Alternative method of reducing soil loss due to harvesting of sweet potato: A case study of low input agriculture in Nigeria

• Hand rubbing method removed 91–96% of adhering soils relative to that of washing method.
• More days are required to wash the same quantity of tubers than using hand rubbing method.
• A farmer could save an average of #50,973.5 ha−1 season−1 for adopting hand rubbing method.
• Potato yields were significantly different (P ≤ 0.05) among the cultivars.
• Thorough hand rubbing of harvested tubers on the farm is suggested as an alternative to washing.

Soil loss due to crop harvesting (SLCH) has been established as an important soil erosion process that has contributed to soil degradation in many countries of the world. Consequently, researchers have recommended washing of harvested tubers before transporting to market place. Unfortunately, many low resource farmers could not adopt washing method due to scarcity of water during harvesting period (dry season), cost of additional labor and possible tuber spoilage when not dried on time. This has stimulated the need for alternative method of removing soil adhering to tubers. A field experiment was conducted between 2011 and 2012 on an Alfisol derived from basement complex parent rock to (i) compare effectiveness and efficacy of hand rubbing process with washing process of harvested potato tubers and (ii) examine sweet potato cultivar effects on soil loss during harvesting. Ten commonly grown cultivars of sweet potato in Africa were planted in an experiment laid out in a randomised complete block design with four replications. Total harvested tubers from each replication were weighed and shared into two equal weights of tubers for hand rubbing and washing respectively to remove soil sticking to tubers. Soil collected was analysed to estimate plant nutrients contained in it. All data collected on soil loss and cost of removing soil from tubers were analysed using ANOVA. Contribution of hand rubbed soil loss to total soil loss ranged from 93.2% (Ex-igbaraian) to 98.2% (Shaba) in 2011 and ranged from 95.4% (Benue) to 97.0% (TIS87/0087) in 2012. Total SLCH was significantly (P ≤ 0.05) different among the cultivars and largely determined by the size of the tubers as significant (P ≤ 0.05) correlation coefficient between yield and soil loss was obtained. Average soil nutrient losses for two growing seasons were 32.8 g org. C ha−1 harvest−1, 10.0 g N ha−1 harvest−1, 16.4 g P ha−1 harvest−1, 6.3 g K ha−1 harvest−1, 6.9 g Ca ha−1 harvest−1, and 10.4 g Mg ha−1 harvest−1. The average potato yield ranged from 2.0 t ha−1 (TIS 8441) to ≈0.2 t ha−1 (Akwide). Averagely, cost analysis of soil removal revealed that farmers would have saved 42, 600 ha−1 season−1 and 36, 400 ha−1 season−1 in 2011 and 2012 respectively by adopting hand rubbing technology instead of washing. Thorough hand rubbing of harvested tubers on the farm is suggested as an alternative to washing because the method removed about 96% of soil adhering to tubers. Developing potato harvesters that could mimic the hand rubbing process is suggested on large scale potato farms.