alexa Influence of Integrated Weed Management Practices on Weed Dynamics, Yield Components and Yield of Faba bean (Vicia faba L.) in Eastern Ethiopia | OMICS International
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Influence of Integrated Weed Management Practices on Weed Dynamics, Yield Components and Yield of Faba bean (Vicia faba L.) in Eastern Ethiopia

Nano Alemu* and JJ Sharma

School of Plant Sciences, College of Agriculture and Environmental Sciences, Haramaya University, Dire Dawa, Ethiopia

*Corresponding Author:
Nano Alemu
School of Plant Sciences, College of Agriculture and
Environmental Sciences, Haramaya University
PO Box-138, Dire Dawa, Ethiopia
Tel: +251913483195
E-mail: [email protected]

Received date: July 18, 2017; Accepted date: July 25, 2017; Published date: July 28, 2017

Citation: Alemu N, Sharma JJ (2017) Influence of Integrated Weed Management Practices on Weed Dynamics, Yield Components and Yield of Faba bean (Vicia faba L.) in Eastern Ethiopia. Adv Crop Sci Tech 5: 298. doi:10.4172/2329-8863.1000298

Copyright: © 2017 Alemu N, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

The experiment was conducted to assess the integrated effects of pre-emergence herbicides and hand-weeding on weed control, yield components and yield of Faba bean to assess their economic feasibility for cost effective weed control in Faba bean. The experiment consisted of 12 treatments viz. pre emergence S-metolachlor and Pendimethalin each at three rates S-metolachlor+one-hand-weeding, pendimethalin+one-hand-weeding, two-handweeding, complete weed free and weedy checks arranged in randomized complete block design with three replications. The weed flora consisted of broadleaved and sedge with the relative densities of 81.02 and 18.98% at Haramaya, and 80.83% and 19.17%, at Gurawa, respectively. Application of S-metolachlor and Pendimethalin 1.0 kg ha-1 each supplemented with hand weeding 5 WAE significantly (p ≤ 0.01) affected the broadleaved weeds, sedges and weed dry weight at both sites. S-metolachlor 1.0 kg ha-1 supplemented with hand weeding 5 WAE gave the lowest total number of weeds (8.29 m-2) following the weed free check. Higher grain yield (3555.8 kg ha-1) was produced with S-metolachlor 1.0 kg ha-1 supplemented with one-hand-weeding 5 WAE following complete weed-free at Gurawa. The benefit gained from S-metolachlor and Pendimethalin at 1.0 kg ha-1 each supplemented with one hand weeding 5 WAE were greater than the value recorded from the weedy check by 216% and 198%, respectively. S-metolachlor 1.0 kg ha-1 supplemented with hand weeding 5 WAE treatment resulted in the highest grain yield and economic benefit. However, in case labour is constraint and S-metolachlor herbicide is timely available, pre emergence application of s-metolachlor at 2.0 kg ha-1 should be the alternative to preclude the yield loss and to ensure maximum benefit.

Keywords

Hand-weeding; Pendimethalin; Pre-emergence; Smetolachlor; Vicia faba

Introduction

Faba bean (Vicia faba L.) originated in the Near East and is one of the earliest domesticated legumes after chickpea and pea. It is a major legume crop in Ethiopia, largely grown in the highlands (1800-3000 meters above sea level) where its need for chilling temperature is met. The bean is among the most important pulse crops produced in Ethiopia in terms of area under production, as a source of protein, restoration of soil fertility by fixing atmospheric nitrogen and as a suitable rotation crop with cereals. Despite the importance of the crop in the traditional farming systems, its average yield under small-holder farmers is not more than 1.6 t ha-1 [1] which remains far below the crop’s potential (>3 t/ha). The low productivity of the crop is due to several factors, among which poor soil fertility and inadequate plant nutrition, poor seedbed preparation, untimely sowing, sub-optimal weed control and the lack of improved varieties are the major ones [2,3].

Weeds are plants which compete with crops for nutrients, space, light exerting a lot of harmful effects by reducing the quality and quantity of the crop if their populations are left un-controlled [4,5]. The major problem facing the production of Faba bean in Ethiopia is weeds, because of the low competitive ability of the bean during its early stages of growth. Uncontrolled weed populations can substantially reduce the yield of the Faba bean up to 80% [6]. Integration of weed control methods is an effective and workable practice that is ecologically and economically viable to the farmers. Herbicides constitute a new and highly efficient technique for controlling weeds hence increasing yields, improving quality and reducing labour in crop production [7]. According to Bascur and Cook [8,9] several investigators have reported that satisfactory weed control in faba bean was achieved by application of a number of herbicides. However, concerns about crop injury, herbicide carryover, commodity prices, herbicide resistance, environmental and human health hazards associated with herbicides, unavailability of adequate labour during peak period of weeding and difficulty in use of mechanical weeding in heavy soil as well as receiving heavy rains limitations to effective weed management have forced Faba bean growers to implement integrated weed management (IWM) practices. These include a combination of cultural, mechanical, and chemical weed management techniques [10].

Efficacy of Pendimethalin and S-metolachlor herbicides combined with hand weeding has not yet been evaluated in faba bean growing in mid and highlands of eastern Ethiopia. Hence, the objectives of this study was to investigate the effect of two pre emergence herbicides (Smetolachlor and Pendimethalin) with or without hand weeding on weed control, and yield components and yield of Faba bean and to assess the economic feasibility of supplementing herbicides with hand weeding for effective and cost effective weed management.

Materials and Methods

Description of the study sites

The experiment was conducted in the 2014 cropping season at Haramaya (09°26'N latitude, 42°03'E longitude, and altitude of 2006 meters above sea level) and Gurawa (09°10'51.7"N latitude, 41°47'29.3"E longitude, and altitude of 2355 meters above sea level) in eastern Ethiopia. The soil of the experimental site at Haramaya had organic matter content of 1.0%, total nitrogen content of 0.17% available phosphorus content of 8.72 mg kg soil-1 pH of 8.13 with sandy loam texture [11-13]. Similarly, the soil of Gurawa had organic matter content of 2.8% total nitrogen content of 0.18% available phosphorus content of 17.50 mg kg soil-1 pH of 6.15 and with clay loam texture. Total rainfall during the cropping season was 690 and 1019 mm at Haramaya and Gurawa respectively. The mean minimum and maximum temperatures during the cropping season were 10.56 and 22.3°C at Haramaya respectively with the corresponding records of 9.5 and 21.7°C for Gurawa (Figure 1).

Treatments and experimental design

The experiment consisted of 12 treatments viz. pre emergence Smetolachlor (1.0, 1.5 and 2.0 kg ha-1), Pendimethalin (1.0, 1.25 and 1.5 kg ha-1) S-metolachlor at 1.0 kg ha-1+hand-weeding at 5 weeks after crop emergence (WAE) Pendimethalin+hand-weeding at 5 WAE onehand weeding at 2 WAE, two-hand weeding at 2 and 5 WAE, complete weed free and weedy checks. The treatments were arranged in randomized complete block design with three replications.

Experimental procedure and management

The experimental fields were prepared to fine tilth. The gross plot size was 3.2 m × 2.4 m (7.68 m2) with 40 and 10 cm inter-and intrarow spacing respectively. The Faba bean variety ‘Gachana’ was planted on 10th and 14th July 2014 at Haramaya and Gurawa respectively. Fertilizer and di-ammonium phosphate (18% N; 46% P2O5) was drilled in furrows at the recommended rate of 100 kg ha-1 at planting [14]. The herbicides were applied as per the treatment in the assigned plots one day after planting. Herbicide spray volume with water as carrier was 500 l ha-1. Spraying was done with Knapsack sprayer (15 L capacity) using flat-fan nozzle. Weeds were removed by hoeing as required in the case of weed free treatment. One row from each side of the plots and four plants from each end of the rows were considered as border. Thus, the net harvestable area was 2.4 m × 1.6 m (3.84 m2). Harvesting was done manually at harvest maturity on 11th and 29th November 2014 at Haramaya and Gurawa respectively. The biomass after harvest was sun dried for 10 days and threshing and winnowing were done subsequently.

Data collection and analysis

The weed flora present in the experimental fields were recorded from weedy check plots in each replication just before crop flowering by placing a quadrat (0.25 m × 0.25 m) randomly at two spots in each replication and converted into m-2. The species were categorized according to their families with the aid of flora books [15,16] and e experts. The weeds at this stage were also cut near to the ground and after three days of sun drying, the samples were oven dried at 65°C to a constant weight to determine aboveground dry weight.

Number of days to flowering was recorded as the number of days from planting to the time when 50% of the 10 pre-tagged plants showed first flower. Days to 90% physiological maturity was recorded in each plot, as the number of days from planting to when 90% of the 10 pre tagged plant leaves showed yellow colour and their pods turned yellow. Plant height (cm) was recorded from 10 randomly selected plants per plot before harvest from the base of plant to the tip of main stem and was expressed on per plant basis.

Total number of pods in 10 randomly selected plants in each plot was counted at harvest and expressed as the number of pods plant-1. From these pods the seeds were counted to determine the number of seeds pod-1. Hundred seeds were counted from each plot, and their weight was recorded. Aboveground dry biomass weight was measured at physiological maturity after cutting 10 randomly sampled plants at ground level and sun dried. This was multiplied by the number of plants in the net plot area and converted into kg ha-1.

Grain yield (kg) was recorded from each net plot area. The moisture content was determined for each treatment and the grain yield was adjusted at 10%. Harvest index (%) was calculated as the ratio of grain yield to the total aboveground dry biomass yield.

The data were subjected to analysis of variance (GLM procedure) using SAS software program version 9.2 [17]. Homogeneity of variances was evaluated using the F-test as described by Gomez [18] and since the F-test has showed homogeneity of the variances of the two sites combined analysis of variance was used. Least significant difference (LSD) test at 5% probability level was employed to separate treatment means where significant treatment differences existed.

Partial budget analysis

The partial budget analysis as described by International Maize and Wheat Improvement Center [19] was done to determine the economic feasibility of the weed management practices. Economic analysis was done using the prevailing market prices for inputs at planting and for the outputs at the time of crop harvest. It was calculated by taking into account the additional input and labour cost involved and the gross benefits obtained from weed management practices. Average yield was adjusted downward by 10% to reflect the difference between the experimental yield and the yield farmers could obtain from the same weed management practices as described by International Maize and Wheat Improvement Center [19]. The field price of Faba bean was calculated as (sale price minus the costs of harvesting, threshing, winnowing, bagging and transportation). The total cost that varied included the sum of cost of herbicides and labour where hand weeding required. The net benefit was calculated as the difference between the gross field benefit (ETB ha-1) and the total costs (ETB ha-1) that varied.

Results and Discussion

Weeds

Weed species in the experimental fields: The weed species found in the experimental fields were grouped into broadleaved weeds and sedges with the relative densities of 81.02 and 18.98% at Haramaya, and 80.83 and 19.17%, at Gurawa, respectively (Table 1). The predominant broadleaved weeds that infested the experimental plots at Haramaya were Galinsoga parviflora and Plantago lanceolata L. with 30.72 and 13.86% relative weed densities, respectively At Gurawa: Guizotia scabra (Vis.) Chiov and Galinsoga parviflora with 23.31 and 13.53% relative weed densities were the major broad leaf weeds observed. Other weeds included; Argemone ochroleuca (6.63%) at Haramaya; Equisetum arvense and Oxalis corniculata L. each with 5.64% relative density at Gurawa. Only one sedge species (Cyperus rotundus ) was present with relative weed densities of 18.98 and 19.17% at Haramaya and Gurawa respectively (Table 2). The probable reason for more species occurrence at Gurawa could be the difference in soil type, previous crop, and relatively more rainfall at Haramaya during the early stages of crop growth. Similarly Tamado [20] reported altitude, rainfall, month of planting, number of weeding and soil type were the major environmental/crop management factors that influence the species distribution of weeds in eastern Ethiopia.

Common name Trade name Chemical name
S-metolachlor Dual Gold 960 EC [2-chloro-6-ethyl-N-(2-methoxy-1-methylethyl) acet-o-toluidide]
Pendimethalin Stomp Extra 38.7% CS [N-(1-ethylpropyl)-2, 6-dinitro-3, 4-xylidine]

Table 1: Description of herbicides used for the experiments. CS=Capsule Suspension; EC=Emulsifiable Concentrate.

Weed species Family Haramaya Gurawa
WD
(m-2)
RD
(%)
WD
(m-2)
RD
(%)
Broadleaved          
Argemone ochroleuca  L. Papaveraceae 22 6.63 18 6.77
Commelina benghalensis L. Commelinaceae 25 7.53 21 7.89
Equisetum arvense L. Equisetaceae 26 7.83 15 5.64
Galinsoga parviflora Cav. Asteraceae 102 30.72 36 13.53
Guizotia scabra (Vis.) Chiov Asteraceae - - 62 23.31
Medicago polymorpha L. Fabaceae 23 6.93 - -
Oxalis corniculata   L. Oxalidaceae - - 15 5.64
Plantago lanceolata L. Plantaginaceae 46 13.86 27 10.15
Solanum nigrum L. Solanaceae 25 7.53 21 7.89
Total     81.02   80.83
Sedge          
Cyperus rotundus L. Cyperaceae 63 18.98 51 19.17

Table 2: Species, families, Density (m-2) and relative density (%) of weeds found in weedy check plots at Haramaya and Gurawa during the 2014 cropping season. WD=Weeds density; RD=Relative density.’

Density (m-2) and total numbers of the sedges and broadleaved weeds

Sedge weeds density (m-2): The sedge density was significantly (P<0.01) affected in response to weed management practices. The lower sedge density was observed in the plots treated with the application of S-metolachlor at 1.0 kg ha-1 supplemented with one hand weeding 5 WAE at both sites, which was statistically at par with the weed free check at both sites (Table 3). Further at Haramaya no significant differences existed between S-metolachlor and Pendimethalin both at 1.0 kg ha-1 supplemented with one hand weeding 5 WAE. Application of both S-metolachlor and Pendimethalin herbicides at low dose (1.0 kg ha-1) supplemented with one hand weeding at 5 WAE resulted in significantly lower sedge density than Pendimethalin or S-metolachlor application alone.

Weed management practices Broadleaved weeds density Sedges density Dry weed density
  Haramaya Gurawa Haramaya Gurawa Haramaya Gurawa
S-metolachlor 1.0 kg ha-1 27.92e 38.75e 43.67f 33.75d 136.2f 131.5e
S-metolachlor 1.5 kg ha-1 21.33f 28.17f 33.7g 26.58e 104.7g 99.3f
S-metolachlor 2.0 kg ha-1 15.73g 21.7g 26.1h 21.58e 79.6h 78.5f
Pendimethalin 1.0 kg ha-1 47.5b 70.75b 91.5b 73.5b 264.5b 261.7b
Pendimethalin 1.25 kg ha-1 41.42c 54.5c 77.17c 48.92c 225.7c 187.6c
Pendimethalin 1.5 kg ha-1 38.17c 48.25d 68.08d 39.33d 202.2d 158.9d
S-metolachlor 1.0 kg ha-1 + one-hand weeding 5 WAE 3.25ij 3.67ij 5.33jk 4.33gh 16.3jk 14.5hi
Pendimethalin 1.0 kg ha-1 + one hand weeding 5 WAE 6.08hi 7.87hi 10j 7.53fg 30.6j 27.9gh
One hand weeding at 2 WAE 32.5d 44.83d 55.17e 35d 166.8e 144.8de
Two hand weeding at 2 and 5 WAE 9.58h 13.42h 17.67i 11.72f 51.9i 45.6g
Weed free check 0.0j 0.0j 0.0k 0.0h 0.0k 0.0i
Weedy check 93.33a 131.17a 146.17a 107.67a 455.8a 433.3a
LSD(0.05) 4.495 6.033 6.944 7.121 18.60 23.13
CV (%) 13.85 13.52 12.55 18.03 11.14 15.169

Table 3: Effects of weed management practices on density (m-2) and weed dry biomass (gm-2) of broad-leafed weeds and Sedges in Faba bean at Haramaya and Gurawa during the 2014 cropping season CV=Coefficient of Variation, LSD=Least Significant Difference, WAE=Weeks after emergence, Means in columns of same parameter followed by the same letter(s) are not significantly different at 5% level of significance.

The density of sedge decreased significantly with the increase in Smetolachlor and Pendimethalin application rates at both sites except between S-metolachlor at 1.5 and 2.0 kg ha-1 rates at Gurawa (Table 3). On the other hand, significant differences was existed between one and two hand-weeding at both sites and they were resulted in significant reduction in sedges densities over Pendimethalin at 1.0, 1.25 and 1.5 kg ha-1 at Haramaya and Pendimethalin at 1.0 and 1.25 kg ha-1 at Gurawa.

Broadleaved weeds density (m-2): Broadleaved weed density showed a significance difference (P<0.01) due to different weed management practices. Similar to sedge density, lowest density of broadleaved weeds was recorded when S-metolachlor at 1.0 kg ha-1 supplemented with one hand weeding 5 WAE used at both sites. This was statistically as effective as weed free check and Pendimethalin at 1.0 kg ha-1 integrated with one hand weeding 5 WAE at both sites, while the weedy check plots had the highest density (Table 3). The broadleaved weed density decreased with the increase in herbicide application rates at both sites except between Pendimenthalin at 1.25 and 1.5 kg ha-1 rates at Haramaya. Application of S-metolachlor at 2.0 kg ha-1 resulted in significant decrease of broadleaved weed density over S-metolachlor at 1.0 and 1.5 kg ha-1 at both sites. Two hand weeding at 2 and 5 WAE was significantly reduced the broadleaved weeds density over one hand weeding 5 WAE, S-metolachlor at 1.0, 1.5 and 2.0 kg ha-1, Pendimethalin at 1.0, 1.25 and 1.5 kg ha-1 rates but no significant differences existed between Pendimethalin at 1.0+one hand weeding 5 WAE at Haramaya (Table 3).

Total weed density (m-2): The total weed density was significantly (P<0.01) affected in response to weed management practices and site while its interaction with the sites had no significant effect. In this respect, the total weed density was significantly lower at Gurawa. This might be due to lower temperature and rainfall at early crop emergence (Figure 1) and lower weed density at Gurawa (Table 2) compared to Haramaya. The lower dose (1.0 kg ha-1) of S-metolachlor and Pendimethalin supplemented with one hand weeding were statistically in parity but significantly reduced total weed density than other herbicides and hand weeding treatments (Table 4). Using of Smetolachlor and Pendimethalin each with 1.0 kg ha-1 and one hand weeding 5 WAE were reduced the total weed density by 96.5% and 93.4%, respectively over weedy check.

Treatments Total weed density
Site:  
Haramaya 75.95a
Gurawa 72.75b
LSD (0.05) 3.00
Weed management practices:  
S-metolachlor 1.0 kg ha-1 72.04f
S-metolachlor 1.5 kg ha-1 54.89g
S-metolachlor 2.0 kg ha-1 42.56h
Pendimethalin 1.0 kg ha-1 141.62b
Pendimethalin 1.25 kg ha-1 111c
Pendimethalin 1.5 kg ha-1 96.92d
S-metolachlor 1.0 kg ha-1+ one  hand weeding 5 WAE 8.29j
Pendimethalin 1.0 kg ha-1 + one hand weeding 5 WAE 15.74j
One hand weeding at 2 WAE 83.75
Two hand weeding at 2 and 5 WAE 26.19e
Weed free check 0.0k
Weedy check 239.17a
LSD(0.05) 7.887
CV (%) 13.1

Table 4: Main effect of total weed density at Haramaya and Gurawa as influenced by weed management practices during the 2014 cropping season. CV=Coefficient of Variation, LSD=Least Significant Difference, WAE=Weeks after emergence, Means in column followed by the same letter(s) are not significantly different at 5% level of significance.

Similarly Sajid [21] reported the highest weeds density in weedy check; while, the lowest weeds density was noticed with application of S-metolachlor in pea (Pisum sativum L.). The significantly higher weed density with lowest S-metolachlor and Pendimethalin application rate at both sites was in line with the finding of Khan [22] who stated that reduced rates of herbicide are not advisable under heavy weed pressure. Moreover, at higher rates of application, absorption and translocation of the herbicide might have failed to keep pace with its metabolism compared to lower rates of application, thus weeds surrendered to higher rate of application and proved more effective in reducing the density.

Weed dry weight: The effect of weed management practices on weed dry weight was followed similar trends with broadleaved weeds and sedges at both sites. In line with this, the minimum weed dry weight was recorded with S-metolachlor 1.0 kg ha-1 suplemented with one hand weeding 5 WAE which was statistically in parity with weed free check at both sites (Table 3). Also the results revealed that application of 1.0 kg ha-1 of S-metolachlor and Pendimethalin each supplemented with one hand weeding was reduced weed dry weight by 96.4 and 93.3% at Haramaya and by 96.7 and 93.6% at Gurawa respectively over weedy check.

On the other hand, two hand weeding at 2 and 5 WAE gave significantly minimum weed dry weight of 51.9 and 45.6g m-2 at Haramya and Gurawa, in that order; compared to weed dry weight obtained with the application of S-metolachlor (1.0, 1.5 and 2.0 kg ha-1), Pendimethalin (1.0, 1.25 and 1.5 kg ha-1) and one hand weeding 2 WAE under both sites. However, at Gurawa, no significant difference observed between two hand weeding and Pendimethalin 1.0 kg ha-1 supplemented with one hand weeding 5 WAE. The application of Smetolachlor (1.0, 1.5 and 2.0 kg ha-1) was significantly performed better than Pendimethalin at (1.0, 1.25 and 1.5 kg ha-1) across both sites. Sajid [21] also reported better performance of S-metolachlor in reducing weed dry biomas as compared to Pendimethalin, Metribuzin and Isoproturon in pea. Sajid [23] also reported that minimum dry biomass was recorded for Pendimethalin, which was statistically comparable with S-metolachlor. At the same time as comparing one hand weeding at 2 WAE with two-hand weeding at 2 and 5 WAE, weed dry weight decreased similar to broadleaved weeds and sedge densities at both sites (Table 3). This might be due to the extent to which the weed species and or the density differed at both sites.

On the other hand, the higher weed dry weight in weedy check might also be due to higher weed density that provided an opportunity to the weeds to compete vigorously for nutrients, space, light, water and carbon dioxide resulting in higher biomass production. These results are in agreement with the findings of Alfonso [24] and Das [25] who reported maximum weed dry weight in weedy check.

Crop phenology and growth

Days to 50% flowering and 90% physiological maturity: Both days to 50% flowering and 90% physiological maturity were significantly influenced by weed management practices. Faba bean plants at Haramaya attained flowering earlier by 12 days than at Gurawa. This might be due to the higher temperature and rainfall at early crop emergence at Haramaya compared to Gurawa (Figure 1). The results revealed that under weed free check, days to flowering was statistically in parity with 1.0 kg ha-1 of S-metolachlor and Pendimethalin each supplemented with one hand weeding 5 WAE, two hand weeding at 2 and 5 WAE, S-metolachlor (1.5 and 2.0 kg ha-1) and one hand weeding at 2 WAE at Haramaya. However, at Gurawa it was statistical at par with S-metolachlor and Pendimethalin each at 1.0 kg ha-1 and integrated with one hand weeding 5 WAE (Table 5). In weedy check the shading of crop plants by weeds might have reduced sunlight interception thus prolonged the vegetative growth resulting in delayed days to flowering.

advances-crop-science-maximum-temperatures

Figure 1: Rainfall (mm), minimum and maximum temperatures (°C) recorded during the 2014 cropping season at Haramaya and Gurawa (Source: Jigijiga Meteorological Station).

Weed management practices Days to flowering Days to physiological maturity
Haramaya Gurawa Haramaya Gurawa
S-metolachlor 1.0 kg ha-1 48.3bcd 60.0cd 105.0bcd 120.0de
S-metolachlor 1.5 kg ha-1 47.0cde 60.00cd 104.0cde 119.3de
S-metolachlor 2.0 kg ha-1 47.3cde 59.40d 103.3def 118.6ef
Pendimethalin 1.0 kg ha-1 49.6b 62.333ab 106.6bc 124.33b
Pendimethalin 1.25 kg ha-1 48.6bc 62.00b 107.6b 122.6bc
Pendimethalin 1.5 kg ha-1 48.6bc 61.33bc 106.3bc 121.0cd
S-metolachlor 1.0 kg ha-1+ one  hand weeding 5 WAE 45.6e 57.0f 102.3def 114.0g
Pendimethalin 1.0 kg ha-1 + one hand weeding 5 WAE 46.3de 57.67ef 102.0ef 114.3g
One hand weeding at 2 WAE 47.3cde 60.33cd 103.0def 120.0d
Two hand weeding at 2 and 5 WAE 46.3de 59.0de 102.3def 117.0f
Weed free check 45.3e 56.33f 101.0f 113.6g
Weedy check 52.66a 63.67a 111.3a 127.33a
LSD(0.05) 2.23 1.535 2.749 2.32
CV (%) 2.760 1.513 1.552 1.152

Table 5: Effect of weed management practices on days to flowering and physiological maturity of Faba bean at Haramaya and Gurawa during the 2014 cropping season CV=Coefficient of Variation, LSD=Least Significant Difference, WAE=Weeks After Emergence, Means in columns of same parameter followed by the same letter(s) are not significantly different at 5% level of significance.

In line with this result Sunday [26] identified that the plants in not weeded plots took the highest time to reach 50% flowering in cowpea. The influence of weed management practices on 90% days to physiological maturity was followed similar trend to 50% days to flowering at both sites; however, in case of 90% days to physiological maturity, application of 1.5 kg ha-1 S-metolachlor had no statistical in parity with weed free check at Haramya. The physiological maturity of the crop was earlier by 9 and 13 days at Haramaya and Gurawa respectively over low dose of S-metolachlor and Pendimethalin each supplemented with one hand weeding 5 WAE at both sites. The probably reason for differences in maturity across site could be due to the differences in amount and distribution of rain fall, temperature and elevation, while the earlier or delayed maturity in weedy check plots might be due to the shading effect of weeds on crop plants might have reduced interpretation of sunlight thus prolonged the length of growing season resulting in delayed of crop physiological maturity.

The plants in weedy check plots attained significantly higher height (131.32 cm) than others weed management practices. This was followed by the application of Pendimethalin at 1.0 kg ha-1 (126.73 cm) Pendimethalin at 1.25 kg ha-1 (121.60 cm) which did not show significant difference with the height measured in plots treated with Pendimethalin at 1.25 kg ha-1, one hand weeding at 2 WAE, Smetolachlor 1.0 kg ha-1 and S-metolachlor 1.0 kg ha-1, S-metolachlor 1.5 kg ha-1 (Table 6). Alike the effect of S-metolachlor at 1.0 kg ha-1 and Pendimethalin at 1.0 kg ha-1 each supplemented with one hand weeding was statistically the same in height as compared to plants height in weed free check plots. This might be due the better broadleaved weeds control in the plots treated with these treatments (Tables 3) that might have reduced a severe competition to the crop for growth resources specially the nutrients and moisture as the plants belonging to the same morphology are more competitive than the plants with dis-similar morphology.

Plant height

Site and weed management practices but their interactions significantly (P<0.01) influenced plant height. The Faba bean plants at Gurawa were significantly taller by 3.84% than at Haramaya (Table 6). The more height attained by the plants at Gurawa could be due to relatively higher seasonal rainfall than at Haramaya (Figure 1).

Factors Crop Stand (ha-1) Plant height
(cm)
Seeds per pod Hundred seed weight (g)
Sites:        
Haramaya 182917b 117.384b 3.425 46.66b
Gurawa 186806a 122.072a 3.530 49.188a
LSD (0.05) 3429.8 1.3734 NS 0.9612
Weed management practices:        
S-metolachlor 1.0 kg ha-1 187083bcd 120.00cd 3.48abc 47.80ef
S-metolachlor 1.5 kg ha-1 184583d 118.76cde 3.60abc 48.27def
S-metolachlor 2.0 kg ha-1 193750abc 116.50ef 3.40cd 49.65cde
Pendimethalin 1.0 kg ha-1 174167e 126.73b 3.13de 41.800h
Pendimethalin 1.25 kg ha-1 175000e 121.60c 3.41bc 44.88g
Pendimethalin 1.5 kg ha-1 183750d 121.77c 3.58abc 45.20g
S-metolachlor 1.0 kg ha-1+ one  hand weeding 5 WAE 196667a 113.20f 3.68ab 54.27b
Pendimethalin 1.0 kg ha-1 + one hand weeding 5 WAE 194583ab 115.7ef 3.53abc 51.73c
One hand weeding at 2 WAE 185833cd 121.28c 3.48abc 46.66fg
Two hand weeding at 2 and 5 WAE 190417abcd 116.67de 3.650abc 50.23cd
Weed free check 198333a 113.20f 3.73a 57.32a
Weedy check 154167f 131.32a 3.03e 37.30i
LSD (0.05) 8401.3 3.364 0.2675 2.3543
CV (%) 3.91 2.417 6.619 4.22

Table 6: Crop Stand (ha-1), Plant height (cm), Seeds per pod and hundred seed weight (g) of Faba bean as influenced by the main effects of sites and weed management practices during the 2014 cropping season CV=Coefficient of Variation, LSD=Least Significant Difference, WAE=Weeks After Emergence, NS=Not Significant, Means in column followed by the same letter(s) are not significantly different at 5% level of significance.

Grishin [27] reported a great demand for light, space, moisture and nutrients by plants with similar morphology and physiology. In agreement with present result [28] found differences in plant height due to various intensities of weed competition with crop plants.

Yield components and yield

Stand count at harvest: Site and weed management practices had significant influence (P<0.01) on stand count ha-1. The crop stand was significantly higher by 2.13% at Gurawa than at Haramaya. The lowest total weed density as well as weed dry weight at Gurawa than at Haramaya might have contributed for the higher survival of crop plants (Tables 3 and 4). Weed free check gave the highest stand count ha-1 (198333) which did not vary significantly with S-metolachlor at 2.0 kg ha-1, S-metolachlor at 1.0 kg ha-1+one hand weeding 5 WAE, Pendimethalin at 1.0 kg ha-1+one hand weeding 5 WAE and two hand weeding at 2 and 5 WAE (Table 6). The possible reason for the higher stand count in these treatments could be due to their better weed control might have competitive advantage to the crop over the weeds (Tables 3 and 4). Further, the plants in weedy check had the lowest stand count ha-1(154167), which was significantly lower than the other weed management practices. Weeds might have suppressed the crop plants due to severe competition for growth resources particularly for space and light that suppressed crop plants to the extent that the crop plants could not survive. Two hand weeding at 2 and 5 WAE was not significantly different from the rest of the treatments, except Pendimethalin at 1.0 kg ha-1 and weedy check treatments. Similar results were reported by [29].

Treatments Number of pods plant-1 Grain yield (kg ha-1) Aboveground dry biomass (kg ha-1) Harvest index (%) Yield loss (%)
Haramaya Gurawa   Haramaya Gurawa Haramaya Gurawa Haramaya Gurawa Haramaya Gurawa
T1 10.5jkl 12.1fgh 1730.9ij 3040.8d 5238.9gh 8036.9b 33.0fg 38.0bcd 48.0 23.1
T2 11.3hijk 12.7efg 1957.7hi 3045.4d 5626.1fgh 7745.0bc 35.0ef 39.33ab 41.2 23.0
T3 11.2hijk 13.1def 2052.6gh 3217.0cd 5802.8efg 8465.0b 35.3ef 38.0bcd 38.3 18.6
T4 9.1m 9.7lm 1083.3l 2038.4gh 3953.7i 6886.4cd 27.3j 29.66hij 67.4 48.4
T5 10.0lm 10.4kl 1256.7kl 2266.9fg 3957.4i 5970.6defg 31.66gh 38.0bcd 62.2 42.6
T6 10.4kl 10.9hijkl 1338.7kl 2474.7ef 4156.3i 6339.0def 32.0gh 39.0b 59.8 37.4
T7 13.4cde 15.5b 2667.3e 3555.8b 6892.3cd 8535.7ab 38.6bc 41.6a 19.8 10.0
T8 12.5efg 14.4bc 2522.1ef 3431.7bc 6932.5cd 8580.9ab 36.3cde    40.0ab 24.2 13.2
T9 10.6ijkl 11.7ghi 1487.4jk 2713.1e 4619.5hi 6960.4cd 32.0gh 39.0b 55.3 31.4
T10 11.7ghi 13.6cde 2428.8ef 3287.5bcd 6745.2cde 8362.9b 36.0de 39.3ab 27.0 16.8
T11 14.3cd 17.0a 3327.1bcd 3952.5a 8755.6ab 9492.6a 38.0bcd 41.6a 0.0 0.0
T12 7.6n 9.1m 722.8m 1166.0s 2535.6j 3861.8i 28.66ij 30.33hi 78.3 70.5
LSD (0.05) 1.202 298.5 1026.7 2.345  
CV (%) 6.21 7.68 9.707 3.991  

Table 6: Crop Stand (ha-1), Plant height (cm), Seeds per pod and hundred seed weight (g) of Faba bean as influenced by the main effects of sites and weed management practices during the 2014 cropping season CV=Coefficient of Variation, LSD=Least Significant Difference, WAE=Weeks After Emergence, NS=Not Significant, Means in column followed by the same letter(s) are not significantly different at 5% level of significance.

Number of pods per plant: Number of pods plant-1 had significant effect on the site, weed management practices and their interaction. The highest number of pods per plant (17.0) was obtained from the weed free check plots at Gurawa. This was followed by S-metolachlor 1.0 kg ha-1+one hand weeding at 5 WAE at the same site, which had statistically in parity with Pendimethalin 1.0 kg ha-1+one hand weeding 5 WAE at Gurawa (Table 7). This might be due to reduced weed competition (Table 3) in plots treated with these weed management practices that made growth resources (nutrient, moisture and light) more accessible for individual plant. As a consequence it might result in higher net assimilation rate thus retaining more flowers. The development of more and vigorous leaves under low weed infestation might have also helped to improve the photosynthetic efficiency of the crop and supported large number of pods [30]. The interaction of two hand weeding at 2 and 5 WAE with site showed significant difference with each other, however the use of this treatment at Haramaya was failed to proved significantly number of pods plant-1 compared to one hand weeding across both sites, whereas its interaction with Gurawa was proved significantly better than one hand weeding at 2 WAE.

  Weed Management Practices Average
yield
(kg ha-1)
Adjusted
yield
( kg ha-1)
Gross
benefit
( ETB ha-1)
Total
variable cost (ETB ha-1)
Net
benefit
( ETB ha-1)
S-metolachlor 1.0 kg ha-1 2385.85 2147.27 36504 583 35921
S-metolachlor 1.5 kg ha-1 2501.55 2251.40 38274 687 37587
S-metolachlor 2.0 kg ha-1 2634.8 2371.32 40312 791 39521
Pendimethalin 1.0 kg ha-1 1560.85 1404.77 23881 1117 22764
Pendimethalin 1.25 kg ha-1 1761.8 1585.62 26956 1302.5 25653.5
Pendimethalin 1.5 kg ha-1 1906.7 1716.03 29173 1488 27685
S-metolachlor 1.0 kg ha-1+ one  hand weeding 5 WAE 3111.55 2800.40 47607 1903 45704
Pendimethalin 1.0 kg ha-1 + one hand weeding 5 WAE 2976.9 2679.21 45547 2437 43110
One hand weeding at 2 WAE 2100.25 1890.23 32134 2640 29494
Two hand weeding at 2 and 5 WAE 2858.15 2572.34 43730 3960 39770
Weedy check 944.4 849.96 14449 0 14449

Table 8: Partial budget analysis to estimate net benefit for weed management practices of Faba bean averaged over sites in 2014 cropping season. ETB=Ethiopian Birr; WAE=Weeks after crop emergence; Cost of Pendimethalin and S-metolachlor 742 and 208 ETB kg-1, respectively; Spraying 375 ETB ha-1; Cost of hand weeding and hoeing 2 WAE 48 persons, 35 DAE 24 persons @Birr 55/ person; Sale price of Faba bean 19.50 ETB kg-1; Field price of Faba bean 17 ETB kg-1; Cost of harvesting, Threshing and winnowing 170 ETB 100 kg-1; Packing and material cost 6 ETB 100 kg-1 and Transportation 7 ETB 100 kg-1;  ETB=0.0450690 USD (October10, 2016).

The lowest number of pods per plant (7.6) was recorded from weedy check at Haramaya, which was significantly lower than all other interactions across both sites. On other hand, number of pods per plant obtained from weedy check at Gurawa was significantly lower than all the interactions, except the interactions of weedy check and Pendimethalin at 1.25 kg ha-1 at Haramaya as well as Pendimethalin at 1.0 kg ha-1 at both sites (Table 7). These results are in line with Hadi [31] who observed an increased number of pods plant-1 where weed population was reduced by management techniques. Similarly, Pereira [32] and El-Metwally [33] stated that the number of pods produced per plant or maintained to final harvest depends on a number of environmental and management practices.

Number of seeds per pod: Number of seeds pod-1 had a significant effect due to weed management practices. The number of seeds pod-1 not increased significantly with an increase in S-metolachlor and Pendimethalin rates except application of Pendimethalin at 1.0 kg ha-1 resulted in significant lower number of seeds pod-1 as compared to the value obtained from Pendimethalin at 1.25 and 1.5 kg ha-1 (Table 6).

Also, the results showed the highest number of seeds pod-1 (3.73) was obtained from weed free check plots which was statistically similar with all other treatments other than S-metolachlor at 2.0, Pendimethalin at 1.0 kg ha-1, Pendimethalin at 1.25 kg ha-1 and weedy check. Due to the reduced interference of weeds (Tables 3 and 4); the vigorous leaves might have helped to improve the photosynthetic efficiency of the crop that supported large number of seeds pod-1. Nevertheless, the plants in weedy check gave significantly lower number of seeds pod-1 (3.03).

The poor seed filling in weedy check plots might be due to high competition of weeds with crop plant with moisture, light, space and nutrients. The severe weed competition between the weeds and crop in weedy check prominently reduced the nutrient mobility towards grains which might have affected the seed development potential of the Faba bean plant. In consistent with this result Gupta [34] also indentified lowest number of seeds pod-1in weedy check plots.

Hundred seed weight: Sites and weed management practices significantly (P<0.01) influenced hundred seed weight while their interaction had no significant effect on 100 seed weight. The seed weight at Gurawa was significantly higher than at Haramaya by 5.42% (Table 6). The relatively optimum rainfall, temperature and suitable soil conditions at Gurawa during the cropping season might have helped Faba bean plants to produce well filled and heavier seeds. On other hand, significantly higher hundred seed weight (57.32 g) was obtained from weed free check. This might be due to the plants raised under complete weed free environment utilized available resources to their maximum benefit leading to increased seed weight. Moreover, the more and vigorous leaves under weed free environment might have improved the supply of assimilate to be stored in the seed, hence, the weight of 100 grains increased.

Among the weed control treatments, application of 1.0 kg ha-1 of Smetolachlor supplemented with one hand weeding 5 WAE gave the highest seed weight (54.27 g), followed by application of 1.0 kg ha-1 Pendimethalin supplemented with one hand weeding 5 WAE, two hand weeding at 2 and 5 WAE, S-metolachlor at 2.0 and 1.5 kg ha-1. However, two hand weeding at 2 and 5 WAE did not vary significantly with Pendimethalin 1.0 kg ha-1+one hand weeding 5 WAE, Smetolachlor at 2.0 and 1.5 kg ha-1 (Table 6). Similarly Peer [35] reported that effect of different weed management practices might have resulted in attaining variable hundred seed weight. Meanwhile, significantly lower hundred seed weight (37.30 g) was recorded from Weedy check plots. In agreement with this findings, Peer [35] and Getachew [29] observed lowest number of hundred seed weight of soybean in weedy check plots.

Grain yield

Faba bean grain yield was significantly (P<0.01) influenced by the site, weed management practices and their interaction. The highest grain yield (3952.5 kg ha-1) was obtained from complete weed free at Gurawa. However, as comparing the weed control treatments, the highest grain yield was recorded with S-metolachlor 1.0 kg ha-1 supplemented with one hand weeding 5 WAE at Gurawa, which was statistically in parity with pendimethalin 1.0 kg ha-1 supplemented with one hand weeding 5 WAE and two hand weeding at 2 and 5 WAE at the same site and weed free check at Haramaya (Table 7). Furthermore, interaction effect revealed that no significant difference was existed among the grain yield obtained with two-hand weeding at 2 and 5 WAE and 1.0 kg ha-1 of S-metolachlor and pendimethalin each supplemented with one hand weeding 5 WAE at Haramaya and one hand weeding 2 WAE at Gurawa. Among the alone application of herbicides, S-metolachlor at 2.0 kg ha-1 recorded highest grain yield (3217 kg ha-1) at Gurawa which was statistically at par with Smetolachlor at 1.5 and S-metolachlor at 1.0 kg ha-1 at the same site. Generally, interaction effect of S-metolachlor at all rates with sites were proved grain yield significantly better than Pendimethalin at all rates across both sites. The increased grain yield in these treatments might be due to the proper utilization of moisture, nutrients, light and space by the Faba bean in the lesser of weed competition.

The results are corroborating with those reported by Getachew and Mengesha [29,36]. Moreover, the yield obtained at Gurawa, was significantly higher than at Haramaya under all of their respective weed management practices. This difference might have been partially due the differences that existed in number of pods plant-1 and hundred seed weight (g) between the sites (Tables 6 and 7). Similar reports by Singh and Abdel [37,38] also concluded that proper weed management improve the yield of crops.

Aboveground dry biomass yield: The interaction of weed management practices and sites significantly (P<0.01) influenced aboveground dry biomass. The interaction of weed free check at Gurawa gave highest aboveground dry biomass (9492.6 kg ha-1), however this was at par with the interaction of weed free check at Haramaya (8755.6 kg ha-1), Pendimethalin and S-metolachlor each at 1.0 kg ha-1 and supplemented with one hand weeding at Gurawa (Table 7). The increased aboveground dry biomass in these treatments might be due to the crop plants utilized the resources more efficiently that resulted inhigher final crop stand (Table 6). Similar with present results, Mohammadi and Tilahun [39,40] reported good suppression of weed growth by cultural and herbicidal control measures that lead to low competition by weeds for light, space and nutrients by which the crop could utilize both biotic and abiotic resources efficiently, leading to higher dry biomass production. On the other hand, the significantly lower aboveground dry biomass yield (2535.6 kg ha-1) was obtained in weedy check at Haramaya (Table 7). This might be due to severe competition for growth resources resulting in lower availability of nutrients for the crop thus causing reduction in number of tillers thereby low straw yield. Alike number of pods plant-1 and grain yield, aboveground dry biomass yield also increased with increasing frequency of hand weeding from one (at 2 WAE) to two (at 2 and 5 WAE) across both sites and a greater significant increase in aboveground dry biomass yield over the weedy check was observed at Gurawa (Table 7). However, increase in both herbicides rates did not bring a significant increase of aboveground dry biomass yield at both sites.

Harvest index

The interaction effect of weed management practices and the sites revealed significantly highest harvest index (41.6%) with weed free check and S-metolachlor 1.0 kg ha-1 with one hand weeding 5 WAE at Gurawa. This had statistically in parity with the harvest index obtained in the interaction of the same site with application of Pendimethalin 1.0 kg ha-1 supplemented with one hand weeding 5 WAE and two hand weeding at 2 and 5 WAE (Table 7). The result also showed no significant variation in harvest index between Haramaya and Gurawa when Pendimethalin at 1.0 kg ha-1 was applied. Furthermore, at both sites, no significant difference existed among all rates of S-metolachlor applications whereas similar trends were not observed with rates of Pendimethalin applications.

It was found that with Pendimethalin at 1.0 kg ha-1, the harvest index was significantly reduced at Haramaya but it had statically in parity with weedy heck at the same site compared to the others weed management practices at both sites (Table 7). However, weedy check plots at Gurawa, resulted in statistically similar harvest index with Pendimethalin 1.0 kg ha-1 at Gurawa and Pendimethalin (1.25 and 1.5 kg ha-1), one hand weeding 2 WAE and weed free check plots at Haramaya. This lower harvest index might be due to severe weed competition with the crop for the growth factors, which restricted the growth and development of the crop in weedy check plots. In contract with this, Mizan and Singh [41,42] reported that increased vegetative growth duration and allocation of more assimilates for shoot rather than root growth.

Yield Loss

The amount of grain yield loss in Faba bean was affected by weeds in various weed management practices. As comparing weed management practices with each others, the highest yield loss (78.3%) was observed in weedy check plots over weed free check at Haramaya. The next yield loss (70.5%) was obtained from the same treatment but at Gurawa, while comparing to weed free check, the lowest yield loss was recorded from s-metolachlor 1.0 kg ha-1 supplemented by one hand weeding at 5 WAE (Tabale 7). In generally, the minimum yield loss was recorded with the application of 1.0 kg ha-1 of s-metolachlor and pendimethalin each supplemented with one hand weeding 5 WAE at both sites. As the applied rates of both S-metolachlor and pendimethalin increases, the percent of the yield loss due to weeds under both sites become decreases. In line with this finding Patel [43] and Tesfay [44] reported that the presence of weeds reduced grain yield by 82% over complete weed free check.

Partial budget analysis

An economic analysis on the combined results using the partial budget procedure International Maize and Wheat Improvement Center [19] was done due to grain yield was significantly affected (Table 7) by weed management practices. The results in Table 8 of this study showed that the two-hand weeding at 2 and 5 WAE had maximum (3960 Birr ha-1) total variable cost. This was followed by one hand weeding at 2 WAE and Pendimethalin at 1.0 kg ha-1 integrated with one hand weeding 5 WAE which had 2640 and 2437 Birr ha-1 total variable cost, respectively. The higher cost with hand weeding and hoeing than the other treatments was due to the difference in the cost incurred for manual weeding. The highest (47607 Birr ha-1) gross benefit was obtained when 1.0 kg ha-1 of S-metolachlor supplemented with one hand weeding at 5 WAE was used. This was followed by Pendimethalin 1.0 kg ha-1+one hand weeding 5 WAE (45547 Birr ha-1) and two hand weeding at 2 and 5 WAE (43730 Birr ha-1).The higher gross income in these treatments than in the other treatments was due to their higher yield.

The lowest (14449 Birr ha-1) gross return was recorded in the weedy check plots. Similar to the gross benefit, the highest (45704 Birr ha-1) net benefit was obtained with the application of S-metolachlor 1.0 kg ha-1 supplemented with one hand weeding 5 WAE. This was followed by Pendimethalin 1.0 kg ha-1 supplemented with one hand weeding 5 WAE (43110 Birr ha-1) and two hand weeding at 2 and 5 WAE (39770 Birr ha-1). The highest benefit in these treatments was due to the increased gross benefit despite their higher variable input cost. Similar results were also obtained when total variable input cost of the treatments was considered.

Conclusions

Application of 1.0 kg ha-1 of S-metolachlor and Pendimethalin each integrated with one hand weeding at 5 WAE (critical period of weed removal) are the most appropriate methods for effective weed management and economic benefit of Faba bean. Thus, controlling weeds with application of S-metolachlor and Pendimethalin each at 1.0 kg ha-1 supplemented with one hand weeding at 5 WAE proved to increase the grain yield and economic benefit of Faba bean. Nevertheless, in case labour is constraint and s-metolachlor herbicide is timely available, pre emergence application of S-metolachlor at 2.0 kg ha-1 should be the alternative to preclude the yield loss and to ensure maximum benefit. The results of this study further imply that, if farmers are unable to carry out weeding at early stage due to labour constraint, low dose of herbicides at early stage are the best alternative could use for enhancing the yield of the crop in the study area later on they can supplement it with hand weeding.

Acknowledgments

The Authors would like to thanks Mrs. Alem Eshetu and Mr. Birhanu Lenjisa of Highland Pulse Crops Research Program Staffs of Haramaya University; for data collection and compilation. The corresponding author would like to thank Dr. Mengesha Kebede for his kindness and encouragement. The Financial support provided by Haramaya University is also dully acknowledged.

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