Leaf Area, Dry‐Matter Accumulation, and Carbohydrate Reserves of Alfalfa and Birdsfoot Trefoil Under a Three‐cut Management1

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Abstract
‘Vernal’ alfalfa (Medicago sativa L.) and ‘Empire’ birdsfoot trefoil (Lotus corniculatus L.) were grown in the field in pure stands and cut three tinies before September 1. Alfalfa accumulated leaf area and dry matter (DM) more rapidly than trefoil during spring growth. After the first and second cuttings, leaf area initially accumulated more rapidly in alfalfa than in trefoil; but, by the third or fourth week, the leaf area index (LAI) values of trefoil exceeded those of alfalfa.No consistent differences were found in mean net assimilation rate between the species. The greater LAI developed by trefoil was the main factor in the higher mean crop rates of trefoil compared with alfalfa after the first and second cuttings.Residual leaf area remained on the trefoil stubble after the first two cuttings and may have contributed to the recovery. No residual leaf area remained on the trefoil stubble after the third cutting, and regrowth was initially slow. Trefoil increased leaf area rapidly and accumulated more aboveground DM than alfalfa during regrowth after the first and second cuttings.The total nonstructural carbohydrate (TNC) levels alfalfa roots followed the characteristic depletion and accumulation cycles during all regrowths. Even though alfalfa was at 14% bloom at the second cutting, TNC levels had not been restored to the levels present at the time of first cutting when it was at 10% bloom. In contrast to alfalfa, trefoil root TNC levels declined during spring growth and remained at very low levels until late summer. The LAI values required to initiate net accumulation of TNC in alfalfa roots were 2.4 for spring growth and 1.6, 0.8, and 1.8 for regrowth after the first, second, and third cuttings, respectively.

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