Nitrogen capture by plants grown in N-rich organic patches of contrasting size and strength

This study investigated the response of root proliferation plant N capture and soil microbial activity in a Lolium perenne sward to L-lysine (N-15/C-13 dual-labelled) patches of contrasting size and strength. Three patch treatments provided the same quantity (c. 5.6 mg) of N, but at different concentrations (i.e. 200 mM x 1 ml; 100 nM x 2 ml; 40 mM x 5 ml), while the other two treatments provided five times (1 M x 1 ml) or 0.2 (40 mM x 1 mi) as much N. control patches were added as 1 mi H2O. Root production and root mortality in the patch addition zone were! measured in situ using mini-rhizotron tubes and were! found to differ between the various treatments Instantaneous root birth rates were significantly (P < 0.05) greater in the highest N added patch (1 M x 1 ml) at day 14 only, indicating a more marked proliferation response in this treatment compared to those containing less N. However, of the total N available, roots in the 1 M x 1 ml L-lysine patch captured significantly (P < 0.05) less (29%) than in the other four treatments (40-47%), which did not differ significantly from each other. Microbial activity was significantly (P < 0.05) greater in the highest N added patch (1 M x 1 ml) than in all other treatments. The response of roots and micro-organisms in relation to N capture is discussed.