EFFECT OF DEFLORATION AND N DISTRIBUTION ON POTATO YIELD AND YIELD COMPONENTS

Potato is the most important crop after cereals and legumes in Iran. The influence of N partitioning and defloration on crop yield and quality was investigated in two potato cultivars (Agria and Concord). There was a competition between shoot and tuber on nutrient absorption and resource allocation. A split plot with the two potato cultivars was conducted and the effects of 3 N distribution (270 N kg.ha^-1) [(one half at pre-planting + one half on soiling), (2/3 before flowering + 1/3 at pre-planting) and (1/3 at pre-planting + 1/3 on soiling + 1/3 before flowering)] and 3 defloration levels (at flower budding, full blooming and control) were studied. Results showed that changes in Agria’s measured attributes were higher than Concord, which can relate to its long growth period, more use of N and long period of tuber bulking. Defloration at flower budding led to significant increase in tuber yield, tuber number and weight. There was a 16.59% increase on Agria’s yield (31.74 ton ha^-1). Favorite N distribution with dis-budding at flower budding led to significant increase in tuber yield. On Agria application of 180+90 kg.ha^-1 led to 30.42 % increase in tuber yield (35.14 ton.ha^-1). Longer growth period and less plant height of Agria was vindicator of this phenomenon. Concord yielded 33.55 ton.ha^-1 with 135+135 kg.ha^-1, which was 24.91% higher than control. Excess N application at sowing led to higher vegetative growth and shorter growth period was indicator of lesser yield in Concord. There was a high positive correlation between tuber yield and tuber weight in cultivars.