Determination of critical soil water content and matric potential for wind erosion

Purpose  

Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θ_crit.) for deflation was extended to include matric potential (Ψ_crit.) as well. The focus of this paper is to quantify the Θ_crit. and Ψ_crit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψ_crit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height.     

Litter decomposition in fertilizer treatments of vegetable crops under irrigated subtropical conditions

In the coastal Batinah plain of Oman, a litterbag experiment was carried out in an irrigated field, investigating the effects of organic fertilization and mineral fertilization on the cultivation of carrots and cauliflower. Two straw varieties and two green-harvested crops were used, simulating the properties of green manures. The loss of C in the litterbags declined in the order maize (−94%) > alfalfa (−89%) > wheat (−80%) > canola (−69%). For all these materials, the concentration of muramic acid, as an indicator of bacterial C, as well as galactosamine was generally increased in comparison with the initial values. In contrast, fungal glucosamine and consequently also the ratio of fungal C/bacterial C declined for canola and wheat straw. The loss of N, P, and S was generally smaller than that of C and showed strong substrate-specific patterns. Fertilization and crop cultivation had no effect on C losses. Organic fertilization resulted in significant increases in S, Mg, and Al in the litterbags in comparison with mineral fertilization. Cultivation of carrots led to significantly lower ash, N, P, Ca, K, Na, and Al concentrations than cultivation of cauliflower. Organic fertilization and carrot cultivation both led to stronger fungal colonization of the litter retained in the litterbags in comparison with mineral fertilization and cauliflower cultivation, respectively. More information is required on the interactions between initial plant surface colonizing microorganisms and soil-derived colonizers.     

Einfluss der Zwischenlagerung auf die anfängliche Entwicklung rekultivierter Oberböden

Influence of temporary stockpiling on the initial development of restored topsoils Due to increasing construction and open‐cast mining activities on fertile agricultural land, excavation, stockpiling, and restoration of soils have become important issues in soil protection. In this study, we performed a restoration experiment to investigate how the conditions during stockpiling may influence initial soil development and plant growth on a restored site. Four topsoils, which originated from two depths (with uninhibited and inhibited aeration) of a nontrafficked and a trafficked topsoil deposit, were repacked in strips and sown with three meadow‐seed mixtures in strips perpendicular to the soil strips. During stockpiling as well as during the first 2 years after restoration, we assessed the physical and mechanical properties of the topsoils and (after restoration) also plant growth. None of the investigated properties of the topsoils was influenced by the depth in the deposit. In contrast, the coarse porosity and compression index were lower, whereas the bulk density and precompression stress were higher in the trafficked than in the nontrafficked topsoil deposit. However, these differences largely disappeared already in the course of soil restoration. Contrary to our expectations, the plants grew better on the soil of the trafficked topsoil deposit than on the soil of the nontrafficked topsoil deposit in the year of restoration. This might be attributed to the extremely dry and hot summer of that year. In the course of the 2 years following restoration, also the differences in plant growth tended to disappear. The remaining differences in bulk density and plant growth could not be attributed to differences in stockpiling conditions. The results suggest a re‐examination of current soil restoration guidelines. The maximum permitted stockpiling heights for topsoils might be increased in order to reduce the areas required for temporary stockpiling.     

Pot and field experiments on the suitability of lignite as soil improving agent

Effects of raw brown coal ("Kohletrübe"), brown coal modified with ammonia water, NH3, ("Ammonkohle") and composted brown coal ("Biomineraldünger") on plant yield and on selected soil fertility characteristics of a colloidpoor and a coal-bearing dump soil are tested in a pot and field experiment. The results confirm already published results. Therefore chemical modified nitrogen enriched brown coal is a humus fertilizer the influence of which sustained the water and nutrient storing capacity as well as the nutrient transformation ability of colloid-poor dump soils. Soil improving and yield increasing effects of coal fertilisation depend on particular conditions.     

Functional dependencies of soil CO2 emissions on soil biological properties in northern German agricultural soils derived from a glacial till

Agricultural soil CO₂ emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO₂ emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO₂ emissions were found in grassland (20.40 µg g^?1 dry weight h^?1) compared to arable land (5.59 µg g^?1 dry weight h^?1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO₂ emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO₂ emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO₂ emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.     

Viscoelasticity and shear resistance at the aggregate scale of structured and organic carbon-free Chernozems

Soil rheology characterises the flow behaviour of soils at the particle-particle to aggregate scale. Amplitude sweep tests (ASTs) are often the method of choice for parameterizing soil flow properties, such as the shear strain values at the end of the linear viscoelastic range (i.e., the deformation is mainly elastic) and at the yield point (i.e., elastic equals plastic deformation). Samples from seven soil profiles and five soil depths of Chernozems, collected in the Maidanetske study area, clo...