Considered the following factors in designing prilled urea applicator (PUA): 1) machine should be as simple and easy to operate, assemble, dis-assemble, and maintain; 2) depth of fertilizer placement should be 5 - 7 cm; 3) line to line spacing should be adjustable; 4) the cost of the machine need to be within the capacity of rural small farmers; 5) ensured the covering of prilled Urea; 6) a single person should operate it; and 7) lightweight for easy handling.

The applicator designed with field line to line spacing of 20 cm, and the distance between two skids was 40 cm (centre to centre). The prilled urea applicator was fabricated using locally available materials. Prilled Urea (PU) is chemically the same as fine Urea; however, size is less or more equal. Since the physical properties (size, diameter, bulk density) of the Urea are similar, it has no chance of spillage/blockage from the aperture on the hopper wall (Table 1). The physical properties were used to design the fertilizer meter units’ component [23]. Moreover, the actual capacity of each hopper is 1500 g, but it is 1000 g maintained to prevent overlapping.

The complete and different views of the BRRI prilled urea applicator are shown in Figure 1 and Figure 2. The manual push type PUA was designed and fabricated in the Farm Machinery and Postharvest Technology (FMPHT) divisional research workshop of Bangladesh Rice Research Institute (BRRI), Bangladesh. The manual push type PUA consists of the following major parts: skid, metering device, hopper, drive wheel, and frame with a handle. During design, all components of the applicator were modified by the trial and error method. The PUA is made with plastic (Poly Vinyl Chloride (PVC)), except an adjustable part of the frame and handle. The PVC is readily available, durable, and long-lasting.

The descriptions of different significant parts are given here in:

1) Skid: Two skids help the applicators to protect from penetration into soft muddy soil and smoothly to move. The skid also assists in sharing the dispersed weight load of the applicator. The total length and width of the skid were critically selected, 83.5 and 11.5 cm, respectively. The inclined part, furrow opener, and furrow closer are an integral part of the skid (Figure 3 and Figure 4). The front inclined part was arranged with 32-degree angles with the skid to facilitate the applicator’s running. Also, the furrow opener’s inclined shape protected the muddy soil from entering into the opener and secured clogging. Moreover, the inclination parts length was 17 cm. The applicator’s furrow opener was connected at the bottom of the skid, maintaining a sliding angle of 47 degrees. It helps to make a furrow easily. 6.0 cm height and 8.7 cm length of furrow opener was designed that allows granules dispensed easily to the field. The furrow closer inclination was 8 degrees with 8.5 cm length, and 1.2 cm height assists the furrow closed with soft soil.

2) Metering Mechanism: Disk diameter was 10.2 cm, with 12 spikes/teeth connected at the outer edge (Figure 5 and Figure 6). The cups help dispense Urea to the output channel from a cylindrical hopper (Figure 3(a)). The thickness and width of the teeth of the metering device were 2.0 mm and 10 mm, respectively. The outer and internal diameter of the metering device was 100 and 86 cm, respectively. The drive wheel is directly connected to the metering device. Moreover, the urea dispensing rate and drive wheel speed were simulated to the recommended urea fertilizer rate. Also, for easy dispensing of prilled Urea to the applicator’s channel, an impeller was connected below the tank, as well as a metering device that conveyed Urea without clogging. The length and width of the impeller were 9.8 and 1.6 cm. Both sides of the impeller were twisted about 35˚ angles with its horizontal axis (Figure 5), an essential part of the machine.

The dispensing rate of Urea depends on its adjustment. In this applicator, the gap between the impeller centre and discharge outlet lever has readjusted to increase pressure on the urea release lever without changing the impeller. If pressure increases on the urea release lever, then it opens more and dispenses more Urea. The gap between the impeller centre and release lever for Boro rice season varieties and Aman/Aus season varieties were 19 mm and 37 mm, respectively. The adjustment is made by using three (03) nuts. The fertilizer is controlled by nuts as 3 nuts Boro season and 2 nuts for Aus/Aman season added below in the impeller.

3) Hopper with Funnel, Case, Side Guard and Discharge Channel: The capacity of each hopper was about 1500 gm. (Figure 7 and Figure 8). The hopper’s height and diameter were 31.5 and 11.0 cm, respectively, with round tapering at the bottom. The hopper was attached to the case/dispensing chamber, whose diameter was 11.0 cm. The funnel of the tank was attached on a 3.3 cm diameter hole, and a small hole of 1.1 cm diameter was found at the bottom of the dispensing chamber. Moreover, a funnel (larger diameter 10.2 cm, smaller diameter 3.2 cm, and height 5.5 cm) was attached at the bottom of the hopper. The discharge tube was attached under the small hole of the dispensing chamber. The

discharge tube and hopper were made of plastic, and thickness was 2.5 mm. The height and diameter of the dispensing tube were 27 and 2.5 cm, respectively. The top of the hopper was cover to protect falling Urea from the top.

4) Drive Wheel: The diameter and periphery of the drive wheel were 61.0 and 192.0 cm, respectively. Due to direct coupling, the metering device can rotate with the rotation of the drive wheel. As a result, PU was collected from the hopper continuously and dispensed in 192 cm distance per one cycle of the drive

wheel (Figure 9). The driving wheel also worked as a power transmission device to put the dropped PU into the soil. Adjust 20 lugs on the periphery of the driving wheel, which makes traction during field operation. During operation, the developed traction depends on the applicator’s lug dimensions, soil condition, and weight. The lugs dimension was determined by trial and error basis view of different soil conditions and the applicator’s weight. The width and height of the lug were the same (5.0 cm).

5) Frame with Handle: The frame is an essential component for holding different parts as a skid, handle, drive wheel, and hopper of the applicators (Figure 10). The structure was made of plastic, and the handle was made of mild steel (MS) road. The length, height, and width of the frame were 75.1, 34.0, and 47.3 cm, respectively. The structure was tightened with skids and a driving wheel using a nut and bolt. The handle is made of a round pipe of 163.5 cm in length and attached with a V shape connector (Figure 11). The length of the handle is 7.5 cm, which is connected with the skid. To hold the discharge tube tightly between the mainframes and skid used two rectangular shape frames.

For better performance, several operational procedures should be followed, such as:

± Handle height differs with the operator’s height, so height adjustment is a significant issue for effective operation in the field;

± The PUA design force is pushing. Any kinds of pulling will create a blockage in the furrow opener as well as Urea dispensing channel;

± Minimum standing water (0.5 - 1 cm) need to maintain during field operation. It will help to keep the soil soft that helps the applicator for smooth running with proper furrow opening and closing;

± The walking speed should be standard (1.72 km/h).

As urea fertilizer is a prime source of nitrogen for rice cultivation, it varies with season, climatic condition, and soil fertility status. The rice-growing season is classified as Aus, Aman, and Boro, likely the fertilizer rate also differs. The Bangladesh Rice Research Institute (BRRI) recommendation rate of urea fertilizer for Bangladesh is 220 kg/ha in Boro and 140 kg/ha in Aus/Aman season. The developed PUA has an impeller by which can be controlled the dispensing rate. The PUA was designed for urea application rate 8 - 9 kg/10 decimal for Boro and 5 - 6 kg/10 decimal for the Aus/Aman season (70% of the recommended rate). For field application, the impeller with the drive wheel was adjusted until the urea dispense rate in each tube of 13.5 - 14 gm for Boro and 9 - 10 gm for Aus/Aman season for each revolution of the drive wheel.

When an operator pushes the applicator by the handle, the forward movement of the machine skids and driving wheel assist in rotating the metering device in the hopper. The teeth conveyed the PU from the hopper and dropped on the dispensing tube. After that, the urea enters to subsurface furrow, which is made by an opener. When the application moves forward, the urea is covered by the furrow closer. Figure 12 represent the laboratory and field operations of PUA.

The theoretical concerns were studied by [3] [16]. The leading factors for the performance evaluation of PUA include the weight of an applicator, capacity, dispensing rate, depth of placement, over falling percentage, walking speed, field capacity, field condition, ease of operation, adjustment of the applicator, soil type, land topography, field size, and shape, etc.

Operator walking speed, land condition, soil type, operator strength, and skill influence an applicator’s capacity. Varying levels of walking speed were set up to determine the capacity of laboratory conditions and presented in Table 2. The average capacity and walking speed of the machine were 0.16 ha/h and 1.99 km/h for Aus and Amon season, respectively. On the contrary, for Boro season, 0.16 ha/h and 2.02 km/h where the capacity and walking speed, respectively.

The field capacity of the applicator was measured in the BRRI research field on a trial basis. Time was recorded, including turning and losing time. During field testing incorporating three different labour and measured total distance. The average field capacity was 0.13 ha/h (Table 3).

The size and shape of the Urea mostly uniform, because average weight of 10 granules is 0.22 gm (Table 1); hence the weight of Urea not varied significantly. Due to the Urea’s shape, there is no possibility to block the dispensing passage and missing. The over falling were determined and presented in Table 4. The over falling percentage of both hoppers was 5.35%. Overfill occurred due to small sizes, low speed, and shaking because of the uninformed walking speed in both the hoppers.

N.B: Constant effective width = 80 cm.

Urea dispensing efficiency was measured in the laboratory. The applicator was set up on a high platform for easing to move the drive wheel for the dispensing test. Each hopper was filled with 1.5 kg of PU. The drive wheel was rotated 20 times continuously at an average speed of 2.0 km/h; the dispensed Urea was collected from the bottom of the output channel. This method was applied separately for Aus/Aman and Boro’s recommended rate. Dispensing efficiency was measured by weighing the gather of dispensing Urea. Average dispensing efficiency was 98.52% for Aus/Aman season and 98.63% for Boro (Table 5).

The prime aim of the study was to place the PU at the desired depth for increasing the nitrogen use efficiency. The depth of placement varied on soil conditions and the penetration of the applicator. Different depth of urea placement was found during the operation is presented in Table 6. The average Depth of PU placement was 6.38 cm.

Field-tests outcomes of pushing force, necessity are presented in Table 7. With the machine weights of 11 kg (including Urea), the mean pushing force was found at 63.89 N, which suggests the ease of handling of the applicator. Pushing

force is extremely correlated with two leading issues, such as the weight of the PUA and the amount of moisture in the muddy soil.

The weight of the applicator is 9 kg (without Urea), which is easy to carry from one field to another field. The pushing force was 63.89 N, which was based on a pushing angle of 35˚. Consequently, one man and woman can push the applicator very easily. The fabrication of the applicator is also easy and simple. It has the advantage of necessarily less energy and easy to adjust and operate. The overall specification of the applicators is shown in Table 8 and Table 9.

Note: Average work day = 8 hr at 0.13 ha per hr.; Labor/operator charge = 500 Tk/day, 1 US$ = 85 BD TK.

The cost analysis of the PUA is presented in Table 10. The price of the applicator varied with the quality of the materials. The working life of the applicator was considered five years. The operating cost of the applicator was 3642 Tk/ha (43 USD), however, the traditional (manually application) cost was over 4000 Tk/ha (54 USD).