Potato response to crop sequence and nitrogen fertilization following sod breakup in a Gleyed Humo-Ferric Podzol

Meadow soils could supply significant amounts of N for several years and reduce N requirements for the potato (Solanum tuberosum L.). We examined a combination of three crop sequences, three cultivars and six N rates in relation to tuber yield and quality. Superior, Kennebec and Snowden were grown as follows on a Tilly silty loam between 1993 and 1995: (1) 3-yr continuous potato cropping of Superior, (2) 3-yr continuous potato cropping starting with Snowden and followed by 2 yr of Kennebec, and (3) 3-yr sequence of Kennebec, oat (Avena sativa L. 'Marion') and Superior. There were six N treatments (0, 70, 105, 140, 175 and 210 kg N ha−1) and a split application of 140 kg N ha−1 (half at seeding and half before hilling). The seasons were either favorable to growth (1993), relatively wet (1994) or relatively dry (1995). In 1993 and 1994, total yield varied between 37 and 50 t ha−1. In 1995, continuous cropping of Kennebec and Superior produced 28 t ha−1 compared with 37 t ha−1 under crop rotation. The rotation increased total yield of Superior by 34% and graded yield by 42% in 1995. The N requirement was closely related to yield, rather than cultivar. Compared with continuous cropping of Superior, tuber-quality index was highest with the rotation for rhizoctonia (Rhizoctonia solani) (67 vs. 57) and common scab (Streptomyces scabies) (90 vs. 82). The incidence of both diseases decreased when at least 70 kg N ha−1 was applied. For common scab, skin coverages was higher at rates of 0, 175 and 210 kg N ha−1 than at intermediate rates of 70–140 kg N ha−1. Mineral N accumulated in the 0–60-cm layer in the interrow and increased rapidly when N rates exceeded 105 kg N ha−1. After sod breakup an N rate in the range of 70–100 kg N ha−1 and crop rotation with cereals sustained the productivity of the potato during 3 yr while minimizing the environmental impact of mineral N. Key words: Crop rotation, common scab, rhizoctonia, reduced N rates, Solanum tuberosum L.