الخلاصة

Field experiment was conducted in AL-Najaf Governorate during the season of 2011 in two cultivations (spring and autumn) .The aim was to study the effect of different concentrations of organic manure ,different sizes of tuber seeds and Ascorbic acid spraying on growth and yield of potato plants (Solanum tuberosum L.) cv. Proventa. The experiment included 24 treatments, i.e. the interactions of four levels of organic manure (0, 75,100 and 125 kg/furrow), three tuber sizes (big, medium and small) and two concentration of ascorbic acid (0 and 150 mg/l.,the ascorbic acid was sprayed twice during the growing season with 15 days intervals, that was done on 45 days from cultivations. Factorial experiment conducted with Randomized Complete Block Design (R. C. B. D.) was used with three replications. Means were compared according to Duncan's Multiple Range Test at probability of 0.05. Results can be summarized as follow: 1- The use of different amounts of organic manure had significant effect on all measured vegetative growth parameters (plant length, aerial stem number and shoot dry weight(g),125 kg/furrow gave the highest means for the measured parameters for both cultivations. On the other hand , tuber size that used in cultivation plants produced from big size tuber gave significantly bigger plants with higher means for measured parameters compared to that plants produced from small and medium tuber. Meanwhile, ascorbic acid addition on vegetative growth had a positive significant effect on most measured parameters. The interaction among the three factors gave the same trends on vegetative growth parameters. 2- There were significant effects for the use of organic manure on marketable yield for both cultivations. Treatment of 125 kg/furrow gave the highest means for the measured parameters compared to control treatment that gave the least means values. Moreover, the size of used tuber at cultivation produced significant effects on marketable yield for both seasons. Bigger tubers produced the highest marketable yield compared to that plants produced from medium and small tuber size at cultivation for both seasons. Ascorbic acid spraying gave higher amount of marketable yield compared to non sprayed plants (control). Interactions of the three tested factors were significant on marketable yield amounts giving 35.93 and 24.98 ton/h. from the interaction of 125 kg/furrow big tuber size at cultivations and spraying with ascorbic acid compared to that amount of marketable yield (11.81 and 10.07ton/h.) obtained from the interaction of with out using organic manure (control), small size tuber at cultivation and with out ascorbic acid spraying (control).