Determination of Critical Period for Sustainable Weed Management and Yield of Jute (Corchorus olitorius L.) under Sub-Tropical Condition

Abstract

A field investigation was run to ascertain the critical period of weed control in jute (Corchorus olitorius). The study consisted of two distinct sets of treatments, with one set of weeds being left to invade the crop for a longer period of time, specifically, for 15, 30, 45 and 60 days after sowing (DAS) and up to harvest. In the other set of treatments, the plants remained weed-free for progressively longer periods, i.e., 15, 30, 45 and 60 DAS, and until harvest. The reduction in fibre yield (FY) was recorded as 53.39% when weed interference was permitted from the beginning to harvest, as opposed to the season-long weed-free period. The critical period for weed competition (CPWC) of jute was calculated as being 11 to 68 DAS and 19 to 59 DAS, based on results of 5% and 10% yield loss, respectively. Under the 5% yield loss condition, although yield was higher (3.36 t ha⁻¹), the benefit cost ratio (BCR) was lower (1.65), whereas yield was slightly lower (3.19 t ha⁻¹) but BCR was higher (1.73) with respect to 10% yield loss. Therefore, jute fields should be kept weed free from 19 to 59 days after sowing, and a weed management strategy should be undertaken accordingly.

1. Introduction

Jute (Corchorus spp.) is a vital fibre and cash crop, and demand for its fibre has, surprisingly, surged in current times, globally as well as in Bangladesh. About 2618 thousand tonnes of jute were produced on 13.09 lakh ha area worldwide in the year 2020–2021 [1]. In Bangladesh, jute farming currently occupies roughly 727,382 ha of land, producing 202,374.79 tonnes of fibre annually [2]. In addition, Bangladesh made BDT 863.141 in the fiscal year 2020–2021, which is about 2.36% of its GDP, and generates about 5–6% of foreign exchange earnings [3] by exporting raw jute and 282 different types of jute goods to various nations around the world [4].

Weeds, being the everlasting crop pest in today’s input-intensive farming systems, cause the greatest potential crop damage (about 34%), followed by diseases (18%) and animal pests (16%) [5]. Overall, weeds cause 45% of yield loss [6], but as weed interference increases, this percentage can rise to 94–96% in rice, 34% in wheat, 50% in pulses, 72% in sugarcane and nearly 90% in almost all vegetables [7,8]. Weed interference is also a significant barrier to jute cultivation because jute fibre yield may decrease by up to 70% under improper weed management approaches [9,10]. Nevertheless, yield reduction is influenced by the invasive weed flora, its population size and the period of competition; type of crop grown; and soil properties such as type, pH level and salt content [11]. In addition, weeds indirectly influence crop productivity by providing a harbour for agricultural pests, interfering with irrigation systems, and decreasing yield quality, consequently driving up processing costs [12]. Furthermore, weeds can grow rapidly and voraciously interfere with the photosynthetic function of jute plants by blocking sunlight and limiting wind flow, which results in stunted crop growth and, consequently, decreases in crop yields [13].

The scheduling of weed management approaches may emerge as a challenge, with different invasive weed species requiring consideration. For some, the initial flush of weeds may appear at sowing, but subsequent weed flushes usually tend to occur over the season. Therefore, these weed flora usually need to be managed on a number of occasions during the season, after precipitation or irrigation activities that lead to weed germination. Weed management approaches initiated by the weed growth phase ensure that weeds are managed before seed setting, but prior to this stage, an economic threshold level is used. Additionally, the weed management threshold must be dynamic in response to the crop development phase, since earlier studies have documented that cultivars show higher susceptibility to early-season weed competition than late-season competition [14,15].

A dynamic economic threshold for managing weeds could be developed employing the CPWC, which specifies the phase of crop growth when the crop is susceptible to weed competitiveness and the loss resulting from weed competitiveness outweighs the expense of suppressing the weeds [15,16]. The CPWC is established through determining the critical time for weed removal (CTWR) and the critical weed-free period (CWFP), and combining them with the yield–loss threshold [14,15]. The CPWC, on the other hand, is a crucial component of integrated weed management (IWM) and can be viewed as the initial stage in developing a weed management strategy [17,18]. Thereby, sustainable control approaches need to be implemented to handle weeds at an appropriate moment and in the proper way based on soil conditions and weed predominance to avert the related environmental and monetary damages [19]. The literature has stated that weed interference was found to have very little impact on crop yield outside of this crucial window [20].

In Bangladesh, manual or hand weeding is a prevalent practice for controlling weeds in jute, but it is impeded by a labour crisis and irregular rainfall throughout the CPWC. Hence, without understanding the precise timing of weeding and its advantages, farmers alter the time of weeding accordingly. However, comprehending the CPWC and the weed-related aspects is crucial for determining the right timing for weed control, and efficient application of herbicide as well [21]. Moreover, CPWC is a crucial approach for lowering crop production costs associated with weeding and yield loss, but there is little information on the CPWC in jute. Hence, this research work was undertaken to determine the CPWC for jute in Bangladesh with a view to preventing extreme crop–weed competition and also providing guidelines for developing effective and economic weed control strategies to ensure high yields and quality of tossa jute/Olitorius jute (Corchorus olitorius) fibre.

2. Materials and Methods

2.1. Study Site, Climate and Planting Materials

The investigation was executed at the Jute Agriculture Experimental Station (JAES) of the Bangladesh Jute Research Institute (BJRI) located at Manikganj district (latitudes: 23°38′ and 24°03′ north and longitudes: 89°41′ and 90°08′ east) at fibre production season during 2018 to estimate the CPWC in jute. The experimental field was situated at about 15 m in elevation from the mean sea level and is part of the Young Brahmaputra Flood Plain Agro-ecological Zone (AEZ-8); it has non-calcareous dark grey floodplain soil [22]. Olitorius jute (Corchorus olitorius L.) variety O-9897 was employed as the study material, and seeds were collected from the Breeding Division of the Bangladesh Jute Research Institute, Dhaka, Bangladesh. Monthwise weather data including average maximum and minimum temperatures, relative humidity and total precipitation throughout the experimental season were recorded from the nearest weather station at Dhaka, about 55 km’s distance from jute research station Manikganj, which has been summarized in Figure 1. Prior to conducting the investigation, the soil of the study area was analysed and the physicochemical properties were documented, shown in

Table 1. Physicochemical properties of soil (0–15 cm) of field experiments.

Soil Properties	Analytical Value
Land type	Medium high
Textural class	Silt loam
pH	6.7
Organic matter (%)	1.65
Total nitrogen (%)	0.09
Available phosphorus (ppm)	9.55
Exchangeable potassium (meq/100 gm soil)	0.24
Available sulphur (ppm)	12.88
Available zinc (ppm)	7.56
Calcium (meq/100 gm soil))	9.12
Cation exchange capacity (meq/100 gm soil)	10.14

.

2.2. Experimental Design and Treatments

The field study (size of each plot 4 m × 2.5 m) was replicated three times following a randomized complete block design (RCBD). Seeds were sown @ 5 kg ha⁻¹ on 30 March 2018, maintaining 30 cm row-to-row distance. Because of the standard prescription of the Bangladesh Jute Research Institute (BJRI), each of the plots was fertilized with urea, TSP, MoP, gypsum and zinc sulphate @ 200, 50, 60, 95 and 110 kg ha⁻¹. Half of the urea and all fertilizers were broadcasted at the end of land preparation as a basal dose. The remaining half of the urea (100 kg ha⁻¹) was top-dressed in another split at 45 DAS. Treatments comprised two sets of the weedy condition, stated as below: one set was the weedy condition, i.e., weedy until 15 DAS (W₁), weedy until 30 DAS (W₂), weedy until 45 DAS (W₃), weedy until 60 DAS (W₄) and season-long weedy (W₅); the other one was in the weed-free condition, i.e., weed free until 15 DAS (W₆), weed free until 30 DAS (W₇), weed free until 45 DAS (W₈), weed free until 60 DAS (W₉) and season-long weed free (W₁₀). A quantitative set of treatments involving two elements, (a) a longer period of weed interference and (b) a longer duration of the weed-free period, was applied in order to figure out the critical period of weed competition (CPWC). Depending on the number of days after sowing (DAS), the timeframe of weed removal was determined. By permitting weeds to compete with crops for 15, 30, 45 and 60 DAS, the first component of the CPWC (increasing duration of weed interference) was evaluated, whereas the second element (increasing length of weed-free period) was determined by allowing the weed-free condition from 15, 30, 45 and 60 DAS. Additionally, season-long weedy and season-long weed-free treatments were considered as the control. Weeds were managed by manual weeding.

2.3. Data Collection

2.3.1. Weed Data

The quadrates (0.5 m × 0.5 m) were randomly positioned longitudinally at four different locations in each plot and were used to collect weed data. Weeds were removed to the ground, washed, separated into species, numbered and kept in ovens at 70 °C for 72 h. Weed density (WD) and dry matter (DM) were estimated and expressed as m⁻² and g m⁻², accordingly. The summed dominance ratio (SDR) was calculated using the following formula to identify the dominant weed flora [23]:

$$\mathrm{S}\mathrm{D}\mathrm{R} \mathrm{o}\mathrm{f} \mathrm{a} \mathrm{w}\mathrm{e}\mathrm{e}\mathrm{d} \mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}=\frac{[\mathrm{R}\mathrm{e}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e} \mathrm{d}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}\left(\mathrm{R}\mathrm{D}\right)+\mathrm{R}\mathrm{e}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e} \mathrm{d}\mathrm{r}\mathrm{y} \mathrm{m}\mathrm{a}\mathrm{t}\mathrm{t}\mathrm{e}\mathrm{r}\left(\mathrm{R}\mathrm{D}\mathrm{M}\right)]}{2}$$

(1)

where

$$\mathrm{R}\mathrm{D}\left(\%\right)=\frac{\mathrm{D}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y} \mathrm{o}\mathrm{f} \mathrm{a} \mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{f}\mathrm{i}\mathrm{c} \mathrm{w}\mathrm{e}\mathrm{e}\mathrm{d} \mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}}{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{w}\mathrm{e}\mathrm{e}\mathrm{d} \mathrm{d}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}}\times 100,$$

(2)

$$\mathrm{R}\mathrm{D}\mathrm{M}\left(\%\right)=\frac{\mathrm{D}\mathrm{r}\mathrm{y} \mathrm{m}\mathrm{a}\mathrm{t}\mathrm{t}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{a} \mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{f}\mathrm{i}\mathrm{c} \mathrm{w}\mathrm{e}\mathrm{e}\mathrm{d} \mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}}{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{w}\mathrm{e}\mathrm{e}\mathrm{d} \mathrm{d}\mathrm{r}\mathrm{y} \mathrm{m}\mathrm{a}\mathrm{t}\mathrm{t}\mathrm{e}\mathrm{r}}\times 100$$

(3)

Data on the plant population (PP) were collected using 1 m² quadrates, which were randomly positioned longitudinally at three different spots in each of the plots during the growing stage and then counted and made average, which was expressed as plant m⁻². The base diameter (BD) was calculated at the base of the plant by slide callipers from ten randomly selected plants and documented in mm. After collecting all data from each of the plants, the plant wise fresh weights of root, stick, bar and leaves were taken, then afterwards oven-dried at 70 °C for 72 h separately and weighed to estimate dry matter (DM), which was expressed as g plant⁻¹.

2.3.2. Determination of CPWC

By averaging the yields over the three blocks for each treatment, the season wise relative yield (RY) under the season-long weed-free control for each set of treatment groups was determined. RY data for the weedy or weed-free treatments were compared to the increasing weed interference period or the increasing weed-free time in order to determine the CPWC. The logistic equation was proposed by Hall et al. [24] and updated by Knezevic et al. [25] to characterize the influence of increasing durations of weed interference on fibre yield and identify the start of the CPWC.

Y = [(1/(exp (c × (T − d) +f)) + (f − 1)/f)) × 100]

(4)

Here, Y = % relative yield of weed-free condition, T = duration of weed-free period during weed interference (days), d= inflection point in day or days at 50% yield loss; c and f are constants.

The following Gompertz model [24,25] was used to facilitate a satisfactory fit to RY as to how the increasing length of the weed-free period affected the RY and to determine the end of the CPWC for yield loss levels of 5 and 10%, chosen arbitrarily [26].

Y = [A × exp(b × exp(−k × T))]

(5)

Here, Y = Y = % relative yield of weed free condition, A is the asymptote, T = duration of weed-free period (days); b and k = constants.

2.3.3. Yield Data

After harvest, fibre was separated following the procedure described by BJRI and then sun dried and weighed, and FY was measured as kg plot⁻¹ (10 m²), which was converted to t ha⁻¹.

2.4. Statistical Analysis

Analysis of variance (ANOVA) was estimated by Statistical Analysis System (SAS 9.1) software and means were compared following a protected LSD procedure at 5% level of probability [27] using the Duncan Multiple Range Test (DMRT). Data from the two seasons were examined independently. The analysis of variance for weed density and dry weight was performed following a square root transformation to normalize the data.

3. Results

3.1. Weed Composition

The naturally existing weed community in the research area had a wide weed spectrum, including 12 weed species representing 5 different families, of which 6 belonged to Poaceae, 3 to Euphorbiaceae and 1 of each to Solanaceae, Cyperaceae and Asteraceae (

Table 2. Family, life cycle, types, density and dry matter of different weeds as per season-long weedy plots of Olitorius jute.

Name of Weeds	Family	Life Cycle	Weed Type	Density (no. m−2)	DM (g m−2)
Cyperus rotundus L. (Purple nut sedge)	Cyperaceae	P	Sedge	265.0	132.84
Echinochloa colonum L. (Jungle grass)	Poaceae	A	Grass	49.67	19.38
Digitaria sanguinalis L. (Crab grass)	Poaceae	A	Grass	43.67	21.52
Eleosine indica L. Gaertner (Goose Grass)	Poaceae	A	Grass	23.00	9.77
Physalis heterophylla (L.) Nees. (Clammy ground cherry)	Solanaceae	A	Broadleaf	4.00	13.87
Paspalum distichum L. (Knotgrass)	Poaceae	A	Grass	11.33	9.70
Cynodon dactylon L. (Bermuda grass)	Poaceae	P	Grass	16.67	6.32
Setaria viridis (L.) Beauv. (Green foxtail)	Poaceae	A	Grass	9.33	9.56
Phyllanthus niruri L. (Gale of the wind)	Euphorbiaceae	P	Broadleaf	10.33	6.59
Enhydra fluctuans Lour. (Buffalo spinach)	Asteraceae	A	Broadleaf	3.00	5.01
Euphorbia microphylla Lam. (Prostate spurge)	Euphorbiaceae	A	Broadleaf	2.83	1.22
Euphorbia hirta L. (Asthma plant/Sneeze weed)	Euphorbiaceae	A	Broadleaf	2.67	1.23
Total	-	-	-	441.50	237.03

A—Annual, P—perennial.

). Of these species, nine annuals and three perennials were found to infest the experimental field. Considering weed class, sedges comprised highest density (265 m⁻²) and dry matter (132.84 g m⁻²) (

Table 3. Density and dry matter of different weed groups in season-long weedy plot of Olitorius jute.

Weed Types	Density (m−2)	Dry Matter (g m−2)
Broad leaved	22.83	27.93
Sedge	265.00	132.84
Grass	153.67	76.26
Total	441.50	237.03

). According to the findings, Cyperus rotundus (RD 60.02%) occupied more than ½ of the total jute field, followed by Echinochloa colonum (RD 11.25%), Digitaria sanguinalis (RD 9.89%), Eleosine indica (RD 5.21%) and Cynodon dactylon (RD 3.78%) (Figure 2). The aforementioned weed species produced more RDM as well, but in a different rank and order (Figure 3). Based on weed class, RD and RDM were higher in sedges (Figure 4 and Figure 5). Depending on the SDR, the five most dominant weed species were Cyperus rotundus (58.03%), Echinochloa colonum (9.72%), Digitaria sanguinalis (9.49%), Eleosine indica (4.67%) and Physalis heterophylla (3.38%), whereas Euphorbia hirta (0.56%) was revealed as the least-infested weed species in the jute fields (Figure 6). From the morphological viewpoint, sedge (SDR 58.03%) was the highest-infested weed, followed by grasses (SDR 33.49%) and broadleaves (SDR 8.48%) (Figure 7).

3.2. Effect of Weed Interference Period on WD and DM in Olitorius Jute

The WD and DM of weeds were statistically affected by several weed interference periods in Olitorius jute (

Table 4. Effect of weed interference period on WD (m⁻²) of major weed species of Olitorius jute field.

Weed Interference Period	Cyperus rotundus	Digitaria sanguinalis	Echinochloa colonum	Eleosine indica	Physalis heteropfylla	Euphorbia hirta
W1	30.67 h	17.67 f	13.67 g	1.00 de	4.34 f	0.33 d
W2	161.00 f	25.00 de	20.33 f	2.00 cd	6.00 de	0.83 cd
W3	215.00 d	36.67 c	30.33 d	2.67 bc	7.11 cd	1.33 bc
W4	240.00 c	40.67 bc	37.67 c	3.78 ab	9.33 b	2.00 ab
W5	265.00 a	49.67 a	43.67 a	4.00 a	11.33 a	2.67 a
W6	251.67 b	44.00 b	40.33 b	3.78 ab	10.33 ab	2.33 a
W7	232.00 c	37.00 c	36.00 c	3.00 a–c	7.67 c	1.82 ab
W8	180.00 e	28.00 d	26.33 e	2.00 cd	6.25 c–e	1.33 bc
W9	75.33 g	23.00 e	15.33 g	1.33 d	4.89 ef	0.67 cd
W10	0 i	0 g	0 h	0 e	0 g	0 d
LSD (0.05)	2.559	10.132	4.186	1.634	1.635	0.923
CV (%)	3.58	8.09	5.66	7.76	12.82	4.38

Here, columns with treatment means those with similar letters did not vary significantly. W₁—weedy until 15 DAS, W₂—weedy until 30 DAS, W₃—weedy until 45 DAS, W₄—weedy until 60 DAS, W₅—season-long weedy; W₆—weed free until 15 DAS, W₇—weed free until 30 DAS, W₈—weed free until 45 DAS, W₉—weed free until 60 DAS, W₁₀—season-long weed free.

and

Table 5. Effect of weed interference period on DM (g m⁻²) of different weed species of Olitorius jute field.

Weed Interference Period	Cyperus rotundus	Digitaria sanguinalis	Echinochloa colonum	Eleosine indica	Physalis heteropfylla	Euphorbia hirta
W1	5.70 g	2.12 g	1.57 h	0.44 e	0.90 e	0.16 d
W2	50.17 f	8.96 e	7.56 f	3.20 d	4.19 d	0.24 cd
W3	104.85 d	14.35 c	14.99 d	6.05 c	6.15 bc	0.63 bc
W4	126.08 b	17.03 b	19.89 b	9.58 b	8.76 a	1.10 a
W5	134.49 a	19.38 a	21.52 a	13.87 a	9.70 a	1.23 a
W6	132.84 a	17.19 b	19.90 b	10.84 b	8.85 a	1.08 a
W7	118.41 c	14.44 c	17.72 c	6.48 c	6.57 b	0.84 ab
W8	98.17 e	10.92 d	12.96 e	3.59 d	5.36 c	0.62 bc
W9	48.12 f	5.68 f	5.87 g	2.13 de	3.25 d	0.31 cd
W10	0.00 h	0.00 h	0.00 i	0.00 e	0.00 e	0.00 d
LSD (0.05)	1.182	5.186	1.465	0.650	0.682	0.399
CV (%)	3.69	7.76	5.65	25.10	12.57	37.37

Here, columns with treatment means those with similar letters did not vary significantly. W₁—weedy until 15 DAS, W₂—weedy until 30 DAS, W₃—weedy until 45 DAS, W₄—weedy until 60 DAS, W₅—season-long weedy; W₆—weed free until 15 DAS, W₇—weed free until 30 DAS, W₈-weed free until 45 DAS, W₉—weed free until 60 DAS, W₁₀—season-long weed free.

). All the aforesaid weed parameters tended to increase during longer weed interference periods, but tended to decrease during longer weed-free periods. However, Cyperusrotundus was found to be the most densely populated (265.00 m⁻²) and productive of DM (134.49 g m⁻²) weed in the jute fields in the season-long weedy condition (Table 4 and Table 5). The other weeds under this treatment having densities of more than 40 plants m⁻² were Digitaria sanguinalis (49.67 m⁻²) and Echinochloa colonum (43.67 m⁻²) (Table 4). Conversely, Euphorbia hirta was the least densely populated (2.67 m⁻²) and DM-producing (1.23 g m⁻²) weed in the season-long weedy condition, followed by Physalis heterophylla. For Cyperus rotundus, the season-long weedy condition produced the highest WD and DM, followed by weedy from 15 DAS to harvest (251.67 m⁻² and 132.84 g m⁻²), weedy up to 60 DAS (240 m⁻² and 126.08 g m⁻²) and weedy from 30 DAS to harvest (232 m⁻² and 118.41 g m⁻²), whereas the lowest weed density and dry matter was found in the weedy up to 15 DAS condition (30.67 m⁻² and 5.70 g m⁻²). For other weed species, the WD and DM trend followed a similar pattern.

3.3. Effect of Weed Interference Period on Plant Growth of Olitorius Jute

PPs differed significantly due to the weed interference period at various days after sowing (Figure 8). The greatest PP, 154.67 m⁻², 104.67 m⁻², 81.33 m⁻², 73.00 m⁻² and 43.33 m^−2, was found at 30, 45, 60, 75 and 110 DAS under the season-long weedy treatment followed by weedy from 15 DAS to harvest and weedy until 60 DAS, and the lowest plant population was observed at the season-long weed-free treatment at all DAS. Results also revealed that with the advancement of growing time, all the treatments showed a declining trend of PP at all sampling dates (Figure 8).

The BD and DM in Olitorius jute were affected significantly by the weed interference periods at different days after sowing (Figure 9 and Figure 10). The highest BDs (2.45 mm, 5.73 mm, 10.77 mm, 12.76 mm and 18.95 mm at 30, 45, 60, 75 and 110 DAS, respectively) and the highest plant dry matter were documented under the season-long weed-free period, followed by weedy until 15 DAS and weedy from 60 DAS to harvest, and the lowest BDs and DMs were recorded in the season-long weedy plot. These three growth parameters were found to be the lowest at the early growing period and gradually increased with the advancement of time. Considering the season-long weed-free period, the highest BD was found at 110 DAS (18.95 mm), followed by 75 DAS (12.76 mm), 60 DAS (10.77 mm), 45 DAS (5.73 mm) and 30 DAS (2.45 mm) (Figure 9). Furthermore, in the case of the season-long weed-free period, the highest DM value was recorded at 110 DAS (48.61 g plant⁻¹), followed by 75 DAS (18.47 g plant⁻¹), 60 DAS (12.36 g plant⁻¹), 45 DAS (7.02 g plant⁻¹) and 30 DAS (1.69 g plant⁻¹) (Figure 10).

3.4. Effect of Weed Interference Period on Yield Attributes of Olitorius Jute at Harvest

The yield attributes were significantly different due to the weed interference period at the harvest of Olitorius jute (

Table 6. Effect of weed interference period on the growth, fibre yield and quality of Olitorius jute at harvest.

Weed Interference Period	PP (m−2)	BD (mm)	DM (g Plant−1)	FY (t ha−1)	Relative Fibre Yield (%)	Fibre Yield Loss (%)	BS (lb/mg)	FN (µ)	BN (%)
W1	40.00 d	18.58 a	47.63 a	3.27 b	92.37	7.63	9.00 a	18.63 fg	40.68 a
W2	40.67 d	17.13 b	41.60 b	2.75 c	77.68	22.32	8.53 b	19.96 e	37.32 b
W3	41.67 c	16.52 b	35.33 cd	2.26 d	63.84	36.16	8.13 c	21.28 cd	35.00 c
W4	42.33 bc	15.03 c	31.81 e	1.90 e	53.67	46.33	7.90 d	22.62 b	29.70 e
W5	43.33 a	13.69 d	25.67 f	1.65 f	46.61	53.39	7.24 f	24.01 a	26.09 f
W6	42.67 ab	14.92 c	26.52 f	1.88 e	53.11	46.89	7.65 e	23.82 a	27.56 f
W7	42.33 bc	15.36 c	32.40 de	2.24 d	63.28	36.72	8.09 cd	22.11 bc	33.14 d
W8	41.67 c	17.08 b	37.19 c	2.73 c	77.12	22.88	8.50 b	21.03 d	35.55 c
W9	40.33 d	17.20 b	42.47 b	3.24 b	91.53	8.47	8.90 a	19.32 ef	37.67 b
W10	40.00 d	18.95 a	48.61 a	3.54 a	100.00	0	9.03 a	18.06 g	41.72 a
LSD (0.05)	0.916	1.166	3.221	0.134	-	-	0.199	0.983	0.887
CV (%)	1.29	4.13	5.09	3.07	-	-	1.40	2.72	1.50

Here, columns with treatment means that those with similar letters did not vary significantly. W₁—weedy until 15 DAS, W₂—weedy until 30 DAS, W₃—weedy until 45 DAS, W₄—weedy until 60 DAS, W₅—season-long weedy; W₆—weed free until 15 DAS, W₇—weed free until 30 DAS, W₈—weed free until 45 DAS, W₉—weed free until 60 DAS, W₁₀—season-long weed free, PP—plant population, BD—base diameter, DM—dry matter, FY—fibre yield, BS—bundle strength, FN—fineness, BN—brightness.

). The maximum PP (43.33 m⁻²) at harvest was recorded in the season-long weedy treatment followed by weedy from 15 DAS to harvest, weedy up to 60 DAS and weedy from 30 DAS to harvest, and the minimum (40 m⁻²) was observed in the weedy up to 15 DAS and the season-long weed-free treatments (40 m⁻²) (Table 6). However, the findings were totally different in the case of BD and DM of the plants⁻¹. At the harvesting time, the lowest BD (18.95 mm) and DM (48.61 g plant⁻¹) were found in the season-long weed-free period treatment, followed by weedy until 15 DAS, weedy from 60 DAS to harvest, weedy until 30 DAS. The lowest dry matter of plants⁻¹ (25.67 g plant⁻¹) was observed in the season-long weedy plot (Table 6). Additionally, the results of the current study revealed that the PP increased with the increasing weed interference period, but showed a decreasing trend with the increase of the weed-free period. Conversely, the BD and DM completely showed the reverse trend of growth compared to PP.

3.5. Effect of Weed Interference Period on Fibre Yield of Olitorius Jute

The FY was substantially affected by the weed interference period in jute (Table 6). The greatest FY (3.54 t ha⁻¹) was documented in the season-long weed-free period, followed by weedy until 15 DAS, weedy from 60 DAS to harvest and weedy until 30 DAS, and the lowest FY (1.65 t ha⁻¹) at the time of harvest was recorded in the season-long weedy plot (Table 6). Moreover, FY increased with a decreasing weed interference period, whereas it decreased with a decreasing weed-free period. As per the results, the relative fibre yield and fibre yield loss were not significantly influenced by the weed interference period in jute, but the relative fibre yield and fibre yield loss were increased with the decreasing weed interference period and vice versa. Compared to the season-long weed-free period, the greatest fibre yield loss (53.39%) was computed for the season-long weedy treatment, followed by weedy from 15 DAS to harvest, weedy up to 60 DAS and weedy from 30 DAS, and the minimum yield loss (7.63%) was documented for the weedy up to 15 DAS condition (Table 6).

3.6. Effect of Weed Interference Period on Fibre Quality of Olitorius Jute

BS, FN and BN were significantly affected due to the weed interference period in Olitorius jute (Table 6). The highest BS (9.03 lb mg⁻¹) and BN (41.72 %) were found for the season-long weed-free period followed by weedy until 15 DAS, weedy from 60 DAS to harvest, weedy until 30 DAS; the lowest fibre bundle strength (7.24 lb mg⁻¹) and BN (26.09%) were recorded for the season-long weedy treatment (Table 6). Similarly to the other yield attributes and yield, BS and BN increased with the decreasing weed interference period, whereas these traits declined with the increasing weed-free period. However, the present study revealed the opposite results in the case of FN.

3.7. Determination of Critical Period of Weed Completion (CPWC) and Economic Analysis in Response to Weed Interference of Olitorius Jute Production

The CPWP was computed assuming random yield reduction limits of 5% and 10%, which are deemed to be acceptable considering the current profitability of weed control. Figure 11 displayed the projected and actual relative jute fibre yield as influenced by weed interference and weed-free periods. Responses were exceptionally significant, as indicated by higher R² values. As the number of days with weed interference rose, the fibre output decreased, and the pattern of this decline was fitted into a logistic equation. In contrast, fibre output dramatically rose when the weed-free period was extended up to 110 DAS. After that, the rise in fibre output plateaued, and the Gompertz equation was adjusted to the rising trend in fibre output (Figure 11). Considering a 5% level of yield loss, the start of the CPWP was 11 DAS and the end of critical period for the weed-free period was 68 DAS (

Table 7. Estimated critical period of weed completion for varying crop losses in Olitorius jute.

Yield Loss Levels (%)	Critical Period of Weed Competition (DAS or Days)
	Beginning of CPWC (DAS)	End of CPWC (DAS)	Days
5	11	68	57
10	19	59	40

), with the estimated gross income and BCR of BDT 224,412 ha⁻¹ and 1.65, respectively (

Table 8. Economic analysis in response to weed interference of Olitorius jute production.

Weed Interference Period	FY (Kg ha−1)	FP (Tk ha−1)	SY (Kg ha−1)	SP (Tk ha−1)	GI (Tk ha−1)	TC (Tk ha−1)	NR (Tk ha−1)	BCR
	1	2	3	4	5 (2 + 4)	13	14 (5–13)	15 (5/13)
W1	3273.33	180,033	6371.17	38,227	218,260	160,346	57,914	1.36
W2	2753.33	151,433	5360.93	32,166	183,599	148,346	35,253	1.24
W3	2260.00	124,300	4399.97	26,400	150,700	136,346	14,354	1.11
W4	1900.00	104,500	3763.30	22,580	127,080	124,346	2734	1.02
W5	1646.67	90,567	3253.33	19,520	110,087	88,346	21,741	1.25
W6	1883.33	103,583	3666.37	21,998	125,582	100,346	25,236	1.25
W7	2240.00	123,200	4360.60	26,164	149,364	112,346	37,018	1.33
W8	2730.00	150,150	5315.27	31,892	182,042	124,346	57,696	1.46
W9	3243.33	178,383	6313.97	37,884	216,267	136,346	79,921	1.59
W10	3543.33	194,883	6890.00	41,340	236,223	160,346	75,877	1.47
95% yield of W10	3366.17	185,139	6545.50	39,273	224,412	136,346	88,066	1.65
90% yield of W10	3189.00	175,395	6201.00	37,206	212,600	124,346	88,254	1.73

Here, W₁—weedy until 15 DAS, W₂—weedy until 30 DAS, W₃—weedy until 45 DAS, W₄—weedy until 60 DAS, W₅—season-long weedy; W₆—weed free until 15 DAS, W₇—weed free until 30 DAS, W₈—weed free until 45 DAS, W₉—weed free until 60 DAS, W₁₀—season-long weed free, FY—fibre yield, FP—fibre price, SY—stick yield, SP—stick price, GI—gross income, TC—total cost, NR—net return, BCR—benefit cost ratio.

). In contrast, the start of the CPWP was 19 DAS and the end of critical period for the weed-free period was 59 DAS when considering a yield loss of 10%; estimated gross income and BCR were BDT 212,600 ha⁻¹ and 1.73, respectively (Table 7 and Table 8).

4. Discussion

Generally, the existence, structure, abundance, importance and ranking of weed vegetation in a particular site depends on several components of environmental, edaphic and biotic factors such as soil structure, soil reaction, minerals, moisture contents, type of crops and history of cultivated crops [28], as well as local weed seedbank status [29]. A total of 12 weeds were examined in the study, of which Cyperus rotundus was the most infested species, and comprised almost 50–60% of the total weeds. The results are backed up by Islam et al. [30], who mentioned about 6 major weeds in jute fields out of 22 in Manikganj district. They also reported that Cyperus rotundus was the most dominant weed at both Corchorus capsularis (Manikganj, Chandina and Kishoreganj) and Corchorus olitorious (Faridpur and Rangpur) jute fields. Additionally, Hossain et al. [31] also noted that from 2009 to 2011, sedge comprised 68% of the weed population, followed by grass (26%) and broad-leaved weeds (6%) in Manikganj, Kishoreganj and Cumilla; Cyperus rotundus was also the most dominant weed, which is highly in agreement with the present study. Because Corchorus olitorius is typically unable to thrive in stagnant water, it is grown on high land with the seeds planted between mid-April and mid-May [32]. However, the prevailing dry edaphic condition [33] as well as the hot and humid environment during April–May is also very conducive to the profuse germination and growth of Cyperus rotundus [34]. Martin et al. [26] noted that WD has been revealed to be significant in defining the start of the CPWC. According to their results, WD as well as DM were enhanced due to an increasing weed interference period and declined with an increasing weed-free period. The result is identical to the findings of [35,36,37]. Similarly to the present findings, most of the studies found that weeds did not exert much effect on crops after 60 days of sowing [31,35,36,38,39]. Kumar et al. [37] also supported the present findings regarding WD and DM in Olitorius jute and stated that these parameters substantially increased with weed interference, which is backed up by Ali et al. [40] and Anwar et al. [36]. They documented that statistically greater WD and DM in wheat was observed in a 60-days competition. Higher WD resulted in the critical time beginning earlier than it would have at lower densities, but WD had no effect on when the critical period terminated. In conditions of medium to severe weed pressure, the critical timeframe for weed suppression might boost herbicide effectiveness and maximize alfalfa returns, whereas it may not exist at minimum weed severity [41].

Crop–weed competition occurs due to different growth-limiting factors, for example light, air, water, space and nutrients during the crop growing period [42], and negatively influences the height, tillering behaviour and advancement of crop plants [43]. The present study revealed that the PP was increased with weed interference, whereas it decreased with the weed-free period, and the least value was found for the season-long weed-free treatment at all DAS. A similar trend was observed by Mandal and Mukherjee [44]. However, other traits, such as BD and DM, were found to increase with the increasing weed-free period and to reduce with the increasing of the weed interference period. This result is corroborated by Ayyadurai and Poonguzhalan [45]. In the case of BD and DM, the present findings were in agreement with most of the scientists, such as Mandal and Mukherjee [44] and Hassan et al. [46].

The study confirmed that high sensitivity was observed in jute crops to weed interference and in the weed-free period. Because of following regular weeding after 15 DAS, BD, yields and fibre quality were enhanced with the increase of weed-free conditions and declined with the increasing length of weedy conditions. With increases in the weed-free period from 15 DAS to 60 DAS, a substantial rise in fibre output was also perceived in the current study; however, a rise in fibre output during the remaining weed-free period until the harvest was insignificant. This finding was confirmed by Kumar et al. [37], who also noted that weed control is not mandatory throughout the entire growing period because successive flushes of weeds can sometimes not pose a significant threat to the crops or because crops can sometimes effectively suppress all of those weeds. Additionally, other studies noted that identical results in wheat yields showed significant positive responses with each decrease in a period of crop–weed competition [40,47,48]. Moreover, the weed interference periods of 0–15 DAS and 60 DAS to harvest did not exert much adverse impact on the different qualities of jute fibre, and Ayyadurai and Poonguzhalan [45] confirmed this with similar results.

Each crop plant possesses a distinct CPWC due to its morpho-physiological make-up [25], but this is not a genetic attribute of the crop plant; instead, it is considered as an assessment indicator of crop–weed–environment interaction [12]. Theoretically, one third of the crop’s lifespan is regarded as crucial for weed management [49]. Furthermore, weed interference prior to or after this crucial window was found to have very little impact on crop yields [20,25]. Additionally, CPWP can produce results that may vary considerably between places, seasons and varieties because of variations in sowing time and ecological factors. The present study revealed that the start of the critical period was 11 DAS and the end of the critical time for the weed-free period was 68 DAS, with a BCR of 1.65 (considering a yield loss of 5%). In contrast, the start of the critical period was 19 DAS and the end of the time for the weed-free period was 59 DAS, with a BCR of 1.73 (considering a yield loss of 10%). The former report of Kumar et al. [37] and Gogai and Kalita [50] indicated that the CPWP in Corchorus spp. ranged between 7 and 42 DAS, and 15 and 60 DAS, respectively. Johnson et al. [51] determined the CPWC in West Africa for lowland irrigated rice to be 0–32 DAS during the rainy period, whereas it was 4–83 DAS during the summer period, to achieve 95% output. Begum et al. [52] in Malaysia determined that flood-irrigated rice ought to be kept free from weed competition from 14 to 28 DAS, whereas Juraimi et al. [53] recommended keeping direct-seeded rice weed free for 2–71 DAS at saturation and 15–73 DAS in flooded conditions (based on the 5% yield loss). Meanwhile, Chauhan and Johnson [7] calculated that rice in the Philippines would take 18–52 DAS to produce a 95% weed-free output. However, the early emergence of weed flora, weed profiles at the concerned area, and degree of weed infestation, as well as the sorts of crops grown, all contributed to how the CPWP began and ended [26]. Generally, the chilli pepper crop required a mean of 12.2 weeks of weed-free maintenance to avoid losses above 5%, but Amador [54] reported that the length of the critical period of weed control was 14 weeks in 1991 and 11.2 weeks in 1993, but was reduced to 5.1 weeks in 1992, at a 5% yield reduction level. They also suggested that weed flora needs to be managed in the first half of the crop’s growing season with a view to preventing yield reduction. The variance in the crop–weed interaction between years and locales may be explained by the comparative timing of weed and crop emergence and densities [55]. Additionally, Knezevic et al. [25] emphasized how crucial the timing of weed establishment is to the CPWC, reporting that prior weed establishment may result in an earlier start to the critical period. However, the above discussion highlighted that the general implications of critical period research include developing weed control plans by investigating the dynamics of weed–crop relationships and controlling weeds during CPWPs to prevent yield losses caused by weed competition [11,18]. In this context, it can be concluded that the weeding practices in jute should be adopted during the CPWP (19 to 59 DAS at 10% acceptable yield loss) for obtaining the optimum fibre yield.

Finally, weed control techniques can help to maintain weed damage below threshold levels. By the use of controlling tactics such mechanical, cultural, biological, chemical and integrated weed management methods, a period of weed-free maintenance is required after jute emergence to provide maximum yield. This can lead to sustainable crop production systems that are agronomically viable, commercially viable and environmentally sound [56]. The final success of a weed management program is determined by the selection of herbicides. At critical stages of the crop’s growth, herbicides play a critical role in reducing weed competition with the crop.

5. Conclusions

This study indicated that Cyperus rotundus was the most infested species, having the highest relative density, relative dry matter and summed dominance ratio. Although the weedy up to 15 days after sowing treatment produced the highest as well as the best quality fibre yield, the weedy from 60 days after sowing to harvest (BCR 1.59) treatment was revealed as the most economic in the study of different weed interference periods. The critical period of the weed competition of Olitorius jute (Corchorus olitorius L.) was determined considering 5% and 10% yield losses. The critical period of weed competition with jute was 11 to 68 DAS and 19 to 59 DAS based on 5% and 10% yield loss, respectively. Therefore, jute fields should be kept weed free from 19 to 59 days after sowing, and the weed management strategy should be designed accordingly.