Lettuce, Lactuca sativa L. ‘Summer Bibb’ and tomato, Lycopersicon esculentum Mill. ‘Westover’ were grown 4 weeks in plastic market packs (MP) in 3 experimental media and a commercially available (Maryland Mix) control. The experimental media were prepared by combining equal parts, by volume of: 1) screened composted sewage sludge (CSS) (made from lime dewatered ferric chloride treated sewage sludge and wood chips), peat moss (PM), and perlite (PL) (CSS-PM-PL); 2) CSS, PM, and vermiculite (VL) (CSS-PM-VL); and 3) CSS-PL-VL. A commercially prepared medium, Maryland mix consisting of silt loam, peat, perlite, and vermiculite (1:2:1:1 by vol) was used as a control. The market packs containing 6 transplants each, were arranged in a completely randomized design and replicated 4 times. One set of seedlings were grown in Maryland mix and CSS-PM-PL and fertilized at the end of the 1st, 2nd, and 3rd week after transplanting with a commerical 20N-8.6P-16.6K (20-20-20) fertilizer. Another set of seedlings were grown for 4 weeks in the control mix and 3 experimental media and fertilized at 1st and 3rd week after transplanting with only N fertilizer.
For both lettuce and tomato plants, only 270 mg of N per MP per growing period produced marketable size transplants when grown in the CSS-PM-VL medium. These seedlings had no toxic levels of Zn, Cd, Pb, and Ni and contained adequate N, P, K, Ca, Mg, Mn, Fe, and Cu as compared to plants grown in the control medium.
Scientific Article A-4840 Contribution no. 7866 of the Maryland Agricultural Experiment Station. This research was supported in part by a cooperative agreement with the Biological Waste Management and Organic Resources Laboratory, U.S.D.A., Beltsville, MD 20705.
2Former graduate stUdent, Associate Professor and Professor, resp. Department of Horticulture, University of Maryland, College Park, MD 20742.
3Research Agronomist, Soil-Microbial Systems Laboratory, USDA. BARC, West Bldg. 318, Beltsville, MD 20705.