Seuri, Pentti and Kahiluoto, Helena (2005) Evaluation of nitrogen utilizsation by means of the concept of primary production balance. Paper presented at Researching sustainable systems : first scientific conference of the International Society of Organic Agriculture Research (ISOFAR), held in cooperation with IFOAM and NASAA, Adelaide, South Australia, 21-23 September 2005, page pp. 48-51. International Society of Organic Agriculture Research (ISOFAR), Bonn; Research Institute of Organic Agriculture (FiBL), Frick.

EVALUATION OF NITROGEN UTILIZATION BY MEANS OF THE CONCEPT OF
PRIMARY PRODUCTION BALANCE
Pentti Seuri, Helena Kahiluoto
MTT Agrifood Research Finland, Huttulantie 1, FI-51900 Juva, Finland, Tel. +358 15 321230,
pentti.seuri@mtt.fi, helena.kahiluoto@mtt.fi, www.mtt.fi
Key Words: nitrogen utilization, nutrient balance, primary nutrient, secondary nutrient, nutrient loading
Abstract
Primary production balance (PPB) indicates the ratio (*) between harvested nutrients and nutrients put into
crop production from outside the system (=primary nutrients). The PPB is independent of the final output
(crop vs. animal products) and can be used to evaluate different systems (farms). The utilization of nitrogen
(N) was evaluated by means of the PPB on nine organic farms, stockless and mixed ones, in eastern Finland.
The mixed farms were able to reach a remarkably higher primary production balance (1.0 – 1.2) compared
with the stockless ones (0.5). Values higher than 1.0 indicate recirculation of nutrients. Other components of
the high PPB were legumes as nitrogen source and optimum livestock density.
Introduction
Nutrient balances (farm-gate balance, surface balance or cattle balance) only indicate an absolute load of
nutrients as a difference between input nutrients and output nutrients (kg or kg/ha); basically they do not tell
anything about the efficiency of nutrient utilization.
It is also possible to count a ratio between output and input. Sometimes this type of ratio has been used as a
measure of efficiency of nutrient utilization. As long as the system is simple enough, i.e. stockless farm
without any recycling nutrients, the output/input ratio indicates the efficiency of nutrient utilization.
However, as soon as a system involves recycled nutrients, the output/input ratios are difficult to interpret
(Myrbeck 1999).
From an ecological point of view there is only one production process in the agricultural system, i.e. crop
production or primary production. Primary production can be used either directly as human food or fed to
animals. Nutrient load and nutrient utilization, i.e. efficiency to utilize nutrients, are two separate
dimensions. If only crop products are produced, the nutrient load is less than an equal amount (kg nitrogen)
of animal products, even the efficiency to utilize nutrients is equal. This is because more crop products are
needed to produce an equal amount of animal products.
In order to reduce the nutrient load there are two choices: either to produce less or to improve the efficiency
of nutrient utilization. Since the amount of primary production is highly dependent on the priorities in the
human diet, it can be taken as a given constant. According to this assumption, the harvested yield (Y) to
external nutrient input (=primary nutrients, P) ratio alone indicates the nutrient utilization in any system. The
concept of primary production balance (PPB) is based on this fact (Seuri 2002).
The aims of this study were:
To introduce a new method, primary production balance, for the evaluation of nutrient utilization
To demonstrate and find the key factors to reach a high utilization rate of nutrients
(*) Note: the term “balance” is used to indicate a difference (input – output) or ratio (output/input); the unit
of difference is kg or kg/ha, the unit of ratio is either per cent or no unit.
Methodology
A more profound analysis was made on nitrogen utilization on nine organic farms in eastern Finland. Data
was collected by personally interviewing farmers in 2004. An overall picture was drawn on how the farms
were functioning and, to ensure the validity of data, the results were discussed personally with the farmers.
The estimations of harvested yield (dry matter & nitrogen) were adjusted with the number of animals and
total animal production. The nitrogen contents of all organic materials within the system (crops, fodder,
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bedding materials, seeds, animal products, purchased manure) were estimated by means of standard figures,
unless measured values were available. Atmospheric deposition, 5 kg nitrogen/ha, was included as input.
All the main nutrient flows were identified. However, because of the steady-state assumption (i.e. balanced
systems, no change in reserve nutrients in soil) and estimation of biologically fixed nitrogen the results may
include some error.
Biological nitrogen fixation was estimated using harvested legume yield: the assumption was 50 kg nitrogen
per 1000 kg harvested dry matter of legume. That means that roughly 70 % of the total nitrogen content in
the legume biomass originated from BNF. The assumption was derived from the Swedish STANK model
(STANK 1998), the Danish model by Kristensen et al. (1995) and the Finnish model by Väisänen (2000).
On all farms the most important legume was red clover. However, some white clover and alsike clover were
grown in perennial mixture lays, too. Besides pea, which was the most important annual legume crop, some
annual vetch was grown.
Farm-gate balance, surface balance and primary nutrient balance were calculated for each individual farm
(Table 1). Primary nutrient balance can be calculated from the following two equations (Seuri 2002):
(I) PPB = Y/P where Y = total harvested yield
P = primary nutrients (=external nutrients)
(II) PPB = U x C where U = utilization rate (=surface balance)
C = circulation factor = (P + S)/P
S = secondary nutrients (=recirculated nutrients)
Equation (I) follows the definition of PPB. Equation (II) illustrates two components of PPB: utilization rate,
which is equal to surface balance, and circulation factor, which indicates the importance of recirculated
nutrients in the system. There is a major difference between stockless farms and livestock farms. Since there
are no recirculated nutrients (S) on stockless farms, the circulation factor is always 1.0. On livestock farms
the circulation factor is always higher than 1.0.
To illustrate the difference between primary and secondary nutrients and to point out the role of
recirculation in order to improve the nutrient utilization, some simple simulation was made on two stockless
farms. The farms produce some fodder and receive some farmyard manure (FYM) from the neighbouring
farm. The initial balance (A) indicates utilization in case manure from the neighbouring farm is external
nutrient input (primary nutrient). The simulated balance (B) indicates the utilization in case all the harvested
fodder yield is used on the farm for dairy cattle. It is assumed that 25 % of the nitrogen in the fodder is sold
out from the farm in the form of milk and beef and 25 % is lost in the gaseous form before the manure is
spread on the field. The rest of the nitrogen (50%) remains in the manure.
The average utilization rate of the primary nitrogen in the agriculture in Finland was calculated from
statistics. Rough estimations and comparisons were made between the farms in this study and national
average utilization rates.
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Results and brief discussion
Table 1. Comparison between primary production balance (PPB), surface balance (SB) and farm-gate
balance (FGB) of nitrogen on nine organic farms in eastern Finland. Farms 8B and 9B are
simulated from 8A and 9A, respectively.
Farm Production Primary 	Total N 	Harvested PPB 	SB 	FGB 	Circulation N surplus
type   N input 	on field 	N yield 				factor
           (kg/ha) 	(kg/ha) 	kg/ha) 					(kg/ha)
1 	dairy 60 		92 	69 	1.15 	0.75 	0.34 	1.53 	40
2 	dairy 68 		108 	75 	1.11 	0.69 	0.3 	1.60 	49
3 	dairy 53 		83 	56 	1.06 	0.68	0.3 	1.56 	44
4 	beef   69 		113 	84 	1.22 	0.7 	0.18 	1.64 	60
5 	beef  65 		113 	73 	1.13 	0.65 	0.20 	1.74 	53
6 	beef(+crop) 52 	89 	50 	1.06 	0.62 	0.17 	1.70 	48
7                   goat(+crop) 56 	73 	45 	0.80 	0.62 	0.30 	1.30 	55
8A 	crop   87 		87 	49 	0.56 	0.56 	0.56 	1.0 	39
8B 	” dairy” 63 		87 	49 	0.77 	0.56 	0.19 	1.39 	51
9A 	crop 66 		66 	34 	0.51 	0.51 	0.51 	1.0 	33
9B 	”dairy”(+crop) 49 	66 	41 	0.84 	0.62 	0.3 	1.36 	34
The PPB of nitrogen fell in the range 1.0 – 1.2 on all mixed farms except for farm 7, i.e. the farms were able
to harvest more nitrogen than they received as an input into the crop production from outside the farm.
Both stockless farms reached a PPB as low as around 0.5; the dairy farm simulation increased the PPB up to
0.8.
The SB of nitrogen fell in the range 0.6 – 0.75 on all mixed farms and by definition PPB and SB are
identical in a stockless system (around 0.5), i.e. in any system without re-circulated nutrients. The FGB of
nitrogen correlated strongly with production type, being around 0.3 on dairy farms and around 0.2 on beef
farms. Analogously to PPB and SB, FGB was identical on stockless farms (around 0.5). The dairy farm
simulation decreased the FGP down to 0.19 on farm 8 and down to 0.3 on farm 9.
Simulation on farm 8 shows clearly the role of recirculation and the difference between PPB and SB. On
farm 8, the only difference between the real farm and the simulated farm is the method of definition of the
origin of input nitrogen, i.e. the initial yield harvested and the initial amount of nitrogen available in the field
are exactly the same. On farm 8A, all the nitrogen in FYM from the neighbouring farm is considered as
primary nitrogen analogous to the nitrogen in artificial fertilizers or the nitrogen from BNF. This is
analogous to any nitrogen input which increases the total amount of nitrogen in the system. On farm 8B, the
nitrogen in the FYM from the neighbouring farm is considered as secondary nitrogen analogous to the
nitrogen in FYM originating from the farm. This is analogous to any recycled nitrogen which does not
increase the total amount of nitrogen in the system. However, the SB method does not identify the origin of
the nutrients in the field, i.e. unlike PPB, SB remains constant on farm 8. The higher PPB value on the
simulated farm 8B indicates higher efficiency of primary nitrogen utilization, thereby a lower nitrogen load
potential.
On farm 9B there are some green manure fields, from which yield is harvested instead of ploughing directly.
Therefore the SB is influenced by simulation on farm 9, but otherwise it is analogous to farm 8.
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In Finland (1995 – 1999), calculation of nitrogen balance in agriculture shows that the annual total primary
nitrogen input (artificial fertilizers, atmospheric deposition and symbiotically fixed nitrogen) is about 100
kg/ha. The total harvested nitrogen yield is about 74 kg/ha, respectively (Lemola & Esala 2004). Thus, the
PPB in agriculture averages 74 kg/ha / 100 kg/ha = 0.74, indicating serious lack of nutrient re-cycling.
However, there is huge potential to recycle nutrients in agriculture, because 80 % of the total crop yield is
used as animal fodder.
In this study, all the livestock farms exceeded the value 0.74, range 0.8 – 1.2, average around 1.0. The high
PPB on nitrogen was not only due to recycling but also to biological nitrogen fixation. The main source of
primary nitrogen input was symbiotic fixed nitrogen by legumes. The utilization rate of nitrogen by legumes
is clearly higher than for any other source of nitrogen into a system. In most cases about the same amount of
nitrogen was harvested than was symbiotically fixed, i.e. the utilization rate is approx. 100%.
In addition, the balance between livestock and field area (fodder production) was of major importance in
reaching a high PPB. Whenever the livestock density was increased by means of purchased fodder, the
utilization of farmyard manure was poor and resulted in lower PPB (farms 3, 6 and 7). Self-sufficient fodder
production was the optimum. The farms with high PPB had also a slightly higher yield level than farms with
lower PPB.
On the other hand, two stockless organic farms indicated that without recirculation an organic system cannot
utilize nitrogen very efficiently. On these farms the primary source of nitrogen consisted of legumes, but
because the legume crop was partly used as green manure, there were heavy losses of nitrogen with resultant
lower total PPB.
Conclusions
It was fairly easy to calculate the primary production balance for each of the nine farms included in this
study. The estimation of biological nitrogen fixation and harvested nitrogen yield are, however, obvious
sources of error. The assumption of steady state is not necessarily valid in all cases.
Even though crop production causes only minor nutrient load compared with animal production, it does not
necessarily mean that crop farms utilize nutrients effectively. Using the PPB it is easy to compare different
farms. The results of this study show clearly that livestock farms are able to reach a remarkably higher PPB
compared with crop farms despite the very low farm-gate balance on livestock farms.
References
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