WATER ABSORPTION BY SWELLING LEGUMINOUS SEEDS AS AFFECTED BY WATER POTENTIAL AND EXTERNAL MECHANICAL CONSTRAINTS

Abstract

The Collis-George/Melville model of water uptake by swelling seeds was used to determine the diffusivity to water of pea, chickpea and vetch seeds as affected by external solution and water potential. These values were compared with the Hadas/Russo results for the same seeds. Soil density changes at the seed-soil contact interface were calculated and the approximate pressures exerted on the soil by the swelling seeds were evaluated from consolidation test data for the sand and silty soils used in the experiments. Seed diffusivity to water according to the Collis-George/Melville model was in close agreement with the Hadas/Russo data only for the later part of the imbibition process when the seeds are fully imbibed or nearly so. The non-swelling Hadas/Russo model cannot be expected to yield accurate values at low seed moisture contents. The Collis-George/Melville model failed to yield consistent values for vetch seeds due to their partially impermeable seed coat. As expected, the calculated diffusivities to water of the seeds decrease as the external potential becomes more negative. Due to soil compaction during the imbibition process, the volume of the germinating seeds was smaller than that of free-swelling seeds under the same external water potential conditions. Soil mechanical constraints and water stress caused delayed germination but did not affect final germination. Their specific effects could not be differentiated under the present experimental conditions.