Optimizing nitrogen fertilization in ley : Evaluating the usage of N-sensor and other tools for optimized nitrogen fertilization

Sammanfattning: Nitrogen is an essential nutrient for plant growth. It has several functions in the plant and a lack of nitrogen can cause severe yield losses. Because of this nitrogen fertilization is important in modern agriculture, but as nitrogen prices are increasing and the fact that nitrogen leakage has a negative effect on the environment, optimizing the fertilization becomes important. Different tools can be used to optimize nitrogen fertilization. With a N-sensor the reflected light from plants is measured and based on this information the nitrogen uptake (SN value) can be calculated. Other tools for optimization are unfertilized and over optimal fertilized areas. An unfertilized area in the field can show how much nitrogen the soil can provide to the plant. An over-optimal fertilized area in the field can tell how high the plant’s potential nitrogen uptake in the field is. The aim of this thesis was to study the usage of these tools in ley and suggest recommendations for field optimized nitrogen fertilization in ley. To study this, field trials with a system of 5-6 fertilization treatments without replicates were established on farms in Halland 2021 and 2022 and in Kalmar 2022. Included treatments were, 1. No added nitrogen, 2. Only slurry added, 3. Only mineral fertilizers added, 4. The farm’s normal nitrogen fertilization and 5+6. Addition of nitrogen non-limiting for plant growth. The plots were measured with a Yara N-sensor and samples were cut for N-analysis at up to 4 occasions during the cropping season, with the last measurement being performed at harvest. The results showed that the Yara N-sensor overall underestimated the nitrogen uptake in ley one week before harvest and at harvest. In the unfertilized area there was a linear correlation between the SN value and the result from the N-analysis whereas in the Farm’s fertilization and in the plots where nitrogen was unlimiting there were no linear correlation. This indicates that the sensor algorithm for ley need to be adjusted for Swedish leys. The nitrogen uptake at harvest in the unfertilized area differed between the regions with significant differences between Halland 2022 and Kalmar 2022. There were also differences between farms within the regions. This is in line with previous studies which have shown that the soil delivery of nitrogen can differ between fields. Another explanation for the differences in nitrogen uptake was different proportion of legumes in the leys. There was overall no significant difference between the Farm’s fertilization and the treatment with extra nitrogen added for nitrogen uptake, dry matter yield or crude protein content between the regions. It was possible to see differences between farms within the regions which indicates that the potential nitrogen uptake differs at different fields. The nitrogen efficiency in the different treatments were estimated and differed, both within and between the regions. By knowing the soil delivery of nitrogen, the nitrogen efficiency of the fertilizers and how high the potential nitrogen uptake is, it could be possible to better plan for future nitrogen fertilizations in ley. Keywords: nitrogen efficiency, optimized fertilization, SN value, unfertilized area, Yara N-sensor