Geoscience Reference
In-Depth Information
oxysporum
var.
redolens
reduced biomass yields by 73.6-
88.2% and essential oil yields by 69.1-87.1% in Bourbon and
Algerian cultivars of rose-scented geranium (
Pelargonium
graveolens
) (Rao, 2002).
Finally, human beings are the most significant biotic factor
shaping ecosystems. Human beings who manage these factors
in terms of irrigation, nutrient input, pest control, land prepara-
tion, mixed/relay cropping and other practices are also a biotic
component of agroecosystems. Chemical composition in plants
is dependent on biosynthetic pathways controlled by several
enzymes which are produced by numerous genes, abiotic and
biotic factors, including human management that exerts consid-
erable influence on the same. Several agronomic studies taken
up on medicinal and aromatic plants invariably examine the
quality in relation to agronomic management. A number of
studies reported the effects of agricultural practices on the sec-
ondary metabolites in medicinal and aromatic plants (Verma
et al., 2009, 2011, 2012, 2013).
Planting dates influence growth yield and secondary
metabolite production as reported in
Artemisia annua
(Singh
et al., 2009b), rose-scented geranium (Kalra et al., 1992) and
Silybum marianum
(Rahimi and Kamali, 2012). In studies
conducted in the temperate region of the Himalayas, artemis-
inin yield in the dried leaves of
Artemisia annua
was found
to be maximum among the plants that were transplanted in
March (24.39 kg ha
−1
) and minimum to those transplanted in
November (3.39 kg ha
−1
) (Verma et al., 2011).
Plant density and irrigation methods are the two important
factors that directly affect the yield and flower number, amount
of essential oils and yield components (Marisol et al., 2003;
Saif et al., 2003; Tiwari et al., 2003; Verma et al., 2008; Singh
et al., 2009a).
Gengaihi and Abdallah (1978) reported that the number of
umbel per plant, seed yield per plant and plant height increased
at wider spacing. According to the results of Verzalova et al.
(1988), row spacing did not affect the plant height but the num-
ber of umbel and seed yield per plant was increased at wider
spacing. Naghdibadi et al. (2002) who studied the effect of
different plant densities on the yield of dry material of thyme
(
Thymus vulgaris
) showed that a higher yield of dry material
was obtained with 15 cm densities of planting.
Sharifi and Abbaszadeh (2003) investigated the effect of
N fertiliser on essential oil content and composition of the
aerial parts of fennel (
Foeniculum vulgare
Mill) and found
that N application increased the essential oil content. Ram
