Yard Trimming-Biosolids Compost: Possible Alternative to Sphagnum Peat Moss in Tomato Transplant Production

Large volumes of yard trimmings (YT) and biosolids (BS) co-compost have recently become available to the Florida vegetable industry. Compost used as vegetable transplant medium may be less expensive than traditional Sphagnum peat moss, since it can be locally produced. ‘Agriset 761’ tomato (Lycopersicon esculentum Mill.) seed were sown in five combinations of compost, peat, and vermiculite amended media: 0:70:30 (control), 18:52:30, 35:35:30, 52:18:30, and 70:0:30 % by weight, respectively. The experiment was repeated 3 times over a one-year period to accommodate the Florida transplant production season. YT-BS compost were sieved to a particle size less than 2.4 mm (33 % by weight) to be utilized as a transplant media.

The YT-BS compost had a high initial EC that restricted plant growth in one of the three batches used. By mixing YT-BS compost with peat and vermiculite the EC was reduced to an optimal 0 to 2 dS·m^?1 in the Fall 1997 and Spring 1998a experiments, but not for Spring 1998b.

Transplant media with YT-BS compost increased tomato seedling leaf area and shoot dry weight 21, 28, and 35 DAS (days after seeding) compared with the control. Additionally, YT-BS compost increased root dry weight 28 DAS and final stem diameter 35 DAS compared to the untreated control. Leaf area and shoot dry weight 21 DAS and shoot and root dry weight 28 DAS decreased linearly as compost rate increased. Although root dry weight differences among YT-BS compost rates 21 and 28 DAS were evident, these differences disappeared 35 DAS indicating no effect of compost rate on transplant characteristics. Number of leaves 21, 28 and 35 DAS were similar among all treatments. Utilization of YT-BS compost in the Spring 1998a experiment at any rate provided a slow-release source of nutrients that produced a tomato transplant with higher quality characteristics compared with the traditional peat:vermiculite medium and mineral fertilizer application. Once transplanted to the field, the differences that existed in the transplants grown in compost amended soilless medium disappeared. Fruit yields and size (i.e., large, extra-large, average fruit weight) between the control and compost treatments or among the compost rates were similar, except for the third harvest where the control had more tomato size medium than YT-BS compost treatments.

The results suggest that YT-BS compost can be used as an alternative to peat media for tomato transplant production, and that the percentage of substitution for peat is not critical. However, a lack of product physical and chemical consistency would compromise vegetable transplant and bedding plant production. Our results indicate more quality control is required with this YT-BS compost before it can be used wholesale in these markets.