Pedobiochemical indicators for eutrophication and the development of ”︁black spots” in tidal flat soils on the North Sea coast

The increasing eutrophication of tidal flat soils on the North Sea coast and the appearance of ”︁black spots” gave rise to this study. The aim was to find pedobiochemical indicators for the development of ”︁black spots”. Artificially eutrophicated soils were compared with untreated soils in the field and laboratory. The pH values of the artificially eutrophicated and natural soils often differed by nearly one unit. The treated soils mostly showed lower redox potentials (˜ —300 mV) than the untreated samples (˜ —250 mV). The mean sulfate concentrations were 2.2 mM in the eutrophicated laboratory soils and 13.1 mM in the eutrophicated field soils, compared with 12.5 mM and 20.2 mM in the untreated ones. Consequently, the SO₄^2—:Cl^— ratios and SO₄^2— differences were lower in the treated soils. Non‐eutrophicated soils showed methane concentrations of < 5 nmol cm^—3, whereas the eutrophicated soils showed up to 217.0 nmol cm^—3 in the field and 479.1 nmol cm^—3 in the laboratory. Differences between field and laboratory data were mainly due to a continuous sulfate supply and reoxidation process only possible in the field. Although all parameters showed differences between the eutrophicated and untreated soils, only the methane data did not overlap with their interquartile ranges. Those of the untreated soils were 2—7 nmol cm^—3 and those of the treated were 12—360 nmol cm^—3. Thus, threshold values can be defined. Methane concentrations of approximately > 10 nmol cm^—3 refer to the beginning eutrophication process and those in the range of > 100 nmol cm^—3 to advanced processes, phenologically forming ”︁black spots”.     

Andosols and soils with andic properties in the German soil taxonomy

The presence of soils with andic properties on German territory has been suspected for decades and there are numerous reports of sites where they may potentially occur. Andic properties, however, are not adequately represented by the German soil‐classification system. The German taxonomic category “Lockerbraunerde” has not been revised or reconciled with international taxonomic categories since the year 1957, when it was initially proposed. With this review, we show that there are true Andosols of both the silandic (allophane‐containing) and the aluandic (Al‐Humus‐dominated) type in Germany and that their properties differ substantially from other soils which merely exhibit low bulk density. By (1) comparing soil carbon storage between some German Andosols, Chernozems, and nonandic Cambisols with particularly low bulk density and (2) elucidation of the differential pedogenetic pathways leading to Andosol formation, we further demonstrate that Andosols are important objects of study in research issues of contemporary interest. We propose that appropriate measures be taken to lay the foundations for the protection and conservation of these soils, because they are valuable as archives of natural history and provide opportunities to study unique soil processes.     

Secondary minerals from extrapedogenic per latus acidic weathering environments at geomorphic edges, Eastern Nebraska, USA

Acidic weathering of the sulfidic Upper Cretaceous Carlile and Pierre Shales in Nebraska has led to the precipitation of the Al sulfate–hydroxide minerals aluminite, alunite, “basaluminite”/felsöbányaite (e.g.,), the aluminum hydroxides gibbsite and bayerite, and the rare Al phosphate hydroxide vashegyite. Kaolinite has also been produced as a result of this acidic weathering. These minerals do not appear as neoformed constituents in any extant soils in the region, and their existence underscores the ability of pyrite oxidation to produce major changes in mineralogy on a Holocene to Recent time scale. Jarosite, hydronium jarosite, gypsum, halotrichite, and melanterite also appear as secondary minerals in the weathered shales. Acidic weathering and the formation of new minerals is extrapedogenic because it occurs well below the limit of modern soil sola. These processes also occur at the edges of major landscape elements and can be considered to have a strong lateral component processes, making them “per latus” processes in our usage.     

Assessing Impacts of Crested Wheatgrass AND Native Species Establishment on Soil Characteristics in Reclaimed LAND Using Bayesian Posterior Predictive Distributions

We examined the interacting effects of drastic disturbance and re‐vegetation communities on the development of soil properties over time. We compared soil characteristics from an undisturbed reference site with reclaimed mine sites that differed by vegetation type and time since reclamation: Three sites were seeded solely with crested wheatgrass (Agropyron cristatum) (11, 16, and 29 years old), and two were seeded with native cool‐season grass mixes (14 and 26 years old). We sampled soil at two depths (0–5 and 5–15 cm) for soil macroaggregate and microaggregate weights, aggregate carbon to nitrogen (C : N) ratios, and microbial abundance. We employed a Bayesian bivariate model to account for potential correlations in soil properties across depths and compared soil properties across sites using posterior predictive distributions. We found that all reclaimed soils, regardless of vegetation type, had total aggregate weights that were similar to the undisturbed reference soil but had a larger proportion of macroaggregates than the reference soil. Aggregate C : N ratios were similar between the undisturbed reference and crested wheatgrass soils, while the reclaimed native cool‐season grass soils had lower C : N ratios in the top 5 cm. Total microbial abundance in soils seeded with crested wheatgrass was an order of magnitude lower than that in soils occupied by native species (both reclaimed and undisturbed). The presence of crested wheatgrass on the reclaimed sites alone did not differentiate all soil properties across our reclamation sites, but seeding this single, aggressive species may have contributed to maintaining different belowground characteristics on reclaimed soils. Copyright © 2015 John Wiley & Sons, Ltd.     

Rhizodeposition: Its contribution to microbial growth and carbon and nitrogen turnover within the rhizosphere

A greenhouse rhizobox experiment was carried out to investigate the fate and turnover of ¹³C‐ and ¹⁵N‐labeled rhizodeposits within a rhizosphere gradient from 0–8 mm distance to the roots of wheat. Rhizosphere soil layers from 0–1, 1–2, 2–3, 3–4, 4–6, and 6–8 mm distance to separated roots were investigated in an incubation experiment (42 d, 15°C) for changes in total C and N and that derived from rhizodeposition in total soil, in soil microbial biomass, and in the 0.05 M K₂SO₄–extractable soil fraction. CO₂‐C respiration in total and that derived from rhizodeposition were measured from the incubated rhizosphere soil samples. Rhizodeposition C was detected in rhizosphere soil up to 4–6 mm distance from the separated roots. Rhizodeposition N was only detected in the rhizosphere soils up to 3–4 mm distance from the roots. Microbial biomass C and N was increased with increasing proximity to the separated roots. Beside ¹³C and ¹⁵N derived from rhizodeposits, unlabeled soil C and N (native SOM) were incorporated into the growing microbial biomass towards the roots, indicating a distinct acceleration of soil organic matter (SOM) decomposition and N immobilization into the growing microbial biomass, even under the competition of plant growth. During the soil incubation, microbial biomass C and N decreased in all samples. Any decrease in microbial biomass C and N in the incubated rhizosphere soil layers is attributed mainly to a decrease of unlabeled (native) C and N, whereas the main portion of previously incorporated rhizodeposition C and N during the plant growth period remained immobilized in the microbial biomass during the incubation. Mineralization of native SOM C and N was enhanced within the entire investigated rhizosphere gradient. The results indicate complex interactions between substrate input derived from rhizodeposition, microbial growth, and accelerated C and N turnover, including the decomposition of native SOM (i.e., rhizosphere priming effects) at a high spatial resolution from the roots.     

Effects of a plastic cover on soil moisture change in a Mediterranean climatic regime

Water deficit is a serious problem for most agricultural crops, especially in arid–semiarid regions, and limits sustainable development. Production can be improved by reducing evapotranspiration and loss of infiltrated water by the use of a plastic cover. We monitored soil moisture fortnightly over 1 yr using a neutron probe near four trees in an olive grove (Olea europaea, var. Arbequina), two of which had a plastic cover buried in the topsoil around them. These trees were monitored using three neutron probe access tubes per tree to compare the behaviour of soil moisture over time with two other identically instrumented and nearby trees with no cover. Analysis was based on the resultant moisture profiles. The plastic cover retained moisture and increased soil water residence time. During the dry season, the amount of water retained in the plots was at most 15–20% greater in the mid‐season and at least 5–6% greater at the end of season than in the central part of the plots near the trunk. The plastic cover was effective to ca. 50 cm with maximum water content near the soil surface. During the wet season, the cover did not affect soil water. Soil moisture was greater near the tree trunk as a result of stemflow and throughfall.     

What drives farmers to increase soil organic matter? Insights from the Netherlands

Soil organic matter (SOM) is an important resource base for arable farming. For policies on SOM to be effective, insight is needed on why and under which conditions farmers are willing to increase SOM content. This study used the theory of planned behaviour to analyse what prevents or encourages Dutch farmers to increase the SOM content of their fields. In an online survey, 435 arable farmers were asked questions to understand their attitude (perceived benefits), subjective norm (social pressure) and perceived behavioural control (anticipated impediments and obstacles) related to management of SOM. Farmers’ answers were related to their intention to increase SOM content, use of organic materials and perceived increase in SOM content. Our results showed that Dutch farmers are well aware of the possible benefits of SOM content for crop productivity. Farmers’ attitude, subjective norm and perceived decrease in SOM content were significantly related to their intention to increase SOM content. In our farm survey, this intention was very strong: 90% of the farmers stated a high or very high intention to increase the SOM content of their fields. A higher intention to increase SOM content was correlated with the use of organic materials as expressed as total and effective C (P  = 0.003 and P  = 0.002, respectively), but this did not lead to a perceived increase in SOM content. From a farmer's point of view, this indicates that increasing SOM content is to a large degree beyond their direct influence. The Dutch Manure and Fertiliser Act, costs of organic inputs and the need to cultivate profitable crops (such as potatoes or sugar beet) were indicated as important impeding factors for increasing SOM content.     

Soil quality indices for evaluation of long‐term land use and soil management practices in semi‐arid sub‐tropical India

Land use changes and soil management can potentially alter soil quality. A study was conducted to assess the long‐term (>20 years) effects of perennial trees (PT), vegetable crops (VC), rice–wheat (RW) system, sewage‐irrigated fields (SF), maize–wheat (MW) system and uncultivated soils (US) on soil quality. Soil physical quality parameters were significantly affected only in the SF system when compared with the US soil, particularly for bulk density (BD 1·51 Mg m⁻³ in SF vs. 1·34 in US). Among chemical parameters, electrical conductivity was high in SF, and soil nutrients (N, P, K, S, Zn, Fe, Cu and Mn) were well above the critical limits of deficiency in all the systems. Soil parameters were integrated into soil quality indices (SQIs) by unscreened transformation and principal component analysis (PCA). SQI observed under each system were compared with the US to assess the degree of degradation. Mean SQI differences showed that PT (+16·02 per cent), VC (+4·80 per cent), RW (+10·04 per cent), and MW (+11·30 per cent) are aggrading, whereas SF (−2·06 per cent) is degrading with respect to the reference soil (US). Adoption of MW system proved to be better than traditional RW; and in general agricultural crops have a significant advantage than VC, in terms of maintaining soil quality. Sewage irrigation is not a sustainable practice and long‐term use may degrade the soil. Among the SQIs, PCA with nonlinear scoring function (NLSF) based SQI was effective in judging land degradation due to soil quality changes as affected by long‐term land use and soil management practices. Copyright © 2008 John Wiley & Sons, Ltd.     

Zinc–nitrogen interaction effect on wheat biofortification and nutrient use efficiency

Background : The enhancement of zinc (Zn) concentration in cereal crops without compromising yield is a global challenge with crucial health and food security implications. Aims : To achieve Zn biofortification in wheat through the appropriate management of fertilization with both Zn and nitrogen (N), due to the synergistic effect between them, using natural organic sources of Zn. Methods : We carried out a field experiment using a rainfed winter wheat (Triticum aestivum L.) crop fertilized with four Zn sources (Zn‐sulphate, Zn‐lignosulphonate, Zn‐amino acids and Zn‐gluconate) and three N application rates under semi‐arid conditions. Results : The strategy of increasing the N rate by 50% with respect to the recommended N rate (i.e., 120 kg N ha^?1) did not improve either wheat yield or grain Zn‐N concentration. The combined effect of applying natural organic Zn complexes and the recommended N rate tended to increase grain Zn concentrations (by an average of 14%), although this increase was significantly higher when Zn‐sulphate was applied (63%) due to its higher recommended Zn application rate. Natural organic Zn fertilizers achieved the highest grain yields, probably due to the enhancement of N uptake. The natural organic Zn fertilizers resulted in higher Zn utilization efficiency compared with the Zn‐sulphate fertilizer. Conclusions : In calcareous Zn‐deficient soils, our results suggest that Zn–N co‐fertilization involving Zn‐sulphate combined with the recommended N application rate would be advisable for obtaining grain Zn biofortification, while the highest yields can be obtained with the application of natural organic Zn fertilizers.     

Seasonal Patterns of Microbial Community Structure and Enzyme Activities in Coastal Saline Soils of Perennial Halophytes

Perennial halophytes are known to be one of the most influential parameters in coastal ecosystem affecting ecosystem processes. The aim of this study was to investigate the changes in soil microbial community structure and enzyme activities in different halophyte‐covered soils (Arthrocnemum indicum , Aeluropus lagopoides , Heleochloa setulosa and Suaeda nudiflora ) with control soil (un‐vegetated) that were collected in three seasons (rainy, winter and summer) from intertidal coastal soils of Gujarat, India. Soil microbial community structure was assessed using phospholipid fatty acid (PLFA) profiling. Halophytes influenced significantly soil micro‐environment by exerting effects on the soil chemical characteristics, enzyme activities and microbial community structure. The activities of β‐glucosidase, urease and alkaline phosphatase were significantly higher in halophyte‐covered soils than in control soil. Among four halophyte‐covered soils, the highest amounts of total, bacterial, actinomycetes and fungal PLFAs were observed in Arthrocnemum soil. The concentrations of total, bacterial, actinomycetes and fungal PLFAs were also significantly higher in summer and winter seasons than in rainy season, whereas enzyme activities also vary with seasons. The non‐metric multidimensional scaling analysis PLFA profiling revealed that the structure of microbial community significantly differed in all seasons as well as between control and halophyte‐covered soils. These shifts in microbial community were due to the higher abundance of Gram‐positive, total bacterial and actinomycetes PLFAs in summer and winter seasons than in rainy season, whereas abundance of fungal biomarker was significantly higher in rainy season than in other seasons. Among halophytes, significantly higher abundance of Gram‐positive, Gram‐negative and total bacteria was observed in Arthrocnemum , Heleochloa and Suaeda whereas the lowest in control soil. Halophytes exhibited improved soil microbial activities, which is important for healthy ecosystem. Copyright © 2017 John Wiley & Sons, Ltd.     

The costs of alternative methods of managing ‘set-aside’ land within the European Community

With low annual income from compensatory payments in the European Community set-aside scheme, the cost of managing such land is critical. The scheme was designed to temporarily remove land from production of arable crops that are in surplus. Based upon field experiments in the UK, over 2 years and 5 years, respectively, cultivations and herbicides are shown to be more expensive than mowing for vegetation control on set-aside land. They are highly effective but until recently have been discouraged by The Ministry of Agriculture, Fisheries and Food on environmental grounds. Mowing has been shown to cost less even when a final application of herbicide is included. In the 5 year set-aside scheme mowing does not produce serious agronomic problems for future crops. It is therefore recommended as the most appropriate management method. Hay-making on set-aside land is unlikely to be economically viable.     

Impact of biochars on swell–shrinkage behavior,mechanical strength,and surface cracking of clayey soil

Swell–shrinkage, cracking and stickiness of expansive clayey soils usually lead to their low yield. Improvement of these poor soil physical properties is a key goal for enhancing the crop productivity of expansive clayey soils. This article presents results of a study on the impact of three biochars produced from wheat straw (SB), woodchips (WCB), and wastewater sludge (WSB) on the swell–shrinkage behavior, mechanical strength, and surface cracking of a clayey soil. The soil was treated with biochars at the rate of 0, 20, 40, and 60 g biochar kg^?1 soil, respectively; and incubated for 180 d in glasshouse. Application of biochars decreased significantly (p < 0.01) the coefficient of linear extensibility (COLE) of the soil, the effect of SB being most prominent. The tensile strength (TS) of the clayey soil was originally 937 kPa, which decreased to 458 kPa, 495 kPa and 659 kPa for 6% SB‐, WCB‐, and WSB‐amended soils, respectively. Shear strength tests indicated that biochars significantly reduced cohesion (c) and increased internal friction angle (θ). Biochar significantly reduced the formation of soil surface cracks, surface area, and length of the cracks. The surface area density of cracks in the 6% biochar‐amended soils decreased by 14% for SB, 17% for WCB, and 19% for WSB, respectively, compared with control. The results suggest that biochar can be used as a soil amendment for improving the poor physical properties of the clayey soil, particularly in terms of reduction in swell–shrinkage, tensile strength and surface area density of cracking.     

Nitrous oxide emission from a transplanted rice field in alluvial soil as influenced by management of nitrogen fertiliser

We investigated nitrous oxide (N₂O) emission from an irrigated rice field over two years to evaluate the management of nitrogenous fertiliser and its effect on reducing emissions. Four forms of nitrogenous fertilisers: NPK at the recommended application rate, starch–urea matrix (SUM) + PK, neem‐coated urea + PK and urea alone (urea without coating) were used. Gas samples were collected from the field at weekly intervals with the static chamber technique. N₂O emissions from different treatments ranged from 11.58 to 215.81 N₂O‐N μg/m²/h, and seasonal N₂O emissions from 2.83 to 3.89 kg N₂O‐N/ha. Compared with other fertilisers, N₂O emissions were greatest after the application of the conventional NPK fertiliser. Moreover, SUM + PK reduced total N₂O emissions by 22.33% (P < 0.05) compared with NPK during the rice‐growing period (P < 0.05). The results indicate a strong correlation between N₂O emissions and soil organic carbon, nitrate, ammonium, above‐ and below‐ground plant biomass and photosynthesis (P < 0.05). The application of SUM + PK in rice fields is suitable as a means of reducing N₂O emissions without affecting grain production.     

The Impact of Allolobophora molleri on Soil Biology Under Different Organic Amendments

We investigated the effects of the endogenous Allolobophora molleri earthworm on the enzyme activities, the humus–enzyme complexes and the microbial community of a Plagic Antrosol soil which had been amended with different sources of organic matter. During a period of 300 days, the soil was amended with the organic fraction of a municipal solid waste at a rate of 10% or poultry manure at a rate of 7·6%, respectively, in order to apply the same amount of organic matter to the soil. At the end of the experiment, soil enzymatic activities were highest in organic amended soils with earthworms, followed by the organic‐amended soils without earthworms. The reason being, the earthworms stimulate microbial action by increasing the surface area for microbial colonization of the substrate and enzymatic through comminuting the organic wastes. The evolution of soil humus–enzyme complexes indicated the highest values of enzymes adsorbed to humus with the highest humic acid contents. The presence of A. molleri in organic‐amended soils significantly (p < 0·05) increased the soil microbial diversity. Possibly, the progressive breakdown of organic matter applied to the soil by earthworms does appear to produce new organic substrates which therefore promote the appearance of new microorganisms in the soil capable of degrading these substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

The effects of freeze‐and‐thaw cycles on phosphorus availability in highland soils in Turkey

Ongoing global warming may result in colder soil and thawing cycles and will increase the frequency of soil freezing‐and‐thawing‐treated cycles (FTCs) during winter in the cool‐temperate and high‐latitude regions. The purpose of this study was to determine the effects of repeated freeze–thaw cycles on the solubility and adsorption of P in lab and field experiments on Pellustert, Argiustoll, Haplustept, Fluvaquent, and Calciorthid soils, the major soil groups in E Turkey. The results demonstrated that, depending on the soil type, the freeze–thaw cycle could increase the adsorption and desorption of P within a certain temperature range. Repeated freezing and thawing decreased equilibrium P concentration (EPC) and increased P adsorption. EPC and P adsorption were strongly correlated with the number of FTCs. The highest P adsorption and the lowest P desorption was found in Pellustert followed by Argiustoll, Calciorthid, Haplustept, Fluvaquent when refrozen at –10°C for 15 d, then thawed at +2.5°C for 18 h, and 9 times FTC. However, in the field study, the adsorption value was lower than the value obtained from the laboratory condition. It appears that increasing the frequency of freeze–thaw processes depending on increase in temperature that leads to decreased plant‐available soil P pools, thus requires more P fertilizer in soil solution to supply adequate P during the plant‐growth period.     

Recreating Sink Areas on Semiarid Degraded Slopes by Restoration

The patchy distribution of semiarid ecosystems determines productivity and controls the retention of resources within the system. Resource fluxes depend on a number of biophysical and soil variables, besides the amount and intensity of particular rainfall events. At two Mediterranean experimental sites with contrasted composition and spatial vegetation arrangement, we evaluated a straightforward way to simplify some of these processes by using different planting techniques that modify the runoff generation threshold and redirect runoff towards the planting hole (M) and enhance the water infiltration and conservation in it (MDW). Traditional planting technique (H) and M were combined with the addition of composted biosolids. Soil moisture was increased with treatments during drought periods in the first 2 years after planting with mean values of 10·1, 8·9 and 6·9% in MDW, M and H, respectively. Lower landscape organization values at the site resulted in sinks being more efficient at retaining resources, with 3·68‐fold more organic matter accumulation on the soil surface of the planting hole, better growth of the Olea europaea‐planted seedlings and a better response to compost application in MDW than in H. At the site with better landscape organization, planting techniques only showed improvement in seedling survival (+20% in MDW than in H). We discuss ecosystem properties, such as plant composition and spatial arrangement, that determine the effectiveness of these techniques as dryland restoration tools and the hierarchy between water and nutrients as essential resources in these semiarid Mediterranean areas. Copyright © 2016 John Wiley & Sons, Ltd.     

Long‐term fertilization and manuring effects on physically separated soil organic‐matter pools under continuous wheat cropping at a rainfed semiarid site in China

An essential prerequisite for a sustainable soil use is to maintain a satisfactory soil organic‐matter (OM) level. This might be achieved by sound fertilization management, though impacts of fertilization on OM have been rarely investigated with the aid of physical fractionation techniques in semiarid regions. This study aimed at examining changes in organic C (OC) and N concentrations of physically separated soil OM pools after 26 y of fertilization at a site of the semiarid Loess Plateau in China. To separate sensitive OM pools, total macro‐OM (> 0.05 mm) was obtained from bulk soil by wet‐sieving and then separated into light macro‐OM (< 1.8 g cm^–3) and heavy macro‐OM (> 1.8 g cm^–3) subfractions; bulk soil was also differentiated into light OM (< 1.8 g cm^–3) and mineral‐associated OM (> 1.8 g cm^–3). Farmyard manure increased concentrations of total macro‐OC and N by 19% and 25%, and those of light fraction OC and N by 36% and 46%, compared to no manuring; both light OC and N concentrations but only total macro‐OC concentration responded positively to mineral fertilizations compared to no mineral fertilization. This demonstrated that the light‐fraction OM was more sensitive to organic or inorganic fertilization than the total macro‐OM. Mineral‐associated OC and N concentrations also increased by manuring or mineral fertilizations, indicating an increase of stable OM relative to no fertilization treatment, however, their shares on bulk soil OC and N decreased. Mineral fertilizations improved soil OM quality by decreasing C : N ratio in the light OM fraction whereas manuring led to a decline of the C : N ratio in the total macro‐OM fraction, with respect to nil treatment. Further fractionation of the total macro‐OM according to density clarified that across treatments about 3/4 of total macro‐OM was associated with minerals. Thus, by simultaneously applying particle‐size and density separation procedures, we clearly demonstrated that the macro‐OM differed from the light OM fraction not only in its chemical composition but also in associations with minerals. The proportion of the 0.5–0.25 mm water‐stable aggregates of soil was higher under organic or inorganic fertilizations than under no manure or no mineral fertilization, and increases in OC and N concentrations of water‐stable aggregates as affected by fertilization were greater for 1–0.5 and 0.5–0.25 mm classes than for the other classes. Results indicate that OM stocks in different soil pools can be increased and the loose aggregation of these strongly eroded loess soils can be improved by organic or inorganic fertilization.