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Recent studies have attempted to optimize the configuration of sample sites for estimation of the variogram by the usual method-of-moments. This paper shows that objective functions can readily be defined for estimation by the method of maximum likelihood. In both cases an objective function can only be defined for a specified variogram so some prior knowledge about the spatial variation of the property...
In arid lands, the soil surface commonly is characterized by textural and structural differentiation compared with deeper horizons. This is traditionally attributed to mechanical transfer of material by wind and runoff that contributes to sealing and crusting. Another process, however, was previously interpreted in the Niger Republic, at the surface of irrigated alluvial soils. The process, called...
Soil degradation, especially compaction, due to wheeling with heavy machinery is a problem on arable land, which may rise in the future due to increasing weight. In a combined laboratory and field experiment, the rehabilitation of soil structure was investigated. We tried to differentiate between the rehabilitating effects of intrinsic soil processes and that of biological activity, especially earthworm...
In undisturbed tropical forest ecosystems, the phosphorus (P) cycle is essentially ''closed'' with minimal short-term losses or gains of P. The forms and dynamics of soil P, however, can be greatly affected by land use changes, which often involve changes in vegetation cover, biomass production and nutrient cycling in the ecosystem. Sequential extraction and 31 P nuclear magnetic resonance...
This paper presents a method that can be used to quantify and map soil losses at field scale produced by extreme rainfall events. The amounts of sediment produced by overland flow and concentrated overland flow (inter-rill, rill and gully erosion) at the agricultural plot scale are evaluated from elevation differences computed from very high resolution digital elevation models (DEMs), from before...
The effects of the activity of seed harvesting ants (Messor bouvieri) on the fertility, rainfall infiltration, structural properties and water repellency of top soils were investigated in a semi-arid rangeland in SE Spain. The soil surfaces had a low vegetative cover and bare areas had a sieving crust. Rainfall simulation experiments were carried out over ants' nest mounds and on control areas without...
Long-term (5- and 9-year) effects were evaluated of two tillage regimes (conventional tillage: CT; and no-tillage: NT) and two cropping systems (oat/maize: O/M; and oat+vetch/maize+cowpea: O+V/M+C) on characteristics of humic acids (HAs) from surface layer (0 to 25 mm) of a subtropical Brazilian Paleudult soil. Generally, soil HA samples from conservation management systems with no soil disturbance...
The activity of microorganisms and the availability of composting substrates for decomposition are seriously affected by drying and rewetting cycles. We have measured microbial biomass C (B C ) and ninhydrin reactive N (B NIN ) of samples of composting material taken at different times from a pile of ligno-cellulosic wastes. Dynamics of these two parameters in control samples...
Neglecting the spatial variation in soil nutrient status may result in unused yield potential and in environmental damage. Site-specific management has been suggested to reduce inappropriate fertilization that can adversely affect soil, ground and surface water. Decision criteria for determining variable-rate nitrogen fertilization are, however, lacking. This paper analyses the spatial variation of...
An arable landscape (150 ha) comprising a broad variety of soil types had been cultivated conventionally for many years. A small section had been intensively managed (hops), while another had been used as grassland. For 2 years at the beginning of our study, all arable land was cultivated with cereals only. After that, management was changed to integrated or organic farming, grassland or fallow land...
Changes in management practice are reflected by soil carbon and nitrogen status, in particular by the proportion of soil organic matter (SOM) being easily transformed (active SOM). We describe SOM quality for three management practices, Organic Farming system (OF), Integrated Crop Production (ICP) and pasture sites (G), which intend to achieve sustainable management practice. The experimental sites...
1 4 C-isoproturon residues were incorporated in wheat plants by growing seedlings for 18 days in quartz sand with nutrient solution which was treated with ring-labeled 14 C-isoproturon, resulting in 14 C-concentration equivalent to 15.4 nmol isoproturon per g dry shoot mass. The residues were characterized by extraction and HPLC-analysis, and were shown to consist...
Using the modeling tool Expert-N, daily fluxes of water, carbon and nitrogen in potato fields were simulated in this study. The crop growth model Soil-Plant-Atmosphere System Simulation (SPASS) was integrated in Expert-N and adapted for the simulation of potato growth. The aim of the study was to investigate the extent to which the SPASS model, tested thus far only for winter wheat, is suitable for...
In spite of the known below-ground biomass production of plant roots that concurrently introduce significant amounts of carbon and nitrogen into the soil, the effects of these inputs on N cycling in the soil-plant system are seldom considered. Here, we report on two field experiments carried out between 1995 and 1997 at the FAM Research Station Scheyern: (1) a N-turnover experiment to determine the...
Modern agricultural production systems need to reduce their environmental contamination potential. Within the test site of the FAM Research Network on Agroecosystems, the existing agricultural system was modified from intensive to sustainable land use practices. The aim of this study was to quantify the long-term effects of these new practices on the surface and subsurface water quality at the Research...
In hilly areas of south Germany with tertiary and quaternary sediments, percolation has been studied applying an isotope tracer of the water molecule in small-scale field experiments to better understand the hierarchies and interconnections of quick and slow seepage. On a catchment-related scale, these results have been connected with traditional and environmental isotope analysis of discharge to...
Sampling and analytical methods were developed to examine the input of various pesticides on noncultivated areas of the FAM (Research Network on Agroecosystems) Research Station Scheyern. Off-target drift from pesticide application on nearby cultivated land, as well as input due to long-range atmospheric transport, were measured. The wet deposition was determined by a cooled wet-only sampler. Bulk...
The large temporal variation in nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) flux rates is a major source of error when estimating cumulative fluxes of these radiative active trace gases. We developed an automated system for near-continuous, long-term measurements of N 2 O, CH 4 and CO 2 fluxes from cropland soils and used it to...
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