عنوان مقاله [English]
Application of bio-fertilizers as one of the most important and sustainable strategies for soil fertility management and plant nutrition, Application of arbuscular mycorrhizal fungi (AMF), as bio-fertilizer, improve plant nutrients and water uptake and enhance plant resistance to stress conditions leading to improving plant growth and productivity. The objectives were evaluating the effect of different fertilizer sources (chemical fertilizer and AMF as biofertilizer) and harvesting time on the quantity and quality characteristics of peppermint under drought stress conditions.
Materials and methods
A field experiment study was carried out as split split plot design based on a randomized complete block design (RCBD) with 36 treatments and three replications at the faculty of Agriculture, University of Maragheh, The first factor was three irrigation levels included irrigation after depletion of 30% available water as control, depletion of 50% of available water as mild stress and depletion of 70% available water as severe stress. The sub factor was different fertilizer sources including (C: control, NF: 100% nitrogen fertilizer, AMF: arbuscular mycorrhizal fungi (Rhizophagus intraradices), 75% NF+ AMF, 50% NF+ AMF and 25% NF+ AMF), and also the third factor was harvesting time . In AM fungi treatments, 80 g of the soil containing mycorrhizal fungi hyphae and the remains of the root and spores was added to soil in planting times. The aerial parts of peppermint were harvested at 50% of flowering stage on the first harvest and the second harvest.
Results and Discussion
The results showed that plant height, number of nods per plant, number of leaves per plant, number of lateral branches per plant, spad index, dry matter yield, essential oil content and yield was significantly affected by interaction of fertilizer sources× irrigation levels, harvesting time, harvesting time× irrigation levels. The highest and lowest of morphological characteristics, leaf greenness, dry matter yield and essential oil yield of peppermint was achieved in non-stress conditions with application of 75% nitrogen fertilizer+ AMF and sever water stress without fertilization, respectively. The maximum (2.4%) and minimum (1.2%) of essential oil content was observed in mild water stress fertilized with 75% nitrogen fertilizer+ AMF and sever water stress without fertilization, respectively. Based in the essential oil chemical analysis, the main essential oil compounds were menthol, menthone, 1,8 cineol and menthofuran. The highest menthol and menthone content was recorded in the mild water stress fertilized with 75% nitrogen fertilizer+ AMF and non-stress conditions fertilized with 25% nitrogen fertilizer+ AMF. By comparison between two harvesting time, the morphological characteristics, dry matter yield, essential oil content and yield in first harvest was higher than second harvest due to longer growth period and better growth conditions in first harvest compared with second one.
The results demonstrated that the plant height, number of nods per plant, number of leaves per plant, number of lateral branches per plant, SPAD index, dry matter yield and essential oil yield decreased significantly with increasing stress level. In contrast, application of AMF reduced the adverse effects of water stress, so that in severe water stress condition (irrigation after depletion of 70% available water), individual and integrative application of AMF with nitrogen fertilizer increased the mentioned traits, when compared with control. In addition, the mentioned traits in the first harvest increased by 127.8, 194.6, 159.8, 147.7, 17.7 and 37.9% in comparison with second harvest. Also, the essential oil content of peppermint enhanced with increasing water stress to the mild stress. So that, the essential oil content in mild stress increased by 11.4 and 39.7% respectively, when compared with non-stress and severe stress. The highest essential oil yield was achieved in first harvest with integrative application of 75% NF+ AMF. Also, the major essential oil compounds of peppermint (menthol) was recorded in mild stress integrated with 75% nitrogen fertilizer+ AMF. Generally, considering that the economic purpose of cultivating of medicinal plants is extracting the maximum content of secondary metabolites, and since the productivity of peppermint essential oil increased significantly by integrative application of 75% nitrogen fertilizer+ mycorrhiza in mild stress, so it can be suggested as a superior treatment