Use of grape marc compost as substrate for vegetable seedlings

An experiment was conducted to study the potential of compost made from dealcoholised grapevine marc and grape stalk (GM) as growing medium component in plug seedlings production of lettuce, tomato, pepper and melon. Four media were prepared: GM, a commercial peatmoss-based plug medium (Pt), used as control, and two GM + Pt mixtures (1:1 and 1:2, v:v). Their physico-chemical characteristics were analysed, and bioassays were carried out for the detection of their phytotoxicity and nitrogen drawdown index (NDI). Seedlings grown in a greenhouse in Seville, during spring 2007, were irrigated 5 days a week with a Hoagland solution. Each species was arranged in a randomised block design with four replications. Substrates showed no phytotoxicity or nitrogen immobilisation. Physical characteristics of GM suggested some limitations for use as growing medium in plug seedlings production (total available water content of 12.7% in GM and 25.9% in Pt), although it can be avoided by blending with other substrates and by managing irrigation. At the time of transplant lettuce seedlings showed only differences in green colour intensity measured by SPAD, which was higher in GM (20.3) that in Pt (18.7). Seedling height of pepper, melon and tomato grown in GM was on average 30% lower than that achieved in Pt. The height increased as the proportion of Pt in the substrates did so. There were also differences in dry weight and root neck diameter in tomato and melon that were lower in GM than in Pt. Both parameters improved with the proportion of Pt in the mixtures. Plants analyses showed significant differences that did vary depending on the species and the treatment, and they suggest nutrient imbalances in seedlings. These results would indicate that, under a correct irrigation and fertilisation management, GM and GM + Pt blending could be used successfully as medium component for plug production of vegetable seedlings. (C) 2012 Elsevier B.V. All rights reserved.