Quantification of soil loss due to white cocoyam (Colocasia esculentus) and red cocoyam (Xanthosoma sagittifolium) harvesting in traditional farming system
Introduction
Soil loss due to crop harvesting has been established as important soil erosion process that has significantly contributed to soil degradation in highly mechanized agriculture (Isabirye et al., 2007). Such losses are associated with tuber and root crops such as cassava (Manihot spp.), sweet potato (Ipomea batatasL. (Lam)), potato (Solanum tuberosum L.), cocoyam (Colocasia esculenta), yam (Discorea spp.) ((Isabirye et al., 2007, Ruysschaert et al., 2006). During harvest, soil adhering to these crops and loose soil or clods and stones are harvested and exported from the field to the market place. Consequently, the soil profile is lowered. This process of soil erosion is called soil loss due to crop harvesting (SLCH).
Traditionally, tuber crops such as cassava, yam, potato and cocoyam are major staple foods of most African people. These crops are planted on heaps, mounds or ridges. In most cases, mound cultivation is done for easy harvesting of the crop without any regard for the physical condition of the soil. Cocoyam ranks third in importance after cassava and yam among the root and tuber crops that are cultivated and consumed in Nigeria. Currently, Nigeria is the world leading producer of cocoyam (Taro) accounting for up to 3.7 million metric tonnes annually. Cultivars of two species, Colocasia esculentus (Taro), Xanthosoma sagittifolium (Tannia) are generally grown for food. In some parts of Nigeria and indeed in the humid tropics, some farmers raise their tuber and root crops on flat especially on the coastal plain sands of Nigeria. Cocoyam tuber is used mainly for animal and human consumption. Nutritionally, cocoyam is superior to cassava. Yam and Taro starch are also more readily digested. The corm and cormels of cocoyam which are the major economic part contains about 15 to 39% carbohydrates, 2 to 3% protein and 70 to 77% water. The young leaves contain 2% protein and are also rich in thiamine, riboflavin, niacin, calcium, phosphates and iron (Ndon et al., 2003). Cocoyam has nutritional value comparable to potato but easier to digest (Sefa-Dedeh and Sackey, 2002). It is commonly grown among small scale farmers who operate within the subsistence economy. Cocoyam thrives better in a well drained sand loamy soil (ICS, 2013). It produces optimum yields when planted in fertile soil with good water retention capacity. Most cocoyam varieties mature in about 8 months from planting. Harvesting is done by pulling up the plant to uproot it and bring out the cormels while those cormels remain in the soil are dug out. The harvested tubers are usually transported in basket. Cleaning of cocoyam tubers before transportation is not a usual practice of African farmers. After harvesting, farmers normally leave crop residues in the field. Like other root and tuber crops (Srivastava et al., 1996), harvesting of cocoyam is associated with soil degradation in the form of nutrient depletion or mining which is similar to soil loss due to water erosion (Nkedi-Kizza et al., 2003, Ebanyat et al., 2003). The occurrence of soil clods harvested with crop explains why SLCH was significantly larger for mechanically harvested potato in Belgium compared to the manually harvested potato in China (Ruysschaert et al., 2006). Ruysschaert et al. (2006) reported that the total soil loss during potato harvest was on average 3.2 Mg− 1 ha− 1 harvest− 1 and ranges from 0.2 to 21.4 Mg− 1 ha− 1 harvest− 1. They concluded that the presence of soil clods induced the largest variability in total SLCH could be explained by soil moisture content at harvesting time while the loose and total SLCH appeared to increase by increasing contents of clay which was attributed to the complex clod formation and destruction processes. Ruysschaert et al. (2006) also reported that significant differences in SLCH were found among the countries studied and they attributed the same to rainfall depth during the harvesting season, difference in soil type, harvesting technique, agronomy practices and crop yield. Research conducted in highly mechanised agricultural areas in Belgium (Poesen et al., 2001) showed that the mean SLCH was similar to those of other soil loss erosion processes. This justifies the need to incorporate SLCH into the future assessments of soil degradation. However, it is important to know whether this soil erosion process is also significant in traditional agriculture as practised in Africa. Average sediment export from crop land in Hander was 3.7 Mg− 1 ha− 1 in 2002, of which 46% was due to harvesting of cocoyam under traditional farming (Anikwe et al., 2006). These soil losses can be of the same order of magnitude as soil losses caused by water erosion processes but are often neglected in soil erosion research. This study was therefore conducted in Southwestern Nigeria to compare (i) the amount of soil loss due to harvesting of white and red cocoyam tubers and (ii) the quantity of soil loss due to hand rubbing and washing processes of the harvested cocoyam tubers (iii) the cost of producing cocoyam under hand rubbing and washing processes in traditional farming systems.
Section snippets
Study area
The crop and soil samples were collected from Ajibode village near the University of Ibadan, South western Nigeria (longitude 7°27′N and latitude 3°54′E). Crops that are commonly grown by the farmers of the area are maize, cassava, cocoyam, potato and yams for their livelihood (Ojanuga, 2006). Over the past 30 years, land degradation has been linked to reduced vegetation cover and inappropriate agricultural practices that are major sources of soil degradation (Babalola and Zagal, 2000). The mean
Soil properties and erodibility of the sites.
The soil particle size distribution of the experimental sites at the harvesting time was summarized in Table 1. The soil textural class of the farms under both white and red cocoyam was loamy sand. The mean soil bulk density values under white and red cocoyam sites were 1.24 and 1.30 Mg m− 3 respectively. There was no significant difference between the soil physical properties and volumetric moisture content (Ө) of the farms at the time of harvesting of both the white and red cocoyam indicating
Conclusion
This research compares the efficiency of hand rubbing process as an alternative to washing of the harvested cocoyam tubers under the traditional farming system. Significant amount of soils adhering to the cocoyam tubers was removed by bare hand rubbing before subjecting them to a washing process. This indicates that farmers lacking water and enough human resources for washing could remove substantial amount of soil adhering to the tubers by hand rubbing on the field. In addition, soil loss per
Acknowledgements
The author appreciates the contributions of Revd. John A. Okesipe, Revd. Niyi Adedayo and the technical staff of the Department of Agronomy, University of Ibadan. My unreserved appreciation goes to Miss Omoniyi O. Akintunde of the Department of Agricultural Economics, University of Ibadan, who helped in analysing the cost of producing cocoyam under traditional farming system.
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2019, CatenaCitation Excerpt :Soil loss due to tuber crop harvest (SLCH) – the adherence of soil particles to root crops during harvest – is increasingly recognized as an important contributor to global land degradation (Mwango et al., 2015a; Parlak and Blanco-Canqui, 2015; Dada et al., 2016; Oshunsanya, 2016a, 2016b; Faraji et al., 2017).
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2018, Soil and Tillage ResearchCitation Excerpt :For example, measured sheet and rill erosion (6.9 t ha−1 year−1) and ephemeral gully erosion (5.4 t ha−1 year−1) in central Belgium (Poesen et al., 2001) versus SLCH values of 12.9 Mg ha−1 harvest−1 caused by the potato harvest in Turkey (Parlak and Blano-Canqui, 2015), and 4.6 Mg ha−1 harvest−1 caused by the red cocoyam harvest in Nigeria (Oshunsanya, 2016a). Continuous removal of soils from the field coupled with nutrient uptake by the crops could result to land degradation by lowering the depth of top soil (Mwango et al., 2015b; Oshunsanya, 2016b). In addition, SLCH has economic and environmental consequences attributed to soil transport, cleaning of crop-root and storage and disposal of soils into the streams (Oztas et al., 2002; Yu et al., 2016).
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2018, Soil and Tillage ResearchCitation Excerpt :One of the additional factors can be the root morphology. Soil is easily attached to rough, kinked, and branched roots (Oshunsanya, 2016b). The SLCHcrop was positively correlated with bulk density, average root mass, and crop yield, increasing with an increase in average root mass and crop yield.