New Zealand Journal of Agricultural Research abstracts
Effect of serpentine rock and its acidulated products as magnesium
fertilisers for pasture, compared with magnesium oxide and Epsom salts,
on a Pumice Soil. 2. Dissolution and estimated leaching loss of
fertiliser magnesium
P. Loganathan
J. A. Hanly
L. D. Currie
Fertilizer and Lime Research Centre
Institute of Natural Resources
Massey University
Private Bag 11 222
Palmerston North, New Zealand
P.Loganathan@massey.ac.nz
Abstract The dissolution rate of magnesium (Mg)
fertilisers controls their effectiveness in supplying Mg to plants and
the potential for fertiliser-Mg to be lost via leaching. Results from a
field trial, conducted on pasture on an Immature Orthic Pumice Soil (pHwater
6.3) treated with different types of Mg fertilisers (100 kg Mg ha–1),
showed that Mg dissolution over a 29-month period differed, being
15–20% for serpentine rock products, 50–98% for acidulated serpentine
products, 95% for E-mag (magnesium oxide), and 98% for Epsom salts. The
percentage dissolution of applied fertiliser-Mg was related to the
water solubilities for all the fertilisers except E-mag, which had a
high dissolution rate in soil but a very low solubility in water.
However, E-mag had high Mg solubility in citric acid, consistent with
its dissolution rate in soil. Epsom salts, E-mag, and acidulated
serpentine products significantly increased exchangeable Mg in soil
samples collected 9 and 29 months after fertiliser application,
whereas the unacidulated serpentine rock increased exchangeable Mg only
in soil samples collected after 29 months and only when it was
re-applied annually for 3 years. The recovery of fertiliser Mg in
pasture herbage was positively related to the Mg dissolution rate over
the duration of the trial, being 4–8% for serpentine rock products,
19–22% for acidulated serpentine products, 17% for E-mag, and 25% for
Epsom salts. For all fertilisers, except E-mag, total recovery of
fertiliser Mg in the soil (0–15 cm depth) and herbage combined was
lower for fertilisers with the higher rates of Mg dissolution, being
51% for Epsom salts, 53–90% for acidulated serpentine products, 91–95%
for serpentine rock products, and 90% for E-mag. Fertiliser Mg not
recovered was assumed to have been leached below the 0–15 cm soil
depth (49% for Epsom salts, 10–47% for acidulated serpentine products,
5–9% for serpentine products, and 10% for E-mag). The very high
fertiliser Mg recoveries in soil (0–15 cm depth) and pasture
herbage, and consequently low estimated fertiliser Mg leaching losses
from the less water-soluble fertilisers, suggests that these
fertilisers have potential for supplying Mg to pasture over a prolonged
period if the rate of fertiliser Mg dissolution does not appreciably
slow down with time. However, re-applications of these less soluble Mg
fertilisers may be required on a regular basis to ensure that the
supply of Mg is adequate for pasture growth and to meet stock
requirements.
Keywords fertiliser; fertiliser magnesium
dissolution; fertiliser magnesium recovery; hypomagnesaemia; magnesium;
magnesium fertiliser; magnesium leaching
A05014; Received 8 April 2005; accepted 12 August 2005; Online
publication date 11 October 2005
New Zealand Journal of Agricultural Research, 2005, Vol. 48:
461–471
0028–8233/05/4804–0461 © The Royal Society of New Zealand 2005
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