Soil test based fertilizer cum manurial recommendation for cassava growing soils of Kerala

Abstract

Soil fertility evaluation to asess the nutrient status of a soil can be considered as the key factor to fertilizer and manure recommendation. In the present era of increased environmental damages and declining soil productivity due to indiscriminate and non judicious use of fertilizers and enhanced fertilizer cost, soil test based fertilizer recommendation deserves special attention. Taking into consideration, the significance of cassava as an energy rich and nutritious staple of Kerala, an attempt was made to develop a recommendation module comprising of manures and fertilizers for the major cassava growing soils of Kerala. The initial evaluation of the soils of the selected 9 major districts of Kerala growing cassava indicated wide variation in all the soil chemical characteristics including primary, secondary and micronutrient status though there was not much difference between the upland and lowland soils of the same district. The organic carbon status of the soil was used as the basis to determine the quantum of FYM and N requirement of the soil. The available P, exchangeable K, Mg and available Zn status of the soil were used to determine the P and K, Mg and Zn requirement for the soil. The fertilizer recommendation evolved based on the methodology showed wide variation among the districts regarding the requirement of organic manures and chemical fertilizers. The reasonably high organic carbon status of the soils of the surveyed districts indicated reduction in the FYM as well as N fertilizer application. The very high value of P observed in 90% of the districts revealed the need to avoid the use of P fertilizers and the medium to high K status of these soils also indicated 10-20% reduction in the use of K fertilizers in 90% of the districts. As Mg and Zn are found to be the other two key nutrients in cassava production, their status in the soil revealed the need for their application to increase tuber yield, improve tuber quality and maintain soil productivity. The demonstration trial conducted to validate this information supported the need to resort to a soil test based fertilizer recommendation for cassava so as to avoid the present indiscriminate use of fertilizers to minimize the cost of cultivation as well as to maintain soil health.