Fig. 2 Percent recovery of ¹⁵N added as nitrate to (a) control, (b) autoclaved and (c) g -irradiated organic soils. Mean % recovery reported (n=3) and error bars are 1 S.D. of mean. Statistically significant differences between means at a =0.05 (t-test) reported as different letters above consecutive bars. Total = total ¹⁵N recovered in soil immediately after addition (t=15 min.) or after 24 h incubation at 20° C. Organic-N = ¹⁵N remaining in soil after mineral-N extraction. Nitrate = ¹⁵N recovered in form added. Soluble N = difference between total recovery and mineral N forms; SD calculated by propagation of error method.