Browsing by Subject "Stickstoffdüngung"

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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.
Combining remote sensing and crop modeling techniques to derive a nitrogen fertilizer application strategy
(2020) Röll, Georg; Graeff-Hönninger, Simone
The crucial question in this thesis was how can remote sensing data and crop models be used to derive a N fertilizer strategy that is capable to lower the environmental side effects of N fertilizer application. This raised the following detailed objectives: The first objective (i) how N content determination via spectral reflectance is influenced by different leaves and positions on the leaf was investigated in Publication I. Different wheat plants were cultivated under different N levels and under drought stress in two hydroponic greenhouse trials. Spectral reflectance measurements were taken from three leaves and at three positions on the leaf for each plant. In total, 16 vegetation indices broadly used in the literature were calculated based on the spectral reflectance for each combination of leaf and position. The plant N content was determined by lab analyses. Neither the position on the leaf nor leaf number had an impact on the accuracy of plant N determination via spectral reflectance measurements. Therefore measurements taken at the canopy level seem to be a valid approach. However, if other stress symptoms like drought or disease infection occur, a differentiation between leaves and positions on the leaf might play a more crucial role. Publication II dealt with the second objective on (ii), how to incorporate leaf disease into the DSSAT wheat model to enable the simulation of the impact of leaf disease on yield. An integration of sensor information in crop growth models requires the update of model state variables. A model extension was developed by adding a pest damage module to the existing wheat model. The approach was tested on a two-year dataset from Argentina with different wheat cultivars and on a one-year dataset from Germany with different inoculum levels of septoria tritici blotch (STB). After the integration of disease infection, the accuracy of the simulated yield and leaf area index (LAI) was improved. The Root mean squared error (RMSE) values for yield (1144 kg ha−1) and LAI (1.19 m2 m−2) were reduced by half (499 kg ha−1) for yield and LAI (0.69 m2 m−2). A sensitivity analysis also showed a strong responsiveness of the model by the integration of different STB disease infection scenarios. Increasing the modeling accuracy even further a MM approach seems to be suitable. Assembling more models increases the complexity of the simulation and the involved calibration procedure especially if the user is not familiar with all models. To avoid these conflicts, Publication III evaluated the third objective (iii) if an automatic calibration procedure in a MM approach for winter wheat can eliminate the subjectivity factor in model calibration. The model calibration was performed on a 4-yr N wheat fertilizer trial in southwest Germany. The evaluation mean showed satisfying results for the calibration (d-Index 0.93) and evaluation dataset (d-Index 0.81). This lead to the fourth (iv) objective to use a MM approach to improve the overall modeling accuracy. The evaluation of a fertilizer trial showed an improved modeling accuracy in most cases, especially in the drought season 2018. Based on the combination of a MM approach and the incorporation of sensor data, a Nitrogen Application Prescription System (NAPS) was developed. The initial NAPS setup requires long term recorded data (yield, weather, and soil) to ensure proper MM calibration. After calibration, the current growing season conditions are required (weather, management information) until the N application date. Afterward, the NAPS incorporates remote sensing information and generated weather for running future N application scenarios. The selection of the proper amount of N is determined by economic and ecological criteria. Furthermore, in order to account for differences in in-field variabilities and to deliver a N prescription site-specifically, the NAPS concept has to be applied on a geospatial scale by adjusting soil parameters spatially. The NAPS concept has the potential to adjust the N application more economically and ecologically by using current sensor data, historical yield records, and future weather prediction to derive a more precise N application strategy. Finally, this concept exhibits the potential for reconciliation of the issue of an economic, agricultural production without harming the environment.
Economic evaluation of nitrogen application in the North China Plain
(2008) Barning, Roland; Zeddies, Jürgen
Today, China had solved its long-standing problem of inadequate grain production, but there are two new targets for rural China. Firstly, one goal is rural development towards an improved income generation of rural households in order to slow down the increasing income disparity in China, especially between rural and urban residents. Secondly, decades of inefficient utilisation of resources and high consumption of materials led to overexploitation of water and land resources. Over-fertilisation and low nitrogen use efficiency are representative for the production system in the North China Plain, which is characterised by small-scale farm households who traditionally cultivate winter wheat and summer maize. This thesis is embedded in the Sino-German Research Training Group "Modeling Material Flows and Production Systems for Sustainable Resource Use in Intensified Crop Production in the North China Plain", a cooperation of the University of Hohenheim in Stuttgart and the Chinese Agricultural University in Beijing. The overall hypothesis of this project is that substantial changes in farming systems and management practices can reduce environmental pollution and at the same time stabilise or increase income of farmers. As a subproject, this thesis focuses on the identification and evaluation of applicable instruments for this goal. The final target of this thesis is the simulation of scenarios in order to estimate the impact of identified instruments on the nitrogen balance as well as on the net income of farm households. The literature review indicates that nitrogen application in the cultivation of wheat and maize in the North China Plain shows a broad variation. A considerable high share of farm households applies nitrogen input levels far beyond the crop demand. This situation raises the question, what do over-fertilising farm households have in common or in another way, which factors lead to nitrogen overuse. This question is the basis of the discussion on applicable instruments to reduce the described nitrogen overuse and finally the intended simulation approach. The analysis of impact factors on the nitrogen application level requires a broad analysis of the cultivation system, the farm household characteristics, and the income sources of the farm households. The descriptive results of the farm survey on 340 farm households in the North China Plain conducted in 2005 are presented in chapter 5. The farming system at the survey sites is characterised by farm households, who cultivate the wheat and maize rotation system. In most cases, it is extended by cash crops such as cotton or peanuts. The farm size is on average 0.5 ha of allocated farmland per farm household. About two thirds of the farm households have some kind of additional off-farm income source, which usually exceeds the income share from farming. Farm households without off-farm income sources generate only half of the average farm household income. The average farm household income reaches 10 150 ¥ (1 015 ?) per year, but there is a broad variation within the survey sites as well as between the surveyed townships. As mentioned already, over-fertilisation is prevalent for farming in the North China Plain. On average 360 kg of nitrogen per ha are applied in wheat and 220 kg in maize, while CHEN (2003) recommends 180 kg per ha for wheat and maize. Further, fertilizer costs are the major share of variable costs at all cultivated crops. The major nitrogen fertilizers are urea and ammonium carbonate. Nearly 80 per cent of the applied nitrogen originates from these fertilizers. Manure is only applied in wheat and it plays only a minor role as nitrogen source. About one third of the farm households cultivates wheat exclusively for own consumption and these farm households apply more nitrogen in wheat cultivation than the remaining farm households. The average yield of 5.7 t per ha in wheat and of 6.4 tons in maize enables gross margins of about 4 000 ¥ (400 ?) per ha, while in cotton and cultivation of peanuts the average gross margin is twice this amount. In chapter 6 the efficiency of the agricultural system is analysed. This analysis includes an impact analysis on nitrogen input and yield as well as an economic and ecologic optimum analysis of the nitrogen input. Nitrogen application rates show a broad variation at all cultivated crops. The impact analysis on nitrogen input does not show any clear and unique influence from the income structure of the farm household. Hence, additional cash income and less available family work force for farm work have no impact on the nitrogen application level. The analysis of the fertilizer costs instead of the amount of applied nitrogen confirms this statement. The nitrogen input analysis provides the nitrogen price as major impact factor. Higher nitrogen input levels are connected with lower nitrogen prices. Differences in nitrogen price result from the composition of the applied fertilizer, which differs in the ratio between fertilizer price and nitrogen content. The yield of wheat and maize indicates a high variation within the survey sites, but especially between the surveyed townships. A multifactorial regression analysis identified the location as the only significant influencing factor on yield. From the agronomic point of view, nitrogen is a major yield factor, but the survey data do not indicate a clear impact of nitrogen input on yield. The estimated relationship between nitrogen input and wheat yield provides a constant-shaped yield function. This result allows the assumption that due to the long term high nitrogen inputs the crop demand for nitrogen is fulfilled in the short term and additional nitrogen input is without impact on the yield. The quadratic regression models of nitrogen input and yield in wheat and maize fail to provide applicable economic optima of nitrogen input. For this reason, the concept of KRAYL (1993) is considered to estimate an applicable production function for wheat and maize. This concept is based on a location independent production function, which can be transferred into a location specific production function by the consideration of a location specific optimum nitrogen input and the corresponding yield. In this case the recommendations of ZHEN et al. (2005) are considered, which recommend for wheat a nitrogen input of 220 kg per ha in order to harvest 5.3 t per ha. The economic optimum nitrogen input levels are higher than the nitrogen recommendations of ZHEN et al. (2005), but still lower than the average nitrogen application rates. Hence, the present nitrogen price does not support the implementation of the recommended nitrogen application rates. The estimation of the economic optimum nitrogen input considers a production function based on the concept of KRAYL (1993) which is enlarged by factor and product prices. These are the crop prices and the costs of the other variable inputs, which are the variable costs excluding fertilizer costs. In this way, the gross margin can be described as a function of nitrogen input including the uniform factor crop price and the constant "other fertilizer costs". The calculated maximum gross margin in wheat of 4 057 ¥ per ha is achieved at a nitrogen input of 272 kg per ha. This level of nitrogen input is lower than the present average nitrogen input, but higher than the recommendations presented by ZHEN et al. (2005). Similar to the gross margin, the nitrogen balance is described as a function of nitrogen input, which considers the nitrogen input from fertilizer and straw left on the field from the previous cultivation as nitrogen inflow and the nitrogen content of the harvested crops as nitrogen outflow. Natural inflows and outflows are not taken into account. A nitrogen input of 205 kg per ha would result in the maximum accepted nitrogen surplus of 50 kg per ha and a gross margin of 3 365 ¥ per ha. Chapter 7 focuses on the estimation of the nitrogen balance and the analysis of relevant impact factors. The estimated nitrogen balances show at all crops, but especially in wheat cultivation a high level of nitrogen surplus, which is on average 200 kg of nitrogen per ha. The corresponding figures for maize, peanuts, and cotton are less than 100 kg of nitrogen per ha. Similar to nitrogen input, the nitrogen balance is indicated by a broad variation. This variation allows a classification of farm households into three nitrogen balance types: "equalized nitrogen balance", "slight nitrogen surplus", and "heavy nitrogen surplus". The farming system of "heavy nitrogen surplus" farm households can be characterized by low yields, high nitrogen input, and low calculated gross margin. These farm households have a share of 32 per cent of all farm households and cultivate about one third of the wheat of all surveyed farms, but their cumulated nitrogen input amounts to 50 per cent. Furthermore, this group of farm households accounts for 67 per cent of the cumulated nitrogen surplus. This situation leads to the question, which factors lead to that kind of nitrogen overuse. A binary logistic regression model is used to analyse the impact of pre-selected factors on the probability of a group membership interval, in this case to the "equalized nitrogen balance" as well as the "heavy nitrogen surplus" group. The covariates "family size", "education", "farmland", and "off-farm activities" do not show any significant influence. Similar to the nitrogen input analysis, a low nitrogen price and the application of manure increases the probability of a farm households of membership of the "heavy nitrogen surplus" group. Also, a low village average wheat yield and a high village average nitrogen input in wheat increases the probability. In order to identify parallel impacts of farm household characteristics on the nitrogen balance the group of farm households of "heavy nitrogen surplus" and "equalized nitrogen balance" are clustered. The farm households of the major cluster of the "heavy nitrogen surplus" group are characterized by less farmland and low farm households income without off-farm activities. Farm households of these characteristics are found at a minor cluster of the "equalized nitrogen balance" group, as well. A low income does not automatically lead to nitrogen application rates beyond the crop demand. Indeed, the combination of low income and high nitrogen input shows a higher probability than the combination of high income and high nitrogen input. Without doubt, the assumption that a lower income leads to a lower nitrogen input must be rejected. The nitrogen price might be a clear indicator for classification of farm households, but this criterion requires the analysis of the cultivation system of the considered farm household. For this reason, easy observable dichotomous variables are pre-selected and analysed whether a certain pattern can be used as criterion for identification as a part of a target group specific instrument. This approach does not provide applicable results. Chapter 8 deals with the simulation of scenarios of the nitrogen surplus reduction and the estimated impact on the net income of farm households. In the first step, the instrument independent potential nitrogen surplus reduction is estimated. The cumulated nitrogen surplus of wheat cultivation of all surveyed farm households can be reduced by more than 60 per cent, if all farm household would follow the nitrogen input recommendations and harvest the target yield of ZHEN et al. (2005). This scenario shows no changes in net income. However, the approach that all farmers would modify their present nitrogen application level to the recommended application rates might be too ambitious. Hence, it might be more realistic to consider a theoretical shift of half of the farm households belonging to the "heavy nitrogen surplus" group to the "slight nitrogen surplus" group. The nitrogen surplus reduction in wheat would be 18 per cent. The affected group of farm households represents 17 per cent of the wheat cultivation area, but accounts initially for 32 per cent of the total nitrogen surplus in wheat. This hypothetical shift considers the modification of the share of farm households belonging to a certain nitrogen balance type. The average nitrogen surplus and gross margin in combination with the share of farm households of nitrogen balance type is taken to estimate the overall nitrogen surplus and net income from farming of the considered nitrogen balance type. A change in the share of farm households modifies the overall nitrogen surplus and net income from farming of each nitrogen balance type and these modified values are considered as the impact of the evaluated instrument, which originate that change of share. The individual gross margin multiplied by the individual cultivation area of all farm households is summed up and it is considered as net income from farming. In the following step, the impact of an instrument on the nitrogen balance and the net income is simulated. The variable nitrogen price shows a highly significant influence towards the classification of nitrogen balance type. For this reason, a modification of the nitrogen price is selected as considered instrument. A higher nitrogen price reduces the probability of "heavy nitrogen surplus" and this difference in probability can be regarded as the share of farm households, which convert form "heavy nitrogen surplus" to "slight nitrogen surplus". In addition, a theoretical shift of "slight nitrogen surplus" farm households into "equalised nitrogen balance" farm households is considered. As instruments, a percental increase of the nitrogen price by 10 per cent is simulated. An increased nitrogen price by 10 per cent results in a reduction of the total nitrogen surplus of 4.9 per cent. The estimation of the impact on the net income from farming considers the described theoretical shift of farm households to another nitrogen balance type and a multiple regression model of the gross margin. The latter model considers all farm households and indicates a negative impact of the nitrogen price on the gross margin. A combination of both models results in a marginal reduction of net income from farming by 0.6 per cent, in case of a 10 per cent nitrogen price increase. In addition, a target simulation focuses on a more noticeable nitrogen surplus reduction. The average nitrogen price increase by 159 per cent to obtain a nitrogen surplus reduction of 50 per cent, but the net income from farming shows a reduction by 15.3 per cent. Summarized, the considered instrument "nitrogen price modification" fulfils the demand partly. It allows a nitrogen surplus reduction without a strong impact on the net income, but there are two major disadvantages. Firstly, huge nitrogen price modifications are required to gain a noticeable impact on nitrogen surplus reduction. Secondly, a nitrogen price modification affects all farmers, but there is a broad variation of the nitrogen balance and a high share of farm households actually has an equalized nitrogen balance. The discussion about the reasons for nitrogen overuse in the wheat and maize farming system in the North China Plain leads to the following results. This thesis cannot provide a comprehensive answer on the question, what the core reasons for the described surplus at the nitrogen balance are. The described high variation in nitrogen input and the reported low rate of farm households, which follow the recommended nitrogen application rates, leads to the assumption that an insufficient knowledge transfer system is the key reason for the inadequate use of the traditional cultivation system in terms of fertilizer application in the North China Plain. Lack of knowledge might be an explanation that low income farm households without off-farm activities do not have less fertilizer costs, but even have a higher probability to apply above average nitrogen rates than farm households, which have additional income from off-farm activities. The discussion about applicable instruments focuses on nitrogen tax, implementation of new agricultural technologies, and improvements in education and agricultural skills. The modification of the nitrogen price by a nitrogen tax is considered as an economically applicable instrument, but there are the described disadvantages. Furthermore, an economic instrument might not be suitable, if a noticeable share of the target group seems not to consider their farm level economic optimum as criterion in their determination of the applied nitrogen. In addition, a low nitrogen price is a suitable indicator for nitrogen overuse, but not its explanation. The nitrogen price represents the composition of the used fertilizer. An unfavourable composition can be regarded as an insufficient use of the cultivation system, which results in the described nitrogen overuse. Hence, an improvement in application of the cultivation technology might be more successful than an economic instrument. The discussion about new technologies focuses on their implementation. Only a minority of farm households follows the presently recommended nitrogen application rates and at a noticeable share of farm households the traditional cultivation system is not free of cultivation mistakes, especially in terms of nitrogen application. This raises the question, how successful a new agricultural technology can be implemented. The correct application present of the cultivation system and a proper working knowledge transfer system are the preconditions for the implementation of new technologies. For this reason, improvement in education and agricultural skills are the base instruments as well as the basis for all advanced instruments, because a sustainable cultivation system requires a sustainable implementation of its correct use.
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.
Integrated technical approach for differentiated nitrogen application based on expert knowledge and multiple parameters
(2023) Heiß, Andreas; Griepentrog, Hans
Variable rate nitrogen (N) application is subject to spatio-temporal dynamics of multiple parameters and a high dependency on specific local conditions. Furthermore, existing algorithms are barely capable of considering agronomic expert knowledge and common application technology limits the precise in-field realization. This work approached the complexity of site-specific N management in terms of the decision making, as well as the technical and organizational realization in a systemic manner. A commercial real-time N-sensor system’s behavior was transferred into a fuzzy expert system and extended with soil information. The incorporation into a real-time control included also the spatial synchronization of dose rate determination and realization. A digital process chain to facilitate decision making, data management and execution in the field was conceptualized and evaluated with a prototypical implementation. The N-sensor’s algorithms were precisely imitated with a maximum percentage root mean square error of 0.14%, while the multi-parametric system has implied more robust decisions. In field tests, the real-time control has shown acceptable synchronization errors largely below 1 m and with medians in the range of 0.25 m under realistic conditions. The integrated system architecture has shown a high consistency in terms of straightforward and situative expert knowledge acquisition, as well as the suitability for different sensor and application technologies. The work represents a systemic approach for a derivation and employment of machine-readable algorithms from agronomic expert knowledge defining the cause-effect relationships for a site-specific N application. Its generic properties allow a supplementation by other models and can in turn strengthen them further.
Investigation and Modeling of the Optimization Potential of Adapted Nitrogen Fertilization Strategies in Corn Cropping Systems with Regard to Minimize Nitrogen Losses
(2005) Link, Eva Johanna; Claupein, Wilhelm
The aim of this study was the "Investigation and Modeling of the Optimization Potential of Adapted Nitrogen Fertilization Strategies in Corn Cropping Systems with Regard to Minimize Nitrogen Losses". The background for the investigation could be seen in the increasing number of environmental pollution by agricultural land use. The dissertation was embedded in the context of the Graduiertenkolleg "Strategies to Reduce the Emission of Greenhouse Gases and Environmental Toxic Agents from Agriculture and Land Use" at the University of Hohenheim. The objective of this Graduiertenkolleg was to develop methods for quantifying and modeling the origin and the emission of greenhouse gases and environmentally toxic agents from agriculture and land use and for assessing them economically in the sense of practicable avoidance strategies. In order to determine the optimization potential of adapted nitrogen fertilization strategies in corn the study was organized in the following parts: 1. Investigation of the spatial variability and temporal stability of corn grain yield on three fields in the Upper Rhine Valley. 2. Determination of underlying yield-limiting factors in each field by the use of simple and complex models. 3. Development of adapted nitrogen fertilization strategies in consideration of the yield variability and the underlying yield-limiting factors. The area of investigation was located in the Upper Rhine Valley, which is characterized as a region with intense corn cultivation. At the same time this region belongs to the most important water protection areas in Europe. Thus, a conflict between agricultural land use associated with high fertilizer inputs on one hand and the protection of water bodies on the other hand rose, because measured nitrate concentrations in the groundwater increased constantly within the last decades. The study was conducted on three farm fields in the boundary of Weisweil, which is located northwest of Freiburg, Germany. Since 1998 the three fields were planted continuously with corn. In a 7-year field experiment spatial variability and stability of yield could be indicated. The determined yield pattern in each field raised assumptions about varying growth conditions within and among the fields. Thus, on the one hand the corn yield seemed to be influenced by temporal variations in cultivar, climate and management and by spatial and temporal variation of possible yield-limiting factors like nutrient availability or water supply on the other hand. In order to optimize management strategies the underlying yield-limiting factors causing the spatial and temporal yield variability needed to be determined in these three fields. Whereas plant yield parameters did not explain the existing yield variability very well, soil characteristics were identified as the major factors affecting the observed yield variability in all three fields. Significant relationships were found between combinations of soil nutrient levels, soil characteristics and yield. Based on these results, it appeared that soil characteristics were the primary factor affecting spatial yield variability in the three farmer fields in the Upper Rhine Valley. However, some of the spatial yield variability remained unexplained by simple regression analysis. In a more complex approach crop growth models were implemented to simulate the spatial yield variability within the field and to get information about the underlying yield-limiting factors. Therefore the process-oriented crop growth model APOLLO was implemented to evaluate the causes of spatial yield variability of corn in the three fields. APOLLO (Application of Precision Agriculture for Field Management Optimization) is a precision farming decision support system, which is based on the CERES and CROPGRO family of crop growth models and includes different soil parameter to calibrate the model. In general the APOLLO model performed well in simulating spatial yield variability in the fields. The results indicated that the spatial yield variability was mainly affected by a varying restrictive layers and reduction of root growth within the three fields. The correlation between simulated and measured yields provided information about the strength of the soil parameter affecting the yield within these fields. The calibration results were influenced by the grid size. Whereas smaller grids provided more random monitor yield data, larger grids provided a more representative set of yield monitor data, due to the coverage of a larger area. Consequently, the APOLLO model performed better when yields belonging to larger grids were used for model calibration. The applicability of the APOLLO model can be extended by developing prescriptions for different management strategies and thus enhancing the possibilities of successfully implementing site-specific management strategies. Thus, APOLLO was used to simulate the current uniform nitrogen management strategy of the producers in Weisweil over a 28-year period. Additionally an optimum uniform management and an optimum variable-rate management were developed and simulated. For these strategies also the different weather pattern were taken into account. All three strategies were evaluated based on the simulated yield, the simulated leaching potential and the simulated economics. It was obvious, that variable-rate nitrogen fertilization strategies were most advantageous compared to the other strategies, especially, when the nitrogen application rates were differentiated for dry, normal and wet weather scenarios. Adapted nitrogen fertilization strategies, as optimum uniform management and variable-rate management indicated a potential to reduce the amount of nitrogen, which is left in the soil after harvest, and associated that the potential nitrate leaching was reduced. In a case study the cumulative denitrification under these weather and fertilization scenarios over the growing season was simulated. The results indicated a reduction of cumulative denitrification under adapted fertilization strategies when compared to current uniform management. Summarizing, the results of this study suggest, that the implementation of adapted fertilization strategies (especially the variable-rate management of nitrogen) could lead to a reduction of nitrogen losses, as nitrogen leaching and nitrogen emissions could be minimized. Generally, the optimization potential for adapted nitrogen fertilizer strategies (optimum uniform management and variable-rate management) could be improved for cropping systems that were associated with higher risk for nitrogen losses.
Spatial combination of sensor data deriving from mobile platforms for precision farming applications
(2019) Zecha, Christoph Walter; Gerhards, Roland
This thesis combines optical sensors on a ground and on an aerial platform for field measurements in wheat, to identify nitrogen (N) levels, estimating biomass (BM) and predicting yield. The Multiplex Research (MP) fluorescence sensor was used for the first time in wheat. The individual objectives were: (i) Evaluation of different available sensors and sensor platforms used in Precision Farming (PF) to quantify the crop nutrition status, (ii) Acquisition of ground and aerial sensor data with two ground spectrometers, an aerial spectrometer and a ground fluorescence sensor, (iii) Development of effective post-processing methods for correction of the sensor data, (iv) Analysis and evaluation of the sensors with regard to the mapping of biomass, yield and nitrogen content in the plant, and (v) Yield simulation as a function of different sensor signals. This thesis contains three papers, published in international peer-reviewed journals. The first publication is a literature review on sensor platforms used in agricultural research. A subdivision of sensors and their applications was done, based on a detailed categorization model. It evaluates strengths and weaknesses, and discusses research results gathered with aerial and ground platforms with different sensors. Also, autonomous robots and swarm technologies suitable for PF tasks were reviewed. The second publication focuses on spectral and fluorescence sensors for BM, yield and N detection. The ground sensors were mounted on the Hohenheim research sensor platform “Sensicle”. A further spectrometer was installed in a fixed-wing Unmanned Aerial Vehicle (UAV). In this study, the sensors of the Sensicle and the UAV were used to determine plant characteristics and yield of three-year field trials at the research station Ihinger Hof, Renningen (Germany), an institution of the University of Hohenheim, Stuttgart (Germany). Winter wheat (Triticum aestivum L.) was sown on three research fields, with different N levels applied to each field. The measurements in the field were geo-referenced and logged with an absolute GPS accuracy of ±2.5 cm. The GPS data of the UAV was corrected based on the pitch and roll position of the UAV at each measurement. In the first step of the data analysis, raw data obtained from the sensors was post-processed and was converted into indices and ratios relating to plant characteristics. The converted ground sensor data were analysed, and the results of the correlations were interpreted related to the dependent variables (DV) BM weight, wheat yield and available N. The results showed significant positive correlations between the DV’s and the Sensicle sensor data. For the third paper, the UAV sensor data was included into the evaluations. The UAV data analysis revealed low significant results for only one field in the year 2011. A multirotor UAV was considered as a more viable aerial platform, that allows for more precision and higher payload. Thereby, the ground sensors showed their strength at a close measuring distance to the plant and a smaller measurement footprint. The results of the two ground spectrometers showed significant positive correlations between yield and the indices from CropSpec, NDVI (Normalised Difference Vegetation Index) and REIP (Red-Edge Inflection Point). Also, FERARI and SFR (Simple Fluorescence Ratio) of the MP fluorescence sensor were chosen for the yield prediction model analysis. With the available N, CropSpec and REIP correlated significantly. The BM weight correlated with REIP even at a very early growing stage (Z 31), and with SAVI (Soil-Adjusted Vegetation Index) at ripening stage (Z 85). REIP, FERARI and SFR showed high correlations to the available N, especially in June and July. The ratios and signals of the MP sensor were highly significant compared to the BM weight above Z 85. Both ground spectrometers are suitable for data comparison and data combination with the active MP fluorescence sensor. Through a combination of fluorescence ratios and spectrometer indices, linear models for the prediction of wheat yield were generated, correlating significantly over the course of the vegetative period for research field Lammwirt (LW) in 2012. The best model for field LW in 2012 was selected for cross-validation with the measurements of the fields Inneres Täle (IT) and Riech (RI) in 2011 and 2012. However, it was not significant. By exchanging only one spectral index with a fluorescence ratio in a similar linear model, it showed significant correlations. This work successfully proves the combination of different sensor ratios and indices for the detection of plant characteristics, offering better and more robust predictions and quantifications of field parameters without employing destructive methods. The MP sensor proved to be universally applicable, showing significant correlations to the investigated characteristics such as BM weight, wheat yield and available N.