Browsing by Subject "Nitrogen fertilization"

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Analyse von Wachstum und Qualität von Weizen unter ansteigender CO2 Konzentration als Folge des Klimawandels
(2019) Dier, Markus; Zörb, Christian
The atmospheric CO2 concentration is expected to increase to 500–620 ppm in the future. Such an elevated atmospheric CO2 concentration (e[CO2]) increases grain yield, but can decrease tissue N concentrations by about 9% in wheat. This could endanger global food security. Moreover, in previous studies, a decrease of grain N concentration by e[CO2] has closely been associated with that of gluten proteins, indicating a decreased baking quality under e[CO2]. The mechanisms by which e[CO2] decreases N concentration are still unclear and FACE studies investigating CO2 x N interactions on the formation of grain yield and the quality of winter wheat are scarce. The first main objective was the analysis of a decreased N concentration in the grain by e[CO2] in winter wheat based on a two-year FACE experiment with widely differing N levels (35 to 320 kg N ha-1) and different N forms (NO3- and NH4+). The focus was on key processes of grain N acquisition that are leaf NO3- assimilation, N remobilization and post-anthesis N uptake. The hypotheses were: e[CO2] inhibits leaf NO3- assimilation, e[CO2] decreases N remobilization (Nrem) by decreased N concentrations at anthesis and e[CO2] decreases post-anthesis N uptake (Nabs) by inhibition of leaf NO3- assimilation or acceleration of senescence. The second main objective was the simultaneous analysis of the e[CO2] effect on the grain proteome and baking quality with the hypothesis that e[CO2] reduces gluten proteins and thereby baking quality. e[CO2] increased grain yield in all N levels by 10% to 17% mainly through enhanced grain number per m2 ground area. This was due to increased radiation use efficiency (chapter 2). These increases were smaller under N deficiency compared with high N supply. The reasons were a reduction of photosynthesis capacity by e[CO2] and a sink limitation concerning grain yield due to N deficiency during ear growth. The indication for the reduction of photosynthesis capacity was a decrease of leaf N concentration under e[CO2] regardless of green leaf area index under N deficiency. An indication for sink limitation of grain yield was the decrease of harvest index by e[CO2] because of a strong and small stimulation of stem and ear growth, respectively by e[CO2]. Grain N yield was increased by e[CO2] under all N levels (chapter 3). There was a strong linear relation between grain N yield and grain number that was unaffected by e[CO2]. In contrast with the hypotheses of an decreased Nrem and Nabs under e[CO2], e[CO2] resulted in an increase of Nrem, Nrem efficiency and Nabs, causing the increase of grain N yield. Nevertheless, e[CO2] slightly decreased grain N concentration (by 1 to 6%), whereby the smallest effect of 1% was found under N deficiency. This decrease was primarily related to a growth dilution effect due to an increased individual grain weight under e[CO2]. A further reason was a stronger increase of grain number than an increase of vegetative N yield at anthesis by e[CO2] and thereby a decrease of the ratio between the N source and the N sink. Indication for an e[CO2] induced inhibition of leaf NO3- assimilation was not found as e[CO2] did not result in a decreased activity of leaf nitrate reductase under all N levels at both cool (17 °C) and warm (28 °C) temperatures (chapter 4). Furthermore, the e[CO2] induced stimulation of growth and N acquisition was not stronger under NH4+ compared with NO3- based N-fertilization. Reduction of grain protein concentration by e[CO2] was associated with reduced albumin/globulin and gluten concentrations under all N levels (chapter 5). Under optimal N supply, the grain protein composition was changed by e[CO2] with altogether 19 decreased and 17 increased protein spots. 15 out of the 16 identified decreased proteins were globulins, whereas specific gluten proteins were not found to be affected by e[CO2]. Correspondingly, baking quality remained unaffected under e[CO2] under all N conditions. In conclusion, grain N yields were increased by e[CO2] due to an increase of Nrem and Nabs with grain number being the driving force. Grain N concentrations were slightly reduced under e[CO2] with a growth dilution effect and a changed source to sink ratio as the underlying mechanisms. The reduction of the grain N concentration by e[CO2] was not specifically associated with a reduction of gluten proteins.
Characterisation of natural and synthetic nitrification inhibitors and their potential use in tomato cultivation
(2008) Souri, Mohammad Kazem; Römheld, Volker
Summary Besides commercial NIs, many chemicals could also inhibit nitrification. In our study (Chapter 3) regarding efficiency of chloride compared to 3,4-Dimethylpyrazole phosphate (DMPP), it was found that chloride at applied concentration of 30.5 mg per 100g dry soil, could effectively inhibit nitrification. Despite a lag period of 3 weeks in detectable net nitrification, inhibitory effect of chloride continued to persist even after 7 weeks of soil incubation compared to control. Nevertheless, DMPP particularly with higher concentration (2 % of N-NH4+ instead of 1%) stabilized ammonium more strongly than Cl-1. The extent of nitrification inhibition after 5 and 7 week of incubation was in order of: (2 % of N-NH4+) DMPP > (1 % of N-NH4+) DMPP> NH4Cl > KCl > control. The residue ammonium in the soil as well as the produced nitrate concentrations in samples showed a significant NI activity of chloride in both forms NH4Cl and KCl. Nitrification-induced pH decrease, however, showed a better correlation with measured nitrate than ammonium in this experiment. In a second series of experiments undertaken to identify whether the reported NI release by Brachiaria humidicola accession 26159 is an active or passive phenomenon, root exudates of plants grown under various treatments, have been collected in distilled water or in 1 mM NH4Cl. Under various pre-culture conditions such as N form (NH4+ versus NO3-), N concentrations (1, 2, 4 mM), light intensities (180, 240, 350 µmol m-2 s-1), plant age (3-weeks old versus 7-weeks old) and collecting periods (24 versus 6 h), there was no significant NI activity when root exudates were collected in distilled water. However, NI activity was detectable in root washings when the plants were exposed to extended collection times (24 h) in combination with NH4+ supply, but not after short term collection (6 h) or with NO3- in the collection solution. This observation is consistent with the results of Subbarao et al., (2006, 2007), but it also strongly suggests that the observed release of NI compounds was rather a consequence of membrane damage (passive phenomena) due to inadequate collection conditions, than mediated by controlled exudation from undamaged roots. It has been assumed that supplying only ammonium (1 mM) in distilled water as root washing medium over extended time periods (24 h) could lead to rapid ammonium uptake and medium acidification associated with the risk of Ca2+ desorption, which is an important element required for membrane stabilisation and integrity. To test the hypothesis that NI compounds are released from damaged plant cells of Brachiaria, the NI potential of fresh root and shoot homogenates was measured after soil incorporation and incubation. Surprisingly, NI potential was detected in shoot but not in root homogenates. The NI effect of soil-incorporated shoot tissues lasted for at least 8 d, while root tissue even stimulated nitrification with increasing incubation time. This NI effect was independent of the N form. However, the variability of data increased with NO3- form, higher light intensity or higher N concentrations during plant pre-culture. Independent of N forms, further extraction and characterisation of NI compounds in shoot tissue of Brachiaria plants revealed a particularly high activity in the ethanol-soluble fraction, both in plants with NH4+ and NO3- pre-culture. In a third experiment, the role of Ca2+ ions on improvement of tomato growth under ammonium nutrition was investigated. In this experiment root damage, probably by membrane damage and cytosolic sensitivity were hypothesised to be the main cause of toxicity symptoms of NH4+ on tomato plants. At application of 2 mM N as NH4+, plant biomass, number of lateral shoots, and transpiration were strongly inhibited and an increased Ca2+ application into the nutrient solution counteracted these observed negative effects. Transpiration or water consumption was found to be a good indicator of plant performance under NH4+ nutrition. Plants grown under nitrate nutrition had the highest transpiration rates, as well as the best growth characteristics. There was a positive correlation between nitrate concentrations and transpiration rates. On the other hand, plants grown in ammonium (as control, or 3 and 6 split applications of NH4+ during 4 days) showed severe toxicity symptoms including growth inhibition and leaf abscission. However, when ammonium was applied together with 10 mM Ca2+ (as CaSO4), or in a buffered solution of pH 6.6 with CaCO3 (pH or/and Ca2+ effect), transpiration and other growth factors (e.g. root and shoot dry matter, number of lateral shoots), as well as the nutrients especially N concentrations in the biomass were significantly improved. In other words, shoot and particularly root growth inhibited when NH4+ treated plants (control and split applications) did not received CaSO4 or CaCO3. Micro molar concentrations of NH4+ in 6 split applications also could not prevent ammonium toxicity symptoms.
Effects of land-use intensity on functional community composition and nutrient dynamics in grassland
(2024) Walter, Julia; Thumm, Ulrich; Buchmann, Carsten M.; Heinonen-Tanski, Helvi
Land-use intensity drives productivity and ecosystem functions in grassland. The effects of long-term land-use intensification on plant functional community composition and its direct and indirect linkages to processes of nutrient cycling are largely unknown. We manipulated mowing frequency and nitrogen inputs in an experiment in temperate grassland over ten years. We assessed changes in species composition and calculated functional diversity (FDis) and community weighted mean (CWM) traits of specific leaf area (SLA), leaf dry matter content (LDMC) and leaf and root nitrogen of the plant community, using species-specific trait values derived from databases. We assessed above- and belowground decomposition and soil respiration. Plant diversity strongly decreased with increasing land-use intensity. CWM leaf nitrogen and SLA decreased, while CWM LDMC increased with land-use intensification, which could be linked to an increased proportion of graminoid species. Belowground processes were largely unaffected by land-use intensity. Land use affected aboveground litter composition directly and indirectly via community composition. Mowing frequency, and not a land-use index combining mowing frequency and fertilization, explained most of the variation in litter decomposition. Our results show that land-use intensification not only reduces plant diversity, but that these changes also affect nutrient dynamics.
Effects of stand density and N fertilization on the performance of maize (Zea mays L.) intercropped with climbing beans (Phaseolus vulgaris L.)
(2022) Villwock, Daniel; Kurz, Sabine; Hartung, Jens; Müller-Lindenlauf, Maria
Maize is Germany’s most important fodder and energy crop. However, pure maize cultivation has ecological disadvantages. Moreover, its yield is low in crude protein, an important feed quality parameter. Maize–bean intercropping can potentially address both issues. A bean variety specially developed for intercropping was first introduced in 2016. Using this variety, a network of institutions conducted 13 field trials from 2017 to 2020 on four sites in Germany. We sought to determine the effects of stand density and nitrogen (N) fertilization on dry matter yield, crude protein yield, and soil mineral N content (Nmin) at harvest of intercropped vs. pure maize. The three intercropping bean densities we tested (7.5, 5.5, and 4 plants/m2) produced non-significantly different yields of dry matter or crude protein, given a maize density of 7.5–8 plants/m2. Intercropping was inferior to pure maize in dry matter yield, but non-significantly different in crude protein yield. Under neither cropping strategy were significant losses in dry matter or crude protein yield recorded with reduced compared to full N fertilization. At full fertilization, however, both pure maize systems and the 8/4 maize–bean intercrop system left significantly higher Nmin at harvest than the other variants of the corresponding system or N fertilization level and thus an increased risk of nitrate leaching. We encourage further optimization of yield performance in maize–bean intercropping, e.g., through breeding or promotion of biological N fixation via rhizobia inoculation. Furthermore, we recommend reducing N fertilization levels in maize cultivation.
Environmental and economic assessment of the intensive wheat - maize production system in the North China Plain
(2016) Ha, Nan; Bahrs, Enno
To ensure food security for its vast population input intensification in crop production has been one of China’s major strategies in the last decades. However, the negative environmental impact of the highly intensive crop production becomes apparent. Especially the emission of greenhouse gases (GHG) constitutes a major sustainability issue of crop production in China. The winter wheat - summer maize (WW-SM) double cropping system plays a crucial role for China’s national food security. Strong research efforts mainly focusing on field experiments insufficiently consider the economic viability of the proposed improvement strategies and farmers’actual crop management. Therefore this study aims to fill this void by assessing farmers’actual crop management in the WW-SM production system, with regard to its environmental and economic performance to derive suitable improvement strategies for more sustainable crop production in the North China Plain (NCP). This cumulative PhD thesis consists of three papers published or accepted with revisions in international peer-reviewed journals. A field survey conducted in 2011 interviewing 65 WW-SM producing farm households constitutes the core data base for the thesis’analysis. The data was supplemented by expert interviews and specific secondary data. Partial life cycle analysis and economic assessment were conducted, comprising GHG emission, product carbon footprint (PCF), gross margin (GM), variable cost per unit product and life cycle costing (LCC) as key environmental and economic indicators, respectively. The first article describes the status quo of single farm environmental and economic performance of 65 WW-SM producers. The results revealed a huge heterogeneity among farms. Astonishingly no trade-off between productivity and sustainability could be identified in the region. Building on cluster analysis, with farms grouped according to their economic and environmental performance into “poor”, “fair” and “good” producers, the regional GHG mitigation potential was estimated. Under the scenario assumption that all grain in the NCP is produced under “good” production conditions, 21% and 7% of GHG could be mitigated in wheat and maize production, respectively. To be able to address the existing heterogeneity and develop strategies towards attaining GHG mitigation in practice, the second article aimed at assessing the factors determining farmers’ current environmental and economic performance. Using stepwise multiple linear regression (SMLR) it was revealed that nitrogen (N) input and electricity for irrigation were responsible for 0.787 and 0.802 of variability (adjusted R2) in the GHG emission results of the WW and SM production, respectively. Electricity for irrigation and labor were the most significant factors explaining the differences in LCC of WW and SM production, with an adjusted coefficient of determination (adjusted R2) of 0.397 and 0.29. This finding indicates that N input, electricity for irrigation and labor are key target areas for lowering GHG emissions and production costs of the WW-SM production system in the NCP. As revealed in the second article overuse of N fertilizer, which actually constitutes a major current issue in China, offers great potential for reducing GHG emissions and production costs in the WW-SM production system. Therefore in the third article three simple and easily to apply N fertilizer recommendation strategies are tested, which could be implemented on large scale through the existing agricultural advisory system of China, at comparatively low cost. Building on the household dataset, the effects of the three N strategies under constant and changing yield levels on PCF and GM were determined for every individual farm household. The N fixed rate strategy realized the highest improvement potential in PCF and GM in WW; while the N coefficient strategy performed best in SM. The analysis furthermore revealed that improved N management has a significant positive effect on PCF, but only a marginal and insignificant effect on GM. On the other side, a potential 10 % yield loss would have only a marginal effect on PCF, but a detrimental effect on farmers’income. It will be of vital importance to avoid any yield reductions and respective severe financial losses, when promoting and implementing advanced fertilization strategies. Therefore, it is furthermore recommended to increase the price of fertilizer, improve the agricultural extensions system, and recognize farmers’ fertilizer related decision-making processes as key research areas. The presented thesis gives valuable contributions to the development of environmentally and economically more sustainable crop production systems in the NCP. The thesis concludes that an adjustment in the agricultural advisory system is required, supported by more interdisciplinary research, which is able to address the inherent complexity of realizing more sustainable crop production in China.
Gaseous N emissions from a loamy soil as affected by N fertilization strategies, and by the use of nitrification and urease inhibitors - Results from field and incubation experiments
(2023) Guzman Bustamante, Ivan; Müller, Torsten
Agricultural activities are responsible for a substantial share of anthropogenic greenhouse gases. At the same time, agricultural production must feed a growing world population under a changing climate. In the case of wheat, the use of nitrogen (N) fertilizers is needed in order to insure grain yield and quality. Nevertheless, its use is associated with reactive N losses, which are detrimental for the environment and human health. Among the gaseous N species emitted after N fertilization we find nitrous oxide (N2O), a potent greenhouse gas, and ammonia (NH3) that after its deposition can be oxidized to N2O. Chemical compounds such as nitrification and urease inhibitors (NIs and UIs, respectively) are a useful tool, able to raise the fertilizer nitrogen use efficiency, by retarding the nitrification of ammonium based fertilizer in the case of NIs and by retarding the hydrolysis of urea in the case of UIs. A side benefit of the use of NIs is the reduction of N2O emissions. The use of UIs reduces the NH3 volatilization. One of the most used NIs in Europe is 3,4-dimethylpyrazol phosphate (DMPP) which can be applied with ammonium sulfate nitrate (ASN). The relatively new NI, 3,4-dimethylpyrazol succinic acid (DMPSA), acts similarly to DMPP but has a different time of action and can be applied to several fertilizers, unlike DMPP. N-(n-butyl) thiophosphoric triamide (NBPT) is an effective UI that provenly reduces NH3 volatilization by inhibiting the urease enzyme. In a two-year field experiment with winter wheat several fertilizer strategies were tested, including splitting strategies, use of NIs and reduction of N amount. Reducing N amount reduces the amount of soil mineral N, which is the substrate for N2O producing microbiological processes, nitrification and denitrification. Splitting of N fertilizer might reduce soil mineral N as well because N fertilizer applications are better suited to the physiological needs of the wheat plants. Applying NIs in splitting schemes may further mitigate emissions. The relationship between N amount and N2O losses in a wheat production system was investigated by applying lower and higher N amounts than the recommended N application rate. Use of DMPP was able to reduce N2O emissions in both years, not only on an annual basis (by 21 %: 3.1 vs 2.5 kg N2O-N ha-1 a-1 average for both years) but also during winter, when up to 18 % of total annual emissions occurred. A change of the soil microbial community due to DMPP could be the reason for the reduction of winter emissions 8 to 12 months after DMPP application. An economic assessment of N fertilizer amount showed that DMPP applied with suboptimal N fertilizer amounts can maintain yield and at the same time decrease yield scaled N2O emissions compared to an optimal N fertilizer rate without NI. Using CAN together with the NI DMPSA reduced N2O emissions only during the vegetation period. On an annual basis, DMPSA did not significantly reduce N2O emissions. Because DMPSA and DMPP were applied with different N fertilizers with different ammonium and nitrate shares, a direct comparison between these two NIs cannot be made. A traditional threefold split fertilization did not reduce annual emissions compared to a single application of ASN or CAN. Nevertheless, the use of DMPP in twofold split applications reduced annual emissions significantly by 33 % and increased protein content by 1.6 %. Because N2O flux peaks were not as high as expected after N fertilization during the first year, a short experiment investigating the effect of soil moisture, N and C application on N2O fluxes was conducted. A C limitation of the field was found, which explained high N2O emission events when C was available, e.g. after rewetting of dry soil and incorporation of straw after harvest. In this context we tested the removal of wheat straw – which should reduce the organic substrate supply for denitrifiers – as a possible mitigation strategy. Nevertheless, the removal of straw had no effect on N2O emissions. Furthermore, the effect of DMPP on microorganisms was studied in an incubation experiment: the copy number of bacterial amoA genes (nitrifiers) was lowered by the use of DMPP, while the number of archaeal amoA genes was increased by DMPP. Gene copy number of denitrifiers was unaffected by DMPP, nevertheless, soil respiration was reduced when DMPP was applied. It seems as DMPP has an inhibiting effect on heterotrophic organisms, nevertheless, the investigated variables did not support this hypothesis, so that further investigation is needed. The effect of NBPT and straw residues on NH3 and N2O emissions was studied in a two-week incubation experiment with a slightly alkaline soil. NBPT reduced NH3 volatilization and N2O fluxes from urea fertilization almost completely. Incorporation of straw residues significantly increased N2O emissions. In a further four-week incubation experiment, the effect of NBPT in two concentrations and DMPP was studied. A higher NBPT concentration as the recommended rate, reduced NH3 emissions by 53 %; DMPP on the other hand increased NH3 volatilization by 70 %. Regarding N2O, DMPP reduced emissions to the same level as the unfertilized control; NBPT only shifted the emission peak so that by the end of the experiment no difference in the cumulative N2O emission was found between urea and NBPT treatments. These results show that UI can lead to a reduction of N2O emissions, but the ammonium formed by the urea hydrolysis should be used by crops, otherwise it serves as a substrate for N2O production in soils. In the final incubation experiment, the combined application of a NI (DMPSA) and a UI (NBPT) was studied. Lower concentrations than the recommended doses were applied in order to assess synergistic effects. The combined application of DMPSA and NBPT did not lead to synergistic effects in the analyzed variables (soil urea amount, soil mineral N, ammonia volatilization, soil respiration and N2O emission). The higher the NBPT concentration, the slower urea was hydrolyzed and the higher the reduction in NH3 volatilization. A third of DMPSA application rate was enough to reduce N2O emissions; however, the use of NI increased NH3 losses. Our results highlight the importance of annual datasets when assessing mitigation strategies for N2O. For wheat production, a reduction of the N fertilizer amount when a NI is used should be taken into consideration. When elite wheat cultivars are grown split application with NI fertilizers could ensure high protein content and simultaneously reduce N2O emission. Urea fertilizer should be applied with NI and UI so that NH3 volatilization and N2O emission is reduced. Nevertheless, long-term effects of these compounds on soil microbiology must be monitored to avoid unseen ecotoxicological effects. Since some of these compounds or their metabolites might be absorbed by plants and end up in food and feed more research is needed to protect consumers.