Can Germany cut the nitrogen fertilization rate by 20%

Wheat is widely grown than any other staple food crop (see map below) in the world. Nearly, US $50 billion worth of wheat is traded globally, each year. Among others, Germany is one of the champions Wheat growing countries – the world’s 6th important wheat-growing nation.

Figure 1 Global wheat cultivation areas – darker colors indicate areas where more wheat is grown). Image source: https://wheat.org/wheat-in-the-world/.

Nowadays, in Germany, almost half of the input cost of growing wheat is the fertilizer cost and a great share of it is nitrogen fertilizer cost. According to FAO, global nitrogen fertilizer use in agriculture is increasing by 2% every year but in Germany, due to stricter fertilizer regulation, the fertilization rate is decreasing. German fertilizer regulation that was introduced in 2017, aims to cut fertilizer usages by 20%, which puts massive pressure on farmers as they must make lots of effort to comply with the regulation.

Figure 2 German wheat cultivation areas, yield, and nitrogen fertilizer usages.

As the global population is increasing, we simply cannot reduce the fertilizer input at a cost of compromising yield. So, the key question is, can the farmers cut their fertilization input by 20% in Germany and still grow the same amount of food? Let’s find it out.

Methodology for regional Nitrogen uptake, demand, and surplus estimation: In Hessen, there are about 160,000 hectares of wheat cultivated land, which is about 5% of the total wheat-growing areas in Germany. We have selected all the wheat fields, which are more than 1 hectare to avoid mixed-pixel values from our analysis and that sums up to 136,000 hectares. These numbers are constant for the years 2017 – 2019. The reason, why we have chosen these three years is because there was one drought year (2018) and two average years.

Figure 3 Winter Wheat Nitrogen Uptake (end of stem elongation) for the year 2018 (drought year) and 2019(average year)

We have used Sentinel-2 satellite imagery to estimate the Nitrogen uptake and Dry Matter and finally have calculated the Nitrogen Demand to assess if the wheat fields were undersupplied with Nitrogen or not. In Germany, the fertilization rate is already better optimized than in many other countries. So, as expected the Nitrogen Demand of wheat crop, at the growth stages steam elongation to Anthesis was “Zero” for all three years. An interesting thing to observe here is that the Nitrogen Uptake of most of the fields in 2018 was relatively lower than in 2019 but the Nitrogen demand was still “Zero”. The reason is that the plant growth was limited due to water shortage in 2018 and thus the Nitrogen demand was also lower. But the average farmers in Germany have applied the full Nitrogen rate in 2018, which they usually also apply in the average years (178 N kg/ha). So, the Nitrogen loss in 2018 was greater. The loss (N surplus) of N is summarized for Hessen, in the table below.

Figure 4 N uptake by crops, N removal by grain yield, and N surplus estimation for the years 2017 - 2019

Findings: First, the drought impact on plant growth thus nitrogen uptake was obvious (10% less nitrogen uptake for the year 2018). Moreover, we also can observe that there is a high correlation between the nitrogen uptake and yield, which is also expected.

We also have calculated the N removal based on the yield and thus estimated the N surplus. According to various studies, the optimistic estimation of the Nitrogen use efficiency (NUE, which is the total N outputs divided by total N inputs) for Germany is 61%. In our study, we also have found that in Hessen the NUE for the wheat crop is 61% (excluding the draught year 2018).

In 2020, we also have conducted a pilot with 23 farmers in Germany. The average wheat yield of the pilot farmers was 8.2 t/ha, and the average fertilization rate was 178 kg/ha. According to our estimation, the fertilization rate should have been 142 kg/ha, which is about 30% less than the rate that the farmers have applied (More details about our pilot study can be found here). And according to this case study on all the wheat fields of Hessen, we also can see that the average N surplus in Hessen is about 38%, which is also coherent with our pilot study result.

Conclusion: Based on these findings, we can confidently say that it is possible to cut the Nitrogen fertilization rate by 20%, without compromising the wheat yield in Germany. And this is the right thing to do because the wheat yield gap in Germany is about 10 – 15 %, which means trying to increase yield does not make much sense. But to be able to cut the fertilization rate by 20%, farmers need better insights on their crop Nitrogen uptake and Nitrogen Demand so that they can split and adjust the fertilization rates over 2-3 nitrogen applications, as the season progresses. Moreover, It is critical that the farmers are fertilizing their field 2-3 times with the right type of fertilizer otherwise the fertilization optimization might not be that effective. Whatever it is, the way you tell your story online can make all the difference.