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Fifty years have passed since the first commercial inoculants were manufactured in Australia. Before 1953, various Government Agencies supplied mostly agar cultures with New South Wales Department of Agriculture issuing the first peat-based inoculants. There are no data to indicate the quality of these inoculants, but in the early commercial cultures rhizobia were often outnumbered by contaminants and field failures were widespread. A comprehensive system of quality control was developed from discussions between CSIRO and the University of Sydney. Succeeding quality control bodies have continued on the basis of the original scheme. It set inoculant standards, approved and supplied mother cultures to manufacturers annually, tested all batches of peat inoculants before sale and sampled inoculants at the point of sale. In this paper we describe the history of Australian legume inoculants, list the commercial firms and key people involved and the period during which they were active. We tabulate the strains involved, indicate the period of their use and highlight some of the problems encountered with them and with inoculant production. We indicate the personnel who have been particularly active in the quality control of inoculants, the funding bodies who have supported the work and stress the reliance of the control laboratories on the help of many agricultural scientists in Australia. An important part of the control scheme has been the implementing of standards without resort to legislation. This has depended on the cooperation of the manufacturers involved and has allowed flexibility in applying the standards.

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JumimY. The growth and survival in peat culture of 3 strains of Rhizobium representing 3 inoculation groups, were affected by the source of the peat, pH and method of pH adjustment, method of sterilization, drying temperature and moisture content. The choice of a peat for culture production can be made only on actual tests of its suitability as a medium for rhizobial growth and survival. Sterilization always permitted more rapid growth of the rhizobia and favoured their viability during storage. For the cowpea strain sterilization was essential. Sterilization by y radiation was generally superior to autoclaving: temperatures > 100" at the time of drying adversely affected survival and multiplication. Heat of wetting, which kills many of the added rhizobia, and the production of inhibitory substances, which prevents subsequent multiplication and accelerates death during storage, are important factors. Temperatures of 80-100"were safe and sufficient to dry peat spread in a thin layer. A moisture content of 4&50% (on a wet weight basis in the finished culture) was optimal.PEATS AND SOILS rich in organic matter are widely used in. the final stage of the preparation of legume inoculants, and generally constitute a suitable carrier for this purpose. Immediately after mixing a broth culture of Rhizobium with partially dried peat, there is likely to be a period of multiplication followed generally by a relatively slow decline in the number of viable bacteria. For commercial purposes a safe storage period of 6 months can be expected, provided the initial level of rhizobia is sufficiently high and storage is a t 10-15".Multiplication of rhizobia in the freshly mixed peat culture, and the speed with which the bacteria subsequently die, are likely to be affected by such factors as the nature ofthe carrier, whether it has or has not been sterilized, its water content, and conditions of aeration and temperature to which it is exposed (Hedlin & Newton, 1948 ; Newbould, 1951 ; Date, 1959). Calculations (Vincent, 1958) based on published work showed a weekly logarithmic death rate (Ic) ranging from nil in sterilized peat stored at 5" and with minimal water loss to 0-19 at 25" under conditions that permitted considerable loss of water. In packaged commercial cultures in unsterilized peat k varied from * Present address :

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Three closely related strains of Rhizobium japonicum, equally effective in N2 fixation, were used to inoculate each of three successive crops of soybeans [Glycine rnax (L.) Merr. cv. Bragg] grown on the same block of land. The soil was a vertisol previously free of R. japonicum, and inoculant was applied at different rates by spraying a suspension of peat culture into the seed bed at time of sowing the seed. The populations of rhizobia that developed in rhizosphere and soil were counted at intervals during crop growth and in the fallow period between crops. There was usually a substantial decline in recovery of inoculant strains immediately after sowing. In soil initially devoid of R. japonicum, populations in the rhizospheres of young seedlings were related to rates of inoculation, but differences disappeared as the plants aged. Shortly after harvest, the soil contained large populations of rhizobia which increased up to 200 times during the fallow period between crops, probably due to release of bacteria from disintegrating nodules. The size of these populations was maintained up to the time of sowing the following crop. Although strains used for second- and third-year crops were dominated by already established rhizobia in rhizosphere colonization and nodule formation, the magnitude of the domination could be reduced by increased rates of inoculation. In soil already containing R. japonicum, the proportion of nodules formed by inoculant strains was greater than the relative number of inoculant rhizobia in the soil or the rhizosphere; this was ascribed to an advantage of specific placement of the inocula in that zone of the soil where infection foci first formed. The results are explicable in numerical terms and are discussed in relation to an inoculation strategy for maximum nodulation by applied inoculant in competition with rhizobia already established in soil.