Modeling of wheat imbibition and germination as influenced by soil physical properties

A theoretical model that was used previously for predicting maize (Zea mays L.) seed imbibition, and subsequently, germination, is applied to wheat (Triticum aestivum L.) seeds. The proposed model takes into account the seed-soil water movements in both liquid and vapor phases under nonlimiting aeration conditions. The main variables that govern the imbibition process are (i) the seed-soil water potential difference, (ii) the seed contact area as affected by vapor or liquid transfers, and (iii) conductive properties of the seed for both liquid and vapor phases. Laboratory experiments show that (i) the imbibition process occurs both in liquid and vapor phases, (ii) wheat seed must reach a critical moisture content before germination (0.27 kg kg-1 approximately), and (iii) the rate of the imbibition depends upon the seed surface area affected by liquid or vapor transfers and on the water potential of the external medium that governs the ability of the seed to reach its critical moisture content. The proposed model is regarded as satisfactory after calibration of the seed conductive properties in liquid and vapor phases. Field experiments involved irrigated and nonirrigated treatments (31.7% clay, 42.5% loam, 25.8% sand) and manual or mechanical sowing. Moisture content, bulk density profiles, and soil porosity analyses were used to estimate the seed-soil contact area. The previous imbibition model was applied to field experiments, combining field data with the laboratory results. This model accurately predicted wheat imbibition and germination. Finally, simulated results compared the effects of climatic conditions and sowing techniques on wheat germination for three climatic sequences. Climate was the major limiting factor illustrating the importance of selecting the suitable sowing techniques to optimize the seed imbibition and germination processes.