Showing papers in "Journal of Plant Nutrition and Soil Science in 2022"
TL;DR: In this article , a detailed overview of the history of application of molecular modeling tools and developing structural concepts of soil organic matter (SOM) is provided. But, their binding to reactive mineral soil constituents can be also in the form of individual molecules or subaggregates, depending on the interacting environment.
Abstract: Background Knowledge of the stabilizing mechanisms of soil organic matter (SOM) is extremely important for numerous soil functions. For this, insight into the nature of organic matter through appropriate model concepts are crucial. Aims For several years, a heated debate has emerged on the transformation and stabilization of SOM. In the present work, we try to contribute to this debate using molecular modeling and providing a comprehensive overview of the history of application of molecular modeling tools and developing structural concepts of SOM. Methods Molecular modeling methods based on quantum and/or classical mechanics were used to model SOM and related properties including interactions with reactive surfaces of soil minerals. Results Modeling of SOM aggregates revealed that hydrogen bonds and cation bridges are the main stabilizing factors in soil solution, whereas pH modifies the stability. The modeled supramolecular SOM aggregates exhibit physicochemical properties, similar to those of humic substances (HS) described in literature. The interactions of the HS models with surfaces in kaolinite nanopores led to a partial disintegration of the aggregates into individual molecules and/or smaller subaggregates. Conclusions From the molecular modeling point of view, supramolecular microaggregate models that exhibit the properties of HS are stable in the soil solution. However, their binding to reactive mineral soil constituents can be also in the form of individual molecules or subaggregates. Thus, HS microaggregate stability is relative, depending on the interacting environment. This reconciles two points of view of HS: either as small molecules and/or supramolecular structures.
12 citations
TL;DR: In this paper , the authors derived site-specific organic carbon (SOC) benchmarks for German mineral soils under agricultural use based on the dataset of the first German Agricultural Soil Inventory.
Abstract: Background Soil organic carbon (SOC) storage is highly variable across sites and primarily depends on site properties and land use. It is therefore difficult for farmers to evaluate the actual SOC status of a site. To aid the interpretation of measured SOC contents, easy-to-use frameworks for the assessment of SOC contents are needed. Aims The aim of this study was to derive site-specific SOC benchmarks for German mineral soils under agricultural use based on the dataset of the first German Agricultural Soil Inventory. Methods The dataset was stratified into 33 strata by land use, soil texture, C/N ratio and mean annual precipitation. Lower and upper SOC benchmarks were calculated for all strata (0.125 and the 0.875 quantile). Results The SOC benchmark value ranges were lower for cropland (6.8–48.9 g kg–1) than for grassland (14.1–76.6 g kg–1), and increased with rising clay content and precipitation. Sandy soils with a wide C/N ratio and high SOC content due to their heathland or peatland history were divided into separate strata. The number of strata only decreased the SOC benchmark ranges slightly. Around 15–20 sites were required as a minimum to quantify SOC benchmarks for one stratum. Conclusions The presented framework is easy to use, requiring only four readily available stratification factors to perform a comparative classification of SOC contents. It allows farmers and extension services to compare where their measured SOC contents fall within the expected SOC value range for their site, and can thus help develop an initial evaluation of the SOC status of a site with regard to soil-specific differences.
8 citations
TL;DR: In this article , the authors highlight the importance of a holistic approach to soil health assessment and monitoring, which is not only related to soil functional biodiversity but also considers the genetic horizons of the soil profile and not just the topsoil.
Abstract: Maintaining or recovering soil health is becoming a goal of many policies carried out at national, continental and global scales to promote global health. This viewpoint is aimed at stressing the relevance of a holistic approach to soil health assessment and monitoring, which is not only related to soil functional biodiversity but also considers the genetic horizons of the soil profile and not just the topsoil. We highlight that soil health has different connotations depending on the environmental setting and may show high spatial and temporal dynamics. Although the biological activity is often concentrated in the surficial horizon, we report increasing evidence that deep soil horizons host relevant biological communities, which are regulated by soil conditions that are usually different from those present in the topsoil. The processes responsible for the formation of surface and subsurface soil genetic horizons produce soil features that select the presence of organisms. The natural self-organization of soil features is at the basis of the soil classification systems and of their ability to differentiate soil taxa and appreciate pedodiversity. Examples are reported of surface and deep soil genetic horizons as an important interpretative tool of soil functional biodiversity and soil health. Therefore, the assessing and monitoring of soil health should not be carried out at fixed depth, but according to soil genetic horizons. We conclude that the loss of the natural self-organization of genetic horizons is a form of soil health degradation.
8 citations
TL;DR: In this article , the authors compared six different extraction methods for Na, K, and Cl content in plant tissue and found that Na and K concentrations varied little among different methods as compared to the VDLUFA standard method and all extractions resulted in similar tissue Cl concentrations.
Abstract: Background and aims Determination of sodium (Na), potassium (K), and chloride (Cl) content in plant tissue is required for research related to salinity resistance in plants. Standard methods are available to extract these elements from dried plant material, but these methods are often costly, relatively dangerous, or time consuming. Many authors modify extraction methods substantially without proof of comparability across methods. Methods Here, dried tissues of two varieties of rice and three varieties of sweet potato subjected to salt stress were extracted for Na and K using six different extraction methods (1–6) and for Cl using three Cl-free extraction methods (2, 4, 5) for Cl: (1) the VDLUFA standard method, consisting of ashing, and heat extraction in hydrochloric acid (HCl), (2) hot water pressure extraction via autoclave, (3) extraction with 1 M HCl overnight, (4) hot water extraction at 90°C for 1 h, (5) acetic acid extraction in hot 1 M acetic acid for 2 h, and (6) extraction with a microwave using nitric acid. Na and K were determined via flame photometer and Cl via automated flow analysis. Results Na and K concentrations varied little among different extraction methods as compared to the VDLUFA standard method, and for Cl, all extractions resulted in similar tissue Cl concentrations. Conclusions Ultimately, the choice of extraction method depends on the instrumentation and lab equipment necessary, available budget, the available amount of sample, and time constraints which should be decided according to the experiment. For reasons of comparability among publications, methods applied should be clearly described since results vary depending on the method chosen.
7 citations
TL;DR: In this article , the authors aimed at quantifying the random soil organic carbon (SOC) stock error caused by a minimum shift in sampling location of one profile and assessing whether an increase in the number of profile pits to three could significantly decrease the resampling errors caused by spatial variability of relevant parameters.
Abstract: Background Detecting changes in soil organic carbon (SOC) stock requires systematic and random sampling errors to be kept to a minimum. Especially in soil monitoring schemes based on soil profiles pits, it is important to understand if a minimum spatial shift of that profile pit during resampling could render resampling errors caused by spatial variability negligible. Aims We aimed at (1) quantifying the random SOC stock error caused by a minimum shift in sampling location of one profile and (2) assessing whether an increase in the number of profile pits to three could significantly decrease the resampling error caused by spatial variability of the relevant parameters. Methods Eight croplands and grasslands in northeast Germany were sampled. Three sampling designs were compared: one profile resampled (1) by one, (2) by three profiles or (3) three profiles resampled by three. In addition, 16 soil cores were taken per site to characterise overall plot-scale heterogeneity and assess general patterns of spatial dependence of relevant parameters. Results Spatial dependence of all assessed parameters was weak. Accordingly, the resampling of one profile by one induced a high mean absolute error of 5.1 and 7.6 Mg C ha–1 at a 0–30 cm depth for croplands and grasslands (7.5% and 8.5%). This error was reduced by approximately 50% when three profiles were resampled by three profiles. Conclusions Even with the smallest spatial shifts possible, monitoring of SOC stocks relies on replicated resampling to detect management or climate change-induced trends in reasonable and relevant timescales.
5 citations
TL;DR: In this paper , the authors developed a N fertilization approach to reduce the risk of NO3− leaching in field-grown spinach production without adversely affecting crop yield and quality at an early and late harvest stage.
Abstract: Background Spinach is a nitrogen (N) demanding crop with a weekly N uptake of up to 60 kg ha–1. Consequently, a high N supply is required, which can temporarily lead to high quantities of nitrate (NO3–) being at risk of leaching. Aims The objective of this study was to develop a N fertilization approach to reduce the risk of NO3– leaching in field-grown spinach production without adversely affecting crop yield and quality at an early and late harvest stage. Methods Ten fertilization trials were conducted to compare different base fertilization rates and splits of top dressings. For top dressings, granulated fertilizers or foliar sprays were used. In a further treatment, N supply was reduced by withholding the second top dressing of 50–70 kg ha−1. Results Nitrate concentration at risk of leaching was considerably reduced by decreasing the base fertilizer rate as well as by splitting the top dressing. However, at an early harvest stage, total aboveground dry mass was reduced by, on average, 6% by these measures across all seasons. In contrast, at a later harvest stage, spinach was less affected by the fertilizer schedule. Urea foliar sprays proved to be insufficient in promoting plant growth and caused leaf necrosis. A reduced N supply led to impaired plant growth and yellowish leaves in both spring and winter. Conclusions Base N fertilization of spinach is only required in spring, but not in other seasons. Despite slight yield reduction, the top dressing should be split to reduce the risk of NO3− leaching after an early harvest.
5 citations
5 citations
TL;DR: The Askov long-term experiment (LTE) as mentioned in this paper is one of the few LTEs in the world that continued for more than 125 years, and has been used extensively for agricultural field experiments.
Abstract: Long-term agricultural field experiments are essential for quantifying changes in soil properties and associated crop productivity that occur slowly but continue over long periods. Initiated in 1894 in the South of Denmark, the Askov long-term experiment (LTE) is among the few LTEs in the world that continued for more than 125 years. The experiment compares different rates of nitrogen, phosphorus, and potassium applied in mineral fertilizers or animal manure with abundant treatment replicates. With well-managed treatments, detailed yield records, and a soil archive dating back to 1923, today the Askov-LTE represents a unique platform for research not envisioned at the start of experiments. Here, we provide a short description of site characteristics and experimental layout, examples of historic crop yields and changes in soil carbon (C) content. We provide short overviews of some of the studies that have used the Askov-LTE as a research platform. These include crop yield-related research; models simulating changes in soil C; availability of soil P reserves; indicators of biological, chemical, and physical soil quality; and studies related to prehistoric archaeology. Finally, we offer some reflections on long-term field experimentation.
5 citations
TL;DR: In this paper , the authors call for interdisciplinary physical, biological, microbiological, chemical, and applied soil science research with a special focus on biocrusts of managed soils from mesic environments, to better understand their impact on overall ecosystem health and resilience.
Abstract: Biological soil crusts, or “biocrusts”, are biogeochemical hotspots that can significantly influence ecosystem processes in arid environments. Although they can cover large areas, particularly in managed sites with frequent anthropogenic disturbance, their importance in mesic environments is not well understood. As in arid regions, biocrusts in mesic environments can significantly influence nutrient cycling, soil stabilization, and water balance; however, their persistence may differ. We call for interdisciplinary physical, biological, microbiological, chemical, and applied soil science research with a special focus on biocrusts of managed soils from mesic environments, to better understand their impact on overall ecosystem health and resilience, particularly with regard to climate change.
4 citations
TL;DR: In this paper , the dynamics of nitrogen (N), phosphorus (P), and sulfur (S) were studied and how soil water is coupled to the cycling of these elements and related stoichiometric controls across different scales within agroecosystems.
Abstract: Soil water status, which refers to the wetness or dryness of soils, is crucial for the productivity of agroecosystems, as it determines nutrient cycling and uptake physically via transport, biologically via the moisture-dependent activity of soil flora, fauna, and plants, and chemically via specific hydrolyses and redox reactions. Here, we focus on the dynamics of nitrogen (N), phosphorus (P), and sulfur (S) and review how soil water is coupled to the cycling of these elements and related stoichiometric controls across different scales within agroecosystems. These scales span processes at the molecular level, where nutrients and water are consumed, to processes in the soil pore system, within a soil profile and across the landscape. We highlight that with increasing mobility of the nutrients in water, water-based nutrient flux may alleviate or even exacerbate imbalances in nutrient supply within soils, for example, by transport of mobile nutrients towards previously depleted microsites (alleviating imbalances), or by selective loss of mobile nutrients from microsites (increasing imbalances). These imbalances can be modulated by biological activity, especially by fungal hyphae and roots, which contribute to nutrient redistribution within soils, and which are themselves dependent on specific, optimal water availability. At larger scales, such small-scale effects converge with nutrient inputs from atmospheric (wet deposition) or nonlocal sources and with nutrient losses from the soil system towards aquifers. Hence, water acts as a major control in nutrient cycling across scales in agroecosystems and may either exacerbate or remove spatial disparities in the availability of the individual nutrients (N, P, S) required for biological activity.
4 citations
TL;DR: In this paper , the authors used mid-infrared spectroscopy (MIRS) for soil spectral libraries (SSL) and applied it to the European Land Use/Land Cover Area Frame Survey 2009 (LUCAS).
Abstract: Background Mid-infrared spectroscopy (MIRS) is commonly recognized as a rapid and high throughput measurement technology for numerous soil properties, given that appropriate prediction models are calibrated. Soil spectral libraries (SSL) may reduce effort and costs for MIRS practical application. Aims To calibrate MIR-SSL-based prediction models for soil properties and to test their applicability to independent sample sets at regional scale (e.g., for soil survey) and at field scale (i.e., for precision agriculture, PA). Methods Spectra of 1013 arable topsoil samples of the European Land Use/Land Cover Area Frame Survey 2009 (LUCAS) from Belgium, the Netherlands, Luxembourg, and Germany formed the basis for the MIR-SSL. Leave-one-out cross-validation (LOOCV) via partial least squares regression served to calibrate (1) generic prediction models including all samples, and (2) stratified models for different parent materials. Test-set validation (TSV) was conducted on samples from independent campaigns at (1) regional scale with a sample set from Schleswig-Holstein (Germany; n = 385) and (2) field scale for four individual fields in Germany (n = 513). Results Generic LOOCV models successfully predicted soil organic carbon, total nitrogen, sand, silt, clay, carbonate, and pH. Calibration for available nutrients failed. The TSV was successful for the regional sample set for all variables (2.5 ≤ RPIQ ≤ 5.9), except for carbonate (RPIQ = 0). At field scale, the validation was highly variable for different sites and parameters. Stratified models using soil parent material as auxiliary variable improved only occasionally the applicability at field scale, that is, on single fields and only for clay and carbonate. Conclusions Although the MIR-SSL in its present state cannot be recommended for nutrient management, it provides valuable support for soil survey and PA.
TL;DR: In this article , the authors focus on the non-steady-state technique which is widely used for manual measurements but also in automatic systems and share lessons learnt and pass on experiences in order to assist the reader with possible questions or unexpected challenges.
Abstract: Soils represent a major global source and sink of greenhouse gases (GHGs). Many studies of GHG fluxes between soil, plant and atmosphere rely on chamber measurements. Different chamber techniques have been developed over the last decades, each characterised by different requirements and limitations. In this manuscript, we focus on the non-steady-state technique which is widely used for manual measurements but also in automatic systems. Although the measurement method appears very simple, experience gained over the years shows that there are many details which have to be taken into account to obtain reliable measurement results. This manuscript aims to share lessons learnt and pass on experiences in order to assist the reader with possible questions or unexpected challenges, ranging from the planning of the design of studies and chambers to the practical handling of the chambers and the quality assurance of the gas and data analysis. This concise introduction refers to a more extensive Best Practice Guideline initiated by the Working Group Soil Gases (AG Bodengase) of the German Soil Science Society (Deutsche Bodenkundliche Gesellschaft). The intention was to collect and aggregate the expertise of different working groups in the research field. As a compendium, this Best Practice Guideline is intended to help both beginners and experts to meet the practical and theoretical challenges of measuring soil gas fluxes with non-steady-state chamber systems and to improve the quality of the individual flux measurements and thus entire GHG studies by reducing sources of uncertainty and error.
TL;DR: In this paper , the main and interactive effects of N fertilization and bioenergy crop type on central tendencies and spatial heterogeneity of soil moisture, pH, DOC and DON were investigated in switchgrass and gamagrass croplands.
Abstract: Background Soil moisture, pH, dissolved organic carbon and nitrogen (DOC, DON) are important soil biogeochemical properties in switchgrass (SG) and gamagrass (GG) croplands. Yet their spatiotemporal patterns under nitrogen (N) fertilization have not been studied. Aims The objective of this study is to investigate the main and interactive effects of N fertilization and bioenergy crop type on central tendencies and spatial heterogeneity of soil moisture, pH, DOC and DON. Methods Based on a 3-year long fertilization experiment in Middle Tennessee, USA, 288 samples of top horizon soils (0–15 cm) under three fertilization treatments in SG and GG croplands were collected. The fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 in urea) and high N input (HN: 168 kg N ha−1 in urea). Soil moisture, pH, DOC and DON were quantified. And their within-plot variations and spatial distributions were achieved via descriptive and geostatistical methods. Results Relative to NN, LN significantly increased DOC content in SG cropland. LN also elevated within-plot spatial heterogeneity of soil moisture, pH, DOC and DON in both croplands though GG showed more evident spatial heterogeneity than SG. Despite the pronounced patterns described above, great plot to plot variations were also revealed in each treatment. Conclusion This study informs the generally low sensitivity of spatiotemporal responses in soil biogeochemical features to fertilizer amendments in bioenergy croplands. However, the significantly positive responses of DOC under low fertilizer input informed the best practice of optimizing agricultural nutrient amendment.
TL;DR: In this paper , the authors identify the entry pathways of total and specific polyphenols in F. japonica and test whether polyphenol inhibit nitrification with Cu contamination.
Abstract: Background The invasive plant species Fallopia japonica is suspected to use polyphenols as a novel weapon to inhibit nitrification in soil. Both specific polyphenols and their entry pathways are yet to be determined. As plants may increase the production of polyphenols under copper (Cu) stress, an additive effect can be expected in contaminated (riparian) areas. Aims This study aimed to identify the entry pathways of total and specific polyphenols in F. japonica and to test whether polyphenols inhibit nitrification with Cu contamination. Methods Combining F. japonica and a Cu gradient in a 2-year mesocosm experiment, total polyphenol, emodin, and resveratrol concentrations were analyzed in the plant (roots, root exudates, vital and senescent leaves) and soil (rhizosphere, non-rooted soil) representing different entry pathways. We measured the potential nitrification rate (PNR) under stress caused by F. japonica and Cu as well as the response of PNR under resveratrol and emodin addition. Results Emodin and resveratrol were detected in all plant tissues. Emodin concentrations significantly increased in senescent leaves under Cu stress, while no Cu effect was observed for resveratrol or total polyphenols. Resveratrol decreased the PNR. The stressors had neither a synergistic nor additive effect. Nitrification inhibition was lower in the rhizosphere compared to the non-rooted soil, suggesting that F. japonica reduced nitrate availability for co-occurring plants. Conclusions Joint occurrence of F. japonica and Cu did not amplify the PNR inhibition over the individual effect. Our study emphasizes the effectiveness of F. japonica in inhibiting the PNR in invaded riparian ecosystems with potentially negative effects on biodiversity.
TL;DR: In this paper , the authors identify tree species and mycorrhizal association effects on forest floor, topsoil and subsoil organic C and N stocks and vertical distribution and drivers for soil OC and N distribution.
Abstract: Background Forest soils are considered sinks for atmospheric C. Many studies revealed that tree species and their mycorrhizal association affect forest floor and topsoil organic C (OC) and total N, while the knowledge of their effect on subsoil OC and N is still scarce. Aims We aimed to identify (1) tree species and mycorrhizal association effects on forest floor, topsoil (0–30 cm) and subsoil (30–80 cm) OC and N stocks and vertical distribution and (2) drivers for soil OC and N distribution. Methods We sampled forest floor, topsoil and subsoil under Fagus sylvatica L., Quercus robur L., Acer pseudoplatanus L. and Fraxinus excelsior L. in four Danish common garden experiments along a gradient in soil texture and determined OC and N stocks. Results Total N (forest floor + soil) was higher under oak than beech, while total OC was unaffected by species. Forest floor C and N were higher under oak and beech, both ectomycorrhizal species (ECM), compared to under maple and ash, which are both arbuscular mycorrhizal species (AM). Relatively more OC and N were transferred to the topsoil under AM than ECM species, and this could be explained by greater endogeic earthworm biomass in AM species. In contrast, a higher proportion of OC was stored under ECM than AM species in the subsoil, and here OC correlated negatively with anecic earthworms. Subsoil N was highest under oak. Conclusions Tree species and in particular their mycorrhizal association affected the vertical distribution of soil OC and N. Tree species differences in topsoil OC and N were not mirrored in the subsoil, and this highlights the need to address the subsoil in future studies on AM- versus ECM-mediated soil OC and N stocks.
TL;DR: In this paper , the changes in soil organic carbon (SOC), total nitrogen (N) and phosphorus (P) stocks under different gap sizes in the Hyrcanian oriental beech forest were investigated.
Abstract: Background In the Hyrcanian temperate forests, different canopy gaps sizes have been created by logging under silvicultural methods. Understanding the effects of gaps on forest ecosystems can help in the planning and decision-making of forestry practices. Variations in ecological conditions caused by canopy gaps may have an impact on the forest stand, particularly soil nutrients. Aims The purpose of the present research was to investigate the changes in soil organic carbon (SOC), total nitrogen (N) and phosphorus (P) stocks under different gap sizes in the Hyrcanian oriental beech forest. Methods We measured SOC, N and P stocks of soil at the depth of 0–20 cm among 15 artificial gaps along with adjacent closed stand which was created by single-tree selection system in oriental beech stand, northern Iran. In the center and four cardinal positions of the edge of gaps as well as in the four adjacent closed canopy forests at the distance of 20 m from gaps, the soil sampling was performed. Results The difference in C, N and P stocks among the artificial canopy gaps was statistically significant, and higher mean values were observed in large gaps. No significant difference was observed between gaps and adjacent closed stands with regard to soil C, N and P stocks. At artificial gaps and closed stands, the SOC stock was negatively correlated with clay and positively correlated with bulk density, sand, N and OC. With increasing bulk density, sand, N, P, and OC, N stock was increased in gaps. In gaps, SOC and P stocks were both positively related to soil microbial C and soil microbial P, respectively. Conclusion Generally, it can be stated that there are similar relative ecological conditions between artificial gaps and closed stands, and the interaction among soil properties in gaps demonstrates gap dynamics in deciduous, broad-leaved beech forest.
TL;DR: In this article , waste-derived, low water-solubility sources can potentially increase sugarcane's P uptake compared to triple superphosphate by reducing adsorption to the soil.
Abstract: Background The use of highly water-soluble phosphorus (P) fertilizers can lead to P fixation in the soil, reducing fertilization efficiency. Waste-derived, low water-solubility sources can potentially increase sugarcane's P uptake compared to triple superphosphate by reducing adsorption to the soil. Aims We aimed to test struvite, hazenite, and AshDec® for their agronomic potential as recycled fertilizers for sugarcane production in a typical tropical soil. We hypothesize that these sources can reduce P fixation in the soil, increasing its availability and sugarcane's absorption. Methods In a greenhouse pot experiment, two consecutive sugarcane cycles, 90 days each, were conducted in a Ferralsol. The recovered sources struvite, hazenite, AshDec®, and the conventional triple superphosphate were mixed in the soil in three P doses (30, 60, and 90 mg kg–1), aside a control (nil-P). At both harvests, sugarcane number of sprouts, plant height, stem diameter, dry mass yield, shoot phosphorus, and soil P fractionation were investigated. Results At 90 days, struvite and hazenite performed better for dry mass yield (70.7 and 68.3 g pot–1, respectively) than AshDec® and triple superphosphate (59.8 and 57.4 g pot–1, respectively) and for shoot P, with 98.1, 91.6, 75.6, and 66.3 mg pot–1, respectively. At 180 days, struvite outperformed all treatments for dry mass yield (95.3 g pot–1) and AshDec® (75.5 mg pot–1) for shoot P. Struvite was 38% and hazenite 21% more efficient than triple superphosphate in P uptake, while AshDec® was 6% less efficient. Soil had higher labile P under struvite, hazenite, and AshDec® than triple superphosphate by the end of the first cycle, while only the later increased nonlabile P by the end of the experiment (180 days). Conclusions Waste-derived P sources were more efficient in supplying P for sugarcane and delivering labile P in 180 days than triple superphosphate.
TL;DR: In this article , the potential use of inorganic soluble polyphosphates (Poly-P) as slow-release fertilizer under drip fertigation was investigated, and two Poly-P fertilizers, differing in their polymerization rate, were compared to an orthophosphate (Ortho-P), and a treatment without P application (control).
Abstract: Background Phosphorus (P) fertilizer properties and nutrient management strategies substantially affect soil P availability as well as uptake and consequently crop yield. Aims The present study aims to study the potential use of inorganic soluble polyphosphates (Poly-P) as slow-release fertilizer under drip fertigation. Methods A pot experiment was conducted using an alkaline soil. Two Poly-P fertilizers, differing in their polymerization rate (Poly-53 with 53% and Poly-100 with 100% Poly-P of the total-P content), were compared to an orthophosphate (Ortho-P) and a treatment without P application (control) under three drip fertigation frequencies (Fsow: P fertilizer applied at sowing, Fweek: once a week, and F3days: every 3 days). Soil samples were taken at 40 days after sowing and at harvest from 3 layers (0–5, 5–10, and 10–20 cm) to determine P availability in soil (Olsen-P) and its relocation into deeper soil layers. Furthermore, plant growth, yield, P uptake, P use efficiency, as well as water productivity were investigated. Results Soil P availability varied significantly between fertilizer forms and fertigation frequencies. At higher polymerization rate of the Poly-P fertilizer, P becomes less mobile in the soil, but its availability is maintained until harvest. The analysis of Olsen-P at harvest showed that the higher P availability in soil was obtained with Poly-P forms with higher values in the 0–5 and 5–10 cm soil layers than in the 10–20 cm. In addition, weekly fertigation (Fweek) revealed the best results in terms of P availability compared to other P fertigation regimes, and all P fertilizers significantly improved chickpea grain yield, seed quality, and water productivity, compared to the unfertilized control. Conclusion Poly-P fertilizers can be recommended as an effective source of phosphorus for plants, due to their slow-release properties. Using Poly-P, the frequency of P application through the drip fertigation system can be reduced while ensuring high crop yields.
TL;DR: In this article , the authors explored the effect of litter decomposed at different levels on soil N dynamics in the presence of labile carbon and showed that the effects of litter on soil nitrogen transformation might change with the varying status of decomposed litter.
Abstract: Background It is well known that litter releases dissolved organic carbon (DOC), which would impact the role of litter in soil nitrogen (N) transformation. Thus, this study aimed to explore the effect of litters decomposed at different levels on soil N dynamics in the presence of labile carbon. Methods An incubation experiment was carried out with fresh litter (SF), partially decomposed litter (SP) or the combined addition of glucose and alanine in soils for 210 days. The influence of litter addition on soil was investigated by changes of soil soluble organic N, NH4+−N, NO3−−N and microbial biomass N (MBN). Results There was higher soil NH4+−N and NO3−−N in SF, nonetheless lower in SP than control. Litter addition decreased soil dissolved organic N (DON), but increased DOC compared to control. These results suggested that the effects of litter on soil N might change with the varying status of decomposed litter. Alanine addition increased each soil N form, which was more of DON and less of MBN in SP than SF. After adding amino acids, the priming amount of DON was computed positive at 0.5 day with the highest soil MBN, simultaneously. Moreover, the net N transformation rate preceded the gross rate. Glucose addition also improved soil NH4+−N and DON more in SP than SF, while lessened MBN in SF than SP. These results indicated that the differential effect of labile C sources, alanine and glucose, on soil N might be related to the chemistry of the differently decomposed litter. As a labile C source, glucose had a lesser effect on soil N than alanine. Conclusions Our findings highlighted the coexistence of litters at varied decomposition status and C sources released from litters, which are contributed to the N dynamics in soil and are critical for the ecological functioning of the degraded litter.
TL;DR: In this article , a single biochar (BC) application of 72 t ha−1, significantly higher N2 fluxes were measured from BC-treated soil using the helium gas flow soil core method compared with the control.
Abstract: Four years after a single biochar (BC) application of 72 t ha−1, significantly higher N2 fluxes were measured from BC-treated soil using the helium gas flow soil core method compared with the control. Nitrous oxide was below the detection limit. Soil moisture and temperature significantly affected N2 fluxes, which were highest at 70% water-filled pore space and 5°C. The BC-treated soil was characterized by higher organic C and NO3–N concentrations and a wider C/N ratio of the microbial biomass.
TL;DR: In this article , the unique Raman signature of each pure calcium phosphate species was determined by confocal μ-Raman spectroscopy and used subsequently as a reference spectrum to identify the compound in each soil matrix.
Abstract: Background Raman spectroscopy is a promising but largely underexplored tool for the detection of phosphates (P) in soil. Although it requires minimal sample preparation, it has been demonstrated mainly in test matrices or substrates to circumvent the typical signal interference caused by fluorescence of organic matter in actual agricultural soils. Aims The aim of this study was to highlight the Raman spectroscopic detection and identification of distinct calcium phosphate species amended in contrasting soil matrices—including a real arable soil. Methods Pure calcium dihydrogen phosphate [Ca(H2PO4)2·H2O], calcium hydrogen phosphate (CaHPO4), and β-tricalcium phosphate [β-Ca3(PO4)2] were each amended in Luvos® healing earth, loess from a C-horizon, and a loam arable soil from an Ap-horizon at a dose of 1 mmol (10 g soil)–1. The unique Raman signature of each pure calcium phosphate species was determined by confocal μ-Raman spectroscopy and used subsequently as a reference spectrum to identify the compound in each soil matrix. Controls without added P were also analyzed. Results Ca(H2PO4)2·H2O, CaHPO4, and β-Ca3(PO4)2 were each unambiguously detected in the treated soils. Native hydroxyapatite [Ca5(PO4)3(OH)], quartz (SiO2), feldspar (NaAlSi3O8), calcite (CaCO3), and dolomite [CaMg(CO3)2] were also identified, for example, in the Raman microscopic image of the control Luvos® healing earth sample. Intrinsic β-Ca3(PO4)2 and Ca5(PO4)3(OH) present in Ap-horizon loam were detected and distinguished from each other by a Lorentzian fitting, which deconvoluted the individual Raman signals from an unresolved peak. Conclusions The usefulness of confocal μ-Raman spectroscopy to detect distinct P species present in agricultural soil could be shown as a proof of concept.
TL;DR: In this paper , an improved profile probe for model-based soil gas flux analyses that allows in situ monitoring of soil CO2 profiles with high temporal resolution, including non-diffusive transport processes, including soil-atmosphere CO2 flux, and soil respiration profiles.
Abstract: Background Gas exchange between soil and atmosphere is of great importance for greenhouse gas cycles. As gas transport in soil is generally dominated by diffusion, the soil gas diffusion coefficient (DS) is crucial to understand fluxes between soil and atmosphere. Estimating DS is still a great source of uncertainty when calculating soil gas fluxes such as soil respiration from soil gas profiles. In situ measurement of the effective exchange coefficient (Deff) not only reduces this uncertainty, but also allows to quantify non-diffusive transport processes in addition to the purely diffusive exchange (DS), which cannot be investigated by laboratory measurements or the application of soil gas diffusivity models. Even though several methods for in situ Deff measurement exist, they often lack in the temporal resolution to identify short-term effects on Deff or require laborious set-ups, which makes them unsuitable for a fast and mobile application. Aims Our objective was to test an improved profile probe for model-based soil gas flux analyses that allows in situ monitoring of (1) soil CO2 profiles with high temporal resolution, (2) soil gas transport coefficients, including non-diffusive transport processes, (3) soil–atmosphere CO2 flux, and (4) soil respiration profiles. Methods We developed a CO2 profile probe with build-in sensors that can easily be installed in soil to gain continuous CO2 concentration profiles. The probe includes the option to inject CO2 as a tracer gas to estimate Deff. To account for changes in natural CO2 concentrations in the soil, we tested two approaches: firstly, a differential approach using two probes, an injection probe and a reference probe, and secondly, a stand-alone approach in which changes in natural CO2 concentrations are estimated by a statistical model using its main environmental drivers. The resulting tracer gas profiles were used to fit a finite element gas diffusion model to derive Deff. Using the derived Deff values and the CO2 profiles allowed calculating CO2 fluxes. The approach was tested with controlled laboratory experiments using different mineral substrates to compare the diffusivity estimates of the in situ method with laboratory measurements on soil cores. Additional laboratory experiments included artificial CO2 sources to simulate soil respiration in order to evaluate the gradient-based estimation of soil respiration profiles. In a second step, both approaches were tested under natural conditions in the field. Results The derived Deff values agreed well with laboratory measurements of DS and DS-transfer functions. The artificial CO2 sources could accurately be estimated with the gradient method. In the field under calm conditions, both approaches for the estimation of the changing natural CO2 profile gave comparable results. Under windy conditions, the stand-alone approach gave unrealistically high values, whereas the differential approach using a reference profile still gave reliable results. We observed a clear relationship between Deff and wind-induced pressure pumping in the topsoil. The estimated surface CO2 efflux agreed well with chamber measurements. Conclusions This new set-up enables monitoring of diffusive and non-diffusive soil gas exchange and soil respiration in situ with high resolution and relatively low effort.
TL;DR: In this article , the authors examined the effect of elevated CO2 on the critical concentrations of soil available P and shoot P for plant growth in soils with contrasting P-sorption capacities.
Abstract: Background Rising atmospheric CO2 concentrations can increase crop yields; however, it is poorly understood if plants require higher phosphorus (P) inputs to support increased production. In addition, soils with contrasting P-sorption capacities may alter plant response to elevated CO2. Aims We examined the effect of elevated CO2 on the critical concentrations of soil available P and shoot P for plant growth in soils with contrasting P-sorption capacities. Methods Response curves to P applications were generated for wheat (Triticum aestivum L.) grown in a low P-sorption Sodosol and a high P-sorption Ferrosol. Plants were grown for 5 weeks under ambient (400 ppm) and elevated (800 ppm) CO2 concentrations at nine P application rates. The concentrations of plant P and soil P extracted using Olsen, Bray and Resin methods were analysed. Results Elevated CO2 increased biomass production in both soils. Plants grown in the Ferrosol but not in the Sodosol required higher P inputs to achieve maximum biomass production in response to elevated CO2. Elevated CO2 increased the critical Olsen-P but decreased the critical Bray-P concentrations for shoot biomass production in the Ferrosol. Elevated CO2 decreased the critical P concentration in shoots of plants grown in the Sodosol but not in the Ferrosol. Conclusions The effect of P fertilisation on plant response to elevated CO2 depends on soil type. Elevated CO2 also potentially alters P acquisition mechanisms of plants, which requires adjustment of the critical P concentration in shoot and in soil depending on soil P-sorption capacity and the analytical method used to assess P availability.
TL;DR: In this paper , an in-vivo application of the auxin indole-3-acetic acid (IAA) to maize plants at flowering led to an improved hexose uptake and finally to a better kernel set.
Abstract: Background The kernel number of maize (Zea mays L.) at maturity is mainly determined at the time around pollination. Kernel abortion frequently occurs during this period, leading to grain yield depressions. Plasma membrane (PM) H+-ATPase was identified as a key enzyme responsible for supply of assimilates to the developing maize kernels shortly after pollination. Aims This study aimed at stimulating PM H+-ATPase activity in the kernels by in vivo application of the auxin indole-3-acetic acid (IAA) to maize plants at flowering, leading to an improved hexose uptake and finally to a better kernel set. Methods Maize plants were cultivated under well-watered conditions using the container technique. IAA was applied to unstressed maize plants twice, 2 days before controlled pollination and at pollination (application rate per plant: 1.9 mL of 1.5 mM IAA). The developing kernels were harvested 2 days after pollination, and PM vesicles were isolated and purified using two-phase partitioning. Results The in vitro hydrolytic activity of the PM H+-ATPase was significantly stimulated by 22% due to in vivo IAA application (control: 0.99 ± 0.05, IAA treatment: 1.21 ± 0.03* μmol inorganic phosphate mg–1 protein min–1). Vmax was significantly increased by IAA treatment, whereas Km was reduced. The maximal pH gradient (ΔA492) at the PM was increased by 10% (control: 0.071 ± 0.002, IAA treatment: 0.078 ± 0.002*). IAA caused a significant increase of PM H+-ATPase abundance in the vesicles. Concentrations of sucrose and hexoses as well as acid invertase activity in the kernels were unaffected by IAA treatment. However, at maturity kernel numbers per cob were significantly decreased causing grain yield reductions of 19%. Conclusions Increased PM H+-ATPase activity could not be translated into grain yield improvements. Probably the auxin application occurred too early during kernel development. As cytokinins play a key role during pollination, auxin application at this stage may have disturbed the phytohormone balance, causing disruption of cell division and a rather early onset of cell extension due to increased IAA concentrations. In further studies, it should be tested if applications of cytokinin at flowering or of IAA at a later growth stage have positive impacts on kernel set.
TL;DR: In this article , the authors investigated how the size of biochar and organic fertilizers interactively influence N2O emission from a tropical vertisol, using pigeon pea (Cajanus cajan) stalks and further processed to obtain two size fractions (<0.25 mm or 0.00 mm).
Abstract: Background Nitrous oxide (N2O) emission from agriculture is increasing alarmingly due to intensive application of inorganic and organic fertilizers. Recently, biochar has been identified as a promising additive to improve agriculture by enhancing soil function and mitigate greenhouse gas emission. However, it is unclear how biochar of different size fractions influences N2O emission from agricultural soil. Aims The current experiment aims to understand how the size of biochar (BC) and organic fertilizers interactively influence N2O emission from a tropical vertisol. Methods BC was prepared using pigeon pea (Cajanus cajan) stalks and further processed to obtain two size fractions (<0.25 mm or 0.25–2.00 mm). Organic fertilizers (vermicompost [VC], poultry manure [PM], or farmyard manure [FYM]) and BC were added to soil to evaluate N2O emission potential. BC was added to soil at 10% (w/w), whereas the organic fertilizers were added at 80 kg N ha–1. Emission of CO2 and the abundance of 16S rRNA and amoA gene copies were estimated after incubation period. The interactive effect of BC size fractions and organic fertilizers were statistically evaluated. Results Both BC and organic fertilizers stimulated N2O emission in soil. BC of larger size stimulated N2O emission (µg N2O produced g–1 soil d–1) more than smaller size. Of the three organic fertilizers, PM resulted highest N2O (0.380) emission followed by FYM (0.240) and VC (0.210). BC (0.25 mm) + PM produced least N2O. Abundance of heterotrophic bacterial 16S rRNA gene copies and ammonia-oxidizing bacterial (AOB) amoA gene copies were highest in PM + BC and lowest in control. Significant relation (p < 0.0001) existed among N2O emission, CO2 emission, and microbial abundance. Conclusions BC of small size fraction along with organic fertilizers can be an effective strategy to mitigate N2O emission from tropical vertisol.
TL;DR: In this paper , the authors investigate patterns of microbial properties and their controls to understand whether they differ between soils derived from geochemically contrasting parent material in tropical montane forests, and they conclude that parent material is an important driver of microbial property.
Abstract: Background Soil microbes are key drivers of carbon (C) and nutrient cycling in terrestrial ecosystems, and their properties are influenced by the relationship between resource demand and availability. Aims Our objective was to investigate patterns of microbial properties and their controls to understand whether they differ between soils derived from geochemically contrasting parent material in tropical montane forests. Methods We measured microbial biomass C (MBCSoil), potential extracellular enzyme activity (pEEA), and assessed microbial investments in C and nutrient acquisition at the beginning and end of a 120-day laboratory incubation experiment using soils developed from three geochemically contrasting parent material (i.e., mafic, mixed sediment, and felsic) and three soil depths (0–70 cm). Results We found that MBCSoil and pEEA were highest in soils developed from the mafic parent material. Microbial investment in C acquisition was highest in soils developed from mixed sedimentary rocks and lowest in soils developed from the felsic parent material. We propose that our findings are related to the strength of contrasting mineral-related C stabilization mechanisms and varying C quality. No predominant microbial investment in nitrogen (N) acquisition was observed, whereas investment in phosphorus (P) acquisition was highest in subsoils. We found lower microbial investment in C acquisition in subsoils indicating relatively high C availability, and that microbes in subsoils can substantially participate in C cycling and limit C storage if moisture and oxygen conditions are suitable. Geochemical soil properties and substrate quality were important controls on MBCSoil per unit soil organic C (MBCSOC), particularly after the exhaustion of labile and fast cycling C, that is, at the end of the incubation. Conclusion Although a laboratory incubation experiment cannot reflect real-world conditions, it allowed us to understand how soil properties affect microbial properties. We conclude that parent material is an important driver of microbial properties in tropical montane forests despite the advanced weathering degree of soils.
TL;DR: In this article , a model-based approach for estimating indirect N2O emissions through NO3− leaching and runoff from agricultural soils for use in Germany's national GHG inventory is presented.
Abstract: Background Conversion of leached and runoff nitrate (NO3–) from agricultural land into emissions of the greenhouse gas (GHG) nitrous oxide (N2O) by denitrification in water bodies has to be reported in national GHG inventories. The global IPCC default methodology for estimating these indirect N2O emissions assumes that a fixed fraction of nitrogen (N) inputs (Fracleach) is lost through leaching and runoff. However, this method does not consider all relevant country-specific conditions that may influence NO3– leaching. Aims The aim of this study was to apply a model-based approach for estimating indirect N2O emissions through NO3– leaching and runoff from agricultural soils for use in Germany's national GHG inventory. Methods High-resolution spatial data and a comprehensive model system (RAUMIS-mGROWA-DENUZ) were used to derive regionally differentiated and temporarily dynamic Fracleach values from N surplus and hydrogeological conditions. These were then used to estimate indirect N2O emissions in accordance with the IPCC methodology. Results The nationwide average of the new implied Fracleach values was 0.099 kg N (kg N input)−1 in 2019. The new estimate of indirect N2O emissions was 10.4 Gg N2O in 1990 and 5.7 Gg N2O in 2019, which are 27 and 52% less than the calculation based on the 2006 IPCC Tier 1 methodology. Conclusions The model-based method for estimating Fracleach incorporates relevant factors that influence NO3– leaching and runoff and considers site-specific, spatially varying conditions and differences in the agrarian structure. The use of N surplus as the model driver allows annual changes in cropping conditions and the effects of N-regulating policies and mitigation measures to be represented.
TL;DR: Zhang et al. as mentioned in this paper evaluated the direct effects of environmental factors in shaping prokaryotic communities under three natural contiguous areas (severe saline-alkaline field with no vegetation, moderate and mildly salinealkaline fields with Suaeda glauca, and mild and moderate saline-alkaline field fields with natural grass vegetation) on the Songnen plain in northeast China.
Abstract: Background The Songnen Plain in northeast China was one of three major grasslands in China and has now become one of the most concentrated areas of sodic-saline soil worldwide due to soil parent material characteristics, hydrological conditions, and overgrazing. Aims The aim of this study was to evaluate the direct effects of environmental factors in shaping prokaryotic communities under three natural contiguous areas (severe saline-alkaline field with no vegetation, moderate saline-alkaline field with Suaeda glauca, and mildly saline-alkaline field with natural grass vegetation) on the Songnen Plain in northeast China. Methods Physicochemical properties of the soil pH, electric conductivity (EC), and soil organic carbon (SOC) were determined in three soil types with or without vegetation, while the metabarcoding analysis of the prokaryotic diversity and composition were analyzed by Illumina Miseq sequencing. Results Our study revealed that the moderate and mildly saline-alkaline soil exhibited lower pH by 0.614% and 10.17%, and significantly lower EC by 47.96% and 89.22%, respectively, in comparison to severe saline-alkaline field soil. Prokaryotic 16S rRNA gene amplicon analysis revealed that mildly saline-alkaline soil with native grasses had significantly higher alpha-diversity. The composition of the prokaryotic community was highly correlated with the soil physicochemical properties, but the SOC was the most important driving forces for the prokaryotic composition. Random matrix theory (RMT) network analysis revealed the keystone operational taxonomic unit (OTU) (OTU3096, OTU137, OTU3198 and OTU2210) that was significantly affected by the soil physicochemical properties in the three contiguous areas. Conclusions Collectively, these findings demonstrate that the mildly saline-alkaline soil with natural grass vegetation has a beneficial impact on the soil physical properties and prokaryotic community relative to severe saline areas in the Songnen Plain of northeast China.
TL;DR: In this article , the effect of 2-week waterlogging at the end of tillering stage (Feekes Stage 6) and ear emergence stage (feekes stage 10.1) on grain yield, yield components, S-uptake and its partitioning, and composition of grain storage proteins (glutenins and gliadins) of hybrid (Hyvento) and inbred (Kredo) winter wheat varieties were evaluated.
Abstract: Background Waterlogging at early and later growth stages could affect sulfur (S) uptake, distribution, yield, and quality of winter wheat. We hypothesized that the hybrid winter wheat variety (Hyvento), with a high degree of heterosis and genetic diversity, is likely to uptake and utilize S more efficiently and withstands waterlogging better than the inbred wheat variety (Kredo). Aims The objective of the present study was to investigate the effect of 2-week waterlogging at the end of tillering stage (Feekes Stage 6) and/or ear emergence stage (Feekes Stage 10.1) on grain yield, yield components, S-uptake and its partitioning, and composition of grain storage proteins (glutenins and gliadins) of hybrid (Hyvento) and inbred (Kredo) winter wheat varieties. Methods Plants were grown in large containers (120 L) in a semi-controlled greenhouse and harvested three times immediately after each waterlogging treatment and at agronomic maturity. Grain yield, S concentration in different plant organs, total protein content, and patterns of gluten proteins (gliadin and glutenin) and their subunits (by sodium dodecyl sulfate–polyacrylamide gel electrophoresis) in grains were evaluated. Results Grain yield of the inbred variety was more negatively affected under early and late waterlogging than the hybrid variety and was associated with reduced grain size. The decline in grain yield was significantly higher under late waterlogging (30%–31%) than early waterlogging (17%–18%). Compared to the hybrid variety Hyvento, the waterlogging-induced decline in S concentration in grains, husk, and straw was markedly lower in the inbred variety Kredo. While early waterlogging did not affect total grain protein content in either of the varieties, late waterlogging significantly reduced the total grain protein content (18%) in the inbred variety Kredo. Similarly, the grain gliadin content of the hybrid variety was not affected by both waterlogged conditions, whereas 32% and 23% reductions were recorded for the inbred variety under early and late waterlogging, respectively. Nevertheless, waterlogging significantly increased the proportion of S-poor high-molecular-weight glutenin subunits and ω-gliadin in the inbred variety. Conclusion It could be inferred from the present study that hybrid winter wheat variety is relatively resistant to waterlogging than the inbred wheat variety, and thereby produces higher grain yield. Efficient uptake and metabolism of S could be one of the mechanisms conferring waterlogging resistance in winter wheat.