Abstract: This study was conducted to determine the effects of different plant densities (20x50 cm, 30x50 cm, 20x100 cm, 30x100 cm) on plant growth characteristics and fruit yield of paprika pepper (Capsicum annum L.) in open field. Plant height, leaf chlorophyll content, flower number, yield, fruit seed number, 1000 seed weight and vitamin C were assessed at immature and mature. The results indicated that vegetative growth characteristics (plant height, lateral stem length and leaf chlorophyll content) reduced as plant density increased. The highest lateral stem number and leaf number were obtained in plants density 30x100 cm. Plant density affected on flowering factors (node number to first flower, days to 1st flowering and flower number). The days to 1st flowering increased as plant density increased. It was observed that fruit volume, fruit average weight, plant yield and seed number decreased with increasing plant density, but total yield ha-1 increased with increasing plant density. The highest and lowest of yield ha-1 were obtained by 20x50 cm and 30x100 cm spacing, respectively. Also plant density significantly affected on Vitamin C. The highest and lowest vitamin C were observed in 30x100 cm and 30x50 cm spacing, respectively.
INTRODUCTION
Pepper (Capsicum annum L.) which belongs to Solananceae, is known as a vegetable and consumed both as fresh and dehydrated spices (Bosland and Vostava, 2000). International spices traders use the term paprika for non-pungent red Capsicum powder. Besides being used as colorant, it is also used for flavouring and garnishing of eggs, cheese, meat dishes, sea foods, salads etc. The commercial importance of paprika both as a spice and a vegetable with large scale cultivation in both tropical and sub tropical regions are increasing (Kannan et al., 2009). Cultural factors such as transplant age, fertility, plant population and delayed harvest influenced pepper yield (Decoteau and Graham, 1994). Studies on plant density for different types of pepper including bell, cayenne, pepperoncini and Jalapeno have shown that plant density and plant arrangement can influence plant development, growth and the marketable yield of peppers (Khasmakhi-Sabet et al., 2009). Plant density is an important determinant of yield. Yield per unit area tends to increase as plant density increases up to a point and then declines (Akintoye et al., 2009). An increase in spacing of rice induced vigorous plant growth as well as increased the number of panicles per hill, grain yield per hill, filled grains per panicle and 1000 grain weight (Baloch et al., 2002). Nasto et al. (2009) reported that increasing plant density resulted in greater yield ha-1 of bell pepper. Wider spacing on the other hand led to increase in fruit yield per plant with bigger fruits and more cracked fruits per plant in tomato (Law-Ogbomo and Egharevba, 2009). Decreasing plant density significantly reduced the total yield of radish but markedly enhanced root quality (El-Desuki et al., 2005). It was reported with increasing plant density decreased pepper root dry weight and was positive relationship between fruit weight and root weight (De-Viloria et al., 2002). Azizi and Kahrizi (2008) reported that plant density affected on Seed yield, biological yield, harvest index and percentage of seed essential oil of cumin. An increasing in yield with higher plant density was a result of increased numbers of fruit ha-1 in direct-seeded paprika pepper (Cavero et al., 2001). The main aim of this experiment was to determine the influence of plant density on growth, yield and fruit quality of paprika pepper in open filed.
MATERIALS AND METHODS
Plant preparation: The research was conducted from March 9 to November 21, 2006 at Research Farm of Birjand University, Iran (latitude 32°53' N, longitude 59°13' E and 1470 m elevation). This site represents the range of dry conditions. Annual rainfall ranges is between 91 and 120 mm and mean annual relative humidity is 37%. Soil sample (0-30 cm depth) was taken with auger after the site had been prepared for cultivation. The sample was analyzed for physical and chemical properties using standard laboratory procedures described by Mylavarapu and Kennelley (2002) and data shown in Table 1. The experimental field was cleared, ploughed, harrowed and divided into plots. Phosphorus (P2O5) and potassium (K2O5) were applied 100 and 50 kg ha-1 each at the time of soil preparation. Paprika pepper seeds were established in a greenhouse in large trays with a 1:1 mixture of sand and peat [1:1 v/v]. Irrigation was done after sowing when necessary. Six-week-old pepper plants were hand-transplanted into well-prepared beds in the field on 19 Apr. 2006. Nitrogen fertilizer (urea) was applied at 75 kg ha-1 that was splited into three equal parts and applied at ten Days after Transplanting (DAP) as basal and remaining portions were used as top dressing at 30 and 50 DAP. Plots were irrigated when necessary during the growing season. All practical managements included, mulching, weeding and other horticultural operations were done traditionally.
Treatments: Treatments consisted of four levels of population plant (20x50 cm, 30x50 cm, 20x100 cm, 30x100 cm) that achieve planting densities of 100000, 6666, 50000 and 33333 pph, respectively.
Measurements: Ten plants in each replication were used to assess plant height, leaf number, number and length of lateral stem and internodes length at three growing stages including vegetative, flowering and reproductive. Leaf chlorophyll content was measured by a portable chlorophyll meter, SPAD-502 (Minolta Corporation, Ramsey, NJ). Leaf samples were oven dried at 75°C for 72 h to the constant leaf dry weight for each plant was weighed using digital balance and recorded in gram (Ouda and Mahadeen, 2008). The number of days to the first flowering was estimated for each plot and the number of flowers per plant was evaluated based on the method by Remison (1997). Mature fruits were harvested at 10-14 day intervals to assess the volume of fruits (cm3), average fruit weight (g) and fruit yield per plant (g plant-1).
| Table 1: | Soil characteristics of experimental field |
Fruit yield per hectare was obtained through the conversion of the net plot yield. Vitamin C was determined based upon the quantitative discolouration of 2,6-indichlorophenol 6 indophenols (Merck KgaA, Darmstadt, Germany) titrimetric method as described in AOAC methodology No. 967.21 (AOAC, 2000).
Experimental design and statistical analysis: The experiment was arranged in a Completely Randomized Block Design (CRBD) with four treatments and three replications, each replication with ten plants. Data were analyzed using MSTAT-C and means were compared by Duncan’s Multiple Range Test (DMRT) at 5% level of confidence.
RESULTS AND DISCUSSION
Data (Table 2-5) showed that plant density significantly affect pepper growth, yield and fruit quality.
Vegetative growth: Results obtained indicated significant differences for Plant height (Table 2). The highest plant height at vegetative and reproductive stages were observed in density 20x100 cm with 21.09 cm and density 30x100 cm with 42.67 cm, respectively and these variables decreased as plant density increased (Table 2), Similar results were also reported by Elattir (2002), De-Viloria et al. (2002) and Ara et al. (2007). The effects of plant density on the stem characteristics of pepper were significant. Number and length of lateral stems reduced at both vegetative and reproductive stages as plant density increased (Table 2). This result is the same trend with the findings of Jovicich et al. (2003a) and Hosseini et al. (2006). The reduction in plant height and number and length of lateral stems as plant population density increased might be attributed to the possible competition for soil moisture and nutrients. It is explained that as plant population density increases, competition for available water, mineral nutrients and light increases (Abubaker, 2008). Leaf number at flowering and reproductive stages decreased with higher planting density (Table 3).
| Table 2: | Effect of plant density on vegetative characteristics of pepper |
| Veg.: Vegetative stage; Flower: Flowering stage; Rep.: Reproductive stage. Within each column, same letter indicates no significant difference between treatments at 5% levels | |
The highest leaf number at flowering stage (59.76) and reproductive stages (90.76) were observed in 30x100 cm but there was no significant difference between treatments at leaf number at vegetative stage (Data not shown). This result is in agreement with the findings of Elattir (2002), De-Viloria et al. (2002) and Pervez et al. (2004). Plant density significantly affected leaf chlorophyll content at flowering and reproductive stages. As data shown, the lower plant density, the higher chlorophyll content (Table 3). The highest leaf chlorophyll content was observed in density 30x100 cm and 20x100 cm (67.30, 65.96 at flowering and reproductive stages, respectively). However, the reduction of leaf chlorophyll content could be explained partially by the effects of shading of the lower canopy, causing poor canopy interception of the photosynthetically active radiation (Brahim et al., 1998). If we look at the plant basis, then at the wider spacing the area for the development of a single plant is larger as well as the possibility for more lush growth and the development of fruitful branches. In high densities, plants compete with each other for nutrients, water and light and therefore develop poorly (Maynard and Scott, 1998). Also, the strong interplant competition due to the crowding and the shallow taproot system of these plants may have prevented the absorption of water and nutrients at deeper soil profiles (Brahim et al., 1998).
| Table 3: | Effect of plant density on vegetative characteristics of pepper |
| Veg.: Vegetative stage; Flower: Flowering stage; Rep.: Reproductive stage. Within each column, same letter indicates no significant difference between treatments at 5% levels | |
| Table 4: | Effect of plant density on reproductive characteristics of pepper |
| Within each column, same letter indicates no significant difference between treatments at 5% levels | |
Reproductive growth: Because of higher vegetative growth by high spacing, the node numbers to the first flowering increased, however the number of days to the first flowering decreased (Table 4). The highest and the lowest node numbers to the first flowering were obtained at the density 20x100 cm with 11.09 nodes and 20x50 cm with 10 nodes, respectively; that was in agreement with Abubaker (2008) and Law-Ogbomo and Egharevba (2009). Flower and fruit numbers in lateral stems were affected by plant density (Table 4). The highest flower and fruit numbers in lateral stems were in the lowest plant density (30x100 cm) with 5 flowers and 2.59 fruits, while the lowest flower and fruit numbers in lateral stems were in the highest plant density (20x50 cm) with 4 flowers and 1.67 fruits, which were in agreement with the findings of Jovicich et al. (2003a) and Ara et al. (2007). Higher plant density also restricts light penetration and dry matter accumulation, thus reducing flowering bud development (Foster et al., 1993).
Results obtained indicated that plant densities 30x100 cm and 20x100 cm produced the highest weight (74 g) and volumes of fruit (156.3 cm3) respectively, while the lowest fruit weight (66 g) and fruit volume (142.5 cm3) was related to plant density 20x50 cm. The similar findings of increased average fruit weight with wider spacing were reported by Miyao (2002) and Jovicich et al. (2003b). This is likely due to the competition associated with the higher plant populations resulting in the lower weight and volume mean fruit. It was observed that planting density had remarkable effects on Seed characteristics (Table 5). Seed numbers per fruit and 1000-seed weight increased as plant space increased. The maximum of seed numbers (145) and 1000-seed weight (5.52 g) were observed in the density 30x100 cm and 20x100 cm, respectively. These results confirm earlier observations by Nerson (2005), Dong et al. (2005) and Hosseini et al. (2006). Increased seed numbers and 1000-seed weight caused by the decreasing in plant population agree with the hypothesis that lower plant population may results in heavier seeds. Heavier seeds may provide superiority in the germination and the establishment as they have more resources to enable them to emerge from greater depth. The production of the heavier seeds by the lowest plant population may be due to the less competition for nutrients and moisture between plants which, in turn, influences supply of assimilation of the seeds as reported by Egli (1998).
| Table 5: | Effect of plant density on yield and fruit quality characteristics of pepper |
| F.W.: Fresh Weight; Vol.: Volume; W.: Weight; No.: Number. Within each column, same letter indicates no significant difference between treatments at 5% levels | |
| Fig. 1: | The correlation between plant density and pepper yield per plant |
The total fruit yield plant-1 decreased as the planting density increased (Table 5). The lowest and the highest yield (plant-1) were observed in the 20x50 cm with 928.8 g and 30x100 cm with 1211 g, respectively. This result is in conformity with the findings of Cavero et al. (2001), Ara et al. (2007) and Nasto et al. (2009). This might be due to the effect of competition. This arises due to the fact that the competition is less in the low planting density than at the high planting density. The competition might be high for nutrients, physical spaces and water (Law-Ogbomo and Egharevba, 2009). The relationship between plant density and pepper yield is shown in Fig. 1. The equation was: Y = 94.59 X + 814.65 where Y is yield in g plant-1 and X is levels of plant density.
Results obtained indicated significant differences for yield per hectare (Table 5). Yield (ha-1) increased as plant density increased. The highest density (20x50 cm) produced the highest fruit yield (93800 kg h-1) while the lowest yield per hectare (33420 kg h-1) was recorded at density (30x100 cm). Similarly, Russo (2003), Nasto et al. (2009) and Khasmakhi-Sabet et al. (2009) reported that greatest fruit yield ha-1 of sweet pepper and other plants were obtained from plants grown at the high densities. The lower plant densities per unit area produces more vigorous crops than at the higher population densities, but this could not compensate for the reduced number of plants per unit area. The total yields ha-1 increased with the higher plant densities. This was probably due to the increasing in the number of plants per unit area, which might contribute to the production of extra yield per unit area leading to the high yield (Law-Ogbomo and Egharevba, 2009). The relationship between plant density and pepper yield per hectare is shown in Fig. 2. The equation was: Y = 16.896X + 105.45 where Y is yield in ha-1 and X is levels of plant density. This formula could be used when making a recommendation for pepper plant density application and when the conditions are the same or very close to those in this experiment.
| Fig. 2: | The correlation between plant density and pepper yield per hectare |
A significant difference among the plant density treatments was found on the vitamin C (Table 5). The highest vitamin C at green (135.4 mL/100 g) and ripping stage (204.7 mL/100 g) was observed in the density 30x100 cm, while the lowest vitamin C at green (132.3 mL/100 g) and ripping stage (199.3 mL/100 g) was observed in the density 30x50 cm.