Effect of nitrogen, phosphorus and time schedules of haulm cutting on production of small sized (up to 40 g) tuber in seed potato (Solanum tuberosum)crop

Field experiments were conducted from 1995-95 to 1998-99 at Jalandhar to de velop suitable technology for producing maximum number and yield of small s eed tubers. The treatments comprised the combinations of 2 levels of N (75 and 150 kg/ha), 2 levels of P (33 and 66 kg/ha) and 3 schedules of haulm cu tting (60,70 and 80 days after planting). The interaction between N and P r ates on tuber number weighing <10g and >40g was significant but the interac tion between N/P rates and haulm cutting time schedules on either tuber num ber or yield was not significant. The application of 150 kg N/ha along with 66 kg P/ha gave maximum number of tubers/ha. The effect of higher rate of P was modified by the availability of soil P. In 1995-96, effect of higher rate of P (66 kg/ha) on tuber number and yield of 10-25g and 10-40g seed si zed tubers was not significant while the effect of 66 kg P/ha was significa nt in 1996-97 and 1997-98 as the available soil P in 1995-95 was 18 kg/ha w hile it was 5 kg/ha in other years. Halum cut at 70 to 80 days after planti ng gave 87-89% of the total number of tubers (697-731 thousands/ha) as smal l sized tubers (up to 40 g size). The seed produce of the crop with haulm c ut at 70 to 80 days after planting gave better sprout growth, taller plants , more stems and gave higher yield than the seed produce of 60 days haulm c ut crop. The yielding potential of seed tubers was further in accord with t heir size. The seed tubers of <10 g gave 22 tonnes/ha while 25 to 40 g gave 33 tonnes/ha of tubers.