Yield and Quality of RS-2, a Quackgrass X Bluebunch Wheatgrass Hybrid

Abstract

Understanding the effect of defoliation frequency and N fertilization on plant growth, forage yield, and quality of RS-2, a quackgrass [Elytrigia repens (L.) Nevski.] x bluebunch wheat grass [Pseudoroegneria spicata (Pursh.) Love] hybrid, will help promote efficient use of this hybrid in livestock production systems. Plants were fertilized with 0, 112, or 224 kg N ha-1 in spring 1988 and 1989, or with a 112 + 112 kg N ha-1 split in spring and summer. One set of plants was unmowed or mowed to a 5cm stubble height once in July or August in 1988 and another set was mowed initially in May, June, July, August, September, or October 1989 and monthly thereafter through October. Peak standing crop of unmowed plants was 3,470 kg ha-1 in 1988 and 5,850 kg ha-1 in 1989. In 1989 yields of fertilized plants exceeded those of unfertilized plants by 1,000 kg ha-1. In 1988, crude protein exceeded 12% in unmowed forage and in 1989 varied from 20% in May to 8% in August. After fertilization, crude protein was increased by 2 to 4 percentage units in 1988 and by 2 percentage units in 1989, but fertilization had no effect on in vitro digestible organic matter. Regrowth contained more crude protein (15-22%) and digestible organic matter (29-40%) than unmowed forage. Sequential harvesting enhanced quality of regrowth, but standing crops did not exceed 350 kg ha-1; except in June 1989. Sixty percent of the accumulated yield was harvested with the first mowing during May through August. Plots harvested initially in September and October were only harvested once. Our findings indicate an increase in forage yield potential and forage quality of RS-2 after harvesting and fertilizing the RS-2 hybrid.