Response Of Soyabean (Glycine Max (L.) Merill) To Integrated Weed Management In A Forest-Savanna Transition Ecosystem In Oyo State, Nigeria

ABSTRACT

Weed infestation of soyabean field causes 65% yield reduction in the forestsavanna

transition ecosystem of Nigeria. Single weed control method is often less

effective. However, Integrated Weed Management (IWM), will ensure more effective

and environment friendly control. There is little information on IWM application

on soyabean field. This study was therefore aimed at investigating response of

soyabean to IWM.

Field study was carried out in the 2008 and 2009 planting seasons to asses

the effectiveness of the integration of various weed control methods in the

production of soyabean (TGx 1414E) at Apapa village, Akinyele local government

area, Oyo state. The effects of Tillage (Tilled, Non-tilled), mulching (no mulch,

grass, plastic) and herbicides (no herbicides, metolachlor, pendimethalin) on

growth and yield of soyabean were assessed in a 2x3x3 factorial experiment

arranged in randomized complete block design with four replications and at

0.05x0.6m spacing. Data were collected at 16 weeks after planting on weed

diversity and abundance using 0.25m2 quadrat. The Relative Importance Value

(RIV) of each weed was determined using standard procedures. Also ten soyabean

plants were assessed per plot for growth and yield parameters (biomass, height,

number of pods and grain yield). Data collected were analysed using descriptive

statistics and ANOVA at p=0.05.

The most abundant weed was Spilanthes sp., with RIV of 58.5%, followed by

Chromolaena odorata (L.) R.M. King and Robinson with RIV of 7.5%. The highest

weed biomass of 136.4±18.5g/m2 was obtained in nontilled/

pendimethalin/grass treatment, followed by non-tilled/plastic

(20.0±5.1g/m2) and tilled plastic (18.2±3.0g/m2) but lowest in nontilled/

pendimethelin/plastic (15.4±2.9g/m2). Tilled/metolachlor/plastic reduced

weed biomass yield by 97.5%, tilled/plastic by 97.2%, tilled/grass by 82.6%,

control by 72.7%. The plants grown in the control plot had a mean height of

82.0±5.4cm in 2008 and 71.6±3.3cm in 2009. The lowest height of 51.6±5.6cm

was recorded in 2008 in the non-tilled/metolachlor/grass treatment and was

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50.8±4.6cm in 2009 in the non-tilled/pendimethalin/grass treatment. Plants

grown in tilled/metolachlor/plastic had highest pod numbers of 52.4±10.5 in

2008 and 57.3±4.0 in 2009 in tilled/pendimethalin/plastic and the lowest value

of 19.0±12.6 in 2008 and 24±0.8 in 2009 in the non-tilled/pendimethalin/grass.

The highest grain yield of 3.9±0.3 tons/hectare (2008) and 3.7±0.9 tons/hectare

(2009) were recorded in the tilled/pendimethalin/plastic treatment while the

lowest value of 1.6±0.3 tons/hectare and 1.7±0.4 tons/hectare was recorded in

the non-tilled/pendimethalin/grass treatment in 2008 and 2009 respectively. The

treatments are significantly different with regards to weed biomass, and grain

yield of soyabean in the two years. However, all plastic combined treatments

were not significantly different.

The tilled/plastic treatment ensured best weed suppression and highest

grain yield. Adopting it as an integrated weed management alternative may

reduce the amount of herbicides and labour input better than other strategies.

Key words: Integrated weed management, Metolachlor, Pendimethalin,

Soyabean, Spilanthes.