Nutrition of containerised pine (Pinus patula Schlecht. et Cham.) seedlings grown in pine bark.
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Increasing demands for timber and timber products have resulted in the rapid expansion of containerised forestry seedling production. The lack of available information on pine seedling fertilization has forced nurserymen to use overseas recommendations which are based on peat and vermiculite as growing media, and not composted pine bark. Six fertilization trials were conducted in plastic enclosed "tunnels" to provide fertilization recommendations and optimum foliar nutrient concentrations for P. patula seedlings grown in composted pine bark. It was concluded that pre-enrichment of the pine bark should include micronutrients, preferably in the form of Micromax®, a soluble micronutrient fertilizer, at 1000 g.m(-3). Pre-enrichment with lime was unnecessary for pine bark media since pine bark contains sufficient Ca and Mg. At an unlimed pH of 4.5, the availability of micronutrients was adequate for pine seedling growth. The addition of an N-P-K fertilizer and scheduling of nutrients, to correlate with seedling growth stage, are essential for maximum pine seedling production. Slow release forms (SRF) of N-P-K fertilizers were not beneficial, although their use may be warranted when the cost of SRF is similar to that of conventional fertilizers. Nitrogen in the form of NH(4+)-N at 80 mg.l(-1) was shown to produce the best quality P. patula seedlings. The addition of Si, in the form of pre-enriched silicate slags and si nutrient solutions, reputed to improve growth by decreasing cuticular water loss and increasing plant rigidity, provided no added advantage to pine seedling growth under the trial conditions. It was concluded that individual nurseries should formulate a nutritional programme for their own situation, based on these guidelines. Care should be taken when extrapolating these results to other substrates and it is recommended that the medium be analysed before a nutritional programme is decided on.