The net contributions of fixed N by crop legumes in low rainfall farming systems

Michael Moodie1, Mark Peoples2, Laura Goward2, Nigel Wilhelm3

1Mallee Sustainable Farming, PO Box 843, Irymple VIC 3498;

2CSIRO Agriculture and Food, Black Mountain Laboratories, Canberra, ACT 2601

3 South Australian Research and Development Institute, Glen Osmond 5064, South Australia


The inclusion of grain legume crops in low rainfall farming systems of south-eastern Australia can improve subsequent cereal crop productivity where nitrogen (N) is a limiting factor.  However, little is known about either the productivity or the capacity of crop legumes to contribute N in this low rainfall environment.  Over three seasons (2013-2015) break crop comparison trials were sampled to measure dry matter (DM) production and symbiotic N2 fixation of chickpea, field pea, lentil, lupin, faba bean and vetch crops grown in the Victorian and South Australian Mallee.  On average, shoot DM produced across species and seasons was in the order of 3 – 4 t DM/ha while average grain yields for all species across the three years was around 1 t/ha.  Chickpea fixed significantly less shoot N than the other species, which on average fixed ~60 kg N/ha in the above-ground DM across the three seasons.  After taking account of the amount of N removed in harvested grain across the three seasons, and including estimates of the likely contributions of fixed N associated with the nodulated roots, 12 of the 15 crop by season combinations were calculated to have provided agronomically significant net inputs of fixed N for the potential benefit of following crops.  Therefore it was concluded that legume crops appear to be a viable mechanism to maintain or improve the N fertility of cropping soils in low rainfall Mallee farming systems.

Rhizobial and non-Rhizobial nodulators of Pueraria phaseoloides

M. M. Wedage1, D. Gunawardana1,2

1Department of Botany, University of Sri Jayewardenepura, Sri Lanka.

2 Corresponding author (E-mail) –


 Pueraria phaseoloides is a widely grown legume cover crop in Sri Lanka. Nitrogen fixation is performed by nodular inhabitants of this cover crop. We endeavored to isolate the whole array of diazotrophs colonizing the root nodules of this economically-significant cover crop. Four isolates were isolated by streaking a macerate of an active nodule from Pueraria phaseoloides and the identification of Rhizobial and Non-Rhizobial species was carried out using colony and cell morphology. One isolate from Pueraria phaseoloides (Sub 1), a gram negative bacterium contoured by a coccobacillus cell shape, (suggesting a likely non-Rhizobial identity), was a potent nodulator of Pueraria phaseoloides seedlings. A further three cultures (Sub 2, Sub 3 and Sub 4) too were able to nodulate Pueraria phaseoloides seedlings but were not as effective as Sub 1 in their nodulation potency. All four bacteria secreted to the extra-cellular medium cellulases suggesting their likely involvement in nodule formation and also showed characteristic patterns of motility to the chemoattractant proline. DNA extracted from Sub 1, Sub 3 and Sub 4 gave a PCR amplicon of the anticipated size (360 bp) using universal nifH primers, which indicated that the genetic foundation for the production of a unit of the nitrogenase enzyme, was found in the genome of these isolates.  In summary, we have unearthed here, a strong, likely non-Rhizobial nodulator, in the legume cover crop Pueraria phaseoloides, and three other bacilli bacteria, perhaps Rhizobia, capable of efficient nodulation. Further characterization of these isolates using molecular biology tools is ongoing.

Estimates of the apparent net mineralisation of legume N and comparisons of the subsequent recovery of legume or fertiliser nitrogen by wheat

Mark Peoples1, Tony Swan1, Laura Goward1, James Hunt1,2

1 CSIRO Agriculture & Food, Black Mountain Laboratories, GPO Box 1600 Canberra, ACT 2601, Australia;

2 Current address: Department of Animal, Plant and Soil Sciences, La Trobe University, Bundoora, VIC 3086, Australia


Results from experimentation undertaken near Junee in southern New South Wales, Australia indicated that concentrations of soil mineral (inorganic) nitrogen (N) measured just prior to sowing wheat in 2012 (0-1.6m) were 42 or 92 kg N/ha greater following lupin grown for either grain or brown manure (BM) than where the preceding crop in 2011 had been wheat or canola. The apparent net mineralisation of lupin organic N over the 2011/12 summer fallow was calculated to be equivalent to 0.11-0.18 kg N/ha per mm rainfall and 7-11 kg mineral N per tonne lupin shoot residue dry matter (DM), representing 22-32% of the total residue N estimated to be remaining at the end of the 2011 growing season. The higher concentrations of soil mineral N after the 2011 lupin treatments resulted in 55-80 kg N/ha more N being accumulated by the 2012 wheat crop (50-74% increase) compared to wheat following wheat and improved grain protein contents from ~9.8% to 12.4-13.6%. The additional N uptake was equivalent to 28% of the lupin residue N from 2011. The uptake of N by wheat grown after either the 2011 wheat or canola treatments was 25-30 kg N/ha higher (21-28% increase) when top-dressed with an additional 51 kg fertiliser-N/ha prior to stem elongation. This represented an apparent recovery of 47-59% of the fertiliser N.

Nitrogen contribution from forage legumes in maize farming system in West Timor, Indonesia

Evert Hosang1, Jacob Nulik1, Debora Kanahau1, Yandri Abi1 and Lindsay Bell2 

1 NTT Assessment Institute for Agriculture Technology, Naibonat, Indonesia, Email:

2 CSIRO, 203 Tor St, Toowoomba Qld 4350, Australia.


Maize is the important staple food crop cultivated in West Timor, Indonesia. However, maize productivity in West Timor is low (2.7 t/ha in 2010) compared to the national average (4.2 t/ha in 2010), due to low use of fertilisers. Integrating forage legumes into maize cropping systems has the potential to assist in improving maize nutrient supply and also provide high quality forage for livestock. The experiment was conducted on the island of West Timor, Indonesia to evaluate biomass production of herbaceous forage legumes in West Timor environment and to quantify potential nitrogen contribution from forage legumes in to maize in a rotation farming system. Butterfly pea, and Centro (both varieties) produced the most biomass (>6 t DM/ha), estimated shoot N was >150 kg N/ha and had the largest impacts on growth of a subsequent maize crop. Growing legumes and retaining their biomass on the field contributed significant nitrogen supply to the following maize crop, increasing N uptake by 30-50 kg/ha. Grain yields of a following maize crop were increased by 50% (1.4-1.6 t/ha) where legume was cut and removed, and by 90% (2.6-2.8 t/ha) where legume biomass was retained.  This study has shown that Butterfly pea and Centro, can be used in legume-maize rotation farming system in West Timor to improve soil fertility and increase maize production.

Annual crop legumes may not mitigate greenhouse gas emissions because of the high carbon cost of nitrogen fixation

David F Herridge1 and Philippa M Brock2

1 School of Environmental and Rural Science, University of New England, Armidale, NSW, 2351 Australia,,

2 Department of Primary Industries, “Tocal”, Tocal Road, Paterson, NSW 2421, Australia


A large uncertainty in constructing grain cropping Life Cycle Assessments (LCAs) is the effect of a particular crop, or sequence of crops, on soil C stocks. We propose that the C cost of legume N2 fixation, estimated to be ca. 20 kg CO2/kg N fixed, will be expressed as reduced residue C returned to the soil and a possible net loss of soil C. Published pre-farm + on-farm greenhouse gas (GHG) emissions associated with N-fertilised wheat (60N) and canola (100N) and N2-fixing field pea, grown in Australia’s southern grains region, were combined with modelled effects of the same crops on soil C stocks. When effects of the crops on soil C were assumed to be neutral, canola had the highest emissions at 840 kg CO2-e/ha with field pea the lowest (530 kg CO2-e/ha). When estimated changes in soil C were included in the LCAs, canola’s GHG emission were totally offset (-100 kg CO2-e/ha), compared with a more than doubling of emissions for field pea to 1270 kg CO2-e/ha. This is somewhat counter-intuitive to current thinking that the substitution of fertiliser N with legume fixed N is an effective strategy for GHG emissions mitigation and highlights the need for simple, accurate methodologies for determining net changes in soil C for individual crops.