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3 March 2020 Nitrogen release from shoots and roots of crimson clover, hairy vetch, and red clover
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Nitrogen (N) release from legume cover crops is a key N source for subsequent crops in rotation. In this study, chopped fresh shoots or roots (<5 mm) of crimson clover (CC), hairy vetch (HV), and red clover (RC) were incorporated into a 50:50 mixture of air-dried sandy loam soil (<2 mm) and washed builders sand at a rate of 300 mg N kg-1. The mixtures were packed in leaching tubes (four replicates), leached with 100 mL of 5 mmol L-1 CaCl2, and then incubated for 10 wk (22 °C, 0.33 bar matric potential) with weekly leaching. Total N and inorganic N (NH4+ plus NO3-) in leachate were quantified and organic N was determined as the difference between total N and inorganic N. More N was released from shoots (63.4%–70.0% of initial N) than from roots (27.3%–50.7% of initial N). Mineralized organic N and inorganic N followed the first order, single N-pool mineralization model [Nt = N0(1 – e-kt); R2 = 0.94-0.99]. Potentially mineralizable N (N0, as % of initial N) was similar for shoots (CC = 75.1%, HV = 74.2%, and RC = 71.3%), but varied for roots (CC = 36.2%, HV = 52.6%, and RC = 53.0%). The N0 pool in shoots had a half-life (t1/2 = ln 2/k) of 11.0, 9.8, and 15.1 d for CC, HV, and RC, respectively; and a half-life in roots of 23.9, 8.5, and 25.7 d, respectively. Hence, HV released its stored N in both roots and shoots faster than CC and RC. The results in this study would help farmers optimize their choice in legume cover crops and termination times to better synchronize N release with crop uptake.

© Her Majesty the Queen in right of Canada 2020. Permission for reuse (free in most cases) can be obtained from RightsLink.
X.M. Yang, C.F. Drury, W.D. Reynolds, and L.A. Phillips "Nitrogen release from shoots and roots of crimson clover, hairy vetch, and red clover," Canadian Journal of Soil Science 100(3), 179-188, (3 March 2020).
Received: 10 December 2019; Accepted: 24 February 2020; Published: 3 March 2020

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