Ten grassland and arable soils show variable microbial responses to realistic pesticide mixtures

Abstract    Under the predicted climate change scenarios, heavy precipitation could result in prolonged flooding (PF) and flooding-drying (FD) of soils in agriculture. The influence of PF and FD on soil greenhouse gas fluxes and nitrogen (N) dynamics of arable and grassland soils, which are the dominant land use types in UK soil, is still unclear. Two months of soil incubation experiments were conducted to find out the impact of PF and FD on soil nitrogen dynamics and greenhouse gas fluxes from arable and grassland soil. The result showed the developed ion selective electrodes (ISE) sensor was working to measure NH4+ in the first 5 days of real-life application under both grassland and arable soil. There were less N2O-N emissions in grassland and arable soil when soil moisture was higher than 100% water-holding capacity (WHC). Arable soil had more N2O-N emissions when soil moisture was higher than 100% WHC compared to grassland soil due to a low pH. Grassland soil had more N2O-N emissions when soil moisture was lower than 100% WHC compare to arable soil due to a high carbon and nitrogen source. When soil moisture was greater than 100% WHC, the available NO3--N in the soil controlled N2O-N emissions of grassland more effectively. The N2O-N emissions of grassland soil were more controlled by soil stable NH4+-N and NO3--N when soil moisture was lower than 100% WHC. The emissions of N2O-N and CO2-C were increased with the time of FD. FD significantly increased N2O-N, CO2-C, and CH4-C emissions in grassland soil compared to arable soil by 0.93, 2.15, and 37.29 times, respectively. Converting arable land use to grassland could increase the greenhouse gas (GHG) emissions under climate change (heavy rain). Further research needs to be done to find out how to reduce the GHG emissions under climate change after transfer arable to grassland.

The effect of long-term soil management on the physical and biological resilience of a range of arable and grassland soils in England

Vegetation effects on soil solution composition and evapotranspiration—potential impacts of set-aside policies

The mountainous region of the Himalayas is covered with forest, grassland, and arable land, but the variation in ecosystem functions has not been fully explored because of the lack of available data. This study appraises the changes in soil properties over the course of a year (spring, summer, autumn, winter) for forest, grassland, and arable soils in a typical hilly and mountainous region of Azad Jammu and Kashmir, Pakistan. Soil samples were collected from major land-cover types in the mountain region: natural forest, grassland, and cultivated land (arable). The natural forest served as a control against which changes in soil properties resulting from removal of natural vegetation and cultivation of soil were assessed. Soil samples were collected from depths of 0–15 and 15–30 cm six times during the year and examined for changes in temperature, moisture, electrical conductivity (EC), micronutrients [iron, manganese, copper, and zinc (Fe, Mn, Cu, Zn, respectively)], and microbial population. Significant differences were found in soil temperature, soil moisture, Fe, Mn, Cu, Zn, and number of bacteria, actinomycetes, and fungi among the three land-cover types. Soil under cultivation had 4–5 °C higher temperature and 3–6% lower moisture than the adjacent soils under grassland and forest. Electrical conductivity (EC) values of forest, grassland, and arable soil were 0.36, 0.30, and 0.31 dS m−1, indicating that soil collected from the forest had 18–20% more EC than the adjacent arable and grassland soils. On average, amounts of Fe, Mn, Cu, and Zn in the soil collected from the arable site were 6.6, 5.7, 1.7, and 0.8 mg kg−1, compared with 24.0, 12.1, 3.5, and 1.2 mg kg−1 soil in the forest soil, showing that arable had two to four times less micronutrients than grassland and forest. Populations of bacteria, actinomycetes, and fungi in the forest were 22.3 (105), 8.2 (105), and 2.5 (103), respectively, while arable land exhibited 8.2 (105), 3.2 (105), and 0.87 (103). Season (temperature) and depth showed significant effects on microbial activity and nutrient concentration, and both decreased significantly in winter and in the subsurface layer of 15−30 cm. Different contents of the parameters among arable, grassland, and forest soils indicated an extractive effect of cultivation and agricultural practices on soil. Natural vegetation appeared to be a main contributor to soil quality as it maintained the moisture content and increased the nutrient status and microbial growth of soil. Therefore, it is important to sustain high-altitude ecosystems and reinstate the degraded lands in the mountain region.

Enhanced soil toxic metal fixation in iron (hydr)oxides by redox cycles

Several climate change scenarios have predicted that heavy precipitation could result in prolonged flooding (PF) and flooding–drying (FD) of soils under agriculture. The influence of PF and FD on soil greenhouse gas (GHG) fluxes and ammonium‑nitrogen (NH4+-N) and nitrate‑nitrogen (NO3−-N) dynamics of arable and grassland soils, the dominant land-use types in the UK, remain unclear. A two-month soil incubation experiment was conducted to determine the impact of PF and FD on soil N dynamics and GHG fluxes from arable and grassland soils. Arable soil emitted more N2O-N when soil moisture exceeded 100% water-holding capacity (WHC) compared to grassland soil under PF. Grassland soils exhibited increased N2O-N emissions than arable soils when soil moisture was lower than 100% WHC under FD. When soil moisture exceeded 100% WHC, the available NO3−-N in the soil contributed 58% of N2O-N emissions potentially by denitrification from grassland. When soil moisture was lower than 100% WHC, soil NH4+-N and NO3−-N contributed 71% of N2O-N emissions, which suggests coupling of nitrification-denitrification processes in driving high emissions from grassland soils. The N2O-N and CO2-C emissions increased with the incubation time under FD. Moreover, FD significantly increased N2O-N, CO2-C, and CH4-C emissions in grassland soil by 0.93, 2.15, and 37.29 times more than arable soil, respectively. These findings points to important tipping points in the source strengths of GHG fluxes from the two land use types differently. Future land use changes should consider the contribution of the changing dynamics of GHG fluxes in light of climate extremes and its implications for net zero greenhouse gas emission ambitions.

The objectives of this study are to analyse soil structure of representative crop (45 sites) and grassland (58 sites) soils and furthermore to identify differences in soil structure features between these sites in Northern Germany. Using the Compaction Verification Tool (CVT), published by Zink et al. (2011), the present state of soil structure was investigated. Additionally, the orientation of the pore system was analysed by combining the vertical and horizontal hydraulic conductivity. Finally, the influence of soil structure features on crop yield of different arable plants was determined according to the concept of the Muencheberg Soil Quality Rating (Müller et al., 2013). While (sub-) soil compaction within the transition layer, connecting top- and subsoil, was identified on 15 % of the on arable sites, on grassland sites in contrast only a negligible small proportion showed these features. Regarding the correlation of soil quality and crop yield, the results also show differences between arable and grassland sites: on arable soils a correlation was found with a coefficient of determination of nearly 50 % (R²=0.46), on grassland sites in contrast this correlation could not be identified. The conclusions of this study are the overriding importance of soil structure on arable soils regarding plant yield and management efficiency. In contrast, plant growth and yield on grassland soils are more likely determined by management practices (e.g. fertilisation, number of cuts) and the influencing groundwater than by soil structure features. Furthermore, the results show investigation methods should be adapted to grassland soils in order to analyse the complex interactions of soil, sward (including the dense rooting system) and environmental conditions. • Comparative investigations regarding the present state of soil structure on arable and grassland sites were carried out. • 15 % of the arable soils showed clear features of soil compaction. • On grassland sites only a very small proportion of sites exhibited clear indications of soil compaction. • While on arable soils crop yield depends on soil quality properties, yield of grassland sites was proved independent from these features.

Land‐use intensification can reduce soil carbon stocks and changes microbial community biodiversity and functionality. However, there is a lack of consensus on whether management consistently affects microbial biodiversity across geographic scales, and how this relates to altered soil function. From a regulatory and monitoring perspective, there is a need to identify functionally relevant indicators of land use in order to evaluate the progress of soil restoration approaches. We performed a landscape‐scale survey of unimproved calcareous grasslands paired with local arable contrasts, and assessed the consistency of responses in a variety of soil, biotic and functional measures. In addition, adjacent grasslands undergoing restoration were assessed to identify soil microbial indicators of recovery. Organic matter content was consistently larger in grasslands than in arable fields, and increased with time in the restoring sites. Molecular comparisons of grassland versus arable soils revealed numerous bacterial, archaeal and fungal indicators, with more representatives of Ca. Xiphinematobacter , DA101 , Bradyrhizobium , Rhodoplanes , Mycobacteria and Mortierella in old grassland soils, whereas Nitrososphaera , Sporosarcina and Alternaria infectoria were more abundant in arable soils. Extracellular enzymatic responses were more variable, with none of the eight investigated enzymes being consistent indicators of grassland or arable soils. Correlation analyses, incorporating the molecular and enzymatic responses across all surveyed soils, revealed that molecular indicators were more strongly correlated with soil organic matter increases with restoration of arable soils. Our results highlight that microbial taxa are among the most sensitive indicators of soil restoration, and we identify consistent responses of specific taxa to management across geographic scales. This discovery will be important for both the instigation and monitoring of soil restoration. Highlights Soil microbes are key drivers of soil ecosystem services and are affected by management Calcareous grassland exhibited abundant Verrucomicrobia; cropping increased Nitrososphaera These taxa responded to SOM increases with grassland restoration, more so than enzymes and fungi Microbes provide consistent, site‐independent indicators for calcareous grassland soil function restoration

Soil chemistry and leaching losses of nutrients from semi-natural grassland and arable soils on three contrasting parent materials

Temperature changes and the ATP concentration of the soil microbial biomass

Previous investigations observed that when soil was fumigated with ethanol-free CHCl3 for 24h and then incubated under appropriate conditions, after the initial flush of CO2 was over, soil organic carbon (SOC) mineralization continued at the same rate as in the non-fumigated soil. This indicates that, following fumigation, the much diminished microbial population still retained the same ability to mineralize SOC as the much larger non-fumigated population. We hypothesize that although fumigation drastically alters the soil bacterial community abundance, composition, and diversity, it has little influence on the bacterial C-metabolic functions. Here, we conducted a 30-day incubation experiment involving a grassland soil and an arable soil with and without CHCl3 fumigation. At days 0, 7, and 30 of the incubation, the bacterial abundances were determined by quantitative PCR, and the bacterial community composition and diversity were assessed via the 16S rRNA gene amplicon sequencing. PICRUSt was used to predict the metagenome functional content from the sequence data. Fumigation considerably changed the composition and decreased the abundance and diversity of bacterial community at the end of incubation. At day 30, Firmicutes (mainly Bacilli) accounted for 70.9 and 94.6% of the total sequences in the fumigated grassland and arable soil communities, respectively. The two fumigated soil communities exhibited large compositional and structural differences during incubation. The families Paenibacillaceae, Bacillaceae, and Symbiobacteriaceae dominated the bacterial community in the grassland soil, and Alicyclobacillaceae in the arable soil. Fumigation had little influence on the predicted abundances of KEGG orthologs (KOs) assigned to the metabolism of the main acid esters, saccharides, amino acids, and lipids in the grassland soil community. The saccharide-metabolizing KO abundances were decreased, but the acid ester- and fatty acid-metabolizing KO abundances were elevated by fumigation in the arable soil community. Our study suggests functional redundancy regarding the bacterial genetic potential associated with SOC mineralization.

European scale analysis of phospholipid fatty acid composition of soils to establish operating ranges

The quantity and quality of organic carbon (Corg) input drive soil Corg stocks and thus fertility and climate mitigation potential of soils. To estimate fluxes of Corg as net primary production (NPP), exports, and inputs on German arable and grassland soils, we used field management data surveyed within the Agricultural Soil Inventory (n = 27.404 cases of sites multiplied by years). Further, we refined the concept of yield-based Corg allocation coefficients and delivered a new regionalized method applicable for agricultural soils in Central Europe. Mean total NPP calculated for arable and grassland soils was 6.9 ± 2.3 and 5.9 ± 2.9 Mg Corg ha−1 yr−1, respectively, of which approximately half was exported. On average, total Corg input calculated did not differ between arable (3.7 ± 1.8 Mg ha−1 yr−1) and grassland soils (3.7 ± 1.3 Mg ha−1 yr−1) but Corg sources were different: Grasslands received 1.4 times more Corg from root material than arable soils and we suggest that this difference in quality rather than quantity drives differences in soil Corg stocks between land use systems. On arable soils, side products were exported in 43% of the site * years. Cover crops were cultivated in 11% of site * years and contributed on average 3% of the mean annual total NPP. Across arable crops, total NPP drove Corg input (R2 = 0.47) stronger than organic fertilization (R2 = 0.11). Thus, maximizing plant growth enhances Corg input to soil. Our results are reliable estimates of management related Corg fluxes on agricultural soils in Germany.

Relationships between mycelial and bacterial populations in stored, air-dried and glucose-amended arable and grassland soils

Summary Our aim was to determine whether the soil microbial biomass, which has developed naturally over many years in a given ecosystem, is specially adapted to metabolize the plant‐derived substrate C of the ecosystem within which it developed or whether the nature of recently added substrate is the more important factor. To examine this, soils from three sites in close proximity (woodland, grassland and arable from the Broadbalk Experiment at Rothamsted Research, Harpenden, UK) were each amended with air‐dried wheat straw ( Triticum aestivum ), ryegrass leaves ( Lolium perenne ) or woodland leaf litter (mainly Quercus robur and Fagus sylvatica ) in a fully replicated 3 × 3 factorial laboratory experiment. The initial mineralization rates (evolved CO 2 ‐C) were determined during the first 6.5 hours and again, together with the amount of microbial biomass synthesized (microbial biomass C), at 7, 14, 21, 30 and 49 days of incubation. The hourly rate of CO 2 ‐C production during the first 6.5 hours was slowest following leaf litter addition, while the added grass gave the fastest rates of CO 2 ‐C evolution both within and between soils. Ryegrass addition to the arable soil led to approximately four times more CO 2 ‐C being evolved than when it was added to the woodland soil, at an overall rate in the arable soils of 41 μg C g −1 soil hour −1 . In each soil, the net amounts of CO 2 ‐C produced were in the order grass > straw > leaf litter. In each case, the amount produced by the added leaf litter was significantly less ( P < 0.05) than either the added grass or straw. Overall, the trend was for much slower rates of mineralization of all substrates in the woodland soil than in either the arable or grassland soils. During 49 days of incubation in the woodland and grassland soils, the net total amounts of CO 2 ‐C evolved differed significantly ( P < 0.01), with grass > straw > leaf litter, respectively. In the arable soil, the amounts of CO 2 ‐C evolved from added grass and straw were significantly larger ( P < 0.01) than from the leaf litter treatment. Our findings indicated that the amounts of CO 2 ‐C evolved were not related to soil management or to the size of the original biomass but to the substrate type. The amount of biomass C synthesized was also in the order grass > straw > leaf litter, at all stages of incubation in the woodland and grassland soil. In the arable soil, the same effect was observed up to 14 days, and for the rest of the incubation the biomass C synthesized was in the order grass > straw > leaf litter. Up to three times more biomass C was synthesized from the added grass than from the other substrates in all soils throughout the incubation. The maximum biomass synthesis efficiency was obtained with grass (7% of added C). Overall, the woodland soil was most efficient at synthesizing biomass C and the arable soil the least. We conclude that substrate type was the overriding factor that determined the amount of new soil microbial biomass synthesized. Mineralization of substrate C by soil microorganisms was also influenced mainly by substrate type and less by soil management or size of original biomass.