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Lebender U.,Institute for Plant Nutrition and Environmental Research | Senbayram M.,Institute for Plant Nutrition and Environmental Research | Senbayram M.,University of Gottingen | Lammel J.,Institute for Plant Nutrition and Environmental Research | Kuhlmann H.,Leibniz University of Hanover
Journal of Plant Nutrition and Soil Science | Year: 2014

Nitrogen fertilizers are supposed to be a major source of nitrous oxide (N2O) emissions from arable soils. The objective of this study was to compare the effect of N forms on N2O emissions from arable fields cropped with winter wheat (Triticum aestivum L.). In three field trials in North-West Germany (two trials in 2011/2012, one trial in 2012/2013), direct N2O emissions during a one-year measurement period, starting after application of either urea, ammonium sulfate (AS) or calcium ammonium nitrate (CAN), were compared at an application rate of 220 kg N ha-1. During the growth season (March to August) of winter wheat, N2O emission rates were significantly higher in all three field experiments and in all treatments receiving N fertilizer than from the non-fertilized treatments (control). At two of the three sites, cumulative N2O emissions from N fertilizer decreased in the order of urea > AS > CAN, with emissions ranging from 522-617 g N ha-1 (0.24-0.28% of applied fertilizer) for urea, 368-554 g N ha-1 (0.17-0.25%) for AS, and 242-264 g N ha-1 (0.11-0.12%) for CAN during March to August. These results suggest that mineral nitrogen forms can differ in N2O emissions during the growth period of winter wheat. Strong variations in the seasonal dynamics of N2O emissions between sites were observed which could partly be related to weather events (e.g., precipitation). Between harvest and the following spring (post-harvest period) no significant differences in N2O emissions between fertilized and non-fertilized treatments were detected on two of three fields. Only on one site post-harvest emissions from the AS treatment were significantly higher than all other fertilizer forms as well as compared to the control treatment. The cumulative one-year emissions varied depending on fertilizer form across the three field sites from 0.05% to 0.51% with one exception at one field site (AS: 0.94%). The calculated overall fertilizer induced emission averaged for the three fields was 0.38% which was only about 1/3 of the IPCC default value of 1.0%. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Lebender U.,Institute for Plant Nutrition and Environmental Research | Senbayram M.,Institute for Plant Nutrition and Environmental Research | Senbayram M.,University of Gottingen | Lammel J.,Institute for Plant Nutrition and Environmental Research | Kuhlmann H.,Leibniz University of Hanover
Nutrient Cycling in Agroecosystems | Year: 2014

Nitrogen fertilizers are a major source of nitrous oxide (N2O) emissions from arable soils. The relationship between nitrogen application rates and N2O emissions was evaluated during the growth period of winter wheat (~140 days) at six field sites in north-western Germany. Nitrogen was applied as calcium-ammonium-nitrate, with application rates ranging between 0 and 400 kg N ha-1. One trial was conducted in 2010, three trials in 2011 and two trials in 2012. Additionally, post-harvest N2O emissions were evaluated at two field sites during autumn and winter (2012-2013). The emission factors (during the growth period) varied between 0.10 and 0.37 %. Annual N2O emissions ranged between 0.46 and 0.53 % and were consistently lower across all sites and years than to the IPCC Tier 1 default value (1.0 %). Across all sites and years, the relationship between N2O and N application rate was best described by linear regression even if nitrogen amounts applied were higher than the nitrogen uptake of the crop. Additionally, annual N2O emissions per unit of harvested wheat grain were calculated for two field sites to assess the environmental impact of wheat grain production. Yield-scaled N2O emissions followed a hyperbolic function with a minimum of 177 and 191 g N2O-N t grain yield-1 at application rates of 127 and 150 kg N ha-1, followed by an increase at higher N application rates. This relationship indicates that wheat crop fertilization does not necessarily harm the environment through N2O emissions compared to zero fertilization. Thus, improving nitrogen use efficiency may be the best management practice for mitigating yield-scaled N2O emissions. © 2014 Springer Science+Business Media Dordrecht. Source


Senbayram M.,University of Gottingen | Trankner M.,University of Gottingen | Dittert K.,University of Gottingen | Bruck H.,Institute for Plant Nutrition and Environmental Research
Journal of Plant Nutrition and Soil Science | Year: 2015

The increasing probability of seasonal droughts and freshwater scarcity emphasizes the importance of crop traits such as water-use efficiency (WUE) and its relation to nutrient management. In an earlier study using soil substrate in a pot experiment, we reported significant positive effects of N supply on biomass WUE of tobacco. However, there was a debate that the latter may be due to indirect effects of N supply (hidden drought), most likely because plants supplied with adequate N generally have greater biomass and hence faster depletion of soil water in the root zone. In pot and in field situation, therefore, it is difficult to relate any variation in leaf or biomass WUE to the direct effect of N supply. In this context, the aim of the current study was to re-examine to what extent N fertilization directly affects biomass WUE and related parameters under non-limiting water supply in hydroponics. About 2 weeks after the transfer of tobacco seedlings into nutrient solution containing 2 mM N, plants were treated with high-N or low-N in the form of NH4NO3. A marked decrease in CO2 assimilation with low-N supply compared to high-N supply was measured already 5 d after onset of treatments (DAO). In contrast, three different experiments clearly showed that stomatal conductance (gs) remained almost constant until 5 DAO resulting in significantly lower leaf WUE under low-N compared to high-N. Leaf WUE decreased gradually (up to 42% lower leaf WUE) at later stages. Surprisingly, biomass WUE and whole-plant δ13C values were not affected by N supply at any harvest date, which is in contrast to our earlier report where we observed clearly positive effects of N supply on biomass WUE of the same tobacco variety in a pot experiment with soil substrate. Night-time respiration and transpiration rates (measured by gas exchange and thermal imaging) were significantly higher with high-N supply than with low-N supply. The data show that 48.6% and 9.8% of the beneficiary effect of N on daytime leaf WUE were lost when nocturnal stomatal conductance and night-time respiration of the same leaves were taken into consideration. Thus, we conclude that earlier reports showing positive effects of N supply on biomass WUE and δ13C values in soil or field experiments may be due to indirect effect of N supply (e.g., hidden/mild drought). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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