Runoff Weed Seed, Sediment, Infiltration and Weed Establishment as Affected by PAM in Furrow-Irrigated Corn
Table 3.   Seasonal Weed Seed Loss in Runoff (seeds ha-1)
Treatments Weed Seed Loss
PAM Herbicide 1997 1998
Mean SD Mean SD
No PAM Dual 2,312,466 817,363 3,450,989 1,191,928
Eradicane 3,880,329 1,443,608 3,590,129 3,181,630
None 1,768,564 505,343 1,621,754 1,086,615
Average 2,653,786 1,285,909 2,887,624 2,021,396
NRCS STD Dual 1,347,161 741,537 457,018 348,594
Eradicane 1,435,024 1,137,479 121,109 94,181
None 1,264,142 102,254 37,491 40,449
Average 1,348,776 684,853 205,206 264,546
Patch Dual 1,556,513 2,054,687 264,003 293,789
Eradicane 892,208 334,202 678,763 403,673
None 434,320 95,898 94,728 110,021
Average 961,014 1,150,844 345,831 364,780
Average Dual 1,738,713 1,246,320 1,390,670 1,673,882
Eradicane 2,069,187 1,665,163 1,463,333 2,275,146
None 1,155,675 639,658 584,658 950,915
Table 3.   Seasonal Weed Seed Loss in Runoff

In 1997 weed seed loss in runoff was reduced 49% for the NRCS standard PAM treatment and 64% for the patch application method.  In 1998 reductions were 88% and 93%.  Because there was a 30 to 40% increase in weed retention in 1998, despite similar sediment loss reductions across PAM treatments and years, it seems likely that PAM effects on weed seed loss are not simply tied to reductions in erosion (ie, excavation of weed seed from the soil weed seed bank).  Weed seed retention likely also relates to annual changes in the size and stratification of the weed seed bank in the soil and, possibly on the soil surface.  While the specific interactions are not yet completely understood, it is clear that PAM reduces weed seed migration from one point in the field to another, or from one field to another in runoff that is utilized for irrigation down stream.
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