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The foothill areas of eastern Turkey are an arid and semiarid region with natural salinization, where calcareous alluvial saline soils (Calcaric Fluvisols) are circulated as a result of floods of the Aras River. In this study, the effects of salinity and alkalinity on soil aggregate size distribution and enzyme activities at different aggregate size were investigated. For this purpose, soil samples were collected with three replicates at saline, alkaline, saline-alkaline and non-saline–alkaline areas and passed through into different sieves (2, 1, 0.850, 0.425, 0.106 and 0.02 mm) by dry sieving method for determining aggregate weight distribution in each macro (2–0.45 mm) and micro (0.45–0.02 mm) aggregates. For determining aggregate size distribution, sieves were shaken using a horizontal shaking machine (Retsch, AS 200 basic, Haan, Germany). The soil enzymes were determined in these aggregate sizes (2–1, 1–0.850, 0.850–0.425, 0.425–0.106, 0.106–0.02 mm) for all soil types. All soils belonged to the clay loam with the carbon content in the range of 0.5–0.8%, while the percentage of exchangeable sodium for the non-saline–alkaline and alkaline–saline soils was from 3.5 to 22%, but the pH diapason from 8.3 to 8.9. Results showed that soil salinity and alkalinity decreased the weight of macro aggregates and increased the weight of micro aggregates, besides soil salinity and alkalinity decreased soil enzyme activities. But soil salinity decreased enzyme activity more than alkalinity. Furthermore, the highest urease and catalase activities were in macro aggregates (0.850–0.425 mm aggregate size) for all soil types. The reason may be that macro aggregates contain higher organic matter and organic carbon than micro aggregates. Consequently, the highest enzyme (urease and catalase) activities were detected in macro aggregates. [ABSTRACT FROM AUTHOR]

• Simulated warming caused a rapid loss of OC in mountainous grassland soils rich in OM. • SOC loss was associated with a disruption of large-macroaggregates. • Intensive grassland slightly offset OC losses and promoted SM formation. • Soil perturbation effects have to be differentiated from climate change effects. Mountainous grassland soils are considered one of the most unique biological hotspots, rich in organic carbon (OC). At the same time, they are exposed to great threats, as climate warming is more pronounced in mountainous regions than in lowland areas. In this study, we assessed the effect of simulated warming (+1K, +2K, and + 3 K) on OC stocks and soil structure in grassland soils of the Northern Limestone Alps in Germany by translocating plant-soil mesocosms from high- (1260 m a.s.l., Rendzic Phaeozem) and mid- (860 m a. s. l., Haplic Cambisol) to low-elevation (600 m a.s.l). Plant-soil mesocosms were exposed to both extensive and intensive grassland management practices. Four years after translocation, we observed a rapid decrease of topsoil SOC stocks under intensive (−1.0 t C ha yr−1) and extensive management (-2.2 t C ha yr−1), under the highest temperature increase. Intensive management with about 1 t C ha−1 yr−1 higher manure C return than extensive management (1.6 vs. 0.8 t C ha−1 yr−1 intensive and extensive, respectively) may explain the difference in SOC losses between different management treatments. Under both management practices, the loss of SOC was mainly associated with a decrease of large macroaggregates, at both management practices. In addition, different aggregate specific OC loss rates resulted in an altered distribution of OC among the aggregate size classes. Our study provides evidence that simulated climate change induced a rapid and substantial decline of SOC in mountainous, OC-rich grassland soils, which may be attributed to decreased physical OC protection within large macroaggregates. Optimized grassland management in form of increased application of organic fertilizers could only partially offset the SOC loss by improved formation of small macroaggregates. [ABSTRACT FROM AUTHOR]

[Display omitted] • Topsoil SOC stocks and soil structure recovered 26 years after topsoil removal. • Topsoil buried under the plough layer non-linearly lost 30–50% of SOC in 55 years. • Topsoil SOC recovery and stability of buried SOC was dependent on N fertilisation. Erosion of fertile topsoil means severe land degradation and yield loss. Here, we show that reformation of the fertile topsoil and crop yield increase is possible by good agricultural management within a few decades. Evidence relies on a unique long-term field experiment in NE Germany, where in 1964 the sandy soil (Luvisol) had been excavated to 52 cm and refilled with subsoil material of 52 cm thickness. Undisturbed trials served as controls, these were all combined with either no fertilisation, mineral fertilisation or a combined mineral and organic fertilisation. It took only 26 years until new topsoil had been formed. Its soil organic carbon (SOC) and total N stocks and the aggregate size distributions equalled that of the other treatments; SOC sequestration corresponded to 28 Mg SOC ha−1. The former topsoil buried below the plough layer lost 30–50 percent of its SOC during 5 decades in a non-linear manner. We conclude that our current agricultural tools can restore degraded arable land rather fast and contribute to climate change mitigation through a significant SOC sequestration as well. [ABSTRACT FROM AUTHOR]

• Apple replant disease is reflected in a huge in-field variability of tree growth. • Plants showing most stunted shoot growth revealed lowest δ 15N values in the rhizosphere. • Apple replant disease severity is correlated to a reduced micronutrient supply of Mn and Co for infected plants up to 100 cm shoot length. Orchards affected by apple replant disease may show a distinct in-field variability of the severity of apple replant disease (ARD) symptoms. As abiotic soil properties can affect pathogen survival but show considerable variability at the scale of a few meters, we hypothesized that the variability of abiotic soil properties may be used to explain parts of the in-field variability of ARD. We sampled soil and rhizosphere of 32 apple trees with different degree of ARD symptoms after two years of growth at the horticultural research station Heidgraben, Germany. The sandy soils correspond to Entic Podzols. Soil analyses comprised soil aggregate-size fractionations, the assessment of the stocks of nitrogen and essential macro- and micronutrients, as well as a tracing of stable δ 15N natural abundance both in rhizosphere and non-rhizosphere soil. The results showed that there was indeed a huge in-field variability of tree growth, following a Gaussian distribution, but classified here in shoot heights of < 40, 40–80, 80–120, and >120 cm, respectively. An effect of soil aggregation on ARD or vice versa was not detected. Elevated tree growth, however, went along with a consumption of soil macronutrients (R2: = 0.3 – 0.8 for the n = 4 ARD classes; significant only for K on individual plant basis). Intriguingly, opposite correlations were observed for micronutrients, where reduced tree growth occurred at subsites short in micronutrient supply (R2 = 0.9 for Mn and Co, significant for Mn and Co for ARD infected plants up to 100 cm shoot length on individual plant basis). Moreover, the plants showing most stunted shoot growth revealed lowest δ 15N values in the rhizosphere, as typical for reduced N cycling. Our data therefore confirm that at least parts of the in-field variability of ARD severity is correlated to reduced micronutrient supply and N cycling, possibly via effects on habitat properties of pathogenic soil microbiota. [ABSTRACT FROM AUTHOR]