Take home messages
- There is a benefit in inoculating chickpeas where there are limited rhizobia present in the soil.
- Granular inoculants present an opportunity to assist with sowing logistics, with no reduction
in nodulation or yield. - It is important to understand how your seeding system may impact on efficacy of inoculants,
including liquid placement, seed dressings, seed box.
Background
Australian soils do not naturally contain rhizobia specific to chickpeas because they are not native to Australia. As a result, it is essential these are added to the system to allow chickpeas to fix nitrogen (Cullen 2011). This has traditionally been done using a peat slurry applied to the seed immediately prior to sowing. This presents somewhat of a logistical challenge, due to the labour required to prepare this seed and the need to sow in a timely fashion following inoculation. In recent years, alternative products have been developed in granular form and liquid form, suitable for injection into the furrow, which are not as perishable as the traditional peat slurry method. Use of these products may be a tool to allow more flexibility into the farming system, providing they work as effectively as the traditional method.
Aim
To compare a range of inoculant products on chickpea root nodulation, yield and nitrogen (N)
fixing ability.
Paddock details
| Location: | Pyramid Hill |
| Crop year rainfall (Nov-Oct): | 317mm |
| GSR (Apr-Oct): | 122mm |
| Soil type: | Clay loam |
| Paddock history: | 2017 barley |
Trial details
| Crop type: | PBA Monarch chickpeas |
| Treatments: | Nil, Alosca® granular, freeze dry liquid injection, Nodulator® granular, Peat slurry applied to seed, TagTeam® granular |
| Target plant density: | 35 plants/m² |
| Seeding equipment: | Knife points, press wheels, 30cm row spacing |
| Sowing date: | 31 May 2018 |
| Replicates: | Four |
| Harvest date: | 29 November 2018 |
| Trial average yield: | 0.34t/ha |
Trial inputs
| Fertiliser: | Granulock® Supreme Z + Impact® @ 60kg/ha @ sowing |
| Herbicide: | Weeds managed as per best practice |
| Insecticide: | Insects managed as per best practice |
| Fungicide: | Disease managed as per best practice |
Method
A replicated field trial was established in a paddock with limited Group N rhizobia expected to be present to highlight any differences observed. The traditional peat slurry was applied the morning of sowing, all granular treatments were sown mixed with the seed, the freeze dry treatment was applied through a liquid injection system, below the seed.
Nodulation assessments, on a scale of 0-10 with 0 being no nodulation, were undertaken at flowering as a measure of the effectiveness of the various products (Alosca Technologies 2018).
Protein was assessed using an near infra red (NIR) and mineral soil nitrogen (N) was measured post harvest to allow any residual N to be ascertained.
Results and interpretation
Nodulation and crop vigour
The nodulation and vigour assessments undertaken at flowering time showed significant benefits of inoculating seed at sowing, however there was no great differences observed between the inoculant types. Given the moist conditions at sowing time, differences between the peat slurry and the granular inoculants were diminished. Previous observations have shown significant benefit in using granular inoculants when sowing in dry conditions (Denton et al. 2018). All inoculants excluding the freeze dry, resulted in significantly greater nodulation and increased vigour than those not inoculated (Table 1).
The freeze dry inoculum was applied by liquid injection approximately 2-3cm beneath the seed, which may be the cause of its poor performance. In demonstration strips performed alongside the trials (data not presented), where the freeze dry inoculum was applied with the seed, nodulation and vigour was similar to the peat slurry method of inoculation. TagTeam® granular inoculant resulted in the greatest nodulation, followed by Nodulator® then Alosca®. It is proposed that this is due to the variable numbers of rhizobia present in the Alosca® granules as has been observed previously (Denton et al. 2009). Moreover, it is suggested the particle size of the better performing inoculants was smaller, resulting in improved distribution of inoculum within the furrow, increasing the probability of getting the inoculant as close to the seed as possible (Drew et al. 2012). In addition, it is suggested the combination of the seed dressing (P-Pickel T) and the peat applied as slurry to seed has resulted in slightly reduced nodulation from the peat treatment (Brill et al. 2010).
Table 1. Nodulation and crop vigour at flowering.
Yield and grain quality
The observed differences in nodulation and vigour at flowering didn’t fully translate to yield and grain quality, however similar trends were present with all inoculants yielding greater than those not inoculated (Table 2). Given a softer finish to the season, it is anticipated that greater differences may have been observed. Furthermore, the presence of high levels of soil available N (140kg N/ha to 70cm depth) may have contributed to the compressed yields across treatments (Xia et al. 2017).
Table 2. Yield and grain quality data.
Residual soil nitrogen
Similar trends observed in nodulation and yield were observed in residual soil N content, with
improved nodulation generally resulting in increased levels of soil N (Table 3). It is important to consider the N removed in grain as increased yields will result in greater depletion of the soil N content. When this is considered, the trends were much more evident with the TagTeam® and Alosca® granular inoculants resulting in higher levels of N removed in grain and remaining in the soil. Once again, it is anticipated that a lower starting N would have resulted in these differences being exacerbated.
Table 3. Residual soil N and removed in grain.
Commercial practice and on-farm profitability
There is a benefit from inoculating seed at sowing, even in a dry season. In the moist sowing
conditions there was no significant differences between the inoculation methods (excluding the freeze dry), therefore this may present an opportunity for improved efficiencies in the sowing program as well as adding some logistical flexibility. Given the higher input costs of using the granular inoculants, it would need to increase efficiencies significantly to make this worthwhile, in this season (Table 3).
Table 4. Partial gross margin of various products.
An improvement in inoculant efficacy and consequently nodulation, may have some indirect benefits for following crops. In particular, reducing the depletion of soil mineral N, and may present an opportunity to increase this for the following crop. In this instance, the inoculants providing the best nodulation resulted in approximately 15kg N/ha remaining in the soil which will be approximately $5/ha that could be saved on urea costs for the following crop. It is important to consider paddock history when choosing inoculants, as it is anticipated that had there been chickpeas grown in this paddock in the recent past, differences observed would have been less evident, however given a better season these differences would have likely been heightened in this situation. It is also important to consider paddock condition, product availability, cost, ease of use and practicalities of applying the different forms (machinery) as these will all be factors contributing to this decision.
References
Alosca Technologies (2018) ‘Nodule rating system for pulse legumes’ [Verified 20 December 2018].
Cullen C (2011) Legume inoculation. 2011 BCG Season Research Results, 37-40.
Acknowledgements
This research was funded by the GRDC and Agriculture Victoria as part of the ‘Understanding the implications of new traits on the adoption, crop physiology and management of pulses in the southern region’ project (DAV00150).
