Quantification of soil loss due to white cocoyam (Colocasia esculentus) and red cocoyam (Xanthosoma sagittifolium) harvesting in traditional farming system

- White and red cocoyam yields were 2.0 t ha− 1 and 1.3 t ha− 1 respectively.
- Soil loss ratio (hand rubbing/washing) was ≈ 5:1 for white cocoyam.
- Soil loss ratio (hand rubbing/washing) was and ≈ 4:1 for red cocoyam.
- Hand rubbing of cocoyam after harvest offers the cheapest alternative.

Soil loss due to crop harvesting (SLCH) refers to nutrients, colloids and other soil particles exported from the field in the process of harvesting of root and tuber crops such as cocoyam, yam, potato, carrot and cassava. During harvest, soil adhering to the crop, loose soil, clods and stones are transported from the field to the market place or storage. Consequently, the depth of the top soil is reduced. Only few studies, however, tried to estimate SLCH values for cocoyam but there is no available information on the influence of cocoyam species on SLCH. This study was conducted on basement complex rock derived soil (Typic Kandiustalf) in Southwest Nigeria between 2011 and 2012 to compare the quantity of soil loss due to harvesting of white and red cocoyam. Traditional hand rubbing was compared with hand rubbing + washing. The energy dissipated and cost analysis for harvesting of both cocoyam species were compared. The soil sticking to the harvested tubers was hand rubbed thoroughly before washing to determine SLCH. Mean weight of the tubers after washing of white and red cocoyam was 2.0 t ha− 1 and 1.3 t ha− 1 respectively. Averagely, soil loss value per unit of crop mass (SLCHspec) of white and red cocoyam was 14.6 kg− 1 ha− 1 harvest− 1 yr− 1 and 15.1 kg− 1 ha− 1 harvest− 1 yr− 1 respectively. Soil loss ratio (hand rubbing/washing) was 3:1 for white cocoyam and ≈ 3:1 for red cocoyam in 2011. Corresponding ratio for 2012 was ≈ 6:1 for white and 5:1 for red cocoyam. The energy dissipated in harvesting white cocoyam (124.7 J mound− 1) was higher than red cocoyam (121.5 J mound− 1) due to higher white cocoyam root density. The cost analysis of cocoyam production using conventional (unwashed tubers) and the innovative approach (hand rubbing followed by washing of tubers) suggests that hand rubbing after harvest offers the cheapest alternative. Differences in SLCHspec could be due to skin roughness of red cocoyam leading to higher soil loss per unit yield. Morphology was another factor that explains the variation in the soil loss at cocoyam harvesting. The amount of soil loss due to cocoyam harvesting justifies the need to conduct further investigations on this process of soil erosion under mechanised agriculture.