Does sequential harvesting affect the quality of and income from organically grown potatoes?

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Lack of effective storage facilities to mitigate post harvest losses threatens the profitability of organic farming. In rural KwaZulu-Natal, small scale farmers use traditional storage and sequential harvesting to keep potatoes post maturity while waiting to sell. The effect of these practices on potato quality has not been studied and documented. This study set out to investigate if traditional practices (sequential harvesting and traditional farmer’s store) of the Ezemvelo Farmers Organisation in Umbumbulu affect the quality and marketable quantity of organically grown potatoes. Specifically the study set to investigate the effect of traditional farmer’s store, in situ and controlled storage on the carbohydrate content and sensory quality of potatoes organically grown in Embo by EFO farmers; determine consumer quality expectations of organically and conventionally grown potatoes; investigate the effect of sequential harvesting on the potato quality expectations of consumers and to investigate the produce and income losses experienced by small scale organic farmers at harvest and during storage. Experiments were conducted to compare the effect of sequential harvesting, farmer’s store and controlled cold storage (7oC and 90% relative humidity) on the sensory, appearance and keeping quality of organically grown potatoes. A survey of 100 consumers (40 organic and 60 conventional consumers) was conducted to ascertain consumer appearance and keeping quality expectations of potatoes. In addition, a survey of 101 farmers investigated the storage practices of the EFO farmers who grew potatoes and the type of losses incurred in storage. Preference ranking was used to investigate if time of harvesting post maturity affected potato quality. Produce losses experienced by the farmers were quantified. A co-research group of three seasoned farmers of the EFO participated in the research. They produced potatoes used in the study and provided valuable input to ensure that the study adhered to storage practices of the farmers. The lowest and highest sugar levels were observed in potatoes stored in situ and under controlled conditions, respectively. Potatoes left in situ also recorded higher starch content. Potatoes stored in situ were significantly preferred by sensory panellists (p<0.05) over those stored in both farmer’s store and in controlled storage. Preference rank scores were negatively correlated to total sugar content and positively correlated to starch content. Consumers in the study highlighted five desirable appearance qualities in potatoes: absence of greening, absence of sprouting, smooth skin texture, absence of blemishes and light skin colour. No significant differences in the quality expectations between participating organic and conventional potato consumers were found. The majority of consumers expected potatoes to store for at least three weeks post purchase. Sequentially harvested potatoes met this expectation when potatoes were left in situ for a maximum of six weeks post maturity. Potatoes in situ also maintained good appearance and sensory quality. The highest produce losses were experienced in summer owing to soft rot problems. Production in the drier seasons (autumn and winter) increased the proportions of potatoes too small to be sold as table potatoes. With the exception of completely rotten potatoes, poor quality potatoes were consumed, used as seed potatoes and sold to the local market as seed and for food. Poor potato quality resulted in reduced income for the farmers. This investigation pioneered research into the effect of sequential harvesting on the quality of organically grown potatoes. The findings demonstrate that sequential harvesting provides resource-poor small scale organic farmers with an efficient storage option where other storage methods and technologies may be inappropriate, ineffective or unaffordable. It is recommended that government and other players in the agricultural sector plan initiatives to educate small scale potato farmers on the benefits of sequential harvesting as an effective short term method of potato storage. Research with other potato cultivars in different agro-ecological settings is needed to optimise sequential harvesting. Government policy aimed at training and developing farmer capacity in organic seed potatoes production is essential to ensure that farmers access disease and pest free seed. Farmers also need assistance to access to irrigation resources to improve production.