Soil loss due to crop harvesting – a spotlight on research gaps and the need of further research activities at the global scale

Worldwide, soil erosion is one of the main causes of soil degradation and the loss of important soil functions. Wind, water and tillage erosion and their environmental, economic and social impacts have been researched for decades. Soil erosion by root and tuber crop harvesting (SLCH), however, is rarely focused in research, although erosion rates can reach up to 22 Mg ha^-1 harvest^-1 (Parlak et al. 2016).
The aim of this study is to raise awareness of SLCH and to advance research on this topic. To achieve this aim, all available peer-reviewed studies on this topic are used to provide an overview of investigated soil erosion rates worldwide and to identify the environmental impact of SLCH. In addition, the differences between SLCH and other forms of erosion are highlighted. Furthermore, important future research aspects for an enhanced understanding of SLCH are identified.
Comparing soil loss due to crop harvesting with other forms of erosion, it can be stated that (i) erosion rates of SLCH are as high as for water erosion and wind erosion, (ii) SLCH always and only occurs during the harvest of tuber and root crops, which affected 8.4 % of the world’s arable land in 2019 (1.1 million km²), (iii) SLCH can occur at any relief position and any parent material, thus it can be the only erosion process of an affected field without the appearance of wind or water erosion and (iv) SLCH always affects entire fields that are harvested multiple times over several years, depending on the crop rotation.
Based on the reviewed studies, the following further research activities are necessary for a better understanding of the processes of SLCH: (i) global data collection of crops whose erosion rates have not been studied yet, (ii) conduct studies on continents such as North America, South America and Oceania, where data on SLCH erosion rates are currently missing, (iii) development of models to predict SLCH erosion rates and (iv) monitoring the distribution of the adhering soil to evaluate the environmental effects of SLCH.
This review shows that further studies on the topic of SLCH are necessary to quantify actual data on erosion rates for different crops in different regions and provide more awareness of this topic in erosion research.