Fertiliser use effciency by containerised nursery plants 1. Plant growth and nutrient uptake
Authors: Huett D. O. 
Published: August 2004

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) the standard treatments of Osm
(43–57% 4-week, 65–70% 10-week) = Nut
(44–56%, 65–71%), which exceeded
(P < 0·05) DL (21–43%,
24–29%). Nitrogen, P, and K concentrations in shoots showed
similar effects. Doubling the standard fertiliser rates increased
(P < 0·05) N, P, and K concentrations in
shoots of the 4-week species but had no effect (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)
than for species grown with constant LF, indicating the inability of single
pre-plant fertiliser applications to maintain adequate nutrient supply.
Blending a 40-day Nut formulation with the 90-day formulation apparently
improved nutrient release characteristics, because shoot P and K
concentrations and growth increased (P <
0·05). Compared with LF, shoot dry weights were 87% in spring
(similar 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.