Nikolaus J. Kuhn

Comparative measurements with seven rainfall simulators on uniform bare fallow land

To assess the inflfl uence of rainfall simulator type and plot dimensions on runoff and erosion, seven small portable rainfall simulators from Freiberg, Tubingen, Trier (all Germany), Valencia, Zaragoza (both Spain), Basel (Switzerland) and Wageningen (the Netherlands) were compared on a prepared bare fallow fifi eld. The experiments were carried out during an international rainfall simulator workshop, organized at Trier University (Germany) from 30th of June to 1st of July 2011.The tested rainfall simulators differ in design, rainfall intensities, rain spectra, etc. and represent most of the devices which have been used over the last decade in Europe. The plots for the different rainfall simulators were selected as similar as possible concerning soil physical and chemical properties, aspect and inclination and were chosen to be placed side by side in horizontal direction. Test procedure was standardized in order to examine the inflfl uence of the rainfall simulator andplot dimension only. The results show a clear and consistent relationship in runoff, erosion and infifi ltration behaviour of the different used rainfall simulators. With all the devices total soil loss is measurable, but different plot sizes, intensities and kinetic energies of the simulated rainfall caused differences in soil loss and runoff quantities per unit of area. Regarding course characteristics over runs, similarities could be observed especially in runoff behaviour. The rainfall simulators (> 1 m² plot size) are able to reproduce infifi ltration and interrillerosion processes. With an increase of plot size (≥ 1 m²), rill-erosion will be also reflfl ected. Therefore it can be concluded that up to a certain plot size, the results of the different simulators are comparable and depend in their magnitude on the properties of the applied rainfall. The increase in process complexity with increasing plot size shows, that the scale of the simulation is one of the most important parameters to be taken intoaccount when comparing values of erosion and runoff.

Effect of ridge tillage, no-tillage, and conventional tillage on soil temperature, water use, and crop performance in cold and semi-arid areas in Northeast China

In cold and semi-arid Northeast China, insufficient soil accumulative temperature and low water use efficiency (WUE) are the limiting factors for the further development of agriculture. Ridge tillage (RT) has been proposed to improve soil temperature and water conservation. Data from a 3-year field experiment conducted at two locations (Sujiatun and Lanxi) in Northeast China were used to compare RT, no-tillage (NT), and conventional tillage (CT) in a spring maize cropping system. At both sites, RT and NT significantly (P < 0.05) increased mean soil temperature to 0.10 m depth, relative to CT, by 0.7–2.4°C in the cold season during the spring maize growing stage. Mean soil moisture depletion in the RT treatment was greater by 1.2–4.1% (Sujiatun) and 0.6–3.0% (Lanxi) than in NT and CT, respectively. Mean maize yields over 3 years for RT were ~9.9% greater than for CT, whereas the yield advantage in the NT treatment was only slight. In Sujiatun, WUE was 8.0% and 8.6% greater under RT than under NT and CT, respectively, and in Lanxi, WUE was 7.7% and 9.6% greater under RT than NT and CT. Ridge tillage is recommended to the farmers to obtain higher crop yield and WUE in Northeast China.

Soil structure and crop performance after 10 years of controlled traffic and traditional tillage cropping in the dryland Loess Plateau in China

Soil degradation and the accompanying decline in crop yields are the main limiting factors for the further development of agriculture on the Chinese Loess Plateau. A 10-year experiment was conducted in Linfen on the Loess Plateau to assess the potential benefits of controlled traffic on agricultural production. In this region, long-term traditional ploughing with straw removal has resulted in a decline of soil productivity and poor soil structure. Several treatments were compared: controlled traffic with no-tillage and straw cover (NTSC), controlled traffic with shallow tillage and straw cover, and traditional tillage (TT) in a winter wheat (Triticum aestivum L.) monoculture. Results show clear benefits of controlled traffic farming. Winter wheat growth in ploughed plots was much slower than in controlled traffic plots. Mean yield from 1998 to 2007 was 11.2% lower for traditional tillage than for controlled traffic plots. The best results were achieved by a no-tillage straw cover and controlled traffic system (NTSC), which resulted in the greatest benefits to soil structure after 10 years. The NTSC significantly improved soil organic matter content in the top 30 cm by 27.2%, total N by 10.8%, and available P (top 10 cm) by 92.3% compared with TT. Aeration (>60 &mgr;m) and capillary porosity (2-60 &mgr;m) were 155.0% and 16.1% greater, respectively, in NTSC plots than in TT plots. Consequently, for NTSC, final water infiltration rates were 67.4% greater than for TT, whereas water content in the top 130 cm was 14.9% higher than in TT, respectively. We conclude therefore that controlled traffic combined with no-tillage and straw cover is a valuable system for restoring soil productivity and quality of seriously degraded soils on the Loess Plateau for the sustainable development of agriculture in dryland China.

Does the invasive plant, Impatiens glandulifera, promote soil erosion along the riparian zone? An investigation on a small watercourse in northwest Switzerland

PurposeThe invasive plant, Impatiens glandulifera (common English name: Himalayan Balsam), is now found in many river catchments in most European countries. Its preference for damp, nutrient-rich soils, along with its intolerance to cold weather and rapid dieback, has implicated it in promoting soil erosion along the riparian zone. Despite the implication, its influence on the sediment dynamics of river systems remains unconfirmed. This communication reports the preliminary findings of ongoing work to investigate a possible link between I. glandulifera and accelerated erosion rates in inland river systems.Materials and methodsErosion pins, a micro-profile bridge, and a digital caliper were employed to measure changes in the soil surface profile (SSP) at six separate locations, each contaminated with I. glandulifera, along the riparian zone of a small watercourse in northwest Switzerland. Changes in SSP were also measured at an identical number of nearby locations supporting natural vegetation, in order to establish baseline erosion conditions. Soil surface profiles at all 12 locations were re-measured on seven separate occasions, from October 2012 to May 2013. This covers the time before dieback occurred to the germination and seasonal regrowth of new plants.Results and discussionA total of 720 individual SSP measurements were recorded during the above monitoring period. Increasingly negative values relative to initial values were documented at most transects, indicating a net reduction in soil surface elevations. This is interpreted as evidence of the removal (i.e., erosion) of surface material. Paired samples statistical analysis of the data indicate that erosion from contaminated sites was significantly greater than erosion from topographically comparable reference sites (t =−5.758; P < 0.05; N = 359) supporting natural vegetation.ConclusionsThe results provide tentative yet compelling evidence that I. glandulifera promotes soil erosion along the riparian zone of the watercourse investigated. Given the unrelenting spread of this notoriously invasive plant throughout inland river systems in many countries, the likelihood of greater quantities of nutrient-rich sediment entering into aquatic environments may steadily reduce water quality in all affected catchments. An absence of effective control measures capable of halting or even slowing its rate of invasion may make it increasingly difficult for affected European Union member states to meet and then maintain key water quality standards set by the Water Framework Directive (WFD) when fully implemented in 2015.

Variations in soil structure and reflectance during a controlled crusting experiment

The results of an experiment to show variations in the directional reflectance factor of a Luvisol during a controlled crusting experiment are described. Soil sampled in the field after tillage was sieved into free‐draining trays, and exposed to artificial rainfall for differing periods of time, ranging from 5 to 60 min. The resulting samples demonstrated different stages in the development of the soils structural crust. The topography of each dried sample was characterized over a 5×5 cm area using a laser profilometer, and digital surface models (DSMs) were subsequently analysed using variogram models. DSMs were also used to generate statistical measures of random roughness. Directional reflectance factors of each sample were characterized in the solar principal plane under clean skies using an ASD FieldSpec Pro spectroradiometer, using an 8° foreoptic attached to an A‐frame device. Directional reflectance factors were analysed in relation to spatial statistical measures obtained from the laser profilometer data. The results demonstrate that changes in the sill variance of soil samples following crusting, and hence changes in soil structure, were best described by backscattered radiation measured at +30° in the visible and near‐infrared (e.g. R 2 = 0.947 (658 nm)), and at +15° in the short‐wave infrared (e.g. R 2 = 0.992 (1700 nm)). View zeniths are expressed from the nadir, and were relative to the solar zenith angle, which ranged from 80.76° to 74.55° during the measurement sequences. The results from these tests show great promise for broader‐scale monitoring of soil condition, particularly when considered in the context of the new pointable remote sensing systems in operation, coupled with new‐generation sensors with in‐built directional capabilities.

Traffic and tillage effects on runoff and soil loss on the Loess Plateau of northern China

This paper reports the outcome of 5 years of field plot runoff monitoring, 2 years of water erosion measurement, and a rainfall simulation experiment on moderately sloping farmland on the loess plateau of north-west China. The objective was to test different conservation tillage systems compared with the control treatment, conventional mouldboard plough practice (CK). Tillage, residue cover, and compaction effects were assessed in terms of runoff and soil erosion. Results from the runoff plots showed that conservation tillage, with more residue cover, less compaction, and less soil disturbance, could substantially reduce runoff and soil erosion compared with the control. No tillage with residue cover and no compaction produced the least runoff and soil erosion. Compared with the control, it reduced runoff and soil erosion by about 40% and 80%, respectively. At the start of the experiment, residue cover appeared to be the most important factor affecting soil and water conservation, particularly when antecedent soil moisture was limited. With the accumulation of tractor wheeling effects over the course of the experiment, soil compaction appeared to become a more important factor affecting runoff. Rainfall simulation was then used to assess the effect of non-inverting surface tillage and different levels of residue cover and wheel compaction on infiltration and runoff. This confirmed that wheel compaction effects could be greater than those of tillage and residue cover, at least under the 82.5 mm/h rainfall rate produced by the simulator. The wheeling effect was particularly large when the treatment was applied to wet soil, and severe even after wheeling by small tractors.

The role of wind-driven rain for soil erosion – an experimental approach

Recent research has shown that wind can have a signififi cant inflfl uence on velocity, impact angle and kinetic energy of raindrops, and subsequently increases soil erosion. The aims of this study were to 1) quantify the inflfl uence of wind on water erosion, 2) specififi cally observe the difference in processes betweenwindless rain (WLR) and wind-driven rain (WDR) simulations and 3) test the device’s and test sequence’s practicability. The Portable Wind and Rainfall Simulator (PWRS), recently developed at Trier University for plot-scale in situ assessment of differences in soil erosion with and without the inflfl uence of wind on raindrops, wasused. To facilitate extraction of the inflfl uences of WDR on soil erosion, to avoid systematic errors, and to reduce variability between test plots, a defifi ned order of four consecutive test runs was established: 0) wind simulation, 1) WLR simulation on dry soil, 2) WLR simulation on moist soil, 3) WDR simulation. The tests were conducted on homogenous sandy substrate deposited on an area of 15.2 m 60 m with uniform and smooth surface and low inclination (1°) in the Willem Genet Tunnel of Wageningen University. The results show an increase of eroded sediment ranging from 113 % up to 1108 % for WDR simulations in comparisonto WLR simulations. The increase in runoff was considerably lower (15 % to 71 %), resulting in an increase of sediment concentration between 56 % and 894 %. The results indicate an immense impact of WDR on soil erosion of sandy cohesionless substrate. The experimental setting and measurement proved reliable and reproducible and enables a clear process observation and quantififi cation in the fifi eld.

Managing the impact of climate change on the hydrology of the Gallocanta Basin, NE-Spain.

The Gallocanta Basin represents an environment highly sensitive to climate change. Over the past 60 years, the Laguna de Gallocanta, an ephemeral lake situated in the closed Gallocanta basin, experienced a sequence of wet and dry phases. The lake and its surrounding wetlands are one of only a few bird sanctuaries left in NE-Spain for grey cranes on their annual migration from Scandinavia to northern Africa. Understanding the impact of climate change on basin hydrology is therefore of utmost importance for the appropriate management of the bird sanctuary. Changes in lake level are only weakly linked to annual rainfall, with reaction times between hours and months after rainfall. Both the total amount of rainfall over the reaction period, as well as individual extreme events, affect lake level. In this study the characteristics and frequencies of daily, event, monthly and bi-monthly rainfall over the past 60 years were analysed. The results revealed a clear link between increased frequencies of high magnitude rainfall and phases of water filling in the Laguna de Gallocanta. In the middle of the 20th century, the absolute amount of rainfall appears to have been more important for lake level, while more recently the frequency of high magnitude rainfall has emerged as the dominant variable. In the Gallocanta Basin, climate change and the distinct and continuing land use change since Spain joined the EU in 1986 have created an environment that is in a more or less constant state of transition. This highlights two challenges faced by hydrologists and climatologists involved in developing water management tools for the Gallocanta Basin in particular, but also other areas with sensitive and rapidly changing environments. Hydrologists have to understand the processes and the spatial and temporal patterns of surface-climate interaction in a watershed to assess the impact of climate change on its hydrology. Climatologists, on the other hand, have to develop climate models which provide the appropriate output data, such as reliable information on rainfall characteristics relevant for environmental management.

A simple spectro-goniometer for collection of multiple view angle reflectance factors

Field spectroradiometers are widely used for environmental applications where data describing visible and near-infrared reflectance factors are of interest. Recent developments in spaceborne and airborne instruments with multiple view angle (MVA) capabilities have resulted in a demand for ground measurements to support these missions. Lightweight portable spectroradiometers offer an appropriate means of collecting MVA spectral reflectance factor data because they are more easily manoeuvrable than other spectroradiometers, but their physical capabilities have not yet been explored in this context. This letter presents the results of a focused experiment aimed at evaluating the field capabilities of a miniaturized Ocean Optics instrument in MVA settings for soil surface roughness applications. MVA hemispherical-conical reflectance factors were collected in situ from soil surfaces whose roughness was determined using a laser profiling survey. The results showed a significant negative relationship (R 2 = 0.74; p < 0.01) between directional reflectance factors measured at 870 nm in the forward-scattering region and a soil structural measure derived from laser profiling data. This corroborates the results of other published studies and suggests that Ocean Optics instruments can be used to support hyperspectral MVA investigations.

Mapping Decadal Land Cover Changes in the Woodlands of North Eastern Namibia from 1975 to 2014 Using the Landsat Satellite Archived Data

Woodlands and savannahs provide essential ecosystem functions and services to communities. On the African continent, they are widely utilized and converted to subsistence and intensive agriculture or urbanized. This study investigates changes in land cover over four administrative regions of North Eastern Namibia within the Kalahari woodland savannah biome, covering a total of 107,994 km2. Land cover is mapped using multi-sensor Landsat imagery at decadal intervals from 1975 to 2014, with a post-classification change detection method. The dominant change observed was a reduction in the area of woodland savannah due to the expansion of agriculture, primarily in the form of small-scale cereal and pastoral production. More specifically, woodland savannah area decreased from 90% of the study area in 1975 to 83% in 2004, and then increased to 86% in 2014, while agricultural land increased from 6% to 12% between 1975 and 2014. We assess land cover changes in relation to towns, villages, rivers and roads and find most changes occurred in proximity to these. In addition, we find that most land cover changes occur within land designated as communally held, followed by state protected land. With widespread changes occurring across the African continent, this study provides important data for understanding drivers of change in the region and their impacts on the distribution of woodland savannahs.