Dia 1

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Implementation of farm gate nutrient balances as
a management tool towards sustainability
Prof. Stefaan De Neve Department of Soil
Management and Soil Care University of
Gent Belgium
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• Contents of the presentation
• What is a nutrient balance
• Why calculate a nutrient balance/ why for
  Hungarian agriculture/ why on farm level
• N and P cycles at farm level
• Components of a nutrient balance
• How to calculate a nutrient balance
• Example of a nutrient balance and possible
  problems

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• 1. What is a nutrient balance?
• Definition of nutrient balance at farm level

Bookkeeping of all in- and outflows of the most
important nutrients (N, P, K)
Constant inflow/input of products ? constant
outflow/output of products ? implies constant
inflow and outflow of nutrients track these
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2. Why calculate a nutrient balance? The aim of
drawing up a nutrient balance
Learn to know nutrient surplus (or deficit!) in a
given entity/region/farm/field

• Reduce surplus decrease nutrient inflow,
  increase nutrient outflow
• Reduce deficit increase inflow
• For both reduce losses ? should have effect on
  inflow and/or outflow

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• Why calculate a nutrient balance for Hungarian
  agriculture?
• Chronical deficit of nutrients inflow reduced
  yields/ reduced soil fertility ? reduced produce
  quality/farm income
• Chronical surplus of nutrients risk of nutrient
  losses/environmental pollution/produce quality
• Chronical only long term trends are meaningful!!
• Hungarian agriculture strong duality with regard
  to nutrients
• surplusses of nutrients more in Western and
  Central Hungary
• deficits of nutrients more in Eastern Hungary
• ? nutrient balances to identify degree of
  deficits/surplusses of farms
• ? nutrient balances to identify reasons for
  deficits/surplusses
• ? identify possibilities for remediation

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• Why calculate nutrient balances at farm level?
• Reduction of nutrient deficit/surplus all
  measures to be considered at farm level!
• ? holistic (integrated) approach all
  compartments of nutrient cycles are
  interconnected
• Individual measures may effectively reduce
  overall losses
• or may shift losses! Examples
• covered slurry storage
• reduced NH3 emission, but higher losses upon
  field application
• emission-poor application of slurry
• reduced NH3 emission but nitrate leaching,
  denitrification??
• Combine farm gate nutrient balances with
  knowledge on soil fertiliy will allow to prevent
  soil mining and reduce nutrient losses to the
  environment

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N and P cycles at farm level No good
interpretation of nutrient balances possible
without a thorough knowledge of farm N and P
cycle!
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N cycle at farm level
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P cycle at farm level
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Components of a farm gate nutrient balance
Arable farm
Animal production
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Mixed farm
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External flows of nutrients sufficient to
calculate balance But Internal flows of
nutrients (including soil related
data) necessary to optimize measures to be
taken
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How to calculate a farm gate nutrient
balance? Nutrients in in-/outflow total amount
of product ? nutrient content of product Stock
difference (kg nutrient) supply at the start of
the calculation period - supply at the end of the
calculation period Surplus kg nutrient total
input total output Surplus (surface area)-1
kg nutrient ha-1 efficiency
recovery (including e.g. manure,
crop residues) surplus/deficit 100 -
utilisation
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Example mixed farm co-operative New Life in
Baracska Some characteristics of the
farm Arable crops maize, wheat, sunflower,
barley, silage 2100 ha Pasture 330
ha Livestock - On average 370 cows (beef
cattle) (350 calving year-1, sold at 250
kg) (summer pasture, winter stable) - On
average 350 sows (7700 piglets year-1, sold at
100 kg) Animal feed mixed on farm (90 for
pigs, 10 for cattle)
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Co-operative New Life in Baracska nutrient
balance
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• Efficiency of 41 and recovery of 45 seem
  small, but are much better than in e.g. Belgium,
  The Netherlands
• Efficiencies and recoveries in animal production
  are inferior to plant production
• Animal production
• large inputs (concentrates, mineral fertilizer)
• animal efficiency is much smaller than plant
  efficiency
• large part of nutrients ends up in manure gt
  gaseous losses, nitrate leaching
• Crop production
• inputs mainly through mineral fertilizer
• larger efficiency (smaller losses)

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• Problems related to nutrient balances
• Stock differences
• Uncertainties in balance components
• 1. Stock differences
• Changes in stocks of any of the components of the
  nutrient balance will complicate calculations

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• 2. Uncertainties in balance components
• Reasons for uncertainties
• inacurate estimates of quantities of inputs and
  outputs
• parameters (almost) not measurable
• lack of resources to measure nutrient contents

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2.1. Inacurate estimates of inputs and outputs
(Mulier et al. 2003)
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• 2.2. Parameters that are not measurable
• N fixation
• only very rough estimates are possible
• strongly dependent on general soil
  properties/fertility
• highly variable
• Variation from 0 to 500 kg N ha-1 year-1
• Can make a very significant contribution to
  overall N input
• Deposition
• makes only a small contribution (18 kg N ha-1 in
  Hungary)

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• 2.3. Lack of resources to measure
• Nutrients in fertilizers, fodders, plant produce
  are easily measured, but at a cost
• Balance calculations require many components to
  be measured
• Time and money is limited
• ? use fixed concentrations per input/output
  component
• Some examples
• Crops/roughage
• N and P content fluctuate strongly in function of
  soil nutrient status (e.g. 30 lower P content in
  grains in P deficit soils)
• ? 30 error possible when using fixed
  concentrations
• (measure 10 error)

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Concentrates Maximum acceptable deviation is
-10 and -30 for N and P resp. Very large
coefficients of variation are found (up to 30
for N and 40 for P) Animals and animal
products Lower variability (10) Mineral
fertilizers Tolerated variability is 5 for N
and 10 for P Real level of variability is small
compared to other categories Manure/slurry Extre
me variability, with CV up to almost 100! Very
important component of the balance and of
recovery
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Conclusions of uncertainties Input-output
quantities have limited influence Main errors
from slurry/manure, plant products, N fixation ?
uncertainties make a one year nutrient balance
highly uncertain ? longer term nutrient balances
are needed to obtain reliable information