Zinc Nutrition of Tuber Crops in Ultisols of Kerala

Abstract

Cassava, sweet potato, elephant foot yam, yams, taro, tannia, arrow root and coleus are the important tropical tuberous vegetables grown for their edible tubers and leaves which can meet the energy, nutritional and medicinal requirements of the consumers. Among the tropical tuber crops, cassava is most important with respect to higher biological efficiency, area under cultivation, acceptability as a secondary staple, ability to thrive under marginal soil and environmental conditions, tolerance to pests and diseases, quantity and quality of starch, and its excellent physico-chemical and biochemical properties for the preparation of value-added products. Inherently high yield potential of these crops catalyses the nutrient removal from the soil, necessitating their replenishment through external sources. Micronutrient requirements of these crops are very high; deficiency disorders, however, manifest only in extreme cases. Zinc depletion noticed under continuous cultivation of cassava over 14 years under a permanent manurial experiment made us initiate intensive studies on Zn nutrition in tropical tuber crops and we made significant accomplishments in this field. These include Zn dynamics under a long-term fertilizer management, especially with respect to reduction in cyanogen and increase in starch content of tubers; determination of the Zn status of the soils of Kerala; arriving at the Zn content in customized fertilizers developed for elephant foot yam; preparation of a Zn-enriched compost from cassava starch factory solid waste; development of low input management strategy for cassava involving soil test based application of Zn; and their respective on-farm validation trials.