Measurements of NSNF at field sites across eastern Australia (Roper 1983; Roper et al.
Data from field and laboratory experiments (Lynch and Harper 1983; Roper 1983, 1985) indicated that the most favourable temperature range for NSNF was 30-35[degrees]C and that NSNF declined by 20-30% in activity for each 5[degrees]C drop in temperature.
Therefore, in our calculations to estimate potential NSNF, it was assumed that each rainfall event of >5mm provided sufficient moisture to support NSNF for 24 h.
Estimates of NSNF were made for 4 specific sites with long-term farming system trials.
Detailed maps showing the effect on NSNF of moisture and temperature with non-limiting carbon were developed using the calculations described above.
Similar principles were used to develop maps of potential NSNF where available C was the limiting factor.
NSNF bacteria occurred in all soils sampled regardless of soil type or land use (Fig.
Field measurements of NSNF in soils amended with crop residues showed significant seasonal variation.
N contribution from NSNF calculated by difference using an N budget
Over 17 years, there was a total N deficit in the budget of 334-394 kg N/ha or an annual average of ~20 kg N/ha.year deduced to be due to NSNF associated with stubble retention.