2.1 Design considerations
The following factors were considered to design drum seeder with urea supergranule application: i) the machine should be simple in construction and easy to adjustment, ii) the size of the GU, iii) the size of drum, iv) distance between applied GU to GU and row to row placement, v) the row spacing and seed rate should be adjustable, vi) it should be easy to repairable and maintainable, vii) the cost of machine must be within the capacity of rural small farmers and viii) it should be light in weight and easy to operate by a single person (man or women). The distance between applied GU to GU should be maintained 0.4 m for designing the applicator (IFDC, 2007). The diameter of ground wheel was determined by considering the spacing between GU and number of GU fallen per turn of wheel. The wheel diameter was 0.51 m and it was made of plastic materials. The wheels were fixed with a hollow MS shaft (35 mm × 35 mm) by nuts and bolts. As a result, the shaft and metering system were rotated with the rotation of wheels during operation. The following information was considered for determining number of cups in the metering device. Diameter [D] of wheel is considered as 0.51 m. Distance covered per turn of wheel, [πD] is as 1.6 m. Number of turn of wheel is equal to number of turn of metering device, and distance between GU to GU is considered as 0.4 m. Therefore, total number of cups in the metering device is to be [1.6 m/0.4 m].
2.2 Design and development of different parts of the applicator
The metering device is the most important part for the applicator and it is made of M.S sheet. Four cups of 25.4 mm diameter is welded with a flat bar and an attached Furrow opener is designed and attached with the applicator to place the GU at a desired depth. The length of furrow opener is 80 mm and it is made of MS square (20 mm × 20 mm) bar. Tip of the furrow opener is pointed and sharp enough to cut the soil. The bar is welded with 0.18 m long M.S square (20 mm × 20 mm) hollow shaft. The adjusting shaft of the furrow opener is attached with the frame of the applicator and makes a provision to set the furrow opener in a desire depth.
2.3 Working principles of drum seeder with urea supergranule application
When an operator pulls the applicator, the forward movement of the machine rotates the driving wheels which rotate the drum and the metering device in the hopper. One GU is hold in the cup of the metering device and dropped on the furrow made by the furrow opener. After that, the furrow closer covers GU with soil. Figure7 shows the complete drum seeder with urea supergranule application and Figure8 presents the working principle of drum seeder with urea supergranule application. The volume of hopper for urea granules is 1.7×10-3 m 3. The size of the metering cup is designed in such a way so that each cup takes one urea at a time. There is no way to block their passage due to shape of the urea and cup, rubber gate and enough forces applied due to fixed attachment of metering cup with rotating driving shaft.
2.4 Laboratory test of the applicator Weight of single GU is very important for application properly. Therefore, the weight of each 30 GUs was measured by a digital balance. Size of GU is also important to make the cup of the metering device. The size of each 30 GUs was measured by a slide calipers. The weight of the applicator is also important to carry and maneuver in the field. So it was tried to keep the weight of the applicator as low as possible. The weight of the applicator was measured and data was recorded. The capacity of the applicator was considered as the weight of dropped GU per unit time or area. To determine the capacity of the applicator for applying GU, the applicator was lift from ground. Two polythene bags were fixed with two discharge tubes of metering devices. One person rotates the wheel for 25 times as equivalent to the normal walking speed (1.78 km/hr) in the puddle field. The time require for 25 revolutions of wheel was recorded by a stop watch. Uniform speed of wheel rotation was maintained during the experiment. Then, the weight of GUs which was collected in each bag was measured by an electric balance. The capacity of applicator was estimated by following Equation1:
Capacity of the applicator = W / T (kg/h)
where, W is total weight of urea dropped in kg and T is the total time to operate the applicator. The hoppers of the applicator were filled with GUs and the metering device was rotated for one minute by turning the wheels. Number of turn was counted and time was recorded by a stop watch. Dropping GU was also counted and recorded. This experiment was done for 10 times. Then the missing and over a falling percentage of GU were calculated.