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The field experiments were conducted to develop fertilizer best management practice (FBMP) by site specific nutrient management (SSNM) and SSNM zonation maps and customised fertilizer ratios at ICAR-CTCRI, Thiruvananthapuram, Kerala, India, during 2012-2015. The SSNM plot resulted in an average actual tuberous root yield of 36.80, 37.40 and 38.70 t/ha during 2012, 2013 and 2014 respectively against a yield target of 40 t/ha. The average yield difference between SSNM and PR for the three crops grown was 5.50 t/ha (17%, P=0.001) and was similar during all the three years. On an average, plant N accumulation increased by 48 kg/ha (25%, P=0.003), P accumulation by 9 kg/ha (50%, P=0.003), and K accumulation by 39 kg/ha (20%, P=0.005). Among the three crops grown, the AEN increased by 34 kg/kg (72%, P=0.002), REN by 0.04 kg/kg (8%, P=0.003) and PEN by 55 kg/kg (58%, P=0.005). The guidelines in estimating the fertilizer N, P2O5 and K2O required by cassava based on tuberous root yield response to fertilizer N, P and K and efficiency of fertilizer N, P and K use also were developed. Soil fertility maps and agro-ecological units, SSNM zonation maps and customised fertilizer ratios were also developed for all the major cassava-growing regions in India. [ABSTRACT FROM AUTHOR]