Effect of chemical and hand weeding on groundnut productivity

Abstract:

Background:  Weed infestation significantly threatens groundnut productivity, particularly during the later stages of growth. productivity.

Objectives:  To address this, a field experiment was conducted at two distinct locations under rainfed conditions in Nigeria's Southern Guinea Savanna to evaluate the effects of pre-emergence and post-emergence herbicides, combined with hand-weeding, on weed suppression, yield, and seed quality in two groundnut varieties.

Methods:  A split-plot field trial tested two groundnut varieties (SAMNUT 23, 26; main-plot) and eight weed-control regimes (sub-plot).

Results:  Tridax procumbens L., Andropogon tectorum Schumach, and Mitracarpus villosus (Sw.) DC. were the dominant weeds. Two hand-weeding events at 20 and 40 days after treatment (DAT) resulted in the lowest weed density and biomass, while the integrated treatment of butachlor at 1.0 kg a.i. ha⁻¹ + supplementary hoe weeding (SHW) at 40 DAT achieved comparable suppression. These treatments also produced the highest pod yields (2195.20 and 1985.40 kg ha⁻¹, respectively) compared to the weedy check (280.79 kg ha⁻¹). SAMNUT 26 demonstrated superior yield and nutritional profile compared to SAMNUT 23. Mineral analysis revealed high potassium and low iron concentrations across treatments.

Conclusions:  We conclude that butachlor at 1.0 kg a.i. ha⁻¹ + SHW at 40 DAT provides an effective, labour-saving alternative to two hand-weedings and is recommended for adoption by farmers in the Southern Guinea Savanna.

Keywords:
Weed Infestation; Groundnut Productivity; Herbicide Combinations; Hand-Weeding; Yield Improvement

1. Introduction

Groundnut (Arachis hypogaea L.) is a vital legume crop in Nigeria, contributing significantly to food security, income generation, and nutrition for millions of smallholder farmers, particularly in the northern regions (Oladele, Sogunle, 2020). As a legume, it is grown for its high protein (25–30%) and oil (44–49%) (Olayinka et al., 2023).

Despite its importance, groundnut productivity is severely constrained by weed infestation. Weeds compete aggressively with groundnuts for limited resources, including nutrients, moisture, sunlight, and space, hindering pegging, pod production, and dry matter accumulation (Saudy et al., 2021; Ajewole et al., 2021). Weed interference is particularly high during the first 45 days of groundnut growth as the plants grow slowly. If weed populations are not controlled during this critical period, yield losses can range from 15% to 75% (Saudy et al., 2021). Weeds can also absorb 30-40% of available soil nutrients, thereby reducing seed quality (Ajewole et al., 2021).

Effective weed management is therefore crucial in groundnut particularly not to impair its peg penetration and pod development (Olayinka et al., 2023). Pre-emergence herbicides such as pendimethalin, butachlor, and metolachlor are popular for initial control, but they often fail to provide season-long suppression, allowing later weed emergence (Regar et al., 2021; Shittu et al., 2022). To address this, integrated strategies combining pre-emergence herbicides with post-emergence applications or hand-weeding have been explored. Studies have shown increased yields in groundnut using metolachlor and pendimethalin alongside supplementary hoe weeding (Korav et al., 2024; Koroma et al., 2021; Mukilan et al., 2023).

This study addresses the gap in knowledge regarding the comparative efficacy of integrated weed management strategies, specifically combining pre-emergence herbicides with either supplementary hand-weeding or post-emergence herbicide on weed suppression, growth, yield, and seed nutritional quality of two groundnut varieties. We hypothesized that integrated pre-emergence herbicide plus hand-weeding would outperform single methods in both yield and seed quality.

2. Experimental Materials and Methods

2.1 Description of the study area

Field trials were conducted in 2022 at two agronomically distinct locations (Site A and Site B) in the Southern Guinea Savanna agroecological zone of Nigeria. These site differences in soil texture and microclimate were intended to provide environmental heterogeneity for broader applicability of the results. Site A is located at latitude 8°26′ N and longitude 40°35′ E, while Site B is situated approximately 45 km to the east at latitude 8°26′ N and longitude 40°59′36″ E. Site A featured loamy-sand soil and received an average annual rainfall of 1,100 mm, while Site B had sandy-loam soil and slightly higher rainfall of approximately 1,250 mm. The soil at these sites were slightly acidic pH (6.53). Organic matter was low at 7.3 g/kg, nitrogen was moderately high at 2.5 g/kg, and phosphorus was 19.29 mg/kg (ppm). Exchangeable calcium was moderate at 5.20 cmol(+)/kg, exchangeable magnesium was low at 0.57 cmol(+)/kg, potassium was high at 0.17 cmol(+)/kg, and the Effective Cation Exchange Capacity (ECEC) was low at 7.0 cmol(+)/kg.

The soil's physical properties were determined through particle size analysis to classify texture, while its chemical properties—including pH, organic matter, nutrient content, and exchangeable cations—were measured using standard laboratory methods including pH meter readings, chemical extractions, and spectroscopy.

2.2 Experimental Materials

Seeds were obtained from the Institute of Agricultural Research (IAR) Zaria, Nigeria. Groundnut varieties SAMNUT 23 and SAMNUT 26 possess agronomic traits that boost productivity in semi-arid regions. SAMNUT 23 is valued for its high yield potential, pest and disease resistance, and prolific pod formation, making it well-suited for stress-prone areas (Bala et al., 2011). Similarly, SAMNUT 26 thrives in semi-arid climates, shows strong resilience to pests and diseases, and produces consistent pods for reliable yields (Jo et al., 2024). Maturation periods are 90–110 days for SAMNUT 23 and 90–100 days for SAMNUT 26. The herbicides used; pendimethalin, butachlor and imazathaphyl were all obtained from an agrochemical store in Ilorin, Nigeria.

2.3 Treatment and experimental design

The experiment consisted of a factorial combination of two groundnut varieties, SAMNUT 23 and SAMNUT 26, and eight weed control practices (T1–T8) as detailed in Table 1. The varieties were assigned to the main plots, while the weed control practices were assigned to the sub-plots. The treatments were laid out in a randomized complete block design (RCBD) in a split-plot arrangement with three replications. The main plot size measured 13 m × 9 m (117 m²) consisting of 15 rows, each 9 m long. Sub-plots measured 3 m × 2 m (6 m²), separated by 0.5 m alleys. Plant-to-plant spacing was 0.1 m.

Table 1
Table of treatments

Treatment	Weed control practice (T1–T8)
T1	butachlor at 1.0 kg a.i. ha–1
T2	pendimethalin at 1.32 kg a.i. ha–1
T3	butachlor at 1.0 kg a.i. ha–1 + supplementary hoe weeding (SHW) at 40 DAT
T4	pendimethalin at 1.32 kg a.i. ha–1 + SHW at 40 DAT
T5	butachlor at 1.0 kg a.i. ha–1 + post-emergence (POE) application of imazethapyr at 0.05 kg a.i. ha–1 at 40 DAT
T6	pendimethalin at 1.32 kg a.i. ha–1 + POE application of imazethapyr at 0.05 kg a.i. ha–1 at 40 DAT
T7	Two hand-weedings at 20 DAT and 40 DAT
T8	Weedy check

Herbicides were applied using a calibrated knapsack sprayer. Pre-emergence herbicides were applied immediately after sowing. Post-emergence (imazethapyr) was applied at 40 DAT when weeds were at the 2-4 leaf stage. Supplementary hoe weeding (SHW) was performed at 40 DAT as specified. Two hand-weedings were performed at 20 and 40 DAT.

2.4 Agronomic Practices

Healthy seeds were visually selected for sowing. Prior to planting, the seeds were treated with Seedrex (seed dressing chemical) at a rate of 4 kg chemical per 10 kg seed to protect against soil-borne diseases. Planting was done manually, with two seeds sown per hole at a sowing depth of 0.02 m. The spacing between plants was maintained at 0.1 m.

After planting, recommended agronomic practices were followed uniformly across all plots. This included timely irrigation to maintain adequate soil moisture, especially during critical growth stages, and periodic monitoring for pests and diseases. Weed control measures followed the assigned treatment protocols.

2.5 Observations and Data Collection

Weed data were collected at each sampling time using a 1 m² square quadrat. In each experimental sub-plot, two quadrats were randomly placed, and all weeds within these quadrats were identified and counted. Weed species identification followed the taxonomy and descriptions provided in Handbook of West African Weeds by Akobundu and Agyakwa (1987).

Weed species composition was calculated to express the proportion of individual species relative to the total weed population observed. This parameter was computed using the formula:

$$WeedSpeciesComposition\left(\%\right)=\frac{Numberofindividualsofaspecies}{Totalnumberofallweedindividuals}\times 100$$

This measure highlights the dominance and diversity of weed species present in the field (Baker et al., 2018).

Relative abundance further quantified species importance by expressing the contribution of each species to the total weed density. It was calculated with the formula (Kent, 2011):

$$RelativeAbundance\left(\%\right)=\frac{Densityofaspecies}{Totalweeddensity}\times 100$$

The weed density was determined by dividing the total number of weed plants within the quadrat by the quadrat area (which was 1 m²) (Baker et al., 2018; Mengesha et al., 2022). The average density from the two quadrats per sub-plot was used for analysis.

$$WeedDensity=\frac{Numberofweedplantsinquadrat}{1{\text{m}}^2}$$

This density parameter indicates the intensity of weed infestation and potential competition with the crop.

To measure weed biomass, all weed plants within the quadrat were harvested, oven-dried at 65°C until they reached a constant weight, and then weighed. Weed biomass per unit area (g/m²) was calculated as:

$$WeedBiomass=\frac{Dryweightofweeds}{1{\text{m}}^2}$$

2.5.1 Growth Parameters of groundnut

The heights of the groundnut plants were measured using a meter ruler. The number of leaves and number of primary branches were manually counted to estimate the mean number of leaves and number of primary branches per plant. The leaf area per plant was measured using a Leaf Area Meter. The above-ground dry weight was estimated by oven-drying the leaves and stems at 65 °C for 48 hours until constant weight was recorded. Observations of both morphological and physiological growth characteristics were done at 90 DAT using randomly selected plants per plot.

2.5.2 Yield and yield component

The number of pods and seeds per plant were manually counted from three plants per plot. Pod and seed weights per plant were determined after air-drying for 6-7 days. The 100-seed weight was determined from bulk harvested seeds. Pod and seed yield in kilograms per hectare were determined from 10 plants harvested from the two inner rows to avoid border effects following the method of El-Naim et al. (2012), after air-drying to 12% moisture content.

Harvest index was obtained by dividing seed yield in terms of seed weight with some of plant dry weight above ground and seed yield (Coombs and Hall, 1982) as depicted below:

$$\text{Harvest Index}=\frac{\text{Seed}\text{yield}}{\text{Seed}\text{yield}+\text{above aground dry weight}}$$

2.5.3 Proximate and mineral composition

The proximate composition was estimated according to the method of the Association of Analytical Chemists (AOAC International, 2012). Carbohydrate percentage was calculated by subtracting the sum of moisture, ash, protein, crude fat, and crude fibre percentages from one hundred. The calorific value in each sample was calculated by multiplying the percentage of protein and carbohydrate by 4 and the percentage of fat by 9.

For mineral quantification, a dried sample of 0.5 g was digested in a glass tube with 10 ml of nitric acid (HNO₃) overnight at room temperature. Following this, 4 ml of perchloric acid (HClO₃) was added, and the mixture was gradually heated from 50°C to 300°C for 70-80 minutes until white fumes indicated digestion completion. After cooling, the mixture was diluted and filtered. Nitrogen (N) was analyzed using the micro Kjeldahl method, while calcium (Ca), iron (Fe), magnesium (Mg), and zinc (Zn) were measured using an Atomic Absorption Spectrophotometer (AAS). Potassium (K) was determined by Flame Photometer following the method of Rorison et al. (1976).

2.6 Data Analysis

A preliminary statistical analysis of the data collected from both locations revealed no significant interaction between location and treatments (p > 0.05). This justified pooling of data across locations. The results were subjected to Two-way Analysis of Variance and means were separated using the Duncan Multiple Range Test at p ≤ 0.05.

3. Results and Discussion

3.1 Composition and relative abundance of weed species

Eighteen weed species from nine families were identified (Table 2). Broadleaved species accounted for 13 species, while grasses comprised 5 species. The Poaceae family had the highest number of species (6), followed by Euphorbiaceae (3), and Asteraceae and Rubiaceae, each with 2. Annual weeds made up 82% of the total, indicating their predominance over perennial weeds (Table 2). The rank abundance analysis showed that Tridax procumbens was the most abundant, followed by Andropogon tectorum, Mitracarpus villosus, Spegallia anthelmia, Panicum maximum, and Euphorbia heterophylla. Azadirachta indica had the lowest relative abundance among all species (Figure 1).

Figure 1
Relative abundance of the observed weed species

Table 2
Composition of weed species encountered in the plots of two varieties of groundnut (SAMNUT 23 and 26) during 2022 cropping seasons

Family	Weed name	Life cycle
Asteraceae	Ageratum conyzoides linn.	ABL
	Tridax procumbens Linn.	ABL
Euphorbiaceae	Euphorbia hirta Linn.	ABL
	Euphorbia heterophylla Linn.	ABL
	Euphorbia hyssopifolia Linn.	ABL
Fabaceae	Daniella oliveri (Rolfe) Hutch & Dalz	PBL
Loganiaceae	Spigellia anthelmia Linn.
Meliaceae	Azadirachta indica A. Juss	AH
Poaceae	Andropogon tectorum Schmach. & Thonn.	PBL
	Cynodon dactylon (L.) Pers.	PG
	Sorghum arundinaceum (Desv.) Stapf	PG
	Panicum maximum Jacq	AG
	Pennisetum polystachion	AG
	Eleusine indica (L) Gaertn.	AG
Rubiaceae	Mitracarpus villosus (Sw.) Cham. & Schltdl. ex DC	AH
	Oldenlandia herbacea (L.) Roxb.	AH
Solanaceae	Physallis angulata Linn.	AH
Urticaceae	Laportea astuans L.Chews	AH

• Key: ABL: Annual broadleaf; PBL: Perennial broadleaf; AH: Annual herb; AG: Annual grass; PG: Perennial grass

The predominance of broadleaved weeds and annual species, particularly T. procumbens, A. tectorum, and M. villosus, aligns with previous findings in Nigerian groundnut systems (Olayinka, Etejere, 2015; Parthipan, Harisudan, 2020). The dominance of these species suggests they are well-adapted to the Southern Guinea Savanna ecology and represent a persistent challenge that requires targeted management.

3.2 Weed control effect on weed density, biomass, and morphological growth characteristics

Weed biomass and density were reduced significantly in all weed control methods compared to the weedy check (Table 3). T7 (two hand-weedings at 20 and 40 DAT) and T3 (butachlor + SHW at 40 DAT) had the lowest weed density and biomass. Integrated strategies significantly suppressed biomass, with T3 achieving a 75% reduction (27.43 g m⁻² vs. 109.85 g m⁻² in the control).

Table 3
Weed density, weed biomass, and morphological growth characteristics of two groundnut varieties as affected by hand-weeding, pre- and post-herbicides application

Treatments	Weed density (m-2)	Weed biomass (g m-2)	Plant height (cm)	No. of leaves	No. of primary branches	Leaf Area (m2)	Above-ground dry-weight (g)
Variety
V1	21.73a	55.18a	33.46a	208.83b	18.79a	6.63a	38.30b
V2	22.00a	50.81a	33.53a	230.13a	19.50a	7.21a	43.45a
SEM	0.39	2.14	0.30	5.18	0.43	0.24	0.48
Treatment
T1	25.05c	55.07bc	29.65f	151.67f	15.67d	5.27ef	37.11e
T2	28.29b	66.63b	27.28g	94.33g	12.50e	4.46fg	35.79e
T3	8.41g	27.43f	40.40b	325.13b	24.83b	8.96a	48.45a
T4	21.29de	43.95cde	35.17d	237.17d	19.83c	6.66cd	41.06d
T5	19.13e	38.75def	37.70c	267.67c	23.00b	8.06bc	44.30c
T6	23.2cd	48.77cd	32.52e	198.33e	18.00cd	6.37cd	37.96e
T7	15.9f	33.5ef	43.82a	21.83a	30.17a	9.19a	47.47a
T8	33.66a	109.85a	21.42h	59.83h	9.17f	3.37g	30.81f
SEM	0.78	4.28	0.61	10.36	0.86	0.48	0.97
Interaction
V	0.624	0.160	0.870	0.007	0.253	0.098	<0.001
T	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
V x T	0.328	0.997	0.033	<0.001	0.032	0.376	<0.001

• Values followed by same letter in each column are not significantly different at p>0.05. Values are represented as mean. SEM = standard error of the mean. Number of replicates (n) = 3. V₁ = SAMNUT 23, V₂ = SAMNUT 26. T₁ = butachlor at 1.0 kg a.i. ha^–1, T₂ = pendimethalin at 1.32 kg a.i. ha^–1, T₃ = butachlor at 1.0 kg a.i. ha^–1 + supplementary hoe weeding (SHW) at 40 DAT, T₄ = pendimethalin at 1.32 kg a.i. ha^–1 + SHW at 40 DAT, T₅ = butachlor at 1.0 kg a.i. ha^–1 + post-emergence (POE) application of imazethapyr at 0.05 kg a.i. ha^–1 at 40 DAT, T₆ = pendimethalin at at 1.32 kg a.i. ha^–1 + POE application of imazethapyr at 0.05 kg a.i. ha^–1 at 40 DAT, T₇ = Two hand-weedings at 20 DAT and 40 DAT, T₈ = Weedy check

The significant reduction in weed density and biomass under integrated treatments (T3, T4, T5, T6) compared to sole herbicide applications (T1, T2) supports the principle that combining pre-emergence herbicides with either mechanical or post-emergence control provides more effective season-long suppression. This occurs because pre-emergence herbicides control early weed flushes during the critical first 45 days, while supplementary hand-weeding or post-emergence application targets later-emerging weeds that escape initial control (Singh et al., 2018; Wilfred et al., 2020). The high efficacy of T3 (butachlor + SHW) and T7 (two hand-weedings) can be attributed to their ability to maintain weed-free conditions throughout the crop cycle, particularly during pegging and pod development stages when weed competition is most detrimental.

All weed control treatments had greater growth parameters compared to the weedy check (Table 3). T7 and T3 resulted in the highest crop growth parameters, including plant height (43.82 cm and 40.40 cm), number of leaves (421.83 and 325.13), number of primary branches (30.17 and 24.83), leaf area (9.19 m² and 8.96 m²), and above-ground dry weight (47.47 g and 48.45 g). Significant variety × treatment interactions were observed for several parameters, suggesting genotype-specific responses.

The current findings corroborate those of Sandil et al. (2015), Olayinka et al. (2017), and Mukilan et al. (2023), who noted greater morphological growth parameters in areas with effective weed control strategies. Effective weed control methods reduced weed interference, allowing groundnut plants to access resources like light, moisture, nutrients, and space (Ajewole et al., 2021). As observed in this study, controlling weeds at the critical period of weed competition had the advantage of making resources available that would allow an increase in the production of more leaves with larger leaf area for enhanced dry matter accumulation (Mukilan et al., 2023). Also, treatments such as hand weeding at 20 and 40 DAT and in those where butachlor or pendimethalin was supplemented with one hand weeding at 40 DAT or sprayed with imazethapyr after crop emergence created less weed competition and such afforded the groundnut plants access to resources that are needed for greater assimilatory surface and higher dry matter production. The significant variety × treatment interactions for several growth parameters suggest that SAMNUT 23 and SAMNUT 26 have differential responses to weed pressure and management strategies, highlighting the importance of genotype selection in integrated weed management programs.

3.3 Weed control effect on yield components, yield, and harvest index.

The weed control treatments significantly influenced yield components (Table 4). Varietal difference was also significant except for the number of pods and seeds per plant. SAMNUT 26 produced 1,295 kg ha⁻¹—23% pod yield more than SAMNUT 23 (1,054 kg ha⁻¹; p<0.001). All the yield attributes were significantly higher in all the weed control treatments when compared to the weedy check. Groundnut plants that received two hand weeding at 20 and 40 DAT had the highest number of pods per plant (33.83 np^-1) that was at par with those recorded for Butachlor at 1.0 kg a.i. ha⁻¹ + SHW at 40 DAT (32.10 np^-1). These were followed in decreasing order of magnitude by those of butachlor at at 1.0 kg a.i. ha⁻¹ + post-emergence (POE) application of imazethapyr at 0.05 kg a.i. ha⁻¹ at 40 DAT (23.33 np^-1), pendimethalin at 1.32 kg a.i. ha⁻¹ + SHW at 40 DAT (18.83 np^-1), pendimethalin at 1.32 kg a.i. ha⁻¹ + POE application of imazethapyr at 0.05 kg a.i. ha⁻¹ at 40 DAT (17.10 np^-1) butachlor at 1.0 kg a.i. ha⁻¹ (13.66 np^-1) and pendimethalin at 1.32 kg a.i. ha⁻¹ (12.33 np^-1) (Table 6). Other yield components, such as the number of seeds per plant, pod and seed weight per plant, and 100-seed weight, followed a similar pattern as recorded for the number of pods per plant (Table 4).

Table 4
Yield components, yield and harvest index of two groundnut varieties as affected by hand-weeding, pre- and post-herbicides application

Treatments	No. of pods per plant	No. of seeds per plant	Pod weight per plant (g)	Seed weight per plant (g)	100-seed weight (g)	Pod yield/ hectare (kg ha-1)	Seed yield/ hectare (kg ha-1)	Harvest index (%)
Variety
V1	19.42a	38.83a	23.71b	17.47b	39.81b	1054.00b	776.22b	43.35b
V2	19.67a	39.33a	29.13a	21.20a	40.44a	1295.00a	942.26a	46.56a
SEM	0.75	1.5	0.42	0.27	0.11	18.78	12.06	0.80
Treatment
T1	13.66e	25.10e	19.67e	13.75f	36.30f	918.57e	655.27f	39.82d
T2	12.33e	24.67e	17.15f	11.27g	36.22f	762.15f	500.62g	31.42e
T3	32.10a	61.10a	37.92b	35.67b	43.64a	1985.40b	1574.33b	45.10a
T4	18.83cd	37.67cd	26.47d	19.26d	40.56d	1176.10d	855.84d	42.97c
T5	23.33c	46.00c	30.89c	22.08c	43.82c	1373.00c	981.31c	42.95c
T6	17.10d	34.33d	22.57e	17.44e	39.60e	1003.30e	774.89e	42.11c
T7	33.83a	62.67a	39.39a	36.47a	44.82a	2195.20a	1673.33a	45.96a
T8	6.33f	12.67f	6.32g	4.75h	29.04h	280.79g	190.94h	25.52f
SEM	1.50	3.00	0.85	0.54	0.23	37.55	24.12	1.61
Interaction
V	0.815	0.815	<0.001	<0.001	0.001	<0.001	<0.001	0.008
T	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
V x T	0.731	0.731	<0.001	<0.001	<0.001	<0.001	<0.001	0.003

• Values followed by same letter in each column are not significantly different at p>0.05. Values are represented as mean. SEM = standard error of the mean. Number of replicates (n) = 3. V₁ = SAMNUT 23, V₂ = SAMNUT 26. T₁ = butachlor at 1.0 kg a.i. ha^–1, T₂ = pendimethalin at 1.32 kg a.i. ha^–1, T₃ = butachlor at 1.0 kg a.i. ha^–1 + SHW at 40 DAT, T₄ = pendimethalin at 1.32 kg a.i. ha^–1 + SHW at 40 DAT, T₅ = butachlor at 1.0 kg a.i. ha^–1 + post-emergence (POE) application of imazethapyr at 0.05 kg a.i. ha^–1 at 40 DAT, T₆ = pendimethalin at at 1.32 kg a.i. ha^–1 + POE application of imazethapyr at 0.05 kg a.i. ha^–1 at 40 DAT, T₇ = Two hand-weedings at 20 DAT and 40 DAT, T₈ = Weedy check

Pod and seed yield that were estimated in kilograms per hectare and harvest index were affected by weed control treatments (Table 4). Varietal difference was also significant. Higher pod and seed yield were recorded from groundnut grown under two hand-weeding at 20 and 40 DAT and butachlor + one hand-weeding at 40 DAT with mean values of 1,985.40 kg ha^-1 and 1,574.33 kg ha^-1 respectively when compared to other weed control treatments. The weedy check had the lowest pod and seed yield with mean values of 280.79 kgha^-1 and 190.94 kg ha^-1 (Table 4). SAMNUT 26 had a significantly higher harvest index than SAMNUT 23. The weed control treatment effect on harvest index followed a similar trend as recorded for the number of pods per plant (Table 4).

The increase in yield components, yield and harvest index in all the weedy control treatments, most importantly two hand weeding at 20 and 40 DAT compared to the weedy check is traceable to reduction in weed growth and higher leaf area that resulted in greater photosynthetic activity and partitioning of assimilate to pod development or pod filling. Earlier researchers have posited weed control strategies that reduced weed growth at early and later stages of crop growth until harvest could lead to an increase in yield attributes over all other treatments that did not provide season-long weed control suppression (Mukilan et al., 2023; Olayinka, Etejere, 2015). Findings from this study were also consistent with previous studies by Sahoo et al. (2017), where the authors posited that an increase in pod and seed yield has its root in the increase in yield components, leaf area, and dry matter accumulation. Other researchers had reported higher pod yield under two hand weeding at 20 and 40 DAT and application of herbicides in combination with hand weeding (Kumar et al., 2019; Mukilan et al., 2023).

3.4 Weed control effect on proximate composition.

The results of proximate composition and energy value differed significantly by treatment and variety except for moisture (Table 5). SAMNUT 23 seeds contained higher protein (37.07%) than SAMNUT 26 (33.45%), whereas SAMNUT 26 had greater carbohydrates (10.55% vs. 8.89%) and energy (597.3 vs. 593.9 kcal; p<0.001).

Table 5
Proximate composition of two groundnut varieties as affected by hand-weeding, pre- and post-herbicides application

Treatments	Moisture	Ash	Crude Fibre	Crude Protein	Total Fats	Carbohydrates	Energy (kcal)
	%
Variety
V1	4.25±0.011a	1.96±0.01b	2.28±0.01b	37.07±0.03a	45.57±0.04b	8.89±0.05b	593.90±0.21b
V2	4.25±0.01a	2.01±0.01a	2.93±0.01a	33.45±0.03b	46.83±0.04a	10.55±0.05a	597.29±0.21a
SEM	0.011	0.01	0.01	0.03	0.04	0.05	0.21
Treatment
T1	4.13±0.02de	1.76±0.01ef	2.75±0.03c	34.79±0.07f	46.96±0.08c	9.62±0.10d	600.24±0.41cd
T2	4.27±0.02c	2.04±0.01c	3.15±0.03a	35.11±0.07d	44.60±0.08e	10.84±0.10c	585.15±0.41f
T3	4.28±0.02c	2.78±0.01a	2.58±0.03d	35.11±0.07d	46.24±0.08d	9.01±0.10e	599.74±0.41d
T4	4.40±0.02b	1.77±0.01e	2.85±0.03b	35.42±0.07c	44.21±0.08f	11.43±0.10b	584.94±0.41f
T5	4.16±0.02de	1.32±0.01g	2.24±0.03e	35.70±0.07b	47.99±0.08a	8.61±0.10f	601.84±0.41b
T6	4.12±0.02e	1.96±0.01d	2.52±0.03d	35.03±0.07de	44.56±0.08e	11.82±0.10a	588.46±0.41e
T7	4.46±0.02a	2.56±0.01b	2.20±0.03e	36.00±0.07a	47.59±0.08b	7.19±0.10g	601.10±0.41bc
T8	4.20±0.02d	1.72±0.01f	2.55±0.03d	34.89±0.07ef	47.43±0.08b	9.22±0.10e	603.31±0.41a
Interaction
V	0.951	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
T	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
V x T	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001

• Values followed by same letter in each column are not significantly different at p>0.05. Values are represented as mean. SEM = standard error of the mean. Number of replicates (n) = 3. V₁ = SAMNUT 23, V₂ = SAMNUT 26. T₁ = butachlor at 1.0 kg a.i. ha^–1, T₂ = pendimethalin at 1.32 kg a.i. ha^–1, T₃ = butachlor at 1.0 kg a.i. ha^–1 + SHW at 40 DAT, T₄ = pendimethalin at 1.32 kg a.i. ha^–1 + SHW at 40 DAT, T₅ = butachlor at 1.0 kg a.i. ha^–1 + post-emergence (POE) application of imazethapyr at 0.05 kg a.i. ha^–1 at 40 DAT, T₆ = pendimethalin at at 1.32 kg a.i. ha^–1 + POE application of imazethapyr at 0.05 kg a.i. ha^–1 at 40 DAT, T₇ = Two hand-weedings at 20 DAT and 40 DAT, T₈ = Weedy check

Percent moisture, ash, fibre, protein, fat, and carbohydrate ranged from 4.16–4.46%, 1.72–2.78%, 2.20–3.15%, 34.99–36.00%, 44.21–47.90%, and 7.19–11.82%, respectively (Table 5). The treatment effect on proximate composition showed inconsistent results. However, pendimethalin + one hand-weeding that showed the highest moisture content value of 4.40% had the lowest fat content value, 44.21%, when compared to other weed control treatment and weedy check. The ash content in seeds was greatest in groundnut plots that were sprayed with butachlor + one hand-weeding at 40 DAT (2.78%). Lowest ash content value of 1.32% was recorded with butachlor + post imazethapyr. Two hand-weedings at 20 and 40 DAT had the lowest fibre value of 2.20% but the highest accumulation of protein value of 36.00%. The highest fat content value of 47.99% was recorded with butachlor + post imazethapyr at 40 DAT that showed lowest ash content as earlier mentioned. Carbohydrates that was lowest in those treatments such as butachlor at 2l/ha + post imazethapyr at 40 DAT recorded the highest fat accumulation. Highest carbohydrate value of 11.43% was recorded under the treatment which had highest moisture content which in this case was pendimethalin + one hand-weeding at 40 DAT (Table 5). The results of energy value ranged from 584.94 kcal in sole pendimethalin at 2l/ha to 603.31 kcal in weedy check (Table 5). The lowest energy recorded under pendimethalin could not be unconnected with fat accumulation which was low in this treatment (Table 5).

The proximate composition results revealed complex treatment effects. The higher protein content in T7 seeds (36.00%) compared to other treatments suggests that prolonged weed-free conditions may enhance nitrogen assimilation and partitioning to seeds. Conversely, the high fat content in T5 (butachlor + imazethapyr) seeds (47.99%) but low ash content suggests a trade-off between oil accumulation and mineral uptake, possibly due to herbicide-induced physiological stress altering resource allocation.

The reported moisture values in this study aligned with the data reported by Olayinka, Etejere (2015). It differed from that of Musa et al. (2010) which ranged from 6.60 to 8.90%. The observed difference could be the time spent in drying the seeds. The general low moisture content is beneficial with respect to storability and shelf life (R. Singh et al., 2022). Samples with higher percentages of ash content are expected to have concentrations of various mineral elements that speed up the rate of metabolic processes and improve growth and development (Olayinka et al., 2023). Similarly, samples with low fibre content may not be good sources of roughages which play an important role in peristaltic movement in the human gut (Olayinka, Etejere, 2015).

The protein recorded in groundnut plots under two hand-weeding and other weed control treatments over the weedy check will make the seeds a good source of food necessary for growth and development (Olayinka et al., 2023). The Sample with low carbohydrate might be ideal for patients requiring low sugar diets. In this study, sole pendimethalin recorded low energy value because of low-fat accumulation. Varietal differences indicated that ash, fibre, fat, carbohydrate, and energy values were higher in SAMNUT 26 than SAMNUT 23. As earlier mentioned, differential genetic makeup of the varieties may be responsible for the observed variation (Olayinka et al., 2023).

3.5 Weed control effect on mineral composition.

Data pertaining to mineral elements were influenced by weed control treatment and variety. Varietal differences indicated that SAMNUT 26 had higher Ca, Mg, and K in their seeds when compared to SAMNUT 23. Conversely, significantly higher Zn and Fe were recorded in the seeds of SAMNUT 23 (Table 6). Regardless of the treatment, Ca, Mg, K, Zn, and Fe had respective ranged values of 0.25-0.51 mg/kg, 1.51-2.19 mg/kg, 3.14-3.88 mg/kg, 0.15-2.20 mg/kg, and 0.08-0.19 mg/kg. Potassium was highest in seeds, while Fe had the lowest values regardless of the treatments and variety. Treatment effect showed that sole Butachlor at 1.0 kg a.i. ha⁻¹ enhanced better accumulation of Ca, Mg, K, and Zn over all other treatments except for K where a significant difference was not recorded between Butachlor at 1.0 kg a.i. ha⁻¹ and Pendimethalin at 1.32 kg a.i. ha⁻¹. Treatments where Butachlor at 1.0 kg a.i. ha⁻¹ and Pendimethalin at 1.32 kg a.i. ha⁻¹ were followed with one hand-weeding at 40 DAT recorded lowest accumulation of all the mineral elements except for K (Table 6).

In this study, groundnut seeds generally have low iron (Fe) with high potassium (K). The mineral elements determined have been shown to play a significant role in human nutrition (Lawal et al., 2023; Olayinka, Etejere, 2018). The weedy check tends to limit the mineral contents of the seeds with the exclusion of magnesium (Mg). Aside from iron (Fe), sole Butachlor at 2l/ha generally showed a greater amount of the mineral elements over all other treatments. This finding aligns with observations by Little et al. (2021) that weed management strategies can inadvertently affect nutrient uptake dynamics. The consistently high potassium and low iron concentrations across treatments reflect inherent characteristics of these groundnut varieties grown in this agroecological zone, with implications for nutritional value.

4. Conclusions

This study demonstrates that integrated weed management strategies combining pre-emergence herbicides with supplementary hand-weeding can achieve yields comparable to intensive two-hand-weeding while reducing labour requirements. Butachlor at 1.0 kg a.i. ha⁻¹ + SHW at 40 DAT (T3) proved to be the most efficient treatment, providing effective weed suppression, high yield, and acceptable seed quality. SAMNUT 26 outperformed SAMNUT 23 in yield and several nutritional parameters, making it the preferred variety for this region. The finding that integrated treatments can affect mineral accumulation warrants further investigation. For practical adoption, we recommend that farmers in Nigeria's Southern Guinea Savanna adopt the combination of butachlor at 1.0 kg a.i. ha⁻¹ with one hand-weeding at 40 DAT using SAMNUT 26 to optimize productivity while managing labour costs.

• Funding
  This research received no external funding.

Data Availability

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

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Edited by

• Editor in Chief:
  Carol Ann Mallory-Smith

• Associate Editor:
  Aldo Merotto Junior

Publication Dates

• Publication in this collection
  24 July 2026
• Date of issue
  2026

History

• Received
  30 Apr 2025
• Accepted
  30 Apr 2026