عنوان مقاله [English]
Introduction: In recent years, the effect of exogenous organic amendments on soil properties and plant growth characteristics has received renewed attention. Although the utilization of mineral fertilizers could be viewed as the best solution in terms of plant productivity, this approach is often inefficient in the long-term in tropical ecosystems due to the limited ability of low-activity clay soils to retain nutrients. Intensive use of agrochemicals in agricultural systems is also known to have irreversible effects on soil and water resources.
Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost can greatly enhance the physical structure of soil. Decomposing organic amendments slowly release nutrients which may be taken up by plants and thus result in improved agroecosystem productivity.
Vermicompost is currently being promoted to improve soil quality, reduces water and fertilizer needs and therefore increases the sustainability of agricultural practices in tropical countries. Vermicomposting is a process which stabilizes organic matter under aerobic and mesophilic conditions through the joint action of earthworms and microorganisms. The products of vermicomposting have been successfully used to suppress plant pests and disease as well as increase crop productivity.
Cow manure is an excellent fertilizer containing nitrogen, phosphorus, potassium and other nutrients. It also adds organic matter to the soil which may improve soil structure, aeration, soil moisture-holding capacity, and water infiltration.
Plant density is the number of individuals of a given plants that occurs within a given sample unit or study area. Planting density can impact the overall health of plants. Plantings that are too sparse (the density is too low) may be more susceptible to weeds, while planting that are too dense might force plants to compete over scarce nutrients and water and cause stunted growth .
Despite of many studies on the effect of organic fertilizers and plant density on different crops, information on the effects of these factors for many medicinal plants is scarce. Therefore, in this study the effect of organic fertilizers and plant density on morphological characteristics and yield of Echium amoenum was studied in a low input cropping system.
Materials and methods: In order to evaluate the plant density and comparison of organic and chemical fertilizers on Iranian Ox-Tongue (Echium amoenum), a split plots experiment in time based on RCBD design with three replications was conducted in 2011-2014 growing seasons, in Ferdowsi University of Mashhad, Iran. The main plots included factorial combination of 3 plant densities (3, 5 and 10 plants per m2) and 4 different types of organic and chemical fertilizers (compost, vermicompost, cow manure, nitrogen chemical fertilizer and control) and the sub plots included agronomic years (2 and 3 agronomic years).
Results and discussion:The results showed that the effect of plant density on dry flower yield was significant, so that the highest dry flower yield (816 kg.ha-1) obtained for 5 plants per m2 and in this treatment dry flower yield was 23% and 15% more than 3 and 10 plants per m2 treatments, respectively. In both of agronomic years, effect of different organic and chemical fertilizers was intensified in 5 plants per m2, for example in second agronomic year, compost in 5 plants per m2 increased seed yield 30 and 25% compared to 3 and 10 plants per m2 densities, respectively. Although the use of chemical fertilizers to improve yield and yield components of Iranian Ox-Tongue was no ineffective, its impacts was much less than organic fertilizers. In general, the results of this research showed that the use of organic fertilizers in optimal plant densities can be reducing environmental risks of chemical fertilizers and develop sustainable agriculture and protect the health of the products.
Organic fertilizers are among the most significant resources for development of agricultural soil quality and increase in the yield of different medicinal plants. It has been reported that this ecological inputs provide favorable conditions for plant growth and development through improvement of physical, chemical and biological properties of the soil, therefore, it can be concluded that improvement of the most studied traits in the present study were due to use of organic fertilizers.
It seems that plants compete with each other over scarce nutrients and water in high plant density and cause stunted growth . Some other studies have reported that suitable plant density can increase the growth and yield of some medicinal plants such as coriander (Coriandrum sativum L.) (Akhani), Ajwain (Carum copticum L.) , lemon balm (Melissa officinalis L.) and anise (Pimpinella anisum L.).
Conclusion: In general, the results of this research showed that the use of organic fertilizers in optimal plant densities can be reducing environmental risks of chemical fertilizers and develop sustainable agriculture and protect the health of the products.