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Abstract

A large proportion of Tasmanian and Victorian potatoes are grown on ferrosols,
which have the highest Phosphorus (P) fixing capacities of any agricultural soils in
Australia. Phosphorus rates well in excess of maintenance dressings are commonly
used on potato crops grown on ferrosols. This is an increasing economic cost to
growers and a cost to soil and potato quality because of the significant addition to
soil P and cadmium (Cd) loads. Starter fertilisers have proved successful at
improving the initial P nutrition and subsequent fertiliser efficiency of crops but have
not been extensively trialed with potatoes. Field trials investigating the use of starter fertilisers on cv. Russet Burbank potatoes
were conducted over three years on ferrosol soils on the North West Coast of
Tasmania. Granular starter bands were used in the first year and liquid starter
treatments were applied in the second year. In the final year granular starter bands in
combination with hill-placed dripper and standard sprinkler irrigation were trialed.
The distribution of potato roots was measured and correlated with soil strength and
moisture properties and the fate of irrigation water applied to the potato canopy was
studied on field grown plants and by a computer model. The effects of P rate and
irrigation method on ground cover development were also measured. Glasshouse
and laboratory trials were conducted to investigate the effects of starter fertiliser
treatments and soil conditions on plant and root growth. No starter phosphorus application improved final tuber yield. Initial petiole weight
and nutrient responses were found in the first year to starter P application and from
drip irrigation of conventionally banded P, but not from the starter P band. Liquid
starter P improved the P nutrition of glasshouse grown plants but had no effect on
early plant nutrition or final tuber yield of field grown potatoes. Subsequent
glasshouse experiments indicated that higher strength liquid solutions could be used
without long term injury to potato plants. Ground cover development was hastened
by P applications of 100 kg P ha-1 or more and by drip irrigation in the absence of
applied P. Total tuber yield was moderately correlated to ground cover
measurements and there were indications that higher P applications improved the
utilisation of solar radiation. There was evidence of root proliferation in the region of conventionally banded
fertilisers but no indications of proliferation in the region where starter fertilisers
were applied. When potato plants were left unhilled roots were able to grow out to
and beyond the perimeter of the canopy. There was a prominent absence of root
growth in the wheel-compacted soil of both unhilled and hilled potatoes with only
sparse root growth into soil regions with bulk densities of 1.05 Mg m-3 and greater.
Penetration resistance of soils with bulk density> 1.1 Mg m-3 increases sharply with
drying to reach strengths capable of restricting root growth. Soils of lower bulk
density are unable to reach penetration resistances that could inhibit potato root
growth at any moisture content.
Up to 20% of the water applied to the potato canopy can be displaced laterally to the
furrows giving rise to an increased water application of the furrows and a
corresponding decrease in water application to the hill soil. The combined effects of
water shedding from the canopy, a reduction of lateral root growth from the hilling of
potatoes, and furrow compaction, have implications for irrigation efficiency and
phosphorus uptake of potato crops. Potatoes were able to grow a large root system before nutrients from the sett were
exhausted. Conventionally banded fertiliser at 50 mm beside and 50 mm below the
sett appeared to be sufficiently close to supply P before yield-limiting P deficiency
occurs. Poor root contact or unfavourable soil moisture regimes may inhibit the
acquisition of nutrients from fertilisers placed with or above the sett.

Item Type:	Thesis - PhD
Authors/Creators:	Johnson, PG
Keywords:	Potatoes, Potatoes, Phosphatic fertilizers
Copyright Holders:	The Author
Copyright Information:	Copyright 2003 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:	Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references
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