Speaker
Description
1. Introduction
Climate change and the overloaded nitrogen (N) cycle are among the greatest challenges in agriculture (Rockström et al., 2009). Therefore, crop production must increasingly focus on environmental and climate impacts. Legume-based cropping systems are known to be particularly environmentally friendly and have several benefits for farmers and the environment (Zander et al., 2016). Through biological N fixation, mineral N fertilizers can be saved and thus the greenhouse gas balance of crop rotations can be improved (Nemecek et al., 2008). However, there is limited knowledge about the agronomic and environmental effects of legumes under Central European conditions, and in particular climate-relevant nitrous oxide emissions have rarely been investigated (Binacchi et al., 2023).
2. Materials, methods
For this reason, two similar field trials were set up in the north (Kiel) and south (Munich) of Germany in 2022/2023 as part of the “ISLAND” research project to analyze the processes in the N cycle of legume-based cropping systems. In the field trial in southern Germany, the pre-crop effect of soybean and a grass-legume mixture is compared with non-fixing reference crops (spring wheat without and with N fertilization, field grass). In the following year, winter wheat is grown and fertilized with five N rates ranging from 0 to 320 kg per ha. The investigations comprise soil and plant analyses, including yield formation, estimation of N fixation, measurement of soil N dynamics and nitrous oxide emissions, multispectral reflectance measurements as well as root investigations and greenhouse gas balances.
3. Results
The results of the first year show that soybeans can achieve a high grain yield of 4.7 Mg per ha at this site. The spring wheat fertilized with 160 kg N per ha produced a grain yield of 6.7 Mg per ha, which was significantly higher than the unfertilized spring wheat with a yield of only 3.1 Mg per ha. At 16.9 Mg per ha, the dry matter yield of the grass-legume mixture was considerably higher than that of the unfertilized field grass at 7.1 Mg per ha. Fertilized spring wheat had the highest direct cumulative nitrous oxide emissions of 2.09 kg per ha within eight months and the highest soil mineral N stocks in autumn. The nitrous oxide emissions from spring wheat are primarily due to high post-harvest emissions and less to N fertilization. In contrast, the grass-legume mixture and the field grass had extremely low nitrous oxide emissions of 0.03 and -0.06 kg per ha respectively. Nitrous oxide emissions from soybeans were intermediate at 1.39 kg per ha, with the highest fluxes occurring in June and July and in the fall after sowing winter wheat.
4. Discussion
The results indicate that spring wheat has the highest N loss potential in the form of nitrous oxide emissions and nitrate leaching. Interestingly, the grass-legume mixture had very low nitrous oxide emissions despite high dry matter yield, suggesting that biological N fixation per se does not stimulate nitrous oxide production. However, to make a complete assessment of the environmental and climate impact, multi-year data from multiple sites is required. Additionally, the effect on the subsequent crop must be taken into account.
5. References
Binacchi, F., Niether, W., Brock, C., Knebl, L., Brændholt, A., Wolf, B., Gattinger, A., 2023. Demystifying the agronomic and environmental N performance of grain legumes across contrasting soil textures of central Germany. Agric. Ecosyst. Environ. 356, 108645. https://doi.org/10.1016/j.agee.2023.108645.
Nemecek, T., von Richthofen, J.-S., Dubois, G., Casta, P., Charles, R., Pahl, H., 2008. Environmental impacts of introducing grain legumes into European crop rotations. Eur. J. Agron. 28, 380–393. https://doi.org/10.1016/j.eja.2007.11.004.
Rockström, J., Steffen, W., Noone, K., Persson, Å., Chapin, F.S., Lambin, E.F., Lenton, T.M., Scheffer, M., Folke, C., Schellnhuber, H.J., Nykvist, B., de Wit, C.A., Hughes, T., van der Leeuw, S., Rodhe, H., Sörlin, S., Snyder, P.K., Costanza, R., Svedin, U., Falkenmark, M., Karlberg, L., Corell, R.W., Fabry, V.J., Hansen, J., Walker, B., Liverman, D., Richardson, K., Crutzen, P., Foley, J.A., 2009. A safe operating space for humanity. Nature 461, 472–475. https://doi.org/10.1038/461472a.
Zander, P., Amjath-Babu, T.S., Preissel, S., Reckling, M., Bues, A., Schläfke, N., Kuhlman, T., Bachinger, J., Uthes, S., Stoddard, F., Murphy-Bokern, D., Watson, C., 2016. Grain legume decline and potential recovery in European agriculture: a review. Agron. Sustain. Dev. 36, 26. https://doi.org/10.1007/s13593-016-0365-y.
| Keywords | pulses; pre-crop effect; nitrous oxide; GHG emissions; nitrogen losses |
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