Open access publications in the SLU publication database

SUMMARY
Background
The question of different forms of cropping has occupied agronomists for a number of
decades and during the 1980s it reached a wider audience. A major drive was therefore
initiated in 1987 in what was then the county of Kristianstad and three long-term cropping
trials were set up at the county’s agricultural colleges, Bollerup, Önnestad and Östra Ljungby.
These same trials are still running but the objectives changed somewhat in 1999. The main
point is no longer to compare the systems but to improve each of them according to its own
conditions. The results from all study years are available in databases at www.cropping
system.se.
Characterisation of trial sites
Bollerup: A high-yielding traditionally arable soil, texture moderately humus-rich light clay.
Önnestad: A moderately humus-rich to humus rich clayey sand. Despite the light soil texture,
water supply is good, presumably through capillary transport from below.
Östra Ljungby: The harshest of the trial sites. Soil texture moderately humus-rich clayey sand,
with compacted layer below plough depth.
Trial structure and upkeep
Five cropping systems are being compared:
A Conventional cropping, crop production without animals.
B Conventional cropping with ley and manure (with animals).
C Organic-biodynamic cropping with ley and manure (with animals).
D Organic-non biodynamic cropping with ley and manure (with animals).
E Organic cropping, crop production without animals
Treatment A.
Manured, crops protected using best practice with environmental awareness. Straw and
foliage retained. Catch crops used to the greatest extent possible.
Treatment B.
Manured, crops protected using best practice with environmental awareness. Manure brought
in. Straw and sugarbeet foliage removed.
Treatments C and D.
For treatment C biodynamic principles are applied, e.g. composted manure and biodynamic
products used. In treatment D manure is used as in treatment B. No mineral fertiliser or
chemical pesticides in either treatment. Straw and sugarbeet foliage removed.
Treatment E.
No soluble mineral fertiliser and no pesticides. However some phosphorus and potassium are
supplied via ash, sugar factory lime, potato juice and pig urine, in amounts that are
ecologically relevant and can be viewed as extended recycling. Crop residues are retained.
One cropping year is used for nitrogen acquisition via a green manure ley.
Manure doses are based on estimated potential stocking rate in the respective cropping
system. All treatments are limed according to requirements.
Environmental measures
Catch crops and delayed tillage, often spring ploughing, are used to the greatest extent
possible in order to decrease nitrogen leaching. All measures are guided by environmental
considerations underlying Good Agricultural Practice, e.g. adjusted fertilisation.
Yields and quality parameters
Values of yields, quality parameters (e.g. protein content in wheat), and nutrient content are
reported, as are analyses of crop products circulating in the system, e.g. straw, foliage and
green manure. Annual soil analyses are carried out for the topsoil and in some years also for
the subsoil. Complementary analyses have been carried out regarding humus content.
Weed counts and a special study of pea root rot have also been carried out.
In general, it can be claimed that the comprehensive measurements carried out in the trials
provide a good body of information for understanding the processes that lie behind the
changes and for planning ahead.
Yield changes
One trend was for yields of organic sugarbeet to increase during the study period, probably
due to accumulation of experience as regards cropping techniques and a better pre-crop
(currently forage ley or green manure ley). In the most recent round, these yields were approx.
10% below those in the conventional cropping system without animals and almost identical to
those in the conventional ley-based system. For other crops no trends were observed. In the
international literature it is sometimes stated that after conversion to organic cropping, yields
are lower in the beginning but that they increase in the long run. However, these trials have
been running for 18 years but no such increase can be detected for any trial site except the
sugarbeet mentioned above.
Organic cropping without animals (treatment E) has produced 52-59% of the yields in the
corresponding conventional cropping system (treatment A) at the various sites, green manure
year included. Organic cropping with beef animals (treatment D) has given 64-86% of the
yields in the corresponding conventional cropping system (treatment B). These results are
generally similar to those observed for the first two rounds of cropping.
Relative comparisons (%) of average yields between organic and conventional cropping have
been calculated for some of the crops during the years reported here.
In the crop growing system (treatment E/treatment A), the yields of organic sugarbeet were
89% of the conventional, barley 69%, winter wheat 49% and potato 47%.
In the ley growing system with manure (treatment D/treatment B), the yields of organic
sugarbeet were 100% of the conventional, ley I 78%, ley II 75%, barley 75%, winter wheat
64% and potato 60%.
Plant nutrients
In characterising cropping systems, the nutrient balance is of particular interest. The table
below shows average nutrient flows and balances for the three trial sites during the most
recent round of the crop rotation.
Nitrogen Phosphorus Potassium
Removed Added N-fixn. Balance Removed Added Balance Removed Added Balance
A 84 89 12 17 16 15 -1 52 57 5
E 55 17 74 36 8 6 -3 25 18 -8
B 178 174 81 77 25 22 -3 162 156 -6
C 149 64 119 34 20 15 -5 121 97 -24
D 153 81 112 40 20 15 -6 119 88 -31
Nitrogen
The supply of nitrogen in the conventional cropping treatment A is in the form of mineral
fertiliser, the minimal supply of nitrogen in the organic equivalent (treatment E) is in the form
of potato juice at Önnestad and urine at Östra Ljungby. For treatment E, biological fixation is
the main N source. It amounts to 74 kg N/ha, i.e. similar to the mineral fertilisation in
treatment A. The balance, that which cannot be accounted for, is +17 kg N/ha in treatment A
and +36 kg N/ha in treatment E. Nitrogen is limiting for yield in treatment E, which can be seen
in both yields and analyses, but the unaccounted for nitrogen surplus is still greater. Nitrogen
fixation may be high, but it is a problem to get it distributed across the crop rotation. In the
current round, experiments are being carried out to tackle the issue through biogas production,
from which the nutrient-rich biodigestate can be supplied to different crops in the rotation.
I treatments B, C and D nitrogen is supplied as manure, in B complemented with mineral
fertiliser. Nitrogen fixation is very high, with over 500 kg N/ha being fixed by good clover
leys in some years.
Leaching and gaseous emissions and deposition have not been taken into account, nor have
changes in soil nitrogen content. The latter has a certain interest. Önnestad has a high humus
content that is being broken down, with data on humus content indicating that approx. 60 kg
nitrogen is being released per hectare and year. This is no doubt one of the reasons for the
balances at Önnestad being rather low in numerical terms and for the organic treatments
performing better at Önnestad than at the other sites. The opposite applies at Bollerup, where
a certain build-up of nitrogen is occurring in all cropping treatments, for which nitrogen is
required.
Phosphorus
The balances are negative in average terms, as they should be. At Önnestad there are still high
soil reserves which have to be broken down. Bollerup has reached around the right level, but
at Östra Ljungby some treatments are beginning to be critically low. The question there is
how to supply the organic treatments on these sites, especially treatment E where there is no
manure. The solution has been to use various organically approved products that contain
phosphorus. Potato juice and sugar factory lime are also generally established products in
conventional farming. Furthermore, so-called SL-ash, ash from grain waste from the Svenska
Lantmännen plant in Ystad, has been used and is included in the balance. How ash functions
as a long-term solution remains to be seen.
For large-scale organic farming, recycling of nutrients is essential. In these trials this has
begun to happen, but at the same time it can be noted that it has been possible to use the
existing phosphorus reserves in the soil for 18 years, and at Önnestad this will be possible for
as long again.
Potassium
For the potassium calculations, a special study has provided interesting perspectives. As can
be seen from the list below, the balances are negative but it is uncertain whether this depletion
is problematic. The potassium content in the ley crop has declined and become more balanced
during the study period, which applies for all treatments. However, it is not likely that
potassium is limiting yield. Balance calculations (Chapter 8) show a deficit of a few tens of kg
potassium per year. This must be viewed in relation to the following figures on assets and
reserves:
K as K-Al -163 kg/ha
K as K-HCl -3270 kg/ha
K in readily degradable minerals -31100 kg/ha
K in poorly degradable minerals -50600 kg/ha
(Example from Bollerup, but generally applies to all sites)
Of course, not all these reserves can be utilised, but it appears to be important to clarify how
the different potassium pools function in the soil.
Weeds
Incidence of weeds varies widely between sites and cropping systems. Önnestad has the
highest weed pressure, while Bollerup has the lowest. The lowest incidence of weeds is in the
conventional cropping system with animals (B) and the highest incidence in the organic
cropping system without animals (E). Ley growing in the organic cropping systems with
animals (C and D) has a positive effect on the weed pressure of both annual and vegetative
weeds. There is a tendency for somewhat fewer weed species in the organic cropping systems.
The annual seed weeds scentless mayweed, hemp-nettle and fat-hen have the greatest impact
on yield in all cropping systems. However, there are few problems with annual grass weeds
due to the many spring-sown crops in all cropping systems. At Önnestad, Östra Ljungby and
in cropping system E at Bollerup, weeds in legumes and spring cereals have a greater impact
on yield than weeds in winter cereals and winter rape. Legumes in pure stand cause creeping
thistle and perennial sow-thistle to multiply, while the incidence of couchgrass is greatest in
potato. Co-cropping of legumes and cereals decreases the incidence of vegetative weeds and
annual seed weeds.
After the second round of the crop rotation, great problems have arisen with creeping thistle
and perennial sow-thistle in the organic cropping systems. By altering the cropping strategy
and crop rotations this problem has been greatly reduced. However the results show that when
a cropping strategy is selected to get rid of creeping thistle and perennial sow-thistle, there is a
risk of couchgrass being promoted.
Economics
The calculations show that overall, the organic cropping forms have a higher cost per unit
produced than the conventional, mainly due to lower yield per unit area. In a comparison of
the different trial treatments, the organic treatments have better overall gross margin than the
conventional treatments. The trial treatment with potato and/or sugarbeet has a higher gross
margin than those without these crops.
The trial plots at Önnestad generally have the highest yields, while those at Östra Ljungby
have the lowest. This applies to both the organic and conventional systems.
Research projects
Over the years, these broadly structured and well-documented system trials on different soils
have been used by researchers from different disciplines, in studies of e.g. plant nutrient
matters including leaching, soil structure, soil microbiology, climate studies and
investigations of a range of different quality aspects. The system trials have also been used in
several economic evaluations.