The effects of N,P and K fertilizers on the growth and yield of potato (Solanum tuberosum L.) were assessed using cv “Cozima” during 1985 at the Agricultural Experiment Station, Isfahan University of Technology. In this study, four rates of N (0,90,180 and 270 Kg ha1) , three rates of P205 (0,90 and 180 Kg ha) and three rates of K20 (0,100 and 200 Kg ha1) fertilizers were evaluated in a factorial experiment using a randomized complete block design.
The effect of N fertilizer on yield was highly significant (P<0.01) and the maximum yield was obtained with 180 Kg N ha1 . The effect of N fertilizer on percent dry matter of tubers was non—significant, but its effect on dry weight of haulm was highly significant (P< 0.01). The highest vegetative growth was obtained with 270 kg N ha1 . However, the efficiency of haulm productivity at this rate of N fertilizer was reduced, since the higher vegetative growth obtained was not associated with a higher tuber yield. The effect of P fertilizer on yield was significant (P(0.05), and higher yield was obtained with 180 Kg ha1 P205. Phosphorus fertilizer had no effect on percent dry matter of tubers and on haulm dry weight. The effect of K fertilizer on yield, percent dry matter of tubers and on haulm dry weight was non-significant. Apparently, the soil had provided a considerable portion of the plants need for K.
The effects of N x P and P x K on yield and the effects of N x P, N x K and P x K on percent dry matter of tubers and dry weight of haulm were non-significant. But, the effect of N x K on yield was highly significant (P< 0.01). In this case, N was the main determinant of yield. However, the highest yield was obtained with 180 kg ha1 N and 100 kg ha1 1(20. The N x P x K did not affect the percent dry matter of tubers, but significantly (P40.01) affected yield and dry weight of haulm. A two degree polynomial regression of yield on dry weight of haulm was significant (P (0.01). With this regression, the maximum yield (33.6 t ha) is obtainable with 5.6 t ha haulm dry weight. But, the highest actual yield (38.8 t ha1) was obtained with 5.3 t ha1 haulm dry weight and 180-180—100 fertilizer treatment. This fertilizer treatment affected the percent of N, P and K of haulm and tubers.
An appropriate combination of fertilizers rate is required to provide for high yields and efficacy of vegetative organs. Extra use of fertilizers or imbalance of nutrients in soil reduces the efficiency of fertilizers or plant productivity.
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