The role of seed coatings in enhancing rhizobium colonisation and yield increases in pulse crops in the northern Mallee of South Australia

Shane Phillips1, Richard Saunders2

1 Landmark, PO Box 1310, Berri, SA, 5343,

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


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.

Azolla fertilizer as an alternative N source for red spinach production on alluvial and peat soils in West Kalimantan, Indonesia

Dwi P. Widiastuti1, Jessica G. Davis1, Sutarman Gafur2

1 Colorado State University, Dept. of Soil & Crop Sciences, Colorado State University, Fort Collins, CO, USA, 80523-1170,,

2 Tanjungpura University, Jl. Prof. Dr. H. Hadari Nawawi, Pontianak, West Kalimantan, Indonesia, 78124


Food security is an important goal in Indonesia, and each household is expected to utilize their backyard to provide food (vegetables) for their family. One approach to intensify vegetable production is through locally-grown fertilizer. Through biological nitrogen fixation, the Azolla-Anabaena symbiosis can provide N for vegetable production. The objective of this study was to evaluate the contributions and Nitrogen Use Efficiency (NUE) of A. pinnata as a biofertilizer on red spinach production on Inceptisols and Histosols in West Kalimantan, Indonesia compared to commonly-used fertilizers. The experimental design was a Randomized Complete Block Design with three replications. Five N fertilizer treatments were used: control, urea at 50 kg ha-1, chicken manure at 5 t ha-1, Azolla at the urea N rate, and Azolla at the manure N rate. Treatment means were compared using the honestly significant difference Tukey adjusted post hoc test (n=3, P<0.1). Overall, the results showed that Manure had the highest yield in the alluvial soil and it was comparable to Urea; whereas, in the peat soil, the significantly highest yield was also from the Manure treatment, but it was comparable to Azolla applied at the manure N rate. The highest leaf N content was in the Manure treatment (in the alluvial soil) and the Azolla applied at the manure N rate (in the peat soil). The highest NUE was in the Urea treatment in the alluvial soil. Therefore, Azolla applied at the manure N rate can be used as an alternative biofertilizer, especially for peat soil.

Soybean (Glycine max) response to rhizobia inoculation and soil nitrogen

Catherine Mathenge1, 2, Moses Thuita2, Joseph P Gweyi-Onyango1 and Cargele Masso2*

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:


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 2nd 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 2nd 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.

Monitoring the N release from organic amendments using proximal sensing

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

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


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.

Synthesized measurements of reactive nitrogen fluxes onto a forest using gradient and relaxed eddy accumulation method

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 (K. Matsuda)


Synthesized measurements of vertical profiles and exchange fluxes of reactive nitrogen and relevant species, which are fine (PM2.5) and course aerosol components (NO3 , NH4+ SO42-) 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 PM2.5. Decreasing ratio of NO3 in PM2.5 from upper to lower canopy was significantly larger than that of SO42- in PM2.5 or NO3 in coarse aerosols. From the measurements by relaxed eddy accumulation, deposition velocities of NO3 in PM2.5 were larger than those of SO42- in PM2.5. 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.

Microdialysis – a sensitive method for estimating plant-available N released during litter decomposition

Scott Buckley1, Richard Brackin1, Susanne Schmidt1

1 The University of Queensland, Brisbane, QLD, 4072,,


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.

Nitrogen turnover and N2:N2O partitioning from agricultural soils – a simplified incubation assay

Johannes Friedl1, Clemens Scheer1, Johanna Trappe2, David W. Rowlings1, Peter R. Grace1

1Institute for Future Environments, Queensland University of Technology, Brisbane, QLD 4000, Australia.,

2 University of Münster, Germany


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.

Assessing the influence of rice roots and root exudates on nitrogen mineralization in soil using a novel protocol

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


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.

New mobile, field based continuous-flow isotope ratio mass spectrometer system for automated denitrification studies

Daniel I. Warner1, Clemens Scheer1, David W. Rowlings1, Peter R. Grace1

1 Institute of Future Environments, Queensland University of Technology, Brisbane, QLD 4000 Australia,


Terrestrial denitrification, the reduction of oxidized nitrogen (N) to nitrous oxide (N2O) and dinitrogen (N2), is considered the least well understood process in the global nitrogen cycle. This study introduces a novel continuous-flow isotope ratio mass spectrometer (IR-MS) system that can be deployed in the field and continuously measure N2 and N2O emissions. Utilizing the 15N gas flux method this system can provide a better understanding of terrestrial denitrification. The system was tested over 14 days on 2 different agricultural soils (vertosol and ferrosol) which were fertilized with the equivalent of 100 kg ha-1 of N added in the form of KNO3 where the N was 60 at.% 15N. Total gaseous N losses over the 14 day monitoring period resulted in 14.1± 0.53 kg ha-1 and 5.7± 0.92 kg ha-1 for the ferrosol and vertosol soils, respectively. These results clearly demonstrate the ability of the field based IR-MS to measure N2 and N2O emissions from denitrification under field conditions. This system has the potential to improve our understanding of terrestrial denitrification and improve efforts to reduce gaseous N emissions from agricultural systems.

Pools and Fluxes: A snapshot of nitrogen dynamics in Australian soils

Mark Farrell1, Diane Allen2, Ben Macdonald3

1 CSIRO Agriculture & Food, Adelaide, SA, 5064,

2 DSITI, Brisbane, Qld, 4001,

3 CSIRO Agriculture & Food, Canberra, ACT, 2601,


Nitrogen (N) uptake by plants has been researched for well over a century, and continues to be of central importance both from an agricultural productivity and an environmental pollution perspective. Due to its prevalence as a fertilizer, mineral N is usually the only form routinely quantified in soil fertility assessments, despite significant quantities of dissolved organic N (DON) often being present. In the present study, we collected 358 topsoil samples from 89 sites under 13 different land uses. We quantified a wide range of soil N properties including pools and fluxes of organic and inorganic N to develop a better understanding of N cycling in Australian soils. Though nitrate dominated in some land uses, DON and free amino acid-N (FAA-N) were present in significant quantities in most land uses. Rates of N cycling were rapid in most soils, with only very nutrient-poor arid zone soils having particularly low N flux rates. Further research is required to better understand the availability of DON and its accessibility to plants.