Monitoring and Analyzing Yield Gap in Africa through Soil Attribute Best Management Using Remote Sensing Approaches: A Review

Abstract

Africa has the largest population growth rate in the world and an agricultural system characterized by the predominance of smallholder farmers. Improving food security in Africa will require a good understanding of farming systems yields as well as reducing yield gaps (i.e., the difference between potential yield and actual farmer yield). To this end, crop yield gap practices in African countries need to be understood to fill this gap while decreasing the environmental impacts of agricultural systems. For instance, the variability of yields has been demonstrated to be strongly controlled by soil fertilizer use, irrigation management, soil attribute, and the climate. Consequently, the quantitative assessment and mapping information of soil attributes such as nitrogen (N), phosphorus (P), potassium (K), soil organic carbon (SOC), moisture content (MC), and soil texture (i.e., clay, sand and silt contents) on the ground are essential to potentially reducing the yield gap. However, to assess, measure, and monitor these soil yield-related parameters in the field, there is a need for rapid, accurate, and inexpensive methods. Recent advances in remote sensing technologies and high computational performances offer a unique opportunity to implement cost-effective spatiotemporal methods for estimating crop yield with important levels of scalability. However, researchers and scientists in Africa are not taking advantage of the opportunity of increasingly available geospatial remote sensing technologies and data for yield studies. The objectives of this report are to (i) conduct a review of scientific literature on the current status of African yield gap analysis research and their variation in regard to soil properties management by using remote sensing techniques; (ii) review and describe optimal yield practices in Africa; and (iii) identify gaps and limitations to higher yields in African smallholder farms and propose possible improvements. Our literature reviewed 80 publications and covered a period of 22 years (1998-2020) over many selected African countries with a potential yield improvement. Our results found that (i) the number of agriculture yield-focused remote sensing studies has gradually increased, with the largest proportion of studies published during the last 15 years; (ii) most studies were conducted exclusively using multispectral Landsat and Sentinel sensors; and (iii) over the past decade, hyperspectral imagery has contributed to a better understanding of yield gap analysis compared to multispectral imagery; (iv) soil nutrients (i.e., NPK) are not the main factor influencing the studied crop productivity in Africa, whereas clay, SOC, and soil pH were the most examined soil properties in prior papers.

Multi-Sensors Remote Sensing Applications for Assessing, Monitoring, and Mapping NPK Content in Soil and Crops in African Agricultural Land

“…This reviewing study indicates that recent studies in Africa are increasingly adopting remote sensing based spatial prediction approach in comparison to other tools for monitoring the variation of soil and crops NPK content. This is consistent with a recent study [34] that reported the same increasing trend regarding the use of remote sensing for field studies in Africa. The presented case studies showcased a difference in costeffectiveness and performance between remote sensing approach and traditional soil and crop sampling methods.…”

“…Despite its outstanding performance, hyperspectral imaging has been utilized comparatively less in African operational agricultural applications in the past few decades. This might be explained by the high cost of imagery and various other technical and practical challenges (e.g., access to the specialized software needed and the skills to process this the large data volume) [34]. This might also explain why most of the papers reviewed in this study used spectroscopy instead of hyperspectral imaging.…”

“…Nevertheless, it can be a promising technology as it will feature higher capabilities for acquiring a detailed spectral response of NPK content, as opposed to multispectral imaging, hyperspectral images have not been widely used over Africa, most probably due to several limitations (i.e., few operational airborne and spaceborne missions, and dimensionality of the high-volume datasets storage requirements). A recent study by Khechba et al [34] has reported that the African scientific community can typically encounter such limitations [33]. To our knowledge, no research in Africa had previously assessed hyperspectral remote sensing-based models that fall within optimization of NPK rates in arid and semi-arid region in Africa on any kind of crops.…”

Research on the spatiotemporal distribution and evolution of remote sensing: A data-driven analysis

“…Thus, the gap in research work output in Asia was larger than that in Europe (Goga et al, 2019;Chen et al, 2020;Mikhaylov et al, 2021). Moreover, the continental gap in Africa has obviously narrowed due to the increasing investment in scientific research in the current decade (Khechba et al, 2021;Mngadi et al, 2022;Sebola, 2022). Regarding the continental gap between Asia and other continents, the gap between Asia and Africa was the largest, and the gap between Asia and Europe was the smallest (Figure 5A), showing that the gap between the two continents with high research output was not large.…”

Performance Evaluation of the WOFOST Model for Estimating Evapotranspiration, Soil Water Content, Grain Yield and Total Above-Ground Biomass of Winter Wheat in Tensift Al Haouz (Morocco): Application to Yield Gap Estimation

“…In the Mediterranean, for example, a gap of 41% and 29% is recorded in Morocco for rainfed and irrigated wheat, respectively [21], while in Spain a gap of 49% to 66% is observed for rainfed wheat [22]. In addition, yield gap analysis and the importance of finding the main reasons that limit actual yields has been widely studied around the world [21,[23][24][25] and increasingly in Africa [26]. Many agronomic causes are often behind these deficits [27], and they can be lack of nitrogen fertilizer [25,27,28], limited number of spikes per hectare [29], inappropriate sowing date [25,28], soil fertility level [25], biotic stresses [30], water stress [22], low seeding rate, summer fallow, and tillage [31], etc.…”