Management Systems for Biannual Seed Crop of Italian Ryegrass (Lolium multiflorum Lam.) Grown at Various Nitrogen Fertilization: II. Second-Production Year Characterized by Considerable Crop Lodging and Limited Seed Shattering before Direct Combine-Harvesting

Abstract

Multiyear production of Italian ryegrass seed crop is of interest. The impact of management systems on the second-production year of biannual crop was evaluated at various nitrogen fertilization (0, 60, 120, and 180 kg ha−1). Management systems of single-purpose crops were with (SeedPGR-crop) and without (Seed-crop) plant growth regulator (PGR) application. The dual-purpose crops incorporated early (EF-seed-crop) and late (LF-seed-crop) spring forage cut followed by seed harvest. The Seed-crop obtained a maximum yield (1631 kg ha−1) at 120 kg N ha−1, which decreased by 23% at the highest fertilization. This yield loss was associated with early (before heading) and severe lodging that brought about reduced aboveground biomass and lower harvest index due to the increased growth of vegetative tillers. The single-purpose crops had a similar number of reproductive tillers, seed weight, and seed shed; however, the SeedPGR-crops produced larger yields than the Seed-crops at all fertilization levels indicating the positive impact of PGR application on harvest index regardless of lodging intensity. Despite less lodging and lower seed shattering, the dual-purpose crops yielded less than the single-purpose crops primarily due to the reduction in the number of spikelets per ear and florets per spikelet in various ear sections of early- and late-formed ears. Seed yields of the dual-purpose crops were maximized (around 1200 kg ha−1) at 180 kg N ha−1. The LF-seed-crop had the lightest seeds and the smallest seed germination, but fertilization tended to improve these quality traits. The SeedPGR-crop was the best performing management system yielding above 2200 kg ha−1 at the two highest N levels, allowing greater flexibility in fertilization.