EFFECTS OF CARBOHYDRATE APPLICATION ON DIAZOTROPH POPULATIONS AND NITROGEN AVAILABILITY IN GRASS SWARDS ESTABLISHED IN GARDEN WASTE COMPOST

The potential of using free-living nitrogen fixing bacteria (diazotrop hs) as a source of nitrogen nutrition for crops has not been realised in most parts of the world, largely because of the inability of the or ganisms to multiply effectively in temperate agricultural soils. In re cent papers (Keeling et al, 1994, 1996) we showed how populations of d iazotrophs in green waste compost-treated soil can be stimulated to in crease by soil glucose treatment after sward development, and measured an associated increase in grass sward yield of 36% over a 12 month pe riod Here, we describe in detail the changes in bacterial populations over a 12 month period and relate them to grass growth patterns and ni trogen uptake, for compost amended-soil treated with both glucose and soluble starch. It was found that diazotrophic populations were enhanc ed 300% over the long term, and nitrogen uptake by plants increased by over 100% in the first 2 months post 15 gl(-1) glucose treatment in c ompost-grown swards, while soluble starch-treated sward growth was inh ibited. Further a typical field soil similarly treated with glucose fa iled to respond to the treatment; rather; a nitrogen immobilizing effe ct was observed It was concluded that significant nitrogen fixation an d plant N availability was stimulated by the glucose treatment of comp ost, but the mechanisms of these processes require more extensive inve stigation. (C) 1998 Elsevier Science Ltd. All rights resented.