Interacting effects of cation saturation and drying, freezing, or aging on the extractability of nonylphenol and phenanthrene from a sandy soil

Purpose

The structure and properties of the soil organic matter and its interactions with solutes may be altered by changes in soil chemistry and by the aging of soil. The main objective of this study was to investigate the effect of long-term aging and cation saturation of soil on the extractability and degradability of two hydrophobic xenobiotics in soil. In addition, it was tested if drying or freezing of soils can accelerate the relevant aging processes.

Materials and methods

The sandy topsoil was treated by either 0.1?M NaCl, CaCl₂, AlCl₃ solutions or water and samples were sterilized by ??-radiation and spiked with ¹⁴C-labeled nonylphenol (NP) or phenanthrene (Phe) at 10???g?g^?1 of soil. Samples were then used in four parallel experimental setups: (1) 9?months of aging under sterile conditions, (2) inoculation by native original soil with further 7?months of aging (bioaging), (3) drying and wetting or (4) freezing and thawing of soils. After different time intervals, the extractability of xenobiotics with water, cyclodextrin, and ethanol was investigated.

Results and discussion

During 9?months of aging under sterile conditions a continuous decrease of NP and Phe extractability and an increase of the non-extractable fraction occurred. During the 7?months of biologically active aging, the mineralization of NP was lower than of Phe while more NP remained extractable than Phe. In comparison to the sterile aging, the bioaging led to a less formation of non-extractable residues of NP and Phe. The long-term sterile aging effects on NP-extractability were also achieved by short-term freezing and thawing of the soils, while aging of Phe was better mimicked by drying?Cwetting cycles. The effects of cation saturation of soils on xenobiotics extractability were less pronounced.

Conclusions

Sterile aging, bioaging, freezing, and thawing facilitate the formation of the non-extractable fraction of NP and Phe in the soils. Different cation treatments alter soil properties, but the effects on aging of NP and Phe in soils were negligible.     

A study of the effect of the interaction between site-specific conditions, residue cover and weed control on water storage during fallow

In the semiarid central region of Argentina the probability that rainfall meets crop requirements during growing season is less than 10%, therefore fallowing has been the most important practice to assure water availability during the growing season. Various site-specific and management factors have been identified as crucial for defining fallow efficiency (FE) and final available water contents (AW). The objective of the present study was to improve our knowledge about the interactions between residue cover, weed control, soil profile depth and water storage capacity (WSC) on FE. In 10 sites covering the environments of calcareous plains and sandy plains of the semiarid central region of Argentina and with different WSC, experiments with 3 different levels of residue cover (H, M, L) and with and without weed control (C and W respectively) during fallow were set up. A completely randomized block design with four repetitions and splits plots to consider weed control was used. Soil texture and organic matter were determined in samples of the A horizon (0.20 m). Bulk density, field capacity, permanent wilting point and soil water contents (monthly frequency) were measured at depth intervals of 0.20 m to the depth of the calcite layer or to 2.00 m depth. Soil temperature was taken in weekly intervals at 0.05 m depth and weed plants, separated by species, were counted at the end of fallow in 4 repetitions of 0.25 m² in each treatment. An empirical model was developed to predict final AW under these experimental conditions. Model parameters were: Residue level, weed control, WSC, profile depth, and rainfall during fallow. Site-specific conditions (WSC and profile depth) affected water storage during fallow; soils with highest values for both parameters showed highest final AW. Weed density was the most important factor that controlled AW, with on average 35 mm less AW in W than in C treatments. Residue level had a positive effect on final AW in both C and W treatments, with a difference of 18.5 mm between H and L. An interaction between residue level and weed density was observed, indicating weed suppression in H treatments. This was also confirmed by correspondence analysis between residue level and weed species which revealed that different species were related to each level. High residue levels also decreased soil temperature, thus affecting germination of post-fallow crops. The empirical model had an overall average prediction error of 13.7% and the regression between measured and predicted values showed a determination coefficient of 0.77.     

Cluster root allocation of white lupin (Lupinus albus L.) in soil with heterogeneous phosphorus and water distribution

Cluster roots are structures formed by many plants adapted to phosphorus (P)-deficient soils. We investigated the combined influence of spatial heterogeneity in soil water and P distribution on the allocation of cluster root formation in white lupin (Lupinus albus L.). In this study, single plants were grown at a low or a high rate of water supply in containers filled with a P-poor sand to which either no P was added or which was fertilized homogeneously or heterogeneously. Furthermore, heterogeneous soil water distribution was established in half of the containers by using a finer instead of a coarser sand in a lateral third of the containers. Plant growth increased with water supply rate, but P fertilization had no influence on shoot biomass production. Although overall cluster root production decreased with increasing homogeneous P supply, localized P fertilization had no effect on cluster root allocation. However, cluster roots were preferentially allocated in the soil sections with lower water availability when overall water supply rate was low. The results suggest that overall cluster root production was a systemic response to initial plant P status, while cluster root growth was stimulated locally in drier patches when overall water supply was limiting plant growth.     

Plant availability of isotopically exchangeable and isotopically nonexchangeable phosphate in soils

Isotopically exchangeable P (IEP) is usually considered to be completely plant‐available and the major source of P for plant uptake. The aim of the present study is to test whether plants can, besides IEP, also use non‐IEP and if part of the IEP has an equilibrium concentration in soil solution which is below the minimum concentration, C_Lmin, and can therefore not be taken up by plants. A pot experiment was carried out with maize for two years on two soils, an acid sandy and a neutral loamy soil, either without P fertilizer or fertilized with ten P sources of different solubility. Throughout both years of the study, pots were kept moist either without plants or planted twice with maize (Zea mays L., cv. Athletico). At the end of the experiment, plant P uptake, P concentration in the soil solution (C_L), and P accessible to isotopic exchange within 5 d (E_5d) were measured. Plant growth decreased the E_5d which was about equal to P uptake by maize for most treatments in the acid soil. But for some treatments, i.e., five in the acid and eight in the neutral soil, P uptake was up to 50% larger than the decrease of E_5d, indicating that plants had, besides IEP, also used P from non‐IEP sources. At adequate P supply, both soils had an E_5d of about 100 mg P (kg soil)^–1, but about 30 to 40 mg kg^–1 of this IEP had an equilibrium P concentration in the soil solution below C_Lmin of 0.1 μmol L^–1 at which P would actually not be plant‐available. This study shows that plants take up P mainly from IEP, but not the whole IEP is plant‐available. Furthermore, plants may also use P from non‐IEP sources.     

陕北黄土高原森林植被的性质和当前森林培育的策略

对比和分析了前人对陕北黄土高原植被的研究成果后认为陕北黄土高原的阔叶栎林为主的森林界限截止于渭北黄土高原北部,即陇县、彬县、宜君、铜川、黄龙一线。经过植被破坏和土壤侵蚀后土壤基质已经严重旱化和贫瘠化,通过重建植被土壤基质是可以逐步恢复的。植被的重建应该首选择先锋植物种类,造林后应及时进行改造,使其向接近该区天然林(植被)的方向发展,并需要建立一套可持续的森林经营体系。     

GIS‐based regionalization of soil profiles with Classification and Regression Trees (CART)

A map of soil texture profiles was derived from readily available spatial data in combination with information from soil profiles using CART (classification and regression trees). The primary purpose was to provide a regionalized predictor for the vertical hydraulic conductivity profiles to be used as an input variable to an evapo‐transpiration model. In contrast to former studies, the texture of 110 soil profiles taken in the 10 km² area was not averaged vertically but the profiles were grouped according to their hydraulic properties. Therefore, it was possible to include site specific profiles, e.g. with histic or argillic horizons. Despite of small sampling quantities (110 soil profiles grouped into 8 classes) a prediction probability of 60 to 70 % was achieved in most classes. The resulting map provides valuable information for the granulometric and hydrologic characterization of the study area.<?show $6#>     

Zur Parametrisierung der Stickstoff-Mineralisierung in einem Ackerboden unter Feldbedingungen

A functional relationship for the nitrogen mineralization of an arable soil under field conditions In order to characterize the nitrogen mineralization of a poorly drained, loess-derived field soil (Aeric Fragiaqualf, loamy, mesic) a laboratory incubation experiment was carried out. The measured mineralization rate was expressed as a function of soil temperature and soil water content. At the same time, a field incubation experiment with buried soil samples (so-called Runge samples) was conducted. It was found that the laboratory incubation method overestimated the mineralization rate as compared with the field method. Accordingly, the laboratory data were adjusted. Additionally, it was found that management practices (fertilizer application, harvest, soil cultivation) influenced the course and the extent of the nitrogen mineralization.     

Effects of Lime and Fertilizer Application on Soil Solution Composition in an Acid Sandy Forest Soil

In a 40 year old pine stand, soil solution was collected continuously with suction cups from 50 and 200 cm depth over a 42-month period following the surface application of lime and K/Mg-fertilizer. K and Mg showed a much higher mobility than Ca, which hardly increased in 200 cm depth even after 42 months. After an initial nitrate peak, concentrations decreased but remained elevated throughout the entire study period. In 200 cm, Al-, Mn, and Cd-concentrations increased due to exchange processes in the top-soil. Continuously elevated sulfate concentrations in 200 cm indicate S-mineralisation from humus decomposition.     

Comparing costs for different conservation strategies of garlic (Allium sativum L.) germplasm in genebanks

The maintenance of plant genetic resources in living plant collections (genebanks) causes costs due to employment of staff, usage of buildings, equipment and consumables. Since this is especially challenging in vegetatively propagated material, studies were performed for the case of garlic, which is one of the major vegetatively maintained crops in the genebank of IPK Gatersleben. Data were recorded to compare various scenarios of the main strategies field maintenance and cryopreservation. A spreadsheet tool was developed to be used for cost assessment and for drawing conclusions concerning the most effective way of maintenance. Field culture is cheaper in the short term, whereas after a break-even point cryopreservation becomes the more efficient storage method in the long term. This break-even point depends on the particular scenario, which is determined by various factors such as field and in vitro multiplication rates of various genotypes, presence of bulbils in a part of the genepool, the sample size of the accessions as well as the number of stored accessions in cryopreservation. The comparative discussion is exemplified for a 1-year field rotation versus cryopreservation using either in vitro plantlets or a combination of bulbils and unripe inflorescence bases as organ sources. For the more expensive use of in vitro plants cryopreservation becomes less costly than field culture only after 13 years, whereas this is the case already after 8–9 years when using a combination of bulbils in winter and inflorescence bases in summer.     

Hydrolysis rates of inorganic polyphosphates in aqueous solution as well as in soils and effects on P availability

Applications of polyphosphate‐based fertilizers have been reported to have a positive impact on crop yields as compared to orthophosphate sources. Since plants take up P mainly as orthophosphate, hydrolysis rates of polyphosphates into orthophosphates will determine their fertilizer ability. Laboratory and soil incubation experiments were performed to evaluate hydrolysis rates of pyrophosphate (PP), tripolyphosphate (TP), and trimetaphosphate (TMP) in water as well as in two soils having different P‐fixing capacities. P availability was characterized by measuring the orthophosphate (ortho‐P) and polyphosphate (poly‐P) concentration in soil solution as well as the calcium‐acetate‐lactate (CAL)‐extractable amounts of both forms. In water, PP was completely hydrolyzed within 15 d, whereas TMP was hydrolyzed only to about 30% after 90 d. In the two soils, polyphosphates hydrolyzed during the incubation period increasing ortho‐P concentration in soil solution as well as in CAL extract. At the end of the incubation, no significant differences in ortho‐P concentration in soil solution and CAL extract were found in the sandy soil, whereas in the silty‐loam soil, polyphosphate applications resulted in higher soil‐solution ortho‐P concentration. Although polyphosphate hydrolysis is mainly affected by the soil‐specific enzymatic activity, it seems that polyphosphates and/or hydrolysis products are preferentially adsorbed/precipitated compared to ortho‐P in the silty loam, thereby influencing the P availability from polyphosphate sources.