Soil test-based low input nutrient-management strategy: A decade experience in cassava (Manihot esculenta) in Ultisols of Kerala

The research experience under a long-term fertilizer experiment (LTFE) at ICAR-CTCRI, Thiruvananthapuram, Kerala since 1977 revealed the strong and positive response of cassava (Manihot esculenta Crantz) to manures and fertilizers. As a part of the LTFE, since 2005, the comparison made among 4 treatments, viz. soil test-based fertilizer recommendation (STBFR) of farmyard manure (FYM) as source of organic manure and chemical fertilizers as inorganic source, a highest dose of N: P: K @ 125: 50: 125 kg/ha + FYM @ 12.5 t/ha, present Package of Practices (PoP) recommendation of N: P: K @ 100: 50: 100 kg/ha + FYM @ 12.5 t/ha and absolute control (without any manures and fertilizers) for 10 years established the superiority of STBFR over PoP and the sustainability of cassava for continuous cultivation in the same field. The mean organic carbon, available P and K during these years was 1.106%, 99.8 and 223.7 kg/ha, respectively, and the mean FYM, N: P: K recommendation evolved was 7 t/ha, 83.3: 0: 70.6 kg/ha, respectively, with complete omission of P and lower rate of N and K than PoP. Under the absolute control, during these years, the tuber yield ranged from 6.58 to 18.00 t/ha with a mean tuber yield of 14.53 t/ha. The tuber quality parameters, viz. cyanogenic glucosides (HCN) responsible for bitterness of cassava tubers and starch content were significantly influenced by treatments with STBFR giving significantly the lowest HCN and highest starch content. The cost benefit analysis indicated a benefit: cost ratio of 1.959 for STBFR at par with PoP (2.087) with a saving of 54.3 and 51% of input cost over the highest dose and PoP respectively.