The physical properties of seeds are very important to optimize the design parameters of various agricultural equipment used in their production, handling, and storage processes. Determination and use of these properties are also essential for the development of optimum seed metering mechanism and also in the design of a hopper for a planter for precise sowing of seeds. Physical properties such as length, surface area, breadth, roundness, equivalent diameter, sphericity, angle of repose, and coefficient of friction were determined for the development of the seed metering unit. The physical properties of seeds were calculated initially. Three varieties of maize seed Rasi-3033, NMH-589, and KMH-2589. The mean values of seed length, width, thickness, sphericity, geometric mean diameter, surface area, bulk density, coefficient of static friction, angle of repose, and thousand kernel weight were 11.00 mm, 7.75 mm, 4.58 mm, 0.65, 7.09 mm, 158.14 mm^{2}, 746.4 kg m^{-3}, 0.60, 28.17^{o} and 0.23 kg, respectively. These properties were used in the development of efficient planter components to work effectively.

Physical properties are essential in the development of planter components.

The angle of repose is increased with increasing the moisture content of the seeds.

Bulk density is important to design the volume of the seed hopper for the seed planter.

Three varieties of maize were selected for the study Rasi-3033, NMH-589, and KMH-2589 from a local market. Size, sphericity, thousand kernel weight, geometric mean diameter, surface area, bulk density, and angle of repose were measured in a laboratory. These properties were used in the development of efficient planter components to work effectively.

The seed size was determined by length (l), width (w), and thickness (t). Maize seed size is an essential parameter in designing the cell size on the seed metering mechanism. Vernier caliper was used to measure the axial and lateral dimensions of the seeds. Ten seeds were randomly selected, measuring the dimensions. The mean values have been estimated, and this value was used to design the metering mechanism. It was calculated by using the formula specified by (Mohensin 1970). It is shown in

Where

The geometric mean seed diameter was measured with seed dimensions. The geometric diameter was determined using the following relation.

Geometric mean diameter, _{g}^{1/3}, mm

Rasi-3033, NMH-539, KMH-2589 varieties of maize seeds

Sphericity is known as the ratio of the sphere’s diameter having the same volume as that of the particle and diameter of the smallest circumscribing sphere, or the largest particle diameter generally. This parameter indicates the shape character of maize seeds relative to the same volume of a sphere. The dimensions of 10 maize seeds at random were measured using digital vernier caliper to calculate the seed sphericity.

Measuring of seed dimensions by using vernier calipers

Measurement of angle of repose

An electronic weighing balance with a precision of 0.01 g was used to determine the weight of thousand seeds. A sample of 100 seeds was randomly selected and weighed to determine the mean weight of 1000 seeds. To minimize the errors, the procedure was replicated five times.

Angle of repose is an important parameter that helps in the design of the hopper of the planter. A box with a circular base was mounted in the funnel, and three adjustable screws were used to hold the platform horizontally. It was filled with maize seeds. The seed gate on the underside of the funnel was removed so that a conical heap was formed on the surface. Heap height and diameter were measured. The angle of repose was calculated using the following equation. It is shown in

Where

A measuring cylinder was used to calculate the bulk density. A 1000 cc capacity measuring cylinder was taken, and its weight was taken as _{1}. The seeds were filled up to the 1000 cc limit, and the cylinder was gently tapped, and weight was taking as _{2}. The difference between _{2} and _{1} was considered seed weight. Five replications were taken to minimize the error. Bulk density was calculated by using the following formula.

The porosity is the fraction of the space in the bulk seeds which is not occupied by the seeds (Mohensenin, 1986). The porosity of the samples was computed from the bulk and true densities using the following equation:

Where, ρ_{b} = bulk density, kg m^{-3} ρ_{t} = true density, kg m^{-3}

The total area covered around the seed is the surface area of the maize seed. It can be given by the following formula:

Where _{g}

Coefficient of static friction can be expressed in terms of the degree of the seed resistance to flow on a given surface. It is an important property to determine the angle at which the hopper development has to be done so that the constant flow of the seeds from the hopper to the seedbox is achieved. Coefficient of static friction is measured using the inclined plane method. The seeds were filled in a square box having dimensions 60 × 65 × 65 mm, and the box was placed on the surface to measure the static coefficient of friction, then the surface on which the box lies was raised with a screw device. The angle at which the box begins to slide was noted from the graduated scale on the apparatus. The coefficient of static friction was calculated as the tangent of an angle of inclination and is given by the following equation. It is shown in

Coefficient of static friction, µ = tan α

Where α = angle of inclination.

Measurement of coefficient of static friction

Major, intermediate and minor dimensions of the three maize verities are Rasi-3033, NMH-589, and KMH-2589 are given in the

Geometrical properties of selected varieties of maize seeds

Some properties of selected varieties of maize seeds

The average values of angle of repose for three maize seed varieties were 29.49^{0}, 30.20^{0,} and 29.54^{0}. Angle of repose is used to determine the slope of the seed hopper sidewalls to facilitate the free flow of maize seeds.

The bulk density of all four varieties were shown in ^{-3}. The variation in bulk density between the varieties was due to the difference in the individual weight of individual grain and particle distribution i.e, variation in the size among the variety.

The values for the coefficient of static friction for Rasi-3033, NMH-589 and KMH-2589 maize seed varieties found 0.60, 0.59 and 0.55 respectively.

The study on the physical properties of three different maize seed varieties led to the following conclusions. The shape and size of the cell on the metering plate will be affected by the shape of the seeds mostly. From the results, the length, width, and thickness are varied from 10.50 – 11.49, 7.11-8.63, and 4.20 – 4.53 mm respectively. The shape of the maize seeds is in an oblong shape, so the cell shape on the metering plate should be in an oblong shape, and it easy to hold the seed within it. Angle of repose of seeds up to 30.20^{o}, so that the sidewalls of the hopper should be not less than the angle of repose of the seeds. Frictional properties are used in the design of hoppers.