Factors Affecting Yield in Thermal and Non-Thermal Dryland Bluegrass Seed Production Systems.

Factors influencing seed yield of dryland Kentucky bluegrass systems are poorly understood.  Prediction of yield could potentially limit over-application of fertilizers and help farmers decide when to remove a stand from production.  Potential factors contributing to yield include precipitation, amount of non-standing (thatch) residue, nitrogen uptake in above-ground biomass, plant-available nitrogen, and stand age.  Observations were made from 2002 to 2007 on plots located in northern Idaho.  Four treatments investigated include full load burn (FLB), bale and burn (BB), mechanical (M) (non-thermal), and system (S), a yearly-rotating treatment of FLB, BB, or M.  Our experimental design consisted of a randomized complete block with four blocks and a total of 16 plots.  Above-ground biomass and non-standing residue was measured in fall, spring, pre-swath, and post-treatment periods from a 0.25 m² quadrat.  Linear regression revealed that yields increased across all treatments as spring (March-May) precipitation increased (r=0.76).  As stand age increased yields declined on average 120 kg/ha/yr in FLB and 191 kg/ha/yr in M.  Yields across all treatments increased as %N in the fall above-ground biomass increased (r=0.75).  The amount of non-standing residue was inversely correlated (r=-0.73) to yield.  Factors related to yield at this site include stand age, spring precipitation, %N in fall above-ground biomass, and amount of fall non-standing residue.  Data obtained from this long-term study will be used to develop a yield prediction model for Kentucky bluegrass producers.