The Umkreis project in detail
Practical research companies
Naturland Hof Weber
Gut Marienborn
Richerode
Gut Mönchshof
Weidehof
HofCapelle
Lettcheshof
Buchwald
Quellwiesenhof
Wiesenhof
Hofgut Habitzheim
Research partners
University of Kassel
Consulting
Project duration
June 2022 to September 2025
Nitrogen is a limited commodity in organic farming due to the restrictions of the EU Organic Farming Regulation and the various association guidelines. Due to the ban on the use of chemically synthesized mineral nitrogen fertilizers as well as the limitation on the purchase of organic fertilizers and a limited livestock density, organic farmers are forced to bring nitrogen into the agricultural system through various management measures, such as a diverse crop rotation and the use of legumes, and to protect it from various sources of loss.
The UMKREIS project focuses on intercroppingand the associated effects on the nitrogen cycle. The investigations carried out are intended to help optimize the management strategies of intercropping with regard to the temporal dynamics of nitrogen release and thus potential nitrogen losses and nitrogen fixation in the microbial biomass of the soil, thus keeping nitrogen in the agricultural system and making it available for the subsequent crop at the optimum time. This can lead to an increase in yields of the subsequent crop due to a higher, directly available amount of nitrogen, resulting in economic benefits for the farmers involved. In addition, optimized management practices of intercropping can increase the ecosystem services of organic farming by reducing nitrogen losses to the environment. By disseminating the results through various channels, third parties (farmers not involved in the project) should also be able to achieve economic benefits for their farm and environmental services by implementing optimized management measures.
Background
The cultivation of catch crops provides a variety of benefits: Nitrogen that remains in the soil after the harvest of the main crop is absorbed into the shoot mass of the catch crop and thus effectively protected from leaching during the winter leachate period. The soil is covered and thus protected from erosion. Crop rotation is diversified, soil life is promoted and root residues and carbon released in the rhizosphere contribute to humus formation. In organic farming, weed suppression and nitrogen fixation of leguminous catch crops are further important benefits of catch crop cultivation (Federal Office for Agriculture and Food 2018).
The potential of catch crops to reduce nitrogen leaching with seepage water is widely accepted in science and practice. However, there are still many questions regarding the effectiveness of catch crops as a source of nitrogen for the subsequent crop (Sieling 2019).
In practice, despite lush catch crop stands before winter, only low mineralization rates are often observed in spring (Stumm 2021b). As a result, so-called secondary leaching losses can occur later in the more moderate winters after the catch crop with a narrow C/N ratio dies and loses leaves (Bergkvist et al. 2011). In contrast, species with a wide C/N ratio can cause short-term nitrogen immobilization after incorporation through a C/N barrier in the soil (Schliesser et al. 2010).
Both secondary leaching and immobilization can lead to low or even negative effects on nitrogen availability for the subsequent crop in spring. (Schliesser et al. 2010).
Further studies have shown that non-legume catch crops do not increase or even reduce the yield of the subsequent crop compared to a control without catch crops. The nitrogen released from the residues of catch crops can therefore only be used insufficiently, at least by the first subsequent crop (Stumm 2021a)
Furthermore, it was shown that freezing catch crops promote both secondary nitrate leaching and gaseous losses through nitrous oxide (Böldt 2019; Böldt et al. 2021; Böldt et al. 2017). Winter-hardy catch crops with spring incorporation are therefore better suited to retaining nitrogen from the previous year into the spring and tend to increase yields of the following crop in a system with mineral nitrogen fertilization (‘t Zandt et al. 2018).
Under organic farming conditions, however, incorporation in spring can also lead to a nitrogen lock in the soil, especially for species with pronounced root systems that potentially make a high contribution to humus build-up and the C/N ratio (Sieling 2019; Stumm 2021a). The result is a reduction in the yield of the subsequent crop.
In summary, the following problems arise with intercropping:
- Nitrogen losses during freezing catch crops or plowing in late autumn in the form of secondary nitrate leaching and nitrous oxide formation
- Insufficient use of the nitrogen released in spring through mineralization by the first subsequent crop during spring ploughing
- Lack of yield increase of the subsequent crop due to non-legume catch crops compared to the control without catch crops
This shows that although intercropping is an efficient measure to initially reduce nitrogen losses, it is not sustainable per se. Nitrogen transfer and availability for the subsequent crop must be successful, otherwise the problem of losses will only be postponed (Sieling 2019).
The members of the arable farming specialist group are keen to optimize catch crop ploughing in terms of humus performance and nitrogen transfer to the soil and subsequent crops and to reduce nitrogen losses and their negative environmental impact.
Implementation
Farmers want to gear their measures in such a way that the nitrogen does not escape in dissolved or gaseous form, but is absorbed into the soil in organically bound form and is then available to the subsequent crop in mineral form for yield formation. As various studies have shown, this is only partially achieved with the traditional method of plowing before or during winter. Two possible alternatives are shallow incorporation with a tiller in the spring or snapping off the stalks with subsequent raking and soil accumulation in the fall and incorporating the catch crop biomass in the spring with a newly developed ridger. This method promises a rapid microbial decomposition of the harvest and root residues of the catch crops, which only begins in spring. This may reduce nitrogen losses from the agricultural system and environmental pollution.
As part of the project, the influence of all three plowing methods on the nitrogen cycle in the soil, plants and atmosphere will be tested in field trials on the eight participating practical farms and on the Frankenhausen teaching and experimental farm at the University of Kassel.
The overarching objective of the project is to gain a better understanding of the nitrogen cycle under catch crops and the influence of different catch crop cultivation and plowing strategies on the fate of the nitrogen absorbed in the shoot mass of catch crops. The aim is to uncover all possible nitrogen pathways in order to take a look into the black box of the nitrogen cycle in intercropping.
With the help of isotope labeling (labeling with 15N), gas measurements, leachate sampling, root and shoot N measurements and soil samples, a comprehensive process understanding of the nitrogen cycle is to be obtained. The following questions are to be answered by this approach:
- When does secondary N leaching or gaseous N loss occur?
- Is the nitrogen absorbed into the soil or into the microbial biomass?
- When will he be free again?
- Can this time be controlled by certain intercropping and plowing strategies?
The project will combine two approaches to trial design: A fully randomized field trial with four replicates with the necessary plot technology will be carried out and intensively sampled at the Domäne Frankenhausen experimental estate of the University of Kassel. The professional equipment of the field trials and the laboratory infrastructure available at the Department of Organic Farming and Crop Production in Witzenhausen enable scientifically sound processing of the trial questions.
On the individual farms, similar trial variants are planted and maintained by the farmers themselves using the farm’s own technology in a fully randomized strip trial with four replicates. The trials are sampled jointly by the participating scientists and farmers. The aim of setting up these additional trials is, on the one hand, to take into account the heterogeneity of the Hessian farms in terms of location – the results obtained at the Frankenhausen site, which is very favorable in terms of plant cultivation, cannot be transferred without restriction to the site conditions and technical equipment of the various farms. On the other hand, this approach allows the farmers organized in the specialist group to participate in the trial and thus gain a scientifically sound ability to judge the effects of their arable farming measures. The results should help the participating and other farmers to optimize their catch crop cultivation with regard to the contribution to humus formation and the preservation of nitrogen in the soil-plant system.
References
‘t Zandt, Dina in; Fritz, Christian; Wichern, Florian (2018): In the land of plenty: catch crops trigger nitrogen uptake by soil microorganisms. In: Plant Soil 423 (1-2), pp. 549-562. DOI: 10.1007/s11104-017-3540-2.
Bergkvist, Göran; Stenberg, Maria; Wetterlind, Johanna; Båth, Birgitta; Elfstrand, Sara (2011): Clover cover crops under-sown in winter wheat increase yield of subsequent spring barley-Effect of N dose and companion grass. In: Field Crops Research 120 (2), pp. 292-298. DOI: 10.1016/j.fcr.2010.11.001.
Böldt, M.; Loges, R.; Kluß, C.; Taube, F. (2017): Influence of catch crops on nitrous oxide losses and nitrate leaching in organic cash crop production depending on the preceding crop. In: Proceedings of the Scientific Conference on Organic Farming 2017, pp. 346-349.
Böldt, Matthias (2019): Environmental aspects of winter catch crops in organic farming systems in consideration of carbon and nitrogen dynamics. In: Daniel Mühlrath, Joana Albrecht, Maria R. Finckh, Ulrich Hamm, Jürgen Heß and Knierim, Ute and Möller, Detlev (eds.): Innovative thinking for a sustainable agriculture and food industry. Contributions to the 15th Scientific Conference on Organic Farming. Kassel, March 5 to 8, 2019. Berlin: Verlag Dr. Köster. Available online at https://orgprints.org/id/eprint/36147/.
Böldt, Matthias; Taube, Friedhelm; Vogeler, Iris; Reinsch, Thorsten; Kluß, Christof; Loges, Ralf (2021): Evaluating Different Catch Crop Strategies for Closing the Nitrogen Cycle in Cropping Systems-Field Experiments and Modeling. In: Sustainability 13 (1), p. 394. DOI: 10.3390/su13010394.
Federal Office for Agriculture and Food (ed.) (2018): Intercrops and catch crops in crop production. Federal Information Center for Agriculture. 2nd edition. 1060/2018. Bonn: BLE Media Service (1060/2018).
Schliesser, Ingeborg; Schuster, Martina; Kolbe, Hartmut (2010): Influence of different catch crops as preceding crops on the yield and quality performance of silage maize and potatoes. In: Landwirtschaft und Geologie (27), pp. 1-69. Available online at https://orgprints.org/id/eprint/19351/, last checked on 09.07.2024.
Sieling, Klaus (2019): Improved N transfer by growing catch crops – a challenge. In: Journal of Cultivated Plants / Journal für Kulturpflanzen 71 (6), pp. 145-160. DOI: 10.5073/JfK.2019.06.01.
Stumm, Christoph (2021a): Saving nitrogen over the winter – the challenge of catch crops. In: Bioland Fachmagazin, p. 16-18.
Stumm, Christoph (2021b): Critically scrutinizing ploughing. Nutrient efficiency of catch crops – influence on N dynamics over winter. In: LUMBRICO (9), 21-15.
