Effect of Seed Source and Post-harvest Handling Techniques on Seed Quality and Yield of Soybean

Abstract

Soybean (Glycine max) is a multipurpose crop which is utilized for food, livestock feed, industrial raw material and a source of bio-energy. However, its production is constrained by use of poor quality seeds from informal sources and inappropriate post-harvest handling techniques which lead to deterioration in seed quality. This study was carried out to determine the effect of seed source and post-harvest handling practices on soybean seed quality. A survey was conducted in Busia County in three agro-ecological zones (LM I, LM II and LM IV) using a questionnaire to obtain information on sources of seed, constraints and post-harvest handling practices of soybean. Seed samples were collected from sixty farmers, sixty local markets and one agro-dealer outlet and evaluated for analytical purity, seed coat damage, moisture content, germination percentage, fungal seed infection and seedling vigour in the laboratory. A sample from the farmers was used for seed multiplication to evaluate the effect of different threshing and drying methods on seed quality in terms of seed coat damage, germination, fungal seed infection, seedling vigour and crop yield. An experiment was also set up in the laboratory to evaluate the effect of different seed treatments and duration of storage on germination and seedling vigour of soybeans. From the survey, forty eight percent of the farmers used farm saved seeds, 23% and 29% obtained seeds from the local markets and community based organizations respectively. None of the farmers obtained seeds from the Agro-dealer outlets. Eighty percent of these farmers did not treat soybean seeds. Sixteen percent of the farmers reported poor germination and diseases to be the major constraints faced when using farm saved seeds while majority reported to not facing any challenge. The low soybean production could be attributed to the use of seeds from informal sources which have been associated with poor quality. Untreated seeds are not protected from infection by pathogens and may also be source of seed and seedling pathogens. Threshing with sticks was preferred by 92% of the farmers because it did not consume a lot of time

while a few threshed with their hands and beating with sticks inside a sack. Seventy two percent reported three months storage period with about 10% storing for six months and beyond. Uncertified did not meet 98% analytical purity standard but attained over 75% germination standard. Farm saved and local market seeds had the highest percentage of seed coat damage, fungal seed infection and reduced seedling vigour compared to seed from agro-dealers. Hand threshed seeds had the highest percentage of analytical purity, percent germination, seedling vigour and least damaged seeds as compared to the other methods. This could be attributed to minimal damage on the seed coat. Oven dried seeds had minimal seed infection as the temperature used was high enough kill the pathogens but too high to damage the seed. Seeds treated with Monceren (Imidacloprid 233g/L + Pencycuron 50g/L + Thiram 107g/L) and Root guard (Trichoderma spp., Bacillus spp., Pseudomonas spp., Aspergillus spp., Chaetomium spp., Esherchia spp. And Azorobacter spp. 10g/5Kg of seed) gave the highest germination percentage of 90% while Apron star ( Difeneconazole 200g/Kg + Metalaxyl 20g/Kg + Thiamethoxam 200g/Kg) gave the lowest germination percentage of 87.7%. This showed that contact fungicides were superior to systemic fungicides. One up to two months storage periods recorded higher germination percentage. Significant reduction in viability of seeds was observed on extension in duration of storage beyond three months due to depletion of seed’s food reserves. Seed source and post-harvest handling practices significantly affected seed quality of soybean. Farmers therefore, should be advised and encouraged to adopt, hand threshing and oven drying techniques, seed treatment with contact fungicides and systemic insecticides and shorter storage periods as they improve germination and reduce seedling infections.