Silt Loam Research Articles

Aging Dynamics of Polyvinyl Chloride Microplastics in Three Soils with Different Properties.

Microplastic (MP) contamination in soil has been of great concern, but the dynamic aging process and potential pathways of MPs in natural soil systems remain poorly understood. Herein, poly(vinyl chloride) microplastics (5% w/w) were weathered for 12 months in sandy soil, silty clay, and silt loam. The results showed that the continuous increase of C═O and O-H groups (rate constant, k = 0.080-0.424 m-1) with time was observed on the surface of MPs aging in sandy soil due to the leading role of •OH induced by light irradiation. In the loam soil, the abundant coating of aluminosilicates and iron oxides on the MP surface by the formation of mineral-hydroxyl groups inhibited the generation of the C═O group (k < 0.165 m-1). The k of the characteristic bond C-Cl during the first 9 months was 9.51 and 1.93 times higher in clay compared to that in sandy and loam soil, respectively, revealing that dechlorination triggered the first step of the aging process for MPs in clay owing to the participation of degrading bacteria (Phenylobacterium and Caulobacteraceae). The results provide important insights into the aging dynamics of MPs in environmentally realistic circumstance, which account for understanding the different aging processes of MPs in different soils.

Changes in soil mechanical and hydraulic properties through regenerative cultivation measures in long-term and farm experiments in Germany

Regenerative agriculture has been associated with improved soil structure and soil fertility. However, conclusive evidence of its efficacy has remained elusive owing to a lack of long-term experimental studies. In this study, we assessed the impact of diverse regenerative agricultural measures on soil mechanical and hydraulic properties and indicators. Tested treatment factors included reduced tillage versus plowing, along with different levels of compost, mulch, and the application of ferments and compost tea. We measured in situ soil strength via soil penetration (from 0 to 0.8 m depth) and shear resistance (at 0.08 and 0.23 m depth) and assessed field-saturated hydraulic conductivity and ex situ soil aggregate stability (at 0.07 and 0.23 m depth). The experiments were conducted at five sites in Hesse, Germany, including one organic long-term experiment (LTE, since 2010) in Neu-Eichenberg and three organic and one conventional on-farm experiments to cover different soil types, weather conditions, and field practices. The soil types are classified as Luvisol and Vertic Cambisols, and the soil texture ranges from silt loam to silty clay loam. In the LTE, significant differences in aggregate stability and shear resistance were noted between treatments, with a higher geometric mean aggregate diameter at 0.07 m depth in 2021 and 2022 and a higher shear resistance at 0.19 m and 0.23 m in 2020 and in 2021, respectively, in the reduced tillage systems. However, no significant differences were observed among treatments for field-saturated hydraulic conductivity, which was overall very high, showing that reduced tillage did not negatively influence saturated infiltration, albeit bulk density is higher than in the conventionally plowed system. The soil penetration resistance was generally higher for the reduced tillage treatments across depths of 0.0–0.30 m, albeit not statistically significant (p > 0.05). Significantly higher water-stable aggregates and geometric mean diameters were observed for regenerative agricultural treatments in three of the on-farm experiments at a depth of 0.07 m. The shear resistance was significantly higher in regenerative agriculture units in specific years and depths. Although the outcomes are encouraging, the variability of the effects of reduced tillage and organic amendments in affecting soil properties highlights the need for further long-term research including farm trials. This is essential to fully understand the effects of regenerative practices on soil physical quality.

Effects of freeze–thaw on the detachment capacity of soils with different textures on the Loess Plateau, China

Soil detachment capacity (Dc) is a crucial indicator for quantifying erosion intensity. However, the combined actions of freeze–thaw and water flow complicate the erosion process, leaving the variation mechanism of Dc under this condition systematically unexplored. This study examined five loess soils from a seasonal freeze–thaw area. The mechanism driving changes in Dc was quantified through freeze–thaw simulation combined with flow scouring tests, and a Dc prediction model was established. The results revealed that the shear strength (τm), cohesion (Coh), and internal friction angle (φ) in silt loam were higher than in sandy loam. After freeze–thaw cycles (FTC), τm, Coh, and φ of the five loess soils decreased by 1.02–1.37, 1.07–9.15, and 0.92–1.05 times, respectively. As FTC increased, τm and Coh gradually stabilized, while φ showed minimal fluctuation, indicating that FTC had a cumulative effect on the deterioration of soil mechanical properties. During FTC, Dc in Wuzhong sandy loam was the largest, being 1.14–3.24 times greater than in other soils, suggesting a significant main effect of soil type on Dc variation, with a contribution rate of 19.27 %. Dc eventually stabilized with increasing, indicating a critical FTC of around 10 for its impact on Dc. Compared to unfrozen soils, Dc increased by 33.69 %–102.40 % under the combined effects of freeze–thaw and water flow, clarifying that FTC aggravated soil instability. Effective stream power was the optimum hydraulic parameter, contributing the most to Dc (45.94 %). FTC (6.41 %) and initial soil moisture content (8.59 %) were less influential, as FTC initially degraded soil properties, and then the combined action with water flow intensified soil damage, causing the role of freeze–thaw factors to be obscured by other variables. A Dc prediction model using a general flow intensity index estimated well Dc, with both R2 and NSE at 0.94. Model performance comparison emphasized the need for validation when extending the application range beyond development conditions. These findings provide new insights into the detachment mechanisms of different textured soils under compound freeze–thaw and hydrodynamic influence in freeze–thaw region.

Clomazone and Oxyfluorfen Combinations in a Flooded Rice System

Abstract Rice producers battle herbicide-resistant weeds worldwide while producing rice for ≥50% of the world’s population. Oxyfluorfen can provide rice producers with an alternative site of action for barnyardgrass control, as there are no documented cases of grass weeds being resistant to the herbicide in the midsouthern United States. Oxyfluorfen is anticipated to be labeled in the Roxy Rice Production System and may be sold as a clomazone:oxyfluorfen premixture; hence, experiments were conducted in 2021 and 2022 to evaluate preemergence-applied clomazone:oxyfluorfen ratios compared to clomazone alone on silt loam and clay soils. All ratios of the herbicides caused less than 7% injury to rice in two of four site-years on silt loam soils, whereas, in the two other site-years, the mixtures caused 10% to 40% rice injury at all observation timings. All combinations of the two herbicides provided at least 73% barnyardgrass control 5 weeks after rice emergence (WAE) in three of the four site-years on silt loam soils. In at least two of four site-years at 1 and 3 WAE, barnyardgrass control was improved when oxyfluorfen was added to clomazone compared to clomazone alone. On clay soil, barnyardgrass control in both site-years was ≥77% at 5 WAE for all clomazone and oxyfluorfen ratios. Injury to rice ranged from 13% to 30% for all treatments containing clomazone and oxyfluorfen in one of two site-years on clay soil at all observation timings. At 7 WAE, contrasts indicated that the 1:3 ratio of clomazone to oxyfluorfen provided greater barnyardgrass control than the 1:1.5 and 1:2 ratios in one of two site-years. Based on these findings, oxyfluorfen would improve the consistency of barnyardgrass control over clomazone alone in some instances. However, there is an increased risk of injury to rice with the addition of oxyfluorfen.

Impact of microbial activity on fluoride release from sediments in areas with high fluoride groundwater: Mechanisms, sources and the lithology diversity

This study explores the interplay between microbial activity and sediment lithology in influencing fluoride release from sediments. Sediment samples, collected from Yuncheng Basin: a region known for significant groundwater fluoride contamination, exhibit fluoride concentrations well above the global average, ranging from 206.2 mg/kg to 780.9 mg/kg. These samples comprising silt, silt loam, and sandy loam, are enriched with minerals such as quartz, calcite, albite, chlorite, and illite.Microbial batch incubation reveals that microbial activity significantly enhances fluoride release, particularly in silt loam sediments. The results from sequential extraction first timely identified that the carbonate-bound and Fe-Al-bound fluoride fractions are the most affected forms of fluoride by microbial activity, highlighting the roles of mineral dissolution and desorption in fluoride mobilization.Further batch incubation experiments demonstrate significant increases in fluoride concentrations, especially in silt loam sediments, indicating the role of microbial processes in accelerating fluoride release. Additionally, the study unveils diverse patterns of dissolved elemental concentrations during incubation, with varying release patterns for calcium, magnesium, iron, aluminum, and manganese. These findings illustrate the complex biogeochemical interactions that govern fluoride mobilization in these sediments.Sequential extraction studies further elucidate the intricate mechanisms of fluoride release, with microbial activity primarily influencing the release of carbonate-bound and Fe-Al-bound fluoride. This study also sheds light on the co-dissolution of fluoride and calcium, offering valuable insights into geochemical processes driven by microbial interactions within the sediment matrix.

Nitrification inhibitor effect on manganese and phosphorus shoot concentrations in maize under different textured soils from northern Germany

High soil pH can result in Mn2+ and P deficiency, leading to crop yield losses. Therefore, supplying soil with NH4+-N fertilizer in stabilized or unstabilized form can increase soil Mn2+ availability and shoot concentration. Nitrification inhibitors (NIs) have been proposed to lower rhizosphere soil pH, thus improving plant P uptake and preventing P deficiency in soils with high pH. Thus, this study investigated whether NI-stabilized or unstabilized NH4+-N could increase Mn2+ availability in three differently-textured soils (sand, loamy sand, and silt loam) and promote Mn2+ and P shoot concentration in maize. Two greenhouse experiments were conducted to investigate the effects of applying NH4+-N fertilizer with or without the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) combined with different nitrogen (N) sources (calcium nitrate (CN), ammonium nitrate (AN), and ammonium sulphate (AS)). The measured variables were bulk and rhizosphere soil pH and Mn2+ availability, maize biomass, as well as Mn2+ and P shoot concentrations. The results indicated that DMPP-stabilized AS significantly decreased rhizosphere pH by 7.2 % in loamy sand soil texture compared with unstabilized AS. Similarly, only in the loamy sand texture, DMPP-stabilized AS increased Mn2+ availability and shoot concentration by 86 % and 47 %, respectively, relative to unstabilized AS. Furthermore, DMPP-treated AS and AN promoted P shoot concentration by 30 % and 21 % in the loamy sand and silt loam soil textures, respectively, relative to the corresponding N sources without DMPP. Conversely, DMPP did not impact the investigated variables in the sand texture for all N sources. Moreover, AN and AS increased biomass yield, Mn2+ availability, and shoot concentration by 72 %, 30 %, and 46 %, respectively, in relation to the CN fertilizer in the sand soil texture. In conclusion, this study confirmed the effectiveness of DMPP-induced rhizosphere acidification in enhancing Mn2+ and P shoot concentration in loamy sand soil textures, as well as P shoot concentration in fine-textured soil.

Physical–Chemical and Thermal Properties of Clays from Porto Santo Island, Portugal

The use of clays for thermal treatments and cosmetic purposes continues to be a worldwide practice, whether through the preservation of native cultural traditions, pharmaceutical formulations or integrative health and well-being practices. Special clays, such as bentonites, are very common for healing applications due to their high cation exchange capacity (CEC), high specific surface area (SSA) and alkaline pH values and, therefore, are used in multiple therapeutic and dermocosmetic treatments. Numerous bentonitic deposits occur on Porto Santo Island with different chemical weathering degrees. This research evaluates which residual soils have the most suitable characteristics for pelotherapy. The texture of residual soils varies from silt loam to loamy sand and SSA between 39 and 90 m2/g. The pH is alkaline (8.7 to 9.6), electrical conductivity ranges from 242 to 972 µS/cm, and CEC from 50.4 to 86.8 µS/cm. The residual soils have a siliciclastic composition (41.36 to 54.02% SiO2), between 12.52 and 17.65% Al2O3 and between 52 and 82% smectite content, which are montmorillonite and nontronite. Specific heat capacity (0.5–0.9 J/g°C) and cooling kinetics (14.5–19 min) show that one residual soil has the potential to be suitable for pelotherapy according to the literature. Moreover, the residual soils have As, Cd, Co, Cr, Hg, Mn, Ni, Pb, Sb and V concentrations higher than the limits of guidelines for cosmetics and pharmaceutical products.

Effect of salt concentration on osmotic potential in drying soils—Measurement and models

AbstractThe water potential in drying soils, comprising both matric potential and osmotic potential components, can be measured using the dew point method (DPM). By combining DPM data with retention curve data acquired from techniques such as the suction plate method or the simplified evaporation method (SEM), it becomes possible to determine the soil water retention curve across the entire moisture spectrum. However, as the latter methods only determine the matric potential, the osmotic potential component in DPM data must either be negligible or known so that osmotic and matric potential components can be separated. This study aims to critically analyse common approaches for calculating the osmotic potential. To achieve this, we measured the water retention properties of a silt loam, a sandy loam and a sand across the entire moisture range by combining SEM and DPM. By using almost salt‐free soil material, we characterized reference water retention curves with negligible osmotic potential components. The impact of salt on water potential was analysed by conditioning soils with MgCl2 solutions of different concentrations, drying them, and measuring the water potential at different water contents using the DPM. The resulting water potentials were compared to the reference potentials and differences were interpreted as the osmotic potential component. The DPM‐measured water potentials in drying soils can be significantly affected by osmotic potential, especially at higher matric potentials (low suctions). Two models accounting for ideal and one model accounting for non‐ideal electrolyte behaviour were used to compare osmotic potential predictions with measurements. At low to medium salt concentrations, all models performed fairly well. At high concentrations, only the model accounting for non‐ideal behaviour predicted the osmotic potential satisfactorily, whereas at very high concentrations, all models underestimated the impact of osmotic potential on water potential. This suggests that the surface properties of the soil matrix, such as the specific surface area and surface charges, may lead to a decrease in osmotic potential beyond what is expected in pure solutions.

Control of landscape position on organic matter decomposition via soil moisture during a wet summer

Sustainable cropland management requires preservation of soil organic matter (SOM). In spite of in depth understanding gained from ample field and laboratory studies, we have a poor understanding of landscape scale spatial variation of fresh organic matter (OM) decomposition and its conversion into soil organic carbon (SOC). Particularly, local topographic position may be expected to co-control these processes via soil hydrology. In this study, we sought to identify if such control is significant by setting up a field experiment with two contrasting positions across 10 gently sloping cropland fields covering three different soil texture groups, i.e. loamy sand, (sandy) loam and silt loam. We wanted to link OM decomposition to within-field differences in soil moisture, whilst keeping variation in other soil and management factors minimal. Specifically, mesocosms with 13C enriched ryegrass (the OM source) were incorporated in the fields for ten weeks and afterwards, soil was separated into > 500 µm, 53 – 500 µm and < 53 µm sized fractions. Overall, we found that lower located positions were wetter than higher positions with average differences of 11 %, 20 % and 16 % in water-filled pore space for the loamy sand, (sandy) loam and silt loam soil, respectively. Mineralization of added OM was surprisingly independent of landscape position, even though moisture conditions appeared wetter than optimal at the low but not at the high landscape positions. Remaining ryegrass residues > 500 µm did follow local topography-driven gradients in soil moisture with higher amounts in low landscape positions. In other words, drier conditions at high landscape positions improved coarse OM decomposition, with consequently more ryegrass-carbon (C) ending up in finer soil fractions (< 500 µm). Additionally, soil texture affected decomposition of the smallest fraction (< 53 µm) with a stabilizing effect for finer-textured (silt loam) soils. We conclude that, despite significant contrasts in moisture conditions between landscape positions, within-field spatial variability of OM mineralization was overall limited during the observed wet summer period. Nevertheless, landscape position affected the quality of remnant unmineralized C, with relatively more conversion of freshly added OM into OM associated with silt and clay at the drier higher positions, potentially improving the long-term stability of SOM. Likewise observations under different weather conditions are needed to evaluate the necessity of precise modelling of local soil hydrology for predicting SOC stock evolution on the landscape scale.

Temporal Variation Pattern of Runoff and Surface Sediment and Piping Erosion in Silt Loam Soil under Different Slopes Using Artificial Rain Simulator

Temporal Variation Pattern of Runoff and Surface Sediment and Piping Erosion in Silt Loam Soil under Different Slopes Using Artificial Rain Simulator

Mechanical and rheological behaviors of sands containing fines

The present work was carried out with the aim of investigating the rheological behavior, in terms of contractance and dilatancy, and the mechanical behavior, in terms of shear resistance and mechanical characteristics, of sands containing different types of fines. This study is based on direct box shear tests that were carried out on three types of soils which were reconstructed by mixing clean sand with fines, namely silt, clay and clay loam. It is important to indicate that the mass percentages for sand replacement were 0, 10, 20, 30 and 40%. To do this, dry samples were prepared and subjected to shearing, under vertical stresses of the order of 100, 200 and 400 kPa. The results obtained showed that the maximum shear strength and friction angle of sand containing silt decreased while its cohesion increased, as the fines content increased. In addition, the maximum shear strength and friction angle of sand containing clay and silty clay decreased until reaching their minimum values ​​for contents equal to 20% clay and 30% clay and clay loam, respectively. The opposite phenomenon occurred for their cohesion which increased then decreased. It has also been observed that the more plastic the fines are, the higher their content in sand, the more this sand becomes contracting rather than dilatant.

Effects of Muddy Water Infiltration on the Hydraulic Conductivity of Soils

Despite the high sand content of Yellow River water in arid Northwest China, locals in the region opt to use muddy water to meet the demand for agricultural irrigation. Muddy water irrigation is a complex process and is still poorly understood. In this study, six sets of saturated soil column infiltration tests were designed, considering soil texture (silt loam, sandy loam, and sand) and muddy water sand content (3%, 6%, 9%, and 12%) as the influencing factors, with two sets of validation tests. Change in hydraulic conductivity (Kh), the average change rate of hydraulic conductivity (ΔK), and cumulative infiltration volume (I) were experimentally studied in the context of muddy water infiltration to respectively establish the separate functional models and developed to fit their relationship with time. The study results indicated that the hydraulic conductivity (Kh) decreased with increasing muddy water infiltration time. For silt loam and sandy loam, Kh stabilized at 0.0030 and 0.0109 cm/min, respectively, after 70 min of infiltration. In contrast, Kh in the saturated sandy soil column significantly declined throughout the muddy water infiltration, showing a 90.84% reduction after 90 min compared to the saturated hydraulic conductivity of the sandy soil. As the sand content of the muddy water increased from 3% to 12%, Kh decreased by 83.99%, 90.90%, 91.92%, and 92.21% for 3%, 6%, 9%, and 12% sand content, respectively, in the saturated sandy soil columns at the end of the infiltration period. The I values were 21.20, 9.29, 7.90, and 6.25 cm for 3%, 6%, 9%, and 12% sand content, respectively. The ΔK values were 0.0037, 0.0041, 0.0043, and 0.0044 cm/min2 for the respective sand contents, at an infiltration time of 80 min. The validation test demonstrated that the segmented function model accurately emulated the changes in hydraulic conductivity of sandy soil textures throughout the infiltration period. Results from this study provide a significant basis for understanding the mechanisms to hinder muddy water infiltration and to efficiently utilize muddy water for irrigation.

Effect of agricultural management system (“cash crop”, “livestock” and “climate optimized”) on nitrous oxide and ammonia emissions

AbstractThe study aimed to measure soil-atmosphere N2O fluxes and their controlling factors, as well as NH3 emissions and yields for two soils (silt loam and clay loam) in three management systems over two years under subsequent wheat and maize cultivation. The management systems were characterized as follows: (1) cash crop (C) with mineral fertilizer and conventional tillage; (2) livestock (L) with biogas residue fertilization and its incorporation prior to sowing in maize and reduced tillage; and (3) climate optimized (O) with minimum tillage, 8-year crop rotation, with biogas residue fertilization, in maize without incorporation in clay loam soil or incorporation by strip-tillage prior to seeding in silt loam soil. Stable isotope ratios of N2O and mineral N were determined to identify N2O processes. Within the organically fertilized maize treatments, cumulative N2O fluxes were highest in the O-system treatments of both sites (4.0 to 9.4 kg N ha− 1 a− 1), i.e. more than twice as high as in the L-system (1.5 to 3.1 kg N ha− 1 a− 1). Below root-strip till fertilizer application did not enhance N2O fluxes. Fluxes with mineral fertilization of wheat (1.1 to 3.1 kg N ha− 1 a− 1) were not different from those with organic fertilization. Isotopic values of emitted N2O revealed that bacterial denitrification dominated most of the peak flux events, while the N2O/(N2 + N2O) ratio of denitrification was mostly between 0.1 and 0.5. It can be concluded that, contrary to the intention to lower greenhouse gas fluxes by the O-system management, the highest N2O fluxes occurred in the O-system without biogas digestate incorporation in maize. With respect to NH3 fluxes, we could confirm that the application of digestate application in growing crops without incorporation or late incorporation in fertilization before sowing induces high fluxes. The beneficial aspects of the O-system including more stable soil structure and resource conservation, are thus potentially counteracted by increased N2O and NH3 emissions.

Early Season Wheat Response to Electrochemically Precipitated Struvite in Various Soils in the Greenhouse

Fertilizer-phosphorus (P) materials can be recovered from wastewater and used to supplement mined phosphate rock, where one such material is struvite [MgNH4PO4·6(H2O)]. This study aimed to compare electrochemically precipitated struvite (ECST) reclaimed from synthetic wastewater to other commercial fertilizer-P sources in cultivated soils from Arkansas [silty clay loam (AR-SiCL) and silt loam (AR-SiL)], Missouri [(silt loam; MO-SiL 1 and 2)], and Nebraska [silt loam (NE-SiL) and sandy loam (NE-SL)]. A greenhouse pot study was conducted for 60 days with unvernalized wheat (Triticum aestivum) using five fertilizer-P sources [ECST, chemically precipitated struvite (CPST), monoammonium phosphate (MAP), triple superphosphate (TSP), and an unamended control (UC)] to evaluate treatment effects on below (BG)- and aboveground (ABG) and total dry matter (DM) and tissue-N, -P, -K, -Ca, -Mg, and -Fe uptakes. The ECST treatment produced 44 g m−2 larger ABG-DM than CPST in the AR-SiCL, but 181 g m−2 larger than the UC in the MO-SiL 1. The ECST had similar or larger nutrient uptakes than CPST, MAP, TSP, and UC. Belowground-P, -N, and -Mg uptakes for ECST were generally similar for all soil-fertilizer-P source combinations, where ECST was 0.3 to 2.6 g m−2 larger than all other fertilizer-P sources. Plant property response from ECST was generally similar to or greater than CPST, MAP, TSP, and the UC across all soils. Results suggest that ECST is a prime candidate to be used as an effective, alternative fertilizer-P source, suitable for use in wheat production across multiple soil textures.

Quantifying the impacts of varying groundwater table depths on cotton evapotranspiration, yield, water use efficiency, and root zone salinity using lysimeters

Determining the evapotranspiration (ET) of cotton as a water-intensive crop is crucial for effective irrigation planning and water management, especially in regions like Sindh province, Pakistan, where shallow groundwater table depths (WTDs) are prevalent. Despite the importance of cotton, a major cash crop in Sindh, previous studies on ET were conducted decades ago and may no longer be reliable due to ongoing climate change and the introduction of new crop varieties. Thus, we quantified cotton ET across two cropping seasons and at various WTDs (0.45, 0.60, 0.75, 1.50, 2.25, and 2.75 m). The experimental study was based on the data procured from 12 mini lysimeters and 12 large lysimeters for two years (2018 and 2019) and at two soil series. The findings revealed that cotton ET ranged from 1332 to 1437, 1114–1202, 988–1075, 781–821, 690–733, and 637–683 mm at WTDs of 0.45, 0.60, 0.75, 1.50, 2.25, and 2.75 m, respectively. WTDs from 0.45 to 0.75 m fulfilled 94–96 % of cotton ET through groundwater (GW) contribution in Sultanpur soil (silt loam) and 93–97 % in Miani soil (silty clay loam). At 1.50–2.75 m WTDs, irrigation water requirements (excluding rainfall and leaching) were 63–88 % in Sultanpur soil and 67–89 % in Miani soil. The highest yield was observed at a 1.50 m WTD, while the highest water use efficiency was identified at a 2.25 m WTD. However, soil salinity increased by 60–80 %, resulting in a 40–60 % lower cotton yield at 0.45–0.75 m WTD. Therefore, periodic flushing of salts is necessary to utilize shallow WTDs effectively. Considering GW contribution to ET when allocating water for irrigation channels and devising irrigation schedules is crucial. This approach can lead to water savings, prevent land from becoming waterlogged and saline, manage the groundwater table, and reduce the need for drainage channels and labor force for their preparation.

Versatile simplistic correction of T-higrow sensors for improved soil moisture measurement accuracy

The use of soil moisture sensors for irrigation can help reduce water and energy consumption and risks of groundwater contamination, which are essential aspects for pursuing sustainable development goals. However, increased adoption of this technology is limited by calibration requirements, technical complexities, and sensor costs. In this work, a simplified method for reducing the measurement error of a recently released low-cost soil sensor (T-Higrow) is presented. The method only requires measurements of a dry sample from the target soil, which are inputted into a simple correction formula to reduce the measurement error at higher moisture levels. The requirements of the proposed method are simple enough for most labs or extension services. This method was compared to the commonly used linear, polynomial, and logarithmic regression models based on repeated bench-scale experiments within 0%–35% moisture range in silt and sandy loam soils and in silica sand. Uncorrected sensor readings correlated well with soil moisture (r: 0.94–0.98), but with significant overestimation (25%–60% error). The simplified correction method showed comparable error reduction to regression models across all soil types. All methods reduced error down to 2%–10% (0.02–0.1 cm3 cm−3) and maintained high correlations (r > 0.94), except for logarithmic regression which reduced correlation by around 3%. Variability amongst sensor measurements was generally low (Standard Deviation: 0.01–0.03) particularly at moisture ranges below 20%, this was also the case for sensor-to-sensor variability (Standard Deviation: 0.01–0.03). Sensor evaluation and calibration works are needed to increase the accessibility to this technology for improved water and energy conservation.

Soil profile distribution of nutrients in contrasting soils amended with struvite and other conventional phosphorus fertilizers

AbstractPhosphorus (P) can be recovered from wastewater and used as an alternative fertilizer, namely, struvite [MgNH4PO4·6(H2O)]. However, the soil mobility of wastewater‐derived P and other nutrients needs to be evaluated. The objective of this study was to compare the vertical distribution of water‐soluble (WS) soil P and other nutrients from a synthetic‐wastewater‐derived electrochemically precipitated struvite (ECST) to that from a chemically precipitated struvite (CPST), triple superphosphate (TSP), monoammonium phosphate (MAP), and a control in six soils from Arkansas (AR; loam [L] and silt loam [SiL]), Missouri (MO; SiL 1 and SiL 2), and Nebraska (NE; sandy loam [SL] and SiL). A column‐leaching experiment was conducted with the six soils and five fertilizer‐P treatments. Water‐soluble (WS) P from the two struvite materials generally did not differ (p &gt; 0.05) and was similar to that of MAP in the depths of 0–3, 3–6, and 6–10 cm, but was greater than that of TSP in the top 6 cm in four of the six soils. WS P from CPST in the MO‐SiL 2 and NE‐SL soils (6.6 and 12.7 mg kg−1, respectively) was larger than that from ECST, MAP, and TSP. In the AR‐L and MO‐SiL 1 soils, TSP was the only fertilizer‐P source that had increased WS P concentrations in the top 6 cm relative to the other fertilizer‐P sources. Results showed that ECST‐derived, WS P had similar soil profile distributions in the top 10 cm, suggesting that ECST will be equally protective of environmental health and leachate quality across multiple soil textures as other common fertilizer‐P sources.

Effects of fertilization applications on soil aggregate organic carbon content and assessment of their influencing factors: A meta-analysis

Fertilizer application plays an important role in agricultural soil organic carbon (SOC) and its sustainable management. However, there is a lack of consensus about the mechanisms regarding fertilizer application in the soil on the procedure of carbon sequestration and sink enhancement in the aggregates. In this study, the extent by which various fertilization treatments, fertilization durations, climate conditions, soil texture, and land-use types affected the organic carbon (OC) content of different particle-size aggregates was quantitatively assessed using a meta-analysis of 696 treatment comparisons from 36 published studies. Based on the meta-analysis results, fertilization enhanced the OC contents of macroaggregates and clay and silt particles, particularly through replenishing organic material. Long-term fertilization increased the OC content of macroaggregates (>0.25 mm), while the OC content of the clay and silt particles (<0.053 mm) reached a maximum at 15.4 years of fertilization, after which it reached carbon saturation. Organic fertilizer effectively increased the OC content of small macroaggregates (0.25–2 mm) and microaggregates (0.053–0.25 mm) at lower temperatures and precipitation. Compared with inorganic fertilization, combined organic–inorganic fertilization increased OC contents of all sizes of aggregates in sandy or clay loam soils, but decreased OC contents of microaggregates and clay and silt particles in silt loam soils. All fertilization treatments increased the OC content of all particle-size aggregates in upland soils. In contrast, inorganic fertilization and mixed organic–inorganic fertilization reduced the OC content of microaggregates (0.053–0.25 mm) and clay and silt particles (<0.053 mm) in paddy field soils. In conclusion, the application of organic fertilizers is more conducive to the accumulation of OC in agricultural soil aggregates. Whereas the limiting factors for the accumulation of OC content in soil aggregates vary under different conditions, organic fertilizer inputs should be given more consideration, especially in dryland and coarse-textured soils.

Biochar influences soil health but not yield in 3‐year processing tomato field trials

AbstractBiochar can deliver many agronomic benefits, though effects may be greatest in suboptimal agricultural soils. The objective of this study was to investigate biochar in prime agricultural soils in a Mediterranean climate. In 3‐year irrigated processing tomato (Solanum lycopersicum) field trials, in which three biochars were amended to a sandy and silt loam, biochar did not influence yield. Given the global policy focus on biochar for climate change mitigation and adaptation, however, it is essential to measure more than just agronomic parameters. To this end, a soil health assessment was conducted 2.5 years after biochar amendment. In the fertile silt loam and more nutrient‐limited sandy loam, biochars had a variable but positive effect on pH, electrical conductivity, soil potassium, water stable aggregation, and permanganate oxidizable carbon. There was no effect on soil moisture nor potentially mineralizable nitrogen or carbon. In the silt loam, there was no change in microbial biomass or phospholipid fatty acid (PLFA) composition. In the sandy loam, almond shell biochars were associated with a slight increase in total biomass, an increase in the ratio of fungal to bacteria PLFAs, and reductions in multiple PLFA ratios were typically interpreted as indicators of environmental stress. Results of this study demonstrate that biochar may deliver soil health benefits in agricultural soils in a Mediterranean climate. However, increased soil health does not necessarily engender increased agricultural productivity within a 3‐year period. Furthermore, increases in soil health indicators were inconsistent across soil and biochar types, underscoring the need for site‐ and material‐specific investigation.

Effects of Rainfall Intensity and Slope on Infiltration Rate, Soil Losses, Runoff and Nitrogen Leaching from Different Nitrogen Sources with a Rainfall Simulator

The combined effects of slope gradient, rainfall intensity, and nitrogen fertilizer source on infiltration, runoff, soil loss, and nitrogen (N) leaching in agricultural areas are not thoroughly understood, despite their critical importance in sustainable agriculture. Previous studies have focused on these factors individually, leaving a significant gap in knowledge regarding their synergistic impact. Investigating the interplay between slope gradients, rainfall intensities, and N fertilizer sources is vital to developing effective soil and water conservation strategies and implementing sustainable agricultural practices. This study is comprised of two experiments. Experiment 1 was designed as a 3 × 2 × 3 factorial arrangement, incorporating three levels of rainfall intensity (RI) (45, 70, and 100 mm/h), two slope gradients (5 and 8°), and three soil types (sandy loam, silt loam, and clay loam), aimed at assessing runoff, infiltration, and soil loss. Experiment 2, laid out as 3 × 2 × 3 × 3 factorial, expanded on this, adding N fertilizer source (urea, CaCN2, and limestone ammonium nitrate (LAN) at 130 kg/ha N) and assessing N leaching alongside the previous metrics. Both experiments used a rotating disc rainfall simulator and were replicated four times. Results revealed that steeper slopes (8°) led to increased runoff and soil loss, impeding infiltration, while gentler slopes (5°) facilitated greater infiltration and minimized soil loss. Rainfall intensity played a significant role, with 70 mm/h/5° combinations promoting higher infiltration rates (48.14 mm/h) and 100 mm/h/8° resulting in lower rates (37.07 mm/h for sandy loam and silt loam, 26.09 mm/h for clay loam). Nitrogen leaching varied based on N source; urea at 130 kg/ha N led to higher losses (7.2% in sandy loam, 6.9% in silt loam, 6.5% in clay loam), followed by LAN (6.9% in sandy loam, 6.7% in silt loam, 6.3% in clay loam) while CaCN2 at the same rate resulted in lower N losses (6.4% in sandy soil, 4.4% in silt loam, 4.2% in clay soil). This research highlights the critical need to consider both slope gradient and rainfall intensity in conjunction with appropriate nitrogen fertilizer sources when developing strategies to mitigate soil erosion and nutrient loss in agricultural settings.