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Nitrogen Cycling in an Alfalfa and Bromegrass Sward via Litterfall and Harvest Losses
Author(s) -
Tomm Gilberto O.,
Walley Frances L.,
Kessel Chris,
Slinkard Alfred E.
Publication year - 1995
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1995.00021962008700060008x
Subject(s) - agronomy , medicago sativa , plant litter , bromus , bromus inermis , nitrogen , biology , chemistry , poaceae , nutrient , ecology , organic chemistry
Belowground transfer of N from legumes to associated grasses has been extensively documented; however, transfer of N via decomposition of plant material and reabsorption of released N remains poorly understood. This study was conducted to (i) assess the intensity of litterfall and harvest losses of alfalfa ( Medicago sativa L.) and meadow bromegrass ( Bromus riparius Rhem.) under field conditions and (ii) determine the quantity of N transferred from aboveground plant components. Litterfall and harvest losses were quantified over 3 yr. Nitrogen transfer was estimated using the 15 N isotope dilution technique. The return of N to the soil via litterfall losses of alfalfa and bromegrass was 13 and 4 kg N ha −1 yr −1 , respectively. Alfalfa returned an additional 15 kg N ha −1 yr −1 to the soil via harvest losses; bromegrass contributed an additional 7 kg N ha −1 yr −1 . Bromegrass remained a source of N to the N 2 ‐fixing alfalfa, even though it was N‐limited, and alfalfa successfully competed with the N‐stressed bromegrass for available N derived from litterfall and harvest losses. Alfalfa accumulated twice the amount of N from litterfall and harvest losses compared with bromegrass (2 vs. 1 kg N ha −1 yr −1 ). Clearly, alfalfa was a strong competitor for available N and acted as both a source and a strong sink for recycled N. The total amount of N transferred from alfalfa to bromegrass and vice versa via decomposition of aboveground plant components was found to be remarkably similar (≈ 1 kg N ha −1 yr −1 ). Therefore, the net flow of N between alfalfa and bromegrass was negligible, and no net N contribution of alfalfa to associated bromegrass from the decomposition of litterfall and harvest losses was detected. We concluded that, although alfalfa released more N through the decomposition of litterfall and harvest losses than bromegrass, alfalfa also reabsorbed more recycled N. Published estimates of net N transfer between alfalfa and bromegrass, therefore, could not be explained by the input of N from litterfall and harvest losses.