The Impact of Land Degradation on the Quality of Soils in a South African Communal Rangeland

Grassland productivity of communal rangelands is limited by land degradation, which leads to nutrient depletion, soil fertility decline and overall soil quality. However, little is known as to what the soil quality threshold is for different degradation intensities. To address this, we selected a 0.05 m surface soil layer of a communal rangeland site in Drakensburg, South Africa, exhibiting a degradation gradient varying from heavily degraded (0–5%, grass aerial cover), moderately degraded (25–50%) and non-degraded (75–100%) grasslands, to evaluate the effects of land degradation on soil aggregate stability, compaction, bulk density and texture. Results indicate that land degradation decreased soil aggregate stability by 47%, increased soil compaction by 42% and increased soil bulk density by 12%, and these were accompanied by a pattern of lower sand and almost two times greater clay content in heavily degraded grassland compared with non-degraded grassland. Ultimately, this decline in the soil quality of the communal rangeland has serious implications for the ecosystem services and functions it provides, such as storing water, carbon sequestration and nutrient cycling. We recommend the protection and improvement of grass vegetation because of its dense sward characteristics, which intercept raindrop energy, slow surface runoff and increase the structural stability of the soil to minimize and prevent degradation in rangelands

Cover crops do not increase soil organic carbon stocks as much as has been claimed : what is the way forward?

Peer reviewedPostprin

Origem dos microagregados em solos com horizonte B latossólico

Os microagregados, característicos do horizonte B latossólico, podem ser formados a partir de processos físicos, geoquímicos e biológicos. Apesar da quantidade de trabalhos realizados sobre este tema, poucos tem discutido a hierarquia entre os processos que formam estes microagregados. O objetivo deste trabalho foi estudar a gênese dos microagregados numa seqüência de solos localizada em Piracicaba (SP), Brasil. Os solos foram classificados como Nitossolos Vermelhos Eutroférricos latossólicos e desenvolvem-se a partir de sedimentos argilosos vermelhos do Quaternário e diabásio. Para atingir o objetivo deste trabalho foram utilizadas técnicas de microscopia ótica, análise de imagens, microscopia eletrônica de varredura e quantificações elementares de ferro através de fluorescência de raio-X. As investigações micromorfológicas mostraram a presença de três tipos de microagregados: (i) microagregados ovais com grãos de quartzo bem selecionados no seu interior; (ii) microagregados ovais sem grãos de quartzo ou grãos de quartzo mal selecionados no seu interior; e (iii) microagregados poliédricos densos. Estas evidencias morfológicas junto com os dados elementares de ferro e a microscopia eletrônica de varredura mostraram a contribuição de mais de um processo na formação dos microagregados: (i) a ação mecânica da mesofauna seria responsável pela formação do primeiro tipo de microagregados; (ii) processos geoquímicos e biológicos estariam formando o segundo tipo de microagregados; e (iii) a fissuração da matriz do solo por processos de contração e expansão formariam o terceiro tipo de microagregados.Microaggregates that characterize ferralic soils have been hypothesized to have physical, geochemical and/or biological origins. Despite of many studies, the hierarchy between these processes that form microaggregates has seldom been reported. The objective of this work was to study the genesis of microaggregates in a sequence of Ferralic Nitisols developed on Quaternary red clayey sediments and diabase in Piracicaba (SP), Brazil. This issue was tackled by combining optical microscopy, image analysis, scanning electron microscopy and elemental iron quantifications by X-ray fluorescence. Micromorphological investigations showed three different types of microaggregates: (i) oval microaggregates with well sorted quartz grains in their interior; (ii) oval microaggregates without or with poorly sorted quartz grains in their interior; and (iii) dense polyedric microaggregates. These morphological evidences, together with the elemental iron determinations and scanning electron microscopy, revealed the contribution of more than one process for microaggregate formation: (i) the mechanical action of the mesofauna would form the first type of microaggregates (ii) geochemical and biological processes would form the second type and (iii) the fissuration of the soil matrix by expansion and compression processes would form the third type

Evaluation of six high-resolution satellite and ground-based precipitation products over Malaysia

Satellite precipitation products (SPPs) potentially constitute an alternative to sparse rain gauge networks for assessing the spatial distribution of precipitation. However, applications of these products are still limited due to the lack of robust quality assessment. This study compares daily, monthly, seasonal, and annual rainfall amount at 342 rain gauges over Malaysia to estimations using five SPPs (3B42RT, 3B42V7, GPCP-1DD, PERSIANN-CDR, and CMORPH) and a ground-based precipitation product (APHRODITE). The performance of the precipitation products was evaluated from 2003 to 2007 using continuous (RMSE, R-2, ME, MAE, and RB) and categorical (ACC, POD, FAR, CSI, and HSS) statistical approaches. Overall, 3B42V7 and APHRODITE performed the best, while the worst performance was shown by GPCP-1DD. 3B42RT, 3B42V7, and PERSIANN-CDR slightly overestimated observed precipitation by 2%, 4.7%, and 2.1%, respectively. By contrast, APHRODITE and CMORPH significantly underestimated precipitations by 19.7% and 13.2%, respectively, whereas GPCP-1DD only slightly underestimated by 2.8%. All six precipitation products performed better in the northeast monsoon than in the southwest monsoon. The better performances occurred in eastern and southern Peninsular Malaysia and in the north of East Malaysia, which receives higher rainfall during the northeast monsoon, whereas poor performances occurred in the western and dryer Peninsular Malaysia. All precipitation products underestimated the no/tiny (= 20 mm/day) rainfall events, while they overestimated low (1-20 mm/day) rainfall events. 3B42RT and 3B42V7 showed the best ability to detect precipitation amounts with the highest HSS value (0.36). Precipitations during flood events such as those which occurred in late 2006 and early 2007 were estimated the best by 3B42RT and 3B42V7, as shown by an R-2 value ranging from 0.49 to 0.88 and 0.52 to 0.86, respectively. These results on SPPs' uncertainties and their potential controls might allow sensor and algorithm developers to deliver better products for improved rainfall estimation and thus improved watermanagement

Habitat 3.0: A Co-Habitat for Humans, Avatars and Robots

We present Habitat 3.0: a simulation platform for studying collaborative human-robot tasks in home environments. Habitat 3.0 offers contributions across three dimensions: (1) Accurate humanoid simulation: addressing challenges in modeling complex deformable bodies and diversity in appearance and motion, all while ensuring high simulation speed. (2) Human-in-the-loop infrastructure: enabling real human interaction with simulated robots via mouse/keyboard or a VR interface, facilitating evaluation of robot policies with human input. (3) Collaborative tasks: studying two collaborative tasks, Social Navigation and Social Rearrangement. Social Navigation investigates a robot's ability to locate and follow humanoid avatars in unseen environments, whereas Social Rearrangement addresses collaboration between a humanoid and robot while rearranging a scene. These contributions allow us to study end-to-end learned and heuristic baselines for human-robot collaboration in-depth, as well as evaluate them with humans in the loop. Our experiments demonstrate that learned robot policies lead to efficient task completion when collaborating with unseen humanoid agents and human partners that might exhibit behaviors that the robot has not seen before. Additionally, we observe emergent behaviors during collaborative task execution, such as the robot yielding space when obstructing a humanoid agent, thereby allowing the effective completion of the task by the humanoid agent. Furthermore, our experiments using the human-in-the-loop tool demonstrate that our automated evaluation with humanoids can provide an indication of the relative ordering of different policies when evaluated with real human collaborators. Habitat 3.0 unlocks interesting new features in simulators for Embodied AI, and we hope it paves the way for a new frontier of embodied human-AI interaction capabilities.Comment: Project page: http://aihabitat.org/habitat

Evidences of plants’ impact on land degradation and climate change: An urgent call for new multidisciplinary research

International audienceAtmospheric carbon has been stored in soils for thousands of years in the form of organic matter which associates carbon to key plant nutrients. Recent analysis reveals that when facing nutrient deficiency, plants decompose soil organic matter to mine nutrients and carbon is released into the atmosphere which causes land degradation and climate change

Impact of spatial input data resolution on hydrological and erosion modeling: Recommendations from a global assessment

International audienc

Evidences of plants’ impact on land degradation and climate change: An urgent call for new multidisciplinary research

International audienceAtmospheric carbon has been stored in soils for thousands of years in the form of organic matter which associates carbon to key plant nutrients. Recent analysis reveals that when facing nutrient deficiency, plants decompose soil organic matter to mine nutrients and carbon is released into the atmosphere which causes land degradation and climate change

Impact of DEM mesh size and soil map scale on SWAT runoff, sediment, and NO3-N loads predictions

The accuracy of agricultural nonpoint source pollution models depends to a great extent on how well model input spatial parameters describe the relevant characteristics of the watershed. It is assumed that reducing the precision of spatial input parameters affects the simulation results of runoff and sediment yield from the entire watershed. However, there may be no significant increase in the accuracy of models, as a result of more precise topographic or soil information, which increase the input data collection and preparation. The objective of this study was to determine the impact of the mesh size of the digital elevation model, DEM (from 20 to 500 m) and the soil map scale (1/25,000; 1/250,000 and; 1/500,000 scale) within the Soil and Water Analysis Tool (SWAT) to simulate runoff, sediment, and NO3-N loads at the outlet of an agricultural watershed. Results of the Lower Walnut Creek (21.8 km(2), central Iowa) showed that an upper limit to DEM mesh size of 50 m is required to simulate watershed loads. Decreasing the mesh size beyond this threshold does not substantially affect the computed runoff flux but generated prediction errors for nitrogen and sediment yields. Whatever the DEM mesh size considered, a detailed soil map has to be considered to accurately estimate the loads. Finally, the impacts of DEM mesh size and soil map scale on the modeling results are discussed in respect of the relevant characteristics of the watershed and included in SWAT. (c) 2005 Elsevier B.V. All rights reserved