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02.03.2020 - Henning Kage

Prof. Kage criticizes amendment of DüV

Currently - in my view justifiably - but perhaps unexpectedly for many outside the agricultural sector, massive resistance is being voiced by farmers against the plans to amend the Fertilizer Ordinance again. In general terms, the sector still has a clear nitrogen surplus problem; the gross surplus without deducting ammonia losses is still 90 kg N/ha, and only about every second kilogram of nitrogen that enters the farm systems ends up leaving the farms in the form of products. The rest is not only lost unproductively, but also pollutes the climate and the environment at the same time. Although there is a slight trend toward improvement in these figures, this has been significantly weakened in recent years by, among other things, the considerable expansion of the biogas sector financed by all citizens via the EEG levy and the fermentation residues generated therein. Increasing yield fluctuations are also making it more and more difficult to fertilize in line with demand.

So a blanket 20 percent reduction in nitrogen fertilization can't be a bad idea, can it?

No, such an approach is not very effective. Compared with other measures, a blanket reduction in nitrogen fertilization has a poor cost-benefit ratio. It is textbook crop production knowledge that until shortly before the site- and year-specific yield potential is reached, the Nmin residual amounts at harvest and the subsequent nitrogen leaching usually increase only very slightly with increasing fertilization amounts. If indirect land use effects are taken into account, it can also be shown that demand-based nitrogen fertilization is quite close to the climate impact optimum. A strong extensification of production exerts negative climate effects on a global scale through an additional consumption of land, which often overcompensates the local relief. Only if we were to reduce our consumption of feed and food by at least the same amount that is no longer produced in Germany as a result of the upcoming extensification measures would we have done something for the environment.

In my opinion, we do not need blanket extensification and uniform fertilizer rules nationwide, but rather more precision specific to loft, subloft and year on the one hand, and defined upper limits on farm N-balance balances on the other. In recent years, there has been some progress in terms of the knowledge available for more precise fertilization. However, the economic incentive to use this knowledge has often been low. Unfortunately, the 2017 Fertilizer Ordinance was already a step in the wrong direction here. In my view, it was less precise than it could have been with regard to determining nitrogen requirement values. Ultimately, however, rigid requirement values are superfluous if a well-controlled multi-year farm N balance forces the economical use of nitrogen. What is the direction of policy? From an imprecisely defined starting point (DüV 2017), blanket deductions are made and the farm N balance disappears from the regulation for the time being.

Nitrate leaching occurs primarily after harvest in the fall. The accumulation of nitrate takes place through high mineralization rates from the organic soil substance due to nitrogen fertilization that is not in line with requirements or is unnecessary, with a simultaneous lack of nitrogen uptake by a growing plant population. These points can be addressed in a targeted manner, whereby the avoidance or reduction of critical combinations of crop rotation elements (e.g. winter rape/winter wheat, grain legumes/winter wheat corn/maize) and the targeted use of catch crops are important components. Denmark has changed its fertilizer rules away from heavy regulation of fertilizer rates to demanding winter greening targets.

This commentary originally appeared in the 09/2020 newsletter of the German Agricultural Society and can be read here.