Investigation of the effects of vermicompost use on soil fertility, seedling production, yield and quality characteristics in lettuce (Lactuca sativa Var. Crispa) under greenhouse conditions

The aim of this study is to investigate the effects of vermicompost usage on soil fertility, seedling development and quality, plant growth, yield and quality in lettuce (Lactuca sativa var. crispa) cultivation in greenhouse. The effects of the heat treatment applied to vermicompost, which is required by the state regulation, on plant production are also investigated. Within the scope of the study, in the first stage 'Caipira' lettuce (Lactuca sativa var. crispa) seedlings were grown for two consecutive periods (I. and II.), and then, in the second stage, lettuce cultivation was carried out by using seedlings obtained in the first stage. Heat treated (HTVC) and non-heat treated (VC) vermicomposts were added to the seedling growing medium at 0, 30% and 60% in the first stage and at 0, 20, 40 t ha-1 doses in the cultivation stage (second stage) in a greenhouse. Experiments in both stages were conducted according to factorial and randomize block design with three replicates. After the physical measurements (germination rate, seedling length, stem diameter, wet weight, root length) of the seedlings obtained at the end of the seedling stage, biological analysis in the growing medium (urease, alkaline phosphatase, β-glycosidase, dehydrogenase, nitrification, denitrification activities and number of bacteria) pH and EC measurements were performed. During the greenhouse cultivation stage, rhizosphere and normal soil samples taken during plant growth (0, 2nd, 4th, 6th week) are analyzed for biological parameters (urease, alkaline phosphatase, β-glycosidase, dehydrogenase, nitrification, denitrification activities and number of bacteria). On soil samples collected at the end of the experiment chemical analysis (mineral nitrogen forms, pH and EC measurements by macro-micro nutrient analysis) were performed. In addition, after physical measurements (yield and quality parameters) of harvested lettuce, chemical analysis (macro-micro nutrients) were performed to determine the nutritional status of the plants. According to the results, since vermicompost application was observed to reduce the rate of seed output this fertlizer seems to have a limited potential in seedling production. On the other hand, the use of vermicompost in soil is considered to be suitable for lettuce cultivation due to its positive effects. In general, it was determined that HTVC was more effective in terms of biological parameters than VC in both growing periods. Also, fertilizer addition to the seedling medium did not make a significant difference in lettuce production soil. In terms of soil chemical properties and plant mineral nutrition, it was determined that HTVC applications were more prominent in both growing periods. However, the yield and quality of the lettuce was affected iv more positively with VC compared to HTVC. As a result, it was determined that heat treatment application did not adversely affect the chemical properties of fertilizer. On the contrary, it increased the amount of organic matter and some nutrients. Even though the heat treatment significantly negatively affected some of the biological parameters of vermicompost this is not reflected to soil fertility and plant growth. However, there have been signs that heat treatment may slightly suppresses the beneficial effect of vermicompost in terms of plant yield and quality. In this respect, it is understood that there is a need for new studies (molecular diversity and functional gene determination in vermicompost and soil, etc.) covering different plant, climate, soil type and growing period, which are concerned with effect of heat treatment both on vermicompost and plant production. In this way, its importance and place in maintaining and increasing soil fertility will be better understood. KEYWORDS: Number of bacteria, Enzyme activity, Organic fertilizer, Vegetable cultivation, Soil fertility.