Long-term Field Experiment Research Articles

Enhanced seed yield of full-season soybean when rotated with cereals and cover crops as compared to monoculture in a long-term experiment

Soybeans are of great importance to the global economy, but the cultivation as monoculture has shown several negative environmental implications in the long-term. Long-term studies demonstrate the cumulative effects of rotations on soil variables, but few studies have considered changes during consecutive years in a time series of soybean as a monoculture. The inclusion of cereals and cover crops in rotation with soybean increases the intensification sequence index (ISI, time with crops actively growing during the year) and increases in soybean yield are expected. In line with this, some studies suggest that only including a winter cover crop will increase ISI and raise production. However, these comparisons have not been made in the long term. The objectives of this work were to: i) compare the evolution of full-season soybean yield and production when sowed as monoculture and in cropping sequences that include cereal crops and cover crops, and ii) quantify a yield gap in full-season soybean due to monoculture by evaluating the long-term residual effect of crop sequences with different land occupation. Soybean yield time series in a 14-years period in rotation or as monoculture were studied in a long-term field experiment under no-tillage established in 2006 in the Northern Pampas region of Argentina. Rotations consisted in sequences that included soybean (S), maize (M) and wheat (W), and also incorporated wheat as a winter cover crop (CC): S-S, CC/S-CC/S, S-W/S-M, CC/S-W/S-M, M-W/S, and CC/M-W/S, with ISI values of 0.39, 0.69, 0.55, 0.64, 0.65 and 0.80, respectively. In 2021/22 season, full-season soybean was planted in all plots as a "test" crop, to evaluate the long-term residual effect of sequences with different intensification indexes. Seed yield averaged 3249 kg ha−1 among years. During the 14 years under study, seed yield in S-W/S-M surpassed S-S by 28 % in 6 out of 14 years. The differences between S-S with respect to this sequence were observed consistently from the ninth crop season (i.e. since 2017/18). The inclusion of a cover crop within a soybean monoculture (i.e. CC/S-CC/S) showed similar seed yields as in S-S in 11 out of 14 years. The analysis of the test crop showed yield-gaps when soybeans were grown as monoculture (seed yield in rotations minus seed yield in S-S) of 9, 20, 27, 21 and 31 % for CC/S-CC/S, S-W/S-M, CC/S-W/S-M, M-W/S and CC/M-W/S, respectively. In summary, soybean in rotation with cereals showed an average increase of ca. 346 kg ha−1 and including a cover crop within a soybean monoculture did not increase seed yield at the levels observed when rotated with cereals. Finally, when estimating seed yield-gaps in soybean, it is important to set in which rotation soybean is placed, since a higher maximum yield is expected to happen when soybean follows a more intensified rotation.

Soil viral–host interactions regulate microplastic-dependent carbon storage

Microplastic is globally regarded as an important factor impacting biogeochemical cycles, yet our understanding of such influences is limited by the uncertainties of intricate microbial processes. By multiomics analysis, coupled with soil chemodiversity characterization and microbial carbon use efficiency (CUE), we investigated how microbial responses to microplastics impacted soil carbon cycling in a long-term field experiment. We showed that biodegradable microplastics promoted soil organic carbon accrual by an average of 2.47%, while nondegradable microplastics inhibited it by 17.4%, as a consequence of the virus-bacteria coadaptations to the microplastics disturbance. In the relevant functional pathways, nondegradable microplastics significantly (P < 0.05) enhanced the abundance and transcriptional activity related to complex carbohydrate metabolism, whereas biodegradable microplastics significantly (P < 0.05) promoted functions involved in amino acid metabolism and glycolysis. Accordingly, viral lysis enhanced in nondegradable microplastics treatments to introduce more complex organic compounds to soil dissolved organic matters, thus benefiting the oligotrophs with high carbon metabolic capabilities in exploitation competition. In contrast, biodegradable microplastics enriched viral auxiliary metabolic genes of carbon metabolism through "piggyback-the-winner" strategy, conferring to dominant copiotrophs, enhanced substrate utilization capabilities. These virus-host interactions were also demonstrated in the corresponding soil plastisphere, which would alter microbial resource allocation and metabolism via CUE, affecting carbon storage consequently. Overall, our results underscore the importance of viral-host interactions in understanding the microplastics-dependent carbon storage in the soil ecosystem.

Impacts of long-term different fertilization regimes on microbial utilization of straw-derived carbon in greenhouse vegetable soils: insights from its ecophysiological roles and temperature responses

As the largest organic carbon input in the agroecosystems, crop residues can increase soil carbon sequestration and crop production in greenhouse vegetable fields (GVFs). However, the soil microbiological mechanisms driving straw decomposition in GVFs under different incubation temperatures and fertilization treatments are not clear. Thus, soil samples were collected from a long-term field experiment included chemical fertilizer application alone (CF), 2/4 fertilizer N+2/4 organic fertilizer N (CM), 2/4 fertilizer N+1/4 organic fertilizer N+1/4 straw N (CMS), 2/4 fertilizer N+2/4 straw N (CS), and incubated with 13C-labeled straw at different temperatures (15, 25, and 35°C) for 60 days. Organic-amended treatments (CM, CMS, and CS), especially CMS treatment, increased soil bacterial Alpha diversity before and after straw addition. Straw decomposition process was dominated by soil Proteobacteria, Actinobacteria, and Firmicutes for each treatments. The effect of incubation temperature on soil microbial community composition was higher than that of fertilization treatments. Soil Alphaproteobacteria and Actinomycetia were the most predominant class involved in straw decomposition. Gammaproteobacteria (Pseudomonas, Steroidobacter, Acidibacter, and Arenimonas) were the unique and predominant class involved in straw decomposition at medium and high temperatures as well as in the straw-amended treatments. Organic-amended treatments, especially straw-amended treatments, increased the relative abundance of glycosyl transferases (GT) and auxiliary activities (AA). Alphaproteobacteria, Actinomycetia, and Gammaproteobacteria had higher relative contribution to carbohydrase genes. In summary, the long-term organic-amended treatments altered the structure of soil microbial communities and increased soil bacterial diversity, with the CMS having a greater potential to enhance resistance to external environmental changes. Soil Alphaproteobacteria and Actinomycetia were responsible for the dominance of straw decomposition, and Gammaproteobacteria may be responsible for the acceleration of straw decomposition. Fertilization treatments promote straw decomposition by increasing the abundance of indicator bacterial groups involved in straw decomposition, which is important for isolating key microbial species involved in straw decomposition under global warming.

The Jyndevad Experiment: Revealing long-term interactions between liming and phosphorus fertilization in a coarse sand soil

The Jyndevad field experiment, initiated in 1942 on a coarse sand soil in South of Denmark, explores the effect of four liming levels (0, 4, 8 and 12 Mg lime ha−1). These were in 1944 combined with two levels of mineral phosphorus (P) fertilizer (0 and 15.6 kg P ha−1 year−1), with or without a high initial dose of 156 kg mineral P ha−1. This study assesses interactions between liming and P fertilization on soil pH, Olsen-P contents and barley yields covering the last three decades. Annual P application improved barley yield regardless of liming, but the optimal liming level differed from year to year. This emphasizes the need for long-term field experiments to detect the complex interactions between liming and P availability on crop performance. The initial high P dose in 1944 and annual P fertilization increased Olsen-P contents in soil. The unlimed soil with pH(CaCl2) values below 4 had the highest Olsen-P content. The Jyndevad Experiment now harbors wide gradients in soil P (Olsen-P contents: 9–82 mg P kg−1 soil) and pH (3.6–6.9), providing a unique research platform for future studies on interactions between liming and P fertilization on coarse sand soils. We present a selection of studies that have used the Jyndevad Experiment to illustrate the research potential of the experiment.

Performance of different wheat varieties and their associated microbiome under contrasting tillage and fertilization intensities: Insights from a Swiss long-term field experiment

Winter wheat is an important global cereal crop. However, conventional farming practices, characterised by intensive tillage and high fertilizer inputs, pose significant threats to the environment. In response, more conservative management practices are being applied aiming to maintain wheat production while promoting a beneficial microbiome. Here, we evaluated the suitability of three different wheat varieties for less intensive agricultural systems, focusing on reduced tillage and fertilizer intensity. The study was conducted over two consecutive years in a Swiss long-term field experiment comparing conventional versus reduced tillage and full fertilization versus half fertilization. In addition, we investigated the composition of plant-associated microbial communities using amplicon sequencing of phylogenetic marker genes, specifically targeting bacteria and fungi in rhizosphere samples and fungi in root samples. Our results revealed that in our study wheat variety most strongly predicted grain yield and quality, independent of tillage and fertilization intensity. Specifically, wheat varieties demonstrated higher yields and N uptake in plots subjected to conventional ploughing and full fertilization compared to those under reduced tillage and half fertilization. We found no significant effect of wheat variety on the composition of microbial communities. However, tillage emerged as the primary factor influencing microbial community composition in the rhizosphere, while fertilization intensity significantly impacted fungal communities in the root system. These findings underscore the complex interplay between agronomic practices, plant genetics, and microbial dynamics in agroecosystems, emphasizing the need for holistic and adaptive approaches and their further development to ensure sustainable crop production.

Long-term experiments to identify response patterns of available soil nitrogen, rice, and soybeans to rice straw compost in a paddy-upland rotation field in Akita, Japan

ABSTRACT Compost application can enhance soil fertility and is consequently presumed to increase crop production in Japan’s paddy-upland rotation fields. This study aimed to evaluate the effects of rice straw compost (RSC) application on available soil nitrogen (Av-N) levels and rice and soybean plants in a paddy-upland rotation field using data obtained from a long-term field experiment. Data collected between 2005 and 2020 were analyzed from a long-term paddy rice – upland soybean rotation field. The experimental design employed a split-plot arrangement, with RSC application (with and without RSC) representing the whole plot, N fertilizer application (no nitrogen vs. standard fertilizer) representing the split-plot, and years representing the replication factor. The datasets included eight years of rice and soybean cultivation, and the chemical properties of postharvest soil spanned 16 years. The data was analyzed via analysis of variance. Applying RSC increased the Av-N concentration significantly by 63%–67%. The RSC application significantly increased the N concentration in rice shoots at the mature stage by 8%–12% but decreased it in soybean shoots after the seed emergence stage by 4%–8%. Consequently, the rice yield displayed clear responses to RSC application, whereas the soybean yield did not. The lack of soybean yield response might be due to an inhibitory effect of the Av-N gain attributable to the RSC application on biological nitrogen fixation. While applying compost can enhance Av-N content as well as rice productivity in paddy-upland rotation fields, its impact on soybean productivity requires careful evaluation.

Response of soil nitrogen mineralization, nitrification and denitrification to milk vetch (Astragalus sinicus L.) application in a paddy field

We conducted incubation experiments with a paddy soil collected from a long-term field experiment to explore the effect of Chinese milk vetch (Astragalus sinicus L., CMV) application on potential nitrogen (N) denitrification (PDA), nitrification (PNA), mineralization (PNM), soil chemical properties, microbial communities, enzyme activities, yields and nutrient uptake of rice under different fertilization treatments. Five treatments were included: no chemical fertilizers (C0), chemical fertilizers (C100), Chinese milk vetch (M), CMV combined with 100% chemical fertilizers (MC100) and with 80% chemical fertilizers (MC80). Results showed that the M, MC100, and MC80 treatments significantly increased PNM and PNA compared with the C100 treatment (P &lt; 0.05). Meanwhile, the CMV application significantly increased total N, microbial biomass N, and carbon (C) concentrations, the abundances of the bacterial phylum Actinobacteria, and the genera Bradyrhizobium, Mycobacterium, Streptomyces and Reyranella, N-acetyl-glucosaminidase (NAG) activity, yields and N nutrient uptake of rice grain compared with the C100 treatment (P &lt; 0.05). Correlation analyses indicated that grain yield and N uptake of rice, soil total N, microbial biomass C and N, the bacterial phylum Actinobacteria, the genera Bradyrhizobium, Mycobacterium, Streptomyces, Reyranella, and NAG were significantly correlated with PNM under different fertilization regimes, while microbial biomass C and N, Actinobacteria, Bradyrhizobium, and Reyranella were positively related to PNA (P &lt; 0.05). Together, the application of CMV alone or in combination with chemical fertilizers can improve soil properties and rice growth, which may accelerate N mineralization and nitrification in this soil.

Impacts of nitrogen (N), phosphorus (P), and potassium (K) fertilizers on maize yields, nutrient use efficiency, and soil nutrient balance: Insights from a long-term diverse NPK omission experiment in the North China Plain

Context or problemSoil nutrient deficiency is one of the significant challenges in grain production, particularly nitrogen (N), phosphorus (P), and potassium (K). These deficiencies not only reduce crop yields but also cause associated environmental issues, such as soil structure deterioration and ecosystem services diminution. ObjectivesThis research aimed to investigate the long-term effects of NPK fertilizers on soil nutrient properties and maize phenology, further on the grain yield, and to evaluate the nutrient use efficiency and soil nutrient balance under different fertilization managements. MethodsA long-term field experiment was initiated in 1990 in a summer maize field in the North China Plain, including five fertilizer treatments: CK (control), NP, NK, PK, and NPK. The soil nutrient properties, maize yields, crop nutrient uptake amount, nutrient recovery efficiency (NRE), nutrient harvest index (NHI), and soil nutrient balance were annually evaluated from 2005 to 2022. ResultsSignificant improvements in maize yields were found under NPK (9081 kg ha−1), NP (6426 kg ha−1), and PK (2668 kg ha−1) compared with CK (1809 kg ha−1) and NK (1656 kg ha−1). The yield increase was mainly attributed to: (1) enhancing in soil nutrient properties, such as soil organic carbon, soil total N (TN), available N (AN), total P (TP), available P (AP), and available K (AK), and (2) the shortened vegetative period, leading to greater sunshine hours (SH) and accumulative growing degree days (GDD) during the reproductive period. Furthermore, a random forest analysis quantified their importance to grain yield, showing that the edaphic factors (mainly SOC, TN, AK, AN, TP, AP, C:N, and N:P) explained a much greater proportion of yield variation compared with phenological factors (mainly GDD during tasseling and physiological maturity stages, and SH during tasseling stage). Additionally, the significantly higher response ratio of both N and P to NRE and NHI implied that N and P fertilizers having a more pronounced impact on improving nutrient use efficiency than K fertilizer. In terms of soil nutrient balance, a most relative soil nutrient balance was detected under NPK treatment, avoiding either substantial nutrient depletion or accumulation under any nutrient deficiency conditions. ConclusionsSoil deficiencies in N and P had more severe impacts on maize yields and nutrient use efficiency compared with K deficiency. Additionally, a balanced NPK fertilizer regime effectively managed soil nutrient balance. Implications or significanceThese findings elucidate the roles of N, P, and K fertilizers in maize production and soil nutrient conditions from a long-term field experiment, which could provide valuable insights for optimizing fertilization management strategies.

Biological and experimental factors that define the effectiveness of microbial inoculation on plant traits: a meta-analysis

Abstract Bacterial and fungal microbiomes associated with plants can significantly affect the host’s phenotype. Inoculating plants with one or multiple bacterial and fungal species can affect specific plant traits, which is exploited in attempts to increase plant performance and stress tolerance by microbiome engineering. Currently, we lack a comprehensive synthesis on the generality of these effects related to different biological (e.g., plant models, plant traits, and microbial taxa) and experimental factors. In a meta-analysis, we showed that the plant trait under consideration and the microbial taxa used to inoculate plants significantly influenced the strength of the effect size. In a methodological context, experiments under sterilized conditions and short-term periods resulted in larger positive effects on plant traits than those of unsterilized and long-term experiments. We recommend that future studies should not only consider (short-term) lab experiments with sterilized plants and single inoculants but also and more often (long-term) field or greenhouse experiments with naturally occurring microbial communities associated with the plants and inoculated consortia including both bacteria and fungi.

Gains in soil carbon storage under anthropogenic nitrogen deposition are rapidly lost following its cessation.

In the Northern Hemisphere, anthropogenic nitrogen (N) deposition contributed to the enhancement of the global terrestrial carbon (C) sink, partially offsetting CO2 emissions. Across several long-term field experiments, this ecosystem-level response was determined to be driven, in part, by the suppression of microbial activity associated with the breakdown of soil organic matter. However, since the implementation of emission abatement policies in the 1970s, atmospheric N deposition has declined globally, and the consequences of this decline are unknown. Here, we assessed the response of soil C storage and associated microbial activities, in a long-term field study that experimentally increased N deposition for 24 years. We measured soil C and N, microbial activity, and compared effect sizes of soil C in response to, and in recovery from, the N deposition treatment across the history of our experiment (1994-2022). Our results demonstrate that the accumulated C in the organic horizon has been lost and exhibits additional deficits 5 years post-termination of the N deposition treatment. These findings, in part, arise from mechanistic changes in microbial activity. Soil C in the mineral soil was less responsive thus far in recovery. If these organic horizon C dynamics are similar in other temperate forests, the Northern Hemisphere C sink will be reduced and climate warming will be enhanced.

Effect of Long-Term Fertilization Practices on the Stability of Soil Organic Matter in the Northeast Black Soil Region in China

Soil organic matter (SOM) is an important carbon pool in terrestrial ecosystems and plays a key role in soil functions. Nevertheless, the effects of fertilization practices on the physical, chemical, biological, and comprehensive stability of SOM are still unclear. We carried out a long-term field experiment in the northeast black soil region in China with four different fertilization practices: no fertilizer (CK), single chemical fertilizer (NPK), chemical fertilizer + straw (NPKJ), and chemical fertilizer + organic manure (NPKM). The content of particulate organic matter (POM) and mineral-associated organic matter (MAOM), compound composition of SOM, carbon mineralization characteristics, active soil organic matter (ASOM), and inert soil organic matter (ISOM) were tested. The results showed that the application of fertilizers significantly increased the contents of POM and MAOM to 2.59–4.65 g kg−1 and 32.69–34.65 g kg−1 (p &lt; 0.05), but decreased the MAOM/POM values by 37.8–42.4%, indicating reduced the physical stability of SOM. Fertilization practices increased the contents of aromatic, nitrogen-containing compounds and decreased the oxygen compounds of SOM, representing enhancement of the chemical stability. The contents of ASOM and ISOM increased in fertilization practices, while the biological stability index (BSI) under the NPKJ and NPKM treatments was lower than the CK treatment, suggesting that the biological stability decreased under the manure and straw application. In addition, the comprehensive stability of SOM increased by 26–116% through a reduction in the physical and biological stability, coupled with an increase in the chemical stability. Collectively, our study demonstrated that the application of manure and straw enhanced both the comprehensive stability and content of SOM and reduced the physical and biological stabilities while increasing the chemical stability, which made the largest contribution to the comprehensive stability.

Stable isotopes analysis combined with X-ray absorption spectroscopy reveal the fate of organic waste-borne copper and zinc in amended soils

Copper (Cu) and zinc (Zn), two potentially toxic trace elements, are commonly abundant in organic wastes (OWs) recycled in soils as fertilizer. Yet current knowledge on the long-term behavior and fate of Cu and Zn in soil following OW spreading is scant. We addressed this issue by studying the fate of OW-borne Cu and Zn in amended soils from four different long-term field experiments. By combining the stable isotope analysis and X-ray absorption spectroscopy, we identified changes in Cu and Zn concentrations, speciation and isotopic compositions in the amended soils only when OW had been applied at high rates over long periods. Under these conditions, we highlighted that: (i) all OW-derived Cu and Zn had accumulated in the topsoil layer regardless of the soil and OW type; (ii) the amended soil isotopic signatures were the result of the mixing of OW-borne and natural Cu and Zn; and (iii) Cu and Zn exhibited distinct speciation patterns in amended soils. Indeed, the unprecedented persistence of OW-borne crystallized Cu(I)-sulfide in the amended soils contrasted with the complete transformation of pig slurry-borne nanosized Zn-sulfide or household compost-derived amorphous Zn phosphate and Zn complexed by organic matter.

Microbial rrn copy number is associated with soil C: N ratio and pH under long-term fertilization

Soil microbial life-history strategies, as indicated by rRNA operon (rrn) copy numbers, strongly influence agro-ecosystem functioning. Long-term N fertilization causes strong and lasting changes in soil properties, yet its impact on microbial strategies remains largely unexplored. Using long-term field experiments across three agro-ecosystems, we consistently found that N fertilization strongly decreased soil C: N ratio and pH, further increasing the community-level rrn copy number, including both average rrn copy number and total 16S rRNA copy number. Soil C: N stoichiometry balanced by N supplement favored the growth of N-dependent copiotrophic species containing high rrn copy numbers (an average of 2.5) and increased their network connections, predominantly contributing to community-level rrn copy number increase. Decreased soil pH caused by N fertilization also favored the growth of some species whose abundances negatively correlated with pH, partially contributing to the community-level rrn copy number increase. By examining the genomes of two dominant species, we found that microorganisms with a higher rrn copy number (6), e.g., Streptomyces scabiei, possessed more genes related to C and N transport and metabolism. In contrast, the Mycobacterium simiae with a lower rrn copy number (1) has more genes associated with secondary metabolite biosynthesis and lipid transport and metabolism. Our finding challenges the concept of microbial life-strategy regulation solely by nutrient availability, highlighting the important contributions of soil stoichiometric balance and pH to microbial strategies in agro-ecosystems under long-term N inputs.

Investigating the impacts of different degrees of deficit irrigation and nitrogen interactions on assimilate translocation, yield, and resource use efficiencies in winter wheat

Water and nitrogen (N) are recognized as the primary determinants influencing the development and output of winter wheat. They affect the growth of winter wheat not only through their own changes, but also through their interaction. The translocation and accumulation of pre- and post-anthesis assimilates (including dry matter and N) are important physiological processes in winter wheat, which are closely related to the resource use efficiency and yield. However, a dearth of research exists that examines the complex interplay between varying water levels, especially severe water deficit, and N deficiency levels on the growth dynamics of winter wheat. The purpose of this study was to quantify and compare the effects of different degrees of water deficit and N interaction on assimilate translocation, water and N use efficiency and yield of winter wheat. A four-year long-term field experiment conducted under the rain-out shelter including four irrigation and two N levels was launched during 2019–2023. This method avoided the impact of precipitation on water treatment and helped to achieve serious water deficit treatment. The findings indicated that the higher N application improved the wheat's ability by 49.6 % - 362.3 % to utilize the available soil water. The pre- and post-anthesis translocation and accumulation of assimilates (including dry matter and N) in winter wheat increase alongside elevated levels of water and N application, except under severe water deficit treatment. Plants under mild to moderate water deficit were better able to translocate the pre-anthesis assimilates. However, the severe water deficit hindered the re-translocation of assimilates before anthesis. Providing additional N during periods of severe water scarcity leads to a 13.4 % - 44.7 % reduction in water use efficiency (WUE). Furthermore, both the irrigation water use efficiency and WUE diminished by 10.3 % - 60.5 % and 4.5 % - 41.4 % with higher levels of irrigation, while improved by 24.4 % - 48.2 % and 12.6 % - 39.4 % with higher N application rates. Conversely, N partial factor productivity and N use efficiency followed the opposite trend. Similar to WUE, increasing N application under severe water deficit would result in a yield reduction of 38.7 %. The reduction in crop yield resulting from severe water stress was primarily ascribed to the decline in the kernels number per spike (up to 74.9 %), with the reduction in spike number per unit area following closely behind (up to 29.1 %). This integrated approach, combining resource use efficiency with a detailed assessment of assimilate dynamics, provides a holistic view of how water and N management strategies impact winter wheat performance. The findings will offer precise insights for developing targeted irrigation and N scheduling strategies for sustaining both winter wheat production and environmental sustainability.

Fire and ant interactions mediated by honeydew and extrafloral nectar in an australian tropical savanna

Fire is a major disturbance affecting ecosystems globally, but its impact on mutualisms has received minimal attention. Here, we use a long-term field experiment to investigate the impact of different fire regimes on globally important ant–honeydew and ant–extrafloral nectar (EFN) mutualistic interactions in an Australian tropical savanna. These interactions provide ants with a key energy source, while their plant and hemipteran hosts receive protection services. We examined ant interactions on species of Eucalyptus (lacking EFNs) and Acacia (with EFNs) in three replicate plots each of burning every 2 and 3 years early in the dry season, burning late in the dry season every 2 years, and unburnt for > 25 years. The proportions of plants with ant–honeydew interactions in Acacia (44.6%) and Eucalyptus (36.3%) were double those of Acacia plants with ant–EFN interactions (18.9%). The most common ants, representing 85% of all interactions, were behaviourally dominant species of Oecophylla, Iridomyrmex and Papyrius. Fire promoted the incidence of ant interactions, especially those involving EFNs on Acacia, which occurred on only 3% of plants in unburnt plots compared with 24% in frequently burnt plots. Fire also promoted the relative incidence of behaviourally dominant ants, which are considered the highest quality mutualists. Contrary to expectations, frequent fire did not result in a switching of behaviourally dominant ant partners from forest-adapted Oecophylla to arid-adapted Iridomyrmex. Our findings that frequent fire increases ant interactions mediated by honeydew and extrafloral nectar, and promotes the quality of ant mutualists, have important implications for protective services provided by ants in highly fire-prone ecosystems.

The impacts of fire vary among vertical strata: Responses of ant communities to long-term experimental burning.

Fire is a powerful tool for conservation management at a landscape scale, but a rigorous evidence base is often lacking for understanding its impacts on biodiversity in different biomes. Fire-induced changes to habitat openness have been identified as an underlying driver of responses of faunal communities, including for ants. However, most studies of the impacts of fire on ant communities consider only epigeic (foraging on the soil surface) species, which may not reflect the responses of species inhabiting other vertical strata. Here, we examine how the responses of ant communities vary among vertical strata in a highly fire-prone biome. We use a long-term field experiment to quantify the effects of fire on the abundance, richness, and composition of ant assemblages of four vertical strata (subterranean, leaf litter, epigeic, and arboreal) in an Australian tropical savanna. We first document the extent to which each stratum harbors distinct assemblages. We then assess how the assemblage of each stratum responds to three fire-related predictors: fire frequency, fire activity, and vegetation cover. Each stratum harbored a distinct ant assemblage and showed different responses to fire. Leaf litter and epigeic ants were most sensitive to fire because it directly affects their microhabitats, but they showed contrasting negative and positive responses, respectively. Subterranean ants were the least sensitive because of the insulating effects of soil. Our results show that co-occurring species of the same taxonomic group differ in the strength and direction of their response to fire depending on the stratum they inhabit. As such, effective fire management for biodiversity conservation should consider species in all vertical strata.

Modelling and validating soil carbon dynamics at the long-term plot scale using the rCTOOL R package

We introduce rCTOOL, an open-source R package for carbon (C) turnover modelling, featuring comprehensive documentation and a user-friendly interface. As an enhanced version of the widely used Danish C-TOOL model, rCTOOL maintains minimal input data requirements and reliable performance, while addressing the original model's limitations in openness and documentation. To validate rCTOOL, we analysed topsoil Soil Organic Carbon (SOC) dynamics using data from the long-term Askov straw disposal experiment (1981–2019), which quantifies the impact of varying annual straw C inputs on SOC storage. Our validation shows an unbiased global prediction error of less than 10%, with a mean error of 1.1 Mg C/ha (CI -0.7–3.0 Mg C/ha). The discrepancies between observed and predicted values were primarily due to spatiotemporal variability represented by the block and year in the long-term field experiment. We demonstrate how rCTOOL is a reliable asset for diverse applications in SOC management and research.

Optimization of sampling design for soil total organic carbon assessment in the precision agriculture framework: Impact of different variogram models and potentiality of ground penetrating radar (GPR) covariate information

Assessing soil organic carbon (SOC) at the field scale is crucial for efficient environmental and agronomic management, especially within the precision agriculture framework. This enables the implementation of crop and soil management strategies to enhance soil quality, increase carbon sequestration, and improve crop yields. However, the process of sampling and assessing SOC is resource-intensive, demanding both in time and labour. This aspect is particularly relevant in agronomic research, where the need to assess the spatial correlation structure of the investigated variables requires the collection of large datasets with georeferenced data and often measurements need to be repeated over time as in the case long-term field experiments − LTE. Methods for minimizing information loss while reducing the sampling scheme, such as spatial simulated annealing (SSA), are particularly valuable in the scope of SOC assessment, especially when faced with budget and time/labour constraints. Within the structure of the SSA method, two critical components can be identified: i) the inclusion of highly informative covariates for the primary variable (SOC); ii) the selection of the most appropriate variogram model for spatial variability assessment. Covariates strongly correlated with SOC, such as those obtained from ground penetrating radar (GPR) that can be collected at a higher spatial density compared to SOC data, along with a well-performing model, can significantly enhance the efficiency of the sampling scheme reduction process. We conducted a study using data from an agronomic field experiment, which included 71 georeferenced sampling locations and, through an iterative downsizing process utilizing SSA, we progressively reduced the number of sampling points by removing 10, 15, and 20 observations. The sampling scheme was refined according to two distinct variogram models: the spherical and Gaussian-Matérn models, both for the primary variable (SOC) and the covariate GPR variable. This process allowed us to identify the optimal variogram model, which has a key role in maximizing the reduction of redundant points while preserving those with valuable information, and to assess the role of the covariate variable both in improving the optimization of the sampling scheme for SOC and in replacing the primary variable to optimize the sampling scheme. Finally, to assess the impact of sampling scheme reduction, a validation process was performed by estimating the dropped points by means of the remaining points using ordinary kriging and regression kriging and analysing the accuracy of such estimation. Our analysis demonstrated that it was possible to reduce the original sampling scheme by approximately 20%, equivalent to eliminating 15 sampling points out of 71, without compromising its predictive capability.

Biochar and Straw Amendments over a Decade Divergently Alter Soil Organic Carbon Accumulation Pathways

Exogenous organic carbon (C) inputs and their subsequent microbial and mineral transformation affect the accumulation process of soil organic C (SOC) pool. Nevertheless, knowledge gaps exist on how different long-term forms of crop straw incorporation (direct straw return or pyrolyzed to biochar) modifies SOC composition and stabilization. This study investigated, in a 13-year long-term field experiment, the functional fractions and composition of SOC and the protection of organic C by iron (Fe) oxide minerals in soils amended with straw or biochar. Under the equal C input, SOC accumulation was enhanced with both direct straw return (by 43%) and biochar incorporation (by 85%) compared to non-amended conventional fertilization, but by different pathways. Biochar had greater efficiency in increasing SOC through stable exogenous C inputs and inhibition of soil respiration. Moreover, biochar-amended soils contained 5.0-fold greater SOCs in particulate organic matter (POM) and 1.2-fold more in mineral-associated organic matter (MAOM) relative to conventionally fertilized soils. Comparatively, although the magnitude of the effect was smaller, straw-derived OC was preserved preferentially the most in the MAOM. Straw incorporation increased the soil nutrient content and stimulated the microbial activity, resulting in greater increases in microbial necromass C accumulation in POM and MAOM (by 117% and 43%, respectively) compared to biochar (by 72% and 18%). Moreover, straw incorporation promoted poorly crystalline (Feo) and organically complexed (Fep) Fe oxides accumulation, and both were significantly and positively correlated with MAOM and SOC. The results address the decadal-scale effects of biochar and straw application on the formation of the stable organic C pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content. These results are of great implications for better predicting and accurately controlling the response of SOC pools in agroecosystems to future changes and disturbances and for maintaining regional C balance.

Responses of soil microbial metabolism, function and soil quality to long-term addition of organic materials with different carbon sources

Biochar and green manure have been widely applied in agricultural production and are important means to achieve sustainable agriculture. However, there is limited research systematically and comprehensively exploring the response of soil microbiota and the changes in soil metabolomics after the addition of two different carbon source amendments to the soil, and the differential mechanisms of soil metabolomics between them remain unclear. In this study, a long-term field experiment (initiated in 2019) was conducted to investigate the effects of biochar and green manure application on soil nutrients and soil functions driven by soil microbes. Compared to the pure fertilizer treatment, biochar increased soil total carbon by 14.54% to 27.04% and soil available potassium by 4.67% to 27.46%. Ryegrass significantly increased soil available phosphorus and organic matter. Under different fertilization regimes, the ecological niches of soil microbes changed significantly. Network analysis revealed that long-term ryegrass returning reduced the complexity of soil microbial networks. Ryegrass and biochar increased dispersal limitation in fungal assemblages (reaching 93.33% and 86.67%, respectively), with biochar particularly enhancing variable selection in bacterial assemblages (accounting for 53.33%). Variation partitioning analysis based on redundancy analysis indicated that humic substances had the highest explanatory power for microbial community variation, with humic substances explaining 38.49% of bacteria and 52.19% of fungi variation. The ryegrass treatment mainly changed the abundance of carbohydrates (CH), amines (AM), c (AH), and lipids (LP), while the BC treatment mainly altered the abundance of organic acids (AC), amines (AM), and carbohydrates (CH). Meanwhile, both treatments significantly reduced the bisphenol A, one of the soil pollutants. Ryegrass incorporation significantly increased the abundance of genes related to soil C, N, P, and S cycling, especially genes involved in carbon decomposition, while biochar significantly enhanced the abundance of nitrogen fixation genes nifH and Hao in soil. Random forest model results indicated that carbohydrates, alcohols, aromatics (AR), and ester (ES) were the main categories of metabolites in soil influenced by differential microbes, and Finegoldia served as a common important metabolic driving species. In summary, this study reveals the processes of soil function, microbial community succession, and metabolism driven by ryegrass and biochar, providing important insights for optimizing soil management and improving soil quality.Graphical