Soil aggregation is critical for assessing soil health; however, conventional aggregation measurement is laborious and expensive. The performance of near infrared diffuse reflectance spectroscopy (NIR) and basic soil properties for estimation of wet aggregation indices was investigated. Two samples sets representing different soils from across Lake Victoria Basin in Kenya were used for the study. A model calibration set (n = 136) was obtained following a conditioned Latin hypercube sampling, and validation set (n = 120) using a spatially stratified random sampling strategy. Spectral measurements were obtained for air-dried (<2 mm) soil using a Fourier-transform NIR spectrometer. Soil laboratory reference data were also obtained for wet aggregation indices (WSA): macro, micro and unstable fractions using two different wet-sieving pretreatments. Soil properties were screened as candidate predictors of WSA using Classification and Regression Tree (CART regression) analysis. WSA were calibrated to soil predictors and to smoothed first derivative NIR spectra using partial least squares (PLS) regression. Key soil predictors were: soil organic carbon and pH water (macro), water dispersible clay (WDC) (micro) and exchangeable sodium (unstable). Full cross validation of NIR PLS prediction of stable macro, micro, unstable aggregates, and for WDC gave RPD (ratio of prediction deviation) of 1.4–2.0. Independent testing of NIR PLS gave RPD = 1.4 for macro and RPD = 1.2–1.0 for unstable and soil predictors. NIR could estimate macro and unstable fractions with moderate reliability, and; NIR was superior over soil properties for stability pedotransfer purposes. Further efforts should widely test performance for a wider range of soil types and calibration strategies for improved geographic transferability of models. © 2016 IAgrE
Tag: grassland
Carbon finance in extensively managed rangelands: issues in project, programmatic and sectoral approached
Considering their vast geographic area and the documented carbon (C) sequestration effects of a variety of rangeland management practices, there is considerable interest in the potential of C finance in rangelands, where it is still very much in its early stages. Pilot projects are essential to exploring this potential in practice. Ex ante assessments at the project level show areas of positive potential, but have identified several areas where documentation is insufficient, and critical constraints that exist in some contexts. This chapter summarizes these potentials and constraints, and then discusses opportunities and challenges in view of the major options currently being considered for a post-Kyoto agreement that includes agricultural land use: project, programmatic and sectoral approaches (including unilateral mitigation actions, supported mitigation actions and sectoral crediting approaches). The paper describes this emerging architecture for future mitigation options, and analyses the requirements for developing project, programmatic and sectoral approaches. It concludes by highlighting key actions required to promote the development of project, programmatic and sectoral approaches to rangeland-based mitigation
Land use/cover dynamics in northern Afar rangelands, Ethiopia
This study uses a combination of remote sensing data, field observations and information from local people to analyze the patterns and dynamics of land-use/cover changes for 35 years from 1972 to 2007 in the arid and semi-arid Northern Afar rangelands, Ethiopia. A pixel-based supervised image classification was used to map land-use/cover classes. People’s perceptions and ecological time-lines were used to explain the driving forces linked to the changes. A rapid reduction in woodland cover (97%) and grassland cover (88%) took place between 1972 and 2007. Bushland cover increased more than threefold, while the size of cultivated land increased more than eightfold. Bare land increased moderately, whereas bushy grassland and scrubland remained stable. According to accounts from local people, major events that largely explain the changes include: (1) severe droughts in 1973/74 and 1984/85; (2) increase in dry years during the last decade; and (3) immigration and increased sedentarization of pastoralists. If the present land-use/cover change were to continue, coupled with a drier climate, people’s livelihoods will be highly affected and the pastoral production system will be under increasing threat.