Data are reported from three experiments from 1972 to 1974 which examined the effects of two row widths (66 cm and 132 cm) and five planting densities on number of tubers, tuber yields and tuber saleability of two maincrop potato varieties (Désirée and Maris Piper). Fewer tubers were generally found in 132 cm rows than in 66 cm rows; in 1972 reductions were most marked at high densities in both varieties and in 1974 effects were most pronounced in Maris Piper. Row width had little effect on total tuber yield at any stage of growth in either variety. The use of 132 cm rows reduced tuber greening, so that yields of saleable ware tubers at final harvest were not reduced by 132 cm rows in any year and in 1973 were higher in Désirée from 132 cm rows than from 66 cm rows. These results suggest that wider rows than are currently used in practice should be considered for maincrop potatoes, especially where water is not limiting.

Increasing planting density increased total yields in both varieties although the responsesto the final increments in planting density were small. Yields > 38 and > 57 mm declinedat the higher planting densities in Maris Piper and the optimum above-ground stem densities for ware grades differed markedly in the two varieties. Good relationships between tuber yieldsand number of above-ground stems were found in all years and support the use of stems as thebasic unit of density in this crop.