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Abstract

This thesis reports work on the effects of added, decomposable organic
matter as a possible lime substitute on exchangeable and soil solution aluminium in
relation to phosphorus availability and growth of perennial ryegrass (lolium perenne.
L) in acid krasnozems on Tertiary basalt, North-Western Tasmania. Soil was
collected to a depth of 15 cm at three sites in a sequence of increasing elevation and
rainfall, representative of the Burnie, Lapoinya and Yolla series.
The soil materials were first screened for their suitability for later work by
determining certain basic soil properties and by measuring effects on these properties
of glasshouse incubation for four weeks of soils with organic matter added as barley
straw or lucerne chaff at rates equivalent to 0, 3.5 and 7.0 t/ha. There were significant
effects, relative to initial levels of soil parameters, in terms of reduced exchangeable
aluminium, increased available phosphorus and increased soil solution (pF2) ionic
strength, with effects due to the addition of organic matter. Differences in cation
exchange capacity sum of basic exchangeable cations, and soil reaction, were not
significant.
Because it was highest in exchangeable aluminium, lowest in available
phosphorus, and was strongly acid, Burnie soil material was used to study effects of
different rates of added barley straw or lucerne chaff on soil aluminium, phosphorus,
and soil solution ionic strength after different periods of incubation (0, 4, 8, 16
weeks), with and without added urea to bring the C/N ratio of the organic matter to a
value of 12. The pH of the soils with added organic matter was higher than the
controls, both with and without added urea, but the effect of urea on pH decreased
with time. The effect of urea on the increase of pH was obvious in the first 4 weeks
and then slightly varied from week 4 to week 8. Thereafter, the pH was on the
decline. Exchangeable aluminium was lower in soil incubated with organic matter but
differences due to rate of added organic matter were not significant, lucerne chaff had
a greater early effect but the difference versus barley straw was reduced after four
weeks. There was a sharp rise in available phosphorus measured after four weeks in
all soils with added organic matter but this was followed by a rapid fall so that levels
at the end of the experiment (16 weeks) were well below those at its commencement.
Available phosphorus of control soils decreased regularly throughout. There was little
difference in effects due to kind of organic matter. Ionic strength of soil solution
extracts (pF2) from the soils with added organic matter rose sharply and levels were
maintained in soils with added organic matter.
Burnie soil was again used to follow effects of added organic matter on
active aluminium in relation to native available phosphorus and growth of "Nui"
cultivar of perennial ryegrass. Urea was not added in this experiment. Soluble
aluminium was added as Al2(SO4)3. 14H20 after four weeks of incubation of soil
plus organic matter (Sequence (a)) and together with organic matter (Sequence (b)),
both sequences being incubated for a further four weeks before sowing of ryegrass
seed. Differences between the two sequences in effects on pH, soil solution
phosphorus (pF2), phosphorus uptake and dry matter production by the test plant
were not significant. However, there were marked effects within each sequence of
added organic matter in increasing values of each of these parameters in relation to
controls. Exchangeable and soil solution aluminium, especially monomeric
aluminium, were markedly reduced by added organic matter at all rates of aluminium
application and these effects were greater in Sequence (a) than in Sequence (b) soils.
Aluminium remaining in solution was almost wholly in organic complexed forms.
Conversely, available phosphorus was higher. Lucerne chaff was slightly but
consistently more effective than barley straw but these differences were not
significant.
Finally, Lapoinya soil from the "museum" area of Elliott Research Station
was used in a study of effects of both added organic matter and phosphorus
(KH2PO4) on soil aluminium in relation to growth of ryegrass because of its low pH,
very low level of available phosphorus and high level of active aluminium. Reduction
of exchangeable and monomeric aluminium occurred with rate of phosphorus
application, the effect being greater in the presence of added organic matter. Again,
nearly all of the soil solution aluminium was in organically complexed forms in the
presence of added organic matter. Differences between the effects of lucerne chaff and
barley straw were small but consistent, although not statistically significant, with
lucerne chaff having the greater effects. Soil reaction again increased with added
organic matter and an inverse relationship between levels of aluminium (both
exchangeable, monomeric form) and available phosphorus depended on pH. Plant
growth and phosphorus uptake and content responded by increasing sharply with rate
of phosphorus application and were further enhanced greatly by added organic matter.
Plant symptoms of aluminium toxicity/phosphorus deficiency were not evident in the
presence of added organic matter, even at the highest level of aluminium application
(100 ppm, 0.D.).
Both forms of organic matter used whether fresh or partly decomposed, gave
beneficial effects within the period of experimentation in suppressing aluminium
toxicity and enhancing growth of perennial ryegrass in the acid soils used.
Application of organic matter at practical rates may allow reduction of the quantity and
frequency of lime additions.

Item Type:	Thesis - Coursework Master
Authors/Creators:	Bunmongkolrat, S(Sumalee)
Keywords:	Ferralsols, Soil acidity, Plants, Acid soils
Copyright Holders:	The Author
Copyright Information:	Copyright 1989 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Includes bibliographical references (leaves 200-227). Thesis (M.Agr.Sc.)--University of Tasmania, 1991
Item Statistics:	View statistics for this item

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