Nungarin, capeweed, and annual ryegrass were grown, in a glasshouse, in 5-L pots containing sand.
Capeweed shoots were separated into leaf, stem, and flower head (seed was removed).
Net [sup.15]N mineralisation of root residue N also continued over this period with an additional 5% of clover and 2% of capeweed root [sup.15]N being net mineralised between 7 June and 16 July (Table 5).
Using the combined recovery of applied [sup.15]N in soil mineral N and wheat shoots at the final sampling on 20 November 1991 as a measure of total net [sup.15]N mineralisation, total net [sup.15]N mineralisation during the 8-month experimental period was 15% for subterranean clover, 12% for capeweed, and 12% for annual ryegrass shoot residues (Table 4).
The final, total % recoveries of [sup.15]N for shoot residues were 93%, 92%, and 102%, respectively, for subterranean clover, capeweed, and annual ryegrass (Table 4).
The lignin and polyphenol contents were similar for the 3 shoot residues, and similar net [sup.15]N mineralisation occurred from both the capeweed and ryegrass shoots despite a large difference in the C to N ratio (Table 6).
For the shoot residues, the recoveries of [sup.15]N in wheat at wheat maturity (20 November 1991) were, respectively, 9%, 7%, and 7% of the [sup.15]N applied in the subterranean clover, capeweed, and annual ryegrass (Table 4).
The N contents of the mature shoots used in the studies reported here were within the range of N contents commonly observed in the field at pasture maturity (1.3-2.0% for subterranean clover, 1.3-1.7% for capeweed, and 0.6-0.8% for annual grasses; Rossiter 1966).
The smaller net N mineralisation from the capeweed and annual ryegrass shoots than from the subterranean clover shoots is consistent with the lower N contents and higher C to N ratios of these species.