A field experiment was conducted during summer season of 1996–98 (March-July) at Upper Shillong, to evaluate the N efficiency with bio-fertilizers inoculation. Combined inoculation of Azotobacter and phospho-inoculant culture together significantly increased the tuber yield. When these bio-fertilizers inoculated seperately Azotobacter gave 7.9% and phospho-inoculant gave 8.6% higher tuber yield significantly up to maximum level (150 kg N/ha). Azotobacter increased the tuber yield by 24, 10, 2 and 4% at 0, 50, 100 and 150 kg N/ha respectively. In case of phospho-inoculant the corresponding increase was 22, 13, 2 and 4% and with combined inoculation the increase was 29, 19, 10 and 11% respectively. Combined inoculation of both fertilizers along with 150 kg N/ha was the highest yielder and gave the tuber production in the ratio 22: 62: 16 of large, medium and small size tubers, respectively, corresponding to that control had a ratio of 9: 66: 25. The highest net return was also obtained from this treatment.
Bio-fertilizer, Azotobacter, Phospho-inoculant culture, Tuber yield, Tuber size
