What is Nutrient budgeting ?
It is a measure of the nutrient balance of a farming
operation. It takes into account all the nutrient inputs on a farm and
all those removed from the land. The most obvious source of nutrients in
this situation is fertilizer, but this is only one part of the picture.
Other inputs come with rainfall, in supplements brought on to the farm
and in effluent .In
addition, nutrients can be moved around the farm . Nutrients are
removed from the farm in stock sold on, products (meat, milk, wool),
crops sold or fed out off farm, and through processes such as nitrate
leaching, volatilisation and phosphate run-off.
Nutrient budgets are the outcome of a simple accounting process that
tracks inputs and outputs to a given, defined system over a fixed period
of time. Like a bank account, the budget tracks inputs (credits) to the
system and exports (debits) from the system in order to evaluate
changes in nutrient stocks of the system. Accelerated rates of nutrient
loss are evidence of soil depletion and are unsustainable over the long
term and not consistent with organic goals.
Accumulation of high levels
of nutrients, particularly of P and N, are also undesirable, and are
associated with increased pollutant export in the form of leachate or
runoff (P and K), or in gaseous form through denitrification or
volatilization (N).
Nutrient budgeting is most commonly done for the
macronutrients—nitrogen (N), phosphorus (P), and potassium (K)—but can
be done for other nutrients as well, such as calcium (Ca), magnesium
(Mg), or zinc (Zn).
Nutrient budgeting makes sense for organic farms because the organic
standards emphasize the use of renewable resources in production and
processing as a way to avoid pollution and waste.
Nutrient budgeting
methods evaluate inputs and outputs as a way to assess efficiency and
improve resource allocation. Achieving a balance between inputs and
outputs is particularly desirable where external resources are costly
and/or non-renewable.
Evaluations of resource use efficiency are
influenced by the spatial and temporal scale considered. A single year
budget for a field might be most useful to a farmer deciding whether or
not to apply supplemental nitrogen to a plot before planting a N
demanding crop.
Multi-year assessments, for example, are more
appropriate for field scale budgeting in systems that apply fertilizer
or compost one in three or four years.
There are three different types of mass balances or budgeting techniques
that are commonly used in Nutrient budgeting these are:
1) farm gate or whole-farm budgets
2)
field or surface budgets
3) farming systems-level budgets.
Farm gate or whole-farm budgets : Farm gate balances account for external flows to and from the farm
including purchased fertilizers, feed, and sold animal and crop
products.
Field or surface budgets : Field-scale estimates capture this reallocation within the farm as they
consider inputs of mineral fertilizer and animal manure as the main
flows. Some field-scale analysis and most system-level analyses consider
inputs from atmospheric deposition and outputs from crop harvest,
surface run-off, and leaching.
Farming systems-level budgets :System-level analyses require much more information about the sites
being considered, but they are quite useful if they are representative
of the system because they can identify mechanisms or parts of the
system that might be improved by management.
Benefits :
Good nutrient management aims to meet crop requirements, maximise
crop uptake and minimize losses to the environment. A nutrient
budget for farm to integrate available nutrients from a range of
sources, reduce the need for supplementary fertilisers, and results in :
- improved crop uptake, yields and quality
- reduced cost of fertiliser inputs
- reduced risk of nutrient losses, watercourse
- pollution and fines
- improved habitat and fishery quality.
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