The abundance of nitrogen cycle genes and potential greenhouse gas fluxes depends on land use type and little on soil aggregate size

Soil structure is known to influence microbial communities in soil and soil aggregates are the fundamental ecological unit of organisation that support soil functions. However, still little is known about the distribution of microbial communities and functions between soil aggregate size fractions in relation to land use. Thus, the objective of this study was to determine the gene abundance of microbial communities related to the nitrogen cycle and potential greenhouse gas (GHG) fluxes in six soil aggregate sizes (0–0.25, 0.25–0.5, 0.5–1.0, 1–2, 2–5, 5–10 mm) in four land uses (i.e. grassland, cropland, forest, young forest). Quantitative-PCR (Q-PCR) was used to investigate the abundance of bacteria, archaea and fungi, and functional guilds involved in N-fixation (nifH gene), nitrification (bacterial and archaeal amoA genes) and denitrification (narG, nirS, and nosZ genes). Land use leads to significantly different abundances for all genes analysed, with the cropland site showing the lowest abundance for all genes except amoA bacteria and archaea. In contrast, not a single land use consistently showed the highest gene abundance for all the genes investigated. Variation in gene abundance between aggregate size classes was also found, but the patterns were gene specific and without common trends across land uses. However, aggregates within the size class of 0.5–1.0 mm showed high bacterial 16S, nifH, amoA bacteria, narG, nirS and nosZ gene abundance for the two forest sites but not for fungal ITS and archaeal 16S. The potential GHG fluxes were affected by land use but the effects were far less pronounced than for microbial gene abundance, inconsistent across land use and soil aggregates. However, few differences in GHG fluxes were found between soil aggregate sizes. From this study, land use emerges as the dominant factor that explains the distribution of N functional communities and potential GHG fluxes in soils, with less pronounced and less generalized effects of aggregate size

Indicators for the definition of land quality as a basis for the sustainable intensification of agricultural production

Sustainable intensification (SI) is a concept for increasing agricultural production under sustainable conditions to meet the needs of the growing population of the world. To achieve this goal, the intrinsic potential of soils for SI has to be considered. This report aims at identifying indicators for arable soils in Germany, which have the best natural resilience and performance and therefore can be used for SI. Six intrinsic land and soil characteristics (organic C content, clay+silt, pH, CEC, soil depth and slope) were selected as indictors for defining the resilience and performance of land. New data from arable sites from LUCAS topsoil survey 2009 were used and attributed to arable land, applying the Arc Geographical Information System (ArcGIS). The results of this investigation reveal that 39% of the actual analyzed arable land can be recommended for SI in Germany. A comparison with the Muencheberg Soil Quality Rating shows that most of this land reflects the highest potential for agricultural yields. Approximately 61% of the analyzed agricultural land is not suitable for intensification, about 1.5% should be reduced in intensity with a possible conversion to avoid environmental harm. The most frequent limitation factor for SI is a too low cation exchange capacity in German soils

Pore system characteristics of soil aggregates and their relevance to aggregate stability

Aggregates are the structural units of soils, and the physical stability is considered to be a keystone parameter of soil quality. However, little is known about the evolution of the pore system in aggregates and its importance in defining aggregate stability. In this paper, we investigated the pore system and stability of three dominant macroaggregate sizes (1–2, 2–5 5–10 mm) obtained from a fine sand-loamy Chernozem under three distinct land uses (arable, grassland and forest). We used non-invasive X-ray microtomography (XMT) in combination with pore network extraction to characterise PSD (pore size distribution) of aggregates and their potential changes upon continued submergence in water. We showed that smaller aggregates (1–2 mm) have significantly higher total X-ray resolvable porosity than the medium (2–5 mm) and large (5–10 mm) aggregates. Also, using imaging tools, we demonstrated for the first time, that the pore system of stable aggregates from grassland and forest does not undergo significant changes upon continued submergence in water. It can be hypothesised that a physically stable pore structure allows the storage and transmission of water without a structural collapse, thereby contributing to aggregate stability. We found statistically significant positive correlations between different pore groups (closed pores, water holding pores and air space spores) and water stability of aggregates from all three land uses suggesting that pore system characteristics play a significant role in aggregate stability. Our results suggest that PSD is an important factor that determines the stability of soil aggregates

Soil aggregation and soil organic matter in conventionally and organically farmed Austrian Chernozems

In order to study the soil aggregate distributions and soil organic matter (SOM), we sampled top- and subsoils in four intensively farmed croplands (two organic (Org-OB and Org-LA), and two conventional (Con-OB and Con-LA)) on Haplic Chernozems located in Marchfeld in the east of Vienna (Austria). Soil structure and SOM quantity, quality and distribution between free and occluded particulate organic matter and aggregate size fractions (<20 μm, 20-250 μm, 250-5000 μm) were studied by following a density fractionation procedure with low-energy ultrasound treatment. Te relation of the soil physicochemical (e.g., particle size distribution, pH, organic carbon, total nitrogen) and biological properties (e.g., fungal biomass, active fungi) with stable soil aggregate size fractions and SOM was studied. Te mean weight diameter (MWD) showed no significant difference between all studied sites and was between 3.8 mm and 10.0 mm in topsoils and between 6.7 mm and 11.9 mm in subsoils. In topsoils, the contents of calcium-acetate-lactate (CAL)-extractable P, active fungal biomass, dithionite-extractable Fe and sand were significantly positively correlated with the amount of the macroaggregates and with the MWD. We observed that most soil organic carbon, depending on soil texture, was stored in the microaggregate size classes <20 μm and 20-250 μm

Tamanho da parcela para estudos de recuperação de fertilizante-15N por capim-tanzânia Plot-size for 15N-fertilizer recovery studies by tanzania-grass

O entendimento da dinâmica do N em ecossistemas de pastagens pode ser melhorado por estudos em que se utilize a técnica do traçador 15N. Nesses experimentos, deve-se assegurar que o movimento lateral do traçador não interfira nos resultados. Neste trabalho foram determinadas as exigências quanto ao tamanho da parcela para experimentos com 15N em pastagem irrigada de Panicum maximum cv. Tanzânia. Foram consideradas três intensidades de pastejo (leniente, moderada e intensa) em três épocas do ano: inverno, primavera e verão. Parcelas de 1 m², com uma touceira do capim ao centro, foram adequadas, independentemente da intensidade de desfolha ou da época do ano. O aumento na distância da área adubada com 15N influenciou negativamente a quantidade de N proveniente do fertilizante (Npfm) recuperado na forragem. As menores taxas de declínio nos valores de Npfm foram observadas para as intensidades de pastejo leniente e moderada; esse fato pode ser explicado pelas características de crescimento vigoroso dessas plantas. O aumento na intensidade de pastejo determinou a redução na massa da touceira: quanto menor a touceira, maior a sua dependência do N do fertilizante.<br>The understanding of the N dynamics in pasture ecosystems can be improved by studies using the 15N tracer technique. However, in these experiments it must be ensured that the lateral movement of the labeled fertilizer does not interfere with the results. In this study the plot-size requirements for 15N-fertilizer recovery experiments with irrigated Panicum maximum cv.Tanzania was determined. Three grazing intensities (light, moderate and intensive grazing) in the winter, spring and summer seasons were considered. A 1 m² plot-size, with a grass tussock in the center, was adequate, irrespective of the grazing intensity or season of the year. Increasing the distance from the area fertilized with 15N negatively affected the N derived from fertilizer (Npfm) recovered in herbage.The lowest decline in Npfm values were observed for moderate and light grazing intensities. This fact might be explained by the vigorous growth characteristics of these plants. Increasing the grazing intensity decreased the tussock mass and, the smaller the tussock mass, the greater was the dependence on fertilizer nitrogen

SoilTrEC: A global initiative on critical zone research and integration

Soil is a complex natural resource that is considered non-renewable in policy frameworks, and it plays a key role in maintaining a variety of ecosystem services (ES) and life-sustaining material cycles within the Earth's Critical Zone (CZ). However, currently, the ability of soil to deliver these services is being drastically reduced in many locations, and global loss of soil ecosystem services is estimated to increase each year as a result of many different threats, such as erosion and soil carbon loss. The European Union Thematic Strategy for Soil Protection alerts policy makers of the need to protect soil and proposes measures to mitigate soil degradation. In this context, the European Commission-funded research project on Soil Transformations in European Catchments (SoilTrEC) aims to quantify the processes that deliver soil ecosystem services in the Earth's Critical Zone and to quantify the impacts of environmental change on key soil functions. This is achieved by integrating the research results into decision-support tools and applying methods of economic valuation to soil ecosystem services. In this paper, we provide an overview of the SoilTrEC project, its organization, partnerships and implementation. © 2013 Springer-Verlag Berlin Heidelberg

Soil processes and functions across an international network of Critical Zone Observatories: Introduction to experimental methods and initial results

Growth in human population and demand for wealth creates ever-increasing pressure on global soils, leading to soil losses and degradation worldwide. Critical Zone science studies the impact linkages between these pressures, the resulting environmental state of soils, and potential interventions to protect soil and reverse degradation. New research on soil processes is being driven by the scientific hypothesis that soil processes can be described along a life cycle of soil development. This begins with formation of new soil from parent material, development of the soil profile, and potential loss of the developed soil functions and the soil itself under overly intensive anthropogenic land use, thus closing the cycle. Four Critical Zone Observatories in Europe have been selected focusing research at sites that represent key stages along the hypothetical soil life cycle; incipient soil formation, productive use of soil for farming and forestry, and decline of soil due to longstanding intensive agriculture. Initial results from the research show that soil develops important biogeochemical properties on the time scale of decades and that soil carbon and the development of favourable soil structure takes place over similar time scales. A new mathematical model of soil aggregate formation and degradation predicts that set-aside land at the most degraded site studied can develop substantially improved soil structure with the accumulation of soil carbon over a period of several years. Further results demonstrate the rapid dynamics of soil carbon; how quickly it can be lost, and also demonstrate how data from the CZOs can be used to determine parameter values for models at catchment scale. A structure for a new integrated Critical Zone model is proposed that combines process descriptions of carbon and nutrient flows, a simplified description of the soil food web, and reactive transport; all coupled with a dynamic model for soil structure and soil aggregation. This approach is proposed as a methodology to analyse data along the soil life cycle and test how soil processes and rates vary within, and between, the CZOs representing different life cycle stages. In addition, frameworks are discussed that will help to communicate the results of this science into a more policy relevant format using ecosystem service approaches