Experiments conducted over three seasons in southern New South Wales tested the effects of concentrating anhydrous ammonia (AA) and urea fertiliser in bands occupying ~3.5% of the topsoil volume. Yield responses to applied nitrogen (N) were small or negative in a drought but larger (17 kg grain kg–1 N fertiliser) in favourable seasons. There was no consistent difference between AA and urea effects on yield, grain protein or efficiency of fertiliser-N recovery, and there were no consistent differences arising from banding depth or application time. Gaseous loss of ammonia to the atmosphere was negligible from urea granules or AA injected into the soil as gas or liquid. Soil ammonium concentration was >700 μg N g–1 in bands of ~5 cm diameter when measured 6 days after AA application but halved within 5 weeks due to nitrification. Within 1 day of banding AA or urea at sowing, pHwater in the bands rose from 6 to 8.5, leading to transient changes in microbial activity and populations. Immediately after banding, microbial biomass carbon and numbers of protozoa fell by about half, but numbers of ammonia- and nitrite-oxidisers were unchanged. Five weeks later, microbial biomass carbon and protozoa had partly recovered whereas numbers of ammonia- and nitrite-oxidisers increased 5–10-fold. After 7 months, there was a small reduction in microbial diversity in the bands, shown by analysis of fatty acid methyl esters. Seedling growth was slower where N fertiliser was applied in concentrated bands than when mixed throughout the topsoil, supporting previous research showing that roots avoid bands of highly concentrated ammonium. Banding thus provided a slow-release form of N to wheat crops, thereby reducing excessive seedling growth and the risks of haying-off.

Take-all is a root disease of wheat caused by the fungus Gaeumannomyces graminis var. tritici (Ggt). The most common method of control, growing wheat after a break crop, is not always feasible. This study compared the use of a break crop with 5 alternative control methods in a series of field experiments in south-eastern Australia. The methods of control tested were: (1) fungicide added to fertiliser; (2) soil fumigation with methyl bromide; (3) applied chloride; (4) seed treatment with microbial antagonists; (5) a prior brassica break crop; and (6) a 12-month-long fallow. Eight experiments were conducted over 2 years but not all treatments were included in each experiment. The most successful control methods were growing wheat after a brassica break crop or a long fallow. Both methods gave 72% yield increases over wheat growing after wheat. None of the other methods gave consistent, significant, or profitable yield increases or disease control. The mean yield increases in the year of application were 8% for the fungicide, 6% for microbial antagonists, 4% for chloride, and 7% for fumigation. The probable reason that fungicide and microbial antagonists were ineffective was that they were localised in the furrow where they were applied, whereas roots became infected in the inter-row space. Probable reasons that chloride was ineffective were that the background soil chloride levels were generally above the responsive range, and that roots became infected with take-all after the chloride was leached from the topsoil. The limitation of fumigation was that it suppressed natural antagonists of the Ggt, apparently leading to reinfection at higher levels than before. There was also evidence of Ggt re-infection in the second year after break crops, leading to an apparent ‘boomerang’ effect. Take-all inocula at the sites were measured in pre-sowing soil bioassays, whereas disease incidence was determined in seedlings and as ‘whiteheads’ as crops approached maturity. The only consistent pattern among the measurements was low disease incidence after break crops and the long fallow. Otherwise, there were low correlations between the 3 sets of measurements, suggesting that environmental changes after the soil bioassay and seedling assessment played critical roles in the progress of the disease.