Temporal fate of N-15 and C-14 leaf-fed to red and white clover in pure stand or mixture with grass - Implications for estimation of legume derived N in soil and companion species

• The supply of nitrogen (N) from legumes is a key in maintaining soil N fertility in plant production with low fertilizer N inputs. Leaf-feeding of isotope tracers is a commonly used methodology to study the flow of carbon (C) and N from legumes into soil and companion plants. Here we investigated the temporal fate of N-15 and C-14 fed as a single-pulse via leaves to red and white clover in pure stands and in mixtures with grass in order to investigate the suitability of leaf-labeling for estimation of rhizodeposition and N transfer. The N-15 was present in all sampled plant parts of the legumes, soil and companion ryegrass already at the first day after the end of the labeling period. Thereafter, tracer levels remained surprisingly constant especially in the legume root parts. The rapid appearance of N-15 in soil was most likely dominated by tracer in unrecovered root parts, whereas N-15 in companion ryegrass was most likely caused by root exudation. After the rapid phase of tracer translocation, a second slower phase was best described by tracer loss from shoot tissue (phyllodeposition), rather than turnover of root and nodules with time. We conclude that labeling studies with multiple pulses need intensive labeling schemes and greater temporal sampling resolution in order to avoid bias and determine dominating sources of tracer moving from legumes to companion species for N transfer estimation. The study also underlined the importance of identifying the dominating sources of legume C and N losses to soil in order to select the correct approach to estimate rhizo- and phyllodeposition.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Markvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Soil Science (hsv//eng)

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