An investigation of plant growth in an organo-zeolitic substrate and its ecological significance

This work concerns a series of experiments designed to test and understand the effect of ammoniated zeolite on plant growth. The affinity of the zeoli te mineral clinoptilolite for NH4+ is utilised in organo-zeolitic substrate s to enhance plant growth. By comparing plants grown in substrates with and without ammoniated zeolite, an increase in plant dry weight of some 19% wa s shown to be due to the presence of the zeolitic NH4+-N. In this study, ex perimental work has shown that in an organically enriched substrate an expo nential diffusion of NH4+ occurs as a non-equilibrium reaction. It is sugge sted that ion-exchange is taking place in which soil Ca+2 is exchanged for lattice bound NH4+. Nitrifying bacteria, utilising the diffusing NH4+, appe ar to protect seedlings from the effect of ammonium toxicity and in so doin g act as a biological buffer, allowing the plant to take up nitrogen at a r ate which is most advantageous throughout its growth. Leaching experiments confirm the presence of very high soil nitrate concentrations indicating th at a large population of nitrifying bacteria is established. The ionic mobi lity of major cations is also greatly increased in the organo-zeolitic subs trates. This behaviour is already known to produce beneficial effects in th e rhizosphere increasing aeration by flocculating colloidal clay particles and enabling the diffusion of metal ions to occur. Research reported elsewh ere demonstrates that plants grown in organo-zeolitic substrates on toxic w aste sites exhibit low up-take of toxic metals and it would, therefore, app ear that the unique features of organo-zeolitic substrates have both nutrit ional and ecological value.