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March 7, 2003
Australiašs maize growers need to
look hard at nutrient supply, particularly if their crops are
cut and removed for silage, according to a collaborative paper
presented to the recent Fifth Australian Maize Conference
in Toowoomba.
Its message to the conferencešs 170 delegates was that maize has
a high demand for nutrients and that, while nitrogen deficiency
is the main concern, growers also need to look at levels of
phosphorus, potassium and zinc.
"Very exploitive, cut and remove" silage systems removed about
25 kilograms of nitrogen and five kilograms of phosphorus per
tonne of dry matter, compared to 12-16 kilograms and three
kilograms respectively in a grain crop.
While potassium supply was assumed to be adequate in most areas,
a grain harvest removed much less than the 20 kilograms or so
removed per tonne of dry matter in silage.
Deficiencies of other nutrients in maize crops depended on soil
type, with zinc the most widespread.
The paper was prepared by Dr Colin Birch, from the University of
Queenslandšs School of Agronomy and Horticulture at Gatton,
CSIRO researchers Michael Robertson, from Brisbane, and Liz
Humphreys from Griffith and industry consultant Nick Hutchins,
from Darlington Point.
They noted that, while Australiašs maize traditionally has come
from favourable rainfall and irrigation areas, with sorghum
preferred by dryland farmers, the intensive livestock industries
now were looking for increased supplies of maize, both grain and
silage.
The crop also offered an additional option in rotations on
dryland cotton and grain farms, most notably for soil management
and insect and disease control.
"More than half the total Australian crop comes from irrigated
maize in the Murrumbidgee, Murray and Lachlan Valleys of NSW,
where yield is greatly influenced by seasonal variability
particularly temperature with much lower yield potential in
hot summers," Dr Birch said.
"Well grown maize crops produce around 25 to 30 tonnes to the
hectare of biomass, with a harvest index of up to 0.6, so a
major agronomic issue for growers is management of the huge
amount of stubble produced by high yielding maize crops.
"Others are water budgeting and, in some years and situations,
disease and insect management. Increasing the efficiency of
nitrogen fertiliser use by maize crops will become increasingly
important for environmental reasons and to reduce input costs."
Dr Birch said the maize industry needed strategies to
incorporate the crop in agricultural systems and to improve its
water use efficiencies through altered plant populations and
planting geometry issues being researched by Dr Robertson and
his collaborators in a project supported by the
Grains Research & Development
Corporation (GRDC).
Return to the soil of effluent from the intensive livestock
industries using maize grain and silage could reduce fertiliser
requirements and have environmental benefits.
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