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Retention of Nitrogen by a Nitrogen‐Loaded Scotch Pine Forest
Author(s) -
Johannisson C.,
Högberg P.,
Myrold D. D.
Publication year - 1999
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1999.03615995006300020017x
Subject(s) - lysimeter , leaching (pedology) , understory , nitrogen , nitrification , nutrient , chemistry , zoology , leachate , agronomy , environmental science , environmental chemistry , botany , soil water , biology , soil science , canopy , organic chemistry
The capacity of forests to store added N and how this excess N might interact with other nutrients is not well understood. We studied N retention in a Scotch pine ( Pinus sylvestris L.) forest that had received two decades of annual additions of N as NH 4 NO 3 at four rates (N0‐N3, equivalent to 0, 36, 72 and 108 kg N ha ‐1 yr ‐1 ), with and without supplementary additions of P and K. The highest N treatment (N3) was suspended three years before this study. Leaching of inorganic N was measured beneath lysimeters with and without living tree roots inside them, and the fate of 15 N injected into the mor layer was traced by sampling understory vegetation, soil to 20‐cm depth, and leachates. Leaching of inorganic N increased with increasing N dose and was dominated by NO ‐ 3 on plots to which N had been added. In the suspended N3 treatment, leaching of N was lower than in the N2 treatment. The presence of tree roots greatly reduced leaching of N. The occurrence of labeled NO ‐ 3 under lysimeters to which labeled NH + 4 had been added showed that nitrification was important in treatment N2, but not in N1, suggesting that additions of >30 kg N ha ‐1 yr ‐1 are needed to induce larger net nitrification at this site. Our data showed (i) that trees were an important sink for N, (ii) that additions of P and K had a marginal positive effect on N retention, and (iii) that leaching from previously N‐loaded forest rapidly decreased when the N load was removed.