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Development and Evaluation of a rotary power weeder

Olaoye, J. O. and T. A. Adekanye

Department of Agricultural and Biosysytems Engineering, University of Ilorin, Ilorin jolanoye@unilorin.edu.ng

Abstract

Weed control is one of the most difficult tasks in agriculture that accounts for a considerable share of the cost involved in agricultural production. Farmers generally expressed their concern for effective weed control measures to arrest the growth and propagation of weeds. Chemical method of weed control is more prominent than manual and mechanical methods. However, its adverse effects on the environment are making farmers to consider and accept mechanical methods of weed control. Manual weeding is common in Nigerian agriculture. It is the most widely used weed control method but it is labour intensive. The use of mechanical weeder will reduce drudgery and ensure a comfortable posture of the farmer or operator during weeding. This will resultantly increase production. It is against this background that a rotary power weeder was developed. Results of field performance evaluation showed that the field capacity and weeding efficiency of the rotary power weeder were 0.0712 ha/hr and 73%. The cost of operation with this weeder was estimated to be N 2,700.00 / ha as against N 12,000.00 / ha by manual weeding.

Keywords: Rotary weeder; weeding; field performance; tines; weed density

1. Introduction

A weed is essentially any plant which grows where it is unwanted. A weed can be thought of as any plant growing in the wrong place at the wrong time and doing more harm than good (Parish, 1990). It is a plant that competes with crops for water, nutrients and light. This can reduce crop production. Some weeds have beneficial uses but not usually when they are growing among crops. Weeds decrease the value of land, particularly perennial weeds which tend to accumulate on long fallows; increase cost of cleaning and drying crops (where drying is necessary). Weeds waste excessive proportions of farmers’ time, thereby acting as a brake on development. Lavabre (1991).

Weeding is the removal of unwanted plants in the field crops. Mechanical weed control is very effective as it helps to reduce drudgery involved in manual weeding, it kills the weeds and also keeps the soil surface loose ensuring soil aeration and water intake capacity.

Weeding is an important but equally labour intensive agricultural unit operation. There is an increasing interest in the use of mechanical intra-row weeders because of concern over environmental degradation and a growing demand for organically produced food. Today the agricultural sector requires non-chemical weed control that ensures food safety. Consumers demand high quality food products and pay special attention to food safety. Through the technical development of mechanisms for physical weed control, such as precise inter-and intra-row weeders, it might be possible to control weeds in a way that meets consumer and environmental demands. These mechanisms contribute significantly to safe food production

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(Pullen & Cowell, 1997; Fogelberg & Kritz, 1999; Kurstjens & Perdok, 2000; Blasco et al., 2002).

1.2 Weed Control Methods

Weed control is one of the most expensive field operations in crop production. Indeed, the detrimental effects of weeds in agriculture in developing countries far exceed those of all crop pests. Njoku (1996) reported that uncontrolled weeds growth reduces yield of the principal crops while untimely weeding reduces the returns from the overall investments in the production of crops. Igbeka (1984) reported that timeliness rather than frequency of weeding is a major determinant of effective weed control.

Anyawu et al., (1976) reported that biological method of weed control involves the use of parasites to control weeds that is killing weeds with their natural enemies. For this method to succeed, the insects that can feed on the weed are isolated. These insects are made to survive and reproduce in the environment where the weeds grow.

Anyawu et al., (1976) also reported that biological control of weeds includes the use of cover crops and leguminous which are grown in association with the crops. The cover crops creep on the land to cover the soil, thereby preventing development of weeds by chocking them out. The use of mucuna mulch can be used as an effective supplement with mechanical weed control. The effectiveness of supplementing mucuna mulching weed control must be considered with appropriate hand-pulling of weed using a special V-shaped hoe and mowing weeds with about a 2-kW engine mower.

The combination of two or more methods of weed control at low input levels should be considered to reduce the weed competition to the possible minimum level; this was observed as the most appropriate solution to the problem of weed control by Singh et al., (1985). Buckingham (1976) asserted that a complete weed control programme must include primary tillage and secondary tillage planting practices, cultivation of row crops and the use of herbicides. Singh et al., (1981) claimed that herbicides can reduce the labour requirement tremendously, but there was inconsistency in their performance. The inconsistency included the cost of herbicides relative to labour, farmers’ lack of knowledge about the rate, time and method of application. Also, unavailability of herbicides and sprayers are some of the major factors that restrict the use of herbicides by small scale farmers. These limitations make mechanical method of controlling weeds preferable to the use of herbicides. So many researchers had worked on development and analysis of a ridge profile weeder (Odigbo and Ahmed, 1979; Oni, 1990; Nganilwa et al., 2003).

Kepner et al., (1978) claimed that mechanical method of weed control is the best with little or no limitation because of its effectiveness. According to Kepner et al., (1978) and Buckingham (1976), the primary objective of row crop cultivation is to enhance the use of farm machinery for eliminating weeds from the crop land. The effect of this method is to promote plant growth and better quality crops. However, the use of such machine is not common and the availability of a mechanical weeder is scarce.

The objective of this study is to develop and evaluate the performance of a rotary power weeder. The machine is conceived to meet the yearning needs of small farm holders.

2. Material and Method

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2.1 Assumptions

The assumptions made in the design of the rotary weeder are presented in terms of field conditions, machine capacity and energy requirement required to power it.

The machine is to be powered by a 5-hp internal combustion engine. Belt and Pulley arrangement shall be employed for transmission of power. Engine speed is 3600 rpm, diameter of pulley = 50 mm, diameter of pulley on shaft = 50 6 = 300 mm, pulley ratio = 1:6, shaft speed = 600 rpm, maximum soil resistance value = 1.05 kgf/cm2, coefficient of friction = 0.1, efficiency of transmission system = 82%.

2.2 Design Process

Bainer et al. (1978) asserted that in designing row-crop weed control equipment, the age of the weed must be taken into consideration. In the early stages of crop growth, implements such as rotary hoe, the spring tine and spike arrows can be operated directly over the rows to uproot small weeds from established crops.

According to Hunt (1983), cultivators are equipped with various types of tools depending on the soil condition. Shovels are for deep working soil, throwing up rooting weeds. Sweepers are shallow depth weed cutting tools.

Hunt (1983) asserted that, in the design of a rotary hoe, there must be uniform and adequate penetration of the tools. This, he obtained by adding weights to the rotary hoe and to spike-tooth harrow. In the design of a manually operated machine, the power supplied by man working continuously should be taken into consideration. Liljedah et al. (1979), claimed that human being as power units are limited to less than 0.1 kW output. This suggests that the weight of the implement must be considered and made to bear in the selection of the materials for construction.

2.2.1 Power requirement

The power requirement was calculated using the following equations:

(1)

where,

SR = soil resistance, kgf/cm2 ; d = depth of cut, cm:

w = effective width of cut, cm: v = linear velocity of the tine at the point of contact with the soil.

Hence, power requirement is estimated as

2.2.2 Total power required

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The total power required is estimated as 4.23 hp as follows

where,

Pd = Power required to dig the soil:

η= Transmission efficiency.

Thus, a prime mover of 5 hp was required for this weeder.

2.2.3 Belt and shaft selection

The belt, pulley and shaft selection was based on Agricultural Machinery Management Data. D230-4 (ASAE, 1986).

2.2.4 Weeding Tines

Each hoe consists of twelve tines of equal lengths determined as follows (Fig. 1).

Considering sector ABC, length of arc AB which forms the curved tines may be calculated as

(2)

= 138 mm

where,

r = 3R/5 = radius of curvature:

R = outer wheel radius, mm:

= 900

1= outer wheel diameter, mm:

2= Disk hole diameter, mm 2.3 Machine Description

The weeder consists of the following components; a 5 hp-petrol engine, three ground wheels (pneumatic), tool assembly, frame and handle. The weeder is pushed manually and the power to the rotary hoe is supplied from the engine through belt and pulley arrangement (Fig. 2). The weeding tines on a cylindrical discs were arranged radially at equidistance of 30mm along the disc circumference. Each tine was made of steel rod of 12 mm diameter and has an arc of 30mm. The rotary power weeder is to be powered by a 5-hp internal combustion engine (ICE). Belt and pulley arrangement was adopted for transmission of power. The maximum rating of the 5hp ICE was 3600 rpm fixed with a pulley diameter of 50 mm on the shaft carrying the rotary tines. The various components of the machine were constructed while other standard components, such as prime mover and transmission elements were sourced locally and the parts were assembled at the fabrication workshop of the Department

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of Agricultural and Biosystems Engineering, University of Ilorin, Ilorin. The front view and the isometric view of the rotary weeder were shown as Figures 3 and 4.

3. Performance Evaluation and Experimental Analysis

The performance evaluation of the constructed rotary power weeder was conducted on the experimental field of Department of Agricultural and Biosystems Engineering, University of Ilorin, ilorin Nigeria.The performance evaluations were conducted to investigate the effect of weed density on performance of four weeding tools.

The experimental area was infested mostly with weeds like Trifolium repens (clover), cryperus eragrotis (umbrella sledge), cyperus rotumdus (Nut grass), cynodon dactrylon (couch grass), cynosures echinatus (Dog’s Tail), phyllanthus amarus (Petty spurge), Lactuca taracifolia (Wild lettuce), Sida acuta (broom weed), Imperata cylindrical (logongrass), Amarantus spinosus (thorny pig weed) and Eleusine indicae (goose grass).

Prior to each weeding schedule, weed density in each experimental unit was determined by laying-out a squared grid (0.3m 0.3m) in the plot and weeds in the grid were counted. Three such determinations were made for each experimental unit

3.1 Experimental Factors

Experimental factors used in the field evaluation of the constructed rotary power weeder were five (5) levels of speeds in three blocks. The weeding speeds evaluated were 1804 rpm, 2004 rpm, 2435 rpm, 2261 rpm and 3506 rpm

3.2 Performance Indicators

Performance indicators used for this experiment includes the following:

3.2.1 Weeding Index

Weeding index is a ratio between the number of weeds removed by a weeder and the number present in a unit area and is expressed as a percentage (Rangasamy, et al., 1993).

Nine plots of 27m x 2m each were marked out of the main plot for sampling. Weeds in each plot were counted before and after weeding using the constructed rotary weeder. The time taken to perform this operation were noted. Equation 3 was used to calculate weeding index.

(3)

where,

W1 = weeds before weeding W2 = weeds after weeding

3.2.2 Weeding Efficiency

The weeder was tested on the plots described in 4.2.1 to determine weeding efficiency. The weeding efficiency was evaluated by using equation 4.

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(4)

where,

W1 = number of weeds before weeding,

W2 = number of weeds after weeding,

= weeding efficiency

3.2.3 Field Capacity

The weeding tools were tested on the same plots to determine the field capacity of each of them. Field capacity is the amount of area that a weeding tool can cover per unit time as shown in equation 5.

Field Capacity (ha/h) (5)

where,

A = Area covered (m2),

t = Time taken in minutes

4. Results and Discussion

4.1 Weeding Efficiency

This was determined by counting the number of weeds before and after using the developed weeder on the 3 blocks (replicated three times). Detail records are presented in Table 1 and 2. Table 1 shows that higher engine speed leads to higher weeding efficiency. However, Table 2 shows the relationship between forward speed and weeding efficiency, it was observed that operating the weeder at higher speeds above 0.8 m/s was characterized with rough weeding. 2261 rpm is ideal speed for this weeder as shown in Figure 5.

4.2 Effect of Engine Speed on Weed Density

Table 1 shows the number of unremoved weeds after weeding trials at different levels of engine speed. It shows that engine speed has a proportional effect on iron rod tine, i.e. engine speed influenced the efficiency of the weeder.

4.3 Field Capacity

The field capacity of the power weeder at various levels of speed was observed to range from 0.068 ha/hr and 0.079 ha/hr as shown in Figure 6.

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5. CONCLUSIONS

A rotary weeder was designed and constructed to be powered by a 5 hp-petrol engine and to be operated on a three ground wheels (pneumatic).

The results of the performance evaluation of the developed weeder indicated that the engine speed influenced the weeding efficiency of the rotary weeder and rough weeding was observed at a higher speed of 3506 rpm.

The forward speeds of 0.4 m/s to 0.5 m/s and engine speeds of 1804 rpm to 2261 rpm resulted in weeding efficiency of 54.98% to 59.05%.

The machine operated at the field capacity of 0.079 ha/hr and the cost of weeding operation of one hectare was estimated to be N 2,700.00 as against N 12,000.00 by manual weeding.

References

Anyawu, A. C., Anyawu, B. O. and Anyawu, A. A. 1976. Agriculture for school certificate. Africana Education Publication (Nig.) in association with FEP Int. Ltd.

ASAE, 1986. Agricultural Machinery Management Data. D230-4. American Society of Agricultural Engineers. Pp. 159-163

Bainer, R., Barger, E. L. and Kepner, R. A. (1978). Principles of Farm Machinery. Avi publication Co. Inc. Westport, Connecticus. 3rd Edition.

Blasco J., Aleixos N., Roger J., Rabatel E. & Molto E. (2002) Robotic weed control using machine vision. Biosystems Engineering, 83 (2), 149-157.

Buckingham, F. 1976. Fundamentals of machine Operation. John Deere Service Publication, Moline, Iowa, USA

Fogelberg F. & Kritz G. (1999) Intra-row weeding with brushes on vertical Axes-factors influencing in-row soil height. Soil & Tillage Research, 50, 149-157.

Hunt, D. (1983). Farm Power and Machinery Management. 8th Edition. Iowa State University Press. AMES. Iowa USA.

Igbeka, J. C. 1984. Development in Rice Production Mechanization. AMA. 10(1). 27-32. Kepner, R. A., Bainer, R. and Barger, E. L. 1978. Principles of farm machinery, 3rd edition,

AVI publication Co., INC., Westport, Connecticut . Kurstjens D., Perdok U. & Goense D. (2000) Selective uprooting by weed harrowing on

sandy soils. Weed research, 40, 431-447. Kurstjens D. A. G. & Perdok U. D. (2000) The selective soil covering mechanism of weed

harrows on sandy soils. Soil & Tillage Research, (55), 193-206. Lavabre, E. M. (1991). Weed Control. Macmillian Education Ltd., London

Liljedah, J. B., Carleton, P. K. and Smith, D. W. (1979). Tractor and their Power Units. 3rd Edition. John Wiley and Sons. New York.

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Nganilwa, Z. M., Makungu, P. J. and Mpanduji, S. M. 2003. Development and Assessment of an Engine Powered hand held weeder in Tanzania. International Conference on Industrial Design Engineering, UDSM, Dare salam.

Njoku, P. C. 1996. The Role of Universities of Agriculturei Appropriate Manpower Development for Weed Management in Agriculture. Nigerian Journal of Weed Science. Vol. 9, 65.

Odigboh, E. U. and Ahmed, S. F. 1979. Development of a Ridge Profile Weeder. AMA. 21(1): 43-48

Oni, K. C. (1990). Performance Analysis of a Ridge Profile Weeder. Proceeding of Nigerian Society of Agricultural Engineers. 3: 189-199.

Parish S. (1990) A review of non-chemical weed control techniques. Biological Agriculture and Horticulture, 7, 117-137.

Pullen D. & Cowell P. (1997) An evaluation of the performance of mechanical Weeding mechanisms for use in high speed inter-row weeding for Arable Crops. Journal of Agricultural Engineering Research, 67, 27-34.

Rangasamy, K., Balasubramanian, M. and Swaminuthan, K. R. 1993. Evaluation of Power Weeder Performance. AMA. 24(4): 16-18.

Singh, C. M., Moodey, J. and Cho, S. C. 1981. The Efficiency of the Rolling Weeder in Controlling Weeds in Dry-Seeded Rainfall Rice. Paper presented at the cropping system seminar. International Rice Res. Institute. Los Banos, Phillipines, Feb.24.

Singh, C. M., Moodey, J. and Cho, S. C. 1985. Weed Control through Inter-Row Cultivation in Upland Rice. AMA. 16(3): 34-40.

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Table 1: Number of weeds removed and efficiencies at various engine speeds (Rod tine weeder) Engine speed (rpm)

Blocks Weed Density Number of weeds removed

Efficiency (%) Before

weeding After weeding

1804 1 520 242 279 53.7 2 554 242 312 56.4 3 603 278 325 54.9

2004 1 578 246 332 58.5 2 616 266 350 57.8 3 668 291 377 57.5

2261 1 652 275 377 58.9 2 695 292 403 59.1 3 754 316 438 59.1

2435 1 703 262 441 63.7 2 746 277 468 63.8 3 812 303 509 63.7

3506 1 1012 257 755 75.6 2 1075 311 764 72.1 3 1169 335 834 72.4

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Table 2: Time taken, speed and efficiencies for various engine speeds (Rod tine weeder)

Engine speed (rpm)

Distance moved (m)

Time taken (Seconds) Forward Speed (m/s) Efficiency (%) Block 1

Block 2

Block 3

Mean Block 1

Block 2

Block 3

Means Block 1

Block 2

Block 3

Mean

1804 27 55.09 52.33 52.88 53.35 0.4901 0.4551 0.5102 0.4851 53.67 56.37 54.89 54.98

2004 27 51.00 51.44 52.44 51.63 0.5294 0.5249 0.5149 0.5231 58.48 57.81 57.52 57.94

2261 27 47.35 46.23 46.75 46.78 0.5702 0.5840 0.5775 0.5772 58.87 59.11 59.18 59.05

2435 27 45.48 45.41 45.49 45.46 0.5937 0.5946 0.5935 0.5939 63.73 63.79 63.71 63.74

3506 27 31.74 32.00 31.85 31.86 0.8507 0.8438 0.8477 0.8474 75.62 72.10 72.41 73.37

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Fig. 1: Sketch of a disk with tines

Fig. 2: Shematic illustration of Rotary Power Weeder

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Fig. 3: Front View of the Rotary Weeder

Fig. 4: Rotary Power Weeder

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