Rhizobium populations in maize fields of the North Island, New Zealand

Numbers of Rhizobium trifolii Dang. were estimated in soils from 77 maize fields located in 4 regions of the North Island. Forty of these fields were also tested for R. lupini (Schroeter) Eckhardt, Baldwin & Fred. R. trifolii numbers ranged from 14 to 300 OOO/g soil. This was similar to the range of R. lupini numbers found in Waikato fields, but in 12 of the 20 Poverty Bay fields tested no R. lupini were detected. In 7 Waikato and 3 Poverty Bay fields a high proportion of R. trifolii were ineffective in nitrogen fixation with white clover. Linear and partial linear correlations were used to examine relationships between R. trifolii numbers and soil parameters. The possible influence of some soil properties on R. trifolii persistence is discussed.