By Tom Cowlrick, Wayne Pluske and Peter Wylie
Nutrient Management Systems, an independent specialist company providing
advice and recommendations in soil health and plant nutrition through
partnerships across all cropping regions, is undertaking this project
within the NMI. It will establish a foundation for improved nutrient management
by graingrowers, through better understanding information needs and the
constraints and solutions to adoption of improved nutrient management
practices, establishing standards for nutrient management advice and improved
mechanisms for nutrient management information access.
It will work across all other NMI projects to ensure their findings and
recommendations are made available to the industry in forms that enable
ready adaptation and adoption.
The project has begun with a survey of current nutrient management practices/decision
methods, and accessibility of essential nutrient management information.
A vision of best-practice nutrient management for the grains industry
is being developed, along with a nutrient management framework covering
factors to be considered for comprehensive nutrient advice and decision.
A gap analysis will identify constraints to adoption of these best-practice
components and recommend actions to overcome them. A pilot program for
comprehensive nutrient management advice will be run, using farm advisers
located in major cropping regions. A communication program through rural
media, and an electronic project newsletter, will heighten awareness about
nutrient management research, improvement opportunities and programs.
Until the 1980s the "sufficiency approach" was the dominant nutrient
management approach, where crop responses to nutrients could be demonstrated.
Calibrations to populate "sufficiency models" were commenced in 1967 in
the national Soil Fertility Project, which established a large series
of field experiments across Australia to develop fertiliser recommendation
models, primarily for nitrogen and phosphorus, based on soil analysis
for nutrient content.
During the 1980s, the combined effects of changes such as reduced tillage,
introduction of new crops, expansion of graincropping to soils previously
not included in the national Soil Fertility Project, reduction in soil
research funding, increase in the number of fertiliser supply companies
and decline in publicly-funded advisory services resulted in reduction
in the perceived credibility of the original calibrations. This provided
a space for the consideration and introduction of a range of other nutrient
management approaches that at times are at odds with the sufficiency approach.
These include "Maintenance/build-up", "Base cation saturation ratio" and
"removal/replacement", which generally rely less on calibration and more
on concepts with more intuitive and transparent methods of determining
the requirement for nutrients and rates of nutrient addition.
The result is that there are currently many approaches to nutrient management
derived from many sources, ranging from detailed scientific investigation
to cumulative observation and individual or group experience.
To be truly useful to the grains industry there are some key criteria
(described below) that should be applied to all systems of interpretation
and information integration when developing or assessing a nutrient management
program. These criteria should be present in nutrient management strategies
whether they are based on soil and plant tissue analysis data or on other
objective measurement criteria.
Local calibration is the process where the performance of a method of
determining nutrient requirement or the performance of a product or application
strategy is tested and proven under specific conditions of soil, season
and management. Local calibrations are generally an adaptation of globally
accepted principles and should provide some probability with which the
product/nutrient management practice will be successful. They should also
indicate the extent and/or range of likely change.
The definition of local can vary from an individual paddock or farm to
entire continents. In grain production areas of Australia soil type and
climate are generally the main parameters used to define local calibration.
For soil tests, hundreds of "site-years" of experiments are usually required
to develop a local calibration.
Crop nutrition is a function of both supply and demand for nutrients.
The ability to modify recommended inputs according to yield is important
as it allows adjustment of inputs when yield (output) is changed by an
uncontrolled factor such as climate or by a controlled factor such as
management. Yield dependence is essential for developing sensitivity analysis
for inputs (fertiliser prices) and outputs (grain prices) and having the
ability to make tactical decisions as circumstances change in-season.
Sensitivity analysis refers to an ability to vary a single factor or
group of factors (including multiple nutrients) to help understand the
nature of their interactions. Sensitivity analyses allow better optimisation
of inputs for production of outputs and prediction of likely returns and
risk if inputs are altered, sometimes within models that cater for variable
management and/or seasonal conditions. For nutrients this usually includes
the ability to vary yield, value of output commodity, nutrient rate and
its cost to define the most economic rate of nutrient addition. This ability
across a range of scenarios in turn enables risk to be assessed.
Input to decisions by a credible local adviser at worst confirms local
calibrations. More often such input enhances local calibrations and provides
practical information on practices that cannot be or are not completely
specified as variables in local calibrations. Skillful use of the information
gained from practical experience in an area allows an adviser to identify
some of the factors creating scatter in the general local calibration.
By using local experience, an adviser increases the value of the output
of local calibrations and of a recommended course of action.
A holistic approach considers multiple factors that may impact on the
effectiveness of a product or practice in the long and short term. For
nutrient management this may include factors such as the impact of pests,
diseases and weeds, soil physical characteristics, other soil chemical
parameters, economic and social environments and likely off-target effects.
For example, it is now recognised that the effects of soil-borne diseases
and pests on crop performance prior to the introduction of canola contributed
to the unreliability of responses of winter cereals to nitrogen fertiliser
in the southern grain belt. These factors will be included in the nutrient
management framework being developed by this project, which is also linked
to the aims and activities of the FERTCARE program being developed by
the Australian fertiliser industry. With fertiliser now accounting for
up to 30 per cent of some graingrowers" variable costs, the push is on
to improve both the type of information available about nutrient management
and its interpretation, to enable growers to better set and manage nutrient
Tom Cowlrick is managing director and Wayne Pluske a director of Nutrient
Management Systems. Peter Wylie is a farm consultant with Horizon Rural
Management in southern Queensland.
GRDC Research Code NMS00002
For more information: Tom Cowlrick, 07 3206 2124, email@example.com