Armenia, Quindio, Colombia

Cultivation on mountain landscapes has been identified as a main factor triggering soil erosion. Patterns of erosion, transport and deposition of soil particles in agricultural landscapes appears to be closely linked to that of soil nutrients. In this work the redistribution of soil organic carbon and nitrogen and of soil particles is analysed in different geomorphic parts of mountain fields. A southern orientated hillslope was selected as representative of main land uses in mountain farmland of the Central Spanish Pyrenees. In the region, as much as 74% of its surface was abandoned in the last decades and as a result patterns of soil and nutrient losses in the fields were affected by both land abandonment and tillage. A set of cultivated and abandoned fields with different ages of land abandonment, slope gradients and lengths were selected to conduct this study. In each of the fields, total soil depth sampling was done in different parts of the slope to assess the pattern distribution of soil organic carbon (SOC) and nitrogen (SON). Other general soil properties analysed: pH, EC, carbonate content, grain size distribution and additional information derived from fallout caesium 137 provided supplementary information for better understanding the patterns of soil and nutrient redistribution. In the cultivated fields SOC and SON contents were higher and comparable to contents in the older abandoned fields, because the recovery of the natural vegetation after a long-term period of abandonment equalized the nutrient conditions in the cultivated fields that had regular additions of manure. In general SOC and SON percentages increased from the upper slope to the bottom slope of the fields with percentage increases ranging from 4 to 54% and from 1.5% to as much as 77%, respectively. Similarly, significant increases of SOC and SON inventories (45 and 49%, respectively) were registered at the bottom slopes of longer fields by comparison with lower increases (33 and 30%, respectively) in shorter and steeper fields. Soil deposition at the bottom slope as indicated by the 137Cs residuals was paralleled with increases in SOC and SON contents. Under the land use practices in the studied fields the bottom slope positions accumulate soil particles and act as sinks of soil carbon and nitrogen in these mountain agricultural landscapes.► 137Cs as effective tracer of sources and sinks of SOC and SON. ► Soil organic carbon and nitrogen pattern distributions associated with soil particles. ► Paralleled increases of SOC and SON downslope in mountain contoured fields. ► Depositional sites at bottom slopes as effective sinks of SOC and SON. ► SOC and SON contents affected by topography, land use and land abandonment.

The Condensation algorithm, developed for visual tracking, is a variant of particle filter. In the sampling stage of Condensation, no use is made of the information from the current frame in the image sequence. As a consequence, the algorithm requires a large number of particles and is computationally expensive. In this paper, a Kalman particle filter (KPF) and an unscented particle filter (UPF) are applied to contour tracking to try to overcome the problem. These algorithms use the Kalman filter or unscented Kalman filter to incorporate information from the current frame. This sampling strategy can effectively steer the set of particles towards regions with high likelihood, and therefore can considerably reduce the number of particles needed for tracking. Performance comparisons show that the KPF is an improvement over Condensation, while the UPF has a much higher computational cost for equal tracking error.