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The high phosphate retention in andisol soil is often associated with a decrease in potato yield. Additionally, identification of the physical and chemical characteristics of andisols and their correlation to potato yield through soil mapping units (SMUs) is necessary to facilitate field surveys. Therefore, this study aimed to identify the physicochemical characteristics of andisols with a focus on available phosphorus (P) and the correlation to potato production based on SMUs. The experiment was conducted in Karo District, North Sumatra, Indonesia, from July 2022 to February 2023. A descriptive-analytical method was used by overlaying maps of slope, soil types, and altitude until 10 SMUs were selected that were planted with potatoes. Soil physicochemical properties were identified, while Pearson correlation analysis was performed on available-P and potato yield using IBM SPSS software. The results showed that the silt and clay fractions positively correlated with available-P in andisols. All soil physical characteristics were categorized as very weak to weak in supporting potato yield. A total of four SMUs including 1, 5, 8, and 10 were found to have lower available-P and very low to moderate correlations with soil pH, organic-C, C:N ratio, cation exchange capacity (CEC), as well as total-P. Based on the results, potato yield could increase by 1.765 and 0.380 tons ha-1 through the addition of organic-C and C:N ratio in Karo District. Therefore, soil amendment is required as an alternative to improve andisols soil.

Background and aims Dissolved organic matter (DOM) stands out as a highly active component within the organic matter pool. It is hypothesized to play a crucial role by adsorbing onto minerals and serving as a precursor for soil aggregates. However, the impact of DOM substrate types and addition levels on the intricate dynamics of soil aggregates remains elusive. Methods A 28-day short-term incubation experiment was conducted to investigate the responses of a Japanese Andisol to different DOM substrates, exploring the influence of three DOM substrates and two concentration levels. REOs concentrations in three aggregate fractions were measured on 0, 7, 14, and 28 days of incubation to calculate the aggregates transformation paths and relative aggregate change. Results DOM addition significantly increased aggregate stability in Andisols soil, evident in the elevated mean weight diameter (MWD) compared to the control (CK) treatment. The change of aggregate stability during incubation is determined by both DOM types and addition levels. The N-Acetyl-D( +)-Glucosamine (NADG) treatment, peaking at 14 days, whereas the vanillin (VAN) treatment reaching the highest MWD value before incubation (0 days). The increase in aggregate stability was reflected in the transformation paths of aggregates. NADG treatment, VAN treatment, and the NADG&VAN (MIX) mixture all contributed to reduced macroaggregate breakdown and inhibited the microaggregates breakdown. Furthermore, the relative changes in aggregate turnover exhibited varying trends across treatments. Regarding macroaggregate dynamics, the addition of vanillin, especially in the 100%VAN and 100%MIX treatments, significantly enhanced macroaggregate formation, with an increase of over 30% in the 100%MIX treatment after 28 days. Microaggregate dynamics varied among treatments. In the 100%NADG and 100%VAN treatments, there was an initial increase from 0 to 7 days, succeeded by a decrease from 7 to 28 days. The 50%VAN and 50%MIX treatments exhibited an increasing trend from 0 to 14 days, followed by a decrease from 14 to 28 days. Conclusion Overall, these findings highlight the important role of DOM in aggregate dynamics and suggest that the types and addition levels of DOM can significantly impact soil aggregate turnover pathways.

Background and aims Rare earth element (REE) oxides serve as effective tracers to track aggregate dynamics. However, the impact of labeling and sieving processes on aggregate and organic matter dynamics remains uncertain. This study aimed to determine the effect of the labeling and sieving processes on soil aggregate and organic carbon dynamics. Methods Dry and wet sieved aggregates from a Japanese typical Andisol were labeled with REE oxides. REE oxides concentrations and soil organic carbon fractions were measured during the 28-day incubation period to calculate aggregate transformation paths and soil organic carbon dynamics. Results The findings demonstrated that REE oxides are effective tracers to track Andisol aggregate turnover. The labeling and sieving processes showed significant positive effect on aggregate turnover. During incubation, wet sieved macroaggregates displayed more transformation than dry sieved aggregates (5.26% ~ 7.24% vs. 11.03% ~ 12.81%), reflecting a higher turnover rate of macroaggregates resulting from wet sieving relative to dry sieving. Regarding organic carbon fractions, the labeling process significantly affected dissolved organic carbon (DOC), microbial biomass carbon (MBC), and free particulate organic matter (fPOM). Additionally, the degree of interference was linked to the sieving processes, with MBC and fPOM content significantly lower following wet sieving. This effect persisted during incubation, except for fPOM content, which exhibited a rapid increase accompanied by a decrease in occluded particulate organic matter (oPOM) content following the wet sieving method. Conclusion Our results demonstrate that the effects of labeling and sieving processes should be considered when analyzing the relationship between aggregate turnover and organic carbon with REE oxides tracers.

Iron is one of the most abundant elements in agricultural soils, but it is mostly present in non-assimilable forms. The dynamics of Fe is determined by several factors, such as organic matter (OM). Dairy slurry is used to increase total OM content in soils. The objective of this study was to determine the effect of applying dairy slurry over a 12-yr period on the levels of available, amorphous, and total Fe in an Andisol soil as indicators of pedogenic alteration. The contents of available (Fed), amorphous (Feox), and total (Fet) Fe were evaluated by selective extractions. A completely randomized experimental design with repeated measures was used, which consisted of six treatments (2, 4, 6, 8, 10, 12 yr) of slurry application and four replicates. A control treatment (no slurry application) was also included with permanent Lolium perenne L. and Trifolium repens L. grasslands. Dairy slurries were applied at a maximum rate of 150/m3 ha-1. Slurry application in the soil significantly increased Fed and OM contents up to 8 yr in the A (8.2 g kg-1 and 15.7%) and B (7.49 g kg-1 and 10.3%) genetic horizons under study; there was a positive correlation between Fed and OM. This would indicate that increased OM would accelerate the pedogenesis of this soil. In general, Fed-ox values were low and there was a significant decrease (p ≤ 0.05) in the 2-, 4-, and 6-yr treatments with values ranging between 1.0 and 0.7 for the Feox:d ratio, indicating increased pedogenesis.

Agricultural soils account for about 60% of the global atmospheric emissions of the potent greenhouse gas nitrous oxide (N[sub.2] O). One of the main processes producing N[sub.2] O is denitrification, which occurs under oxygen-limiting conditions when carbon is readily available. On grazed pastures, urine patches create ideal conditions for denitrification, especially in soils with high organic matter content, like Andisols. This lab study looks at the effects of Urine-urea-N load on the Andisol potential to emit N[sub.2] O. For this, we investigated the effects of three levels of urea-N concentrations in cow urine on emissions of N[sub.2] O, N[sub.2] , and CO[sub.2] under controlled conditions optimised for denitrification to occur. Results show total N[sub.2] O emissions increased with increasing urine-N concentration and indicate that denitrification was the main N[sub.2] O-producing process during the first 2–3 days after urine application, though it was most likely soil native N rather than urine-N being utilised at this stage. An increase in soil nitrate indicates that a second peak of N[sub.2] O emissions was most likely due to the nitrification of ammonium hydrolysed from the added urine, showing that nitrification and denitrification have the potential to play a big part in N losses and greenhouse gas production from these soils.

Rhizobacterial communities may play a crucial role in phosphorus (P) nutrition of plants. However, our knowledge of how P fertilization modulates rhizobacterial communities in crops and pastures is still poor. Here, we investigated the effect of P addition (phosphate [PHO] and phytate [PHY]) on the composition of total bacterial communities and alkaline phosphomonoesterases (APase)-harboring bacterial populations in the rhizosphere microsites (root tip [RT] and mature zone [MZ]) of L. perenne . Sizes and diversities of bacterial communities were studied by 454-pyrosequencing of 16S rRNA genes, denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR). Our results suggested that phosphorus addition induces significant changes in the rhizobacterial community composition. Despite that pyrosequence analysis showed that members of the Proteobacteria , Actinobacteria , Chloroflexi , and Acidobacteria were the dominant phyla in all sampled rhizosphere microsites, differences in the relative abundances of some bacterial genera were detected (e.g., Arthrobacter and Acidothermus ). Greater richness in rhizosphere microsites of plants supplied with PHY compared with PHO were revealed. With respect to APase-harboring bacterial populations, DGGE ( phoD gene) showed significant differences between microsites supplied with PHO, PHY and controls. qPCR (16S rRNA genes, phoD and phoX ) showed significantly greater abundances of bacteria and APase genes in RT than in MZ microsites. This study contributes to our understanding of the effect P fertilization on rhizobacterial community compositions of pastures grown in Chilean Andisols.

To date, research on the role of organic matter dynamics in maintaining the health of (sub)tropical Andisols (i.e., volcanic ash-derived soils) is limited. High concentrations of poorly and noncrystalline minerals in these soils favor greater soil organic matter (SOM) accumulation than in phyllosilicate-dominant soils, yet SOM abundance and composition vary across volcanic landscapes. In this study, we measured the effects of moisture regime and current land use on soil health and SOM physical fractions and identified the carbon (C) and nitrogen (N) fractions that best predicted soil health scores in Andisols. We collected soil samples across humid (Udands) and dry (Ustands) moisture regimes and three land uses (croplands, pastures, forests) on Hawaiʻi Island. We measured nine dynamic soil properties and integrated them into a soil health score using a structural equation model. Then, we quantified the C and N contents of SOM physical fractions, including light particulate organic matter (LPOM), coarse heavy associated organic matter (CHAOM), and mineral associated organic matter (MAOM). We found that pastures and Udand forests scored highest in soil health while Ustand croplands scored lowest. Pastures contained greater proportions (% of total element) and contents (mg/g soil) of C and N in the CHAOM fraction, suggesting differences in CHAOM composition across ecosystems. All three physical fractions collectively explained 81% of soil health score variation, with MAOM-C explaining substantially more variation than LPOM-N and CHAOM-N. Our framework, which links soil C and N fractions to dynamic soil health properties, holistically captures the unique attributes of (sub)tropical Andisols rich in poorly and noncrystalline minerals.

Plants need the nutrient P to increase growth and yield. P availability is low in Andisol soil and has high retention by 97.8%. Giving the phosphate solubilizing fungi (PSF) is an alternative to increase available P which plants can use to increase growth and yield. This research aims to determine the benefits of providing phosphate-solubilising fungi on the growth and yield of shallots in Andisol. The study used a block randomized design with three replications. The first factor is Andisol soil origin (Karo regency and Tapanuli Utara regency) and the second is isolate of phosphate solubilizing fungi ( Aspergillus niger P13, Aspergillus niger P21, Aspergillus pseudodeflectus BJ21, and Aspergillus niger BJ23). The research results showed that the soil from Karo can increase plant dry weight and root dry weight respectively by 36.38% and 37.66% compared to Tapanuli Utara. The application of Aspergillus pseudodeflectus BJ21 and Aspergillus niger BJ23 fungi was able to increase plant dry weight by 35.10% and 34.25% and root dry weight by 29.38% and 23.46% compared to without PSF application. The soil origin of Karo Regency increased yield by 36.40% from Tapanuli Utara Regency. Giving fungi Aspergillus pseudodeflectus BJ21 and Aspergillus niger BJ23 fungi was able to increase plant dry weight by 35.10% and 34.25% and root dry weight Aspergillus niger P13 was able to increase yield of 65.63% and 63.12% compared to without giving PSF.

The use of coated fertilizers and the concept of the critical N dilution curve are alternatives capable of improving the production efficiency of wheat (Triticum aestivum L.) crops in agro‐ecosystems. The objectives of this work were to evaluate the effect of a slow release urea‐coated fertilizer on (i) the production of wheat's shoot biomass at the anthesis stage, (ii) the concentration of N in the shoot biomass, and (iii) the N availability in the Andisol. Two fertilizers: urea and urea‐coated were evaluated using four increasing N rates and a control treatment (without fertilization), in three application strategies, during two growing seasons (late sowing [S1] and early sowing [S2]). Samples of shoot biomass and soil (0–20‐cm depths) were collected at five wheat growth stages (Z21, Z31, Z39, Z45, Z69 on the Zadoks scale). The average production of shoot biomass was 10.3 t dry matter (DM) ha–1 for S2 and 7.9 t DM ha–1 for S1 and N concentrations was between 1.0–3.0%. When using a coated urea fertilizer in this Valdivian agro‐ecosystem, no statistical differences (P < .05) in shoot biomass or wheat N concentrations were found at anthesis (Z69). Differences were principally between seasons. We therefore proposed a new adjustment to the dilution N curve, with a value concentration critical, Nc start of 3.80%, and 4.15%, for S1 and S2, respectively. Use demand parameters such as Nc adjusted to the agro‐ecosystem for wheat crop, allows to rationalize the fertilization according to inorganic N available from the soil.

Cereal production in southern Chile is based on ash-derived volcanic Andisols, which present suboptimal levels of available selenium (Se). Strategies are needed to improve Se content in cereal crops and concomitantly improve the nutritional quality of grain. Here, we investigated the occurrence of Se-tolerant bacteria (STB) in Andisols and evaluated Se tolerance and accumulation in STB. The inoculation of wheat with STB and the contributions of these bacteria to Se content in plants were also evaluated under greenhouse conditions. The results showed that Se amendment of Andisols stimulated some bacterial groups ( Paenibacillaceae and Brucellaceae ) but inhibited others (Clostridia, Burkholderiales , Chitinophagaceae and Oxalobacteraceae ), as revealed by denaturing gradient gel electrophoresis. Furthermore, we found four STB isolates that displayed 1-aminocyclopropane-1-carboxylate deaminase (ACC deaminase activity) and that carried the acd S gene as revealed by PCR. The selected STB were characterised as Stenotrophomonas , Bacillus , Enterobacter and Pseudomonas according to partial sequencing of the 16S rRNA gene. After 24 h of culture in nutrient broth, the selected STB showed the ability to grow in high Se concentrations (5 and 10 mM) and to accumulate elemental Se in micro- and nanospherical deposits, transforming 50–80 % of the Se initially added. Greenhouse experiments with wheat showed that Se associated with STB (micro- and nanospheres of elemental Se and other intracellular forms) can be translocated into leaves of wheat plantlets.