M. J. Unkovich

University of Adelaide · Waite Research Institute (WRI)

Australian agriculture is dominated by rainfed cropping in environments where evaporative demand greatly exceeds annual rainfall. In this paper we review field measurements of crop transpiration and bare soil evaporation under rainfed grain crops, and crop transpiration efficiencies. Crop transpiration is typically calculated from the difference be...

This paper reviews the interactions between water and nitrogen from physiological, agronomic, economic, breeding and modelling perspectives. Our primary focus is wheat; we consider forage crops, sorghum and legumes where relevant aspects of water-nitrogen interactions have been advanced. From a physiological perspective, we ask: How does nitrogen d...

An agricultural research for development project on the East India Plateau provides the context for reflecting on the conduct of research, the creation of learning opportunities, scaling out of research results, and monitoring research impact. What appears at one level as research into rice agronomy actually has profound implications for climate re...

http://agwine.adelaide.edu.au/research/farming/legumes-nitrogen/17th-australian-nitrogen-fixation-conference-2014.pdf

Methodologies based on 15N-enrichment for estimating the transfer of nitrogen (N) between legumes and companion non-legume species in agro-ecosystems are critically reviewed and classified according to whether they (i) are direct or indirect (ii) are dependent or independent of the measurement of yield and (iii) are estimating transfer of legume N,...

Brazil is the major world coffee producer, using increasing quantities of nitrogen (N) fertilizer as the monoculture expands across the savannas. The fate and efficiency of this fertilizer N were evaluated for one complete cropping cycle using 15N tracer, permitting an N balance at harvest. Annual rates of 200, 400, 600, and 800 kg N ha−1 year−1 of...

Identifying the location and amount of grain crop residues (stubble) in Australia is necessary for determining the viability of potential biofuel plant locations. We combined 22 years of crop statistics with harvest indices and land use to arrive at spatially explicit stubble productivity figures. Stubble quantities using different focal radii and...

Quanstitative measurement of N-2 fixation has rarely been conducted in Australian dairy pastures. The available data indicate that annual N-2 fixation rates in Australian dairy pastures are generally low, due to low pasture legume content. With typical legume contents of grazed pastures less than 30% of total pasture biomass production, annual N-2...

Little is known about the soils that support agriculture in Tibet. The aim of this paper is to investigate the physical and chemical properties of Tibet’s agricultural soils, the nutritional status of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) crops, and the sustainability of current soil management practices. Physical description...

Symbiotic dinitrogen (N2) fixation of crop and pasture legumes is a critical component of agricultural systems, but its measurement is expensive and labour intensive. Simple models which can provide approximations based on crop or pasture dry matter production would be useful for agrononomists and those interested in regional nitrogen (N) cycle flu...

Figure 3 depicted the correlation between shoot dry matter and N 2 fixed but the plotted Y axis data actually depicted total shoot N rather than amounts of shoot N fixed. The correct Figure is presented below, the figure caption remains the same.

Rainfed farming systems in southern Australia have changed during recent decades from a traditional mixed crop–livestock system towards more intensive cropping. New technologies and greater economies of scale have increased productivity and have been accompanied by the adoption of more environmentally sustainable land management systems. Despite in...

Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in an extensive irrigated lucerne growing region where ni...

Rainfed spring wheat (Triticum aestivum L.) is the most important cereal crop on the Western Loess Plateau. Lucerne (Medicago sativa L.) has been very popular. There are problems associated with both continuous cropping and with perennial lucerne systems. The key challenge for rain-fed cropping systems is to adopt strategies that make optimal use o...

For grain crops, harvest index (HI) is the ratio of harvested grain to total shoot dry matter, and this can be used as a measure of reproductive efficiency. The index can also be used to estimate crop carbon (C) balances by applying it to grain yield statistics to determine total shoot dry matter and then calculating crop residues as the difference...

The management of water and nutrients in farming systems that incorporate alternating phases of lucerne pasture with annual grain crops posses additional challenges to rotations with annual crops only. Strategies for balancing water and nutrient resources within and across rotations will be governed by local soil, climatic, skill and economic const...

Dryland agriculture is both a potential source and potential sink for CO2 and other greenhouse gases. Many carbon accounting systems apply simple emissions factors to production units to estimate greenhouse gas (GHG) fluxes. However, in Australia, substantial variation in climate, soils, and management across 20Mha of field crop sowings and 30Mha o...

In the south of the Tibet Autonomous Region of China there is a network of valleys where intensive agriculture is practiced. Although considered highly productive by Tibetans, farm incomes in the region are low, leading to a range of government initiatives to boost grain and fodder production. However, there is limited information available on curr...

A wide range of bacteria capable of nitrogen fixation (free-living and associative) can be found in all agricultural soils across Australia, however measurement of their effectiveness in N2 fixation has proved to be problematic because rates are low compared to symbiotic systems and quantitative methodologies barely adequate. It is generally believ...

Data collected from a field experiment in NE Victoria was compared with simulated wheat and lucerne grown in mixture (companion crop) and wheat in monoculture, using the Agricultural Production Systems Simulator (APSIM). Detailed field soil measurements along with specific management inputs were used to parameterise the model, while observed cereal...

A long-term rotation experiment was established in 2001 to compare conservation tillage techniques with conventional tillage in a semi-arid environment in the western Loess Plateau of China. We examined resource use efficiencies and crop productivity in a spring wheat (Triticum aestivum L.)–field pea (Pisum arvense L.) rotation. The experimental de...

Gansu Province in north western China contains a large portion of China's rural poor. Within this province we compared extant farming systems in lower and higher rainfall areas of the Loess Plateau. The farming systems were dominated by subsistence winter wheat production in the higher rainfall more productive area (Qingyang), and subsistence sprin...

Authorities in the Tibet Autonomous Region of China are concerned about the sustainability and productivity of food production systems, and have initiated a number of projects that aim to boost grain production. However, there is limited information available on current cropping systems, yields and likely yield constraints. To address this knowledg...

An important proportion of crop production in South Australia is carried out on neutral-alkaline soils comprising infertile siliceous sands overlaying sodic subsoils. Crop growth is limited by the infertile nature of the non-wetting, rapidly draining upper soil horizons and also by the lower soil horizons which are generally dense sandy clays, ofte...

In many crops over half the above-ground biomass is not currently harvested and could be used as a feedstock for biofuel production. There is little published information about stubble production, and the implications of harvesting it. We use a survey of field trials reporting Harvest Index (HI), ABS production statistics and APSIM simulations to a...

The terrestrial nitrogen (N) cycle comprises soil, plant and animal pools that contain relatively small quantities of biologically active N, in comparison to the large pools of relatively inert N in the lithosphere and atmosphere, but that nevertheless exert a substantial influence on the dynamics of the global biogeochemical N cycle. After carbon...

Studies of the variation in δ15N values for plants from a fire-prone Banksia woodland in South West Australia showed that pioneer herbaceous, non-mycorrhizal species which were active in nitrate reduction and storage, had the highest values (1.81%c). A detailed study of one such species Ptilotus polystachus demonstrated a close correspondence betwe...

Nitrate was found to be the predominant form of available nitrogen in mulga soils. Nitrate reductase activities on a fresh mass basis of a range of plants from eastern (Queensland) mulga ecosystems 2 weeks after partial relief from drought were uniformly low for both herbaceous species (165 ± 25 pkat g−1) and woody perennials (77 ± 14 pkat g−1). Su...

An experiment at 3 sites (Birchip, Elmore and Speed) in the northern Victorian cropping belt compared dry matter (DM) production of short-term (2 year) pastures and their contributions to soil mineral nitrogen (N) and subsequent wheat and barley production. The pastures included different varieties of subterranean clover, annual medic and lucerne,...

This paper proposes a method for estimating the feed base, grazing pressure and variability as an indicator of risk, in grazing lands. Together, they may be considered as surrogate measures of biophysical sustainability. The paper applies them to four transects, each from unfertilised rangeland to relatively intensive mixed farming in temperate Aus...

Annual crops were grown in alleys between belts of perennial shrubs or trees over 3–4 years at 3 sites across low rainfall (<450 mm) south-eastern Australia. At the two lower rainfall sites (Pallamana and Walpeup), crop grain yields within 2–5 m of shrub belts declined significantly with time, with a reduction equivalent to 45% over 9 m in the fina...

Restoration of native vegetation is a first step in conserving native biodiversity in a given landscape. The landscape in the Victorian Riverina bioregion where intensive agricultural enterprises (e.g horticulture, dairy and viticulture) dominate landuse have reduced levels of native biodiversity. This is primarily because of alienation of native v...

Leaching of nitrate through soil profiles is a major cause of soil acidification. Legume species differ in their ability to take up nitrate (NO3−) and in the degree to which soil NO3− impairs legume nodulation and N2 fixation. This pot experiment examined species variation in N2 fixation and acid production in grain legumes grown for 6 wk on a sand...

This chapter serves as an introduction to the use of natural variations in 15N for estimating N2 fixation by field-grown annual legumes. While all of the examples cited come from Australian studies, the principles illustrated can be applied effectively in any region. Much of the material is extracted from that presented in Unkovich et al. (1994b, 1...

The removal of nitrogen (N) in grain cereal and canola crops in Australia exceeds 0.3 million t N/year and is increasing with improvements in average crop yields. Although N fertiliser applications to cereals are also rising, N2-fixing legumes still play a pivotal role through inputs of biologically fixed N in crop and pasture systems. This review...

In the last two decades technological advances in isotope ratio mass spectrometry have been very rapid, opening up new possibilities for analysis of biological and environmental materials. The new instrumentation has facilitated faster analysis of samples via automated sample preparation and multi-isotope analysis of single samples, resulting in co...

In this paper we review both the methods for estimating N2 fixation and the quantity of N2 fixed by annual crop legumes. Available data on the N difference method for estimating N2 fixation reveal it to be unreliable. Although we advocate the use of isotope-based techniques their limitations necessitate the simultaneous collection of supporting dat...

Nitrogen (N) isotope fractionation and symbiotic N fixation were investigated in the shrub legume tagasaste, growing in the glasshouse and field. In a pot study of effectively nodulated plants supplied with 0, 1, 5 and 10 mM nitrate [stable isotope 15N (δ15N) of 3.45‰], the δ15N of dry matter N of fully symbiotic cultures indicated a greater isotop...

Effects of incursion of water and nutrients from agricultural land on adjoining native Banksia woodland were examined near Moora, Western Australia, by using a 100-m-wide belt transect from the paddock edge into virgin bush. Transect zones 0–20, 20–50 and 100–300 m inwards were designated as ‘hedge’, ‘transition’ and ‘inner bush’, respectively. Num...

A field study measured the rate of soil mineral N supply and its effects on plant biomass and N accumulation in a 13-year-old, naturally regenerating, calcareous grassland. Gross rates of N mineralisation (2 μg g−1 day−1, i.e. 0.69 kg ha−1 day−1), assessed using 15N pool dilution, were at the lower end of the range previously reported for grassland...

Samples of recently produced shoot material collected in winter/spring from common plant species of mulga vegetation in eastern and Western Australia were assayed for 13C and 15N natural abundance. 13C analyses showed only three of the 88 test species to exhibit C4 metabolism and only one of seven succulent species to be in CAM mode. Non-succulent...

The effects of indigenous rhizobial communities on the establishment and functioning of subterranean clover-Rhizobium symbioses was examined using inocula obtained from soils of nine clover pastures and applied as dilute soil suspensions to pot-cultured subterranean clover (Trifolium subterranean cv. Trikkala). The clover was grown without added N...

 This paper reports the results from a medium-term field scale investigation into the effects of simulated climate change on soil N mineralisation in a semi-natural calcareous grassland in southern England. The experiment utilised soil warming cables, automatic rainshelters and a watering system to examine two climate change scenarios: warmer winte...

Plant and soil nitrogen (N) fluxes were assessed in subterranean clover (Trifolium subterraneum L.) based pastures set-stocked at 8 sheep per hectare (light grazing) or grazed at a much higher, but variable, intensity to maintain 1400 kg standing dry matter per hectare (intensive grazing) through the addition or removal of sheep. Pasture compositio...

Nitrogen balances of narrow leaf lupin (Lupinus angustifolius L.), albus lupin (L. albus L.), field pea (Pisum sativum L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare L.) sown over a range of dates were examined in 1992 in a rotation study at Wagga Wagga, NSW. Each N budget included assessment of dependence on fixed as opposed to so...

The effects of low soil pH and lime addition on nodulation and nitrogen fixation in subterranean clover (Trifolium subterraneum L.) were examined in field and glasshouse experiments in south-west Australia. Field data from a number of broadacre pastures indicated that soil acidity combined with high soil aluminium reduced clover dependence on nitro...

Annual pasture legumes play a key role in ley farming systems of southern Australia, providing biologically fixed nitrogen (N) to drive the production of the pastures as well as subsequent crops grown in rotation. Seasonal inputs of biologically fixed N in shoot biomass of the subterranean clover (Trifolium subterraneum) component of grazed annual...

The proportion of legume N derived from the atmosphere by N2 fixation (%Ndfa) was assessed at a number of field sites using δ15N natural abundance methodology for the grain legumes lupin (Lupinus angustifolius L.) and field pea (Pisum sativum L.) and for subterranean clover (Trifolium subterranean L.) in annual pastures. Concurrent assessments of N...

The progress of N2 fixation by subterranean clover (Trifolium subterraneum L.) was followed throughout a growing season in adjacent grazed and ungrazed portions of a pasture at Mount Barker, W.A. Proportions of plant nitrogen derived from the atmosphere (%Ndfa) were determined at a sequence of sampling times using the 15N natural abundance techniqu...

The time courses of above- and below-ground accumulation of biomass and N were followed in a crop of narrowleaf lupin (Lupinus angustifolius L. cv. Illyarrie) at Geraldton, W.A., and concurrent N2 fixation assessed using the 15N natural abundance technique. Crop biomass peaked at 10 t DM and 231 kg N ha-1 with 13% of this N below ground. The crop a...

In an attempt to understand why pasture production in southern Australia has declined markedly in recent years a survey of the symbiotic performance of the legume component of annual pastures on 81 farms (243 sites) was undertaken in the southern coastal region of Western Australia. The 15N natural abundance technique was used to determine the perc...

Precision of estimation of the proportion of legume N derived from N2 fixation (%Ndfa) was assessed in relation to subterranean clover (Trifolium subterraneum L.) pastures and crops of pea (Pisum sativum L.) and lupin (Lupinus angustifolius L.) under south-west Australian conditions. By using a standardized 10-point sampling procedure of paired sam...

The 15N natural abundance (S15N) of the shoot total N of a range of non-N2 fixing potential reference species was compared with that of nodulated field pea (Pisum sativum L.), narrow leafed lupin (Lupinus angustijolius L.) or subterranean clover (Trijolium subterraneum L.) across a range of field sites, to which N fertilizers had not been applied i...

The nitrogen economies of six contrasting field pea (Pisum sativum L.) genotypes were examined at three widely separated sites in south Western Australia, using the 15N natural abundance technique to asssess proportional dependence on fixed N, harvests at peak biomass to assess total N yields and harvests at crop maturity to examine partitioning of...

Methodologies for preparation of plant samples for high precision nitrogen isotope ratio analysis are described, including detailed attention to Kjeldhal digestion, steam distillation, concentration of distillates, and generation of nitrogen gas (N2) from ammonium sulfate [(NH4)2SO4], Apparatus developed in the authors laboratory is illustrated. Us...

ABSTRACTA range of approaches was used to investigate how species within a fire-prone Banksia woodland in South West Australia exploited inorganic soil nitrogen sources and how this changes through the development of the fire chronosequence. Nitrate and ammonium were present in soil solution throughout the chronosequence but nitrate predominated in...

Equipment and procedures for the determination and isotope-ratio analysis of plant samples enriched in 34S are outlined, and field data of labelled fertilizer S uptake using stable isotope methodology are compared with equivalent data obtained from the application of radioactively labelled (35S) fertilizer.

The numbers of news items from the 49th (Auckland) ANZAAS Congress in 16 Australian and two New Zealand papers indicate that, while the major capital-city papers gave the event similar attention to previous Congresses, coverage by other Australian publications was appreciably reduced. Biomedical, psychological and energy topics predominated, with l...

Conservation tillage was evaluated under local subsistence-orientated farming conditions found on the Loess Plateau of western China. Over six years, average wheat grain yield under an experimental no-tillage, stubble-retained treatment (NTS) was 18% higher (2.0 versus 1.7 t/ha) than under the traditional tillage and complete stubble removal treatm...