Abstract
Intercropping fodder plants with medicinal plants, in addition to enhancing productivity, can remarkably reduce the population of weeds, pests and diseases and for naturally meeting of livestock medicinal needs. Two experiments were conducted to evaluate biological yield, essential oil (EO) composition and yield of sweet basil (Ocimum basilicum L.) treated with N2 fixing bacteria in additive intercropping with forage maize during the 2018 and 2019. Treatments were arranged in factorial split-plot-in time in randomized complete block design with three replications. The factors were 100% chemical fertilizer (N), N2 fixing bacteria (Azospirillum brasilense and Azotobacter chroococcum), integration of N2 fixing bacteria + 50% nitrogen chemical fertilizer and control. The cropping pattern factor included of sole cropping basil and the additive intercropping of maize + 25% basil, maize + 50% basil, maize + 75% basil, and maize + 100% basil. The results indicated that the highest essential oil yield (30.8 kg ha−1) and essential oil percentage (0.75%) were obtained in sole cropping with A. brasilense and A. chroococcum + 50% chemical nitrogen fertilizer application in second harvest in 2019. In both cropping systems, the N2 fixing bacteria application significantly increased fresh and dry yield and land equivalent ratio (LER) as compared to control plants. In both years of experiments could remarkably vary depending on type of treatment. In both years, eight constituents including methyl chavicol (17.24–51.28%), Z-citral (neral) (8.33–24.3%), geranial (10.2–31.3%), (E)-caryophyllene (1.05–5.64%), α-trans-bergamotene (0.53–1.7%), α-humulene (0.4–1.69%), germacrene-D (0.2–1.88%), and (Z)-α- bisabolene (1.16–3.86%) were the main constituents of EO. The highest content of methyl chavicol was found through sole cropping of sweet basil with nitrogen chemical fertilizer followed by sole cropping of sweet basil with an integration of A. brasilense and A. chroococcum + 50% nitrogen chemical fertilizer in 2018 and 2019. Intercropping system and N2 fixing bacteria can be effective in reducing chemical fertilizer consumption and environmental pollution and achieving the sustainable agriculture goals.
Highlights
Since the green revolution and the introduction of fertilizerconsuming cultivars, the consumption of chemical fertilizers has been widely increased
The result showed that the highest fresh and dry yields of sweet basil were obtained by sole cropping of sweet basil and using integration of A. brasilense and A. chroococcum + 50% nitrogen chemical fertilizer in second year of experiment (Table 3)
The higher fresh and dry yields in sole cropping of sweet basil can be attributed to the homogeneous environment in monoculture system (AmaniMachiani et al, 2018)
Summary
Since the green revolution and the introduction of fertilizerconsuming cultivars, the consumption of chemical fertilizers has been widely increased. Soil fertility improvement is mainly achieved through the use of chemical fertilizers, which their high consumption is a threat to environment and human health (Kordi, 2017) In this regard, some issues concerning soil like erosion, salinity, acidification, and decline in qualitative and quantitative properties of surface-area soils as well as other issues such as contaminating surface and groundwater, devastating biodiversity, reduced soil biological activities, and increasing cost of crop production are consequences of illogical using of chemical fertilizers (Kordi et al, 2017). Some issues concerning soil like erosion, salinity, acidification, and decline in qualitative and quantitative properties of surface-area soils as well as other issues such as contaminating surface and groundwater, devastating biodiversity, reduced soil biological activities, and increasing cost of crop production are consequences of illogical using of chemical fertilizers (Kordi et al, 2017) Some conditions, such as climatic and nutrient factors suitable for plant growth, are the most important factors affecting growth of medicinal plants and their active components quantitatively and qualitatively (Street, 2012). The utilization of bio-fertilizers (e.g., free-living N-fixing bacteria) is of particular importance in the agriculture sector due to their potential role in healthy food, improving crop yield, and decreasing greenhouse emissions (Ghilavizadeh et al, 2013; Raei et al, 2015). Raei et al (2015) showed that the seeds of sweet basil inoculated with Azospirillum produced plants with higher fresh and dry weights, height, and more lateral branches as compared to controls. Ghilavizadeh et al (2013) showed that inoculating the seeds of fennel with Azotobacter and Azospirillum could increase seed essential oil (EO) content
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