure, and therefore suitable for assessing soil degradation. Validation of the proposed indicators for other soils, climates and land uses is recommended.

Effects of cultivation methods on some soil biological parameters of a meadow chernozem soil (Vertisols)

The effect of extended drought conditions on soil, the unfavourable cultivation technologies and the application of chemicals have been enhancing the processes of physical and biological soil degradation, so the fertility of soil is gradually declining. The effects of two cultivation methods – traditional ploughing (TP) and conservation tillage (CT) – on the biological activity of a meadowchernozem soil were examined in a long term experiment. Different parameters of the biological activity of soil were determined. These arethe numbers of total bacteria, microscopic fungi, aerobic cellulose decomposing bacteria, as well as the activities of some important soilenzymes and CO2 production.Conservation tillage seemed to be a more favourable cultivation method for the majority of microorganisms, the activities of urease anddehydrogenase enzymes and CO2 production, compared to the traditional ploughing system. These parameters increased significantly,especially in the upper layer of conservation tillage plots. Concerning the plant cultures, the majority of microbiological parameters werehigher in the soil of vetch (Vicia sativa L.) depending on the cultivation methods, so involving the pulses to the crop-rotation seems to bevery important in this soil type.According to the ninth year’s results, the importance of conservation tillage as a means of protecting the soil biological activity in meadowchernozem (Vertisols) can be established; it was proven by microbiological investigations.

Negative effects of no-till on soil macrofauna and litter decomposition in Argentina as compared with natural grasslands

No-till (NT) has been recognized as a management system of low environmental impact when applied in combination with crop residue mulch and rotations involving cover crops. It has been suggested, however, that, if these conditions are not met, NT may result in physical, chemical and biological soil degradation. This study evaluates the effect of NT on the litter decomposition process and on soil macrofauna communities and how changes in soil physical, chemical, and physicochemical properties affect litter decomposition and soil macrofauna. We hypothesised (1) that macrofaunal abundance, richness and diversity would be lower in NT soils than in natural grasslands; (2) that this would be a consequence of unfavourable physical and chemical soil conditions and high inputs of agrochemicals; and (3) that these changes in macrofauna would influence soil functioning, reducing litter decomposition rate. The study was conducted during winter and spring 2007 on Typic Haplustolls from southern Córdoba, Argentina (32°41′ and 32°50′S; 63°58′ and 63°44′W). Macrofauna was sampled twice in NT and in natural grasslands (NA) – as a reference situation – by extracting five soil monoliths of 25 cm × 25 cm × 30 cm at each plot. Soil properties were measured using standard methods. The decomposition rate was determined by the litterbag method, using a 2 mm and a 10 mm size meshes to evaluate litter decomposition mediated by macrofauna. NT greatly reduced richness (from 33 species in NA to 12 species in NT) and abundance (from 1870 ind/m 2 in NA to 475 ind/m 2 in NT) of macroinvertebrates, confirming our first hypothesis. Changes in macrofauna community under NT were mainly explained by high compaction and low organic matter content, confirming our second hypothesis. The reduction in earthworm abundance may also be explained by the influence of the intense use of toxic agrochemicals. No-till increased surface horizon bulk density (from 1.22 to 1.33 g/cm 3) and decreased organic matter content (from 3.51% to 2.58%) and pH (from 6.74 to 6.01) compared with NA. The litter decomposition rate was lower in NT, confirming our third hypothesis, and it was correlated with low earthworms abundance and activity. We conclude that in our study area the capacity of soils under NT to maintain ecosystem functions would be at risk.

Thermodynamics of Agricultural Sustainability: The Case of US Maize Agriculture

This paper considers the local, field-scale sustainability of a productive industrial maize agrosystem that has replaced a fertile grassland ecosystem. Using the revised thermodynamic approach of Svirezhev (1998, 2000) and Steinborn and Svirezhev (2000), it is shown that currently this agrosystem is unsustainable in the U.S., with or without tilling the soil. The calculated average erosion rates of soil necessary to dissipate the entropy produced by U.S. maize agriculture, 23–45 t ha−1 yr−1, are bounded from above by an experimental estimate of mean soil erosion by conventional agriculture worldwide, 47 t ha−1 yr−1, (Montgomery, 2007). Between 1982 and 1997, US agriculture caused an estimated 7–23 t ha−1 yr−1 of average erosion with the mean of 15 t ha−1 yr−1 (USDA-NRCS Database). The lower mean erosion rate of no till agriculture, 1.5 t ha−1 yr−1 (Montgomery, 2007), necessitates the elimination of weeds and pests with field chemicals—with the ensuing chemical and biological soil degradation, and chemical runoff—to dissipate the produced entropy. The increased use of field chemicals that replace tillers is equivalent to the killing or injuring of up to 300 kg ha−1 yr−1 of soil flora and fauna. Additional soil degradation, not calculated here, occurs by acidification, buildup of insoluble metal compounds, and buildup of toxic residues from field chemicals. The degree of unsustainability of an average U.S. maize field is high, requiring 6–13 times more energy to reverse soil erosion and degradation, etc., than the direct energy inputs to maize agriculture. This additional energy, if spent, would not increase maize yields. The calculated “critical yield” of “organic” maize agriculture that does not use field chemicals and fossil fuels is only 30 percent lower than the average maize yield of 8.7 tons per hectare (∼140 bu/acre) assumed here. This critical yield would not likely be achieved and sustained by large monocultures, but might be achieved by more balanced organic polycultures (Baum et al., 2008).

Combined use of GIS and environmental indicators for assessment of chemical, physical and biological soil degradation in a Spanish Mediterranean region

Soil is one of the main non-renewable natural resources in the world. In the Valencian Community (Mediterranean coast of Spain), it is especially important because agriculture and forest biomass exploitation are two of the main economic activities in the region. More than 44% of the total area is under agriculture and 52% is forested. The frequently arid or semi-arid climate with rainfall concentrated in few events, usually in the autumn and spring, scarcity of vegetation cover, and eroded and shallow soils in several areas lead to soil degradation processes. These processes, mainly water erosion and salinization, can be intense in many locations within the Valencian Community. Evaluation of soil degradation on a regional scale is important because degradation is incompatible with sustainable development. Policy makers involved in land use planning require tools to evaluate soil degradation so they can go on to develop measures aimed at protecting and conserving soils. In this study, a methodology to evaluate physical, chemical and biological soil degradation in a GIS-based approach was developed for the Valencian Community on a 1/200,000 scale. The information used in this study was obtained from two different sources: (i) a soil survey with more than 850 soil profiles sampled within the Valencian Community, and (ii) the environmental information implemented in the Geo-scientific map of the Valencian Community digitised on an Arc/Info GIS. Maps of physical, chemical and biological soil degradation in the Valencian Community on a 1/200,000 scale were obtained using the methodology devised. These maps can be used to make a cost-effective evaluation of soil degradation on a regional scale. Around 29% of the area corresponding to the Valencian Community is affected by high to very high physical soil degradation, 36% by high to very high biological degradation, and 6% by high to very high chemical degradation. It is, therefore, necessary to draw up legislation and to establish the policy framework for actions focused on preventing soil degradation and conserving its productive potential.

Sustainable land use and soil quality: organic matter as an indicator

In this review the most recent approach to sustainable land use and the role that soil quality plays therein are described briefly. The requirements to which indicators must conform for the meaningful evaluation of the quality of soil and sustainability of land use are also elucidated. Thereafter the processes of physical, chemical and biological soil degradation are given. A concise discussion follows on the extent of physical and chemical soil degradation in South Africa, of which there is reliable information. Biological soil degradation is treated in more detail. Attention is given firstly to the role of soil organic matter in biogeochemical cycles. Thereafter the influence of different land use systems in the central parts of South Africa on the organic matter content and consequently the nitrogen, phosphorus and sulphur reserves of soils is discussed by using examples. The conclusion is that organic matter is an important indicator of soil quality and thus also of sustainable land use.

Changes in the soil organic N fractions of a tropical Alfisol fertilized with 15N-urea and cropped to maize or pasture

Qualitative and quantitative changes in soil and fertilizer-derived organic N fractions were assessed during a cropping season in an intertropical Alfisol, under maize and pasture, fertilized with15 N-urea. Before the sowing, after fertilizing and after the harvest, the organic N of top soil samples was fractionated by a two-step acid hydrolysis under reflux (H1 = 1 M HCl for 3 h; H2 = 3 M HCl for 3 h). The total hydrolysable N (HN) from H1 decreased significantly during the cropping season in both maize and pasture soils. Contrastingly, the content of HN from H2 and that of non-hydrolysable N did not vary significantly during the cropping season. The easily hydrolysable fractions, especially amino acid N, amino sugar N and amide N, were the most active N pools and the major source of N potentially available for plants. The urea-derived N that remained in the soil was mainly in organic forms at both 7 and 108 d after fertilizing (70–82% and 93–98%, respectively), higher figures being found in pasture than in maize soil. The total amount of urea-derived HN decreased significantly during the crop period in both maize and pasture soils. This decrease was largely due to the decline in HN from H1. The amount of non-hydrolysable urea-derived N was significantly higher in pasture than in maize soil and it decreases in the former and increases in the latter, during the cropping season. During the crop period, the decrease of urea-derived organic N was 4.6 to 9.1 times higher than that of native organic N. Shortly after fertilizing, the proportion of urea-derived N in the easily hydrolysable (H1) organic fractions was higher than that of soil N, whereas the reverse was true for the slowly hydrolysable (H2) or insoluble fractions. These differences were less marked, but still significant, at the end of cropping. The easily hydrolysable organic N fractions were more sensitive than total N to the impact of land use intensification and are, therefore, a more useful index for early detection of soil biological degradation.