CLAY ADDITION TO SOILLESS MEDIA PROMOTES GROWTH AND YIELD OF GREENHOUSE CROPS

Clay is a major physical component of soil, and by convention is omitt ed from soilless media. A sterilized, nonswelling chlorite mica clay, sieved to a particle size of <0.3 mm, was used to determine whether it s addition to a sawdust medium would improve the production of greenho use vegetable and flower crops. In early experiments with cucumber, th e clay was applied daily as a suspension in the nutrient solution (0, 1, 5, or 10 g.L-1). The number of marketable cucumber (Cucumis sativus L.) fruit increased significantly with increasing concentration of cl ay. The harvest period in these trials was relatively short (up to 4 w eeks). In subsequent long-term trials (up to 18 weeks of harvest), the clay was mixed into the sawdust before planting at rates of 0, 4.3, 2 1.4, and 42.8 g.L-1 of sawdust. Again, the number of marketable cucumb er fruit increased significantly with increasing clay concentration. I n trials with potted geraniums (Pelargonium xhortorum L.H. Bailey) and hybrid impatiens (Impatiens wallerana Hook.f.), the clay was applied daily to the sawdust as a suspension in the nutrient solution (0, 1, 5 , or 10 g.L-1). In both species, the number of flowers increased signi ficantly with increasing clay concentration, and the size (fresh and d ry mass) of the geraniums also increased. In the absence of plants, ad dition of clay significantly increased water content of the sawdust at matric potentials tested from -1 to -100 kPa, and increased bulk dens ity.