Clover growth in response to naturalised P-solubilising bacteria in New Zealand

For New Zealand pastures the main fertiliser costs are associated with the delivery of nitrogen (N) and phosphate (P). With recognition that increased consumption of N (Parfitt et al. 2006) and P fertilisers and the augmentation in soil Olsen-P levels (Mackay and Lambert 2011) is unsustainable, there is impetus to identify micro-organisms capable of delivering these elements to plants. Legumes, such as white clover (Trifolium repens), are an essential component of the New Zealand pastoral system. Clover has been routinely inoculated with strains of rhizobia selected for high N fixing efficacy. In contrast delivery of P is via application of readily soluble superphosphate. Phosphate solubilising bacteria (PSB) present in the rhizosphere or in nodules (Rodriguez and Fraga 1999; Peix et al. 2001) have the capacity to convert immobilized soil P into plant available P, and promote plant growth. Effective PSB include species of Rhizobium, Pseudomonas and Burkholderia (Rodriguez and Fraga 1999). The potential to identify strains with dual activity of N-fixation and P-solubilisation makes them a promising group for research efforts. This paper describes the effect of 12 New Zealand naturalised P-solubilising bacteria on the growth of three species of clover