Published online by Cambridge University Press: 27 March 2009
Five experiments were carried out in two seasons which studied the effects of seed weight, seed rate and date of harvesting on yield of seed crops of Record (four experiments) and Maris Piper (one experiment) in Scotland. Small seed (35 g) produced more above-ground stems and tubers and higher seed yields at equal seed rates than large seed (105 g). Increasing seed rate with both seed weights increased yield of seed-size tubers. The value of the seed crop was measured as the number of ware hectares which could be replanted from the yield of 20–55 mm tubers and calculated using recommended seed rates (Ministry of Agriculture, Fisheries and Food, 1982). Small seed produced more replantable hectares than large seed at equal seed rates in all experiments with Record and increasing seed rate increased the number of replantable hectares. However, when seed retained for replanting at the same seed rate was taken into account, small seed produced more replantable hectares only when total yield reached approximately 40 t/ha. Seed yield was much higher in Maris Piper than in Record and effects of seed weight were small. Increasing seed rate increased the number of replantable ware hectares but the effect was much reduced after retention of seed for replanting.
The effect of pricing policy for seed and ware on returns to the seed grower was also established. The sale of seed (and ware tubers) at fixed prices per tonne produced lower returns than selling seed at varying prices per tonne in relation to tuber size and equivalent to a fixed ware cost per hectare planted especially where seed yields were high. Delaying harvesting increased sale value but crops reached 85–90% of the final value before many oversize tubers (> 55 mm) were found and large yields of such tubers from low seed rates produced lower returns than from increased seed rates.
The number of ware hectares produced per seed hectare (even net of seed retained for replanting) was high especially in Maris Piper. The results show that the area devoted to seed potato production in U.K. is much too high for the ware area and the significance for the future of seed production is discussed.