Modeling wheat seedling growth and emergence. II. Comparison with field experiments

To improve the understanding and prediction of wheat (Triticum aestivum L.) emergence under dry conditions, a model describing wheat emergence in field conditions is presented. The proposed approach separates three basic processes from sowing to seedling emergence: (i) seed imbibition and germination, (II) root and seedling growth as influenced by soil water potential and temperature, and (iii) seedling emergence as affected by forces exerted by plant coleoptiles and soil surface structure. Previously developed models of each process were combined to predict seedling emergence. Field experiments consisting of irrigated and nonirrigated treatments and hand and mechanical seeding were used to validate the model. Model inputs included soil water content vs. time, mean air temperature (daily basis), dry bulk density, the soil water content/water potential relationship, and soil surface structure. Sensitivity analysis showed a high sensitivity of the model to geometrical characteristics (root and coleoptile tortuosities and root angle) of seedlings under field conditions. Model prediction of germination and emergence were generally satisfactory, although errors occurred after irrigation or rainfall. Discrepancies were explained by changes in the mechanical properties and increasing impedance of the soil surface after wetting and subsequent drying, or by changes in soil temperature after wetting. Finally, simulations of germination and emergence for three climatic conditions (wet, intermediate, and dry), two sowing techniques (hand and mechanical), and two soil surface structures (fine and coarse) demonstrated the effects of those factors on emergence. In the most favorable case, 95% emergence occurred 15 d after sowing. In the most unfavorable treatment, 41% emergence occurred affter 29 d.