Effects of Substrate Type on Plant Growth and Nitrogen and Nitrate Concentration in Spinach

The effects of three commercial substrates (a mixture of forest residues, composted grape husks, and white peat, black peat and coir) on plant growth and nitrogen (N) and nitrate (NO₃) concentration and content were evaluated in spinach (Spinacia oleracea L. cv. Tapir). Spinach seedlings were transplanted at 45 days after emergence into Styrofoam boxes filled with the substrates and were grown during winter and early spring in an unheated greenhouse with no supplemental lighting. Each planting box was irrigated daily by drip and fertilized with a complete nutrient solution. The NO₃ content of the drainage water was lower in coir than in the other substrates. However, shoot NO₃ concentration was not affected by substrate type, while yield and total shoot N and NO₃ content were greater when plants were grown in peat than in the mixed substrate or the coir. Leaf chlorophyll meter readings provided a good indication of the amount of N in the plants and increased linearly with total shoot N.