Nitrogen Contribution and Value of Chichpea and Fababean in Cereal-Production Systems

For established wheat farming soils, there are only three potential sources of N to supplement the N mineralised from the organic matter (humus) bank:
• Legume pasture leys
• Pulses
• Fertiliser and manures
Pasture and pulse legumes fix N. They absorb N2 from the soil atmosphere into small nodules on their roots and the bacteria (rhizobia) in the nodules convert the atmospheric N2 into ammonia (NH3). The ammonia is then converted into organic compounds by the plant and used for growth. The N-rich residues and exudates from the legumes add to the N of the soil to be used by other non-leguminous crops, such as cereals. Nitrogen fixation activity of legumes is strongly linked to productivity and suppressed by soil nitrate.

In the grains belt of northern NSW and southern Qld, wheat, barley and sorghum are the principal crops and all have a substantial demand for N. For example, a 3 t/ha wheat crop at 8% protein needs 65 kg N/ha. At 10% protein, it is 86 kg N/ha and at 12% protein it is 125 kg N/ha. Increasingly, farmers are looking to the winter pulses, chickpea and fababean, to provide at least some of the required N. The pulses are also effective break crops, particularly of the soil- and stubble-borne diseases.

Optimising N2 fixation (and rotational benefits) through agronomic management

Within the constraints of the climate and season, good legume management to maximise productivity will benefit N2 fixation. Examples of legume management include optimising nutrient inputs (e.g. P), and managing weeds, disease and insects. Optimising the basic agronomy is critical in terms of legume productivity and N2 fixation. This means maintaining a good cover of stubble on the soil surface in the pre-crop fallow, sowing on time and establishing the appropriate plant density.

A management option for cropping that has gained popularity in recent years is no-tillage. Data from the NSW Department of Primary Industries (DPI) long-term rotation experiments in northern NSW showed a positive effect of no-tillage on productivity and N2 fixation of both chickpea and fababean (Felton et al. 1998; Marcellos et al. 1998; Herridge et al. 1998). The effect was primarily due to increased soil water and decreased soil nitrate accumulation during the summer (pre-crop) fallow. Water availability and use have an overriding influence on crop productivity in Australian agriculture. Farmers have no control over seasonal weather but they have some control over the efficiency with which water is infiltrated into and stored in the soil (fallowing efficiency), coupled with the efficiency with which the water is used by crops (water-use efficiency). In the rotation experiments involving chickpea, the no-tilled soils had more water at sowing (increase of 35 mm) but less nitrate (decrease of 15 kg nitrate-N /ha) (Table 1). The extra soil water meant more growth (about 16%) and the reduced nitrate meant greater dependence of the chickpea crops on N2 fixation (25% higher). Thus, total crop N fixed was 43% higher (107 kg N/ha for no-tilled chickpea versus 75 kg N/ha for cultivated chickpea).

Table 1. Effects of tillage on soil water and nitrate at sowing, chickpea and fababean growth and grain yield and N2 fixation

A means of 21 site/years of experiments (unpublished data of W. Felton, H. Marcellos, D. Herridge, G. Schwenke and M. Peoples); B Crop N calculated as shoot N x 2
C means of 9 site/years of experiments (unpublished data of W. Felton, H. Marcellos, D. Herridge, G. Schwenke and M. Peoples); D Crop N calculated as shoot N x 1.4

The story was much the same for fababean in the long-term trials (Table 1). More water was stored in the no-tilled soils than in the cultivated soils during the summer fallows (38 mm) and less nitrate (30 kg N/ha). Shoot DM, N and crop N fixed were increased by 5%, 12% and 14%, respectively.

The N2 fixation values for chickpea and fababean in Table 1 (last column) indicate that fababean fixes about 30% more N than chickpea. Such differences are supported by the on-farm survey data of Schwenke et al. (1998). It is likely that field pea in this region would have similar levels of N2 fixation to chickpea (Rochester et al. 1998). These data fit well with the notion that fababean is a strong N2 fixer and chickpea is a medium N2 fixer.

Optimising N2 fixation (and rotational benefits) through inoculation

Pulses must be well nodulated for maximum N2 fixation and rotational benefits. For the majority of situations, farmers will need to inoculate at sowing in order to ensure good levels of nodulation. In other situations, however, there will be adequate numbers of effective rhizobia already in the soil and inoculation will have no effect on either nodulation or crop growth. The NSW Department of Primary Industries and other state Departments of Agriculture take the conservative approach and recommend that all legumes are inoculated at sowing. There are far less problems with unnecessary inoculation than not using inoculants when they are needed. Unnecessary inoculation represents a small cost of production; N-deficient crops can mean substantial reductions in grain yield and income of the pulse and reductions of the rotational benefits.

Until recently, the commonly-used method for inoculation was to apply a peat-based inoculant, produced and marketed by just one or two manufacturers, as a slurry to the seed just before sowing. Now, there are five manufacturers selling a more diverse range of inoculant products with different modes of application.

A farmer’s choice of inoculant will depend to a large extent on personal experience and product availability, relative cost and perceived efficacy. The commercial inoculant manufactures, GRDC and the Rhizobium scientists with the state Departments of Agriculture, the universities and CSIRO work together to ensure than Australian farmers continue to have access to very high-quality legume inoculants. Peat inoculants (NODULAID™, Nodule N™, N-Prove™), applied to the legume seed as a slurry, remain the most widely-used of the formulations and the benchmark for efficacy. Under the right conditions, the freeze-dried formulation (EasyRhiz™) is highly efficacious. The clay and peat granular inoculants (NODULATOR™, ALOSCA®, N-Prove™), applied directly to the soil, are appealing to farmers because of ease-of-use and convenience and in the future may well supplant peat as the inoculant formulation of choice. New co-inoculant products, such as TagTeam® and BioStacked®, are exciting new products that promise yield increases and improved gross margins under certain conditions. Whilst the potential benefits of all formulations and products may be real and appealing, farmers should look for evidence of efficacy in their particular environment. They should also use the products strictly according to the label.

Nitrogen and rotational benefits of chickpea and fababean

Cereals grown after pulses commonly yield 0.5–1.5 t/ha more than cereals grown after cereals without fertiliser N. To generate equivalent yield in the cereal-cereal sequence, 40–100 kg fertiliser N/ha needs to be applied. The rotational benefit is made up of an N benefit and a biological benefit, the latter largely relating to the break effect of the pulse on soil- and stubble-borne diseases of cereals. The disease-break effect could be worth 0.2–0.5 t/ha.

Mike Lucy and colleagues summarised results from more than a decade (60 sites x years) of chickpea-wheat rotation experiments in northern NSW and southern Qld (Lucy et al. 2005) (Table 2). Major observations were:
• Wheat following chickpea outyielded wheat after wheat by an average of 0.7 t/ha in the NSW trials and by 0.6 t/ha in the Qld trials. Proteins were increased by an average of 1% (NSW) and 1.4% (Qld).
• Where water was not limiting, the yield benefit was more than 1.5 t/ha.
• The major factor in the increased wheat yields was nitrate supply. In NSW, there was, on average, an additional 35 kg nitrate-N/ha in the 1.2 m profile after chickpea than in the continuous wheat.
• Chickpea yields were, on average, about 85% of the unfertilised wheat and about 70% of the N-fertilised wheat.

Table 2. Summary of a decade of experimental results from the northern grains belt showing the rotational benefits of chickpea on yield and grain protein levels of the following wheat crop (source: Lucy et al. 2005)

The substantial rotational benefit of pulses on wheat yields tends to last for one season only. Marcellos et al. (1993) published results from 6 sites in northern NSW showing chickpea provided an average soil nitrate benefit of 89% (equivalent to 42 kg nitrate-N/ha) and average grain yield benefit of 46% (equivalent to 1.0 t/ha) for the following wheat crop (Figure 1). Residual benefits of chickpea for a second wheat crop were small and inconsistent.

Figure 1. Benefits of chickpea on soil nitrate levels at the time of sowing and grain yields of the following two wheat crops (Year 2 and Year 3) (source: Marcellos et al. 1993)

Most of the data on rotational benefits of pulses in the northern grains belt relates to chickpea. One of the objectives of the long-term no-tillage experiments of NSW DPI (Felton et al. 1998) was to compare chickpea and fababean in terms of N2 fixation and rotational benefits. The former (N2 fixation) was achieved to some extent whilst the latter (rotational benefits) was compromised by a combination of drought (1994), frost (1995) and a very wet season causing disease (1998). The limited data that are available show:
• no difference between chickpea and fababean in terms of soil nitrate benefits when the legumes are sown into low nitrate soils (Figure 2)
• Possible longer term nitrate benefits of fababean (see Year 2 data in Figure 2)
• slight superiority of fababean in higher nitrate soils in terms of soil nitrate and grain yield benefits (data not shown)

Figure 2. Benefits of chickpea and fababean, relative to wheat, on soil nitrate levels. The Year 2 crops were not sown because of drought and the land lay fallow for 12 months. Thus, nitrate levels for Year 2 are after a 6-month summer fallow and for Year 3 are after an 18-month summer-winter-summer fallow (source: unpublished data of W. Felton, H. Marcellos, D. Herridge, G. Schwenke and M. Peoples)

Knowledge package on legumes and N in farming systems

Evidence for the rotational benefits of pulses in the cereal-production systems of the northern grains belt of NSW and Qld is overwhelming. We now have a large enough data set from both published and unpublished experiments during the 1980s and 1990s to be able to predict N2 fixation and the N benefits of chickpea and fababean in rotation sequences, and to build those algorithms into decision support packages such as the NSW DPI ‘Crop Mate’. The ‘Crop Mate’ package is designed to provide users (farmers and advisers) with up-to-the-minute weather and climate forecasting data to be used together with relevant information on soil N supply and crop N demand, disease and commodity prices to assist in decision making. ‘Crop Mate’ and the algorithms that drive it will be further developed during the next 1–2 years and will be rigorously tested against data sets. If they prove to be accurate, they should become useful management tools for farmers and advisers alike.

References

Felton WL, Marcellos H, Alston C, Martin RJ, Backhouse D, Burgess LW, Herridge DF (1998) Chickpea in wheat-based cropping systems of northern New South Wales. II. Influence on biomass, grain yield, and crown rot in the following wheat crop. Australian Journal of Agricultural Research 49, 401-407.
Herridge DF, Marcellos H, Felton WL, Turner GL, Peoples MB (1998) Chickpea in wheat-based cropping systems of northern New South Wales. III. Prediction of N2 fixation and N balance using soil nitrate at sowing and chickpea yield. Australian Journal of Agricultural Research 49, 409-418.
Lucy M, McCaffery D, Slatter J (2005) Northern Grain Production – a farming systems approach.
Marcellos H, Felton WL, Herridge DF (1993) Crop productivity in a chickpea-wheat rotation. Proc. 7th Australian Agronomy Conference, Australian Society of Agronomy. pp 276-278.
Marcellos H, Felton WL, Herridge DF (1998) Chickpea in wheat-based cropping systems of northern New South Wales. I. N2 fixation and influence on soil nitrate and water. Australian Journal of Agricultural Research 49, 391-400.
Rochester IJ, Peoples MB, Constable GA, Gault RR (1998) Faba beans and other legumes add nitrogen to irrigated cotton cropping systems. Australian Journal of Experimental Agriculture 38, 253-260.
Schwenke GD, Peoples MB, Turner GL, Herridge DF (1998) Does nitrogen fixation of commercial, dryland chickpea and faba bean crops in north-west New South Wales maintain or enhance soil nitrogen? Australian Journal of Experimental Agriculture 38, 61-70.

Contact details

David Herridge
NSW Department of Primary Industries
Tamworth Agricultural Institute, 4 Marsden Park Rd, Calala, NSW 2340
Ph: 02 6763 1143
Fx: 02 6763 1222
Email: david.herrige@dpi.nsw.gov.au

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