Haplic Acrisol Research Articles

Dynamics of structural indices and organic carbon pool across a haplic acrisol under secondary tropical rainforest at Umudike Abia State

Differences in vegetation types over a landscape influences the structural behaviour and organic carbon pool of soils thereby affecting site-specific management decisions. This study aimed at establishing the differences in structural indices and organic carbon pool across a soil under secondary rainforest vegetation. Nine replicates of auger and core soil samples were randomly collected from the site at 0 – 20 cm depth. Soil samples were prepared and analysed at a laboratory. Data obtained were subjected to geospatial analysis using a Geographical Information System (GIS) software package. Results showed that changes in organic carbon storage ranged from 40 – 48 ton / ha, BD ranged from 1.39 – 1.42 mg / m3, clay flocculation index ranged from 50 – 68 %, aggregated silt + clay ranged from 9 – 12 %, clay dispersion index ranged from 32 – 42 %, dispersion ratio ranged from 26 – 32 %, mean weight diameter ranged from 0.75 – 1.05 mm, saturated hydraulic conductivity ranged from 3.1 – 3.8 cm / mins and total porosity ranged from 46.4 – 47.6 %. Regions of weak micro aggregaion dominated the land while regions of increased stability of macro aggregates were dominant. Regions of increased soil organic carbon storage occupied about half portion of the land. Greater portion of the land was noted for increased bulk density, reduced total porosity and saturated hydraulic conductivity. Consequently, there were changes in soil structural properties and organic carbon storage across the studied area.

IMPACT OF FOREST CONVERSION TO PASTURE ON SOIL ENZYMATIC ACTIVITY IN THE NORTHERN AMAZON

The conversion of forests to pastures in the Amazon results in deforestation and the loss of environmental services. This practice affects biogeochemical cycles and impairs soil enzyme activity, which is essential for maintaining soil quality. This study aimed to investigate the impact of converting part of the Amazon forest into pastures, focusing on soil enzyme activity. The study was conducted at Fazenda Canto Verde, Roraima, comparing native forest areas and pastures of Brachiaria brizantha and Brachiaria humidicola, established on Haplic acrisol, without fertilization or tillage, under a management regime of 30 days of grazing and 60 days of rest. Sampling involved 12 mini trenches per hectare at two depths, with analysis of enzyme activity post-incubation. Higher activity of carbon cycle enzymes (Cellulase, Invertase, β-Glucosidase) was observed in the forest compared to pastures, especially with B. humidicola. Nitrogen cycle enzymes (Urease, BAA-Protease) were more active in the forest, while B. humidicola showed the highest Casein-Protease activity. In the phosphorus and sulfur cycles, the forest led in Phosphomonoesterase and Phosphodiesterase, while B. humidicola excelled in Arylsulfatase. This study demonstrates that replacing forest with pastures significantly alters soil functionality, impacting biogeochemical cycles and their ecological functions.

Long-Term Fertilization Contributes to Carbon Saturation in Neutral-To-Alkaline Soils but not in Acidic Soils

ABSTRACT The study investigated the adsorption of dissolved organic carbon (DOC) on Chinese soils from four long-term experiments involving five treatments: (1) no fertilization (control), (2–4) inorganic nitrogen (N), phosphorus (P), and potassium (K) fertilization (N, NP, and NPK), (5) NPK plus manure (NPKM). The results showed that DOC adsorption followed a modified Langmuir isotherm model effectively (R2 = 0.912 ~ 0.991). The maximum adsorption capacity (Q max ) (i.e. saturation deficits) generally increased with increasing soil organic carbon (SOC) due to fertilization in Luvic Phaeozem, Haplic Gypsisols, and Eutric Cambisols. However, it decreased significantly in acidic soils (Haplic Acrisols) from 15.59 g/kg for control, to 13.96, 13.03, 9.30 and 8.02 g/kg for N, NP, NPK and NPKM, respectively. Moreover, long-term fertilization, particularly with organic fertilization (e.g. NPKM), resulted in an increase of carbon (C) saturation by 1.42 g/kg (5.52%) in Luvic Phaeozem, 9.27 g/kg (44.29%) in Haplic Gypsisols, and 3.75 g/kg (27.66%) in Eutric Cambisols; however, there was a slight decrease by 1.70 g/kg (−7.49%) in Haplic Acrisols. Canonical correlation analysis (CCA) revealed that clay content and soil available iron (AFe) might be the crucial factors controlling C deficits, and subsequently, C saturation, along with current SOC. In conclusion, long-term fertilization contributed to C saturation in neutral-to-alkaline soils, but not in acidic soils. Thus, further attention should be paid to the long-term effects of fertilization on C saturation.

Soil carbon and nitrogen stocks following forest conversion to long-term pasture in Amazon rainforest-Cerrado transition environment

The conversion of Amazon rainforest to grasslands has significant implications for regional and global carbon cycling. The description of affected organic pools and their extent is crucial for accurate prediction of forest-to-pasture conversions. We assessed soil C and N stocks in granulometric fractions of soil organic matter (SOM), particulate organic matter (POM) and mineral-associated organic matter (MAOM), following forest-to-pasture conversion in transition environments of the Brazilian Amazon rainforest and Cerrado biomes. Five study situations (SS) were selected in the Lontra River basin, Tocantins state, Brazil. The situations were established by the association between vegetation and soil classes: OFAr (Ombrophilous Forest on Orthodystric Arenosol); OFPt (Ombrophilous Forest on Petric Plinthosol); DCFr (Dense Cerrado on Acric Petroplinthic Ferralsol); DCAc (Dense Cerrado on Haplic Acrisol); and CSAr (Cerrado Sensu Stricto on Orthodystric Arenosol). In each SS, soil samples were collected in pasture areas with different planting times (between 10 and 30 years), in addition to a reference area with natural vegetation. DCFrP30 (30-y-old pasture) and DCFrNV (natural vegetation area) were statistically similar, both having the highest mean C stocks (0–20 cm: 41.5 ± 6.6 t C/ha; 0–40 cm: 64.6 ± 12.3 t C/ha; 0–60 cm: 85.0 ± 14.8 t C/ha; 0–100 cm: 102 ± 21.8 t C/ha) and N stocks (0–20 cm: 3.5 ± 0.6 t C/ha; 0–40 cm: 5.3 ± 0.9 t C/ha; 0–60 cm: 6.9 ± 1.1 t C/ha; 0–100 cm: 8.1 ± 1.5 t C/ha), especially in MAOM. The highest C-C3 (δ13C ≈ −27‰) losses occurred in newer pastures of OFAr and CSAr and in DCFr, while C-C4 (δ13C ≈ −14‰) gains were greater in POM and in 20-y-old pastures of OFPt and DCFr. Our results demonstrate significant change in stocks and distribution of soil C and N in SOM granulometric fractions following the conversion of forest to pasture. Moreover, the results give important insight into the development of strategies focused on the recovery and conservation of environmental quality and mitigation of climate change, particularly for the Amazon region where Cerrado-Amazon rainforest transition areas have been incorporated into agricultural land in recent years.

Identifying Driving Factors and Their Interacting Effects on Sources of Heavy Metal in Farmland Soils with Geodetector and Multi-source Data

The identification of heavy metal sources in farmland soils is essential for the rational health condition management and sustainable development of soil. Using source resolution results(source component spectrum and source contribution)of a positive matrix factorization(PMF)model, historical survey data, and time-series remote sensing data, integrating a geodetector(GD), an optimal parameters-based geographical detector(OPGD), a spatial association detector(SPADE), and an interactive detector for spatial associations(IDSA)model, this study explored the modifiable areal unit problem(MAUP) of spatial heterogeneity of soil heavy metal sources and identified the driving factors and their interacting effects on the spatial heterogeneity of soil heavy metal sources in categorical and continuous variables, respectively. The results showed that the spatial heterogeneity of soil heavy metal sources at small and medium scales was affected by the spatial scale, and the optional spatial unit was 0.08 km2 for detecting spatial heterogeneity of soil heavy metal sources in the study region. Considering spatial correlation and discretization level, the combination of the quantile method and discretization parameters with an interruption number of 10 could be implied to reduce the partitioning effects on continuous variables in the detection of spatial heterogeneity of soil heavy metal sources. Within categorical variables, strata(PD 0.12-0.48) controlled the spatial heterogeneity of soil heavy metal sources, the interaction between strata and watersheds explained 27.28%-60.61% of each source, and the high-risk areas of each source were distributed in the lower sinian system, upper cretaceous in strata, mining land in land use, and haplic acrisols in soil types. Within continuous variables, population (PSD 0.40-0.82) controlled the spatial variation in soil heavy metal sources, and the explanatory power of spatial combinations of continuous variables for each source ranged from 61.77% to 78.46%. The high-risk areas of each source were distributed in evapotranspiration (41.2-43 kg·m-2), distance from the river (315-398 m), enhanced vegetation index (0.796-0.995), and distance from the river (499-605 m). The results of this study provide a reference for the research of the drivers of heavy metal sources and their interactions in arable soils and provide an important scientific basis for the management of arable soil and its sustainable development in karst areas.

Tracing the origin of deposited sediments: A study applying proximal sensing in a drainage subbasin

Erosion is a major cause of soil degradation. Understanding the sources of sediment and the processes that exacerbate this problem is crucial for soil conservation. Remote and proximal sensing technologies have contributed to advance our understanding of soil erosion processes and support soil conservation research. The objective of this study is to use two proximal sensors, a portable X-ray fluorescence spectrometer (pXRF) and a magnetic susceptibilimeter, to identify the origin of sediments deposited in the lower portion of a drainage subbasin by using a fingerprinting approach. Five sediment tracing elements were selected: Fe, Si, Al, Ti, and Zr. The sediment source area is composed of gabbro, granite, and felsic orthogneiss, upon which two soil classes were formed: Rhodic Ferralsol (Dystric) (Latossolo Vermelho Distroférrico típico, LV) and Haplic Acrisol (Argissolo Vermelho-Amarelo Distrófico típico, PVA). In the source area, 35 samples were collected from the topsoil layer (0–2 cm of depth) using a regular grid of 50 × 50 m2. In the deposition area, 24 samples were collected in a regular grid of 7 × 7 m2. The source of the sediments was determined using cluster analysis with data provided by the proximal sensors and topographic attributes. Results indicated that the Haplic Acrisol, which is more susceptible to erosion, contributed most to sediment deposition. Analysis of pXRF data showed its potential to identify and differentiate sediments and their sources. Cluster models based on the abundance of Fe, Si and Al, as well as the Ti/Zr ratio, demonstrated the best results with a global accuracy of 88% and a Kappa coefficient of 0.74. The use of the susceptibilimeter data alone did not yield satisfactory results. Results indicate the usefulness of pXRF in identifying the source of sediments in drainage basins, making it a valuable tool in soil conservation and erosion assessments.

Phosphorus sorption characteristics in the Sahel: Estimates from soils in Mali

<abstract> <p>Crop yield in sub-Saharan Africa is often limited by low phosphorus fertility. Farmers in the region can apply phosphate rock, which should increase the plant-available phosphorus level, but this may be prone to sorption in acid soils of the Sahel. The objective of this study was to determine phosphorus (P) sorption characteristics of four representative soil series in Sahelian Mali namely, Longorola (Gleysol), Danga (Fluvisol), Niessoumana (Arenosol) and Konobougou (Acrisol) under Tilemsi Phosphate Rock (TPR) treatment. Data for phosphorus sorption was obtained by equilibrating 5 g of soils for 7 days at room temperature in 50 ml of 0.01M CaCl<sub>2</sub> containing six (6) rates of phosphate as TPR (0, 10, 20, 40, 80,160 mg/L). The linear form of the Langmuir equation was used to calculate sorption parameters of the soils. The Gleysol with the greatest clay content had the highest phosphorus sorption maximum which was over three times greater than that of the Acrisol with the least clay content. The sorption maxima in the range of 59–200 mg/kg were well estimated with Langmuir sorption isotherm (R<sup>2</sup> ≥ 0.78). Soil organic matter and clay contents influenced phosphorus sorption from the TPR. The degree of phosphorus saturation ranged from 2.39 to 6.47 %, being greater in the Arenosol. In a two-season field experiment on the Haplic Acrisol, we tested on maize, the TPR in two forms (powder and pellet) in addition to water-soluble diammonium phosphate at different rates (0, 11 and 16 kg P /ha). The water-soluble DAP and TPR (powder) had similar effects (p < 0.05) on soil P availability but with DAP producing greater grain yields. This shows that application of TPR in powder form can improve phosphorus availability as water-soluble DAP with positive impact on grain yield. The study provides useful information on P sorption characteristics of TPR amendment in the Sahel.</p> </abstract>

Citric acid modified biochar application at a low dosage can synchronically mitigate the nitrogenous gas pollutants emission from rice paddy soils

Raw biochar with high pH possibly stimulated ammonia (NH3) volatilization in the agricultural soil. We hypothesized that the modified biochar (MBC) with low pH can synchronically decrease the NH3 and nitrous oxide (N2O) losses. We performed a two-year experiment to clarify how citric acid MBC influence the NH3 volatilization and N2O emission as well as the underlying mechanisms. Two typical paddy soils, i.e., Hydragric Anthrosol and Haplic Acrisol, receiving equal urea N with 240 kg ha−1 but varied rates of MBC with 0, 5, 10, and 20 t ha−1 (named Urea, Urea + MBC5, Urea + MBC10, and Urea + MBC20, respectively) were studied. The results showed that MBC-amended treatments effectively mitigated the NH3 volatilization from Hydragric Anthrosol and Haplic Acrisol by 29.6%–57.9% and 30.5%–62.4% in 2017, and by 16.5%–21.0% and 24.5%–35.0% in 2018, respectively, compared to Urea treatment. In addition, significantly lower N2O emissions with averaged 38.3% and 43.1% in 2017, and 51.7% and 26.7% were recorded under Hydragric Anthrosol and Haplic Acrisol, respectively, following the MBC application (P < 0.05). Increased MBC addition performed higher efficacy on mitigating NH3 volatilization, particularly in the first rice season, while this “dosage effect” was not found for N2O reduction. Lowered pH in overlying water, enhanced adsorption of NH4+-N and its nitrification rate likely contributed to the lower NH3 volatilization as result of MBC addition. The nirS and nosZ gene copies were not changed by MBC, while the nirK gene copies were decreased as result of MBC amendment by 8.3%–25.2% under Hydragric Anthrosol and by 21.8%–24.9% under Haplic Acrisol. Consequent lower ratio of nirK/(nirS + nosZ) explained the mitigation effect of MBC on N2O emission. In conclusion, the present two-year study recommends that MBC applied at a low dosage can perform positive effect on controlling the nitrogenous gas pollutants from paddy soil.

Relationship between soil erodibility by concentrated flow and shear strength of a Haplic Acrisol with a cationic polyelectrolyte

To clarify the relationship between rill erodibility in an excess shear stress model for concentrated flow erosion and soil particle–particle interactions, we examined the rill erodibility and aggregation-dispersion behavior of Shimajiri Maaji soil, classified as a Haplic Acrisol, with different amounts of cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC). The effect of particle–particle interaction on rill erodibility was determined by performing shear strength measurements and rill erosion experiments as a function of the PDADMAC dose without changing other soil conditions. Moreover, the mechanisms of particle–particle interactions were examined by comparing the electrophoretic mobility (EPM) with the transmission of the supernatant of the soil suspension and soil shear strength. The EPM and transmission showed that the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction governed the aggregation-dispersion behavior. At the same time, the shear strength monotonically increased with increasing PDADMAC dose, even when charge reversal and electric double layer (EDL) repulsion occurred. This result suggests that the shear strength is sensitive not only to the EDL interaction but also to the interactions, the so-called non-DLVO forces, such as bridging interaction. The difference between transmission and shear strength should be due to the difference in the characteristic length because the transmission is attributed to the collision/approaching process between particles, whereas the shear strength is attributed to the broken/retracting process of particle–particle contact. Rill erodibility decreased with increasing shear strength. Furthermore, our quantitative analysis demonstrated that rill erodibility can be represented by a linear function of shear strength. These results clearly show that a high attractive force between soil particles results in low rill erodibility. The strong particle–particle attraction protects soil particles from peeling off by increasing the shear stress of the flowing water. Our study suggests that shear strength measurement can be used to quickly estimate the effect of soil conditioners on rill erodibility in the field.

Quality reference values for trace metals in Podzols, Ferralsols, and Acrisols of Brazilian Atlantic rainforest

In tropical coastal forest ecosystems, human activities spread rapidly. It is, therefore, necessary to define soil quality. For this, the determination of the natural content of trace metals is an essential step. This study aims to understand the distribution of trace metals in the main soils of tropical coastal rainforest ecosystems: Ferralsols, Acrisols, and Podzols, in Bahia state, Brazil. After morphological, chemical, and physical characterization and classification of the soils, the concentration of trace metals was investigated both in soil profiles and in surface composite samples (national guideline recommendation), in five locations for each soil class. The soils were classified as Geric Ferralsol, Haplic Acrisol, Chromic Acrisol, and Ortsteinic Carbic Albic Endogleyic Podzol. Concentrations of metals differed significantly between soil classes. Even under tropical rainforest climate during soil formation, the parent rock material still influences geochemistry. Al, Fe, Mo, Ni, V, and Zn accumulate in Ferralsols, while Ba, Co, Cr, Cu, and Mn accumulate in Acrisols. In the Podzols, metals highly accumulate in B spodic horizon. The data highlights that composite sampling strictly based on soil layers and not horizons (as the national guideline recommends) can cause significant misinterpretations. Instead, the multivariate regression models provided consistent data, accurately predicting the pseudo-total concentrations of trace metals in individual soil samples. The regression method is fast and low cost and provides a reliable geochemical baseline for the definition of reference values.

Dynamics of soil aggregate stability as induced by potassium in a soil-plant system

ABSTRACT Electrolytes have been verified as a vital internal factor controlling soil aggregate stability (SAS). Several reports have focused on whether potassium promotes or demotes SAS and have shown contradictory results in different soils and clay mineralogy. Only a few studies have investigated such an effect on a soil-plant system, even though this information is critical for soil management practices to maintain soil structural stability. This research studied the dynamics of SAS as influenced by potassium in a soil-plant system. Corn as a test plant was grown on Haplic Acrisols (Typic Paleustults) in a greenhouse. The potassium adsorption ratio (PAR), cation ratio of structural stability (CROSS), and SAS were recorded on the day before planting (day 0), the day of planting (day 1), days 10, 20, 30, and the day of harvesting (day 55) at the tasseling stage. The corn growth, biomass, and potassium uptake were also examined. The relationship between soil and plant parameters was statistically tested. The results showed the existence of SAS dynamics caused by soil potassium change, with agreement among the responses for PAR, CROSS, and plant uptake. Within 24 h of soil treatment with potassium, the SAS move rapidly from 74% to 96%. It remained steady at 96–97% when the corn was in the vegetative stage and then fell significantly (α = 0.05) to 88% when the corn was in the tasseling stage, where the potassium uptake was maximized. The results implied that SAS is a sensitive index of soil physical quality associated with potassium, especially for tropical kaolinitic soils.

Can combined compost and biochar application improve the quality of a highly weathered coastal savanna soil?

Soil fertility decline is a major constraint to crop production in sub-Saharan Africa. The positive effect of biochar and compost applications on soil fertility has been reported by many authors. In this study, a 30-day laboratory incubation experiment was done using 120 g samples each of a Haplic acrisol amended with corn cob biochar (cbio), rice husk biochar (rbio), coconut husk biochar (coco300 and coco700) or poultry manure compost (compost); and co- composted rice husk biochar (rcocomp) or co-composted corn cob biochar (cococomp) at rates of 1 % w/w amendment: soil, respectively. Other treatments in the study were combined poultry manure compost and corn cob biochar or rice husk biochar (1 % compost + 1% biochar: 1% soil w/w), respectively, to examine their effects on basal soil respiration, soil pH; soil microbial carbon; cation exchange capacity; total organic carbon, total nitrogen and available nitrogen concentration. Biochar and compost applied solely or together, and composted biochar increased soil pH by 0.28–2.29 pH units compared to the un-amended control. Basal respiration from the sole compost or composted rice husk, or corn cob biochar or combined biochar and compost were higher than the un-amended control, which was similar to that from the biochar only treatments. TOC in the sole compost and combined corn cob biochar and compost treatments were up to 37% and 117% higher, respectively, than the control. Combined application of rice husk biochar and compost increased MBC by 132% while sole compost addition increased MBC by 247%, respectively, compared to the control. In conclusion, the study demonstrated that sole or combined application of compost and biochar, or composted biochar improved soil quality parameters such as soil pH and MBC, and promoted soil C stabilization through enhanced TOC and reduced soil C loss through basal respiration.

Agronomic performance of urea in pastilled compositions applied on maize fertilization

Urea pastillation is a technology that allows the composite mixture with other elements like sulfur and zinc. This study aimed to provide recommendations of N rates, and to assess the agronomic performance of N fertilizers, including pastille urea and its composition associated with S and Zn, top-dressed on maize. Two experiments were set up in the harvests of 2014 and 2015 in an Acrisol and a Lixisol. The experimental design was the randomized blocks with three replicates in a split-plot arrangement and an additional treatment (no N). In the plot, three N applications rates were tested (75, 150 and 300 kg ha-1); while in the subplots, seven fertilizers were tested, including conventional and pastilled ones. The greater was the N rate applied, the higher were the leaf N content and grain yield of maize. The S content in the leaves increased with the increasing S doses applied with the tested fertilizers. Yields with ammonium sulfate were higher than with prilled urea, pastille urea and pastille urea with elemental S in the harvest mean on the Haplic Lixisol. The rate that corresponded to the maximum economic efficiency for UR was 128 and 119 kg N ha-1 for Haplic Acrisol and Haplic Lixisol, respectively. The recommended dose of ammonium sulfate was 119 kg ha-1, since it provided the greater incomes for both sites.

Genesis and classification of soils along a toposequence in the teaching and research farm of Taraba State University, Jalingo, Nigeria

Investigations were made to reflect the genesis and classification of soils along a toposequence in the Teaching and Research farm of Taraba State University. The topographic map of the farm was developed in the ArcGIS 10.8 environment and a profile graph plotted out. One profile pit was sunk in each elevation range to represent soils in the summit, shoulder, back slope, foot slope and toe slope positions using the free survey approach. The soils were deep, well drained and generally described as A, B, C soils with extensive B horizons that showed clear illuviation of clay and sesquioxides. The soils were brown (7.5YR 3/4), dark brown (10YR 3/3) and dark yellowish brown (10YR 4/6) in the surface and dominated by sand with bulk density values that exceeded 1.5 Mg/m3. Soil pH values were moderately acid to neutral while organic C and exchangeable bases were low in all but foot slope position where high values of organic carbon were obtained in the surface soils. The content of dithionite and oxalate Fe and Al, and their derivatives indicate intense weathering condition of the soils as well as their combined movement with clay to endopedons. However, moderately high CEC and the likely presence of montmorillonite (via CECE/clay) are indications that the soils had good potentials for agriculture. Among the soil forming processes in the area were mineralization, eluviation-illuviation as well as ferritization. The soils were classified as Typic Rhodustults (Pretic Acrisols), Arenic Haplustults (Chromic Acrisols) and Paleustults (Haplic Acrisols).&#x0D; Keywords: pedogenesis, sesquioxides, classification, Basement Complex

Influence of Biochar on Nitrogen Use Efficiency and Root Morphology of Rice-Seedling in Two Contrasting Paddy Soils

Biochar may affect the root morphology and nitrogen (N) use efficiency (NUE) of rice at seedling stage, which has not been clearly verified until now. To clarify it, we conducted a pot experiment regarding to two soil types (Hydragric Anthrosol and Haplic Acrisol), two biochar application rates (0.5 wt% and 1.5 wt %) and two rice varieties (common rice var. Xiushui134 and hybrid super rice var. Zhongkejiayou12-6) meanwhile. Seedling NUE of common rice Xiuhui134 was significantly increased (p < 0.05) by 78.2% in Hydragric Anthrosol and by 91.4% in Haplic Acrisol following biochar addition with 1.5 wt%. However, biochar addition exerted no influence on seedling NUE of super rice Zhongkejiayou12-6 in both soils. Overall, 0.09–0.10 units higher soil pH and 105– 116% higher soil NH4+ -N were observed in Xiushui134 growing two soils with 1.5 wt% biochar. In addition, improved root morphology (including longer root length, larger root surface area, bigger root volume, and more root tips) contributed to the higher seedling NUE of Xiushui134 in two soils. The soil pH and NH4+ -N content, also the root morphology were influenced by biochar, which though could not thoroughly explained the NUE of Zhongkejiayou12-6. In conclusion, biochar application to paddy soil changed soil pH and NH4+ -N content, root growth, and the consequent seedling NUE of rice, which effects are relative with rice cultivar, biochar addition rate, and soil type.

Floating duckweed mitigated ammonia volatilization and increased grain yield and nitrogen use efficiency of rice in biochar amended paddy soils

Biochar (BC) potentially accelerates ammonia (NH3) volatilization from rice paddy soils. In this regard, however, application the floating duckweed (FDW) to biochar-amended soil to control the NH3 volatilization is not studied up-to-date. Therefore, the impacts of BC application with and without FDW on the NH3 and nitrous oxide (N2O) emissions, NUE and rice grain yield were evaluated in a soil columns experiment. We repacked soil columns with Hydragric Anthrosol and Haplic Acrisol treated in triplicates with Urea, Urea+BC and Urea+BC+FDW. Total NH3 losses from Hydragric Anthrosol and Haplic Acrisol were 15.2-33.2 kg N ha-1 and 19.6-39.7 kg N ha-1, respectively. Urea+BC treatment recorded 25.6-43.7% higher (p < 0.05) NH3 losses than Urea treatment, attributing to higher pH value of floodwater. Floating duckweed decreased soil pH and therefore significantly reduced (p < 0.05) the NH3 volatilizations from the two soils by 50.6-54.2% over Urea+BC and by 34.2-38.0% over Urea treatment. Total N2O emissions from Hydragric Anthrosol and Haplic Acrisol were 1.19-3.42 kg N ha-1 and 0.67-2.08 kg N ha-1, respectively. Urea+BC treatment increased N2O emissions by 58.8-68.7% and Urea+BC+FDW treatment further increased N2O emission by 187.4-210.4% over Urea treatment. Higher ammonium content of the topsoil, explained the N2O increases in the Urea+BC and Urea+BC+FDW treatments. Urea+BC slightly reduced the rice grain yield and NUE, while the Urea+BC+FDW promoted both rice yield and NUE. Our data indicate that co-application of FDW along with BC in paddy soil could mitigate the NH3 volatilization and enhance the rice grain yield and NUE.

Application of organic fertilizer improves microbial community diversity and alters microbial network structure in tea (Camellia sinensis) plantation soils

Soil microbiomes contribute to plant growth, health and agricultural production. However, the influence of long-term application of different fertilizers on soil microbial diversity and community structure of tea (Camellia sinensis) plantations remains unclear. Here it was hypothesized that organic fertilizer treatment (OF) would significantly improve the microbial diversity and alter the microbial community structure, leading to the support of more soil ecosystem functions in tea plantation. To test this, we investigated microbial communities of tea plantation soils under different long-term fertilization treatments using both high-throughput 16S rRNA gene Illumina sequencing and molecular ecological network analysis. Soil samples (Red soils, classified as Haplic Acrisol) were collected from 5 large experimental tea plantations under different long-term fertilization treatments (organic fertilizer (OF), chemical fertilizer (CF) and non-fertilizer (NF)) in central south of China in August 2017. Soils under OF treatment had higher microbial diversity compared with soils under other treatment regimes. Unweighted principal coordinate analysis (PCoA) results revealed a clear separation among the groups of tea plantation soils under the three treatment regimes. Relationship analysis between soil properties and microbial communities showed that pH and nitrate nitrogen (NO3-N) concentration were key physicochemical factors that significantly influenced microbial diversity and community structure. Furthermore, network analysis indicated that the network of OF treatment soils contained more functionally interrelated microbial modules than soils with CF treatment and that the topological roles of characteristic microorganisms and key microbial organisms were significantly different between CF and OF treatments. Relative to CF treatment, the relative abundances of organisms belonging to chemoheterotrophy, fermentation, nitrogen fixation, and aerobic nitrite oxidation functional groups in tea plantation soils under OF treatment were significantly increased by 28.74%, 110.10%, 41.16% and 556.64%, respectively (p < 0.05). It was concluded that OF treatment could improve microbial diversity, alter microbial network structure and enhance potential ecosystem function in tea plantation soils.

An integrated approach to exploring soil fertility from the perspective of rice (Oryza sativa L.) yields

Soil fertility should be explored from a productivity perspective because the most important function of the soil is to ensure crop yield. This study presents an integrated and scientific approach to exploring soil fertility based on rice (Oryza sativa L.) yields, using Jinxian County as an example. The main soil types are Haplic Acrisols and Hydragric Anthrosols. Five soil fertility indicators (p-Value < 0.05) were selected according to the generalized additive model (GAM) hypothesis test between the rice yield and each indicator. Furthermore, these indicators were used to assess the quality of soil fertility via Takagli and Sugeno (T-S) fuzzy neural networks models. Finally, the geodetector model was used to explore the restricting indicators of soil quality that can influence rice yields. The results indicate that continuous fertilization for decades has improved the surface soil organic matter (SOM) concentrations in the study area. However, the surface total potassium (KT) was still low at a mean value of 13.95 ± 4.74 mg/kg. The determination power (DP) of exchangeable magnesium (0–20 cm) and KT (20–40 cm) of 0.067 and 0.061, respectively, revealed that the proper use of potassium and magnesium fertilizers can increase rice yields. This integrated soil fertility exploration could scientifically assess the soil fertility and identify mainly restricting indicators of soil fertility in the study area. Moreover, these effective models with minor adjustments could be applied to assess soil fertility in other typical areas.

Arbuscular mycorrhizal fungi inoculation enhances phosphorus use efficiency and soybean productivity on a Haplic Acrisol

There is a growing interest in the use of arbuscular mycorrhizal fungi to partially fulfil the high phosphorus need of legumes. Thus, this study hypothesised that, arbuscular mycorrhizal fungi inoculation would enhance phosphorus (P) uptake, growth and yield of soybean when combined with low P fertilizer rate (15 kg ha−1). A two-year field experiment was conducted on a Haplic Acrisol using two mycorrhizal isolates (Glomus mosseae and Rhizophagus irregularis) inoculated on two soybean lines (TGx 1989-48 FN and TGx 1989-75 FN). The treatments also included three levels of triple superphosphate (TSP) (0, 15, and 30 kg P ha−1). The treatments were arranged in a split-split plot design with three replications. The soybean lines, P rates and mycorrhizal isolates constituted the main-plot, sub-plot and sub-sub plot factors, respectively. Mycorrhizal inoculation combined with 15 kg P ha−1 gave the highest soybean root length colonization, shoot and grain P uptake, shoot biomass and grain yields which were statistically comparable to 30 kg TSP ha−1. Glomus mosseae showed higher soybean root length colonization and P uptake, which resulted in better soybean growth and yield improvement than R. irregularis. Furthermore, inoculation combined with 15 kg P ha−1 reduced soil microbial biomass P by stimulating P release by soil microbes and thus increased soil available P. However, G. mosseae inoculated plots showed higher performance in soybean root length colonization and P uptake, which consequently resulted in better P use efficiency than R. irregularis. Inoculation of mycorrhizal isolates combined with 15 kg P ha-1 gave the highest net benefit and marginal rate of return and is therefore economically profitable for soybean production. Inoculation with G. mosseae or R. irregularis combined with 15 kg P ha-1 is therefore a promising technology that can be used to enhance P uptake and soybean productivity. Future research should focus on understanding the long-term interaction of different benchmark soils, legume species and mycorrhizal species in order to select high quality infective propagules with long shelf life and efficiency under field conditions.

The Contribution of Various Components to pH Buffering Capacity of Acrisols in Southeastern Vietnam

ABSTRACTThis paper examined the contribution of various soil components to pH buffering capacity (pHBC) of haplic Acrisols in an upland area of Southeastern Vietnam. Sampling was conducted in 2016 in Tan Bien district, Tay Ninh province at seven sites from the surface to 60-cm depth. Soils were very acidic (pHH2O 4.53 ± 0.05). The pHBC were very low, 0.46 ± 0.04 and 0.44 ± 0.05 cmol H+ kg−1 pH−1, respectively, for original samples and those from which soil organic carbon (SOC, 0.52 ± 0.09%) were removed. The contribution of Al3+ to pHBC was remarkable while that of SOC was of little significance. The contribution of clay minerals to pHBC was unclear due to the low (9.37 ± 0.76%) and kaolinite-dominated clay content. The current soil conditions indicated a potential for further soil acidification. Liming would be one of the measures to remediate soil acidity in the research area.