Residue mulching shifts nitrogen-source partitioning from atmospheric to non-fixed N during red clover regrowth
Abstract
IntroductionBiological nitrogen fixation (BNF) introduces new nitrogen (N) into legume-based systems, whereas plant-residue mulching primarily recycles N already present within the production system. We investigated whether N returned as mulch supplements atmospheric N acquisition or substitutes for it during red-clover (Trifolium pratense L.) regrowth.MethodsFollowing the first cut, red clover received no N input (TP-0), mineral N as a readily available-N reference (TP-N), red-clover mulch (TP-T), or Italian ryegrass (Lolium multiflorum Lam.) mulch (TP-L), with three replicate pots per treatment. After 55 d of regrowth, the proportion of aboveground N derived from the atmosphere (pNdfa) was estimated using the ¹⁵N natural-abundance method with treatment-specific non-legume references.ResultsAboveground dry matter and total N showed no detectable treatment differences (p = 0.835 and p = 0.840, respectively). In contrast, pNdfa declined from 63.0% in TP-0 to 41.5% in TP-N, 18.7% in TP-T, and 14.8% in TP-L (p < 0.001). Fixed-N accumulation was 0.771, 0.529, 0.223, and 0.190 g N pot⁻¹, respectively, whereas non-fixed N increased from 0.459 to 0.745, 0.948, and 1.028 g N pot⁻¹. Thus, N addition altered the source composition of the aboveground N pool much more strongly than its total size.DiscussionUnder mulch, lower atmospheric-N contribution coincided with greater accumulation of non-fixed N without a detectable increase in total aboveground N. These findings provide quantitative evidence that residue return can shift short-term N-source partitioning in regrowing red clover, with greater reliance on non-fixed N coinciding with reduced reliance on newly fixed atmospheric N.
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BibTeX
@article{ghafoor2026residue,
title = {{Residue mulching shifts nitrogen-source partitioning from atmospheric to non-fixed N during red clover regrowth}},
author = {Abu Zar Ghafoor and Hassan Karim and Christopher Brock and Yongcheng Wu},
journal = {Frontiers in Plant Science},
year = {2026},
month = nov,
doi = {10.3389/fpls.2026.1970507},
url = {https://www.frontiersin.org/articles/10.3389/fpls.2026.1970507},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Residue mulching shifts nitrogen-source partitioning from atmospheric to non-fixed N during red clover regrowth
AU - Abu Zar Ghafoor
AU - Hassan Karim
AU - Christopher Brock
AU - Yongcheng Wu
PY - 2026
DA - 2026/11/06
JO - Frontiers in Plant Science
DO - 10.3389/fpls.2026.1970507
UR - https://www.frontiersin.org/articles/10.3389/fpls.2026.1970507
AB - IntroductionBiological nitrogen fixation (BNF) introduces new nitrogen (N) into legume-based systems, whereas plant-residue mulching primarily recycles N already present within the production system. We investigated whether N returned as mulch supplements atmospheric N acquisition or substitutes for it during red-clover (Trifolium pratense L.) regrowth.MethodsFollowing the first cut, red clover received no N input (TP-0), mineral N as a readily available-N reference (TP-N), red-clover mulch (TP-T), or Italian ryegrass (Lolium multiflorum Lam.) mulch (TP-L), with three replicate pots per treatment. After 55 d of regrowth, the proportion of aboveground N derived from the atmosphere (pNdfa) was estimated using the ¹⁵N natural-abundance method with treatment-specific non-legume references.ResultsAboveground dry matter and total N showed no detectable treatment differences (p = 0.835 and p = 0.840, respectively). In contrast, pNdfa declined from 63.0% in TP-0 to 41.5% in TP-N, 18.7% in TP-T, and 14.8% in TP-L (p < 0.001). Fixed-N accumulation was 0.771, 0.529, 0.223, and 0.190 g N pot⁻¹, respectively, whereas non-fixed N increased from 0.459 to 0.745, 0.948, and 1.028 g N pot⁻¹. Thus, N addition altered the source composition of the aboveground N pool much more strongly than its total size.DiscussionUnder mulch, lower atmospheric-N contribution coincided with greater accumulation of non-fixed N without a detectable increase in total aboveground N. These findings provide quantitative evidence that residue return can shift short-term N-source partitioning in regrowing red clover, with greater reliance on non-fixed N coinciding with reduced reliance on newly fixed atmospheric N.
SN - 1664-462X
ER -