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 km 2 . 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.

The ability to quantitatively and spatially assess soil surface roughness is important in geomorphology and land degradation studies. This paper describes the results of an experiment designed to investigate whether hyperspectral directional reflectance factors can describe fine-scale variations in soil surface roughness. A Canadian silt loam soil was sieved to an aggregate size range of 1-4.75 mm and exposed to five different artificial rainfall durations to produce soils displaying progressively decreasing levels of surface roughness. Each soil state was measured using a point laser profiling instrument at 2 mm spatial resolution, in order to provide information on the structure and spatial arrangement of soil particles. Hyperspectral directional reflectance factors were measured using an Analytical Spectral Devices FieldSpec Pro Spectroradiometer (range 350-2500 nm), at a range of measurement angles (h r ¼ À60°to þ60°) and illumination angle conditions (h i ¼ 28°-74°). Directional reflectance factors varied with illumination and view angles, and with soil structure. Geostatistically-derived indicators of soil surface roughness (sill variance) were regressed with directional reflectance factors. The results showed a strong relationship between directional reflectance and surface roughness (R 2 ¼ 0.94 where h r ¼ À60°, h i ¼ 67°-74°). This fine-scale quasi-natural experiment allowed the control of slope, initial aggregate size and rainfall exposure, permitting an investigation into factors affecting a soil's bidirectional reflectance response. This has highlighted the relationship between fine-scale variations in surface roughness, illumination angle and reflectance response. The results show how the technique could provide a quantitative measure of surface roughness at fine spatial scales.

The enrichment of organic matter in interrill sediment is well documented; however, the respective roles of soil organic matter (SOM) and interrill erosion processes for the enrichment are unclear. In this study, organic matter content of sediment generated on two silts with almost identical textures, but different organic matter contents and aggregations, was tested. Artificial rainfall was applied to the soils in wet, dry and crusted initial conditions to determine the effects of soil moisture and rainfall and drying history on organic matter enrichment in interrill sediment. While erosional response of the soils varied significantly, organic matter enrichment of sediment was not sensitive to initial soil conditions. However, enrichment was higher on the silt with a lower organic matter content and lower interrill erodibility. The results show that enrichment of organic matter in interrill sediment is not directly related to either SOM content or soil interrill erodibility, but is dominated by interrill erosion processes. As a consequence of the complex interaction between soil, organic matter and interrill erosion processes, erodibility of organic matter should be treated as a separate variable in erosion models. Further research on aggregate breakdown, in particular the content and fate of the organic matter in the soil fragments, is required. densities has to be developed as well. Based on a principal understanding of the interaction between soil, interrill processes and SedOM, an applicable model for interrill erodibility of organic matter has to be developed.On a larger scale, the enrichment of organic matter in sediment generated by interrill processes requires research on the on-site fate of the organic matter. Off-site effects of eroded sediment are well documented, and sinks within a watershed can be identified through spatially distributed runoff models (Polyakov and Lal, 2004; Quinton et al., 2006). However, on a field scale, deposition and exposure of sediment enriched in organic matter to the atmosphere potentially enhances mineralization. Therefore, erosion, transport and deposition of interrill sediment enriched in organic matter have to be studied in detail on a within-field scale. Quality and stability of the eroded organic matter also require special attention to assess the role of interrill processes for soil-atmosphere interaction in the global carbon cycle. 802 N. J. Kuhn

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 0.7-2.48C 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.