Commercial inoculant products for subclover that are marketed in the Pacific Northwest were evaluated in field trials (supplemented by appropriate laboratory analysis) at four sites in southwest Oregon. The materials tested were Nitragin (Milwaukee, WI) and Northrup-King (Minneapolis, MN) peat-based inocula, and Celpril (Manteca, CA) inoculated, lime-pelleted subclover seed. Duplicate plots were included for the peat inocula at seeding rates equivalent to 136 kg seed/ha and the seed was inoculated according to the manufacturer's instructions and at twice the recommended dosage. The Celpril seed was tested at 196, 98, 49, and 25 kg seed/ha. (duplicate plots) and subclover variety Mt. Baker was used for all field trials. In plant infection assays, the Nitragin produce contained 3.7 x 10⁵ rhizobia/gram peat which were moderately effective while the Northrup-King peat yielded 3.0 x 10⁴ rhizobia/gram peat which were ineffective. The Celpril seed contained 77.3 rhizobia seed which were highly effective. Laboratory analysis showed that for the peatbased products the probability of ineffective nodulation was high. The field plots were established in October, 1978. The plants germinated and were then exposed to an unusually harsh winter which included the coldest average January temperature ever recorded for Oregon. Most of the plants inoculated with Nitragin and Northrup-King survived the winter and by March, 1979, had developed 12-14 true leaves and an immature, but well nodulated root system. The Nitragin-inoculated plants generally showed higher yields than Northrup-King-inoculated plants, most of the difference between them generally were statistically significant. In the Celpril plots, only a few plants at the higher seeding rates survived the winter. Those which survived showed vigorous growth and dry weights were generally significantly greater than those for the peatbased inoculated seeds. The results indicate that for winter legumes, a commercial product must contain a sufficient number of effective rhizobia, which are able to tolerate wet, cold soil conditions. Above all, no inoculant should contain rhizobia which ineffectively nodulate subclover. Celpril proved to be the superior product. This may be because pelleted products inoculated with single effective rhizobia are superior to multistrain peat-based inocula
