Accumulation of grain nitrogen was studied in the wheat cultivars Argentine IX and Insignia. The pattern of nitrogen removal from several tissues of each cultivar was compared with the pattern of acid proteinase activity. There was a highly significant relation between the rate of nitrogen loss from the tissues and the rate estimated from the enzyme activity measurements. This suggests an important role for acid proteinase enzymes in leaf senescence. Redistribution of nitrogen present in the plant at anthesis accounted for 78.5 and 80.6 % of the final grain nitrogen yield of Argentine IX and Insignia respectively.

The seasonal patterns of leaf nitrate reductase activity were compared in five wheat cultivars which differ widely in their capacities to accumulate grain nitrogen. Significant differences in the average levels of nitrate reductase activity were observed between cultivars. Total seasonal nitrate reductase activity was closely related to total plant nitrogen at maturity. Grain nitrogen was only related to total seasonal nitrate reductase activity when allowance was made for significant differences between cultivars in nitrogen redistribution patterns. The significance of these results with respect to the possible use of nitrate reductase activity levels as a selection criterion for nitrogen productivity is discussed.

The effects of soil fumigation (98% methyl bromide + 2% chloropicrin at 580 kg/ha) and N fertilizer (0, 12.5, 25, 50 or 100 kg N/ha) were examined in field trials on continuous wheat and wheat in rotation with lupins on the Geraldton sandplain. Fumigation increased grain yields at N fertilizer levels more or =25 kg/ha and was associated with reduced incidence and severity of common root rot (Bipolaris sorokiniana)[Cochliobolus sativus]. Grain yield was not significantly affected by rotation. Fumigation increased soil ammonium levels and decreased soil nitrate levels. Rotation of wheat and lupins increased mid-season growth at all levels of applied N but only increased grain yield where no N was applied.

Subterranean clover plants were grown in a glasshouse with sub-irrigation from water tables maintained at depths of 0.30 m, 0.60 m, and 0.90 m. The depth of water table had little effect on the weights of the above-ground parts; there was a non-significant trend towards greater weights with deeper water tables. However, there were striking effects of treatment on root growth. Active root extension occurred while soil moisture content of the soil was between about 25 and 15%. With the deeper water tables, the zones of active root growth moved downwards as the soils dried out, i.e. out of the zones where, through increasing plant intake of water, demand exceeded supply from the water table. By the third harvest (about flowering time of the clover plants) the greatest root density with all treatments was between 0.20 m and 0.30 m above the water table. For the soil type used, this was apparently the height above the water table at which plant intake and upward movement of water from the water table were in equilibrium.