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Blanket recommendation
Fertilizer recommendation for cassava in India started with the establishment and research work initiated in 1960s at Central Tuber Crops Research Institute (CTCRI), Thiruvananthapuram, Kerala, India. From earlier studies on different cassava clones grown with different levels of organic manures and inorganic fertilizers, it was recommended to apply 12.5 t/ha of farm yard manure (FYM) and 100:100:100 kg/ha N, P2O5 and K2O (Mandal et al., 1973). A similar recommendation was also made by Pillai et al. (1985). But, later studies by Kabeerathumma and Ravindran (1996) showed that the rate of P application can be reduced to 50%, thus changing the NPK recommendation to 100:50:100 kg/ha. Based on these and other related studies, Nair et al. (2004) now recommend to apply 100:50:100 kg/ha N, P2O5 and K2O for high-yielding cassava varieties and 50:25:50 kg/ha for M-4 and local cultivars. Half the dose of N and K, and the entire amount of P need to be broadcast at the time of final land preparation and the remaining quantities of N and K are to be applied in short bands around each plant 45-60 days after planting. The classical concept of blanket fertilizer recommendation with fixed rates and timings has been developed based on differential rate fertilizer trials conducted in CTCRI farm or a few other farms. Later studies in many crops indicated the that this kind of fertilizer recommendation cannot be extrapolated to areas other than the sites where the experiments are conducted because of the high temporal and spatial variability of soil and plant properties in farmers’ fields.

Blanket recommendation of N, P2O5 and K2O for cassava in India.
STCR Concept
Swadija and Sreedharan (1998) developed fertilizer rates for targeted yields of cassava based on soil test crop response (STCR) concept in laterite soils of Kerala and Selvakumari et al. (2001) developed the same concept for soils of Tamil Nadu. In STCR concept, fertilizer rates are calculated for a targeted yield based on soil test data and based on a single yield uptake relation function. This is not so in real situation. More importantly, it does not take into account the interactions among the nutrients. Each nutrient requirement is calculated individually, irrespective of the levels of other nutrients in soils. Both the above concepts do not consider nutrient interactions as the main influencing factor for plant nutrient uptake and the internal nutrient efficiency at higher yield levels.
Mandal, R.C., K.D. Singh and S.B. Maini. 1973. Effect of plant density, fertility level and shoot number on tuber yield and quality of tapioca. Indian Journal of Agronomy 18: 498-503.
Pillai, N.G., B. Mohankumar, P.G. Nair, S. Kabeerathumma and C.R. Mohankumar. 1985. Effect of continuous application of manures and fertilizers on the yield and quality of cassava in laterite soil. In: T. Ramanujam, P.G. Rajendran, M. Thankappan, C. Balagopalan and R.B. Nair (Eds.). Proc. Tropical Tuber Crops Nat. Symp., CTCRI, Thiruvananthapuram, India. Nov 27-29, 1985. pp. 109-113
Kabeerathumma, S. and C.S. Ravindran. 1996. Long-term effects of manures and fertilizers in acid Ultisol growing cassava. Annual Report, CTCRI, Kerala, India. pp. 16-17.
Nair, G.M., S. Ramanathan and T. Asokan Nambiar. 2004. Agrotechniques of tuber crops. CTCRI, Kerala, India. 32 p.
Selvakumari, G., R. Santhi and R. Natesan. 2001. Fertilizer recommendations based on STCR technology for the state of Tamil Nadu. In: P. Subba Rao and S. Srivasthava (Eds.). Soil Test Based Fertilizer Recommendations for Targeted Yields of Crops. All India Coordinated Research Project for Investigations on Soil Test Crop Correlation. Indian Institute of Soil Science, Bhopal, Madhya Pradesh, India. pp. 267-297.
Swadija, O.K. and C. Sreedharan. 1998. Fertilizer prescription for targeted yields of cassava in laterite soil. Journal of Root Crops 24(2): 137-142.
Central Tuber Crops Research Institute
Sreekariyam, Thiruvananthapuram, Kerala - 17