Weed competition below ground: Three year study

Authors: BARROSO, JUDIT - Oregon State University; Wuest, Stewart; OREJA, FERNANDO - Oregon State University

Submitted to: Científica: Revista de Ciências Agrárias
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: In the semi-arid region of the inland Pacific Northwest (PNW), Russian thistle (Salsola tragus), kochia (Bassia scoparia), and prickly lettuce (Lactuca serriola) are three important weed species that can regrow after harvest and use water. In a 3-yr field study at the Columbia Basin Agricultural Research Center at Adams, Oregon, individual Russian thistle, kochia, prickly lettuce and spring wheat plants were grown in fallow fields to measure the amount and depth of water use. The soil under a single Russian thistle or kochia plant lost 0.04 kg water/ kg soil compared to the soil without plants and the soil under a prickly lettuce or spring wheat was 0.028 kg water/kg soil and 0.008 kg water/kg soil drier than soil without plants, respectively. In general, these differences were less in the top 60 cm of soil and greater in the deeper soil profile. Russian thistle and kochia roots dried deeper soil more than prickly lettuce and spring wheat.

Technical Abstract: In the semi-arid region of the inland Pacific Northwest (PNW), Russian thistle (Salsola tragus), kochia (Bassia scoparia), and prickly lettuce (Lactuca serriola) are three important weed species that can regrow after harvest and use water. However, the way in which these species compete for soil water, the most limited resource, has not been explored adequately. In a 3-yr field study at the Columbia Basin Agricultural Research Center in Adams, Oregon, individual Russian thistle, kochia, prickly lettuce and spring wheat plants were grown in fallow fields separated 4 m from each other. The experiment was a ramdomized complete block design with five replications. Soil samples, 150 cm deep, were taken at seeding time, wheat harvest time, and when the plants were about to die (early October). The results varied depending on the annual precipitation and plant biomass, but on average, the soil under a single Russian thistle and kochia plant was 0.045 kg water/kg soil drier than the control (soil without any plant), and the soil under a prickly lettuce and spring wheat plant was 0.028 kg water/kg soil and 0.008 kg water/kg soil drier than the control, respectively. In general, these differences increased for the top 60 cm of soil and decreased for the deeper soil profile. Russian thistle and kochia roots dried the soil deeper than prickly lettuce and spring wheat.