Information linking seed movement, along with changes in seed viability, is critical for understanding weed seed dynamics. Studies were conducted to examine the use of passive integrated transponder (PIT) tags placed in nylon mesh packets in combination with GPS (Global Positioning System) technology to track weed seed movement after tillage. Cylindrical PIT tags 11.5, 12, 20, and 23 mm long by 2 mm wide were evaluated in water and soil. Detection improved as tag size increased because of greater signal strength. Tags with the main axis oriented vertically were recovered at greater depths than when placed horizontally. Average detection depths for 12-mm PIT tags were 29.5 cm in water, 18.2 cm in sand, 24 cm in artificial soil, and 21.2 cm in sandy loam soil. Tests also showed that PIT tags and nylon mesh packets were resilient to intense tillage with a rototiller. No significant differences in displacement because of tillage were observed between free PIT tags and PIT-tagged packets. PIT tag performance was further tested in a 2-yr field experiment conducted between September 2003 and October 2005 at six sites in Nebraska and Wyoming. Tilled and no-till blocks were established at each site. PIT-tagged packets in the tilled block and untagged packets in the no-till block were used. Sample burial depths were 0, 2.5, 7.5, and 15 cm. Sample recovery rate did not differ between tilled and no-till blocks. Time of recovery was the main factor affecting recovery of packets buried at 0 and 2.5 cm in both blocks. Seed predation by small rodents and movement of samples beyond the area of study by tillage implements were the main sources of packet loss. Nevertheless, 2 yr after initiation of the study, more than 85% of the samples were recovered. Future development of PIT tag technology will lead to an enhanced ability to monitor seed movement.
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Vol. 24 • No. 3