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Die Beregnungssteuerung ist ein wichtiges Instrument für eine effiziente Wassernutzung bei der Feldbewässerung. Die Ermittlung des Wasserbedarfs der Pflanzen in einem Bestand kann auf unterschiedliche Arten erfolgen. Neben Beregnungsempfehlungen von offiziellen Stellen können unter anderem Berechnungen der Wasserbilanz angestellt werden, eine Inaugenscheinnahme des Bodens erfolgen, oder Messwerte von Sensoren, z.B. zur Bodenfeuchte genutzt werden. Das im Rahmen von EIP-Agri geförderte Projekt 'Sensorgestützte Beregnungssteuerung in Kartoffeln (SeBeK)' befasste sich mit der Entwicklung einer innovativen Methode, den Bewässerungsbedarf in Kartoffeln anhand des Crop Water Stress Index (CWSI) zu ermitteln. Dazu wurden an mehreren Kartoffelschlägen Sensormessnetze installiert, die neben der Blatttemperatur der Kartoffelpflanzen auch Wetterdaten aufgezeichnet haben. Neben den Feldversuchen mit einem regionalen Landwirtschaftsbetrieb wurden auf den Versuchsflächen der Landwirtschaftskammer Niedersachsen Exaktversuche durchgeführt, die verschiedene Beregnungswassermengen zur Entwicklung, Kalibrierung und Prüfung des CWSI, aber auch die Wechselwirkungen zwischen der Wasserversorgung und der Kalidüngung untersucht haben. Für die Vergleichbarkeit der Ergebnisse wurden weitere Ansätze zur Beregnungssteuerung betrachtet. Um den Einfluss der Variabilität lokaler Wetterbedingungen auf die Wasserversorgung der Bestände zu untersuchen, wurden im Projektgebiet Wetteraufzeichnungen an verschiedenen Standorten betrachtet. Die mit Hilfe des CWSI ermittelten Beregnungsempfehlungen decken sich mit den Ergebnissen auf Basis der gravimetrisch ermittelten nutzbaren Feldkapazität. Die Untersuchungen zeigen, dass es prinzipiell möglich ist, anhand einer Sensorüberwachung aussagekräftige Beregnungsempfehlungen zu ermitteln. Das erforderliche Sensormessnetz ist allerdings zu diesem Zeitpunkt nicht praxistauglich. Eine Vereinfachung der Messung und Auswertung zur Bestimmung des CWSI muss das Ziel weiterer Untersuchungen sein. Denkbar sind unter anderem Messungen mit Temperatursensoren, die an landwirtschaftlichen Fahrzeugen (Schlepper) oder an Drohnen montiert sind. Irrigation management is an important contribution to efficient water usage in field irrigation. Different approaches are used to determine crop water demand and the best time for irrigation, such as irrigation recommendations by official consulting services, water balance modelling, visual and physical inspection, and sensor based informations like soil moisture. The 'Sensor based irrigation' research project within the EIP-Agri funding scheme by the European Commission focussed on the development of an innovative method to determine the water demand of potato plants using the Crop Water Stress Index (CWSI). Sensor networks have been installed at different potato fields to monitor not only the (plant) leaf temperature but also to record meteorological parameters. Trials have been set up at different fields of a local farmer and in the research station operated by the chamber of agriculture in the federal state of Lower Saxony to develop, calibrate and test the CWSI as well as studying the interactions between water supply and potash based fertilizers. To compare the results, different approaches to identify the water demand were considered. To study the impact of local variations of weather conditions, several monitoring stations in the region have been evaluated. The findings on the irrigation management following the CWSI approach are congruent to the results based on gravimetrically analysed water holding capacity. The results indicate, that it is possible to develop a sensor based irrigation management with reliable irrigation management information. However, the required sensor network is not practical at this time. A simplification of the monitoring and evaluation process to determine the CWSI should be the focus of further research. It is conceivable that future monitoring will be performed by sensors installed on tractors or drones.

Gefördert im Rahmen des Projekts DEAL

Nitrogen (N) fertilizers increase agricultural yields, but also lead to the release of thegreenhouse gases nitrous oxide (N$_2$O) and ammonia (NH$_3$). This not only reduces the efficiency of N use, but also results in climate change and loss of biodiversity. The use ofnitrification inhibitors may improve the efficiency of N use and reduce the emission ofgreenhouse gases. We tested three inhibitors (NZONE MAX, Piadin and $N$-($n$-butyl) thio-phosphoric triamide (NBPT)) added to two common N fertilizers (urea and urea ammo-nium nitrate (UAN)) and determined emissions of CO$_2$, N$_2$O and NH$_3$ to evaluate theeffectiveness of these three inhibitors and to improve our understanding of the soil ni-trogen cycle. NBPT effectively reduced NH3volatilization by 50% (from 3.0 g NH$_3$-N m$^{-2}$ in urea alone to 1.4 g NH$_3$-N m$^{-2}$ in urea + NBPT). Piadin decreased N$_2$O emissions (from 0.98 g N$_2$O-N m$^{-2}$ in urea alone to 0.15 g N$_2$O-N m$^{-2}$ in urea + Piadin and from 0.81 g N$_2$O-N m$^{-2}$ in UAN alone to 0.39 g N$_2$O-N m$^{-2}$ in UAN + Piadin) by inhibiting the conversion of NH$_4^+$ to NO$_3^-$. However, although Piadin was found to be an effective nitrification inhibitor,the risk of higher NH$_3$ emissions (from 3.0 g NH$_3$-N m$^{-2}$ in urea alone to 4.5 g NH$_3$-N m$^{-2}$ in urea + Piadin) with the addition of Piadin cannot be neglected in environmental andeconomical evaluations. Open-Access-Publikationsfonds 2020 peerReviewed

Chemical composition of root and shoot litter controls decomposition and, subsequently, C availability for biological nitrogen transformation processes in soils. While aboveground plant residues have been proven to increase N2O emissions, studies on root litter effects are scarce. This study aimed (1) to evaluate how fresh maize root litter affects N2O emissions compared to fresh maize shoot litter, (2) to assess whether N2O emissions are related to the interaction of C and N mineralization from soil and litter, and (3) to analyze changes in soil microbial community structures related to litter input and N2O emissions. To obtain root and shoot litter, maize plants (Zea mays L.) were cultivated with two N fertilizer levels in a greenhouse and harvested. A two-factorial 22 d laboratory incubation experiment was set up with soil from both N levels (N1, N2) and three litter addition treatments (control, root, root + shoot). We measured CO2 and N2O fluxes, analyzed soil mineral N and water-extractable organic C (WEOC) concentrations, and determined quality parameters of maize litter. Bacterial community structures were analyzed using 16S rRNA gene sequencing. Maize litter quality controlled NO3- and WEOC availability and decomposition-related CO2 emissions. Emissions induced by maize root litter remained low, while high bioavailability of maize shoot litter strongly increased CO2 and N2O emissions when both root and shoot litter were added. We identified a strong positive correlation between cumulative CO2 and N2O emissions, supporting our hypothesis that litter quality affects denitrification by creating plant-litter-associated anaerobic microsites. The interdependency of C and N availability was validated by analyses of regression. Moreover, there was a strong positive interaction between soil NO3- and WEOC concentration resulting in much higher N2O emissions, when both NO3- and WEOC were available. A significant correlation was observed between total CO2 and N2O emissions, the soil bacterial community composition, and the litter level, showing a clear separation of root + shoot samples of all remaining samples. Bacterial diversity decreased with higher N level and higher input of easily available C. Altogether, changes in bacterial community structure reflected degradability of maize litter with easily degradable C from maize shoot litter favoring fast-growing C-cycling and N-reducing bacteria of the phyla Actinobacteria, Chloroflexi, Firmicutes, and Proteobacteria. In conclusion, litter quality is a major driver of N2O and CO2 emissions from crop residues, especially when soil mineral N is limited.

An increasing area of oilseed rape cultivation in Europe is used to produce biodiesel. However, a large amount of straw residue is often left in the field in autumn. Straw mineralization provides both carbon (C) and nitrogen (N) sources for emission of soil nitrous oxide (N2O), which is an important greenhouse gas with a high warming potential. Some studies have focused on soil N2O emissions immediately post-harvest; however, straw mineralization could possibly last over winter. Most field studies in winter have focused on freeze-thaw cycles. It is still not clear how straw mineralization affects soil N2O emissions in unfrozen wintertime conditions. We carried out a field experiment in northern Germany in winter 2014, adding straw and glucose as a source of C with three rates of N fertilizer (0, 30, and 60 kg N ha−1). During the 26 days of observation, cumulative N2O emission in treatments without C addition was negative at all N fertilizer levels. Straw addition produced –3.2, 11.2, and 5.0 mg N2O-N m−2 at 0, 30, and 60 kg N ha−1, respectively. Addition of glucose surprisingly caused –1.5, 74.6, and 165 mg N2O–N m−2 at 0, 30, and 60 kg N ha−1, respectively. This study demonstrates that oilseed rape straw does not cause high N2O emissions in wintertime when no extreme precipitation or freeze-thaw cycles are involved, and soil organic C content is low. However, N2O emission could be intensively stimulated, when both easily available organic C and nitrate are not limited and the soil temperature between 0 and 10°C. These results provide useful information on potential changes to N2O emissions that may occur due to the increased use of oilseed rape for biodiesel combined with less severe winters in the northern hemisphere driven by global warming.

Chemical composition of root and shoot litter controls decomposition and, subsequently, C availability for biological nitrogen transformation processes in soils. While aboveground plant residues have been proven to increase N2O emissions, studies on root litter effects are scarce. This study aimed (1) to evaluate how fresh maize root litter affects N2O emissions compared to fresh maize shoot litter, (2) to assess whether N2O emissions are related to the interaction of C and N mineralization from soil and litter, and (3) to analyze changes in soil microbial community structures related to litter input and N2O emissions. To obtain root and shoot litter, maize plants (Zea mays L.) were cultivated with two N fertilizer levels in a greenhouse and harvested. A two-factorial 22 d laboratory incubation experiment was set up with soil from both N levels (N1, N2) and three litter addition treatments (control, root, root + shoot). We measured CO2 and N2O fluxes, analyzed soil mineral N and water-extractable organic C (WEOC) concentrations, and determined quality parameters of maize litter. Bacterial community structures were analyzed using 16S rRNA gene sequencing. Maize litter quality controlled NO−3 and WEOC availability and decomposition-related CO2 emissions. Emissions induced by maize root litter remained low, while high bioavailability of maize shoot litter strongly increased CO2 and N2O emissions when both root and shoot litter were added. We identified a strong positive correlation between cumulative CO2 and N2O emissions, supporting our hypothesis that litter quality affects denitrification by creating plant-litter-associated anaerobic microsites. The interdependency of C and N availability was validated by analyses of regression. Moreover, there was a strong positive interaction between soil NO−3 and WEOC concentration resulting in much higher N2O emissions, when both NO−3 and WEOC were available. A significant correlation was observed between total CO2 and N2O emissions, the soil bacterial community composition, and the litter level, showing a clear separation of root + shoot samples of all remaining samples. Bacterial diversity decreased with higher N level and higher input of easily available C. Altogether, changes in bacterial community structure reflected degradability of maize litter with easily degradable C from maize shoot litter favoring fast-growing C-cycling and N-reducing bacteria of the phyla Actinobacteria, Chloroflexi, Firmicutes, and Proteobacteria. In conclusion, litter quality is a major driver of N2O and CO2 emissions from crop residues, especially when soil mineral N is limited. Open-Access-Publikationsfonds 2020 peerReviewed

After repeated warnings by the European Commission regarding high nitrate concentrations in German waters, in 2017, Germany implemented a new fertilizer application ordinance (FO) with stricter nitrate value limits. The new regulations have severely affected agricultural regions in Germany and could lead to a high number of job losses if farmers must conform to the new regulations and do not implement new production methods. Therefore, a simulation game was developed to educate farmers and residents about the new FO and to facilitate adaptation to the new environmentally friendly legislation. The aims of the newly developed simulation game are to educate residents and farmers in affected regions about the new FO and to develop new ideas on how to comply with the new regulations. The aims of the present study are, first, to research participants&rsquo, evaluation of the simulation game and, second, to assess the effect of the simulation game on subjective knowledge, internal efficacy, and attitude towards the new FO. This pre- and post-comparison design study was based on pre-test and post-test with participants in two games (N = 90). The results were analyzed using descriptive statistics, multiple regression analyses, qualitative content analysis, and mean value comparisons. The simulation game had a positive effect on participants&rsquo, subjective knowledge (Cohen&rsquo, s d 0.65) and internal efficacy (Cohen&rsquo, s d 0.36), but it did not have an effect on their attitudes toward the new FO, and it was shown to slightly lower their interest in agriculture politics (Cohen&rsquo, s d &minus, 0.33). The participants reported that the game made them more aware of both the difficulty and necessity of finding compromises in the field of agriculture politics. Overall, the simulation was rated very positively and was perceived as interesting and informative by the participants.