Problems Associated with Nutrient Accounting and Budgets in Mixed by yxm41365

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									Mixed Farming Systems in Europe - Workshop Dronten/Wageningen - 25 - 28 May 1998



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    Problems Associated with Nutrient Accounting and Budgets in Mixed Farming Systems

                              Th. Sveinsson1, N. Halberg2 & I.S. Kristensen2
1
         Agricultural Research Institute, Mödruvellir Experimental Station, Óseyri 2, 603 Akureyri, Iceland.
         E-mail: thorodd@rala.is
2
         Danish Institute of Agricultural Sciences, Department of Agricultural Systems, Foulum Research
         Centre, DK-8830 Tjele, Denmark.
         E-mail: niels.halberg@agrsci.dk , ibs.kristensen@agrsci.dk

INTRODUCTION
Nutrient accounting has been used for decades by many researchers and advisors to estimate
appropriate nutrient management, the potential impact that different agricultural systems have on the
environment and how sustainable different systems are. Materials and methods used to calculate
nutrient balances vary with the objectives but also and primarily between research teams with similar
goals. Our objective was to review strategies for nutrient accounting and discuss problems associated
with different approaches. We will suggest common definitions of concepts and comprehensive
layouts to be used in nutrient accounting.

LITERATURE REVIEW
The main literature reviewed is listed in the references. Our thoughts after this review are recapped in
this chapter.

The criteria for nutrient accounting
Nutrient accounting can be used in directives which objective is to regulate nutrient emission from
agriculture. Then the most appropriate criterion is to look at the farm operation as a single account.
Besides having obligations to comply with environmental regulations, the farmer, on the other hand,
might be more interested in using nutrient accounting as a management tool to optimise nutrient
efficiency within the farm. The farmer's criterion is therefore related to budget making that should be
based on more precise accounting of the farm's internal nutrient cycles.

Terminology of nutrient balances
Nutrient accounting is usually summarised by calculating the nutrient balance of a particular account
that is meant to describe some or all, potential losses from a system. Van Bol and co-workers (1997)
compared three accounting systems and their balances. They concluded that they were not comparable
and therefore called for standardisation. This is because different important inputs and outputs are
omitted due to convenience (or lack of information) rather than negligibility. It is clear though, after
reviewing the literature, that definitions of the term nutrient balance vary considerably, which can lead
to confusion, misunderstanding and misuses. The term nutrient balance needs a non-negotiable and
common definition.

Unbalanced balances
Internal nutrient balances within a farming system are often calculated to locate potential sources of
losses. When these internal balances are summarised they should add up and equal the farm nutrient
balance, which is rarely the case in the literature reviewed. This is not because of miscalculation but
rather because of internal inconsistent definitions of nutrient balances made by the authors.

Negative balances
A nutrient balance that describes losses from a system that transforms nutrients from one stage to
another can in reality never be negative. An accounting system that results in a negative nutrient
balance only reveals that important inputs or properties are unaccounted for. Negative balances often


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 D:\IBDATA\WORDFIL\FARMSYNL.DOC
In Eds. Keulen, H. Van, Lantinga, E.A. & Laar Van H. H.: Mixed Farming Systems in Europe. Workshop
Proceedings Dronten, The Netherlands, 25-28 May 1998. APMinderhoudhoeve-reeks nr. 2. Page 135-140


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Mixed Farming Systems in Europe - Workshop Dronten/Wageningen - 25 - 28 May 1998



occur in accounting systems where N-fixation and/or soil reserves and mineralisation are excluded as
sources of inputs and outputs. The importance of this depends on the objectives of the accounting.

Dilution effects
Nutrient balances used to evaluate the environmental impact of a system are often published as a mean
balance ha-1. Here, some precautions have to be made because of possible inappropriate dilution
effects. Mixed farms have variable access to natural or semi natural areas for grazing, which often
contributes relatively little to the whole farm production and nutrient losses. To include these areas in
a mean balance ha-1 without any corrections is inappropriate. Also, means based on sub balance means
with negative accounts (numbers) do not give a true estimate of the environmental impact of the
system and could result in discrimination between farms.

RESULTS AND DISCUSSION
This review and others unveil the necessity of common rules and layouts for nutrient accounting and
balances. Our suggestions for improvements of the current situation follows.

The rules of nutrient accounting
• Meaningful units or accounts build up the accounting system. The units move, store or transform
    nutrients from one stage to another. Depending on the objectives and criteria, a unit can be a single
    plant or fields, an animal or herds, a farm, a community and etc.
• Each unit has its boundary with gates where nutrient inputs (I) and outputs (O) are registered
    (accounted) over a given period of time. The inputs are all nutrients that enter the unit randomly or
    systematically. The outputs are all useful nutrient products exiting from that unit.
• All units have a nutrient capital (a property) at the beginning (cin) and the end (cout) of a given
    period of time. The difference between the cin and cout describes changes or movement (m) of
    capital in a unit.
• The net difference between the nutrient input and output, i.e.:
                                                   I-O+m
    is called the nutrient balance, which is the expression of the estimated nutrient loss from that unit.
    Sometimes it can be impossible or irrelevant to differentiate some outputs and capital changes. A
    good example is a field or a soil account where it can be difficult to distinguish minearalization
    from nutrient accumulation/depletion. Therefore, the balance describes the potential irreversible
    nutrient loss from a unit. Lost nutrients can only re enter accounts as random inputs.
• A sub unit is a unit within a larger main unit. However, all units obey the same rules and
    definitions of accounting. The sum of nutrient balances from all sub units within a larger main unit
    has to equal the nutrient balance of that main unit.
• The volume or quantity of a nutrient exiting from one account cannot change during or with
    transport to another account.

Nutrient accounting to evaluate the environmental impact of agriculture
The most meaningful unit or account for an assessment of the nutrient environmental impact of a farm
operation is the nutrient balance of the whole farm unit. The advantage of using this balance is that
most information needed to calculate the nutrient balance of a farm is already at hand. This approach
will be introduced as a policy instrument for the Netherlands in 1998 (Munters 1997). Also, Halberg
and co-workers (1998) suggest a similar approach to regulate N-emission from agriculture in
Denmark.
Table 1 shows a comprehensive layout and components for a farm account, based on the rules of
nutrient accounting described before. Actual data are derived from on-farm studies in Denmark.

Nutrient accounting and budgets in mixed-farm management
Using nutrient accounting as a farm management tool needs new criteria and methods that record in
more detail the internal nutrient flow on the farm. Weissbach and Ernst (1994) have given an excellent
summary of methods to optimise on-farm nutrient efficiency. Here, we will concentrate on how
nutrient efficiency can be recorded in a sequential system of accounting and budgeting. The most



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Mixed Farming Systems in Europe - Workshop Dronten/Wageningen - 25 - 28 May 1998



meaningful accounts for this purpose are livestock accounts, field accounts and storage accounts.
Comprehensive layouts with respective nutrient balances for each type of account are shown in table 2
and based on the accounting rules described above. Same source of data as those of table 1 is used.
          A separate livestock account has to be established for each type of herd within the farm. The
most important information for a useful livestock account is to obtain the true quantity and nutrient
composition of the systematic inputs and in particular inputs from internal accounts. This is because
the feed nutrient analysis gives the best checking point for the internal nutrient recycling efficiency.
          A separate field account has to be made for each field within the farm if the accounting is to
be efficient in the nutrient management. Each field has its unique physical and topographical
properties that have to be considered when nutrient budgets are made. Also, these properties are a part
of the farm's cultivation design (set-up). The most challenging and central task for these accounts is to
make accurate estimates on plant available nutrients in the manure and to estimate the nutrient carry-
over capacity in a crop rotation system or long-term pastures. One can expect that the accuracy will
increase with time when the farmer becomes more experienced using the benefits of systematic
accounting.
          The storage accounts are particularly important for keeping good records of manure
utilisation. This is because manure application occurs in pulses which do not always coincide with
other internal accounts, and it is important to update the nutrient content of the stored manure more
frequently than for other accounts. A separate manure account is needed for each storage unit on the
farm.
          A feed storage account is not always meaningful and can easily be included in the livestock
account. The feed storage account is useful for the estimation the feeding efficiency and to estimate
how well the feed is utilised on the farm.
          Appropriate and meaningful time scale and stocktaking for each account can vary from a few
months to years. However, regular synchronisation of internal accounts with the farm account is
important to double-check all balances. This is fairly easy to do in an organised accounting system as
can be seen in table 2.

Table 1. Comprehensive layout for a mixed farm account with a respective nutrient balance (here, kg
N ha-1 year-1). Data are from 2 dairy farms and one pig farm in Denmark (Halberg, Kristensen &
Møller 1998).
       Farm account            Input, kg N ha-1 year-1                 Output, kg N ha-1 year-1
                    Farm no.       D 13     D 5 P 19                      D 13       D5       P 19
Systematic components
                N - fixed                 0       92       0           Milk        53      32         0
               Fertilizers              113        0      71          Meat         14       5       128
             NH3 to straw                 8        0       0          Crops         0       0        99
                          Feed          148       42     393        Manure          0        0       55
Random components
             Precipitation               21       21      21
Capital components
                Livestock                 1        0       0     Livestock           0      0         0
                     Feed                 2        3       0         Feed            0      0         0
                  Manure                  8       24       0       Manure            0      0        23
                    Total               301      182     485                        67     37       305
                Farm balance                                                       234    145       180
                 -components                                       -livestock       20       6       13
                                                                        -field     193     128      132
                                                                     -storage       21      11       35




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Mixed Farming Systems in Europe - Workshop Dronten/Wageningen - 25 - 28 May 1998



Table 2. Comprehensive layouts for internal farm accounts with respective nutrient balances (here, kg
N ha-1 year-1). Data are from 2 dairy farms and one pig farm in Denmark as in table 1 (Halberg,
Kristensen & Møller 1998).
                            Input, kg N ha-1 year-1                      Output, kg N ha-1 year-1
                Farm no.      D 13     D5       P 19                       D 13        D5       P 19
  Livestock account
Systematic components
          NH3 to straw              8         0         0                Milk       53     32      0
       Purchased feed            148         42       393            Meat           14      5    128
     Feed from storage           129         73         0      Sold manure           0      0     55
        Grazed forage             37         88         0    Stored manure         205     86    197
                                                            Grazing manure          31     74      0
Capital components
            Livestock              1         0          0          Livestock         0      0      0
                Total            323       203        393                          303    197    380
      Livestock balance                                                             20      6     13
            -components                                          ammonia loss        20      5     13
                                                                  Other losses        0      1      0
Livestock N -production and -efficiency
Inputs, kg/LU                168        179            99     Outputs, kg/LU         35     33     32
                                                                  Efficiency       21%    18%    33%
    Field account
Systematic components
  Manure from storage            192         99       139       Stored feed        127     70      0
 Manure under grazing             31         74         0       Grazed feed         37     88      0
             Fertilizers         113          0        71            Crops           0      0     99
              N - fixed            0         92         0
Random components
          Precipitation           21        21         21
                  Total          357       286        231                          164    158     99
            Field balance                                                          193    128    132
             -components                                         ammonia loss        43     31     28
                                                                  other losses      150     97    104
       Field production efficiency                                                 46%    55%    43%
   Storage accounts
Systematic components
  Manure from livestock          205         86       197        Manure used        192    99     139
          Feed from field        127         70         0          Feed used        129    73       0
Capital components
                    Feed           2         3          0               Feed          0     0      0
                 Manure            8        24          0             Manure          0     0     23
                   Total         342       183        197                           321   172    162
        Storage balance                                                              21    11     35
            -components                                          ammonia loss        21     11     34
                                                                  other losses        0      0      1




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Mixed Farming Systems in Europe - Workshop Dronten/Wageningen - 25 - 28 May 1998



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