On-farm validation of site-specific nutrient management in cassava (Manihot esculenta) in Thiruvananthapuram district (Kerala)

On-farm experiments were conducted to evaluate the performance of site-specific nutrient management (SSNM) of cassava (Manihot esculenta Crantz) in five important soil series of Thiruvananthapuram district in Kerala, during 2011–12 and 2012–13. Field and crop-specific NPK rates were calculated using quantitative evaluation of fertility of tropical soils (QUEFTS) model. Tuberous root yield increased significantly in SSNM treatment compared to FFP in all five soil series studied. Above 5 tonnes/ha yield increase was observed in SSNM treatment in all soil series compared to FFP treatment. The nutrient uptake was maximum in Thiruvanathapuram series (22.3 kg/ha, 3.3 kg/ha and 17.9 kg/ha N P and K uptake increase in SSNM treatment than FFP) and minimum nutrient uptake (27.9 kg/ha, 1.9 kg/ha and 8.7 kg/ha N P and K uptake increase in SSNM treatment than FFP) was observed in Vellayani series. Large increase in nutrient-use efficiency parameters like agronomic efficiency (19 kg/kg, 17 kg/kg and 33 kg/kg N, P and K respectively) and recovery efficiency (0.14 kg/kg, 0.06 kg/kg and 0.14 kg/kg N, P and K respectively) was observed in SSNM treatment compared to FFP. The SSNM treatment led to a reduction of average fertilizer cost ( 5, 240 crop/ha) and an increase in gross return above fertilizer cost ( 10, 9, 880 crop/ha) compared with FFP.