Field Release

The release site (Fig. 11.2), a 3 x 3 m plot within the site of the RSM2004 release6 had been under rotation with cereal crops since 1989. To comply with the requirements of the U.K. Department of the Environment, the plot was covered by a net to exclude birds and surrounded by two 1 m buffer zones of wheat separated by a fence.

The release took place in July 1994: inoculant granules were placed in drills (10 cm apart), into which 840 untreated Avola peas (PGRO, Peterbourgh, U.K) coated in inoculant were planted at 10 cm intervals. A total of 662 g of peat inoculant containing 9 x 1011 live cells was applied; initial soil samples thus contained 4.9 x 105 cfu CT0370 g-1 soil. Samples were taken immediately before and after the release, then weekly for 10 weeks and then fortnightly. Peas were again planted in May 1995 and July 1995, but without further inoculation. An initial ten-fold drop in CT0370 cfu numbers was observed during the first 10 weeks, to 5 x 104 culturable cells g-1 soil (Fig. 11.3). Subsequently numbers remained around 104, similar to the numbers of native R. leguminosarum in the soil (Fig. 11.3). The inoculant appeared to survive better than RSM2004 which had rapidly dropped to 102 cfu g-1 soil although it subsequently persisted at this level. No CT0370 was detected in any buffer zone samples: the major dispersion mechanism in arable fields is via soil cultivation6 and the buffer zones were not cultivated.

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