EFFECT OF SPECIES AND PROPORTION OF LEGUME ON HERBAGE YIELD AND NITROGEN CONCENTRATION OF LEGUME GRASS MIXTURES

This study evaluated the relationships between legume proportion and dry matter (DM) yield, N yield, and herbage N concentration for three binary legume‐grass mixtures In Uruguay. Two identical trials were established, one in 1983 (Trial 1) and another in 1984 (Trial 2) and were evaluated for 2 years. Treatments were white clover (Trifolium repens L.) (WC), red clover (Trifolium pratense L.) (RC), and birds‐foot trefoil (Lotus corniculatus L.) (BT), each grown with tall fescue (Festuca arundinacea Schreb.) (TF) at four legume proportions, plus pure stands of TF. In Trial 1, annual DM yields of RC‐TF were greater than yields of WC‐TF or BT‐TF and in Trial 2 RC‐TF and BT‐TF yielded more than WC‐TF. The N concentration of either the legume or TF components usually was greater for WC‐TF than other mixtures in both trials. Annual DM yields in Trial 1 were optimized by legume proportions of 47 to 59% for WC, 62 to 67% for RC‐TF, and 57 to 100% for BT‐TF; and N yields were optimized by 70% of WC or RC, and by 100% BT. In Trial 2, which had greater soil‐N availability than Trial 1, optimum DM or N yields were achieved at lower WC proportions than in Trial 1. Changes in legume proportion did not affect legume N concentrations, but N concentration of TF in mixture was always positively and linearly related with legume proportion. It is concluded that DM yields for the first 2 years after seeding were greater for RC‐TF and BT‐TF than for WC‐based mixtures. Herbage DM and N yields of WC‐TF were optimized by lower legume proportions than for RC‐TF and BT‐TF. The N concentration of TF increased linearly with increasing proportions of any of the three legumes. Copyright © 1990, Wiley Blackwell. All rights reserved