effect of organic and biological fertilizers on growth and yield of tomatoes (lycopersicon esculentum mill.) and bacterial colonization

introduction: in recent decades, excessive use of chemical fertilizers causes environmental problems such as water resource pollution and decrease in soil fertility. organic matters are excellent sources of plant-available nutrients and their addition to soil could maintain high microbial populations and activities. in crop studies, prabha et al. (2007) reported that there was excellent plant growth as well as yield in garlic plants that received vermicompost as nutrient in the field (28). recent studies confirmed that, a number of bacterial species mostly associated with the plant rhizosphere, are found to be beneficial for plant growth, yield and crop quality. therefore, the objective of this study is to investigate the growth promoting effects of organic and bio-fertilizers on tomato growth and yield. materials and methods: a factorial experiment in randomized complete block design with three replications was conducted at the college of agricultural, university of shahrood in 2011. geographically, the site is located in bastam (36° 25’e, 54° 58’n, 1349 m a.s.l.).the climate of this region is semi-arid. treatments included three levels of organic fertilizers: vermicompost (1300 kgha-1), cow manure (3350 kgha-1), and control, biological fertilizer in four levels (pseudomonas putyda, pseudomonas fluorescens, azotobacter chrococcum and control). the bacterial suspension for each species was applied at a rate of 3 liters per hectare. metribuzin herbicide (wettable 80% powder) was used at a rate of 1000 gr. ha-1. petopride no. 2' variety of tomato (lycopersicon esculentum mill.) was used in the present experiment. at the time of harvesting, the plant characteristics namely lengths and diameter of stem, number and weight of fruit, weight of stem and leaf were also registered. statistical analyses of data were performed with statistical software mstatc. significant differences between means refer to the probability level of 0.05 by lsd test. results and discussion: there sults showed that main interaction effects of bio and organic fertilizers were significant (p<0.05) on bacterial colonization. the bacterial population increased with application of vermicompost and biofertilizers than other treatmentssignificantly (figure 1).chemical analysis showed that vermicompost had a lower ph, and higher amounts of nitrogen, phosphorous and organic matter compared to the cow manure and soil (table. 1). thus, it seems that vermicompost has been able to provide an appropriate bed for the growth of bacteria. the results indicated that the dry weight and height of tomato stems was improved by 28.5 and 4.7 percent, respectively by application of vermicompost compared to the control treatment (table 4). the number of tomato fruits increased by the application of vermicompost and cow manure by 29.2 and 19 percent compared to the control, respectively. also, the yield of tomato was increased by 15 and 10 percent compared to the control treatment by the application of vermicompost and cow manure, respectively. federico et al. (2007) reported that the yields of marketable tomato fruits per plant increased by 1.8-times in response to a 1:1 vermicompost to soil mixture compared to the control treatment (10). an excreta of earthworm is rich of micro-organisms, especially bacteria and contain large quantities of plant hormones (auxin, gibberellin and cytokinin) that in low concentrations significantly affect plant growth and development (3). phosphorus is an essential nutrient for plant growth and development and is one of the most important elements in crop production. despite its wide distribution in nature, it is a deficient nutrient in most soils, especially in soils which have a high fixation capacity. since a substantial amount of any applied fertilizer is rendered unavailable frequent applications of soluble forms of inorganic p are needed to maintain adequate plevels for plant growth. it is a well-known fact that aconsiderable number of bacterial species, mostly those associated with the plant rhizosphere, are able to exert a beneficial effect up on plant growth. phosphate solubilizing microorganisms render these insoluble phosphates into soluble form through the process of acidification, chelatiation and exchange reactions. in our experiment, probably increasing the availability of p and n fertilizers has improved the growth and yield of tomato plants. azotobacter chrococcum increased dry weight and height of stem and yield of tomatoes by 32.14, 7.23 and 21.2 percent, respectively compared with the control treatment (table 2). in similar results, the use ofn2-fixing bacterial stimulated yield and quality parameters of sugar beet and barley (8). the positive effects of azotobacter bacteria on the yield and growth of tomatoes were explained by promoting abilities of these bacteria for auxin and cytokinin production, n2-fixation, phosphate solubilization and antimicrobial substance production (8). the yield and plant growth enhancement effects of a. chrococcum used in this study on tomato could be explained by similar reasons. conclusion the results of the present study suggested that inoculation of tomato with biofertilizers and the use of organic fertilizers such as vermicompost and cow manure have a potential to increase the growth and yield of tomatoes. considering environmental pollutions with excessive use of synthetic fertilizers and high costsin the production of n and p fertilizers, the bacteria tested in our study maybe a promising alternative as a bio-fertilizer for fruit and vegetable production in sustainable and organic agricultural systems.