Contribution of initial C and N reserves in Medicago sativa recovering from defoliation: impact of cutting height and residual leaf area

Abstract

We studied the effects of stubble carbon / nitrogen (C / N) reserves or residual leaf area (RLA) on the contribution of taproot C / N reserves to shoot regrowth of Medicago sativa L. after cutting. The study assessed the effects of two cutting heights (6 and 15 cm), two RLAs (0 or 100%), and two initial C / N reserve levels (high N or low N) on forage production, nitrogen (N) distribution, and C / N reserve dynamics within stubble and taproot. Alfalfa forage production was mainly affected by the initial taproot C / N reserve levels. However, stubble initial organic reserves (and to a lesser extent the RLA) were also of particular importance during early regrowth. The increase of cutting height led to increased stubble C / N supply to regrowing shoots, which partly offset the negative effect on forage production and on taproot C / N reserve depletion. Unlike taproot reserves, the positive contribution of stubble organic reserves to shoot C / N supply was effective for a single defoliation–regrowth cycle. Alfalfa management strategies that increase cutting height (and RLA) during the penultimate harvest in autumn should be considered in cold regions with significant winter stress in order to improve alfalfa winter survival and persistence, as well as spring herbage regrowth.