Influence of Fertilizer and Residue Management on Grass Seed Production 1

Postharvest residue burning, a standard practice in grass seed production in the Pacific Northwest, may be restricted because of concerns for air quality. This research compares the effects of burning with those of mechanical residue removal on red fescue ( Festuca rubra L.), smooth bromegrass ( Bromus inermis Leyss.), and crested wheatgrass [ Agropyron desertorum (Fisch. ex Link.) Schult.]. The experiments were conducted on a silt loam soil (Pachi Ultic Haploxerolls) as a split‐plot within each grass species. Main plots were three levels of 18‐10‐10‐7 fertilizer applied to supply N at 90, 112. and 135 kg/ha, with an associated increase in P, K, and S. Main plots were split for open burning and two levels of mechanical residue removal. Two crops of red fescue and four seed crops of smooth bromegrass and crested wheatgrass were evaluated. Average seed yields (kg/ha) for burning compared with mechanical straw removal were 636 vs. 495 for red rescue, 1,122 vs. 848 for smooth bromegrass, and 872 vs. 790 for crested wheatgrass. Straw and stubble removal, compared with straw removal alone, increased seed yield of red rescue and smooth bromegrass, but decreased seed yield of crested wheatgrass. Interactions of fertilizer rates and residue management were not significant. Increasing the fertilizer rate did not compensate for the reduction in seed yield associated with mechanical removal of residue. Seed yields of smooth bromegrass and crested wheatgrass were increased by high fertilizer rates as the age of stand increased. The increase in seed production resulting from burning residue apparently was associated with control of downy bromegrass ( Bromus tectorum L.) and increased vigor of autumn regrowth. Diseases and insects were of little consequence and probably had little influence on seed yield in these experiments.