Modeling of field emergence pattern of three weed species in response to soil temperature and moisture

Abstract

Models that predict the timing of weed seedling emergence are used to optimize weed control schedules. This study was carried out with the aim to predict the time of seedling emergence of three weed species, namely, Datura stramonium, Solanum nigrum, and Amaranthus retroflexus in field conditions using soil temperature and moisture. Three planting dates including first of June, first of July, and first of August were studied with three irrigation regimes including every other two, three, and four days and with three weed species. To express the changes in the emergence process, hydrothermal time model () was used. MPa - °C - days required for the emergence was calculated with the base temperature and water potential that was calculated by hydrothermal time model and soil moisture and temperature. Cumulative emergence percentage was plotted with hydrothermal time model and the sigmoid three-parameter model was fitted on it. Then the maximum germination percentage and MPa - °C - days required for 50% seedling emergence was calculated. Results showed that seedling emergence of three weed species was the highest and lowest in the first regime of irrigation in August and third regime of irrigation in June, respectively. Three species seedlings were emerged higher and faster in August than in June and July. Hydrothermal time required for the seedling emergence of these species was varied. D. stramonium had the lowest and S. nigrum had the highest hydrothermal time for 50% seedling emergence. The optimum temperatures for A. retroflexus, S. nigrum, and D. stramonium were 30-35, 37-30, and 29-34 °C respectively in all water potentials.

Keywords

• sigmoid three-parameter model
• soil moisture
• soil temperature
• water potentials
• weed