Effects of nitrogen application and seedpiece spacing on yield and tuber size distribution in eight potato cultivars

The responses of eight cultivars to nitrogen fertilizer and spacing treatments were examined from 1992 to 1996. Experiments were carried out at the Agriculture and Agri-Food Canada Research Farm in Harrington, Prince Edward Island. Four nitrogen rates and three seedpiece spacings were compared. Total and Canada #1 yields were investigated for patterns of responses of the individual cultivars to both treatments, and possible interactions between the treatments. Response surfaces were presented for all cultivars. Nitrogen application increased both total and Canada #1 yields for all cultivars. Increasing rates of nitrogen showed linear and/or quadratic trends for both total and Canada #1 yields in all cultivars, whereas responses to spacing treatments showed linear patterns for total yield, but little change for Canada #1 yields in seven of the eight cultivars. No interactions were detected between fertilizer and spacing treatments for total or Canada #1 yields. Generalized regression equations representing the responses of the cultivars to fertilizer and spacing treatments for both total and Canada #1 yields were also derived. These equations should be useful as a guideline for determining appropriate nitrogen rates and seedpiece spacing for the eight cultivars tested. Ratios of Canada #1 to total yield were higher after initial application of nitrogen (0 to low rate) in all but one cultivar. However, only two cultivars showed higher ratios as nitrogen rate was further increased. Wider seedpiece spacing yielded higher ratios of Canada #1 in five of the eight cultivars tested.