Archive for the category: New methods of measuring reactive nitrogen in the environment

Shane Phillips¹, Richard Saunders²

¹ Landmark, PO Box 1310, Berri, SA, 5343, shane.phillips@landmark.com.aul

² Dodgshun Medlin, 60 East Terrace, Loxton, SA, 5333

Abstract

The colonisation of pulse crops by rhizobia in the northern mallee of South Australia is at times highly variable and in many cases inadequate for optimum plant growth. The aim of this work was to collate recent research publications to develop a seed coating that would enhance colonisation of seed coated rhizobium onto roots in low rainfall cropping regions such as the northern Mallee of South Australia. The coating of chickpeas, peas and lentils in this trial based out of Loxton with a product based on kelp, zinc, manganese, molybdenum and bacterial suspensions (Foundation TN) at 5L per ton of seed had significant benefits in plant growth and development. There was also a visual reduction in the incidence of root disease in treated plants. Statistically significant yield results were seen with Lentils (614kg/ha control to 677kg/ha coated), Field peas (729kg/ha control to 911kg/ha coated). Increases in Chickpeas were not significant (602 to 640kg/ha) but this may have been as a result of the lower seeding rate and severe frosts at flowering. Plants that had coated seeds in conjunction with rhizobia had greater numbers of efficient colonies and reduced root pathogens suggesting that good colonisation by rhizobium suppresses pathogenic infection points.  Trial results over recent years have suggested that appropriate seed coats that enhance root colonisation by rhizobium are highly cost effective and in maximising the symbiotic relationship between rhizobium and the host species.

Catherine Mathenge^{1, 2}, Moses Thuita², Joseph P Gweyi-Onyango¹ and Cargele Masso^2*

¹Department of Agricultural Science and Technology, Kenyatta University, P.O BOX 43844-00100, Nairobi, Kenya
²International Institute of Tropical Agriculture, c/o ICIPE, P.O. Box 30772-00100, Nairobi, Kenya
*corresponding author: C.Masso@cgiar.org

Abstract

Inoculation of soybean is an efficient way of increasing effective rhizobia population in the rhizosphere of the crop, but their performance is limited by soil nitrogen (N). The objective of the study was to determine the critical level of N below and above which, response to inoculation is hindered. Two greenhouse trials were set up and a field trial. The first greenhouse trial included unamended sixty soils (i.e. N: 0.03-0.21 %; organic carbon ≤ 2.10%), with and without inoculation. The 2^nd trial consisted of two soils selected based on the results of the first trial (i.e. 0.06% and 0.08% N) and amended with five rates of vermicompost (phymyx) to various N levels (i.e. N: 0.06/0.08-0.21%), with and without inoculation. The results of the 2^nd greenhouse trial are being validated in field conditions using similar treatments. For the sixty soils, the correlation between soil N and the growth parameters was low because of variability in other soil properties (r: 0.29-0.55); however, shoot biomass was higher in soils with high N. In the two amended soils, the highest shoot dry weight and nodules fresh weight were recorded at soil N level of 0.17%, beyond which nodulation was suppressed and shoot dry weight reduced. There was a significant interaction effect of soil and inoculation for N uptake (p<0.001) as result of the differences in soil properties, while the starter N from vermicompost did not hinder the performance of the rhizobia inoculant.

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.