Summary

Nedfældning af gylle i vintersæd - En evalueringsrapport

In connection with the political agreement between the government, the Danish People's party and the Danish Social-Liberal Party from June 22, 2006, an agreement on regulation of the demands for application of manure was made. One of the demands of the agreement was that animal slurry shall be injected when applied to un-cropped land and to grass fields situated in buffer zones near vulnerable natural resorts. Besides from 2011 all slurry applied to un-cropped land and grass land should be injected. In connection with the evaluation of the Danish Water Environmental Plan (VMP III) in 2008 the agreements’ parties evaluate when similar demands for injection of slurry in winter cereals can be requested. In the light of the above-mentioned, this report provides an evaluation of the technological and financial impact, if the demands for injection of animal slurry are expanded to include injection in winter cereals. Included in that is a professional assessment of the operational, environmental and economic effects by requiring injection of animal slurry into winter cereals.

While an increasing share of the liquid manure in Denmark is injected into un-cropped land and grass, slurry injection in winter cereals does almost not take place. The explanation seems to be that slurry injection to winter cereals causes a line of disadvantages of which the most important are: Application leads to higher application costs and loss of yield due to additional wheel tracks and crop damages caused by the injection devices. The reason for the loss of yield is primarily that injection leads to additional wheel tracks in the field. This is caused by the fact that the working width of injection systems is considerably smaller than the working width of trailing hose application systems. Moreover injection of slurry may increases risks of slurry runoff in hilly areas, and may increases the risk of damage on harvesting machinery on stony areas as well as being problematic when it comes to injection into heavy clay soil.

The injection systems, which today are commercial available for injection into cereal crops are in general developed for injection into grassland. No tests have so far been made about how effective these injection systems abate ammonia emission when used for injection of slurry into winter cereals. However, in the light of tests of the effect of injection in grass land regarding the abatement of ammonia emission, it is estimated that injection in winter cereals may reduce the emission of ammonia from the applied slurry by between 40 and 50 % in comparison with trailing hose application. A general extension of the injection demand to include winter cereals equals a possible limitation of Denmark’s total emission of ammonia by 3,000 tons per year, which again corresponds to 4.2 % of the national ammonia emission. However, as injection increases the energy consumption and the risk of emission of the greenhouse gas nitrous oxide, it is estimated that a general extension of the demands of injection to winter cereals will increase the emission of CO₂ with 294,000 tons per year which corresponds to about 0.5 % of Denmark’s total emission of greenhouse gases.

The lower ammonia emission can increase the nitrogen use of manure with 5-7 %, if it is assumed that the injection does not increase additional wheel track damages. In practice – if the wheel track damages are included – injection will hardly lead to an increased utilization of applied slurry nitrogen.

Injection performed by the systems commercial available today means that the slurry is applied into open furrows, which imply that that the slurry after injection, is still in contact with the atmospheric air. Therefore, injection in winter cereals has a limited effect on obnoxious smells. To ensure an efficient reduction of obnoxious smells all slurry has to be covered with soil.

As previous mentioned injection in winter cereals may lead to a loss of yield. The loss of yield depends on the injection technique and application circumstances, but is according to tests with test equipment and commercial equipment determined to be in an interval between 0.2 and 3.6 kilo per ha, which corresponds to 3.8-63 Euro per ha. On this basis it is estimated that injection in winter cereals in average leads to a yield loss on 1.8 kilo per ha, which corresponds to 34 Euro per ha. Injection of slurry to winter cereals moreover increases the costs of slurry application. The higher costs are primarily due to higher operating and investment costs, lower utilization of application capacity, and loss of yield.

Injection requires better weather and soil conditions than trailing hose application. Therefore, a wet spring can complicate or even prevent injection to winter cereals. The numbers of application days are considerable fewer if slurry application to winter cereals has to take place by injection compared to by trailing hose application, which fundamentally reduces the capacity use of injectors.

It is estimated that a general demand on injection in winter cereals will cost the agriculture additional 40 million Euros yearly. If the yearly additional costs are recalculated to costs per kilo saved ammonia emitted nitrogen loss, concerning a general demand on injection into winter cereals, this corresponds to 13 Euro per kilo saved nitrogen.

Should injection only be demanded in winter cereals situated in buffer zones I and II (0-1,000 m), the yearly additional cost is 9.5 million Euros nationwide, assuming that the additional cost per ton will be the same as if the demand is introduced in general. However, the capacity use could be increased which causes a lower additional cost per quantity of slurry applied. It is therefore estimated that the yearly additional cost in relation to a demand for injection in buffer zones will be around 6.8-9.5 million Euro.

Winter wheat is the most widespread type of winter cereals and winter wheat is the crop which has the longest period of application in the spring. Therefore, winter wheat is the type of winter cereals which has the best opportunity for injection in a suitable drained soil. The other types of winter crops, especially rye, winter rape and triticale have due their early growth such an early application period that the ground is normally impassable when it comes to injection machinery.

Since 2006 several initiatives have been started in order to develop injection systems suited for injection into winter cereals. The new systems seek to limit the costs of injection and to ensure a more efficient reduction of the environmental impacts of slurry application. However, the development is still at such an early stage that the environmental effects and costs of these technologies not yet can be evaluated.

The type and an eventual pre-treatment of slurry affect the environmental impacts of injection. The highest effect of injection is related to slurry types with a high potential of ammonia loss. Slurry treatment technologies like solid-liquid separation and slurry acidification abate ammonia volatilization, and these technologies have just as high or even higher ammonia limiting effect as injection. It should be considered to compare these technologies with injection.

It is estimated that the present demand on injection into un-cropped land and grass situated inside the buffer zones has not lead to serious operational problems. However, the temporary experiences show that injection in grass in early spring increases the risk of damaging soil structure and crop. An opportunity for exemption concerning the demand of injection in hilly areas should be possible in order to limit the risk of slurry runoff. It is also estimated that the environmental advantages of injection in grass on dry clayey soils are very limited, as the hard soil prevents a sufficient efficient injection.

A high share of the slurry applied to un-cropped soil is today injected. It is not estimated that there is a need for any reservations when it comes to injection of slurry to spring crops. If slurry is to be applied to spring crops, the slurry can usually be injected before sowing.