Influence Of Soil Organic Matter Research Articles

Influence of soil organic matter, fertiliser formulation and season on fertiliser nitrogen use efficiency in temperate pastures

Intensively grazed dairy systems use high inputs of fertiliser nitrogen (N), and often supplementary irrigation, to ensure adequate pasture production to support milk output and meet the growing food demand. However, the efficiency of N use in these systems can be low and potential environmental impacts high. This study aimed to test the hypothesis that (1) use of two inhibitors, the urease inhibitor N-(n-butyl) thiophosphorictriamide (NBTPT) and the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) reduced N loss and improved pasture production compared to conventional N fertiliser (urea) in irrigated temperate perennial ryegrass (Lolium perenne L.) dairy pasture, and (2) their efficiency was affected by soil and environmental parameters. The effect of repeated applications of urea, at different rates, and the inhibitors were studied on pasture production and agronomic apparent fertiliser N use efficiency (NUE) over 2.5 years. The fate of a single application of N was determined through recovery of 15N-labeled fertiliser applied at 20 and 40 kg N ha−1 was studied in the field for one year. The highest yield and NUE occurred in spring–summer (from August to February) reflecting optimal growing conditions. The highest NUE occurred at low rates of urea application (20 and 40 kg N ha−1). Mineralisation played a key role in supplying N to pasture with 64–82% of total plant N derived from soil organic matter (SOM). Less than 50% of the applied N was recovered in the pasture (37–43%) with a large component retained in the soil (26–43% after one year, 0–40 cm), and slowly released in small amounts (< 2%) to the pasture over time, highlighting the abundant capacity of the native soil N pool to supply pasture N. Loss of N fertiliser (14–31%) was attributed to primarily ammonia (NH3) volatilisation and nitrate (NO3−) leaching. Use of the inhibitors NBTPT and DMPP did not significantly affect pasture yield or NUE, most likely because fertiliser N saved with the inhibitors only played a minor role in plant nutrition with the majority of the plant nutrition provided by the soil organic matter pool.

ESTIMASI KANDUNGAN BAHAN ORGANIK TANAH DI LAHAN TANAMAN JERUK, KECAMATAN DAU, KABUPATEN MALANG MENGGUNAKAN INDEKS VEGETASI DAN SISTEM INFORMASI GEOGRAFIS

Citrus plants (Citrus sp.) are most plants that grow in Petungsewu Village, Dau District. The decreased productivity of citrus plants causes the availability of citrus plants also to decrease. This needs to be increased to meet citrus plants' needs. The influence of soil organic matter is the main factor causing a decrease in the productivity of citrus plants in Petungsewu Village, Dau District. Therefore, it is necessary to estimate soil organic matter using the NDVI vegetation density index to obtain adequate and efficient results. Reliability testing was also carried out to know the accuracy level of the estimates made. The research was conducted at the Citrus Plantation and Subtropical Fruit Research Institute in Petungsewu Village, Dau District, Malang Regency. Estimation of soil organic matter using the NDVI vegetation density index showed an accuracy rate of 81.1%. The results of the accuracy analysis were strengthened by the presence of a paired t-test with a value of t = 0.01 and a value of p = 0.991.

The Influence of Organic Matter on Phosphorus Fixation in Soils from the Eastern Flank of Mount Cameroon

The maximum phosphate fixation (KF) and phosphorus sorption capacity (PSC) of soil samples collected from the surface and sub-surface horizons of five volcanic soil profiles from the eastern flank of Mount Cameroon were investigated before and after organic matter removal. The aim of this research was to investigate the influence of soil organic matter (OM) on phosphorus (P) fixation. The removal of soil OM from the soil samples was accomplished by the use of sodium hypochlorite. Phosphorus fixation studies were performed on the treated and untreated soil samples using calcium chlorite as the background electrolyte. Fixation data were interpreted with Freundlich adsorption isotherm. The results indicated that the removal of OM had an influence on both KF and PSC. Removal of soil OM decreased PSC and increased KF for all soils. The inhibition of aluminium oxide and the reduction of soil surface area after the removal of OM were the justifications for the increase in P fixation.

Influence of SOM Composition, Clay Minerals, and pH on 2,4-D and MCPA Retention in Peri-Urban Soils

The use of ionic herbicides in urban and peri-urban areas has serious environmental and health consequences due to their common overapplication and mobility in the soil profile. The specific objective of this study was to evaluate the influence of soil organic matter (SOM) fractions and clay minerals on the retention of 2,4-D and MCPA on loamy sand and loam topsoil materials under the pH range of 3–7. The results obtained indicate their weak, unfavorable, and physical sorption, presumably governed by partitioning. 2,4-D exhibited high affinity for polar SOM fractions as well as to kaolinite and montmorillonite, both present in the studied peri-urban soils. MCPA sorption was mainly related to soil fulvic (FA) and humic acid (HA) content; however, the pesticide was sorbed to a lesser extent than 2,4-D due to its great water solubility. This was reflected in MCPA’s low Koc values (41.33 and 84.21), indicating its very high mobility and leachability in the studied soils. Meanwhile, 2,4-D was moderately mobile in sandy soil while classified as a non-leacher in the loam topsoil material. Both herbicides were preferably retained at a low soil pH (3–4), which, together with soil amendment with exogenous, well-humified organic matter, could minimize the potential health and environmental risks of their application.

Electron Transfer, Atom Exchange, and Transformation of Iron Minerals in Soils: The Influence of Soil Organic Matter.

Despite substantial experimental evidence of electron transfer, atom exchange, and mineralogical transformation during the reaction of Fe(II)aq with synthetic Fe(III) minerals, these processes are rarely investigated in natural soils. Here, we used an enriched Fe isotope approach and Mössbauer spectroscopy to evaluate how soil organic matter (OM) influences Fe(II)/Fe(III) electron transfer and atom exchange in surface soils collected from Luquillo and Calhoun Experimental Forests and how this reaction might affect Fe mineral composition. Following the reaction of 57Fe-enriched Fe(II)aq with soils for 33 days, Mössbauer spectra demonstrated marked electron transfer between sorbed Fe(II) and the underlying Fe(III) oxides in soils. Comparing the untreated and OM-removed soils indicates that soil OM largely attenuated Fe(II)/Fe(III) electron transfer in goethite, whereas electron transfer to ferrihydrite was unaffected. Soil OM also reduced the extent of Fe atom exchange. Following reaction with Fe(II)aq for 33 days, no measurable mineralogical changes were found for the Calhoun soils enriched with high-crystallinity goethite, while Fe(II) did drive an increase in Fe oxide crystallinity in OM-removed LCZO soils having low-crystallinity ferrihydrite and goethite. However, the presence of soil OM largely inhibited Fe(II)-catalyzed increases in Fe mineral crystallinity in the LCZO soil. Fe atom exchange appears to be commonplace in soils exposed to anoxic conditions, but its resulting Fe(II)-induced recrystallization and mineral transformation depend strongly on soil OM content and the existing soil Fe phases.

Enhancing phytoremediation of arsenic-contaminated soil by agronomic practices (drip irrigation and intercropping): Influence of soil organic matter

It is essential to improve the efficiency and economic benefits of phytoremediation. In this study, drip irrigation and intercropping were used to enhance the phytoremediation of arsenic-contaminated soil. Meanwhile, the influence of soil organic matter (SOM) on phytoremediation was investigated by comparing the difference in arsenic migration in soils with or without peat addition as well as the arsenic accumulation of plants. The results showed that hemispherical wetted bodies with a radius of approximately 6.5 cm were formed in the soil after drip irrigation. Arsenic in the center of the wetted bodies migrated to the edge of the wetted bodies. Peat inhibited the upward migration of arsenic from the deep subsoil and increased the phytoavailability of arsenic under drip irrigation conditions. To soils without peat added, drip irrigation decreased the arsenic accumulation in crops (planted at the center of the wetted body) while increased the arsenic accumulation in remediation plants (planted at the edge of the wetted body) compared with the flood irrigation treatment. An increase in soil organic matter of about 36 % was found after mixing 2 % peat in the soil, and correspondingly, arsenic concentrations in remediation plants increased by >28 % in both intercropping treatments with a drip or flood irrigation. Drip irrigation coupled with intercropping enhanced the effect of phytoremediation, and the addition of soil organic matter further improved phytoremediation efficiency.

Soil-air partitioning of semivolatile organic compounds in the Lesser Himalaya region: Influence of soil organic matter, atmospheric transport processes and secondary emissions

After decades of imposed regulations about reducing the primary emissions of persistent organic pollutants (POPs), these pollutants are still present in the environment. Soils are important repositories of such persistent semivolatile organic contaminants (SVOCs), and it is assumed that SVOCs sequestered in these reservoirs are being re-mobilized due to anthropogenic influence. In this study, concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in soil and air, their fugacities, fluxes and the soil-air partition coefficient (KSA) were determined for three different land cover types (glacial, remote/mountainous and urban) of the Lesser Himalayan Region (LHR). The concentrations of OCPs, PCBs and PBDEs in soils and air ranged between 0.01 and 2.8, 0.81–4.8, 0.089–0.75 ng g−1; 0.2–106, 0.027–182, and 0.011–7.26 pg m−3, respectively. The levels of SVOCs in the soil were correlated with soil organic matter (SOM) indicating that SOM is a substrate for the organic pollutants in soils. The Clausius-Clapeyron plots between ln P and inverse of temperature (1000/T) suggested that long range atmospheric transport was the major input source of PBDEs and higher chlorinated PCBs over the LHR. The uneven and wide distribution of local sources in LHR and up-slope enrichment of SVOCs explained the spatial variability and altitudinal patterns. The soils near mountain and urban lakes act as local sinks of SVOCs such as β-HCH, pp΄-DDT, CB-28, -118, −153, BDE-47, -99, and −154, with soil-air exchange fluxes tending more toward deposition. However, the soils near glacial lakes acted as local sources of more volatile congeners of α-HCH, γ-HCH, op′-DDT, pp′-DDE and lower to medium chlorinated PCBs such as CB-18, -28, −53, −42 and BDE-47, -99, with soil-air exchange tending more toward volatilization flux.

The Distribution and Migration of 137Cs in Oak (Quercus serrata) and Cedar (Cryptomeria japonica) Forest Organic Fractions

To analyse the 137Cs distribution and migration under various fractions of organic matter layers, this study investigated easily recognizable, originally shaped organic L-fractions, and not easily recognizable, early fermented and fragmented organic F-fractions, of both oak (Quercus serrata) and cedar (Cryptomeria japonica) sampled from Osawa watershed sites at Nihonmatsu City, Fukushima Prefecture, Japan. The organic materials were put on top of soil columns from Field Museum (FM) Tamakyuryo in Hachioji City, Tokyo. The 137Cs vertical distribution in forest soil profiles was analyzed using the relaxation mass depth, ho (kg m−2). Soil columns with both L and F- organic layer fractions of both oak and cedar, labelled as Oak-L, Oak-F, Cedar-L and Cedar-F with four replications (n = 16), were set up by the laboratory column-based method and kept under five months’ incubation period. Soil columns after incubation were sampled at depths of 0–1 cm, 1–2 cm, 2–5 cm and 5–10 cm. Results of 137Cs inventory in the organic fractions showed that 86% (oak and cedar) of the total organic layer fractions 137Cs inventory accumulated within the F-layer, indicating that the transformation of litter is a huge source for potentially mobile 137Cs, especially the oak F-layer (67% 137Cs inventory) and further continuous transfer into the forest soil mineral layers. A higher ho in L treated soils (Oak-L and Cedar-L) compared to the F treatments implied that the low 137Cs amounts penetrated faster and deeper due to their water-soluble nature. Furthermore, Cedar-F showed a higher ho of 24.3 kg m−2 than Oak-F of ho, 14.0 kg m−2, and a significant positive relationship between 137Cs retention and total carbon (TC) (p &lt; 0.05) suggested the influence of soil organic matter on 137Cs penetration and retention. The C/N (carbon nitrogen ratio) results revealed that organic matter fractions of high C/N including 137Cs, as observed in Cedar-F, in which decomposition does not advance, penetrates soil depths while the organic matter fraction of low C/N, observed in Oak-F, showed that decomposition advanced to release 137Cs which was held by adsorption unto the RIP (radiocesium interception potential) of soil surface. In addition, infiltration by water as a transportation process was suggested to largely influence the downward migration and retention of 137Cs at lower depths of Cedar-F.

A Review on Adsorption and Desorption of Different Pesticides in Various Soil

Pesticides are important to the success of agriculture as well as an inevitable factor to maintain good public health. Over the years, the consumption of pesticides has increased manifold, particularly during the past two decades. However, this increase has caused great concern over the presence of residues or leftover pesticides in the environment. The understanding of adsorption and desorption behavior of different pesticides is an important phenomenon to describe the fate of pesticide in soil and other environmental compartment like water and sediment. The soil is considered as ultimate sink of pesticide as these were reached to soil directly or indirectly from the point/non-point sources. Adsorption–desorption processes are necessary in understanding pesticides retention behavior and its potential mobility within the soil. The behavior of pesticides in the soil depends on factors such as the physico-chemical properties of pesticides, the active surface of mineral, organic components and the amount of the pesticide applied. Henceforth, adsorption and desorption of soil applied pesticides needed to deal with greater sincerity. This review primarily ascertains dominant properties of pesticides including surface area, pH, surface functional groups, carbon content and aromatic structure and evaluate the adsorption and desorption of pesticide in agricultural soils. In addition, a vision for future research prospects has been anticipated by considering the pesticide bioavailability as residues in soil, influence of soil organic matter, clay content, pH and soil temperature on pesticide removal, pesticide properties and its behavior in soils.

Potential of VIS-NIR spectroscopy to characterize and discriminate topsoils of different soil types in the Triffa plain (Morocco)

Abstract This study aims to identify the influence of soil organic matter (OM) content and calcium carbonates (CaCO3) on soil reflectance and select the optimum spectral bands for discriminating between topsoils of different soil types situated in the irrigated perimeter of the Triffa plain (Morocco) using VIS-NIR reflectance spectroscopy. Soil samples were collected from the plow layer in 26 sampling sites. The spectral measurements were conducted in the field using an ASD Fieldspec portable spectroradiometer (350–2500 nm), while the soil samples were analyzed in the laboratory. The spectral data were pre-processed to remove the noise effects and then analyzed with the CovSel (selected covariance) method, validated by linear discriminant analysis in order to select the most optimal spectral variables to discriminate between topsoils of different soil types in the plain. The results of the soils reflectance curves showed that low reflectance intensity marked the soils with high OM contents throughout the VIS spectrum. The influence of the soil OM content was very apparent in the VIS range (between 580–750 nm). Regarding the CaCO3 content, it was noted that the soil samples with a high percentage of CaCO3 increase the reflectance in all spectral domains situated between 350 and 2500 nm. The spectral bands of 1999, 686, 1280, 2340 and 1951 nm were the most optimal for the soil discrimination in the Triffa plain. This study concluded that the VIS-NIR spectroscopy demonstrates an excellent ability to characterize and discriminate between topsoils in the Triffa plain.

Sources and key processes controlling particulate organic nitrogen in impounded river–reservoir systems on the Maotiao River, southwest China

ABSTRACTThe δ15N of nitrate (NO3−) and particulate organic nitrogen (PON) was used to study the sources and fate of nitrogen in the impounded Maotiao River, southwest China. During months when the reservoirs thermally stratified, denitrification was the key process in the hypolimnion in Hongfeng and Baihua reservoirs. Based on the δ15N of PON and NO3−, PON in the epilimnion of reservoirs was dominated by NO3− assimilation during stratification. Most δ15N of PON was higher than that of NO3− in the reservoirs in October, indicating that PON in reservoirs was mainly derived from exogenous nitrogen input or denitrification rather than assimilation of NO3− in the epilimnion. Relationships between the molar carbon:nitrogen (C:N) ratio and δ15N-PON indicated the main sources of PON in reservoirs were from phytoplankton, produced in inflowing rivers and the reservoir under the joint influence of soil organic matter, denitrification, and exogenous nitrogen inputs. The δ15N in PON and NO3− increased gradually from upstream to downstream, by 8.21 ± 0.65‰ and 1.74 ± 3.66‰, respectively, suggesting an accumulative effect caused by the downstream waters. Overall, this study provides insight into the nitrogen biogeochemical cycling of river–reservoirs systems using stable nitrogen isotopes and C:N to specify the effects of river impoundment on nitrogen dynamics.

English

In Ethiopia, sorghum is the major crop next to teff grown all over the country. Though the productivity of sorghum has increased in the last few years, the overall national productivity of sorghum is low (2.106 t/ha) compared to the average production of 2.3 t/ha of developed countries. The low productivity of sorghum is attributed mainly to infestation by Striga. The annual yield loss and geographic distribution of Striga infestation in Sub-Saharan Africa is steadily increasing. The region is mainly characterized by poor soil fertility and structure, lower distribution and intensity of rain fall. The average yield loss of sorghum due to striga exceeds 50% and in severe cases complete cop failure can occur forcing farmers to abandon cereal production. A survey was conducted in 2014 to determine the interaction of Striga hermonthica infestation with basic chemical and physical properties of the soil and to assess the association of Striga infestation and population density of sorghum in relation to Tigray region. There was a strong association between the average Striga count and population density of sorghum per unit area of land. Similarly, strong association was observed between Striga infestation and soil pH, available phosphorous, percent organic matter, total nitrogen and soil texture. The influence of soil organic matter on level of Striga infestation was observed superior to other soil chemical and physical properties. The highest level of Striga infestation was recorded at kebeles which had got the highest population density of sorghum, low soil organic matter and available phosphorous and sandy textured soils. Therefore maintaining optimum population of sorghum and improving the fertility status of the soil have been suggested for controlling of S. hermonthica in the region. Key words: Correlation, Striga infestation, sorghum planting density, soil properties, Tigray region.

Nanoscale Titanium Dioxide (nTiO2) Transport in Natural Sediments: Importance of Soil Organic Matter and Fe/Al Oxyhydroxides.

Many engineered nanoparticle (ENP) transport experiments use quartz sand as the transport media; however, sediments are complex in nature, with heterogeneous compositions that may influence transport. Nanoscale titanium dioxide (nTiO2) transport in water-saturated columns of quartz sand and variations of a natural sediment was studied, with the objective of understanding the influence of soil organic matter (SOM) and Fe/Al-oxyhydroxides and identifying the underlying mechanisms. Results indicated nTiO2 transport was strongly influenced by pH and sediment composition. When influent pH was 5, nTiO2 transport was low because positively charged nTiO2 was attracted to negatively charged minerals and SOM. nTiO2 transport was slightly enhanced in sediments with sufficient SOM concentrations due to leached dissolved organic matter (DOM), which adsorbed onto the nTiO2 surface, reversing the zeta potential to negative. When influent pH was 9, nTiO2 transport was generally high because negatively charged medium repelled negatively charged nTiO2. However, in sediments with SOM or amorphous Fe/Al oxyhydroxides depleted, transport was low due to pH buffering by the sediments, causing attraction between nTiO2 and crystalline Fe oxyhydroxides. This was counteracted by DOM adsorbing to nTiO2, stabilizing it in suspension. Our research demonstrates the importance of SOM and Fe/Al oxyhydroxides in governing ENP transport in natural sediments.

Spatial variation in concentration and sources of organic carbon in the Lena River, Siberia

AbstractGlobal warming in permafrost areas is expected to change fluxes of riverine organic carbon (OC) to the Arctic Ocean. Here OC concentrations, stable carbon isotope signatures (δ13C), and carbon‐nitrogen ratios (C/N) are presented from 22 sampling stations in the Lena River and 40 of its tributaries. Sampling was conducted during two expeditions: the first in July 2012 in the south and southeastern region and the second in June 2013 in the northern region of the Lena basin. The data showed significant spatial differences in concentrations and major sources of OC. Mean subcatchment slopes were correlated with OC concentrations, implying that mountainous areas in general had lower concentrations than lowland areas. δ13C and C/N data from tributaries originating in mountainous areas indicated that both dissolved and particulate OC (DOC and POC) were mainly derived from soil organic matter (SOM). In contrast, tributaries originating in lowland areas had larger contributions from fresh vegetation to DOC, while aquatically produced OC was the major source of POC. We suggest that these differences in dominant sources indicated differences in dominant flow pathways. Tributaries with larger influence of fresh vegetation probably had surficial flow pathways, while tributaries with more SOM influence had deeper water flow pathways. Thus, the future export of OC to the Arctic Ocean will likely be controlled by changes in spatial patterns in hydroclimatology and the depth of the active layers influencing the dominant water flow pathways in Arctic river basins.

Relationship between soil organic matter and nematodes in sugarcane fields

Sugarcane plays an important socio-economic role in northeastern Brazil. However, the low yield in this region is associated with several factors (e.g. frequent occurrence of plant-parasitic nematodes). In order to observe the influence of soil organic matter on the nematodes, this study aimed to characterize the spatial nematode distribution in a sugarcane field. The study was carried out in Goiana - Pernambuco State (Brazil), fifty days after sugarcane cutting (10 days after vinasse application). The sampling scheme consisted of a regular 60 × 50-m grid, 10 m spaced, through 0 to 0.2 m depth. Spatial distribution was evaluated by semivariograms fit and performed by ordinary kriging interpolation for mapping. Exponential and spherical models promoted the best fit to semivariograms, resulting in ranges from 16 to 19 m. There was a strong negative correlation between soil organic matter and plant-parasitic nematode population density. Free-living nematodes had a similar distribution pattern as soil organic matter content. These results indicated that soil organic matter had important effects on spatial distribution of both plant-parasitic and free-living nematodes.

Quantitative relationships between the adsorptivity of carbonaceous materials in soil for Pb(II) and soil organic matter content

Strong adsorptivity of manufactured carbonaceous materials (MCMs) mediates the behavior of heavy metals in soil. Laboratory-reported adsorptivity of MCMs often deviates from their actual abilities in soil, because soil organic matter (SOM) can change the adsorptive abilities of MCMs by coating dissolved organic matter (DOM) on the surface of the MCMs. It was considered that the influence of SOM on the adsorptivity of MCMs in soil follows a sequential pathway of SOM releasing DOM in soil solution and subsequent DOM binding onto MCMs, thereby altering MCM surface acidity and hence changing MCM adsorptivity for heavy metals. In this study, we first extracted DOM from ten topsoils collected over a broad region of China with a wide range of SOM. The DOM solutions were then used to load DOM onto four MCMs including activated carbon (AC), multiwalled carbon nanotube (MWCNT), and two biochars (BC400 and BC700), respectively, obtaining a total of 44 MCM-DOM complex samples with known amounts of bound DOM. These MCM-DOM complex samples were then determined for their surface acidities and adsorptive abilities for Pb(II). We found that there were significant correlations between DOM concentration and SOM content, between DOM binding onto MCMs and DOM concentration, between surface acidity of MCM-DOM complexes and DOM binding onto MCMs, as well as between Pb(II) adsorption on MCM-DOM complexes and surface acidity of MCM-DOM complexes. With understanding of these individual linear correlations, linear relationships between the Pb(II) adsorption and SOM content were established by combining individual correlations and by directly plotting the former against the latter. These relationships may be used to accurately predict the adsorptive abilities of MCMs for heavy metals in soils via simply determining SOM.

Light acidification in N-fertilized loess soils along a climosequence affected chemical and mineralogical properties in the short-term

Some evidences indicate that N-fertilization of crops decreased pH values of loess soils of the Argentinean Pampas in the last decades. We analyzed the A-horizons of four N-fertilized (F) and non-fertilized (NF) paired soils, developed on similar parent materials, within a climatic sequence (ustic to udic water regimes), and measured: 1) the extent of pH changes, 2) how these changes affected chemical and mineralogical soil properties and 3) how the soils, according to their H+ buffering substances, can react in the future if N-fertilization and acidification continue. Results indicated that all F- and NF soils were lightly acidified (differences between pHW and pHKCl higher than 1.0) and that fertilization produced pH decreases in all studied soils, but particularly in those with udic water regimes, in agreement with their longer N-fertilization histories. Fertilized ustic soils showed less crystalline illites and kaolinites and higher contents of amorphous Al oxides than NF soils. It remains unclear if the higher contents of amorphous Al are related with the dissolution of phyllosilicates, the transformation of the abundant volcanic glasses of these soils or both processes at the same time. The cation exchange capacity (CEC) and the percent of base saturation (V) did not change between F- and NF soils, probably due to the large influence of soil organic matter (SOM) in the studied soils. If N-fertilization, and consequently pH decreases continue, soils placed in both the moistest- (Argiudolls) and the driest extremes of the climosequence (Haplustolls) would be the less affected. This is because udic soils contain high SOM as well as illitic clays and silts while ustic soils contain free lime and high density charged clay minerals, which have high H+ neutralization capacity. The most affected soils by acidification should be those placed in the intermediate zone of the climosequence (Hapludolls), which have low amounts of substances with high buffer capacity.

Impact of particle nanotopology on water transport through hydrophobic soils

The impact of non- and poorly wetting soils has become increasingly important, due to its direct influence on the water-limited potential yield of rain-fed grain crops at a time of enhanced global competition for fresh water. This study investigates the physical and compositional mechanisms underlying the influence of soil organic matter (SOM) on the wetting processes of model systems. These model systems are directly related to two sandy wheat-producing soils that have contrasting hydrophobicities. Atomic force microscopy (AFM), contact angle and Raman micro-spectroscopy measurements on model planar and particulate SOM-containing surfaces demonstrated the role of the hierarchical surface structure on the wetting dynamics of packed particulate beds. It was found that a nanoscale surface topology is superimposed over the microscale roughness of the packed particles, and this controls the extent of water ingress into particulate packed beds of these particles. Using two of the dominant component organic species found in the SOM of the two soils used in this study, it was found that the specific interactions taking place between the SOM components, rather than their absolute quantities, dictated the formation of highly hydrophobic surface nanotopologies. This hydrophobicity was demonstrated, using micro-Raman imaging, to arise from the surface being in a composite Cassie–Baxter wetting state. Raman imaging demonstrated that the particle surface nanotopography influenced the degree of air entrapment in the interstices within the particle bed. The influence of a conventional surfactant on the wetting kinetics of both the model planar surfaces and packed particulate beds was quantified in terms of their respective advancing contact angles and the capillary wetting force vector. The information obtained for all of the planar and particulate surfaces, together with that obtained for the two soils, allowed linear relationships to be obtained in plots of the contact angle data as a function of the wetting liquid surface tensions. These linear relationships were found to reflect the mechanisms underlying the surface energy parameter requirements for wetting.

Adsorption of imazethapyr on six agricultural soils of Morocco: Evaluation of the impact of soil properties

Imazethapyr herbicide [5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid] is widely used on agricultural field crops in Morocco. It is reported that soil properties largely enhance the sorption of the herbicide in soils, however understanding their impact in soils of Morocco is needed. The present article investigates the sorption behavior of imazethapyr herbicide toward six agricultural soils from Morocco in batch equilibrium experiments at pH 5 and evaluates the effect of the organic matter, the clay content, and the cation exchange capacity (CEC) on the sorption by applying simple and multiple linear regressions. Freundlich isotherm model described well the dynamic of imazethapyr sorption in all studied soils under the experimental conditions. The linear regressions showed significant differences between the soil properties and their impact on the sorption. While simple regression revealed strong positive correlations between the sorption and both the soil clay content (R2=0.91) and CEC (R2=0.92), the multiple regression revealed a noteworthy influence of soil organic matter when combined with clays. Our findings showed a weak adsorption of imazethapyr on the selected Moroccan soils, in addition to a potential role of clay minerals and CEC in the retention of the herbicide compared to the organic matter. The low adsorptive capacity of the Moroccan soils urges the necessity of minimizing herbicide application rates in agricultural regions to prevent environmental detrimental impacts.

Influence of soil organic matter on the sensitivity of selected wild and crop species to common herbicides

Current regulatory protocols for assessing herbicide effects on plants rely heavily on the use of crops grown under controlled greenhouse conditions to indicate risks to wild vegetation. Guideline test protocols call for low levels of soil nutrients, approximately 3% organic matter (OM), to test the worst-case scenario for non-target species growing in poor soils. However, species sensitivity to herbicides may be affected by growing conditions, especially soil nutrient levels. The purpose of this study was to assess the impact of high and low soil OM content on the sensitivity of plants to several common agricultural herbicides (glyphosate, chlorimuron ethyl and dicamba). Ten plant species (wild and crop) with high (nitrophilous) or low (non-nitrophilous) affinity for nitrogen were grown under greenhouse conditions in soil with two levels of OM (3 and 9%) and were exposed to seven doses of the three herbicides in concurrent experiments. Results showed that most species were more sensitive to glyphosate under high OM conditions while chlorimuron ethyl and dicamba results were mixed with respect to OM levels. Overall, 15 species-herbicide combinations were more sensitive in high OM soil, while 11 were more sensitive in low OM soil. No clear pattern in sensitivity emerged among nitrophilous and non-nitrophilous species. Several species showed a difference in response at herbicide levels expected to reach non-target habitats adjacent to crop fields through drift (5% commonly and 25% occasionally). In terms of regulatory testing, guidelines may need alteration to allow testing with nutrient levels that more accurately reflect natural environments.