Submitted to: Agricultural Economics Review
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2003
Publication Date: 1/30/2004
Citation: Young, D.L., Kwon, T., Young, F.L. 2004. Downsizing an agricultural field experiment alters economic results: a case study. Agricultural Economics Review. 26:255-265. Interpretive Summary: Jointed goatgrass, a winter annual grass weed continues to be a problem in winter wheat because herbicides are not available to selectively control this weed in the growing crop. Jointed goatgrass also has several traits that enable it to compete successfully with a winter wheat crop. Presently, growers are limited to cultural methods such as planting spring crops for several years, burning stubble after harvest, fertilizer placement, planting geometry, and delayed seeding in the fall to manage jointed goatgrass. Of these practices, planting spring crops is most often recommended, however, growers and scientists have both noticed that jointed goatgrass is sometimes present in spring planted cereals. A study was conducted at three locations each with four spring wheat planting dates to determine the effects of spring establishment date on jointed goatgrass seed production and spring wheat yield. At the earliest seeding date at all three locations, jointed goatgrass produced spikes, spikelets, and viable seed. Generally, viable seed was not produced the last two spring wheat seeding dates. Spring wheat yield was not affected by weed competition, however, delaying spring wheat seeding 4 wk after optimum seeding date reduced wheat yield up to 51%. Planting spring wheat in lieu of winter wheat is not a 100% guarantee to eliminate jointed goatgrass seed production.
Technical Abstract: The most common strategy recommended for management of jointed goatgrass infestations is to rotate from winter wheat to a spring crop for several years. A field study was conducted at three locations in 1998 and 1999 to determine the effects of spring establishment timing on the ability of jointed goatgrass to flower and produce fertile seed in the presence or absence of spring wheat. The effect of jointed goatgrass competition and crop seeding date on spring wheat grain yield was also evaluated. Spring wheat was seeded on four dates at each location in both hand-sown and natural jointed goatgrass infestations. Jointed goatgrass plants established from hand-sown spikelets flowered and developed spikelets at all seeding dates except the last seeding date. Viable seed were produced at the two earliest seeding dates. Jointed goatgrass plant density from natural infestations was 1 to 12 plants m-2 and spikelet production ranged from 3 to 480 spikelets m-2. Natural jointed goatgrass infestations produced spikelets containing fertile seed on all seeding dates at Lind in 1998, the driest location. Spring wheat yield was not affected by jointed goatgrass competition, however jointed goatgrass spikelet production was reduced by spring wheat competition. The last seeding of spring wheat reduced crop yield up to 51% compared to optimum seeding dates. The decision to manage jointed goatgrass infestations with a spring crop rotation should consider delayed seeding dates to minimize viable spikelet production by spring emergent jointed goatgrass, however, the cost of this decision may be realized in grain yield reduction.