Advances in Crop Science and Technology
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Chamomile (Matricaria chamomilla L.) is an annual plant belonging to the Asteraceae family. Its height varies from 20 to 60 cm, depending on the location and the soil [1]. Chamomile may be considered as an economic substitute of the field crops, irrigated with fresh water since it has the adaptability to a wide range of soil and climatic conditions. Nowadays, chamomile is among the widely used medicinal plants throughout the world [2]. Chamomile is a herb and native to Iran and Europe that grows as a wild plant [3,4]. Chamomile is known to be anti-inflammatory, anti-spasmodic, anti-bacterial, antiseptic and antispasmodic [5]. Its consumption as a folklore medicine has a long history. Medicinal importance of this species is also on the rise and at present, seven pharmaceutical products have been manufactured from chamomile in Iran under the license of the Ministry of Health. Its cultivation has been increased steadily in recent years [2]. Stand density affects plant architecture, alters growth and developmental patterns and influences carbohydrate production [6]. Flower and oil yield of chamomile can be maximized by adjusting the seedling population to match the moisture conditions of the environment, that is, densely populated stands utilize moisture and nutrients more quickly than sparsely populated stands.

Therefore, optimum densities for each crop and each environment should be determined by research. However, there is a limitation of information on the plant population density of chamomile in Wondo Genet Research Center Southern Region, Ethiopia.

The research was conducted at Wondo Genet Agricultural Research Center’s fields, in Southern Ethiopia during 2016-2017 growing seasons to evaluate the influence of plant population density on growth and flower yield of chamomile (Matricaria chamomilla L.). Wondo Genet is located at 7°19'N latitude and 38°38'E longitude with an altitude of 1760-1920 m.a.s.l. The site receives a mean annual rainfall of 1372 mm with minimum and maximum temperature of 11.5°C and 26.2°C, respectively. The soil is a sandy clay loam with an average pH of 7.2. The experiment was conducted using five intra-row spacing (40 cm, 50 cm, 60 cm and 70 cm) and three inter-row spacing (40 cm, 60 cm and 80 cm) with a total treatment combination of twelve that were laid out in factorial RCBD design with three replications.

Seedlings were raised in the nursery for 35 days in polyethylene pots. Transplanting was done in October 2016 and in September 2016 for two consecutive years. Plots were 3.5 m × 3.0 m and final harvest was taken from central rows. There was space 1 m between plots and 1.5 m replication. Weed control was done by hand. Plots were irrigated at 7 days intervals. Harvesting of flowers started when 50% of the flowers matured and continued at two-week intervals by using hand pick. Data on plant height, the number of primary branch per plant, number of flowers per plant, the weight of flowers per plant and fresh and dried flowers yield per hectare, oil yield and oil content percentage were recorded. The extraction of the essential oil content per unit dry flower weight was based on steam distillation using Clevenger apparatus. The collected data were statistically analyzed using SAS computer software version 9.0 English and differences between means were assessed using the least significant difference (LSD) test at P<0.05.

Number of primary branch per plant and plant height

There were significant differences in a number of primary branch per plant between the various intra-row spacing in 2017 cropping season and the pooled mean, however, the main effect of the inter-row was not significant. In 2016 cropping season the main effect of intrarow and inter-row spacing and their interaction was not significant. From the pooled mean analysis the highest number of primary branches per plant (27) was recorded from 70 cm intra- row spacing and the lowest number of primary branch per plant (24) was recorded at the close spacing of 40 cm. Generally, an increase in intra-row spacing led to significantly higher branching. Similarly, the result was reported on Rose Scented Geranium (Pelargonium graveolens) [7]. The data presented in Table 1 show that the plant height chamomile was not affected by intra-row and inter-row spacing in both years and the pooled mean.

Table 1: Main effects of intra-row and inter-row spacing on yield and yield components of chamomile for two consecutive cropping seasons (2016 to 2017).

Number of flowers per plant and weight of fresh flowers per plant

The number of flowers per plant was significantly affected by the main effect of intra-row and inter-row spacing in both years and their interaction in 2016 cropping season and the pooled mean.

The pooled mean analysis revealed that the maximum number of flowers per plant (585) and (572) were recorded from 70 cm intra-row and 80 cm inter-row spacing. The lowest number of flower per plant (482) and (490) were recorded from 40 cm intra-row and 40 cm interrow spacing respectively. Fresh flower weight per plant was significantly influenced by the main effect of intra-row and inter-row spacing and their interaction of pooled mean. The pooled mean analysis revealed that the maximum fresh flowers weight per plant (62.1 g/p) was obtained from the treatment combination of 60 cm intra-row with 60 inter-row spacing which was statistically similar to the value obtained at the combined spacing of 50 cm × 60 cm, 60 cm × 40 cm and 60 × 80 cm (Table 2). At wider spacing, there is less interrow and intra-row plant competition for available resources and the plant have a chance to develop more number of branches and leaf that could be the reason for a maximum number of fresh flowers per plant and weight of fresh flowers per plant obtained than in closer spacing. The increase in a number of flowers and weight of flowers per plant in wider spacing might be also due to the availability of more resources to plants on account of low population density per unit area. This was consistent with the findings who reported that low density resulted in an increased number of flowers per plant in chamomile [8]. These result also in accordance with previous studies [9,10].

Table 2: Main effects of intra-row and inter-row spacing on yield and yield components of chamomile for two consecutive cropping seasons (2016 to 2017).

Weight fresh flowers per hectare and dry flower per hectare

The analysis of variance showed that the main effect of inter and intra-row spacing showed very highly significant (P<0.001) differences in fresh flowers weight per hectare in both years and pooled mean and significantly (P<0.05) influenced by the interaction effect of inter and intra-row spacing in 2017 cropping season and polled mean (Tables 3 and 4). In 2016 cropping season maximum fresh flower weight (2013.9 kg ha^-1) and (2344.9 kg ha^-1) were recorded at 40 cm intra-row and 40 cm inter-row spacing respectively. The lowest fresh flowers weight (922.2 kg ha^-1) and (1018.3 kg ha^-1) were obtained at 70 cm inter-row and 80 cm inter-row spacing respectively. In 2017 cropping season maximum fresh flowers weight (4387.9 kg ha^-1) was obtained from the combined spacing of 40 cm intra × 40 cm inter-row spacing flowed by fresh flowers weight (3939 kg ha^-1) obtained from the combined spacing of 50 cm intra × 40 cm inter-row spacing. The lowest fresh flower weight (1651 kg ha^-1) was recorded at the combined spacing of 70 cm intra × 80 cm inter-row spacing which was statistically similar to the value obtained at the combined spacing of 70 cm intra × 60 cm inter-row, 50 cm intra × 80 cm inter-row and 60 cm intra × 80 cm inter-row spacing (Table 4). The pooled mean analysis also showed that the maximum fresh flower weight (3779 kg ha^-1) was obtained from the treatment combination of 40 cm intra-row with 40 cm inter-row spacing. The highest fresh flower yield at the narrow spacing was due to a high number of plants per unit area. This study clearly indicated that fresh flowers yield increased their yield potential at narrow spacing as compared to wider interims of population number per unit area. This was consistent with the findings who reported that high density resulted in an increased weight of chamomile fresh flowers per hectare [8]. These result also in accordance with previous studies [9,10].

Table 3: The interaction effect of intra-row and inter-row spacing on pooled mean value of chamomile number of flowers per plant, fresh flowers weight per plant and the pooled mean.

Table 4: The interaction effect of intra-row and inter-row spacing on chamomile fresh flowers weight per hectare and oil yield and the pooled mean value.

Dry flower weight was very highly significantly affected by the main effect of inter-row spacing and significantly influenced by intra-row spacing in both year and the pooled mean, however, their interaction was not significant. The maximum pooled mean analysis of dry flower weight (517.2 kg ha^-1) and (586.7 kg ha^-1) was recorded from 40 cm intra-row and 40 cm inter-row spacing. The minimum dry flower weight (392.3 kg ha^-1) and (303.1 kg ha^-1) were recorded from 70 cm intra-row and 80 cm inter-row spacing respectively (Table 2). Similar to fresh flower weight dry flower weight also at the narrow spacing was due to a high number of plants per unit area. This was consistent with the findings who reported that high density resulted in an increased weight of chamomile dry flowers per hectare . There are some reports on producing the same yield in narrow ranges of densities The optimal plant densities for German chamomile were reported for 10 to 80 cm spaces between rows in different condition . Flower yield per hectare increases to a degree, by which the row distance gets smaller.

Oil yield kg ha^-1 and oil content

Oil yield was significantly affected by the main effect of intra-row spacing and very highly significantly influenced by inter-row spacing in each year and the pooled mean. In 2016 cropping season oil yield was significantly affected by the interaction of intra-row with inter-row spacing however in 2017 and the pooled mean did not interact. Maximum oil yield (5.6 kg ha^-1) was obtained from the treatments combination of 40 cm intra-row with 40 cm inter-row spacing, followed by 60 cm intra-row and 40 cm inter-row and 50 cm intra-row and 40 cm inter-row spacing respectively. On the other hand, the lowest oil yield (0.6 kg ha^-1) was recorded from the combination of 70 cm intra-row and 60 cm inter-row spacing which is statistically at par with the value obtained from the combined spacing of 40 cm × 80 cm, 50 cm × 80 cm and 70 cm × 80 cm intra and inter-row spacing respectively (Table 4). The result indicated that the closer spacing accommodates more plant number per unit area than wider spacing that may contribute to more number and weight of flower led to significantly higher oil yield. This was consistent with the findings who reported that high density resulted in an increased number and weight of flowers per hectare in chamomile [8]. The data presented in Table 2 show that the oil content of chamomile was not affected by intra-row and inter-row spacing in both years and the pooled mean.

The two consecutive study years result showed that the highest economic fresh flower weight (3779 kg ha^-1) and oil yield (5.6 kg ha^-1) was recorded from the combined spacing of 40 cm intra-row and 40 cm inter-row spacing. Therefore we, recommend that the bestcombined intra-row and inter-row spacing for Chamomile (Matricaria chamomilla L.) are 40 cm × 40 cm to attain maximum yield under appropriate management conditions for Wondo genet and similar agroecology.

The authors would like to acknowledge Wondo Genet agricultural research center and crop research process for providing the necessary facilities and support during the entire experimentation. Our special thanks to Gizachewu Atinafu, Alemitu Teka, Chrenet Tefera, Abdela Befalo and Beriso Mi’eso for their direct and indirect contribution in field and laboratory work.