Contribution of hay harvest losses and "leaf fall" to N cycling and the N nutrition of intercropped alfalfa and bromegrass
van Kessel, C.
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A significant amount of forage plant biomass is deposited on the ground as senescent leaves, petioles and flowers (leaf fall). In addition, a varying amount of plant biomass is lost during harvest of hay crops (hay loss). These two sources of plant biomass and nitrogen (N) were quantified over a 3-year period in replicated plots of single or inter-cropped alfalfa (Medicago sativa cv. Beaver) and meadow bromegrass (Bromus riparius Rhem. cv. Fleet) swards grown under irrigation near Outlook. Another experiment in the same field provided an estimate of the quantity of N in the hay losses or leaf fall that was recycled between or within the two species. Alfalfa plants grown on 15N-enriched soil supplied 15N-labelled leaf fall and hay loss biomass which was applied to inter-cropped swards. The proportion15of N taken up by bromegrass or alfalfa was estimated. Similarly, N labelled bromegrass biomass was applied to inter-cropped swards and the uptake by each of the species was estimated. Leaf fall from alfalfa, bromegrass or alfafa+bromegrass swards contained an average of 22, 6, and 16 kg N ha-1 yea-1, respectively, whereas hay losses returned an average of 26, 9, and 22 kg N ha-1 year-1, respectively. The accumulation of 15N from those two N sources was detected in neighbouring plants as early as 13 days following application of the simulated leaf fall or hay losses.
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