Planted Soil Research Articles

Dynamics of microorganism population in the soil of pine plantations under technogenic load

The degree of crown closure is an important parameter of tree plantations that determines the environmental conditions for all organisms in the ecosystem. Studies assess the effect of the degree of crown closure on the microorganism dynamics in the rock dump soil with and without a potentially fertile layer. It was found that the amount of soil microorganisms varies significantly during the period, which is associated with variations in the hydrothermal conditions of the soil. The activity of microorganisms decomposing mineral nitrogen and microscopic fungi varies depending on the degree of crown closure.

KAJIAN BEBERAPA SIFAT KIMIA TANAH PODSOLIK MERAH KUNING PADA LAHAN PERKEBUNAN KELAPA SAWIT BERBEDA UMUR DI SEI DAUN, KABUPATEN LABUHANBATU SELATAN, SUMATERA UTARA

Red-yellow podzolic soils are generally acidic and have poor chemical properties, so tolerant plants such as oil palm plants are needed. This research was to determine the effect of differences in the age of oil palms on the chemical properties of the Sei Daun plantation soil. The research was conducted in December 2022 using the method of purposive sampling according to plant age. Samples were taken from 5 lands with oil palm ages 8 years, 14 years, 16 years, and 25 years, as well as land without plants, 5 points were determined from each land, and each point was separated into 3 depths, namely 0-20 cm, 20-50 cm, and 50-70 cm, the 5 points were composited according to depth, producing 3 samples per field. The results of the analysis of soil chemical properties show that increasing the age of oil palm causes soil pH, thereby reducing available P, total N, exchangeable K, and CEC of soil, but increasing soil organic C, also increasing Fe-NH4OAC, Mn-NH4OAC, exchangeable Al but still in low value. Increasing the age of oil palms can lower the soil pH, thereby reducing the availability of nutrients. Fertilizer doses can be adjusted according to the age of the plant because the older it is, the more nutrients the plant absorbs.

INDENTIFIKASI KARATERISTIK KIMIA TANAH DAN EVALUASI STATUS KESUBURAN TANAH PADA LAHAN TANAMAN NANAS DI KELURAHAN WALAMBENO WITE KECAMATAN PARIGI KABUPATEN MUNA

Soil fertility provides an overview of the condition of the soil to provide nutrients. As land management is carried out intensively and over a long period of time, a decrease in soil fertility occurs. The research objectives to identify the chemical characteristics of the soil and evaluate the level of fertility of the soil planted with pineapple plants. This research was carried out in Walambeno Wite Village, Parigi District, Muna Regency, Southeast Sulawesi Province. Walambeno Wite Village is one of the central pineapple areas in Muna Regency. Soil samples were taken using the proportional sampling method on land planted with pineapple plants, at a processing layer depth of 0-30 cm. The soil chemical property parameters analyzed in the laboratory are KTK, pH H2O, C organic, N total, P available, K2O and wet saturation. Determination of soil fertility status is guided by the Soil Research Center. The research results show that the chemical characteristics of the soil in pineapple plantations are soil pH values with slightly acidic to neutral state, low to high C-organic, medium total nitrogen, very high P2O5, low to medium K2O, K2O medium to high KTK and high KB. The soil fertility status is low at location 2, medium at location 2, and high at location 3. The factors inhibiting soil fertility at the research site are low levels of C-organic and K2O.

Studi Sifat Fisika Tanah Gambut pada Kebun Karet dan Kelapa Sawit Rakyat di Kecamatan Rasau Jaya Kabupaten Kubu Raya

This study aims to study the differences in the physical properties of peat soils in rubber and oil palm plantations in Rasau Jaya III Village Rasau District Kubu Raya District. The parameters of this study are, peat depth, peat maturity, measurement of ground water level depth, content weight, water content capacity field, total porosity, permeability, and some chemical properties, peat soil in people's rubber and oil palm plantations in Rasau Jaya District, Kubu Raya Regency. Measurement of peat depth is taken up to the mineral soil boundary, has a 74 cm rubber peat depth and 66 cm oil palm. The level of maturity of both fields at the sapric level. The water resistant surface on rubber land is 70 cm and oil palm land is 58.8 cm. Average bulk density of depth 0 – 30 cm rubber land 0.34 g/cm3, palm 0.31 g/cm3. Depth 30-60 cm rubber 0.28 g/cm3, palm 0.38 g/cm3. Average field water capacity depth of 0-30 rubber fields 74, 63% palm 85.19%. While at a depth of 30-60 cm rubber land has 71.58% oil palm area of 84.58% vol. The average porosity of total soil depth of 0-30 cm palm oil is 86.96% higher than rubber area 82.37%. The average total porosity of soil at a depth of 30-60 cm is lower oil palm 81.82% rubber land 86.82% and both lands are classified as very porous criteria. The mean permeability values based on the t-test results were not significantly different.

Soil depth and recovery interval mediate soil water repellency under different forest types and fire intensity levels in China: Evidence for ecosystem resiliency

Soil water repellency (SWR) is a physical phenomenon whereby the surface of soil particles cannot be, or resists being, moistened by water. The recovery process of fire-induced SWR can provide important evidence for ecosystem resilience, but most existing studies ignored this process. Prescribed burning is a widely used method to reduce the risk of fire and fuel. However, prescribed fires can increase SWR, reducing infiltration and increasing overland flow and subsequent soil erosion. In order to understand the ecosystem resilience process from fire-induced SWR, soil samples were collected before and after prescribed burning. Four different forest types in the Hunan province of China were studied. Soil samples at four different soil depths (0–5, 6–10, 11–15, and >15 cm) and four time intervals (3, 30, 180, and 360 d) after burning at different intensities were collected. No significant difference in SWR was found among the four forest types, but the SWR of soil in plantations was stronger than that in secondary forests before fire. Most soil samples showed slightly increased SWR after burning, SWR increasing with fire intensity. Surface soil (0–5 cm) SWR showed greater sensitivity to fire disturbance than subsurface soil (>5 cm). SWR had a smaller scope of influence and shorter recovery period in burned secondary forests. Although SWR recovered over time, recovery was slower with increasing fire intensity. SWR always recovered to pre-fire levels given sufficient time. Our study revealed the recovery process of SWR, and explored the temporal and spatial mechanisms of forest ecosystem recovery after prescribed burning.

Effects of long-term nitrogen addition on the shift of nitrogen cycle from open to closed along an age gradient of larch plantations in North China

The 15N:14N ratio (δ15N) is often used as an integrated indicator of nitrogen (N) status in natural terrestrial ecosystems. However, the mechanisms by which long-term N addition affects N cycling and status in temperate plantations with different ages remain poorly understood. Here, we used an approach of leaf–soil continuum of δ15N with the combination of incubation experiments to evaluate the effects of three rates of decadal N addition (urea) on N status in young, intermediate, and mature larch (Larix principis-rupprechtii) plantations in northern China. We found that leaf δ15N decreased significantly from 1.6‰ in young trees to −0.5‰ and −1.0‰ in intermediate and mature trees, respectively, due to increases in the use of NO– 3-N relative to NH+ 4-N with stand age, and probably a shift in N acquisition from mineral soil in the young plantation to organic and/or surface mineral soil layers in the intermediate and mature plantations. Decadal N addition decreased leaf δ15N, which was likely to be due to the direct imprints of 15N-depleted urea input, the inhibition of soil net mineralization, and nitrification, and greater dependence on N absorption by ectomycorrhizal fungi after N addition. Soil δ15N decreased with stand age, which was likely to be due to reduced soil N transformation (e.g., mineralization) and/or relative abundance of ectomycorrhizal fungi along the chronosequence; however, soil δ15N was not affected by long-term N inputs. Combined with the decreased enrichment factor (ε = δ15Nleaf – δ15Nsoil), these results suggest a shift from more open N cycling (potentially greater ecosystem N losses) in young plantation to more closed N cycling (facilitation of ecosystem N retention) in mature plantation, which showed negative response to decadal N addition. These findings provide new insights into N acquisition strategies and cycling in the typically N-limited temperate plantations under heightened atmospheric N deposition.

The Distribution Characteristics and Potential Risk Assessment of Lead in the Soil of Tieguanyin Tea Plantations in Anxi County, China.

Assessing the distribution and risks associated with the soil lead content in the Tieguanyin tea plantations of Anxi County is critical, given the county's significance as the primary Tieguanyin tea production area in Fujian Province. This study examined the distribution characteristics of soil lead in Anxi County's tea plantations according to the Kriging spatial interpolation of the parameters of the semivariance function of the exponential model. Moreover, the sources of lead content were analyzed, considering geological backgrounds and anthropogenic influences. Ecological risks and the issuance of early warnings were also assessed. The soil lead content in the rocks of the Tieguanyin tea plantations in Anxi County followed the order: andesite > dacite > rhyolite > granite. The soil lead content gradually decreased from the center toward the east and west, forming four distinct north-south parallel zones. High-lead-content areas were identified at the border of Jiandou, Bailai, and Hushang; in the central part of Lutian; and in the southern part of Huqiu. The high levels of soil lead in the tea plantations possibly originated from industrial and mining activities, automobile exhaust, and agricultural activities. The distribution of single-factor pollution indices and potential risk evaluation based on the Soil Environmental Quality Standard, Environmental Technical Conditions for Tea Production Area, and Environmental Technical Conditions for Organic Tea Production Area indicated that the soil in Tieguanyin tea plantations in Anxi County was clean and safe for tea cultivation.

Biochar-plant interactions enhance nonbiochar carbon sequestration in a rice paddy soil

Soil amendment with biochar is being promoted as a promising strategy for carbon (C) stabilization and accrual, which are key to climate change mitigation. However, it remains elusive on how biochar addition influences nonbiochar C in soils and its mechanisms, especially in the presence of plants. Here we conducted a 365-day soil microcosm experiment with and without adding 13C-labeled biochar into topsoil to quantify changes in nonbiochar C in the topsoil and subsoil in the presence or absence of rice plants and to determine the mechanisms by which biochar controls nonbiochar C accrual in the soil profile. The nonbiochar C content of topsoil was not affected by biochar addition in the absence of rice plants, but was significantly increased by 4.5% in the presence of rice plants, which could result from increases in the soil macroaggregate fraction, iron (Fe)-bound nonbiochar organic C content, and fungal biomass collectively. However, biochar amendment had no effect on the content of nonbiochar organic C in the subsoil. Overall, biochar-plant interactions drive more nonbiochar C sequestration in the topsoil, and the changes of nonbiochar C in planted soils following biochar addition should be quantified to better assess the soil C sequestration potential in agricultural lands.

Fungal complexity and stability across afforestation areas in changing desert environments

The great achievements in combating desertification are attributed to large-scale afforestation, yet we lack verification of how the stability of the fungal community changes in afforestation areas in desert environments. Here, we present the fungal network structure from different niches (root and bulk soil) of plantations of Mongolian pine, a crucial species for afforestation introduced widely in desertification regions. We assessed changes in community complexity and stability of root-associated fungi (RAF) and soil fungi (SF) among different introduction sites: the Hulunbuir Desert (HB), the Horqin Desert (HQ) and the Mu Us Desert (MU). To illuminate the complexity and stability of the fungal network, the differences in topological properties, fungal function, and vegetation and environmental factors between introduction sites were fully considered. We showed that (1) the SF networks had more nodes and edges than the RAF networks. There was a lower ratio of negative:positive cohesion of RAF networks in HB and MU. For SF but not for RAF, across the three introduction sites, a higher modularity and ratio of negative:positive cohesion indicated higher stability. (2) Ectomycorrhizal (EcM) fungi were the dominant functional group in the RAF network (especially in HQ), and were only significantly correlated with vegetation factor. There was a higher relative abundance and number of OTUs of saprophytic fungi in the SF network and they showed positive correlations with soil nutrients. (3) RAF and SF network complexity and stability showed different responses to environmental and vegetation variables. The key determinant of the complexity and stability of the SF networks in Mongolian pine plantations was soil nutrients, followed by climate conditions. The composition and structure of the RAF community was closely related to host plants. Therefore, clarifying the complexity and stability of fungal communities in afforestation areas in changing desert environments is helpful for understanding the interactions between the environment, plants and fungi.

Nitrogen addition suppresses soil positive priming effect in temperate plantations: Evidence from an 8‐year in situ field experiment

Abstract The microbial‐driven soil priming effect (PE) determines soil carbon emissions and is essential for accurately predicting the feedbacks between the terrestrial carbon cycle and global changes. In recent years, human activities have resulted in increased atmospheric nitrogen (N) deposition, but there is limited understanding of the long‐term effects of N deposition on soil microbial communities and their impact on soil PE in temperate plantations. This study utilized Korean pine plantation soils with 8 years of in situ N addition to investigate the mechanisms of the impact of long‐term N addition on PE through carbon (13C) isotope tracing and high‐throughput sequencing techniques. We found that N addition significantly changed the soil bacterial community structure, while the effect on the fungal community structure did not reach a significant level. Addition of 13C‐glucose resulted in soil‐positive PE, which exhibited a significant decreasing trend with increasing N addition. Compared with the control (0 kg N ha−1 year−1), the net carbon balance of the low N (20 kg N ha−1 year−1) showed no significant change, while the medium N (40 kg N ha−1 year−1) and high N (80 kg N ha−1 year−1) significantly increased by 35.47% and 35.79%, respectively, implying that glucose carbon was trapped in the soil much more than organic carbon decomposition. The PLS‐PM explained 69.0% of the total variation in PE among different N additions, showing that bacterial core taxa were the main driver of PE and that carbon enzyme activities (β‐1,4‐glucosidase and polyphenol oxidase) were a direct factor in regulating PE. Our results provide insights into accurately assessing the soil carbon sequestration potential of plantations under the influence of N deposition. Read the free Plain Language Summary for this article on the Journal blog.

Direct and indirect effects of Basta®, a glufosinate-based herbicide, on banana plantation soil microbial diversity and function

Herbicide applications have doubled over the past 30 years to control weeds, but their use may influence soil microbial communities, which mediate important ecosystem services. Here, we characterised the direct effects of a single application of Basta® (glufosinate), at 1× and 2× the recommended rate (5 and 10 kg product ha−1), as well as the indirect effects of vegetation loss on the diversity and function of soil microbial communities within a banana plantation. A 10-month pre-experimental period using Basta® to remove additional vegetation from half of the experimental area created conditions for assessing the indirect herbicide effects. Direct assessments on soil microbial communities began when the Basta® herbicide treatments were applied to the areas with and without vegetation and continued over multiple time-points, for 56 days. Herbicide treatment had no significant direct impacts on basal, and substrate induced respiration rates, or the potential activities of microbial enzymes as inferred from fluorescein diacetate hydrolysis (FDA) and β-glucosidase assays. Similarly, phylogenetic marker gene sequencing indicated that Basta® application did not significantly influence the diversity of soil bacterial or fungal communities. Indirectly, Basta® had a greater influence on the soil microbial activity and functions by removing understory vegetation cover around banana plants. This suggested that continual use of herbicides to reduce soil vegetation cover under bananas had a greater impact on soil microbial communities than a single application of the herbicide. Furthermore, the presence or absence of vegetation cover, significantly altered the abundance of Fusarium oxysporum, plus an additional eight bacterial and ten fungal taxa. Our results indicated that a single application of glufosinate as Basta® at the recommended or double the recommended rate, did not adversely affect soil microbial communities or their activities in banana plantations directly. However, application of herbicides, such as Basta® in crops like banana, indirectly alters soil microbial communities and their activities through loss of vegetation cover and should only be used as a component of an integrated weed management system.

Research on the Detection Method of Organic Matter in Tea Garden Soil Based on Image Information and Hyperspectral Data Fusion.

Soil organic matter is an important component that reflects soil fertility and promotes plant growth. The soil of typical Chinese tea plantations was used as the research object in this work, and by combining soil hyperspectral data and image texture characteristics, a quantitative prediction model of soil organic matter based on machine vision and hyperspectral imaging technology was built. Three methods, standard normalized variate (SNV), multisource scattering correction (MSC), and smoothing, were first used to preprocess the spectra. After that, random frog (RF), variable combination population analysis (VCPA), and variable combination population analysis and iterative retained information variable (VCPA-IRIV) algorithms were used to extract the characteristic bands. Finally, the quantitative prediction model of nonlinear support vector regression (SVR) and linear partial least squares regression (PLSR) for soil organic matter was established by combining nine color features and five texture features of hyperspectral images. The outcomes demonstrate that, in comparison to single spectral data, fusion data may greatly increase the performance of the prediction model, with MSC + VCPA-IRIV + SVR (R2C = 0.995, R2P = 0.986, RPD = 8.155) being the optimal approach combination. This work offers excellent justification for more investigation into nondestructive methods for determining the amount of organic matter in soil.

Abundance of denitrifying genes and their driving factors in soil under different land use types in the karst region of Northwest Guangxi

To understand the role of denitrifying microbes during vegetation recovery in karst regions, we determined the basic physicochemical properties and abundance of denitrifying microbial functional genes (nirS, nirK, fungal nirK, p450nor, and nosZ) of 13 collected soil samples under three land use types (cropland, grassland, and plantation) in Northwest Guangxi, and investigated the changes in the abundance of denitrifying microbial functional genes and their driving factors. Results showed that soil pH, soil organic carbon, total nitrogen (TN), and exchangeable calcium (Caexe) in plantation soil were significantly higher than those in cropland and grassland. The abundance of nirS, nirK, p450nor, and nosZ in plantation soil were significantly higher than those in cropland and grassland. Soil pH, TN, and Caexe were positively correlated with the abundance of denitrifying functional genes nirS, nirK, and p450nor. Results of redundancy analysis showed that soil Caexe, pH and TN were the primary factors influencing the abundance of denitrifying functional genes, which accounted for 34.1%, 20.1%, and 16.1% of the total variation, respectively. Such a result suggested that Caexe was the main driver of changes in denitrifying functional genes under different land use types. Overall, vegetation restoration (plantation) could effectively increase soil denitrifying microbe genes abundance in the karst region of Northwest Guangxi, and consequently influence soil nitrogen cycling.

Insight into the sorption and desorption pattern of pyrrolizidine alkaloids and their N-oxides in acidic tea (Camellia sinensis) plantation soils

Pyrrolizidine alkaloids (PAs) and their N-oxides (PANOs) are phytotoxins produced by various plant species and have been emerged as environmental pollutants. The sorption/desorption behaviors of PAs/PANOs in soil are crucial due to the horizontal transfer of these natural products from PA-producing plants to soil and subsequently absorbed by plant roots. This study firstly investigated the sorption/desorption behaviors of PAs/PANOs in tea plantation soils with distinct characteristics. Sorption amounts for seneciphylline (Sp) and seneciphylline-N-oxide (SpNO) in three acidic soils ranged from 2.9 to 5.9 µg/g and 1.7 to 2.8 µg/g, respectively. Desorption percentages for Sp and SpNO were from 22.2% to 30.5% and 36.1% to 43.9%. In the mixed PAs/PANOs systems, stronger sorption of PAs over PANOs was occurred in tested soils. Additionally, the Freundlich models more precisely described the sorption/desorption isotherms. Cation exchange capacity, sand content and total nitrogen were identified as major influencing factors by linear regression models. Overall, the soils exhibiting higher sorption capacities for compounds with greater hydrophobicity. PANOs were more likely to migrate within soils and be absorbed by tea plants. It contributes to the understanding of environmental fate of PAs/PANOs in tea plantations and provides basic data and clues for the development of PAs/PANOs reduction technology.

Responses of arbuscular mycorrhizal fungal morphological traits and the diversity of spore-associated bacteria to simulated nitrogen deposition and drought in a Cunninghamia lanceolata plantation soil

Arbuscular mycorrhizal (AM) fungi play an important role in plant nutrient absorption and stress resistance. AM fungal spore-associated bacteria are essential for mycorrhizal colonization, but their responses to environmental changes remain largely unknown. We collected surface soil samples from a Chinese fir plantation in both summer and winter to investigate the responses of AM fungal morphological traits and spore-associated bacterial communities to simulated nitrogen deposition (40 kg N·hm-2·a-1 addition) and drought (-50% precipitation exclusion). Our results showed that nitrogen addition and precipitation exclusion significantly affected AM fungal spore density and extraradical hyphal length, respectively. AM fungal intraradical colonization rate, extraradical hyphal length and spore density were significantly differed between the two seasons. Compared to control (no nitrogen addition and no precipitation exclusion treatment), both nitrogen addition and precipitation exclusion significantly reduced spore density in winter, while precipitation exclusion alone and the combined nitrogen addition and precipitation exclusion significantly increased extraradical hyphal length in summer. The dominant spore-associated bacterial phyla were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Planctomycetes. Nitrogen addition and precipitation exclusion did not affect the diversity of spore-associated bacteria. However, the combined nitrogen addition and precipitation exclusion treatment altered the composition of the bacterial community, with significant variations between the two seasons. The spore-associated bacterial diversity was significantly higher and community variability (or turnover) was lower during summer than winter. Soil total nitrogen, nitrate nitrogen and dissolved organic carbon were important factors influencing the bacterial community composition. In all, the effects of nitrogen addition and precipitation exclusion on the morphological traits of AM fungi are seasonally dependent. The combination of nitrogen addition and precipitation exclusion has a significant impact on AM fungal spore-associated bacterial community structure.

Reduction of nitrous oxide emission by using stearic acid combined zinc coated urea in silty clay and sandy loam soils under bare and planted conditions

Overuse of chemical fertilizers in agroecosystems leads to the increased economic burden, low crop production in terms of input and environmental pollution. Due to its improved nutrient management and degrading properties, synthetic slow release fertilizers have become a significant advancement in the fertilizer sector. In this study we evaluated the effect of slow release urea on nitrous oxide (N2O) emission, crop growth and crop nutrient contents. Measurements were carried out in two different texture soils (sandy loam and silty clay) under two different conditions (bare soil and planted). The N2O emission was measured for 15 days from bare soils and 48 days from planted soil. Plant fresh weight, dry weight, chlorophyll contents, N and Zn were measured in the end of the experiment. The results showed that N2O emission was reduced 33–39 % from coated urea as compared to conventional urea in bare soil. In planted soil, the coated urea reduced the N2O emission 29–33 %. The deep placement of urea in silty clay soil reduced the N2O emission up to 22.8 % as compared to surface placement. Plant fresh matter, dry matter, N and Zn contents were significantly (p ≤ 0.05) higher with coated urea as compared to conventional urea. It is concluded that the coating of urea with hydrophobic materials like stearic acid, along with Zn sources i.e. Zn fortified nano-bentonite or the ZnO nanoparticles (NPs) presents opportunities to overcome the environmental pollution and increasing the crop production and quality.

Seven-year N and P inputs regulate soil microbial communities via bottom-up effects on carbon and nutrient supply and top-down effects on protist relative abundance

Information about the interactions between microbial carbon (C), nitrogen (N), and phosphorus (P) mineralization and nutrient inputs will improve our understanding of the effects of global change on soil biogeochemical cycling and ecosystem function. In this study, we explored how N, P, and NP inputs, when applied at low rates (50 kg ha–1 year–1) for seven years, affected the microbial community in an acidic, strongly weathered, red clay soil in a subtropical conifer plantation. N and P inputs regulate microbial communities holistically through influencing soil resources (bottom-up), such as the C and nutrient supply, and predators, such as protists (top-down). We observed that N, P, and NP inputs caused changes in the protist community, which then affected bacterial diversity rather than fungal diversity. The increases in the protist diversity that resulted from the P and NP inputs were associated with increases in the relative abundance of Calditrichaeota, which is involved in C-mineralization, and decreases in the relative abundance of Marinimicrobia, which is involved in N-mineralization. The N and NP inputs caused the soil to become more acidic, exacerbated the microbial C limitation, and reduced the overall microbial functional diversity to carry out C, N, and P mineralisation. We conclude that the nutrient supply directly impacted the C-, N-, and P-mineralising microbial communities (bottom-up), and directly and indirectly affected soil protists (top-down).

Metal cation concentrations improve understanding of controls on soil organic carbon across a precipitation by vegetation gradient in the Patagonian Andes

Tephra-derived soils retain more organic carbon (C) than soils formed from any other parent material, but this C may be sensitive to changes in climate and land use. Here we evaluate the effects of precipitation, temperature, and afforestation on extractable metals and organic C storage in young tephra-derived soils in a temperate climate. We conducted our investigation across five sites in the Patagonian Andes that vary from 250 mm to 2200 mm mean annual precipitation, and 12 to 9.7 ℃ mean annual temperature from east to west. At each of the five sites are paired plots of natural vegetation, varying from grasses and shrubs at the dry sites to closed-canopy forest at the wet, and stands of Pinus ponderosa planted in monocultures 35 years prior to sampling. Previous research at these sites showed that aboveground net primary production and soil organic C increased with rainfall, but total soil organic C content was lower in pine plantations than natural vegetation. Here we assess whether variation in precipitation and vegetation type also affect soil mineral properties that promote soil C stabilization. Soils were collected to the depth of auger refusal and extracted with 0.5 M HCl for 24 h to target the combined exchangeable and adsorbed metals, including secondary short-range-ordered mineral phases and the plant available pools of Mg, Ca, and K. Pine afforestation lowered concentrations of HCl-extractable K (p < 0.1) and Ca (p < 0.01) within the top 0 – 30 cm. Other elements, while not affected by vegetation type, did respond to the rainfall gradient. Al, Si, P, and Mn all increased in the surface soils with increasing rainfall (p < 0.01), suggesting the development of short-range-order volcanic mineral phases that retain nutrients such as P and Mn. The addition of Al and Ca in the linear model to describe soil organic C explained more of the total variance than rainfall and vegetation type alone, indicating the importance of Al complexes and cation (Ca) bridging with secondary minerals to soil C retention. Importantly, the lower concentration of Ca in planted pine soils may signal a long-term decrease in the potential soil C stored in afforested soils due to a lower capacity for cation bridging. Our results show that the chemistry of these young tephra soils is dynamic, responding to both precipitation and afforestation in distinct ways with potential long-term impacts on nutrient cycling and C storage.

Physical and Hydrodynamic Textural Parameters of Soils: The Case of the Rubber Plantations of the Centre National de Recherche Agronomique (CNRA) Anguédédou in South-Eastern Côte d'Ivoire

The rubber tree, a species of Amazonian forest tree, is cultivated for its latex, which is rich in natural rubber. Its cultivation is of economic, social, climatic and environmental importance. However, it is often accused of destroying the soil. To clear up this misunderstanding, a study was carried out to characterise the physical and hydrodynamic characteristics of soils under rubber in south-eastern Côte d'Ivoire. According to the biotope (rubber plantation, abandoned rubber plantations and forest) and the age of the rubber plantations, this study selected 12 plots. These included ten rubber plantations that were divided into four age categories: 1-5 years, 6-10 years, 11-20 years, and 21-40 years. Additionally, a secondary forest was also selected as a control, which was located in close proximity to these plantations. Furthermore, a rubber plantation that had been abandoned for more than eight years was also selected considered as a transition between the active plantations and the secondary forest. In these biotopes, soil samples were taken using an auger and sent to the laboratory to determine soil texture. Using the Yoro sand method and the single ring device, the apparent density, porosity and water infiltration rate of the soils were determined. The results show that the soil texture of the CNRA Anguédédou rubber plantations in southern Côte d'Ivoire is generally clayey. On the other hand, the texture of the soils of the youngest plantations (1 to 5 years old) is silty-clayey with more than 37% clay and a low water content. However, the soils of old rubber plantations with a clay texture have high water content. The soil compactness observed in young rubber plantations is corrected as the plantations age.

NIR Spectral Inversion of Soil Physicochemical Properties in Tea Plantations under Different Particle Size States.

Soil fertility is vital for the growth of tea plants. The physicochemical properties of soil play a key role in the evaluation of soil fertility. Thus, realizing the rapid and accurate detection of soil physicochemical properties is of great significance for promoting the development of precision agriculture in tea plantations. In recent years, spectral data have become an important tool for the non-destructive testing of soil physicochemical properties. In this study, a support vector regression (SVR) model was constructed to model the hydrolyzed nitrogen, available potassium, and effective phosphorus in tea plantation soils of different grain sizes. Then, the successful projections algorithm (SPA) and least-angle regression (LAR) and bootstrapping soft shrinkage (BOSS) variable importance screening methods were used to optimize the variables in the soil physicochemical properties. The findings demonstrated that soil particle sizes of 0.25-0.5 mm produced the best predictions for all three physicochemical properties. After further using the dimensionality reduction approach, the LAR algorithm (R2C = 0.979, R2P = 0.976, RPD = 6.613) performed optimally in the prediction model for hydrolytic nitrogen at a soil particle size of 0.25~0.5. The models using data dimensionality reduction and those that used the BOSS method to estimate available potassium (R2C = 0.977, R2P = 0.981, RPD = 7.222) and effective phosphorus (R2C = 0.969, R2P = 0.964, RPD = 5.163) had the best accuracy. In order to offer a reference for the accurate detection of soil physicochemical properties in tea plantations, this study investigated the modeling effect of each physicochemical property under various soil particle sizes and integrated the regression model with various downscaling strategies.