| Summary: | Numerous soil borne pathogens attack alfalfa roots and crowns and reduce stand longevity by predisposing plants to winter injury. Persistence can be improved by the use of cultivars with good disease resistance and by applying phosphorus (P) and potassium (K). The objective of this study was to examine the productivity and quality of alfalfa cultivars differing in disease resistance, under various fertilizer regimes on three different soils. A completely cross-classified factorial experiment in a randomized complete block design (RCBD) was established in 1990 with three rates of P (0, 33, and 66 kg ha$ sp{-1}$), three rates of K (0, 124, and 248 kg ha$ sp{-1}$), and two cultivars ("Apica" and "Oneida VR"). Treatment combinations were established (with 10% timothy, by seed weight) on three soils with distinctive drainage characteristics (referred to as ideal, intermediate and marginal). Disease ratings, stand counts, yields and herbage mineral content were measured in each of two production years. Yields and plant populations were the lowest on the marginal soil, while disease levels were the highest. Fusarium spp. were the most common fungal isolates from diseased roots and crowns at all sites. Apica tended to persist better than Oneida VR and have lower levels of crown and root rot. Neither P nor K had an effect on yield or persistence at the Ideal site, with positive responses noted on yield at the other sites. Potassium improved persistence at the Intermediate site and had variable but positive effects on disease levels. Increased rates of K fertilizer resulted in reduced herbage Ca, Mg, crude protein (CP) and increased herbage K and Acid Detergent Fibre (ADF) levels. Regardless of management, alfalfa production on soils with inadequate drainage remains risky.
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