Though a precise comparison cannot be made, the results suggest that four of the seven cash crops have produced yields at a level which we would normally expect to find in similar conventional crops, and no crops have shown really low yields. Thus, the crop rotation has for the first few years shown that good yields could be obtained by the methods used, without adding any nitrogen from other sources.
The yearly N removal with the harvested crop parts has been approximately 70 kg N ha-1, and there
have been other N losses from the system. To avoid N depletion of the soil, this requires a high N fixation from the legumes in the crop rotation, and a very efficient use of the N, which is fixed. On the other hand, a build up of organic N could be expected due to the extensive crop cover, and the large amounts of plant matter returned to the soil. The results from the coming years will show whether the
system is becoming N depleted, the yield level can be maintained, or build up of organic N will occur, and an increased N export is found.
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Crop yields from three organic farm
systems at Rugballegaard
F. Oudshoorn1 and I.S. Kristensen2
Danish Institute of Agricultural Sciences
1 Research Centre Bygholm, Rugballegaard, P.O. Box 536, DK-8700 Horsens
2 Department of Agricultural Systems, P.O. Box 50, DK-8830 Tjele
Summary
To meet the demands of knowledge on organic pig production and milk production and the demand for better understanding of the factors affecting the nutrient surplus and utilisation at organic farms, three organic systems were set up at Rugballegaard: a dairy system, a pig system and a mixed system with both cows and pigs. The rotations were designed according to the available knowledge on nutrient flow, and the management is constantly kept in touch with the development of guidelines for organic farming in Denmark and EU.
The dairy system allows for a feed import of 10% (based on energy), and a rotation consisting of 60% grass-clover, which should make it possible to maintain 1.1 LU ha-1. The pig system has a feed import of 25% (based on energy), a manure import of 45 kg N ha-1, and a rotation consisting of 20% of grass- clover, which should be able to maintain 0.7 LU ha-1. The mixed system for dairy and pigs allows a feed import of 15% (based on energy) and a rotation consisting of 40% grass-clover, which should be able to maintain 1.0 LU ha-1.
These livestock rates were established in 1996. The livestock rate, the percentage of grass-clover in the rotation and the import of feed will be kept constant until 2000.
For the first two registered years, average dry matter yields of 58 hkg ha-1 from the dairy system, 43 hkg ha-1 from the pig system and 68 hkg ha-1 from the mixed system were obtained. Due to the different agricultural management (the period before establishment) of the areas involved and the heterogeneous soil type of the three large-scale rotation systems, the harvest levels cannot be compared. If an average on cereals only, were calculated, the pig system would be doing surprisingly well, especially when the somewhat poor soil and the low percentage of grass swards in the rotation system are considered.
Introduction
Systematic registrations over eight years in Denmark on a number of organic farms have shown that organic dairy farms and mixed farms had a nitrogen surplus of 124 kg N ha-1 yr-1. Arable farms showed a lower surplus of about 83 kg N ha-1 yr-1. Although the total nutrient balance especially indicated a surplus of nitrogen, the individual crops often showed clear signs of deficiency. This suggests that there might be ways to increase the efficiency of nutrient use (Kristensen, 1997). The total amount of nutrients entering and leaving the system is relatively easy to measure. However, the nutrient flow through the context of animal digestion and crop production is a different issue. The situation is especially complex because there may be differences between the organic and the conventional systems,
and because the nutrient flow in itself will be influenced by the livestock density (LU ha-1) (LU is livestock units). Also, it will be very important to quantify the gaseous losses of nitrogen. This includes losses due to evaporation of nitrogen from the soil, from manure while in the livestock buildings, during storage or during application on the field (Møller & Andersen, 1999). Different feeding components that change the ammonium content in the manure or the design of the building (deep litter or slurry) may also influence the nutrient flow (Kyllingsbæk et al., 1997). All these elements will, of course, be dependent on the system used, but also very much on the climate and the management. To match the long-term goals, nutrient flows are measured and modelled at the organic research station of Rugballegaard. Unlike the organic pilot farms observed up till now, the three systems established on Rugballegaard are closely supervised by the scientists involved, and they are constantly being developed to match the latest comprehension of nutrient management and flow. The mechanisation of the farms is modern, but not specially designed or atypical. This means that the results obtained at Rugballegaard can be used directly in practice. Also, the scale of the farm systems is comparable to normal size farm systems. Therefore, the energy flow, the use of resources (labour, nutrients) and other agronomic factors can in general be used in the development of organic farming. The objective is not to compare and evaluate the systems, but to understand and develop them.
Materials and methods
In 1996, three crop rotations representing different farming systems were established on an area of 140 ha (Table 1). The area had previously been used for production of roughage for a herd of 200 milking cows. The upper 0-25 cm soil layer is rather heterogeneous. The humus content varies from 3.6 to 6%, and the clay content varies from 5 (coarse sand with clay) to 22% (clay). The average clay content is 11.2% (sandy loam).
Table 1 Characteristics of the three systems at Rugballegaard.
System Area with grass-clover (%) Cereals Feed import1) % Livestock density 2) (LU ha-1) Manure import (kg N ha-1) Total area (ha) Dairy 60 40 10 1.1 0 34.9 Pigs 20 80 25 0.7 45 30.9 Dairy/pigs 40 60 15 1.0 0 71.0
1) Feed import calculated as Scandinavian Feed Units (SFU).
2 1 livestock unit (LU) is equivalent to one 550 kg dairy cow or one sow with 20 pigs.
The dairy crop rotation is as follows, with field 5 split into two sub-fields: 1 Spring barley with undersown grass-clover.
2 Grass-clover 1st year 3 Grass-clover 2nd year 4 Grass-clover 3rd year
5.1*) Spring oats with undersown rye grass 5.2 Winter wheat
The pig crop rotation is as follows with fields 3 and 4 split into two sub-fields: 1 Spring barley with undersown grass-clover
2 Grass-clover 1st year
3.1 Spring oats with undersown rye grass 3.2 Winter wheat
4.1 Winter wheat
4.2 Spring oats with undersown rye grass
5 Spring barley/peas with undersown rye grass
The mixed dairy/pig crop rotation is as follows with fields 4 and 5 split into two sub-fields: 1 Spring barley/peas with undersown grass-clover
2 Grass-clover 1st year 3 Grass-clover 2nd year
4.1 Spring oats with undersown rye grass 4.2 Winter wheat
5.1 Winter wheat 5.2 Fodder sugar beets
The crop rotation on most organic dairy farms in Denmark has 40-60% of grass-clover. Generally, the farms import 15% of the total SFU (Scandinavian Feed Units) demanded. The animal density is in accordance with the Danish organic guidelines, i.e. max. 1.4 LU ha-1 (Kyed & Jensen, 1996).
The slaughter pigs on the organic farm are kept in livestock buildings. The cows graze on grass-clover during the summer for at least 150 days a year, approximately 110 days of which they graze both day and night. The sows are all kept outside in areas with huts (steel plated, insulated). All animals are kept according to the Danish organic rules (Plant Directorate, 1995, 1997, 1999). All spring crops are drilled after ploughing in the spring when the soil is ready. Just before ploughing, the manure (solid or slurry) is applied. The solid manure is ploughed in immediately, whereas for slurry the soil is first harrowed (before 6 hours) and afterwards ploughed. When slurry is applied during the growing season, the soil is harrowed with a tine weeder (Einböck). In the present investigation, all slurry was applied with a 15 t slurry spreader with a spreading width of 12 m and with trailed hoses mounted at intervals of 30 cm. The slurry was sampled for registration of total nitrogen, ammonia nitrogen, K, P and dry matter contents. The amounts applied were registered both by measuring the volume stored in the slurry tank and the weight of the slurry applied. The winter wheat was drilled relatively late, i.e. in the period of 1- 20 October. No manuring was done in the autumn. Manuring of the spring sown fodder beets was done in combination with ploughing in the winter.
Mechanical weed control was primarily done by harrowing with a tine weeder (Einböch), and in fodder beets the weed control consisted of hoeing, harrowing and manual hoeing. The amount of grain drilled per m2 exceeded the normally recommended amount by 20% for fields where large problems with weeds were expected. The drilling was performed at a distance of 24 cm, thereby allowing mechanical hoeing.
The distribution of the slurry and deep-litter manure available was done according to common extension guidelines for organic crop requirements. The grass-clover leys were primarily manured when predestined to silage cutting. Grass-clover fields for grazing were given low priority.
Registration on fields
A systematised registration according to the project "pilot farms" (Kristensen, 1989) was followed at Rugballegaard. The soil was analysed for K, P and Mg contents, and occasionally the N-min content
was analysed, as well. The pH was observed, and Mg-CaCO3 was applied, when necessary. All products harvested on the experimental research station were weighed and analysed for contents of N, P, K and dry matter.
All herd fluctuations were noted, including the grazing periods and the location. The amounts of grass- clover consumed by the grazing cows and sows were calculated as a difference between the feeding standard according to growth or the milking yield and the amount of roughage fed simultaneously. By use of the grazing periods and the location, the amount of grass-clover consumed by grazing animals was calculated. All meat and other animal products leaving Rugballegaard were weighed.
Results
For the first two registered years, average dry matter yields of 58 hkg ha-1 from the dairy system, 43 hkg ha-1 from the pig system and 68 hkg ha-1 from the mixed system were obtained (Table 2). Due to the different agricultural management (the period before establishment) of the areas involved and the heterogeneous soil type of the three large-scale rotation systems, the harvest levels cannot be compared.
The average dry matter yield is a sum of the cereals harvested and the roughage harvested and consumed by the grazing herds belonging to the three systems. Due to the fact that pigs do not digest roughage as efficiently as cows and that the amount of dry matter obtained from roughage crops is considerably higher than from cereal crops, the pig system shows low average yields (Table 3). If, however, an average on cereals only, were calculated, the pig system would be doing surprisingly well, especially when the somewhat poor soil and the low percentage of grass swards in the rotation system are considered.
The total amount of nitrogen available for the crops was quite different for the different systems (Table 4). The low livestock rate in the pig system and the low percentage of leguminous plants resulted in an uptake of only 107 kg N ha-1, whereas an uptake of 176 kg N-1 ha-1 was calculated in the dairy system shows and a content of 134 kg N ha-1 was calculated for the mixed system.
The mixed system has a very efficient production, considering the moderate availability of nitrogen and the rather high production of dry matter (Table 2).
The dry matter yields indicate that there is a lower dry matter production in the pig system. If the cereal dry matter yield is isolated, the opposite will be seen (Table 2). Especially in winter wheat yields the pig system will show a relatively high production (Table 3), considering that the system is situated on the sandy areas of the research station.
It seems that the average yield of roughage obtained at the organic research station is higher than the average yield obtained in practise (Table 5). However, the yields obtained at Rugballegaard were only partially net yields (only grazing). The net amount of silage roughage is not yet known. Losses may easily turn out to exceed 25% of the total material.
Table 2 Yields in dry matter (hkg ha1) for the three systems. The straw yield is not included, because some crops are chopped and not weighed.
Estimated 1997 1998 Dairy system Cereals 34 35 35 Roughage 74 86 74 Average 64 56 59 Pig system Cereals 31 41 + 0.34) 40 Roughage1 42 622) 21 Average 34 49 36 Mixed system Cereals 31 43 + 1.5 36 Roughage 74 83 83 Average 54 713) 65
1) In the pig system the lactating sows use 40% of the grass-clover for grazing, assuming that there is no net use of grass-clover. Of the remaining 60%, only 40% is used as silage.
2) In 1997 the area with grass-clover was twice as large as in 1998, and therefore more grass-clover was used for silage.
3) In the first year of the rotation system an additional 7 ha extra of grass-clover was included. 4) Only some of the spring cereals with undersown grass-clover are used for grazing or cutting after
the harvest, depending on the need of fodder. The grass-clover and the rye grass are cut short before the winter. The material is left on the field as green manure.
Table 3 Yields in dry matter (hkg ha-1) by crop.
Estimated 1997 1998 Dairy system Spring cereals 34 35 33 Winter cereals 43 41 Grass-clover 78 86 74 Pig system Spring cereals 30 44 + 31 41 Winter cereals 34 53 49 Grass-clover 34 62 21 Mixed system Spring cereals 30 44 + 3 41 Winter cereals 36 39 43 Grass-clover 78 82 84
Fodder sugar beets 106 114 115
Wholecrop cereals 52 72 + 2 63
Table 4 Calculated annual nitrogen application (Kristensen & Kristensen, 1997) (kg N ha-1).
Dairy Pigs Mixed
Net excretion by grazing animals 38 30 42
Applied manure 88 98* 67
Estimated available manure N to crop 49 47 32
Estimated fixation by clover and peas 89 30 60
Total 176 107 134
* Including imported 45 kg N ha-1
Table 5 Cereal and roughage net yields (used for fodder or sold) at organic dairy pilot-farms 1989- 92(Kristensen, 1997).
Crop Net yield (hkg DM ha-1)
Spring barley 28 + 4
Winter wheat 42
Grass-clover 75
Fodder beets 105
Whole crop cereals 49+6