Abstract

Uniform germination and subsequent emergence of seedlings is the first and probably the most important factor that could affect final yield of a crop. In order to better understand the impact of physical conditions in the soil, a closer look at the seed-soil interface is needed. Therefore, the objectives of this research were to correlate the germination and emergence of seedlings to the various soil physical edaphic factors, with a particular focus on the seed-soil interface.

Water transport to the seed during the imbibition stage of germination has been considered a critical process which determines the time for germination. Experiments were carried out in order to test certain hypotheses made, based on past literature, in a manner to track the water pathway to the seed from the surrounding soil. The seeds were germinated in a controlled environment. The factors that were controlled or varied in a predetermined manner were soil aggregate size, matric potential of the soil, soil bulk density and soil temperature. The area of contact between the soil aggregates and the seed was studied under a microscope. A new method was devised to measure the permeability of a seed coat.

Some of the important conclusions are: (1) The rate of water uptake by the MAR cotton seeds was unaffected by temperature in the range of 25 to 35$\sp\circ C$ but was found to be significantly lower at 15$\sp\circ C$ and 20$\sp\circ C$. (2) Microscopic study of the contact area between the seed and the soil revealed that there was an increase in contact area during the swelling of the seed. (3) Increasing isotropic pressure from 0 to 68 kPa on the soil in which the seeds were germinated caused the germination time to double. (4) Mean permeability for seed coats of germinated and ungerminated seeds was measured as 16.4 mg cm$\sp{-2}$ day$\sp{-1}$ bar$\sp{-1}$ and 12.3 mg cm$\sp{-2}$ day$\sp{-1}$ bar$\sp{-1}$ respectively. (5) A seedbed of mean aggregate diameters of 0.75 mm to 2.5 mm and matric potential of $-$2.0 to $-$0.1 bar would be good for obtaining a suitable emergence rate.