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The potential of two agricultural waste composts, Tea Waste Compost (TWC) and Tree Bark Compost (TBC), as soil amendments was investigated for container production of ‘Great Lakes 118’ lettuce. Nine growing media mixtures including 3TWC+1Soil (on a volumetric basis), 1TWC+1Soil, 1TWC+3Soil, 3TBC+1Soil, 1TBC+1Soil, 1TBC+3Soil, 1TWC+1TBC, 1TWC+1TBC+1Soil, and Soil (control), were arranged in four blocks. Lettuce (Lactuca sativa cv. Great Lakes) seeds were directly sown in 2 liter pots. No supplementary fertilization was applied until commercial harvest. Due to the variation in date of commercial harvest, lettuce heads in each treatment were harvested as soon as they reached commercial maturity stage. Results revealed that either type of compost increased yield over control (soil based media). However, growth, dry matter accumulation, and head weight was lower in TBC amended media than that of TWC amended media. In addition to head yield, it was shown that crop maturity was positively affected with compost application. Earlier crop obtained in soilless media, while the crop in non amended soil reached maturity 3 weeks later. INTRODUCTION Compost, the final product of controlled degradation of organic wastes, has been revealed to improve soil physical and chemical properties. Generally, composts improve soil physicochemical properties such as formation and stability of soil aggregates, water infiltration, porosity, resistance against compaction and nutrient availability (Alexander, 2000; Fitzpatrick, 2000; Quedraogo et al., 2001; Caravaca et al., 2002; Clik et al., 2004). They also improve soil biological characteristics (Lee et al., 2004). Consequently, compost incorporation into soil can increase growth, yield, and quality of crop (AbouHadid et al., 2001; Smith et al., 2001; Garcia-Gomez et al., 2002). Capability of composts for use in Soilless culture of horticultural crops has also been confirmed in a number of studies (Khalighi and Padasht Dehkaei, 2000; Urrestarazu et al., 2001). A full range of organic wastes, from Municipal wastes to agricultural residues, are being used as composting feedstock, depending on the local availability. Annually, thousands of tones of agro-industrial wastes are produced in Northern part of Iran in Tea Processing and Timber Plants. Disposal of these wastes is economically a burden to these plants and ecologically a challenge for the environment; their inefficient disposal brings about environmental problems such as pest and insect attraction and soil and underground water pollution, especially in those areas with superficial water tables. However, these wastes have been proved to be suitable for application in horticultural cropping systems after a simple composting process (Khalighi and Padasht Dehkaei, 2002; Padasht Dehkaei, 1998). Composting of these wastes is a sustainable solution to the common problem of organic wastes disposal, resulting in a valuable substrate for production of horticultural crops. Tea Waste Compost (TWC) and Tree bark compost (TBC) have been used for Soilless production of ornamental plants with great success (Padasht Dehkaei et al., 2003; Khalighi and Padasht Dehkaei, 2002; Padasht Dehkaei, 1998). Nonetheless, no work has Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 154 been carried out on the application of these composts as a component of growing media for container production of vegetable crops. In order to investigate the effect of these two types of composts on soil characteristics, evaluation of their potential as soil amendments and their capacity for use in container production of vegetable crops, and with the aim of determining the most appropriate medium for pot production of vegetable crops we carried out this experiment. MATERIALS AND METHODS Composts and Growing Media Feedstock of composting came from agro-industrial wastes. Tree bark wastes, including 30% fir bark, 30% alder bark, 20% horn beech bark, 10% beech bark, 5% oak bark, 3% iron tree bark, and 2% bark of other hard wood trees, were obtained from Chouka Timber plant. Tea Waste, including apical shoots, petioles, and leaf vein of tea was also obtained from tea processing plants of Lahijan. These wastes were composted in a 1m passively aerated containers in Flower and Ornamental Research Center, Lahijan, Guilan. Field soil was completely mixed with predetermined volumetric amount of composts to create 6 treatments including 3TWC+1Soil, 1TWC+1Soil, 1TWC+3Soil, 3TBC+1Soil, 1TBC+1Soil, 1TBC+3Soil. Two further mixtures, including 1TWC+1TBC and 1TWC+1TBC+1Soil, were also prepared. Non amended soil medium was chosen as control. Experimental Design and Plant Material Nine media treatments were arranged in a completely randomized Block Design with four replications and each plot included four pots. ‘Great Lakes 118’ lettuce seeds were directly sown in two liter containers filled with media mixtures. Daily hand irrigation started after planting, and continued up to harvest. Seedlings were emerged 4 days later in all treatments. No chemical fertilization, pest and disease control measurements were practiced until harvest. Plant fresh and dry weight was measured 4 and 8 weeks after germination and at the commercial maturity stage head fresh weight was measured. Due to the variation in date of commercial harvest, lettuce heads in each treatment were harvested as soon as they reached commercial maturity stage. Laboratory Analysis Soil Bulk Density (BD) and total porosity were determined according to Blake, and water holding capacity according to Maximum Water Holding Capacity (European Method). Soil organic matter was determined by loss on ignition method. The pH and electrical conductivity (EC) were measured in a 1:3 aqueous solution. Total nitrogen (TN) was determined by the Kjeldhal method, and the organic Carbon (OC) by Walkly-Black method. Available Phosphorus with sodium bicarbonate was determined by colorimetry. Extractable Potassium with ammonium acetate was determined by flame photometry. Statistical Analysis Analysis of variance was performed using SPSS 10.0.5 for windows. Duncan test was used for comparison of mean significant difference at P<0. confidence level. RESULTS AND DISCUSSION Physical and chemical properties of different mixtures of media used in this study are mentioned in Table 1 and 2. Our results revealed that growth of lettuce increased as the contribution of either type of composts in growing media increased (Table 3). However, growth and head fresh weight was higher in TWC amended media in comparison with that of TBC amended media (Table 3), while the increase in growth in TBC amended media over soil was only