عنوان مقاله [English]
Introduction: Broccoli is one of the valuable vegetables among brassicas which has received great attention throughout the world and is cultivated both in soil and soilless culture. Currently, we face restriction in high quality of the soils and water resources as two essential inputs in agriculture. Like other parts of the world, Iran is losing hundred hectares of its arable and fertile land annually due to salinity, alkalinity and waterlogging. One of the important strategies to overcome these adverse conditions is soilless culture systems. Among the different methods of soilless culture, substrate culture is more common and cheaper than others. Different kinds of organic and inorganic substances are used in soilless culture system, but the optimum mixture of growing medium is still a challenging issue. Physical and chemical characteristics of growing media can potentially affect the yield and product quality in direct and indirect ways. A good medium for soilless culture should have easy drainage, appropriate aeration, high water holding capacity and low price, as well as no weed seeds and pathogens. Therefore, this research was aimed to evaluate different prevalent growing media in broccoli soilless culture system.
Materials and Methods: This experiment was conducted as an outdoor soilless culture system in outdoor hydroponic site in Sari Agricultural Sciences and Natural Recourses University (SANRU). To begin with, broccoli seeds were sown in transplanting tray, and after five weeks, the developed transplants were cultivated in growing bags in a soilless system. In this work, different mixtures of culture media were evaluated for yield component and mineral elements of broccoli. Ten kinds of different media comprising of cocopeat, perlite, sand, sawdust, sand+sawdust, sand+vermicompost, cocopeat+perlite, cocopeat+LECA, cocopeat+ pumice, and cocopeat+perlite+ vermicompost were compared in completely randomized design with tree replications. At the end of the growing season, vegetative growth and yield components of broccoli were measured. The macro nutrients including nitrogen (N), phosphorus (P), potassium (k), magnesium (Mg), calcium (Ca) and sulfur (S) were then analyzed in the harvested broccoli. Four important micro elements such as Iron (Fe), cooper (Cu), boron (B) and zinc (Zn) were measured as well. A statistical analysis was performed using analysis of variance in Statistical Analysis System (SAS) software (version 9.1) and means were compared using Duncan’s multiple range test at 0.05 and 0.01 probability levels.
Results and Discussion: According to the results, culture medium showed no significant effect on plant height, dry matter and the number of auxiliary heads, while it significantly affected diameter and weight of main head (p≤0.01). The highest head diameter was seen in sand+vermicompost mixture which had no significant difference from cocopeat, cocopeat+LECA, and prlite+cocopeat+vemicompost. The mixture of sand+vermicompost resulted in the heaviest broccoli heads that were significantly greater than all other growing media used in the experiment. Since vermicompost contains some mineral elements like calcium, magnesium and phosphorus and some growth stimulators as well, mixing this substrate with sand can create an appropriate and ideal culture for root growth and development. Pure perlite and sawdust media contributed to the lowest yield with no significant differences from each other. The macro and micro nutrients of broccoli head were not significantly affected by growing medium, except for nitrogen and zinc. The highest concentration of nitrogen in broccoli head was recorded for pure perlite and sawdust which was significantly more than other media. The highest zinc concentration in broccoli head was observed in Sawdust medium (p≤0.05). A significant negative correlation was observed between plant height and three main macro nutrients (N, P and K). The negative correlation between some macro nutrients and plant growth can be related to the excessive amount of these elements in nutrient solution. Positive and significant correlation was also seen among plant height, head diameter and head weight. In other word, the tallest plants could produce bigger and heavier head.
Conclusion: Based on the obtained results, it can be concluded that a mixture of organic and inorganic substances can be better than a single substance medium. On the other hand, our results showed that role of medium substances and composition is not as important as nutrient solution, so an appropriate nutrient solution with a proper rate can potentially provide all plant's needs regardless of media composition.