New Zealand Journal of Agricultural Research abstracts
Effects and interactions of P fertiliser forms and rates of lime on a clover/ryegrass sward
L. C. SMITH
A. G. SINCLAIR*
AgResearch
Woodlands Research Station
R. D. 1
Invercargill, New Zealand
Abstract Triple superphosphate (TSP), Arad phosphate rock
(APR), and "Longlife" superphosphate (LL) were compared for their effectiveness
as P fertilisers on a ryegrass/clover sward in New Zealand to which lime had
been applied at 0, 1.25, 2.5, and 5 t ha-1. The P fertilisers were
applied annually for five (LL) or six (TSP and APR) years at 24 kg P
ha-1 yr-1; there was also a nil P control. The trial
design was a factorial of four P treatments x four lime treatments. DM yield
responses were initially negligible but increased to a maximum of 27% by Year
5. Mean response to P fertiliser was 5% in spring and 16% in summer and autumn.
There were significant DM responses to TSP and LL from Year 3 onwards and to
APR from Year 4 onwards. Over the final three years, TSP and LL yielded
significantly more DM than APR, but there was no significant difference in DM
yield between TSP and LL. Herbage %P, herbage P uptake, and soil Olsen P were
much more sensitive discriminators between P fertilisers than was DM production
and showed significant differences between all fertilisers throughout most of
the experiment, with the ranking of effectiveness being TSP>LL>APR>nil
P. All measurements showed APR to be a relatively ineffective P fertiliser,
giving only 41% of the response to TSP in Year 6 when averaged over all lime
treatments. Herbage chemical analysis showed effectiveness of APR to be
markedly reduced by 2.5 and 5 t ha-1 lime. Calculations based on
residual PR in soil at the end of the experiment indicated that dissolution
rates of APR with nil, 1.25, 2.5, and 5 t ha-1 lime were 23%, 20%,
7%, and 9% per year, respectively. The slow dissolution of APR was attributed
to its relatively low reactivity as measured by solubility in formic acid. The
PR content of LL (North Carolina PR) also proved very ineffective, with an
average dissolution rate of 13% per year which was unaffected by lime
application rate. It is suggested that granulation of LL depressed dissolution
of its PR component. Lime at 5 t ha-1 raised soil pH from 5.6 to 6.5
one year after application, with intermediate rates having a pro rata effect.
Soil pH subsequently declined, but with considerable year-to-year fluctuations,
at rates proportional to the lime application rate. There were no positive DM
responses to lime but there were significant depressions in Years 5 and 6. Lime
reduced herbage %P in APR treatments only. Lime significantly reduced Olsen P
in control and all fertiliser treatments throughout the experiment, but only
with APR was there an associated reduction in herbage %P.
Keywords fertiliser; herbage P; lime; longlife super; Olsen P
test; pasture; pH; phosphate; reactive phosphate rock; RPR; soil P; TSP
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 75-89
0028-8233/98/4101-0075 $7.00/0 (c) The Royal Society of New Zealand
1998
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