Comparison of tuber yield, nutritional quality and soil health under organic versus conventional production in tuberous vegetables

Field experiments were conducted at the Central Tuber Crops Research Institute, Thiruvananthapuram, Kerala for 5 years during 2004-09 in RBD and 2006-11 in split plot design to assess the comparative agronomic and nutritional advantages of organic management over conventional system in elephant foot yam and yams (Dioscorea spp.), respectively. Organic management resulted in significantly higher yield of 20% (57.10 tonnes/ha) over conventional practice (47.61 tonnes/ha) in elephant foot yam. Organic management also produced significantly higher yield in all the three species of yams (pooled mean of 22.21, 21.96 and 16.83 tonnes/ha for white yam, greater yam and lesser yam respectively). The yield increase observed under organic management in these species was 9%, 11% and 7%, respectively over chemical based farming. Organic management lowered the bulk density by 2.3%, improved the water holding capacity by 28.4% and the porosity of soil by 16.5% in elephant foot yam. There was significant increase in pH (0.46-0.77 unit increase) apart from higher organic C (by 15-19%), available N, P and K, bacterial and fungal populations, N fixers, P solubilizers and dehydrogenase enzyme activity of soil. Organic tubers had higher dry matter, starch, crude protein, K, Ca and Mg and lower oxalate contents. Use of organically produced seed materials, seed treatment in cow-dung, neem cake, bio-inoculant slurry, farmyard manure incubated with bio-inoculants, green manuring, use of neem cake, biofertilizers and ash formed the strategies for organic production