Fertiliser use effciency by containerised nursery plants 1. Plant growth and nutrient uptake

The effectiveness of controlled-release fertilisers (CRFs) and an organic-based fertiliser derived from dehydrated poultry manure in supporting the growth of groundcover species when applied at planting was investigated under a range of irrigation conditions on the northern coast of New South Wales. The CRFs were Osmocote NPK (3–4 month) (Osm) and Nutricote NPK (90-day) (Nut), and the organic-based fertiliser was Dynamic Lifter (DL). They were applied pre-planting at a standard rate equivalent to 800 g N/m3 to pots containing sand, composted pinebark, and hardwood sawdust medium that had received nutrient amendment during formulation. Two experiments conducted over spring-early autumn at a commercial nursery, with high irrigation rates (25 mm/day), produced leaching fractions (volume leached as percentage of volume applied to the surface area of pots) of 104–110%. Five groundcover species from each of 2 groups based on differences in growth rates, a 4-week (transplanting to sale) and 10-week group, were used. As well as the standard rate, fertilisers were applied at twice this rate. A Nut treatment containing a 40-day formulation was included at the high rate for the 4-week species in both experiments and for the 10-week species in the autumn experiment. Plants in these treatments were compared with plants receiving a constant nutrient supply from 6-hourly applications of a commercial liquid carnation formulation (LF). Shoot growth for the 4- and 10-week species of LF plants (100%) exceeded (P 0·05) on the 10-week species and on shoot growth of both species. The N, P, and/or K concentrations in shoots of both species at both rates of fertiliser application were lower (P 0·05), 70% in autumn (P < 0·05) for the 4-week species, and 85% (P < 0·05) for the 10-week species. In a subsequent experiment using an electronic leachate detector with the 4-week species, a reduction in leachate volume from the commercial rate (in Expts 1 and 2) to one-third this rate had no effect on plant growth. This indicates that salt accumulation is unlikely to be a problem when irrigation is scheduled to minimise container leaching. This was further evaluated in a final experiment using the 4-week species, conducted under cover, with a range of leachate volumes from nil to the minimum achieved by the leachate detector (54% leaching fraction). Nil leaching reduced (P < 0·05) plant growth, and a leaching fraction of 25–39% reduced electrical conductivity of the potting medium from 2·1 dS/m (nil leaching) to 1·1–1·5 dS/m (in 1 : 1·5 v/v extract), which prevented growth depression due to salt accumulation.