| Demonstrationsejendomme
for bedre udnyttelse af husdyrgødning
Summary
Background
In 1995-96 the Department of Plant Production in cooperation with local plant production
centres and 15 farmers continued the "Demonstration project for improved use of
farmyard manure", which was initiated in 1991. The background for the continuation of
the project is, among other things, that the results from trials during the period 1991-93
indicated, that the nitrogen requirement on livestock intensive farms was overestimated in
comparison with the nitrogen requirements measured in field trials. Therefore in 1995 and
1996 two to three trials were carried out with increasing amounts of nitrogen per farm in
order to measure the nitrogen requirement. Furthermore trials have been carried out to
examine the use of mineral N measurements shortly after spreading of farmyard manure and
specific measurements of the N-mineralisation during the first year after spreading of
farmyard manure.
Furthermore there was a wish to persue the positive development which had been reached
by improving the use of farmyard manure, thus reducing the use of fertilizer and improving
the nitrogen balance. In 1995 and 1996 the local plant production centres in collaboration
with the department of plant production measured the nitrogen decomposition on the farms
and calculated the utilization percent as well as the nitrogen balances.
Fertilizer trials
In 1995 and 1996 thirteen and twelve were carried out with amounts of nitrogen increasing
every year on the demonstration farms. In 1992-1995 four trials on average were carried
out per year. On the basis of data on application of farmyard manure the previous five
years, previous crop, soil type, yield, and geographic location, an estimate of the
nitrogen requirement was reached, following the 1997-norms stipulated by the Danish Plant
Directorate, the N-min-method, and the fertilization models of the Integrated Farm
Management Program. This calculation proved that the N-requirement measured in the trials
was an average of approx. 20 kg N per ha less than the needs measured on the basis of the
norms of the Danish Plant Directorate. To a large extent the difference is due to the fact
that the need for nitrogen in the 1996-trials was very low due to the historically dry
1995/96-winter, where an adjustment of the application on the basis of the nitrogen
prognosis on farms with optimal mamure was insufficient. A calculation based on 90 trials
with nitrogen application for winter wheat in 1995-97 showed, that on average the norms of
the Danish Plant Directorate indicated the same nitrogen requirements as the one found in
the field trials, and that no tendency was found as to overestimating the N-requirement on
farms with after-effect of farmyard manure. The fertilization model of the Integrated Farm
Management program and the N-method also indicated too high N-requirements on the
demonstration farms, but the mineral N-method indicated a lower N-requirement than the
other methods.
Furthermore, trials were carried out in spring barley, winter barley, (silomajs), and
oat.
Calculation of nitrogen demand
In 1995 and 1996 all field trials on the demonstration farms showed a lower nitrogen
requirement than expected according to the methods of calculation normally used when
stating the nitrogen requirement for fertilizer planning, thus confirming the results
reached in 1991-93. Although data analyses of the many field trials carried out every year
in the agricultural associations cannot in general confirm the results, there is, however,
still reason to continue investigating if the nitrogen requirement on intensive livestock
farm is overestimated.
In 1997 the Department of Plant Production initiated a project in cooperation with the
Danish Institute of Agricultural Sciences aiming at adjusting the methods of calculation
for after-effect of farmyard manure and plant residues.
Nitrogen demand in the field
Every year the nitrogen requirement of the field was determined on the basis of fertilizer
calculations in the Integrated Farm Management program, individual adjustments and, in
some cases, mineral N-measurements. On pig and cattle farms the nitrogen requirements was
falling in general from 1991 to 1996. But an essential reason for the fall was the
1996-nitrogen prognosis, that dictated a nitrogen requirement of 10-30 kg N per ha below
normal. The nitrogen requirement on the farms was approximately 150 kg N per ha.
Pig farms
The nitrogen application in fertilizer went down from 113 kg in 1990 to 63 kg N per ha in
1996. As the application of nitrogen in farmyard manure during the period was almost
constant, the result was an increase in utilization percent for nitrogen in farmyard
manure. In all, the increase went from 35 pct in 1990 to about 55 pct at the end of the
period. Because of the reduced need for nitrogen in 1996, to which the farmers have not
yet fully been adjusted, the utilization percent was, however, only 45 pct in 1996. If the
N-requirements were calculated in exactly the same way for the whole period, the
utilization percent increase was approx. 25 percent units. When estimating the development
of the utilization percent it must be taken into consideration that during the period two
farms have established animal production on "deep beding".
Cattle farms
On cattle farms the application of nitrogen in fertilizer went down from 130 kg in 1990 to
85 kg N per ha in 1996. Since 1992 the use of nitrogen in fertilizer has been stable. The
utilization percent for nitrogen in farmyard manure increased from 30 pct in 1990 to 50
pct in 1995. On cattle farms, as well, the utilization percent went down as a result of
the negative nitrogen prognosis. If exactly the same calculation of nitrogen requirements
is made for all the years, the utilization percent for N in farmyard manure has increased
by approx. 20 pct units.
On the five plant production farms receiving livestock manure from the nabouring farms
the amount of manure received has fallen from 135 kg in 1992 to 72 kg N in 1996. In this
period the fertilizer consumption has been almost stable, which means that the utilization
percent for nitrogen in livestock manure has risen.
N-balance on pig farms
While the utilization percent for nitrogen in farmyard manure is very much effected by the
way the nitrogen requirement is determined, the development of the nitrogen balance is a
more direct expression of the development of the nutrient balance on the farms. As an
average of four pig farms the nitirogen balance has improved from an excess of 176 and 197
kg N per ha respectively in 1990 and 1991 to an excess of 152 and 142 kg N per ha in 1995
and 1996. The improvement of the nitrogen balance is mainly due to the reduction of
nitrogen use in fertilizer, while the removal of nitrogen with the crops remains
unchanged. Compared to a reference curve expressing the nitrogen excess at a very good
utilization of farmyard manure and norm yields, two out of five farms reached a lower
excess, while the excess on the three other farms was higher. An essential reason for the
higher excess on two of the three farms was that a considerable part of the nitrogen was
produced in farmyard manure.
Measured as an average of 4 pig farms, the nitrogen field balance has fallen from an
excess of 150 kg N per ha in 1990 to 100 kg N per ha in 1996. When calculating the farm
balance as well as field balance the substantial uncertainty, which is a result of the
variation in the protein percent in the crops, must be taken into consideration. This
uncertainty is not taken into consideration when calculating the balance on the basis of
norm figures.
N-balance on cattle farms
On the cattle farms the amount of animal units per ha increased from 1,45 to 1,65 during
the period. The effect of this increase was a constant excess of N, approx. 180 kg N per
ha, although the use of N in fertilizer had been reduced. The field balance as an average
of the 5 cattle farms show a reduction from 145 kg to 120 kg N per ha. The calculation of
the field balance for cattle farms is uncertain because of the uncertainty of the
calculation of nitrogen fixation.
Taking all the farms into consideration the calculation of farm balances for nitrogen
show that in order to improve the balance considerably the nutrients in the stable as well
as in the field must be utilized to the optimum. An over-feeding with proteins in the
stable will result in an increase in stable and storage loss, and often the higher amount
of N present in the farmyard manure is not taken into account. If the protein supply for
the livestock is reduced, the amount of nitrogen in the farmyard manure is reduced,
resulting in a reduction of the N-excess. The farm at Kalundborg is a good example of the
development of the nutrient balance in both stable and field. Here the N-excess has been
reduced from about 200 kg N per ha in 1990 to about 100 kg N per ha in 1996. It is hardly
possible to reduce the amount further with the present animal production on the farm.
P-Balance on pig farms
Taken as an average of four pig farms the excess of phosphorus was 20-25 kg, remaining
unchanged during the period. Part of the excess of P is due to the fact that more
phosphorus has been used in fodder phosphates than recommended. Almost all of the P-input
on the farms has happened through animal fodder. When calculating stable and field
balances it must be concluded that estimates of the amount of P in farmyard manure through
analyses are problematic, since there is no correlation between the calculated amount of P
in farmyard manure and the amount calculated by means of analyses. Part of the missing
correlation may be due to the fact that the actual P content has not been used in homemade
fodder. The amount of P in cereals may vary from year to year.
P-balance on cattle farms
The excess of P on the cattle farms was falling slightly during the period and was in 1996
about 10 kg P per ha. Most of the phosphorus is imported through the fodder. As from 1998
the recommended P application with fodder has been reduced considerably which will lead to
a reduction of the P excess on cattle farms in the future.
Urea in the milk
The content of urea in the milk was measured on 5 cattle farms. The relation between the
intake of energy and protein influences the concentration of urea in the milk. But it was
concluded that urea measurements cannot explain the intake of protein in the livestock
N-min measurements after application of manure
In some trials the N-amount in the soil and in the plants was measured shortly after
spreading of manure. Usually it is assumed that measurements of the mineral N content in
the soil can be taken six weeks after spreading, because ammonium nitrogen spread is
immobilized. Measurements in these trials proved that almost all nitrogen applied with
fertilizer and farmyard manure could be measured at sampling 7-13 days after taking
samples in one of the trials, while amounts in the other trial proved to be about 50 kg N
per ha less. This trial showed a considerably lower excess yield for application of N in
farmyard manure, which together with the measurements might indicate a los of nitrogen
through ammonium evaporation.
In eight trials the in situ method was used for measurements of the nitrogen
mineralisation. A considerable variation in the nitrogen mineralisation was found in the
trials. But there is no correlation between the nitrogen mineralisation measured and the
optimum amount of N found.
|