|MILLER, STEPHEN - UNIVERSITY OF WYOMING
|JONES, ORDIE - COLLABORATOR, USDA-ARS
Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/1999
Publication Date: N/A
Interpretive Summary: Weeds are a problem on most farms and they must be controlled to obtain good crop yields. To plan an effective weed control program, producers must know which weeds are present and are most likely to cause a problem. We took soil samples from field plots where dryland grain sorghum and winter wheat were grown for 12 years using no-tillage and stubble mulch tillage in several cropping systems. Seed was separated from soil by a special procedure and live seed was counted under a microscope. Seed of 12 weeds was present, with those of redroot pigweed being present in greatest numbers (50 per pound of soil). Tillage method, cropping system, crop rotation phase, and soil depth did not affect the number of pigweed seed in the samples. Seed numbers for common purslane, witchgrass, large crabgrass, green foxtail, Japanese brome, and Johnsongrass were different in some cases. Of these weeds, purslane was most common. Seed numbers for rhairy nightshade, Russian thistle, kochia, grain sorghum, and winter wheat were small (average less than 0.1 per pound of soil), and were not affected by tillage method, cropping system, rotation phase, or soil depth. Most weed seed was near the soil surface with both tillage methods, but tillage caused no consistent trends in seed numbers. Seed numbers for some weeds also were different due to cropping system and rotation phase. Except for pigweed and purslane, numbers generally were low, but enough seed was present in most cases so that a weed problem could occur, especially when the same crop is grown on the same land each year. When a weed problem occurs, this study shows that it can be reduced by using a rotation of a winter and a summer crop. By using such rotation, the problem weed can be controlled with tillage and/or herbicides when a crop is not growing.
Technical Abstract: Successful crop production depends, to a large extent, on effective weed control, which, in turn, depends on a knowledge of potential weed problems so that effective control measures can be planned and implemented. We determined weed seed banks after 12 years of dryland cropping with winter wheat and grain sorghum under different tillage methods and cropping sequences. Seed was separated from soil by an elutriation procedure and viable seed was counted under a microscope. Seed of 12 weeds was detected. Most abundant was redroot pigweed (113 seeds/kg of soil), but differences due to tillage, cropping system, rotation phase, or soil depth were not significant. Common purslane, witchgrass, large crabgrass, green foxtail, Japanese brome, and Johnsongrass seed numbers differed due to one or more of the above factors. Of these weeds, common purslane was most abundant. Seed numbers for hairy nightshade, Russian thistle, kochia, grain sorghum, and winter wheat were small (less than or equal to 0.107 seed/kg) and not significantly different. Most weed seed was near the surface with both tillage methods (no- and stubble mulch tillage), but tillage methods resulted in no consistent trends for all weeds. Some differences due to cropping systems and rotation phases were significant also. Except for pigweed and purslane, seed numbers generally were low, but adequate seed was present in most cases to cause a problem if proper control measures were not used, especially with continuous cropping. When a weed problem occurs, this study indicates it can be reduced by growing a winter and a summer crop in rotation, which permits controlling weeds with tillage and/or herbicides when a crop is not growing.