Archive for the category: 2016 INI

Daniele De Rosa¹, David W. Rowlings¹, Johannes Biala¹, Clemens Scheer¹, Bruno Basso², Massimiliano De Antoni Migliorati¹, Peter Grace¹

¹Institute for Future Environments, Queensland University of Technology, Brisbane, QLD 4000, Australia d.derosa@qut.edu.au

²Department of Geological Sciences and W.K. Kellogg Biological Station, Michigan State University, East Lansing, MI 48823, USA

Abstract

The use of proximal sensed vegetation indices can reduce the uncertainty linked to the N supplied by organic amendments in a horticultural field by detecting in-season crop N status. This research assessed the applicability of the three vegetation indices (VI) of NDVI, NDRE and CCCI to evaluate the in-season long term optimized strategy of applying organic amendments to a horticultural crop (lettuce) over two seasons. A conventional urea application rate (CONV) was compared with raw (Ma) feedlot manure and Ma combined with standard (Ma+CONV) and optimized urea rate (Ma+Op). NDRE most accurately predicted crop N status at the late stage of lettuce development with an R² of 0.67 (RMSE 0.61), compared to 0.60 (RMSE 0.67) and 0.62 (RMSE 0.66) for NDVI and CCCI respectively. The in-season acquisition of crop reflectance proved to be a valid technique to determine the efficiency of an optimized combination between organic amendments and N-fertilizer.

Kazuhide Matsuda¹, Takaaki Honjo¹, Mao Xu¹, Taiichi Sakamoto¹

¹ Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan,

Email kmatsuda@cc.tuat.ac.jp (K. Matsuda)

Abstract

Synthesized measurements of vertical profiles and exchange fluxes of reactive nitrogen and relevant species, which are fine (PM_2.5) and course aerosol components (NO₃^– , NH₄⁺ SO₄^2-) and gas components (HNO₃, NH₃, SO₂), were carried out in a deciduous forest, suburban Tokyo.  Average vertical profiles in daytime and nighttime during the experiment showed the down ward fluxes (depositions). Differences of decreasing rates among the components were approximately in accordance with theoretical deposition velocities, except NO₃^– in PM_2.5. Decreasing ratio of NO₃^– in PM_2.5 from upper to lower canopy was significantly larger than that of SO₄^2- in PM_2.5 or NO₃^– in coarse aerosols. From the measurements by relaxed eddy accumulation, deposition velocities of NO₃^– in PM_2.5 were larger than those of SO₄^2- in PM_2.5. The large deposition velocity was possibly caused by an effect of shifts in equilibrium between aerosol phase (NH₄NO₃) and gas phase (HNO₃, NH₃) near surfaces. It was indicated that NH₄NO₃ could be quickly removed as well as HNO₃ in some conditions.

Scott Buckley¹, Richard Brackin¹, Susanne Schmidt¹

¹ The University of Queensland, Brisbane, QLD, 4072, http://www.uq.edu.au, s.buckley3@uq.edu.au

Abstract

Given the importance of soil nitrogen (N) availability in controlling N supply of plants and microbes, accurate estimates of soil N forms are vital. However, common extraction methods disrupt the soil environment, biasing estimates of soil N availability. Microdialysis offers an alternative by sampling N fluxes with minimal disturbance, and here we compare ex situ soil microdialysis with traditional potassium chloride or water extractions in the context of crop litter decomposition. We amended soil microcosms with sugarcane (0.68% N) or soybean (2.51% N) litter at realistic rates (0.72, 5 and 14.3 mg C g^-1 soil), quantified microbial activity parameters throughout a 30-day incubation period, and sampled N at day 30. In contrast to soil extractions, the diffusive fluxes generated with microdialysis facilitated a high-resolution snapshot of N availability. Microdialysis revealed that N was immobilised in the presence of sugarcane litter and was mineralised with soybean litter. Nitrogen immobilisation or mineralisation increased mostly with litter dose (although sensitivity varied somewhat between treatments) and in agreement with observed microbial activities. Such N processes were not apparent in soil extractions, indicating uniform N concentrations and forms across litter treatments. The only exception was the high soybean-amended treatments, in which total N increased. Our findings challenge the effectiveness of soil extractions to estimate plant-available N and resolution of N cycling processes in soils. Conversely, microdialysis represents a sensitive method for estimating the fine-scale N fluxes that are relevant to plants and insight into the factors regulating N cycling.

Johannes Friedl₁, Clemens Scheer₁, Johanna Trappe₂, David W. Rowlings_1, Peter R. Grace₁

¹Institute for Future Environments, Queensland University of Technology, Brisbane, QLD 4000, Australia. johannes.friedl@qut.edu.au,

² University of Münster, Germany

Abstract

Nitrogen turnover and related denitrification losses are a major uncertainty when estimating N loss and replacement from agro-ecosystems, due to methodological constraints quantifying N₂ and laborious analytical procedures. We present a novel, simplified incubation assay that combines the ¹⁵N gas flux method with the ¹⁵N pool dilution method, to quantify denitrification losses as a function of N turnover. This assay was tested using a pasture soil from sub-tropical Australia. N-fertiliser (35 µg g^-1 soil) was applied either as a single (NH₄¹⁵NO₃^–) or double (¹⁵NH₄¹⁵NO₃) labelled treatment at 10 atom %, with a third treatment (NH₄¹⁵NO₃^–) at 60 atom % to quantify N₂ emissions. Gross rates of N mineralisation, nitrification and related N₂ and N₂O emissions were measured during 48 hours of incubation at 80% WFPS. Gross N production and gross N consumption was consistent with the directly measured N pool sizes, with denitrification losses (N₂+N₂O) at 7.0 + 1.4 µg N g^-1 soil accounting for 62% of the calculated NO₃^– consumption. N turnover was dominated by mineralisation and nitrification, increasing the NO₃^– pool by a factor of 3. High NO₃^– concentrations shifted the N₂:N₂O ratio towards N₂O, with 60 % of denitrification losses emitted as N₂O. More than 25% of the applied ¹⁵N fertiliser was lost via denitrification, showing the significance of denitrification as a major pathway of N loss from agro-ecosystems. The simplified incubation assay proved to be an efficient tool to quantify N pools and emissions, and as such is an effective method to establish comprehensive datasets of denitrification losses linked to N turnover from agro-ecosystems.

Shamim Ara Begum¹, Md. Abdul Kader*^1,3, Steven Sleutel², Stefaan De Neve²

¹Department of Soil Science, Bangladesh Agricultural University, Bangladesh

²Department of Soil Management, Ghent University, Belgium

³School of Veterinary and Life Sciences, Murdoch University, Murdoch, 6150 Australia

Abstract

Classical nitrogen (N) mineralization experiments are done using uncropped soil, thus completely neglecting the influence of roots and root exudates. Therefore, experiments were conducted at two field sites in Bangladesh during ‘boro’ season (winter rice), using two rice cultivars (BRRI Dhan 29 and BINA Dhan6) to investigate the influence of rice roots and root exudates on N mineralization. Rice cultivars were transplanted in three replicated plots maintaining 25 x 15cm spacing along with three replicated uncropped plots as control. A novel method was used to identify the most suitable location to assess N mineralization in soil having actively growing rice plants. For this purpose, soil samples were collected from three locations in soil namely; 1) rhizosphere (0cm, at the rhizosphere), 2) middle of the two plants (7.5cm apart from rhizosphere) and 3) middle of two rows (12.5cm apart from rhizosphere). There was significant stimulatory effect of rice roots and root exudates on N mineralization at both filed sites. Significant influences of rice varieties were also observed, with BINA Dhan 6 having greater influence on N mineralization than BRRI Dhan 29. Sampling location also had a significant effect on measured N mineralization. The highest stimulatory effects of rice roots and root exudates were recorded when soil was sampled from rhizosphere. Sampling between the plants and between the rows had similar effects. In conclusion, rice roots and root exudates had a large influence on N mineralization and the best sampling location to determine the effects of actively growing rice roots and root exudates on N mineralization, was the rice rhizosphere.