Robert Edis

Prospects of improving efficiency of fertiliser nitrogen in Australian agriculture: a review of enhanced efficiency fertilisers

Fertiliser nitrogen use in Australia has increased from 35 Gg N in 1961 to 972 Gg N in 2002, and most of the nitrogen is used for growing cereals. However, the nitrogen is not used efficiently, and wheat plants, for example, assimilated only 41% of the nitrogen applied. This review confirms that the efficiency of fertiliser nitrogen can be improved through management practices which increase the crops ability to compete with loss processes. However, the results of the review suggest that management practices alone will not prevent all losses (e.g. by denitrification), and it may be necessary to use enhanced efficiency fertilisers, such as controlled release products, and urease and nitrification inhibitors, to obtain a marked improvement in efficiency. Some of these products (e.g. nitrification inhibitors) when used in Australian agriculture have increased yield or reduced nitrogen loss in irrigated wheat, maize and cotton, and flooded rice, but most of the information concerning the use of enhanced efficiency fertilisers to reduce nitrogen loss to the environment has come from other countries. The potential role of enhanced efficiency fertilisers to increase yield in the various agricultural industries and prevent contamination of the environment in Australia is discussed.

Dissimilatory nitrate reduction to ammonium and responsible microorganisms in two Chinese and Australian paddy soils

Dissimilatory nitrate reduction to ammonium (DNRA) and the responsible microflora were studied in two typical Chinese and Australian paddy soils. The DNRA accounted for 14.9% of total reduction of 15N-labeled nitrate added to the soil from Griffith (NSW, Australia) under anaerobic incubation without any exogenous carbon source addition, but only 5% for the soil from Yangzhou (China). Addition of reducing agents (sodium thioglycollate and l-cysteine) resulted in lower redox potentials and enhanced the DNRA process, with the majority of the product of reduction being ammonium. However, redox potential alone could not explain the difference of DNRA potentials between the two soils. Additions of glucose also resulted in substantial increases in DNRA, especially for Griffith soil, with the majority of the product being organic-N. The significantly higher DNRA in Griffith soil compared to Yangzhou soil is consistent with the higher DNRA microorganism population isolated from Griffith soil than that in Yangzhou soil, which is also consistent with higher fraction of labile carbon in Griffith soil than that in Yangzhou soil. In contrast, the denitrifiers population in the Griffith soil was about 10-fold smaller than that in the Yangzhou soil. The results demonstrate that the soil indigenous labile carbon was the key factor influencing the partitioning of nitrate reduction between denitrification and DNRA. Most DNRA bacteria and denitrifiers isolated were spore-forming bacteria.

Comparison of three modeling approaches for simulating denitrification and nitrous oxide emissions from loam-textured arable soils

Received 21 October 2004; revised 17 April 2005; accepted 11 May 2005; published 9 July 2005. [1] Soil denitrification fluxes and nitrous oxide (N2O) emissions from the soil surface simulated by a Water and Nitrogen Management Model (WNMM), with three different gas modules, are compared to measurement data sets from two irrigated wheat-maize systems at two locations in the North China Plain (NCP) (2 years of measurement at the Luancheng site and 1 year of measurement at the Fengqiu site). The three gas modules are the WNMM gas module, the DAYCENT gas module, and the DNDC gas module. The term gas module used in this paper refers to the model component which simulates N2O emission from the processes of soil nitrification and denitrification. Soil water, temperature, organic matter decomposition, other nitrogen (N) transformations, such as mineralization and immobilization, and crop growth are simulated by the WNMM platform. For the 2-year data set from Luancheng, the three gas modules generate similar soil mineral N dynamics in the 0–20 cm topsoil. The daily time step, simply structured WNMM gas module consistently performs the best among the three gas modules for predicting soil denitrification fluxes (R 2 = 0.28, n = 39, p = 0.0006) and N2O emissions (R 2 = 0.45, n = 36, p < 0.0001). Up to 73, 43, and 22% of total N2O emissions are nitrification-induced as simulated by the DNDC, DAYCENT, and WNMM gas modules respectively, in this well-drained loam soil during the 2-year simulation. When applied to the 1-year data set at the Fengqiu site, the WNMM gas module consistently performs better in estimating N2O emissions (R 2 = 0.54, n = 35, p < 0.0001) compared to the other two modules. Simulations using the DNDC and DAYCENT gas modules explain over 40% of the temporal variation of N2O emission from the soil. Further testing on different soils and different agroecosystems is needed to confirm the superior performance of the WNMM gas module observed in this simulation study.

Measurement of greenhouse gas emissions from Australian feedlot beef production using open-path spectroscopy and atmospheric dispersion modelling

Feedlot production of beef cattle results in concentrated sources of gas emissions to the atmosphere. Reported here are the preliminary results of a micrometeorological study using open-path concentration measurements to determine whole-of-feedlot emissions of methane (CH4) and ammonia (NH3). Tunable near-infrared diode lasers were used to measure line-averaged (150–400 m) open-path concentrations of CH4 and NH3. A backward Lagrangian stochastic model of atmospheric dispersion and the software package WindTrax were used to estimate greenhouse gas fluxes from the measured concentrations. We studied typical Australian beef feedlots in the north (Queensland) and south (Victoria) of the continent. The data from a campaign during summer show a range of CH4 emissions from 146 g/animal.day in Victoria to 166 g/animal.day in Queensland and NH3 emissions from 125 g/animal.day in Victoria to 253 g/animal.day Queensland.

Nitrate leaching from temperate perennial pastures grazed by dairy cows in south-eastern Australia

Nitrate (NO3-N) leaching losses were measured over 3 years from a temperate grass/clover pasture with and without 200 kg N fertiliser/ha, applied as ammonium nitrate or urea, using a system of moles and tile drains. Fertiliser was applied in 4 split dressings of 50 kg N/ha in each of the 4 seasons of each year. Drainage was collected continuously and NO3-N concentrations in drainage water were measured in subsamples collected using a flow-proportioned sampler. Pastures were rotationally grazed with dairy cows at stocking rates equivalent to 1.9 or 2.8 cows/ha for the unfertilised and fertilised treatments, respectively. Soil water deficit (SWD) varied markedly between seasons and years, with drainage occurring in the cooler, wetter months (April–October) and not at all through the summer. There were no significant differences between treatments in SWD, drainage events, or drainage volumes. Peak NO3-N concentrations were 19, 50, and 17 mg/L for the control, ammonium nitrate, and urea treatments, respectively. Mean annual flow-weighted NO3-N concentrations over the 3 years were 1.7 and 2.2 times higher from the ammonium nitrate treatment than from the urea and control treatments, respectively. Annual NO3-N leaching loads (kg N/ha) were 3.7–14.6 from the control treatment, 6.2– 22.0 from the urea treatment, and 4.3–37.6 from the ammonium nitrate treatment, for the lowest and highest drainage years, respectively. The experiment confirmed that the application of N fertiliser prior to periods of substantial drainage can result in high losses of NO3-N through leaching. More efficient and environmentally sound use of N fertiliser can be achieved by not combining high N fertiliser rates, high stocking intensity, and nitrate-containing fertilisers prior to periods when there is a risk of substantial drainage occurring.

Modeling Nitrate Leaching and Optimizing Water and Nitrogen Management under Irrigated Maize in Desert Oases in Northwestern China

Understanding water and N transport through the soil profile is important for efficient irrigation and nutrient management to minimize nitrate leaching to the groundwater, and to promote agricultural sustainable development in desert oases. In this study, a process-based water and nitrogen management model (WNMM) was used to simulate soil water movement, nitrate transport, and crop growth (maize [Zea mays L.]) under desert oasis conditions in northwestern China. The model was calibrated and validated with a field experiment. The model simulation results showed that about 35% of total water input and 58% of the total N input were leached to <1.8 m depth under traditional management practice. Excessive irrigation and N fertilizer application, high nitrate concentration in the irrigation water, together with the sandy soil texture, resulted in large nitrate leaching. Nitrate leaching was significantly reduced under the improved management practice suggested by farm extension personnel; however, the water and nitrate inputs still far exceeded the crop requirements. More than 1700 scenarios combining various types of irrigation and fertilizer practices were simulated. Quantitative analysis was conducted to obtain the best management practices (BMPs) with simultaneous consideration of crop yield, water use efficiency, fertilizer N use efficiency, and nitrate leaching. The results indicated that the BMPs under the specific desert oasis conditions are to irrigate the maize with 600 mm of water in eight times with a single fertilizer application at a rate of 75 kg N ha(-1).

The relation between soil structure and solute transport under raised bed cropping and conventional cultivation in south-western Victoria

This study examined the relationship between soil structure and solute transport in a texture contrast soil under 2 different tillage treatments—raised beds and conventional cultivation—in south-western Victoria. Undisturbed soil samples were collected for resin-impregnation and image analysis. This enabled several descriptive parameters of macropore structure to be calculated. Large, undisturbed soil samples were also collected for a solute transport experiment using a KCl solution. A convective log-normal transfer function was used to model Cl − movement. The assessment of soil structure showed that the raised beds contained a better connected pore network than the conventionally cultivated soil. Solute transport was faster through the raised bed soil when close to saturation (at -5 mm tension). Under these conditions, the solute transport parameters showed a smaller ratio of transport volume to soil water volume in the raised bed than the conventionally cultivated soil. Together, these data strongly indicate that the raised beds had greater pore connectivity and were able to transmit solute faster and more efficiently than the conventionally cultivated soil. It is concluded that raised bed soils are better structured and provide less risk from waterlogging than conventionally cultivated soils. However, there is greater potential for preferential flow of pesticides and solutes in raised bed soils.

Desorption of phosphate from sugarcane soils into simulated natural waters

A laboratory-based study of the behaviour of phosphorus (P) was carried out on the soils of the lower Herbert River catchment, Queensland, Australia. The aim was to explore the potential for P sorption or desorption by Herbert soils in associated river and estuary waters, so that the extent of problems associated with sugarcane production and soil-derived inputs to streamwater could be defined. Anion exchange resin was used as a sink for P. The equilibrium phosphate concentration (EPC) measured in simulated soil pore water (0.01M CaCl2), and the EPC in the simulated river and estuary waters were strongly correlated. Based on this, and the close relationship between P sorption and selected soil properties, it was possible to estimate P desorption using commonly measured properties. Much less desorption of P took place in simulated estuary waters than in simulated river water of much lower ionic strength. This suggests that environmental degradation arising from the downstream export of soil-borne P from Herbert cane lands is likely to be concentrated in freshwater areas. Sorption properties of P in soils of the lower Herbert appear to be closely associated with aluminium-rich minerals, rather than with iron (hydr)oxides.

Improved drainage and greater air-filled porosity of raised beds in south-western Victoria

Crop production in south-western Victoria has historically been constrained by waterlogging. As a result raised beds have recently become a popular tillage method on soils prone to waterlogging. Soil water properties, air-filled porosity, plant dry matter, and grain yield were compared for raised beds and conventional cultivation treatments during 2003 and 2004. Although rainfall was less than the long-term average, over the whole period the raised beds had consistently lower water content and drained faster than the conventional cultivation. Air-filled porosity was greater and above the critical value of 10% for longer in the raised beds (e.g. in 2004 air-filled porosity was >10% for 69 days longer in the raised beds). Benefits on the raised bed soil (such as greater soil aeration) were probably due to the increased depth to the B horizon and the soil surface topography created by regular furrows. No waterlogging was observed in 2003 and the crop on the conventional cultivation produced significantly more dry matter. Although visible waterlogging of the crop on the conventional cultivation was observed in 2004, the crop on the raised beds was not affected. Despite the different response in growth for each treatment, there was no significant difference in grain yield in either year. Nevertheless, it is predicted that raised beds should provide a well-drained and aerated soil that maintains crop productivity under average or greater rainfall in south-western Victoria.

Soil nitrogen dynamics in irrigated maize systems as impacted on by nitrogen and stubble management

The soil nitrogen (N) dynamics of an irrigated maize system in which stubble retention and stubble burned treatments were superimposed over treatments of varying N fertiliser rate were studied. The field site was near Whitton, New South Wales, Australia, and the work described here is part a life cycle analysis of greenhouse gas emissions from maize project. The objective of this part of the work was to quantify the fate of fertiliser N applied at the site. Field measurements of denitrification, mineral N content and recovery of 15N-labelled urea from microplots with and without ammonium thiosulfate were complimented with laboratory studies of denitrification and nitrous oxide (N2O) flux. Significantly (P < 0.05) more fertiliser N was recovered in the grain from the stubble incorporated treatment than the stubble burned treatment and there was greater recovery of fertiliser N in the soil at the end of the experiment in the stubble burned treatment. This may indicate that fertiliser N applied to the stubble burned system may be more exposed to soil-N transformations. The reason for the difference in uptake and soil residual is not clear but may be related to soil structure differences leading to less plant accessibility of N in the burned treatment. This difference may lead to more nitrous oxide emission from soil in the stubble burned treatments. Short-term (1 h) static chamber measurements in the field found a strong N-rate dependence of N2O emission rate for fertiliser rates between 0 and 300 kg N/ha. Inclusion of ammonium thiosulfate in the fertiliser formulation did not appear to have a significant impact on fertiliser N recovery.