Arsenio Toloza

Radioisotopic Measurements (137Cs and 210Pb) to Assess Erosion and Sedimentation Processes: Case Study in Austria

Twelve to seventeen percentage of the European soil is threatened by water erosion and around 13% of Austrian territory is affected. Only scarce information based on conventional assessment and measurements are available on erosion and sedimentation rates in Austria. The magnitude of sedimentation processes was evaluated in a small agricultural Austrian watershed using both nuclear techniques (137Cs and 210Pb) and conventional non-isotopic measurements in runoff erosion plots during the 1994–2006 periods. Using the erosion data provided by the plots (29.4 t ha–1 year–1 for the conventional tilled plot, 4.2 t ha–1 year–1 for the plot receiving conservation tillage and 2.7 t ha–1 year–1 for the plot receiving direct seeding treatment) and the 137Cs soil profiles content and the conversion model mass balance 2 (MBM 2), a sedimentation rate of 13.2 t–1 ha–1 year–1 (value determined down slope of the runoff plot under direct seeding treatment) to 50.5 t–1 ha–1 year–1 (value determined in the lowest sedimentation area of the watershed under conventional tillage) was estimated. Under the experimental condition the conservation tillage and direct seeding system were effective in reducing the sedimentation magnitude by 65%. However, due to a high variability of the initial fallout inventory and a high γ-spectrometry measurement error, information provided by the 210Pb method was not usable in the study area. The combined use of conventional erosion measurements and nuclear techniques appears to be a promising and complementary approach to evaluate sedimentation processes.

Potential of flow cytometry for monitoring genetic stability of banana embryogenic cell suspension cultures

Cell suspensions are the material of choice for rapid multiplication and for genetic engineering strategies such as in vitro mutagenesis and genetic transformation. Effective use of cell suspension cultures relies on the knowledge of several key parameters, which include genetic stability, kinetics of the cell cycle and a mode of plant regeneration. Here we report on the use of DNA flow cytometry for quality monitoring of banana cell suspension cultures. The method facilitates detection of ploidy changes and the occurrence of aneuploidy, which result in somaclonal variation of cell-suspension-derived plants. Flow cytometry could also be used to analyse the cell cycle kinetics by calculating the ratio of cells in the G2 and G1 phase of the cell cycle. This is important to determine the most appropriate moment for mutagenic treatment or for genetic transformation but also as an indicator on the proportion of cycling cells. In addition, the unicellular origin of somatic embryos was verified by treating embryogenic cell suspensions with colchicine and by determining the ploidy of regenerated plants by flow cytometric analysis. None of the plants regenerated from colchicine-treated embryogenic cell suspensions were mixoploid (chimeric). The application of flow cytometry will be discussed in relation to (a) the monitoring of genetic instability in DNA content of cell suspensions (b) the analysis of cell cycle and (c) the origin of somatic embryos of bananas and plantains.

Implementation and Optimization of Soil Sampling

Abstract Practical guidance is given for planning and conducting soil sampling. Researchers have several options for undertaking monitoring campaigns starting with some desk exercises followed by specific sampling approaches at field and catchment scales. A set of different sampling tools are also introduced for lateral and vertical soil collection. The authors also provide advice for upscaling and mapping purposes, and for performing cost effective and representative soil sampling investigations. Indeed, optimizing and simplifying soil sampling collection processes could reduce further laboratory measurements that are often intensive in terms of human resource requirements and are costly.

Adapting the Caesium-137 technique to document soil redistribution rates associated with traditional cultivation practices in Haiti

Large-scale deforestation, intensive land use and unfavourable rainfall conditions are responsible for significant continuous degradation of the Haitian uplands. To develop soil conservation strategies, simple and cost-effective methods are needed to assess rates of soil loss from farmland in Haiti. The fallout radionuclide caesium-137 (137Cs) provides one such means of documenting medium-term soil redistribution rates. In this contribution, the authors report the first use in Haiti of 137Cs measurements to document soil redistribution rates and the associated pattern of erosion/sedimentation rates along typical hillslopes within a traditional upland Haitian farming area. The local 137Cs reference inventory, measured at an adjacent undisturbed flat area, was 670 Bq m-2 (SD = 100 Bq m-2, CV = 15%, n = 7). Within the study area, where cultivation commenced in 1992 after deforestation, three representative downslope transects were sampled. These were characterized by 137Cs inventories ranging from 190 to 2200 Bq m-2. Although, the study area was cultivated by the local farmers, the 137Cs depth distributions obtained from the area differed markedly from those expected from a cultivated area. They showed little evidence of tillage mixing within the upper part of the soil or, more particularly, of the near-uniform activities normally associated with the plough layer or cultivation horizon. They were very similar to that found at the reference site and were characterized by high 137Cs activities at the surface and much lower activities at greater depths. This situation is thought to reflect the traditional manual tillage practices which cause limited disturbance and mixing of the upper part of the soil. It precluded the use of the conversion models normally used to estimate soil redistribution rates from 137Cs measurements on cultivated soils and the Diffusion and Migration conversion model frequently used for uncultivated soils was modified for application to the cultivated soils of the study area, in order to take account of the unusual local conditions. The model was also modified to take account of the fact that cultivation in the study area commenced in 1992, rather than predating the period of weapons test fallout which extended from the mid 1950s to the 1970s. Erosion rates on the upper parts of the hillside involved in the study were found to be relatively high and ca. -23 t ha-1 y-1 with low spatial variability. In the lower, flatter areas at the bottom of the slope, deposition occurred. Deposition rates were characterized by high spatial variability, ranging from 6.0 to 71 t ha-1 y-1. Soil redistribution rates of this magnitude are a cause for concern and there is an urgent need to implement soil conservation measures to ensure the longer-term sustainability of the local agricultural practices.