Efficacy of potato (Solanum tuberosum) cultivars under varying levels of nitro- gen and growth duration in eastern Indo-Gangetic plains

A field study was conducted during winter seasons of 2004-05 and 2005-06 at Patna with three potato ( Solanum tuberosum L.) cultivars namely Kufri Giriraj, Kufri Pukhraj and Kufri Jyoti, four nitrogen levels (0, 80, 160 and 240 kg/ha) and two growth durations (75 and 100 days) to work out the optimum level of N, efficiency and eco-friendliness. Kufri Pukhraj gave the highest yield (28.7 t/ha) and N uptake (105.8 kg N/ha) and was most effi- cient in utilizing N from soil and applied N (uptake efficiency 0.54 kg/kg N). The increase in growth durations im- proved the tuber yield at higher N levels (160 and 240 kg N/ha). The highest increase in agronomic and uptake effi- ciencies with increasing growth duration was recorded at 160 kg N/ha (42 for agronomic and 0.1 kg/kg N for up- take efficiency). Yield at economic optimum N was normally higher in longer growth durations with higher nitrogen requirement (9.7 and 7.6 t/ha at 81 and 37 kg/ha, higher N for Kufri Giriraj and Kufri Jyoti, respectively), however, for Kufri Pukhraj economic optimum N dose decreased by 22%. Eco-friendliness with respect to nitrogen utiliza- tion both in absolute and relative indices was maximum in Kufri Pukhraj followed by Kufri Giriraj. Net return and benefit:cost ratio was higher when longer growth duration was given, however, when crop is to be harvested early Kufri Pukhraj is the best option.