Influence of slurry application technique on yield and nitrogen flows in grassland

Measurement series carried out in Switzerland during different seasons as well as an overview of the literature show that with the use of a trailing hose spreader or trailing shoe spreader, 2–3 kg more nitrogen per hectare ends up in the soil per instance of slurry-spreading than with a broadcast spreader, owing to the escape of 30−50 % less ammonia. In a two-and-a-half-year field trial, no difference was noted in yield on the first site between slurry application by trailing hose and broadcast application. By contrast, dilution of the slurry led to an increase in yield. On the second site where this trial was conducted, total yield tended to be higher with trailing hose application than with broadcast application (p = 0.063). A summary analysis of Swiss and European trials of slurry application techniques shows average additional yields for grassland stands of 2.5 % with trailing hose applications and 5.8 % with trailing shoe applications compared to broadcast applications. The current state of knowledge concerning the losses of the nitrogen which additionally enters the soil thanks to the emission- mitigation application technologies remains very patchy. To the best of our current knowledge, leaching and denitrification losses do not increase to such a great extent that a reduction in the yield effect of the applied nitrogen is to be expected. The way in which slurry-spreading technologies influence the dynamics of organic nitrogen in the soil remains wholly unexplored at present.