Organic Matter In Soil Solution Research Articles

Effects of nitrogen deposition on the concentration and spectral characteristics of dissolved organic matter in soil solution in a young Cunninghamia lanceolata plantation.

To study the effects of nitrogen deposition on the concentration and spectral characteristics of dissolved organic matter (DOM) in the forest soil solution from the subtropical Cunninghamia lanceolata plantation, using negative pressure sampling method, the dynamics of DOM in soil solutions from 0-15 and 15-30 cm soil layer was monitored for two years and the spectroscopic features of DOM were analyzed. The results showed that nitrogen deposition significantly reduced the concentration of dissolved organic carbon (DOC), and increased the aromatic index (AI) and the humic index (HIX), but had no significant effect on dissolved organic nitrogen (DON) concentration in both soil layers. There was obvious seasonal variation in DOM concentration of the soil solution, which was prominently higher in summer and autumn than in spring and winter.Fourier-transform infrared (FTIR) absorption spectrometry indicated that the DOM in forest soil solution had absorption peaks in the similar position of six regions, being the highest in wave number of 1145-1149 cm-1. Three-dimensional fluorescence spectra indicated that DOM was mainly consisted of protein-like substances (Ex/Em=230 nm/300 nm) and microbial degradation products (Ex/Em=275 nm/300 nm). The availability of protein-like substances from 0-15 cm soil layer was reduced in the nitrogen treatments. Nitrogen deposition significantly reduced the concentration of DOC in soil solution, maybe largely by reducing soil pH, inhibiting soil carbon mineralization and stimulating plant growth. In particular, the decline of DOC concentration in the surface layer was due to the production inhibition of the protein-like substances and carboxylic acids. Short-term nitrogen deposition might be beneficial to the maintenance of soil fertility, while the long-term accumulation of nitrogen deposition might lead to the hard utilization of soil nutrients.

Evaluating Status Change of Soil Potassium from Path Model

The purpose of this study is to determine critical environmental parameters of soil K availability and to quantify those contributors by using a proposed path model. In this study, plot experiments were designed into different treatments, and soil samples were collected and further analyzed in laboratory to investigate soil properties influence on soil potassium forms (water soluble K, exchangeable K, non-exchangeable K). Furthermore, path analysis based on proposed path model was carried out to evaluate the relationship between potassium forms and soil properties. Research findings were achieved as followings. Firstly, key direct factors were soil S, ratio of sodium-potassium (Na/K), the chemical index of alteration (CIA), Soil Organic Matter in soil solution (SOM), Na and total nitrogen in soil solution (TN), and key indirect factors were Carbonate (CO3), Mg, pH, Na, S, and SOM. Secondly, path model can effectively determine direction and quantities of potassium status changes between Exchangeable potassium (eK), Non-exchangeable potassium (neK) and water-soluble potassium (wsK) under influences of specific environmental parameters. In reversible equilibrium state of , K balance state was inclined to be moved into β and χ directions in treatments of potassium shortage. However in reversible equilibrium of , K balance state was inclined to be moved into θ and λ directions in treatments of water shortage. Results showed that the proposed path model was able to quantitatively disclose moving direction of K status and quantify its equilibrium threshold. It provided a theoretical and practical basis for scientific and effective fertilization in agricultural plants growth.

Factors affecting flocculation performance of synthetic polymer for turbidity control

A multilateral effort into managing nonpoint source pollution from agriculture has gotten much attention for many years. Particularly during the heavy rain season, run-off of turbid water from sloped farmlands, fallow ground and/or unmanaged uplands is deteriorated. Flocculant polymer, commonly used in wastewater treatment facilities, but now exploited to improve control of sediment turbidity by promoting flocculation of particles in construction site. This study used the flocculant polymer to control the discharge of agricultural nonpoint source pollution and focused on the understanding of how soil-water and polymer properties affect flocculation performance. Therefore, a series of flocculation experiments under different conditions was evaluated for better polymer clarification efficiency. Various factors such as flocculant dose, end-over-end inversion of a cylinder, and soil-water properties (pH, NaCl, organic matter) were studied. The effective flocculant dose that fulfilled fast settling rate was 10mg·L-1. Additional findings included that 1) increasing pH decreased the settling rate of soil particle; 2) a positive relationship between the percentage of turbidity reduction and a level of salinity in Kaolin suspension was observed, and 3) organic matter in soil solution inhibited PAM adsorption onto soil particles, which caused the reduction of flocculation performance. The findings of this study revealed that flocculant polymer possess good results as a turbidity reducetion measure and couldfurther provide valuable information to make better decision on establishment of Best Management Practice for handling agricultural nonpoint source pollution.

Storm flow flushing in a structured soil changes the composition of dissolved organic matter leached into the subsoil

Dissolved organic matter increases typically in streams draining forested catchments during heavy rainstorms and snowmelt. Tracer methods and model calculations suggest that the storm flow flushing of dissolved organic matter is either due to lateral near-surface flow, i.e. within the organic forest floor, or preferential flow (funnelling) through the mineral soil. Both pathways should deliver forest floor-derived dissolved organic matter to streams that is hardly changed because of little to no interaction with mineral soil material and microorganisms. Here, we investigated the effect of rain storm induced vertical flushing through the mineral soil on the composition of dissolved organic matter in a structured Rendzic Leptosols under 90-year-old European beech ( Fagus sylvatica L.). During two rainstorm periods in autumn 1998 with elevated transport of organic C, N, P and S from the forest floor into the subsoil, we sampled dissolved organic matter in forest floor leachates (sampled by zero-tension plate lysimeters), subsoil solutions (sampled by suction cups at 90 cm depth) and subsoil seepage (sampled by zero-tension plate lysimeters at 90 cm depth). The chemical composition of dissolved organic matter was characterised by fractionation with XAD-8 macroreticular resin, wet-chemical analyses of carbohydrates and lignin-derived phenols, and determination of the δ 13C. During both rainstorm periods, all tested chemical features of dissolved organic matter in forest floor leachate and subsoil seepage matched each other greatly. In contrast, dissolved organic matter in soil solution contained smaller portions of XAD-8-adsorbable organic C, less lignin-derived phenols, more carbohydrates and showed smaller δ 13C values than that in forest floor leachates and subsoil seepage. These results suggest a rather direct transfer of organic solutes from the forest floor into the subsoil and probably further to ground and surface waters during heavy rainstorms. Dissolved organic matter leaving the soil in heavy rainstorms by rapid water flow through macropores is likely less biodegradable, more UV-digestible and more reactive towards metals and organic pollutants than that released from soil at low rainfall intensity by matric flow.

Effects of dissolved organic matter on toxicity and bioavailability of copper for lettuce sprouts

It is well known that dissolved organic matter in soil solution may affect the toxicity or bioavailability of heavy metals to plants, but existing information on various organic substances is insufficient for treating problems with heavy metal-contaminated soils. To clarify how dissolved organic matter alters the toxicity and bioavailability of metals, we germinated lettuce seeds exposed to solutions containing Cu and several kinds of dissolved organic matters. Low molecular weight organic acids (citric, malic, and oxalic acids) increased the toxicity and bioavailability of Cu, but low concentrations of the synthetic chelators ethylenediamine tetra-acetic acid (EDTA) and diethylenetriamine penta-acetic acid (DTPA) decreased the toxicity and bioavailability of Cu. In contrast, humic acid appeared to be the most effective organic substance for detoxifying Cu, even though it did not significantly decrease the bioavailability of Cu. Consequently, the bioavailability and toxic effects of Cu in soil depend on the nature of coexisting organic substances in the soil solution.

Effects of chronic nitrogen amendment on dissolved organic matter and inorganic nitrogen in soil solution

Increased atmospheric deposition of N to forests is an issue of global concern, with largely undocumented long-term effects on soil solution chemistry. In contrast to bulk soil properties, which are typically slow to respond to a chronic stress, soil solution chemistry may provide an early indication of the long-term changes in soils associated with a chronic stress. At the Harvard Forest, soil solution was collected beneath the forest floor in zero tension lysimeters for 10 years (1993–2002) as part of an N saturation experiment. The experiment was begun in 1988 with 5 or 15 g N m −2 per year added to hardwood and pine forest plots, and our samples thus characterize the long-term response to N fertilization. Samples were routinely analyzed for inorganic nitrogen, dissolved organic nitrogen (DON), and dissolved organic carbon (DOC); selected samples were also analyzed to determine qualitative changes in the composition of dissolved organic matter. Fluxes of DOC, DON, and inorganic N were calculated based on modeled water loss from the forest floor and observed concentrations in lysimeter samples. The concentration and flux of inorganic N lost from the forest floor in percolating soil solution are strongly affected by N fertilization and have not shown any consistent trends over time. On average, inorganic N fluxes have reached or exceeded the level of fertilizer application in most plots. Concentrations of DOC were unchanged by N fertilization in both the hardwood and pine stands, with long-term seasonal averages ranging from 31–57 mg l −1 (hardwood) and 36–93 mg l −1 (pine). Annual fluxes of DOC ranged from 30–50 g m −2 per year. DON concentrations more than doubled, resulting in a shift toward N-rich organic matter in soil solution percolating from the plots, and DON fluxes of 1–3 g m −2 per year. The DOC:DON ratio of soil solution under high N application (10–20) was about half that of controls. The organic chemistry of soil solution undergoes large qualitative changes in response to N addition. With N saturation, there is proportionally more hydrophilic material in the total DON pool, and a lower C:N ratio in the hydrophobic fraction of the total DOM pool. Overall, our data show that fundamental changes in the chemistry of forest floor solution have occurred in response to N fertilization prior to initiation of our sampling. During the decade of this study (years 5–14 of N application) both inorganic N and dissolved organic matter concentrations have changed little despite the significant biotic changes that have accompanied N saturation.

Properties of organic matter in soil solution in a German fen area as dependent on land use and depth

The aim of this study was to identify the differences in the composition of dissolved organic matter (DOM) in soil dependent on both land use and soil depth. Soil solutions of six differently used sites in a German fen area were sampled using ceramic suction cups at three depths (25, 55 and 95 cm) and analyzed for dissolved organic carbon (DOC) over a 2 1/2-year period. Studies on DOM composition included UV and fluorescence spectroscopy as well as a fractionation in hydrophobic and hydrophilic components. The DOC concentration was affected by land use in topsoil only. Degraded peatlands had a high intensity of land use and therefore a low soil carbon content and low DOC concentrations. The DOC concentrations decreased significantly with increasing soil depth. The DOM retention through adsorption or decomposition was much higher at intact peatlands than at degraded peatlands. The degraded peatlands soil DOM had a higher specific absorption at 285 nm and a higher humification index derived from fluorescence spectra than DOM of intact peatlands (low intensity of land use) down to the subsoil. The higher DOM humification was related to strong peat decay. The DOM of degraded peatlands preserved its higher degree of aromaticity and polycondensation down to the subsoil, although highly condensed and substituted aromatic compounds were retained preferentially with increasing soil depth. Therefore, effects of land use on the soil DOM composition are stronger than the effects dependent on increasing soil depth. The DOM fractionation in hydrophobic and hydrophilic components was not sensitive enough to detect the small differences in DOM composition caused by land use and depth.

An evaluation of methods for measurement of pesticides in sorption experiments

The concentration of four pesticides (2,4‐D, atrazine, phorate, and terbufos) in soil solution during sorption experiments was measured using UV spectrophotometry, Gas Liquid Chromatography (GLC), High Performance Liquid Chromatography (HPLC), and radiotracer technique. The presence of water soluble organic matter in soil solution interfered with the measurement of pesticide using the UV spectrophotometry. The use of GLC, HPLC, and radiotracer technique involving 14C gave a good estimate of the concentration of pesticide in soil solution. The pesticide remaining in soil can be quantitatively analyzed by extracting with a scintillation solution containing an organic solvent such as toluene or dioxane. Among the various centrifuge tubes glass tubes with Teflon caps sorbed negligible amount of pesticides and these tubes can be used for the sorption measurements.