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Effect of Defoliation at Vegetative Stage on Dry Mass Production and Yield in Cowpea

M.I. Biswas
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh

M.A. Hossain
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh

M.S.A. Fakir
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh

Abstract/ Executive Summary:

Different degrees of defoliation (0%, 33%, 66%, and 100%) treatments were employed at the vegetative stage (55 days after sowing) to investigate their effects on dry mass (DM) production, pod and seed yield in cowpea (var. Fallon-1). The results revealed that DM was the highest in control (74.3 g/plant) and it decreased significantly with increasing degree of defoliation. Results further showed that pod yield was similar between control and 33% defoliation treatments (average of 31.2 g/plant) and seed yield followed a trend similar to that of pod yield in these treatments (average of 20.5 g/plant). It may be concluded that cowpea varieties like Fallon-1 may sustain partial defoliation at the vegetative stage without affecting pod and seed yield. The practical implication of the results in relation to pest and disease control and fodder yield is also discussed.

Keywords: Defoliation, Canopy structure, DM partitioning, Pod and Seed yield, Cowpea

Location: Field laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh

Start Date: 00-00-1999

End Date: 00-00-2000

Program Area: Knowledge Management

Commodity: Cowpea

Objectives:

Information on the effects of defoliation on total DM production and yield in recommended variety like Fallon is very scanty in Bangladesh (Biswas, 2000; Fakir and Biswas, 2000). There is, therefore, a need to conduct research in this regard under the local conditions with the following objectives: i) to determine the effect of degree of defoliation on canopy structure; and ii) to investigate the magnitude of defoliation on DM production, pod and seed yield.

Methodology:

The experiments were conducted at the field laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh (at 24°75 N latitude and 90°75 E longitude), during the period from November 1999 to April 2000 with the following treatments employed at vegetative stage (55 days after sowing, DAS): i) control (0%, no leaflet was clipped), ii) 33% defoliation (terminal leaflets of fully expanded pinnately trifoliate leaves were clipped), iii) 66% defoliation (two lateral leaflets of fully expanded pinnately trifoliate leaves were clipped), and iv) 100% defoliation (all leaflets of fully expanded pinnately trifoliate leaves were clipped).

The experiment was laid out in a randomized complete block design (RCBD) with three replications. The land was divided into three blocks with each block subdivided into 4 plots where 4 clipping treatments were assigned at random. The plot to plot distance was 0.25 m and block to block distance was 1.0 m. The unit plot size was 4.0 m x 1.25 m. Seeds of cowpea (Vigna unguiculata (L.) Walp.) var. Fallon-1 was collected from the previous experiment of Prof. Dr. M.S.A. Fakir, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh. Three seeds of cowpea were handsown at 5 cm depth at a spacing 50 cm x 25 cm. Gap filling, irrigation, weeding and pest and disease control practices were done as and when necessary. A number of days required to bud initiation, 50% flowering and pod maturity were recorded. The pods were harvested at 80-90% pod maturity (brown pod). Five plants in each replication from central guarded rows were sampled and harvested for collecting necessary data. Roots were extracted carefully between 20 and 30 cm soil depth. Separated plant parts were oven-dried at 80°C ± 2 for 48 h and weighed. The harvest index was calculated by dividing dry grain weight by total dry mass from the entire plot. The oven-dry weights of grain and other plant parts were obtained from sun-dried samples. Total dry mass of plant was recorded excluding root mass.

All collected data were analyzed and the mean differences were compared by Duncan's Multiple Range Test (DMRT), (Gomez and Gomez, 1984) using the statistical computer package program MSTAT.

Source of Information: J. Bangladesh Agril. Univ. 3(1): 13-20, 2005 ISSN 1810-3030

Article Link (Online Journal):

Funding Source:

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Total Budget (Tk.) :

Achievement/Findings:

Therefore, it is not wise to spray pesticides for controlling pests in a variety like Fallon-1 at the moderate loss of leaf surface since 33% defoliation does not affect yield. These results seem to indicate that yield may not be affected by the limitation of 'source' when 33% defoliation is imposed. This further means that photosynthate produced by the rest of the leaves and other green plant parts of the 33% defoliated cowpea plants (variety Fallon-1) seems enough to feed the developing pod and seed. Yield in Fallon-1 does not seem to be, therefore, limited by source, rather yield remained unaffected by management of the source, i.e., by defoliation of 33% at vegetative stage. In Bangladesh, fodder shortage is acute. The farmers are not capable to produce fodder crops replacing rice/wheat/pulse crops. This experiment would be a viable alternative approach to meet up the fodder shortage in Bangladesh as partial to moderate defoliation provided green fodder (3.0-6.0 t/ha) (Table 5). So, partial defoliation in cowpea (variety Fallon-1) benefits in two ways by producing a similar yield on the one hand, and by providing fodder on the other. Removal of leaves in such a way may labour intensive. An investigation is urgently needed whether 33% leaf removal could be done either from the base or top of the plant employing little labour. Currently, investigations in these regards are in progress. It may be concluded that of the different degrees of leaf removal, 33% defoliation at the vegetative stage (55 DAS) decreased TDM/plant whereas yield remained unaffected.

Knowledge Management: Journal