Quantifying the impact of land degradation on crop production: the case of Senegal

Abstract

Abstract. Land degradation has been a persistent problem in Senegal for more than a century and by now has become a serious impediment to long-term development. In this paper, we quantify the impact of land degradation on crop yields using the results of a nationwide land degradation assessment. For this, the study needs to address two issues. First, the land degradation assessment comprises qualitative expert judgements that have to be converted into more objective, quantitative terms. We propose a land degradation index and assess its plausibility. Second, observational data on soils, land use, and rainfall do not provide sufficient information to isolate the impact of land degradation. We, therefore, design a pseudo-experiment that for sites with otherwise similar circumstances compares the yield of a site with and one without land degradation. This pairing exercise is conducted under a gradual refining of the classification of circumstances, until a more or less stable response to land degradation is obtained. In this way, we hope to have controlled sufficiently for confounding variables that will bias the estimation of the impact of land degradation on crop yields. A small number of shared characteristics reveal tendencies of "severe" land degradation levels being associated with declining yields as compared to similar sites with "low" degradation levels. However, as we zoom in at more detail some exceptions come to the fore, in particular in areas without fertilizer application. Yet, our overall conclusion is that yield reduction is associated with higher levels of land degradation, irrespective of whether fertilizer is being applied or not.

Evaluation of tropical coastal land cover and land use changes and their impacts on ecosystem service values

“…Therefore, our findings confirm that there is a large-scale decline in forest land cover across the coastal zone of Tanzania like in many Sub-Saharan African areas (Keenan et al 2015). This decline indicates that population growth is significantly related to expansion of economic activities associated with progressive transformation of land into crops and built areas (Sonneveld, Keyzer, and Ndiaye 2016;Scull et al 2017).…”

“…The net increase in farmland indicates a substantial expansion of cultivated land for crop production. This expansion is supported by Ryan et al (2016) and Sonneveld, Keyzer, and Ndiaye (2016), implying that farming is the persistent driver of land cover change globally. Farmland expansion is characterized mainly by small land holdings and commercial agriculture.…”

“…However, expansion of some investments and human activities, for example, farmland does not necessarily mean increase in yield per unit area (Sonneveld, Keyzer, and Ndiaye 2016). In some cases, land degradation is associated with declining yields in agreement with Sonneveld, Keyzer, and Ndiaye (2016) and Borrelli et al (2017).…”

Combined deep sampling and mass-based approaches to assess soil carbon and nitrogen losses due to land-use changes in karst area of southwestern China

“…Globally, the large-scale conversions of natural ecosystems to croplands and other managed ecosystems have already resulted in historically large emissions of C into the atmosphere (as higher as 320 Pg C), since the dawn of settled agriculture (Lal, 2010). In turn, land degradation due to soil organic C (SOC) loss may damage ecosystem services and functions Costantini et al, 2016;Foley et al, 2005), directly affecting the hydrological and biogeochemical cycles in the earth system García-Díaz et al, 2016;Sonneveld et al, 2016). Thus, the changes in quality and quantity of SOC may inevitably influence the soil degradation, agricultural productivity and food security (Carter, 2002;Janzen, 2015;Srinivasarao et al, 2014).…”

Drought Dynamics and Vegetation Productivity in Different Land Management Systems of Eastern Cape, South Africa—A Remote Sensing Perspective

“…Drought acts as external stress factor to land, which in turn, reinforces ongoing land degradation processes leading to even more severe impacts on cropland and rangeland when a drought event occurs [31,32]. Land degradation results in a loss of vegetation productivity and declining yields describing an ongoing process rather than a state or current condition [33][34][35][36]. If land degradation is triggered by the event of a drought, impacts on vulnerable social-ecological systems are even more severe.…”