PINE BARK AS A SEEDLING GROWING MEDIUM

Most seedling plugs worldwide are grown in peat mixes. A lack of available peat in South Africa resulted in a comprehensive research programme to develop pine bark as a suitable alternate substrate for the extensive containerised seedling industry in South Africa.

Up to 1,5 million m³ of bark, mainly from Pinus patula, P. elliottii and P. taeda is produced as a by product of the paper and pulp industry in South Africa. It is removed by drum and ring debarkers before milling and composting to reduce toxic tannin levels and adjust C:N ratios. Urea is added as the N source, and along with water, a suitable stack size and regular turning the temperature rises to above 70°C.

Particle size distribution is adjusted by sieving to achieve ideal air filled porosity (AFP) for seedling growth. Nutritional research with the composted product has resulted in recommendations for lime, trace element and phosphorus pre-plant fertilisation, as well as post germination nutrient solution application for the production of a wide range of seedlings.