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In the tropics, water erosion is one of the most important factors leading to the degradation and deterioration of agricultural land. Olive orchards have a low canopy coverage, especially during the first years after planting, due to the low density of olive trees. Given the fast expansion of olive orchards in Brazil, this study aimed to evaluate the effect of cover vegetation on soil and water losses under natural rainfall. In addition, it was assessed the crop performance and the vegetation cover index in different management systems in olive orchards. The study was carried out in soil erosion plots, where water and sediment were sampled and measured over two crops season, under the following treatments: in the first season, bare soil with olive cultivation (OBS); olive trees intercropped with spontaneous vegetation (OSV); olive trees intercropped with jack beans (OJB); olive trees intercropped with millet (OM) and, as a control, only bare soil (BS). In the second season, the OM treatment was replaced by olive trees intercropped with sunn hemp (OSH). On bare soils, soil loss was the highest reaching 303.9 Mg ha -1 yr -1 and where the surface runoff amounted to 484.8 mm yr -1 . However, in the absence of competition for resources with other crops, olive trees performed best under this system. The olive orchards planted in shallow and sloping soils without cover crops showed unsustainable soil loss, crusting, and sealing in the superficial soil layer, which can progress quickly for soil degradation in the future. The efficiency in the reduction of loss in relation to bare soil was 4.11 and 12.93 % for the soil loss and 12.15 and 25.17 % for water loss, respectively, for olive with spontaneous vegetation and olive with jack beans. Cover crops combined with olive trees, and reconciled with the crop performance aspects of cultivation in tropical regions, is of great relevance for improving sustainability, especially regarding the reduction of soil and water losses due to water erosion.

Sheet erosion is common on agricultural lands, and understanding the dynamics of the erosive process as well as the quantification of soil loss is important for both soil scientists and managers. However, measuring rates of soil loss from sheet erosion has proved difficult due to requiring the detection of relatively small surface changes over extended areas. Consequently, such measurements have relied on the use of erosion plots, which have limited spatial coverage and have high operating costs. For measuring the larger erosion rates characteristic of rill and gully erosion, structure-from-motion (SfM) photogrammetry has been demonstrated to be a valuable tool. Here, we demonstrate the first direct validation of UAV-SfM measurements of sheet erosion using sediment collection data collected from erosion plots.Three erosion plots (12 m × 4 m) located at Lavras, Brazil, with bare soil exposed to natural rainfall from which event sediment and runoff was monitored, were mapped during two hydrological years (2016 and 2017), using a UAV equipped with a RGB camera. DEMs of difference (DoD) were calculated to detect spatial changes in the soil surface topography over time and to quantify the volumes of sediments lost or gained. Precision maps were generated to enable precision estimates for both DEMs to be propagated into the DoD as spatially variable vertical uncertainties.The point clouds generated from SfM gave mean errors of ~2.4 mm horizontally (xy) and ~1.9 mm vertically (z) on control and independent check points, and the level of detection (LoD) along the plots ranged from 1.4 mm to 7.4 mm. The soil loss values obtained by SfM were significantly (p<0.001) correlated (r 2 = 95.55%) with those derived from the sediment collection. These results open up the possibility to use SfM for erosion studies where channelized erosion is not the principal mechanism, offering a cost-effective method for gaining new insights into sheet, and interrill, erosion processes.

Africa’s lands are largely vulnerable and threatened by soil degradation and low water availability, especially in semi-arid and arid regions, limiting crop and livestock productivity and farmer livelihood options. Therefore, in African agricultural lands, adopting/improving measures that conserve soil and water resources is crucial. This review aims to provide an update on soil and water conservation (SWC) in terms of farmer practices and research actions and explore how SWC technologies and practices represent a pathway to build or re-establish soil health and enhance sustainable agriculture in Africa. It also aims to increase knowledge on best-fit SWC approaches. Soil conservation, which includes measures of controlling soil erosion and maintaining or improving soil fertility, is inseparable from water conservation. On agricultural lands, the two are typically co-addressed. Increasing plant biomass production through improved water, crop and soil management practices, and managing this biomass judiciously, have direct and indirect impacts on conserving soils and water resources, particularly in drylands. This study focuses on rainfed agricultural systems. We discuss the barriers and challenges to scaling up best-bet SWC technological and management options. Moreover, we show that options, such as Conservation Agriculture (CA), Agroforestry (AF), as well as integrated soil fertility management (ISFM) and field-scale rainwater harvesting (RWH), remain promising for the preservation and improvement of soil health in Africa’s farmlands and improving the resilience of agrosystems to climate change and variability as well as droughts.

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