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Soil management in Denmark

Soil Management in Denmark

My travels took me to Denmark because the country has a highly developed agriculture research and advisory base and has been at the forefront of organic farming for many years; 10% of the land is now organic and heading quickly for 20%. Driven by the market and government support Denmark now has the largest organic market share in the world. Ambitious farmers and a thriving research sector would bring me up to speed on what is happening with soil management in northern Europe. Environmental protection and enhancement is at the top of the Danish agricultural policy agenda e.g. there is strict control on nitrogen input (140 kgs N/Ha/year).

Key lessons:

  1. Soil and its management is seen as being of fundamental importance

  2. There is a lack of information and inconsistent advice on soil management

  3. Most farms use conventional soil analysis services for pH, P, K and Mg only

  4. There is limited use of alternative soil and plant analysis techniques

  5. Soil structure is an increasing problem on all farms

  6. Research shows that organic rotations are sustainable in the long term and significantly better results than conventional

My time in Denmark was organised and hosted by colleagues at SEGES, the government funded research and advisory centre at Aarhus; they provided great hospitality and an inspiring and wide ranging programme of meetings and visits.

Agroforestry for the poultry

The farm visit to Gothenborg gave me some perspective of organic poultry farming. 32 ha of grassland, wood pasture and some barley, 2,000 finished table birds per week for 6 months of the year and the most exceptional farm shop and marketing based on tremendous quality birds. The meal in the restaurant was one of my most memorable!

SEGES host Erik Fog and that meal!

While the interest in the link between food quality, soil and health was enthusiastically promoted in fact the information that is available to these farmers to develop that principle was very limited. A conventional soil analysis (pH, P, K and Mg) was undertaken every 5 years or so on all the land; there was no requirement to do so by their organic certification body.

Composted poultry manure - covered

The large dairy farm of Mads Helms at Sommerbjerggaard was another matter altogether: 600 ha of clover ley plus 100 ha whole crop, 700 high yielding cows grazing the platform of 250 ha. Again there was a keen interest and focus on soil management, but Mads was very concerned that he was managing with limited and inadequate information and advice, and worse still the advice differed according to the advisor!

Soil management is based on routine analysis every 4 years, a conventional analysis including pH, P, K and Mg. The acid soils require liming to keep them to his relatively low target pH of 5.5 – 6 and the K deficient soils require the use of 300 kg/ha of Kali Vinasse (from sugar beet waste) every 3 or 4 years. Like many organic farms he is debating the importance of sulphur (S) but is probably getting sufficient from the Kali Vinasse. Phosphate levels are stable with no additions. Soil organic matter and biological activity are recognised as important but there is no monitoring on this farm.

Cubicle housing = slurry

The cows are largely cubicle housed so slurry is the main form of manure. Slurry acidifying slurry additives are used, although some form of sugar might do the same job. Application is important; he uses trailing pipes early in the season and slot drilled later, to avoid volatilisation. He supplies all the solid manure from the calf rearing to a Biogas plant and gets the equivalent N returned in the form of digestate. His experiments with wood chip bedded loose housing has shown that it is not suitable for dairy cows.

Compost from wood chip bedding trials

The Mansson farm the largest producer of organic vegetables in Denmark. The operation is vast. Starting as a small-scale poultry producer 40 years ago the business has expanded exponentially as the market has grown, so that now it comprises 1,200 ha, growing mostly vegetables including onions, brassicas and 20 others. The aim is to establish a truly self contained “sustainable” operation, so the poultry have been expanded to 140,000 layers to complement the vegetables and a new 150,000 tonne biogas plant has been installed to take the manure from the poultry, waste vegetables and other local, mainly organic green crop suppliers to provide phytosanitary digestate for the vegetables and energy for the storage and packing operation.

Axel Mansson and Dorrit Andersen have a highly sophisticated growing system for their crops using all the latest technology, however their soil management is relatively less developed. They routinely test all fields every 3 or 4 years, using a conventional analysis fromEurofins for pH, P, K, Mg and a wide range of trace elements. N min soil analysis is undertaken weekly in sensitive crops. There is no information on soil organic matter or on long-term trends in soil nutrients.

They are undertaking routine plant tissue analysis to confirm past management and make any short-term corrections. Interestingly they have done some limited sap analysis (See my Blog, however they have not found that it provides any additional information.

The Mansson digester

There is widespread support for biogas digesters in Denmark, and enthusiastic use of the liquid digestate by farmers and growers. The digestate is a highly soluble form of nutrients, nitrogen in particular, which means that it is easily leached and needs to be applied in controlled quantities to the growing crop. Mansson injects all the digestate.

In Denmark there is general support for the use of human waste in organic farming, unlike in the US. Struvite has received approval by their technical committee although not has not yet been approved at a national or EU standards level, if necessary they see the possibility of a double loop, growing waste treated green manures on uncertified land and applying the green manure or digestate to organic land.

Then Peter Sorenson showed me round Foulum research centre where they run one of the three longest running organic and conventional rotation trials in the world, in association with other sites in Denmark. A very well managed large plot, arable rotation trial, the results over 20 years are now showing some useful results:

  1. Soil phosphate levels after an initial drop in the organic plots have stabilised at levels above the minimum required, probably partly due to the improved mobilisation of reserves under organic management.

  2. Soil organic matter levels in some organic rotations have been maintained, while others have shown a slight decline. Conventional organic matter levels have declined slightly in comparison on some sites

  3. Weeds have been effectively controlled under organic management

  4. Slurry is more effective if it is injected and there is no indication that this is negatively affecting soil life

  5. Their opinion is that conventional pH, P, K, Mg soil analysis is adequate

  6. Organic rotations with 2 years of green manure are at great risk of nitrogen leaching

  7. Over winter cover crops definitely reduce nutrient leaching

  8. Over winter cover crops seem to provide about 70kgs N/Ha, either by fixing N or preventing leaching

  9. 25 cm row width does not reduce cereal yields

  10. Sulphur use is being researched but the results of its use in organic farming are inconsistent

  11. Manure application and the use of one-year green manures increased organic matter levels, unlike digestate, which had no effect.

  12. Organic plots have higher biological activity than conventional.

Over winter cover crop

Soil structure is identified by advisers and researchers as a widespread general problem in Denmark due to water erosion and compaction due to slurry spreading on cereals.

The visit to the farm of Mads Hansen provided a very different perspective as I went in the company of Martin Beck, an organic adviser who has specialised in the use of Albrecht soil analysis, having trained with some of the US advisers that I met previously. The small 25 ha organic farm is growing a range of crops in the field and in tunnels, notably strawberries, asparagus and early potatoes.

As we have seen in the US the recommendations arising out of Albrecht analysis really are very different; not only is there an aim to get a wide range of nutrients up to a minimum level but there is also a longer term objective to get the cations balanced in the correct ratio of 68% Calcium, 12% Magnesium and 3 – 5 % Potassium. The aim of this is support the biological activity to ensure macro and micro nutrient supply to the plant. Incidentally Martin is against injecting slurry or digestate due to the impact on soil life.

The consequence of this approach at Mads farm is for much higher levels of mineral fertiliser inputs than would be the consequence of following conventional analyses on an organic farm. He is routinely using calcium, partly to improve crop quality and inoculants are used to control iron levels to achieve an optimum manganese:iron ration of 1:2. Trace elements such as Boron and Copper are used, applying them to catch crops rather than to bare soil to encourage them to be incorporated in a biological form. The crop is monitored using sap analysis rather than tissue analysis as this gives a better indication of what is currently available to the plant, and foliar sprays used as needed.

Over winter cover

There remain unanswered questions about Albrecht; the research and expertise always leads back to a small group of enthusiastic exponents , mainly in the US but also in Australia and isolated individuals elsewhere.

Ultimately the question is – is the Albrecht approach cost effective? While there are clearly farmers who are convinced I am still looking for the evidence. Further information is available from a literature review that I was involved with at the Organic Research Centre

My final day was spent with the team at SEGES, including Erik Fog, Sven Hermansen, Tove Mariegaard Pedersen and Anette Vibke Vestergaard. The discussion ranged around soil management and farming in Denmark.

There is strong support for Biogas digesters and the use of digestate on farms; it recycles green waste, creates a phytosanitary product, particularly from animal manures, it may be an effective use of rotational clover leys and of course it generates electricity. The advisers’ view is that it is a very useful fertiliser but that it needs to be used carefully. Injection has the advantage of reducing ammonia emissions and maximising uptake into the crop as it places the nutrients within easy reach of the roots. While some argue that there may be damage to soil life others claim that soil life is very resilient. There does seem to be a greater risk of any weed seeds in slurry germinating, but I would have though that there were no viable seeds in digestate.

Other comments:

  1. In Denmark there is rarely a response from trace elements hence no trace element analysis

  2. Very few conventional or organic farmers are analysing soil organic matter

  3. There is uncertainty about the best analytical techniques for organic matter, humus, effective carbon or stable carbon

  4. The Dexter Index (clay/carbon ratio) is being used at research level to assess carbon depletion in Denmark

  5. pH and calcium is widely too low

  6. Catch crops are particularly important for improving P availability

  7. Organic cereal yields are 60-70% of conventional yields, which is higher than in the UK. This is considered to be particularly due to the use of slurry or digestate injected or trailed pre spring crops and in growing winter crops.

  8. There is a reluctance amongst some organic farmers to actively manage their soils – “being organic is enough”.

  9. There are research needs in Albrecht and organic matter analysis, soil health and soil biology.

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