POTENTIAL FOR INCREASING N-2 FIXATION OF FIELD PEA THROUGH SOIL-MANAGEMENT AND GENOTYPE

The effects of incorporation of straw in soil, liming and genotype on N-2 fixation by field pea were evaluated in glasshouse experiments usi ng the N-15 isotope dilution technique. Soil treatment with the equiva lent of 2.5 to 10 t straw ha(-1) reduced soil NO3- and soil N uptake b y pea, which increased the proportion of pea N derived from N, fixatio n: from 0.67 (nil straw) to a maximum of 0.96 (10 t straw ha(-1)). Tot al fixed N was increased depending on Rhizobium inoculation method and cultivar. When soil and seed were both inoculated, fixed N increased from 153 mg N pot(-1) (nil straw) to 240 mg N pot(-1) (10 t straw ha(- 1)) when the cultivar was Dundale. The amount of N, fixed by pea in re sponse to fertilizer N addition (the equivalent of 50 kg N ha(-1)) var ied significantly with genotype. Total fixed N increased with increasi ng pH over the range of 3.9 to 4.5 or 4.1 to 4.7 in two soils. In one of these (Book Book) the increase in fixed N was nearly 50% of the nil lime control.