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Effect of plastic mulch on growth and yield of chilli (Capsicum annuum L.)

Abstract

In this work a field study was conducted to evaluate the effect of coloured plastic mulch on growth and yield of chilli from October 2005 to April 2006. The plastic mulches were transparent, blue, and black and bare soil was the control. Different mulches generated higher soil temperature and soil moisture under mulch over the control. Transparent and blue plastic mulches encouraged weed population which were suppressed under black plastic. Plant height, number of primary branches, stem base diameter, number of leaves and yield were better for the plants on plastic. At the mature green stage, fruits had the highest vitamin-C content on the black plastic. Mulching produced the fruits with the highest chlorophyll-a, chlorophyll-b and total chlorophyll contents and also increased the number of fruits per plant and yield. However, mulching did not affect the length and diameter of the fruits and number of seeds per fruit. Plants on black plastic mulch had the maximum number of fruits and highest yield. Thus, mulching appears to be a viable tool to increase the chilli production under tropical conditions.

Capsicum annum; chilli; growth; plastic mulch; yield; yield attributes


BIOLOGICAL AND APPLIED SCIENCES

Effect of plastic mulch on growth and yield of chilli (Capsicum annuum L.)

M. AshrafuzzamanI,II,* * Author for correspondence: drashraf2007@yahoo.com ; M. Abdul HalimI; Mohd Razi IsmailII; S.M. ShahidullahII; M. Alamgir HossainI,II

IDepartment of Crop Botany; Bangladesh Agricultural University; Mymensingh 2202; Bangladesh

IIInstitute of Tropical Agriculture; Universiti Putra Malaysia, 43400 UPM Serdang; Selangor - Malaysia

ABSTRACT

In this work a field study was conducted to evaluate the effect of coloured plastic mulch on growth and yield of chilli from October 2005 to April 2006. The plastic mulches were transparent, blue, and black and bare soil was the control. Different mulches generated higher soil temperature and soil moisture under mulch over the control. Transparent and blue plastic mulches encouraged weed population which were suppressed under black plastic. Plant height, number of primary branches, stem base diameter, number of leaves and yield were better for the plants on plastic. At the mature green stage, fruits had the highest vitamin-C content on the black plastic. Mulching produced the fruits with the highest chlorophyll-a, chlorophyll-b and total chlorophyll contents and also increased the number of fruits per plant and yield. However, mulching did not affect the length and diameter of the fruits and number of seeds per fruit. Plants on black plastic mulch had the maximum number of fruits and highest yield. Thus, mulching appears to be a viable tool to increase the chilli production under tropical conditions.

Key words:Capsicum annum, chilli, growth, plastic mulch, yield, yield attributes

INTRODUCTION

Chilli pepper (Capsicum annuum L.) is an important spice and cash crop in many countries of the world. In Bangladesh, chilli is grown round the year in all parts of the country while winter chilli is grown between the months of October to April and accounts for about 70% of total production. At least 32 local varieties are cultivated in Bangladesh (BBS, 2005).

Water deficit often limits the crop growth and development. Chilli is sensitive to water stress. Young chilli seedlings cannot withstand either water deficit or excess soil moisture while older plants can withstand deficit or excess water (Ayoub, 1986). The average yield of chilli in Bangladesh is very low compared to other chilli growing countries in the world (FAO, 2003) due to erratic rainfall and inefficient use of fertilizer. Heavy rainfall is a problem for chilli cultivation because chilli cannot tolerate heavy rainfall. In the winter, production is hampered due to lack of irrigation as well as minimum rainfall. Most determinate crops are sensitive to water stress especially at the time of floral initiation, during flowering, and to a lesser extent, during fruit development (Hegde, 1989). In crops, where the vegetative growth and reproductive processes overlap the reason for water stress becomes difficult to explain (Begg and Turner, 1976). To improve the productivity of crops where either water deficiency or excess frequently occurs, proper water management is necessary (Hale and Orcutt, 1987). In the winter season, the conservation of soil moisture may help in preventing the loss of water through evaporation from the soil facilitating maximum utilization of moisture by the plants. Mulching with plastic is a method by which soil moisture can be conserved (Sandal and Acharya, 1997).

Mulching stimulates the microbial activity in soil through improvement of soil agro-physical properties (Strizaker et al., 1989). Mulching also minimizes the use of N fertilizer (Jones et al., 1977), warms the soil (Singh et al., 1988), improves the soil physical condition (Kwon et al. 1988; Lal, 1989), and suppresses weed growth (Iruthayaraj et al., 1989; Mohler and Calloway, 1992) and could account for increased yield (Siti et al., 1994; Ravinder et al., 1997; Nagalakshmi, 2002).

The present study was undertaken to evaluate the changes in temperature and soil moisture and to evaluate the growth and yield of chilli under tropical conditions grown with plastic mulches.

MATERIALS AND METHODS

The experiment was conducted during the period of October 2005 to April 2006. The field is located at 24º75' N latitude and 95º75' E longitude at 18 m above sea level in the agro-ecological Zone-9 (AEZ-9) termed Old Brahmaputra Floodplain. The soil is a non-calcareous dark grey floodplain. The soil was neutral in pH and silty loam in texture.

Three mulching treatments (transparent, black and blue plastic sheets) along with a control (bare soil) were imposed on a local variety of chilli. The land was prepared by tilling in two directions with a power tiller. Weeds and crop stubble were removed. Plots were 2 × 2 m on 15 cm high raised beds. Urea, triple superphosphate (TSP) and muriate of potash (MP) were applied (260, 200 and 150 kg·ha-1 , respectively). Total amount of TSP, MP and half of urea were broadcast and incorporated to the soil at final land preparation. The rest of urea was top-dressed at 40 days after transplanting (DAT). Well decomposed cowdung was applied (5 t·ha-1) prior to final tilling. Plastic mulches were carefully spread over the plots and holes were punched where seedlings were to be established.

Transplant establishment

Thirty-day old seedlings were transplanted at 25 cm × 25 cm spacing on 21 November 2005. Seedlings were watered after transplanting. Guard rows were established around the entire plot. Gap filling of seedling was with healthy seedlings previously planted in the border area. No additional irrigation was applied during the growing season. At 40 days after transplanting (DAT), weeds were collected from the plots and their fresh and oven dried weights were recorded. The pesticides Actara-25WG at 2.5 g/10L and Kinalux at 2 mL·L-1 were applied at 40 and 65 DAT to prevent insect and disease infestation.

Harvest

Green fruit were harvested at weekly intervals when fruit length was at least 4.5 cm. Harvesting was started on 5 February 2006 and continued till 25 April 2006.

Data collected

Plant height, number of primary branches per plant, main stem base diameter and number of leaves per plant were recorded from four the plants at 15 day intervals. One plant from each plot was carefully uprooted and the roots were gently washed with water to remove the soil. The plant was placed on white paper and the root circumference was marked and measured. Root length, fresh and dry weight of plants, and fresh and dry weight of the weeds at 40 DAT were recorded. The length and diameter of 20 randomly selected mature green fruit were measured from each plot. Number of fruits per plant, fruit yield per plant, fruit yield per plot, fruit yield per hectare, and number of seeds per fruit were recorded at final harvest. Ascorbic acid content of green fruit was estimated with the indophenol dye method (Sadasivam and Manickam, 1992). Chlorophyll content was estimated according to the method described by Yoshida et al. (1976). Soil moisture content was determined gravimetrically from the 0-10 cm soil depth on 21 February 2006 (90 DAT). On this day, the diurnal variation of soil temperature was recorded with a thermometer at the 5 and 10 cm depths starting from 7AM to 5AM at 2 h intervals. Also, air temperature was recorded with a thermometer from 7AM to 6PM at 1 h intervals.

The experiment was arranged in Randomized Complete Block Design (RCBD) with four replications. The data were analyzed using MSTAT-C Statistical Computer Package Programme for a Randomized Completely Block Design. Duncan's Multiple Range Test (DMRT) was performed to separate means.

RESULTS AND DISCUSSION

Soil temperature

Soil temperature at the 5 to 10 cm depth was different due to the presence of mulch and mulch colour (Table 1). Soil temperature varied significantly with type of mulching, time of the day and the depth of soil. Soil temperature was low in the early morning and gradually increased until peaking at 3PM in all the treatments and then declined. Temperature under mulches was higher than that of the control plots for all the times. The maximum difference in temperatures between mulched and control plots was 5.1 to 5.7ºC at 5 cm soil depth at 3PM. The transparent plastic mulch produced higher soil temperatures. In general, soil temperature was higher at 5 cm than at 10 cm depth. Suwon and Judah (1985) reported that soil temperature increased with the use of plastic mulch. The polythene mulches allowed part of the radiation to pass through it but acted as barriers against outgoing thermal radiation (Park et al., 1987). Variability of soil temperature in the upper few cm of the soil was likely due to the color of the mulch (Fortnum et al., 1995; Petrov and Al-Amiri, 1976).

Air temperature

Temperature over the plot surfaces and within the plant canopy varied (Table 2). Canopy and plot surface temperatures increased and peaked at 1PM and 2PM, respectively, followed by a decline. The soil surface temperature ranged from 15.0 to 34.6ºC; canopy temperature ranged from 15.2 to 33.7ºC. There were higher air temperatures over the plastic mulch than bare soil. The highest surface temperature was recorded over the black plastic mulch, followed by the blue and transparent mulches. Mulched plots retained comparatively higher air and canopy temperature than did the control, which might be due to trapping of more solar radiation. Among the mulches, there was little variation between the surface and canopy temperatures. The mulches conserved heat from solar radiation and released it slowly at night resulting in higher surface temperature compared to the control. Increased air temperature at the canopy level at mid-day might be due to stomatal closure resulting in reduced transpirational cooling allowing the heat to escape. Similar results were obtained by Easson and Fearnehough (2000) who reported that plastic mulches increased daily air temperature compared to the control.

Soil moisture

The soil moisture content in the experimental plots under different mulches was measured within 0- 10 cm depth. Results revealed that all the mulches retained higher amount of soil moisture compared to the control (Fig 1). But among the mulches, there was no significant difference in soil moisture content. The transparent polythene mulch apparently showed highest moisture (21.1%), followed by black (20.4%) and blue (19.2%) polythene mulch. The lowest moisture (14.6%) was recorded in the control plot. Increased moisture retention capacity due to mulching with polythene could be attributed to less evaporation from the soil. Because of vapours, the water was further trapped within the mulches, resulting in fog which again dropped into the upper soil layer. Wang et al. (1998) reported that all type of polythene mulch increased the soil moisture content in chilli field compared to control.


Plant height

Plant height was measured from 30 DAT to 105 DAT at 15 days interval. As shown in Fig. 2, the plant height varied significantly due to different plastic mulches at different growth stages and increased with plant age. Plastic mulches showed superior performance in plant height than control, indicating mulches had positive effect on the growth and development of chilli. Transparent plastic mulch always showed superior performance than the others. At the maturity, the tallest plant (78.45 cm) was observed in transparent, followed by black (77.58 cm) and blue (77.03 cm) plastic. The smallest plant (61.15 cm) was observed in control plot. The increased plant height in mulched plants was possibly due to better availability of soil moisture and optimum soil temperature provided by the mulches. Changes in the plant height of chilli have been observed by using different mulches and plastic mulch increased the plant height than other mulches (Shinde et al., 1999).


Number of structural branches

Table 3 showed that the mulches had a significant effect on the number of structural branches per plant. The number of structural branches per plant continually increased with plant age. All the mulches had the positive effect on generating and retaining higher number of branches per plant. The highest number of structural branches per plant was observed in black plastic, followed by blue and transparent plastic. Control always showed the least number of structural branches. Favourable weather condition and moisture of the soil are the important parameters affecting the number of branches per plant. It was reported that mulched tomato plants had more branches than that of unmulched plants, which supported the present results (Srivastava et al., 1994).

Stem base diameter

Stem base diameter at all growth stages in chilli plants was influenced by the treatments (Table 4). Base diameter increased gradually with the advancement of time up to 105 DAT. Mulched plants had a higher base diameter than that in controls at all growth stages, followed by blue and transparent plastic. The plant without mulch had the smallest base diameter at all growth stages. This result was in conformity with the report of Easson and Fearnehough (2000) on forage maize.

Number of leaves per plant

Mulching produced significantly higher number of leaves per plant than that of controls, except at 30 DAT throughout the whole growth period (Fig. 3). The number of leaves per plant increased gradually till through 60 DAT and ther after increased rapidly up to 105 DAT. The maximum number of leaves per plant was found on the plants mulched with black plastic at all growth stages, followed by the blue plastic mulch. The microclimate condition improved by the mulches might have provided a suitable condition for producing higher number of leaves in the plants. The effectiveness of plastic mulches for the production of leaves in maize was better than control as reported by Izakovic (1989).

Root length

Root length in the mulched plants was not different, but higher than the control plants (Table 6). Mulches had significant primitive effects on root elongation. This might be due to the conservation of enough soil moisture (Fig. 1), suitable soil temperature (Table 2) as well as suitable microclimate condition.

Root volume

The effect of plastic mulch on root spread was significant (Table 5). Mulch produced significantly higher root volume compared to the control. The black plastic mulches produced the highest root volume (121.59 cm3), followed by blue plastic mulch. In contrast, control produced the lowest root volume (90.32 cm3). These results coincide with those of Wien (1993) where he reported that polythene mulch stimulates really root growth of transplanted tomatoes.

Fresh and dry weight of root

Mulching produced significantly higher fresh and dry root weights than the controls (Table 5). The highest fresh and dry weight of root was recorded in black plastic mulch (60.56 and 26.23g, respectively), followed by blue (58.54 and 24.51 g, respectively) and transparent plastic (57.58 and 24.34g, respectively). In contrast, control showed the lowest fresh and dry weight of root per plant.

Fresh and dry weight of stem

All plastic mulches produced significantly higher fresh and dry weight of stem compared to the control (Table 5). However, among the mulches, there was no significant difference in stem weight. The highest fresh and dry weight of stem was observed in black plastic mulch, followed by blue and transparent plastic mulch. In contrast, control showed the lowest fresh and dry weight of stem. Mulching increased stem dry weight of tomato as reported by Wien (1993).

Fresh and dry weight of leaf

All mulches produced significantly higher fresh and dry weight of leaf compared to the control (Table 5). However, among the mulches, there was no significant difference in fresh and dry weight of leaf. The highest fresh and dry weight of leaf was observed in black plastic, followed by blue and transparent. Apparently sufficient soil moisture was conserved under black plastic mulch that might have improved the plant growth. The result of the present study supported the finding of Suh et al. (1991). Cooper and Law (1978) found that the soil temperature raised by plastic mulching led to a greater rate of growth and development of leaf.

Chlorophyll content in leaf

The effect of plastic mulches on chlorophyll-a, chlorophyll-b, total chlorophyll and their ratio are presented in Table 6. Results revealed that these were significantly influenced by the plastic mulches; chlorophyll a/b ratio did not differ significantly. The highest value of chlorophyll-a, chlorophyll-b and total chlorophyll was recorded in black plastic mulch (1.73, 0.53 and 2.26 mg·g-1 fw, respectively), followed by blue plastic mulch (1.59, 0.492 and 2.086 mg·g-1 fw, respectively). In contrast, the lowest chlorophyll-a, chlorophyll-b and total chlorophyll were recorded in control (1.302, 0.413 and 1.723 mg·g-1 fw, respectively). Similar result was also reported by Panchal et al. (2001) who found that mulch had significant effect on total chlorophyll contents in chilli and black plastic mulch was the best for total chlorophyll content among the mulches.

Vitamin-C content in fruit

The change in vitamin-C in chilli due to plastic mulch is presented in Table 6. Increased amount of vitamin-C in chilli fruit was observed in all the mulch treated plants compared to control. But among the mulch treatments, there was no significant difference in vitamin-C content of the fruits. The findings were in agreement with Panchal et al. (2001) who reported that black mulches produced higher vitamin-C content in chilli.

Yield and yield attributes

Mulching produced more fruits per plant compared to control (Table 7). It meant that mulch had positive influence on fruit setting in chilli. The highest number of fruits per plant was observed in black plastic mulch (472 plant-1), followed by blue (443 plant-1) and transparent mulch (434 plant-1). In contrast, control showed the lowest fruits per plant (335 plant-1). Ravinder et al. (1997) reported that mulching significantly improved the number of fruits per plant and reduced the percentage of fruit abortion compared to unmulched control that supported the present experimental results.

The increase in the number of fruits per plant of mulched plot was probably associated with the conservation of moisture and improved microclimate both beneath and above the soil surface. The suitable condition enhanced the plant growth and development and produced increased fruit bearing nodes compared to the control. Considering relationship between the soil moisture content and fruit number, it was clear that fruit number was strongly related with soil moisture content (Fig. 1). Fruit length, fruit diameter and number of seeds per fruit were statistically similar over the treatments (Table 7), indicating these traits were mainly genetically, not environmentally controlled.

The effect of different plastic mulches on fruit weight per plant and per unit area was significant (Table 7). Mulching produced higher fruit yield per plant and fruit yield per hectare than for the control, indicating that the mulch had positive effect in generating increased fruit yield. Black plastic mulch produced the highest fruit weight per plant (533.4 g) and per hectare (21.3 ton), followed by blue and transparent plastic mulches. Obviously, control plot showed the lowest fruit yield both in per plant (336.3 g) and per unit area (13.45 t·ha-1). Fruit yield increased in mulched plot because of increased number of fruits per plant. These results coincide with those of Siborlabane (2000), who pointed out that the yield and quality of the fruit for the fresh tomato market varies according to the type of mulch used on the plantation.

Weed population

Weed populations were counted at 40 DAT (Table 8). The highest number of weeds per m2 was recorded in transparent plastic mulch (186.5) and the lowest was in black plastic mulch (54.25). Similar results were found for weeds fresh and dry weight. The weed population increased 11, 5 and 3 times in transparent plastic, blue plastic and control, respectively compared to black, indicating black plastic mulch was more effective than the other mulches in suppressing weed growth.

Transparent plastic mulch produced maximum weed population and dry matter which might be due to direct entrance of solar radiation through them and as well as due to higher soil temperature and soil moisture content, especially at the upper 5 cm depth. The blue plastic also allowed easy entrance of solar radiation through it, hence, produced moderate weed density and biomass. Black plastic mulch produced weeds only through the punch and no weed was found under the plastic, which might be due to lack of percentage of light through black plastic. Black plastic mulch blocked the weeds, except a few, which emerged through the planting holes (Schonbeck, 1998). Zhang et al. (1992) reported that black plastic film mulch resulted in 100% control of all the weeds in maize that supported the present experimental result.

CONCLUSION

Based on the experimental results, it could be concluded that plastic mulches had tremendous effects on the growth, and yield of chilli, and black plastic showed superior performance among the plastic mulches. Black plastic mulch was suppressed the weed growth and thereby, increased the fruits yield. Therefore, the cultivation of chilli using black plastic mulch could bring an ample scope for producing more spices.

Received: November 23, 2009; Revised: February 02, 2010; Accepted: January 06, 2011.

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  • *
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  • Publication Dates

    • Publication in this collection
      15 Apr 2011
    • Date of issue
      Apr 2011

    History

    • Received
      23 Nov 2009
    • Reviewed
      02 Feb 2010
    • Accepted
      06 Jan 2011
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