Soil Chemical Variables Research Articles

Impact of urea nutrition on soil and plant chemical variables and development of Mexican lime

Impact of urea nutrition on soil and plant chemical variables and development of Mexican lime

Faba bean in crop rotation shapes bacterial and fungal communities and nutrient contents under conventional tillage of triticale

Legumes in cropping sequence can strongly moderate soil biodiversity and its biochemical status, which could influence soil fertility and productivity. However, their impact on soil microbes and their relationships with soil chemical variables during the subsequent crop growth is not understood enough. In this study, we analyzed the changes in bacterial and fungal communities structure through 16S rRNA and ITS amplicon sequencing, respectively, across crop rotation with faba bean (faba bean-wheat-triticale, F) and without faba bean (wheat-wheat-triticale, W). Rhizosphere and bulk soil samples were taken during the triticale growth stages (stem elongation and maturity). Soil enzymatic activity and chemical properties were also determined. Study factors (crop rotation, soil compartment, growth stage) affected N, C, and P transformations, as indicated by the activity of soil enzymes, and F was more beneficial than W for protease, urease, and acid phosphomonoesterase activities, as opposed to cellulase activity. Changes in the chemical properties led to the shift in soil microbial communities with different bacterial and fungal communities' responses. F treatment enhanced the abundance of the bacterial genera representatives such as Streptomyces and Candidatus Udaeobacter while suppressing the abundance of Jatrophihabitans and Terrabacter. Crop rotation significantly influenced fungal genera and a greater abundance of Helgardia, Pseudogymnoascus, Monocillium, Fusarium, Chaetomium, and Vishniacozyma under F than W was noted and the adverse situation was noted for Peziza and Rhizopus. Rotation type significantly affected the alfa-diversity of the fungal, but not bacterial community. Beta-diversity analyses (nMDS, cluster) indicated that the main factor grouping samples were soil compartment and growth stage for the bacterial and fungal microbiome, respectively. The PERMANOVA results revealed significant effects of all factors on bacterial and fungal microbiomes. Different soil chemical variables governed bacterial and fungal communities. Corg, pH, P, Mg, and Corg, pH were the most important soil factors regulating bacterial and fungal community structure by crop rotation, respectively. Bacterial and fungal communities were more related to the content of Ntot in rotation with than without faba bean. The findings of this study contribute to a deeper insight into the relation between the faba bean in cropping sequence and soil microbiome, and modulation crucial soil conditions for the productivity of the successive crop.

Production patterns of loblolly pine plantations along a geographic gradient in southern Brazil

Pinus taeda plantations depend directly on the supply of resources (light, water, and nutrients) available to the stand. However, studies quantifying edaphic and climatic factors in P. taeda stands are scarce. This study aimed to identify the main edaphic, climatic and stand factors that influence the productivity and growth pattern of P. taeda plantations in southern Brazil. A total of 24 stands, ranging between 8 and 10 years old were evaluated. Biometric variables such as height, diameter at breast height (DBH), stem analysis, growth rings, specific gravity, and soil chemical and physical variables were evaluated. Site index (SI), stem biomass, mean annual increment without bark (MAI) and correlations between variables were calculated. We observed that by nine years after planting, none of the plots had reached their maximum growth; and MAI, standing stem biomass and SI ranged from 15 to 35 m³ ha−1 year−1, 56–131 Mg ha−1, and 12–19 m, respectively, with higher values in Três Barras site. Stem biomass were positively related with SI (r = 0.89), and stem production was related with higher available water content (r = 0.41), warm temperatures (r = 0.61), and higher relative air humidity (r = 0.58). The study corroborates the role of nutrients, well-drained soils, mild climatic conditions, and low water deficit to explain the high yields of P. taeda in Brazil compared to other locations around the world. Based on these results, studies on fertilization, genetic material, and more frequent use of stem analysis, associated with X-ray densitometry, are recommended for P. taeda.

Dominant herbaceous plants contribute to the spatial heterogeneity of beech and riparian forest soils by influencing fungal and bacterial diversity

Understanding of factors that shape diversity patterns in forest ecosystems is a main challenge in forest ecology and management practices. Although herbaceous plants are known to contribute to the maintenance of the structure and function of temperate forests, their impact on fungal and bacterial communities in soils is largely unknown. Therefore, we conducted a comparative study of soil fungal and bacterial diversity in two Central European deciduous forests, focusing on plots with dominant herbaceous species of contrasting morphology, phenology, reproduction, and ecology, including Allium ursinum and Dentaria enneaphyllos in a beech forest, as well as Aegopodium podagraria and Ficaria verna in a riparian forest. Plots with a mixture of herbaceous species and without plant cover were also studied. In both forests, fungal communities showed the strongest association with spatial location, part of which was explained by between-site variability in soil chemistry and was also influenced by herbaceous vegetation. The community composition of saprotrophic fungi depended on the presence and type of herbaceous vegetation in both forests. In addition, herbaceous plants affected the composition of arbuscular mycorrhizal fungi community in the beech forest, while in the riparian forest they affected endophytes and plant pathogens. For bacteria, soil chemistry played the most important role. Our results showed that dominant herbaceous vegetation is one of the drivers shaping microbial community composition, contributing to spatial heterogeneity of forest sites. Given that herbaceous species, especially those forming monospecific patches, affect the soil biotic properties in temperate forests, they should be included in forest management practices.

Using Principal Component Analysis to Assess Soil Chemical Properties in the Mwea Irrigation Scheme, Kenya: Implications for Rice Agronomic Management

Sub-Saharan Africa faces significant challenges as a net importer of rice, with self-sufficiency rates plummeting to as low as 14% in countries like Kenya. The Mwea irrigation scheme shoulders the bulk of rice cultivation, contributing over 80% of the country’s production. However, productivity within the scheme has seen a concerning decline, dropping from 5.6 ─ 6.0 t ha-1 to 1.3 ─ 4.6 t ha-1 between 1977 and 2018. This decline could be attributed to site-specific nutritional deficiencies and/or toxicities, rendering generalized agronomic recommendations ineffective in certain areas. To address this problem, our study aimed to assess soil chemical properties variability within the Mwea irrigation scheme, identify clusters with similar nutritional status, and tailor area-specific agronomic recommendations. During May to September 2020, we collected and analyzed four hundred samples from five sections of the scheme for total organic carbon, soil pH, macro and micronutrients, and exchangeable cations. Principal component analysis was conducted on the mean values of the soil chemical properties to identify significant contributors to variation and establish zones with similar patterns. Principal components 1 to 4 collectively explained 72.2% of the total variability. Cluster analysis revealed four distinct clusters, namely MW, TB, KT, and MU. Within cluster MW, soil pH was below the optimum range for rice cultivation, suggesting a need for liming. Potassium deficiency was observed across all clusters, with rice straw incorporation recommended as a long-term solution. Furthermore, zinc deficiency was noted in cluster WU, necessitating zinc fertilizer application. Conversely, iron toxicity was a concern in cluster MW, suggesting the adoption of alternating wetting and drying techniques and cultivating tolerant varieties. By proving tailored recommendations based on localized soil conditions, we aim to bolster rice productivity within the Mwea irrigation scheme and contribute to regional food security efforts.

Canopy gap impacts on soil organic carbon and nutrient dynamic: a meta-analysis

Key messageThe forest canopy gaps, formed by natural or anthropogenic factors, have been found to reduce soil carbon content and increase nutrient availability. The magnitudes of these effects have been observed to increase with gap age and size, and are largely influenced by changes in temperature, precipitation, and solar radiation.ContextLocal studies have illustrated the influence of canopy gaps on the spatial heterogeneity of soil carbon and nutrients, playing a pivotal role in driving forest regeneration and succession. Nevertheless, it remains largely unknown whether the response of soil carbon and nutrient content to gap formation is consistent across forest ecosystems at global scale.AimsThe aim of this paper is to assess the homogeneity of the observed responses of soil carbon and nutrients following gap formation among a wide array of forest ecosystems and climatic regions.MethodsWe performed a meta-analysis synthesizing 2127 pairwise observations from 52 published articles to quantify the changes in in soil physical, chemical, and microbial variables resulting from gap creation in natural forests and plantations spanning tropical to boreal regions.ResultsCanopy gaps resulted in significant decrease of soil organic carbon (Corg) and microbial carbon (Cmic). The concentrations of ammonium (NH4+), nitrate (NO3−), and available phosphorus (available P) increased following gap creation. These changes mainly occurred in the growing season and in the mineral soil layer, becoming more pronounced with increasing gap age and size. The change in Corg was negatively regulated by mean annual precipitation, and was associated with the changes in Nt and Nmic. The change in NH4+ was positively regulated by mean annual temperature, and was associated with the changes in available P and oxidoreductases (Ox-EEAs). The model explaining the change in soil carbon content exhibited a higher explanatory power than the one accounting for changes in soil nutrient availability.ConclusionThe results indicated that forest canopy gaps resulted in a reduction in soil carbon content and an increase in nutrient availability. These findings contribute to a better understanding of the role of small-scale disturbances as drivers of forest ecosystem succession.

Assessing the utility of SoilGrids250 for biogeographic inference of plant populations.

Inclusion of edaphic conditions in biogeographical studies typically provides a better fit and deeper understanding of plant distributions. Increased reliance on soil data calls for easily accessible data layers providing continuous soil predictions worldwide. Although SoilGrids provides a potentially useful source of predicted soil data for biogeographic applications, its accuracy for estimating the soil characteristics experienced by individuals in small-scale populations is unclear. We used a biogeographic sampling approach to obtain soil samples from 212 sites across the midwestern and eastern United States, sampling only at sites where there was a population of one of the 22 species in Lobelia sect. Lobelia. We analyzed six physical and chemical characteristics in our samples and compared them with predicted values from SoilGrids. Across all sites and species, soil texture variables (clay, silt, sand) were better predicted by SoilGrids (R 2: .25-.46) than were soil chemistry variables (carbon and nitrogen, R 2 ≤ .01; pH, R 2: .19). While SoilGrids predictions rarely matched actual field values for any variable, we were able to recover qualitative patterns relating species means and population-level plant characteristics to soil texture and pH. Rank order of species mean values from SoilGrids and direct measures were much more consistent for soil texture (Spearman r S = .74-.84; all p < .0001) and pH (r S = .61, p = .002) than for carbon and nitrogen (p > .35). Within the species L. siphilitica, a significant association, known from field measurements, between soil texture and population sex ratios could be detected using SoilGrids data, but only with large numbers of sites. Our results suggest that modeled soil texture values can be used with caution in biogeographic applications, such as species distribution modeling, but that soil carbon and nitrogen contents are currently unreliable, at least in the region studied here.

Summarizing soil chemical variables into homogeneous management zones – case study in a specialty coffee crop

Homogeneous management zones (HMZs) delineation is important for the application of precision agriculture because farm management decisions are based on it. Diverse soil chemical characteristics are important for the HMZs delineation. However, summarizing several variables into homogeneous zoning while taking into account the spatial distribution pattern of soil chemical characteristics is a challenge. Addressing this challenge is important to produce HMZs oriented for practical use for the farmers. In this work, 17 soil chemical variables were jointly analyzed for HMZ delineation by using indicator kriging (IK) to interpolate a soil fertility index (SFI). Soil samples were taken from a 4.5 ha area in a quasi-regular grid at 0 - 0.20 m depths in November 2019 (66 samples) and May 2021 (40 samples). Soil P, K, Ca, Mg, S, Na, H, Mn, Fe, Zn, B, cation exchange capacity, aluminum saturation, total organic carbon, base saturation, and organic matter were analyzed. In May 2021 the coffee yield was sampled together with the soil. Applying the SFI and then interpolating it using IK were effective for summarizing soil chemical variables into binary HMZs, showing a zone with higher priority for fertilization (therefore, lower general soil fertility) and another zone with low priority for fertilization. The summarizing process of several variables into binary HMZ was validated by evaluating the boxplots of each variable in each HMZ. Also, higher soil fertility areas presented a higher average coffee yield. Results indicated that joint use of SFI and IK was adequate to delineate HMZs in terms of summarizing soil fertility and separating coffee yield average variability. Delineating management zones by using the SFI approach is flexible for relatively limited sampled studies (less than one hundred samples) where machine learning and geostatistical methods may fail for lack of data.

Influence of Farmyard Manure Application on Potential Zinc Solubilizing Microbial Species Abundance in a Ferralsol of Western Kenya

Zinc is an important nutrient for plant growth and development. Its availability is influenced by zinc solubilizing microbes (ZSMs). The effects of commonly promoted agronomic practices on the abundance of ZSMs are so far not well understood. In this study, conducted in 2019, we assessed the effects of farmyard manure (FYM) application, either sole or in combination with residue and/or inorganic fertilizer inputs, on ZSM community structure using 11 treatments in a long-term (17 years) integrated soil fertility management experiment located in Western Kenya. Bacterial and fungal community composition were evaluated by amplicon sequencing on an Illumina MiSeq platform. The results showed that putative ZSMs (i.e., the ZSMs generally considered to possess the zinc solubilizing capabilities) were clustered in two major clades based on either the application or no application of FYM. Sole application of FYM significantly (p &lt; 0.05) increased the abundance of several ZSMs under a maize–Tephrosia rotation. In addition, systems with the combined application of FYM with other inputs generally showed significantly increasing trends for some ZSMs under a maize–Tephrosia rotation. Moreover, the combined application of FYM and P rather than only P significantly increased the abundance of some ZSMs under maize monocropping systems. Furthermore, as well as affecting ZSM abundance, soil chemical variables involving soil organic carbon (SOC), total N and Olsen P significantly increased with FYM application. This study indicated that management practices such as the application of FYM that increase SOC, and other soil chemical parameters, also/concomitantly increase ZSM abundance. These results imply enhanced capacities for microbial-linked zinc availability with FYM application.

Grassland management effect on ecosystem services in the livestock system in an oxisol from the Eastern high plains of Colombia

Colombia has a livestock population of approximately 28.2 million heads, of which 20.4% is found in the eastern high plains of the Orinoquia region. The extensive beef cattle system predominates, whose diet is based on native and introduced pastures of the genus Urochloa sp. which is deficiently managed, affecting productive and reproductive indexes due to the low adoption of technology. We evaluated potential sustainable intensive systems for cattle production, which contribute to maintaining the provision of environmental services. Between 2011 and 2015 in Agrosavia’s Research Center at Carimagua (4° 37'N and 71° 19' W) environmental and animal production variables were monitored in the following systems: a) degraded pastures recovered with tillage and fertilization, b) annual crop rotation with pastures, c) forest arrangements in strips, and d) forest remnants in perimeter areas. Productive and reproductive variables were determined in animals such as weight gain, calving interval, among others while the pasture/crop productive variables included yield and forage quality. Regarding soil ecosystem services (ES) the macrofauna biodiversity, biogeochemical cycles, soil physical and chemical variables were considered. Estimation of indicators was carried out through principal components analysis for soil physical, chemical and macrofauna variables to extract the two main components that explain the variance. For climate regulation of ES, measurement of soil organic carbon (SOC) storage at a depth of 20 cm and the annual accumulated greenhouse gas (GHG) emissions were included. The systems that involved lime amendments and fertilizers increased the value in the year of application. Values in the water regulation indicator did not show significant differences among the options implemented during the years. Edaphic macrofauna biodiversity indicator value was sensitive to changes in management practices, with termites being the group with highest abundance. The indicator related to SOC was higher in the forest area compared to the pasture-crop system. Systems under the agroforestry schemes which integrated various practices such as managed and recovered pastures, crop-pasture rotation, patched areas and tree strips contributed to maintain or improve the ES, although each one of the strategies proposed provided improvement in at leas one ES.

Effects of Hederahelix L. removal on the understory early regeneration in an oak temperate forest in Mexico City

BackgroundHederahelix L. is an invasive weed species introduced in several regions of the world, so it is relevant to study its effects on the plant community and the changes occurring after its eradication. We established invaded (with/without removal of H. helix) and non-invaded (with/without removal of the understory) plots to compare some community attributes in an oak forest in Mexico City and monitored them every 2 months for 1 year, taking soil samples to compare some edaphic variables between the plots. If invasive species negatively affect natural regeneration, seedlings of native species would be less abundant in plots invaded by H. helix than in the non-invaded ones. As invasive species modify the soil microbiota through exudates and often allelochemicals, soil chemical variables would differ between invaded and non-invaded plots.ResultsThe abundance of native species was lower in the invaded plots, but the richness and diversity of species were not statistically different. The composition of the two invaded plots was similar to each other and more alike to that of the non-invaded plots. The species composition of the invaded plots was associated with soil potassium and phosphorus concentrations, whereas that of the non-invaded plots was more associated with soil nitrogen concentration.ConclusionsFollowing the removal of H.helix, several native species were registered, leading to a similar species composition as in the non-invaded plots, suggesting that some vegetation recovery can be expected following H. helix removal in 1 year.

Biodiversity-Based Empirical Critical Loads of Nitrogen Deposition in the Athabasca Oil Sands Region

Anthropogenic nitrogen (N) emissions can have considerable effects on terrestrial ecosystems, with chronic N deposition leading to changes in plant species composition. The Athabasca Oil Sands Region (AOSR) represents a large point source of N emissions, which has prompted concern for surrounding habitats. The objective of this study was to determine the relative importance of N deposition as a driver of plant species community composition against bioclimatic and soil chemical variables. Further, we sought to identify community thresholds in plant species composition across a N deposition gradient. This assessment was performed for 46 Jack pine (Pinus banksiana Lamb.)-dominant forest sites surrounding the AOSR spanning Alberta and Saskatchewan. In total, 35 environmental variables were evaluated using redundancy analysis (RDA), followed by gradient forest analysis applied to plant species abundance data. Soil chemical variables accounted for just over 26% of the total explainable variation in the dataset, followed by bioclimatic variables (19%) and deposition variables (5%), but joint effects between variables also explained a significant portion of the total variation (p &lt; 0.001). Total deposited nitrogen (TDN), and sulphur (TDS) along with bioclimatic and soil chemical variables, were identified as important variables in gradient forest analysis. A single, definitive threshold across TDN was identified at approximately 5.6 kg N ha−1 yr−1 (while a TDS threshold was found at 14.4 kg S ha−1 yr−1). The TDN threshold range was associated primarily with changepoints for several vascular species (Pyrola asarifolia, Pyrola chlorantha, Cornus canadensis, and Arctostaphylos uva-ursi) and bryophyte and lichen species (Pleurozium schreberi, Vulpicida pinastri, and Dicranum polysetum). These results suggest that across Jack pine-dominant forests surrounding the AOSR, the biodiversity-based empirical critical load of nutrient N is 5.6 kg N ha−1 yr−1.

Recurring heavy rainfall resulting in degraded-upgraded phases in soil microbial networks that are reflected in soil functioning

• We assess the recovery of microbial networks underneath crust to repeated rainfall.• The network fragmentation after the second heavy rain was milder than at the first one.• Cohesive networks were related to high enzyme activity involved in C, N, and P cycles.• Loose networks were related to high Ca, K, Mg, NH4 and organic N.• The network in dry-crusted soils collapsed after the second heavy rain.Biological soil crusts (BSCs) are an important multi-trophic component of arid ecosystems in the Mediterranean region. In a mesocosm experiment, the authors investigated how the network of interactions among the members of the soil microbial communities in four types of soil sample responded when soils were exposed to two simulated extreme rain events. The four types of soil samples were: covered by Cladonia rangiformis and previously hydrated (+BSC+H), covered by C. rangiformis and dried (+BSC−H), uncovered and hydrated (−BSC+H), uncovered and dried (−BSC−H). Network analysis was based on the co-occurrence patterns of microbes; microbes were assessed by the phospholipid fatty acids analysis. The authors further explored the relations between networks’ metrics and soil functions denoted by enzymatic activity and soil chemical variables. All networks exhibited Small world properties, moderate values of clustering coefficient and eigen centrality, indicating the lack of hub nodes. The networks in −BSC−H soils appeared coherent during the pre-rain phases and they became modular after rains, while those in +BSC−H soils kept their connectivity till the second rain but this then collapsed. The network metrics that were indicative of cohesive networks tended to be related to enzyme activity while those that characterized the loose networks were related to Ca, K, Mg, NH4+ and organic N. In all mesocosms except for +BSC−H, networks’ fragmentation after the second heavy rain was milder than after the first one, supporting the idea of community acclimatization. The response of microbial networks to heavy rains was characterized by the tendency to exhibit degradation-reconstruction phases. The network collapse in the crusted only mesocosms showed that the communities beneath crusts in arid areas were extremely vulnerable to recurring heavy rain events.

Vegetation changes in coastal wetlands of the outer estuary of the Río de la Plata as a result of anthropic-induced hydrological modifications

Samborombón Bay in Argentina is one of the largest coastal wetlands of South America. The Ajó wetlands are located to the south of Samborombón Bay and despite being protected natural areas, the land is privately owned and used for extensive cattle ranching where producers build embankments to reclaim salt marshes land and expand cattle grazing areas. The aim of this study is to identify the occurrence of embankments in the landscape of the Ajó coastal wetlands, to describe their effect on-plant communities' structure (composition and species abundances), and environmental features (soil and water physical and chemical variables). Embankments were mapped using satellite images and aerial photographs. Based on the mapping, 7 sampling areas of marshes with embankments were selected for the study of vegetation, water, and soil. Each sampling area has an embankment that interrupts a tidal channel dividing the marsh into two sectors, one connected to the tidal flow and the other disconnected. Vegetation and soil sampling were performed along a transect covering 3 relative topography levels (High salt marshes, Low salt marshes, and Mudflat-tidal channel) on each side. The results show that embankments and livestock activity modify the plant community structure and environmental features. Disconnected marshes compared to connected ones have a higher abundance of grassland species, freshwater species, salt-tolerant species, and exotic species. Surface water has a greater range of variability in electrical conductivity and the majority ions and soil salinity is higher in disconnected high marshes than in connected ones. In a context of global change, there is uncertainty about the tendency of these observed changes. In this sense, the study carried out based on the monitoring of vegetation, soils, and water is a relevant tool for detecting environmental impacts in wetlands whose hydrology has been anthropically modified.

Organic amendments from recycled waste promote short-term carbon sequestration of restored soils in drylands

Soils are considered as a major reservoir for terrestrial carbon and it can act as a source or sink depending upon the land management activities. In semi-arid areas, the natural recovery of soils degraded by mining activities is complicated. A possible solution to recover soil quality and functionality, plant cover and carbon sequestration capacity could be the application of organic amendments. This work focuses on a restoration carried out in 2018 by applying with different composted organic amendments (stabilized sludge, gardening and greenhouse waste) in a limestone quarry under semi-arid climate (SE Spain). The objective was to evaluate the effects of different organic amendments on net CO2 exchange in two microcosms: soil-Stipa tenacissima and soil-spontaneous vegetation. Soil physical and chemical properties, environmental and ecological variables and their interrelationship were studied in amended and unamended soils. The results obtained under soil-forming factors in the study area showed an increase in soil organic carbon and nitrogen content, improved moisture and plant growth, and plant canopy development in amended soils. Soil moisture, soil temperature and plant cover significantly influenced net CO2 exchange. In general, microcosms with S. tenacissima showed higher carbon sequestration rates than soils with only spontaneous plant cover. Soils treated with a vegetable-only amendments showed higher plant cover and CO2 fixation rates after significant rainfall. On the other hand, the plots treated with sludge compost presented more soil respiration than photosynthesis, especially in the wet seasons. Soils with sludge and greenhouse compost mixed had higher CO2 fixation rates than soils restored with a mixture of sludge and garden compost. Soils with greenhouse waste compost showed CO2 fixation in the microcosm with plants in all campaigns, being the best treatment to promote atmospheric CO2 sequestration in soil restoration.

Using Advanced Machine-Learning Algorithms to Estimate the Site Index of Masson Pine Plantations

The rapid development of non-parametric machine learning methods, such as random forest (RF), extreme gradient boosting (XGBoost), and the light gradient boosting machine (LightGBM), provide new methods to predict the site index (SI). However, few studies used these methods for SI modeling of Masson pine, and there is a lack of comparison of model performances. The purpose of this study was to compare the performance of different modeling approaches and the variability between models with different variables. We used 84 samples from the Guangxi Tropical Forestry Experimental Centre. Five-fold cross-validation was used and linear regression models were established to assess the relationship between the dominant height of the stand and different types of variables. The optimal model was used to predict the SI. The results show that the LightGBM model had the highest accuracy. The root mean square error (RMSE) was 3.4055 m, the relative RMSE (RMSE%) was 20.95, the mean absolute error (MAE) was 2.4189 m, and the coefficient of determination (R2) was 0.5685. The model with climatic and soil chemical variables had an RMSE of 2.7507 m, an RMSE% of 17.18, an MAE of 2.0630 m, and an R2 of 0.6720. The soil physicochemical properties were the most important factors affecting the SI, whereas the ability of the climatic factors to explain the variability in the SI in a given range was relatively low. The results indicate that the LightGBM is an excellent SI estimation method. It has higher efficiency and prediction accuracy than the other methods, and it considers the key factors determining site productivity. Adding climate and soil chemical variables to the model improves the prediction accuracy of the SI and the ability to evaluate site productivity. The proposed Masson pine SI model explains 67.2% of the SI variability. The model is suitable for the scientific management of unevenly aged Masson pine plantations.

Soil chemical variables improve models of understorey plant species distributions

AbstractAimSpecies distribution models (SDMs) assume that all ecologically relevant predictor variables are included. This assumption is frequently violated in SDMs of plant species, as soil variables are rarely included. Here, we used in‐situ, soil geochemical variables along with more commonly used topo‐climatic and remotely sensed variables to create SDMs of understorey plant species. We evaluated whether the potential importance of soil variables is greater than generally described in SDM literature, which predictors are most important, and whether a standard subset of predictors can be used to effectively model all species.LocationNorthern Appalachian Mountains.TaxonVascular, forest understorey plants.MethodsWe fit models for the presence of 41 forest understorey plant species across 158 plots using soil, topographic and spectral predictors.ResultsModels containing all three predictor types performed best. Soil and topographic variables had comparable importance; spectral variables were of lesser importance. The best predictor variable was B horizon carbon to nitrogen ratio (B C:N), followed by topographic position index, elevation and B horizon exchangeable calcium (B Ca). A standard subset of variables did not effectively model all species.Main conclusionsOur results and those of other SDMs that include in‐situ soil geochemical data suggest that soil variables are increasingly important with more detailed descriptions of soils. Soil fertility data, such as B C:N and B Ca, are particularly important in acidic, forest soils where pH is a poor indicator of fertility. Commonly used topo‐climatic variables provide meaningful predictions but are limited by their use of indirect predictor variables, inhibiting transferability and interpretability. The poor performance of a standard subset of variables highlights the uniqueness of each species' niche and the need to have a variety of predictor variables.

Long Term Influence of Fertility and Rotation on Soil Nitrification Potential and Nitrifier Communities

The agricultural imprints on soil microbial processes manifest at various timescales, leaving many temporal patterns to present slowly. Unfortunately, the lack of long-term continuous agricultural field sites in North America has left gaps in our understanding of agricultural management on biogeochemical processes and their controlling microbiota. Nitrification, ammonium oxidation by bacteria and archaea, is a critical control point in terrestrial nitrogen fluxes by oxidizing cationic ammonium to anionic nitrate, promoting nitrate leaching. Moreover, nitrous oxide is produced during nitrification, contributing to massive nitrous oxide emissions from fertilized agroecosystems. Nitrification is sensitive to many macro and micro-ecological filters, as nitrifiers are obligate aerobes and are sensitive to numerous non-growth substrates and metal ions. This study sought to understand the long-term implications of various rotation and fertilizer regimes on nitrification potential and nitrifying bacterial communities in the Morrow Plots (Urbana, IL). The Morrow Plots was established in 1876 and are the longest continuous field experiments in North America, making it the only site in America capable of assessing the impact of over 140 years of agricultural management on nitrification. The Morrow Plots contrasts fertilizer (manure, inorganic, unfertilized) and rotation (continuous corn, corn-soy, corn-oat alfalfa), allowing us to explore how conventional vs. regenerative agriculture practices impact nitrifier communities. The results of this study suggest that fertilizer and rotation interact to promote distinct bacterial nitrifier communities. Nitrification potential is highest in manure corn-oat-alfalfa plots, suggesting ammonium availability is not solely responsible for active nitrifier communities. Various soil chemical variables, like CEC, Mg, and Ca, significantly influenced nitrifier community beta-diversity, using 16S rRNA amplicon sequencing, suggesting long-term accumulation of specific cations diverge microbial community assembly. While this study only uses nitrification potential enzyme activity instead of isotope analyses, it sheds light on the importance of various physiochemical drivers on nitrification potential and communities. The results support the need for a more precise exploration of the mechanisms controlling field-scale nitrification rates over large temporal scales. Put together, this study supports the importance of long-term field sites for understanding agricultural manipulations of microbial biogeochemical cycling and sheds light on the micronutrients influencing nitrifier communities and potential activity.

Do Spatially Structured Soil Variables Influence the Plant Diversity in Tabuk Arid Region, Saudi Arabia?

Plant diversity is affected by spatial variables as well as soil physical and chemical variables. In this study, plant species and soil variables were investigated in five sites of Tabuk Province (Saudi Arabia), namely Aldesah, Alzetah, Alawz, Harra and Sharma, to understand if the spatially structured soil variables (pH, electric conductivity (EC), soil texture, calcium, potassium, phosphorus, phosphate, total organic matter (OM), bicarbonate and sodium) influence the plant diversity. A total of 163 plant species belong to 41 families and 124 genera were reported from the 5 sites. Diversity indices including the species richness (alpha), evenness, Brillouin, Menhinick, Margalef, equitability and estimated Chao-1 were significantly different among the studied sites with pronounced high values in Sharma and Aldesah. The highest value of beta diversity was reported in Aldesah (0.253) followed by Sharma (0.171). According to the principal coordinates of neighbourhood matrix (PCNM) analysis, 11 positive spatial vectors (variables) were found. However, after running the forward selection procedures (using 2 stopping criteria), only 3 spatial vectors were retained (PCNM 1 (adj–R2 = 0.043, F = 5.201, p = 0.004), PCNM 2 (adj–R2 = 0.027, F = 3.97, p = 0.006) and PCNM 3 (adj–R2 = 0.019, F = 3.36, p = 0.007)). The linear models between the selected spatial variables (PCNM vectors) and soil variables were produced to investigate their spatial structure. In the first model, the first PCNM 1 axis showed significant relationship with pH and potassium (adj–R2 = 0.175, p = 0.046). In the second model, the second PCNM 2 axis had a significant relationship with OM and sodium (adj–R2 = 0.561, p &lt; 0.001). Lastly, sodium was the only factor significantly correlated with the third PCNM 3 axis (adj–R2 = 0.365, p = 0.002). In conclusion, the spatially structured variables of soil did not show strong influence on plant diversity except pH and potassium, which were correlated with PCNM 1, OM and sodium, which were correlated with PCNM 2, and sodium, which was correlated with PCNM 3.

Nitrous oxide responses to long-term phosphorus application on pasture soil

ABSTRACT Nitrous oxide (N2O) is a greenhouse gas emitted from grazed pasture systems. The influence of phosphorus (P) fertility on these emissions is not understood. This study examined if fertiliser P affected N2O emissions following nitrate application to soil from the Winchmore long-term P fertiliser trial. We hypothesised increasing P fertility would enhance soil carbon (C) supply and N2O emissions via denitrification. Using mesocosms, N2O and CO2 fluxes were measured over 29 days following KNO3-15N and glucose additions, along with soil chemical and biological variables. Microbial biomass P increased (P < 0.001; R 2 = 98.2%) with increasing Olsen-P. Fertiliser P enhanced net N mineralisation. Cumulative CO2 fluxes were unaffected by P treatment regardless of KNO3 addition. Fluxes of N2O increased one day after KNO3 addition with higher emissions at 250 kg ha−1 of superphosphate. Relatively low N2O-15N enrichment indicated minor denitrification contributions to the N2O flux. Subsequently, glucose addition enhanced N2O-15N enrichment and denitrification in the KNO3 treatment. Following glucose addition, the emission factor increased with P fertiliser. Denitrification derived N2O emissions will increase with P fertilisation but only if C limitation is overcome.