Aged biochar affects gross nitrogen mineralisation and nitrogen recovery: a 15N study in two contrasting soils

Shamim Mia1, Feike A. Dijkstra1 and Balwant Singh1

1Center for Carbon, Water and Food, Faculty of Agriculture and Environment, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, 2570, Australia.

Corresponding author: Shamim Mia, email:


Biochar is pyrolysed biomass and comparatively more resistant to biodegradation than to its original biomass. When applied to soils, it could increase agricultural productivity through increased nutrient retention. Here, we examined the effects of a biochar after 21 months of application (20 t/ha) in two soil types, i.e., Tenosol and Dermosol, on gross nitrogen (N) mineralisation (GNM) and 15N recovery in a grassland field experiment using a 15N-labelled ammonium sulphate. The experiment also included a phosphorus (P) addition treatment (1 kg ha-1). The Demosol is clayey (52% sand and 29% clay) while the Tenosol is sandy (82% sand and 8% clay). We only found an increased GNM in the Tenosol, when it received both biochar and P. Biochar along with P addition possibly enhanced microbial activity in the nutrient limited Tenosol. Biochar significantly increased total 15N recovery in the Tenosol (on average by 12%) and reduced leaching to sub-surface soil layers (on average by 52%). Overall 15N recovery was greater in the Dermosol, but was not affected by biochar or P treatment. The increased N retention with biochar addition in the sandy Tenosol may be due to NH4+-N retention at cation exchange sites on aged biochar in the soil. Our results suggest that aged biochar may increase N use efficiency through reduced leaching or gaseous losses in sandy soils.

Harvest index for biomass and nitrogen in maize crops limited by nitrogen and water

  1. Chakwizira*, E.I. Teixeira, J.M. de Ruiter, S. Maley and M.J. George

The New Zealand Institute for Plant & Food Research Limited, Private Bag 4704, Christchurch, 8140, New Zealand. Phone: +64 3 3256400, Fax: +64 3 3252074

* Corresponding author: Email:


Nitrogen (N) is one of the major yield-limiting nutrients for crop production. At high application rates the efficiency of N use is reduced and the risk of N loss in soil-plant systems is increased. The N taken up by maize crops is partitioned between vegetative (e.g. leaves and stems) and reproductive organs (e.g. grains) that have economic value. The ratio of grain N to total crop N, defined as the nitrogen harvest index (NHI), provides an indication of how efficiently the plant converts absorbed N into grain. Two field experiments with the maize hybrid ‘Pioneer 39G12’ were undertaken to investigate how N rate and irrigation affected NHI and grain quality of maize grown. Harvest index (HI) and NHI increased with increasing water supply, from 0.47 to 0.53 (HI) and 0.43 to 0.60 (NHI), for the dryland and irrigated crops, respectively. However, neither HI nor NHI was significantly affected by N rate. The grain N concentration (Ng%) increased from 0.97% to 1.1% with water supply, and from 0.92% for the N control to 1.25% for the 200–250 kg N/ha crops in both experiments. However, Ng% did not significantly increase at the higher rates of fertiliser N. The NHI was closely related to HI, which suggests that management options to improve the HI of maize crops would also improve the crops’ ability to utilise N. The response of both HI and NHI to moisture stress, but not fertiliser N, highlights the importance of soil moisture in crop production in this environment, due to its influence on N uptake. Treatments with high water availability caused higher NHI values in crops and therefore we conclude that water management was of more value than N fertiliser rates for increasing NHI up to reported critical thresholds up to ±0.65.

Recovery of soil and fertiliser nitrogen in irrigated cotton in Australia

John Smith1, Mike Bell2

1 NSW Department of Primary Industries, 2198 Irrigation Way East, Yanco, NSW, 2703,,

2 The University of Queensland, School of Agriculture and Food Sciences, Gatton, QLD, 4343


Lint yield of irrigated cotton is typically responsive to the application of fertiliser nitrogen (N).  However, the applications of high rates of fertiliser N that exceed crop requirements result in unnecessarily low nitrogen recovery efficiency (NRE).  Three field experiments with eight N application rates were established across overhead and flood-furrow irrigation systems to determine N response curves for lint yield in irrigated cotton.  Lint yield was considered to be at its maximum where there was no further statistical increase from additional N application, this occurred between 145-245 kg/ha of total N supply (mineral N at planting + applied fertiliser N) with plant N uptake levels of 134-170 kg/ha.  NRE was determined by dividing crop N uptake at defoliation by the total N supply.  Where starting soil N levels were similar, overhead irrigation offered 34% higher NRE compared to flood.  The NRE at maximum lint yield was 6-28% higher than that achieved using farm practice at each site.

Sensing Technology for Measuring Crop Nitrogen

Glenn J Fitzgerald1, Eileen M Perry2

1 Agriculture Victoria, 110 Natimuk Rd., Horsham, VIC, 3400,

2 Agriculture Victoria, Cnr. Midland Hwy and Taylor Street, Epsom VIC 3551


Quantitative remote sensing has advanced in its ability to measure plant and canopy parameters, with nitrogen being one of the principal components of interest for crop N management. A plethora of sensors and imagers including multispectral, hyperspectral and fluorescence with different characteristics (e.g., passive vs active) have provided researchers and the agricultural industry with choices for measurement. Platforms for mounting sensors range from handheld and tractor mounted to satellites and unmanned aerial vehicles (UAVs). How to quantify canopy N using these hardware tools with spectral indices has been the focus of research for some time. Examples of recent work integrating sensors, platforms and spectral indices will be presented for ground-based proximal fluorescence sensing and passive sensing using ground and aerial platforms.

Dissimilatory nitrate reduction to ammonium, denitrification and anaerobic ammonium oxidation in paddy soil

Arjun Pandey1, Helen Suter1, Jizheng He1, Deli Chen1

1 Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Victoria 3121, Email:


Nitrogen (N) is the most important yield-limiting nutrient for rice production. Flooding of rice paddies for an extended period of time creates anoxic conditions in soil which can favour a simultaneous occurrence of several microbial N transformation processes, such as dissimilatory nitrate (NO3) reduction to ammonium (NH4+) (DNRA), denitrification and anaerobic NH4+ oxidation (anammox). Little is known about the role of DNRA and anammox in N cycling in paddy soils, and of the simultaneous occurrence of these N transformations. This study utilized a 15N isotopic approach to determine the rates of DNRA, denitrification and anammox processes simultaneously in a paddy soil. The paddy soil was collected from the Riverina region in New South Wales, Australia and studied under laboratory conditions. The rates of the processes were investigated after a week of flooding of paddy soil after a basal dose of N application at the rate of 1.6 g N m-2 (farmers practice in the region). Results showed that DNRA contributed to the formation of 0.34 µmole NH4+-N hr-1 kg-1 soil. Denitrification and anammox produced 3.35 µmole N2 and 0.65 µmole N2 hr-1 kg-1 soil, respectively. Denitrification was the major pathway contributing to N2 production which accounted for 83% of total N2 produced. Anammox contributed to 17% of total N2 production. Considering the bulk density of soil (1.3 g cm-3), it can be estimated that DNRA can retain 0.03 g N m-2 day-1, whereas denitrification and anammox can contribute to a loss of 0.58 and 0.11 g N m-2 day-1, respectively,  after the first week of flooding of paddy soil.

Strip planting decreases nitrogen fertilizer requirements while retention of more residue increases them in a rice-wheat-mungbean sequence on a subtropical floodplain soil

Md. Abdul Kader*1,2, Md.Jahiruddin1, Md.Rafiqul Islam1, Md.Enamul Haque1, Md. Sahed Hasan1,SutupaKarmaker1, Md. Mortuba Ali1, Richard Bell2

1Department of Soil Science, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

2School of Veterinary and Life Sciences, Murdoch University, Murdoch, 6150 Australia


Conservation agriculture (CA) has not been well developed for intensively cultivated (2-3 crops yr-1) rice-based cropping systems which produce large amounts of crop residues annually. Thus, we examined the effects of two crop establishment systems (minimum soil disturbance by strip planting (SP) or conventional tillage (CT)), two residue retention levels (low and high) and five N rates (60, 80, 100, 120 & 140% of the recommended N fertilizer doses (RFD) on nine consecutive crops on an Aeric Haplaquept under rice-wheat-mungbean sequence. Rice yields were comparable between the crop establishment types but system yields were significantly higher with SP in two out of three years compare to CT. Increased residue retention did not significantly influence rice yield but positively influenced system yields. No substantial differences in optimum N rate was estimated between CT and SP for 90% of maximum yield goal (MYG) for all the three years but substantially decreased in SP compared to CT in two out of three years for 95 and 99% of MYG. The N fertilizer requirement was 6-22% higher with high residue retention compared to low residue retention plots for all the three yield goal levels. High residue retention also increased soil organic carbon (SOC) at 0-6 cm depth in both tillage treatments. In conclusion, introducing CA did not alter the N fertilizer requirements of rice for 90% of MYG but reduced the requirement for 95 and 99% of MYG compared to CT. However, there was evidence that the retained crop residue immobilized N and increased the fertilizer N requirement.

Contribution of nitrous oxide in life cycle greenhouse fas emissions of novel and conventional rice production technologies

Md. Khairul Alam1, Richard W. Bell1, Wahidul K. Biswas2

1 Land Management Group, School of Veterinary and Life Sciences, Murdoch University, Western Australia 6150, Australia

2 Sustainable Engineering Group, School of Civil and Mechanical Engineering, Curtin University, Bentley, Western Australia 6845, Australia


Nitrous oxide (N2O) production and emission under wetland rice (Oryza sativa L.) is difficult to predict due to the trade-off between methane (CH4) and N2O emissions for different establishment and management practices.  Any novel technology with the potential to reduce the emissions of both CH4 and N2O under wetland rice could make a significant contribution to total agricultural global warming mitigation. A streamlined life cycle assessment (LCA) approach to quantify the C footprint of rice production process in the Eastern Gangetic Plains (EGP) was adopted. The GHG emissions from one tonne of rice production were studied for the following cropping practices: a) conventional puddled transplanting with low residue retention (CTLR); b) conventional puddled transplanting with high residue retention (CTHR); c) unpuddled transplanting following strip tillage with low residue retention (UTLR) and; d) unpuddled transplanting with high residue retention (UTHR). Total pre–farm and on–farm emissions for 1 tonne of rice production amounted to 1.11, 1.19, 1.33 and 1.57 tonne CO2–eq for UTLR, UTHR, CTLR and CTHR, respectively, in the 100-year time horizon. For all four treatments, the predominant GHG emission was soil CH4 (comprising 60-67% of the total) followed by emission from on-farm machinery use. The UTLR was the most effective GHG mitigation option (it saved 29% of the total GHG emissions in comparison with CTHR) in wetland rice production. N2O emission contributed 2–3.5% to the total on–farm GHG emitted for rice production of which the lowest portion was shared by UTLR and UTHR. The UTLR reduced both CH4 and N2O emissions simultaneously. The novel minimum tillage establishment approach for rice followed by UT has potential to increase global warming mitigation of wetland rice in the EGP, but further research is needed to assess the contributions of N2O in the LCA of rice production in other similar rice growing areas.

Benchmarking and mitigation of nitrous oxide emissions in temperate vegetable cropping systems in Australia resulting in improved nitrogen use efficiency

Ian Porter1 and David Riches1

1 School of Life Sciences, La Trobe University, Bundoora, Vic 3086, Australia,


Vegetable producers in some temperate regions of Australia use up to 1 tonne of nitrogen (N) as inorganic (fertilizers) and organic N (chicken manure) to produce 3 to 4 crops from the same land each year. Trials in Victoria showed great potential to reduce N inputs and to mitigate N2O losses from soil by use of nitrification inhibitors on manures and fertilizers compared to the standard grower practice (SGP) used at the sites without reducing yield. Annual N2O emissions ranged from 9.1 to 12.5 kg-N/ha for the unfertilized soil, and the combined fertiliser and manure program, respectively. Higher daily emission rates occurred when manures were applied to the soil and these were up to 20-fold greater for a single event than those from fertilizers. The inhibitors, DMPP and to a lesser extent 3MP/TZ, reduced N2O emissions from the fertilizer and manure program, with a maximum reduction of 64% occurring over the three crops, compared to the SGP. Pre-plant application of chicken manure resulted in short periods where daily N2O fluxes ranged from 70-213 g N2O-N/day and DMPP reduced the net N2O cumulative emission by 53% over this period. Annual cumulative N2O emissions were up to 40-fold higher at the Victorian site than reported in similar trials in Queensland and Tasmania. The Emission Factor of 0.45% from the SGP was considerably lower than the IPCC default value (1% of N applied). Nitrogen measurements indicate that up to 60% of the applied N may be lost to the atmosphere or leached in high N use vegetable systems in Victoria.

Nitrate-N losses in drainage water under irrigated vertosols of north-western NSW

Tim Weaver1, Nilantha Hulugalle2, Hossein Ghadiri3, Steven Harden4

1NSW Department of Primary Industries, Locked Bag 1000, Narrabri, NSW 2390,,

2Fenner School for the Environment and Society, Australian National University, Canberra, ACT 0200

3Griffith School of Environment, Environmental Futures Research Institute, Griffith University, Nathan, Qld 4111

4NSW Department of Primary Industries, Calala, NSW 2340


A comparison on the effects of soil and crop management practices in irrigated farming systems on the quality of drainage water in Vertosols has not been reported in the literature. The objective of this study was to quantify nitrate-N in drainage water in the subsoil (0.6, 0.9, 1.2 m) of sodic and non-sodic Vertosols under selected crop rotations, viz. continuous cotton (Gossypium hirsutum L.), cotton–dolichos (Lablab purpureus L.) and cotton–wheat (Triticum aestivum L.). A cotton–wheat rotation was sown at Wee Waa and Myall Vale; wheat stubble was incorporated in the former and retained as in situ mulch in the latter. At Merah North, there were three cropping sequences; viz. continuous cotton, cotton–wheat, and cotton–dolichos sown between 1993 and 2000 in adjacent plots with identical land management histories. The three treatments were sown with cotton during the 2000–2001 and 2002–2003 growing seasons, wheat during the 2001 winter and sorghum during the 2001–2002 growing season with stubble being incorporated. Drainage water was sampled with 50-mm diameter ceramic-cup samplers from depths of 0.6, 0.9 and 1.2m in six sites in each plot and irrigation water from the head ditch after irrigation between mid-October and late February during the cotton-growing seasons of 2000-2001 and 2002–2003. Soil water extracted from the ceramic-cup samplers was analysed for nitrate-N. The nitrate-N concentrations in drainage water varied among sites, and reflected variations in soil properties, fallow length since the preceding crop, fallow rainfall and irrigation water quality.

Rootzone reality – A network of fluxmeters measuring nitrogen losses under cropping rotations

Norris M1, Johnstone P1, Green S2, Clemens G3, van den Dijssel C2, Wright P4, Clark G4, Thomas S3, Williams R3, Mathers D5 and Halliday A6

1The New Zealand Institute for Plant & Food Research Limited, Havelock North, 4130

2The New Zealand Institute for Plant & Food Research Limited, Palmerston North, 4474

3The New Zealand Institute for Plant & Food Research Limited, Lincoln, 7608

4The New Zealand Institute for Plant & Food Research Limited, Pukekohe, 2676

5Foundation for Arable Research, Havelock North, 4130

6Horticulture New Zealand, Wellington, 6011



Nutrient losses are an important economic and environmental consideration across the New Zealand cropping sector. Between August 2014 and May 2015 we established a network of passive-wick drainage fluxmeters (DFMs) on commercial cropping farms in the Canterbury, Manawatu, Hawke’s Bay and Waikato/Auckland regions to measure nitrogen (N) losses in drainage water below the root zone. Results from this study will provide growers and regional authorities with measured N losses from cropping farms across a range of sites and seasons. The experimental design across the DFM network includes three sites each across four monitor regions, and uses 12 fluxmeters per site. Individual sites were chosen to provide a range of cropping systems, soil types, climatic conditions and management practices relevant to each region. Across the DFM network, measured losses have ranged from 0.2 kg N/ha to 226 kg N/ha for the period between DFM installation and 30 September 2015 with N lost primarily in the Nitrate-N form. Most drainage (78–100%) occurred over the mid-autumn to early spring period (April to September). Variability in N losses between sites reflect the duration of the monitoring period (five to 13 months) as well as the wide range of climate, management and soil characteristics.