CONTRIBUTIONS OF SHOOT N, P AND K TO TUBER YIELD OF IRISH POTATO (Solanum tuberosum L.) AT SAMARU, NIGERIA

Trials were conducted during the dry seasons of 1998/99 and 1999/2000 at the Irrigation Farm, Institute for Agricultural Research, Samaru to test the response of four varieties of Irish potato (Greta, Nicola, RC 767-2 and WC 7321) to four rates of NPK fertilizer (0, 300, 600 and 900 kg/ha), two forms of seed tuber (whole and cut-tubers). Positive and highly significant correlation (P = 0.01) was observed between tuber yield and shoot N (r = 0.47, 0.74 and 0.57), P (r = 0.51, 0.41 and 0.57) and K (r = 0.33, 0.48 and 0.47) during the dry seasons of 1998/99 and 1999/2000 and the combined of the two seasons, respectively. A strong and positive relationship (P = 0.01) was also found when shoot N, P and K contents were correlated among each other during the two seasons and the two year combined except in 1998/99 dry season when a positive though non significant correlation was observed between shoot N and shoot K (r = 0.15). The direct contributions of shoot N and P to tuber yield were generally much higher than the indirect contributions except for shoot K whose indirect contribution to tuber yield out weighed that of the direct contributions in most cases. The indirect contributions to tuber yield were generally higher through either shoot N or shoot K. Shoot N (25.21%) generally made the highest percent contribution followed by Shoot K (3.37%) and finally shoots P (2.36%). Combined percent contribution from shoot N + P (9.11%) was more than that from shoot N + K (7.75%), and the least was from shoot P + K (2.77%). Shoot N and P contributed more to tuber yield individually and in the combined form, directly and indirectly.