Modeling the Emergence of Winter Wheat in Response to Soil Temperature, Water Potential, and Planting Depth

Abstract. Seedling emergence is a critical stage in wheat (Triticum aestivum L.) establishment, particularly in dryland agriculture. Soil temperature, water potential, and planting depth are important factors influencing emergence. These factors can have considerable spatio-temporal variation, making it difficult to predict the timing and percentage of wheat seedling emergence. Our objectives were to: (1) measure the effect of soil temperature, water potential, and planting depth on seedling emergence of winter wheat; and (2) develop a population-based hydrothermal model to estimate time and percentage of winter wheat emergence planted at a given soil depth. The experiment was a 3 (wheat cultivars) × 3 (planting depths) × 5 (temperatures) × 5 (water potentials) factorial in a randomized complete block design (RCBD) with three replicates. Decreasing soil water potential from 0 to -1 MPa delayed emergence of Moro, Buchanan, and Rod by 13, 14, and 18 days after planting and prolonged the time to reach maximum emergence by 19, 21, and 27 days after planting, respectively. Decreasing soil temperature from 25°C to 5°C delayed the average starting emergence of the three wheat cultivars by 19 days and delayed their average maximum emergence by 25 days after planting. Increasing soil planting depth from 5 to 10 cm delayed starting emergence time for Moro, Buchanan, and Rod by 6, 4, and 7 days, while maximum emergence was delayed by 12, 16, and 9 days after planting, respectively. Increasing the planting depth from 5 to 15 cm hindered the three cultivars from reaching 50% emergence. A hydrothermal time emergence model was developed that estimated observed emergence with 154 out of 207 data points having a root mean square error (RMSE) of ≤15%, whereas 19% of the simulated results did not exceed 19% RMSE and only 7% of the simulated data had RMSE greater than 20%. The simulations of the emergence model for maximum percent seedling emergence (E_max) and number of days after planting to reach maximum emergence (DAP_max) were compared with field data for three years and two cultivars (Rod and Moro). The emergence model gave reasonably good simulations of E_max and DAP_max for both winter wheat cultivars and in the three years of sowing dates.