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 (¹⁵N/¹³C 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 mM 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 ml) as much N. Control patches were added as 1 ml 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 1ml) than in all other treatments. The response of roots and micro-organisms in relation to N capture is discussed.Key words: Lolium perenne, L-lysine patches, N capture, microbial activity, decomposition.