Author
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Forcella, Frank |
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Submitted to: Seed Science Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/20/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Computer software called WeedCast was developed to simulate (1) weed seed dormancy, (2) timing of seedling emergence, and (3) seedling height growth using on-farm weather data. Weather data includes only daily rainfall and air temperatures. Air temperatures are converted to soil temperatures at 2" soil depth based on soil type, tillage system, and previous years' crop residue type. Daily rainfall and soil temperature estimates are combined to estimate soil water stress at the 2" depth. Daily estimated water stress or soil temperatures are used to predict dormancy in weed seeds. Soil growing degree days (GDD) are calculated from soil temperatures, and are used to forecast emergence times of weed seedlings. Emergence ceases on days when water stress falls below threshold values specific to each species. Lastly, GDD based on air temperatures are used to estimate seedling height growth. All three types of simulations provide information that allows farmers and crop consultants to answer important weed management questions. These types of questions include, but are not limited to, the following: (1) are soil-applied treatments necessary, (2) how late can preemergence herbicides be applied, (3) when should mechanical control be implemented, (4) when should field-scouting commence and end, and (5) when should postemergence herbicides be applied? Information supplied by WeedCast can help producers reduce costly chemical treatments, which is also beneficial to the environment. Technical Abstract: Computer software called WeedCast was developed to simulate weed seed dormancy, timing of seedling emergence, and seedling height growth in crop environments in real time and using actual or forecasted weather data. Weather data includes daily rainfall and minimum and maximum air temperatures. Air temperatures are converted to average daily soil temperature at 5 cm soil depths using a series of equations that are specific for soil type, tillage system, and previous years' crop residue type. Daily rainfall and soil temperature estimates are combined to determine soil water potential (MPa) at 5 cm depths. Daily estimated MPa or soil temperatures are matched to empirically-derived threshold values that induce secondary dormancy in seeds of certain species. Soil growing degree days (GDD), calculated from soil temperatures, are used to project maximum emergence rates of weed seedlings. Emergence ceases on days when MPa falls below threshold values specific to each species. GDD based on air temperatures are used to estimate postemergence seedling height growth. All three types of simulations provide information that allows users to answer important weed management questions in real time. These types of questions include, but are not limited to, the following: (1) are soil-applied treatments necessary, (2) how late can preemergence herbicides be applied, (3) when should mechanical control be implemented, (4) when should field-scouting commence and end, and (5) when should postemergence herbicides be applied? |
