INFLUENCE OF WEED CONTROL AND N FERTILIZATION AT ESTABLISHMENT ON GROWTH AND NODULATION OF BIRDSFOOT TREFOIL

Abstract

Leo birdsfoot trefoil (Lotus corniculatus L.) was established on check (no weed control), handweeded, and 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB)-2,2-dichloroproprionic acid (dalapon)-treated plots with N applied at 0, 25, 50, or 100 kg/ha as NH4NO3 at the emergence of forage legume. The preceding crops were barley (Hordeum vulgare L.) and timothy (Phleum pratense L.) in locations 1 (soil OM 3.4%) and 2 (soil OM 3.8%), respectively. In the year of seeding, N. applications increased dry matter (DM) yields of birdsfoot trefoil up to 115% over zero N treatment in location 1. Similarly, the growth of weeds was increased up to 69% applied N in location 1. In location 2, applied N did not influence the growth of birdsfoot trefoil and weeds. A 2,4-DB-dalapon treatment in both locations controlled the weeds, but it also suppressed the growth of birdsfoot trefoil. The mean number of birdsfoot trefoil plants/m2 in location 1 was decreased both by N fertilization and by 2,4-DB-dalapon treatment. The growth of birdsfoot trefoil in the 2nd yr was not influenced by N fertilizer applied at establishment. Heavy weed growth in location 2 during the 1st yr resulted in low DM yields of birdsfoot trefoil the following year. Nodulation of birdsfoot trefoil was promoted in location 1 by small N applications (25 kg/ha). In location 2, nodulation was reduced by fertilizer N, as compared to zero N treatment. Treatment with 2,4-DB-dalapon caused some reduction in the nodulation of birdsfoot trefoil as compared to check or handweeded plots in location 1. It is concluded that applied N may improve the early growth of birdsfoot trefoil only where soil N level is low and almost no weeds are present.