Take home message

• Intercropping increased productivity (yield), and on average required 14% (and up to 42%) less land than monoculture crops to grow the same amount of grain
• Wheat had a competitive advantage over chickpea, and therefore the chickpea proportion (plant population) needs to be at least 50% of the total intercrop mix
• No productivity gains were observed between sowing species in alternating rows verses mixed within the rows. However, alternate rows showed a small grain yield increase to the chickpea component
• Termination of the wheat or chickpea component within the companion mix reduced productivity by 63% and 10%, respectively
• Soil nitrogen benefit of ~73 kg N/ha was derived from the chickpea monoculture compared to the wheat monoculture. Residual N increased (by up to 40 kg N/ha) as the chickpea proportion increased from 25% to 75% of the total intercrop mix
• Crop stubble type and configuration had no effect on soil water accumulation over the fallow period due to a wet summer/autumn fallow period in 2022
• Compared to wheat monoculture, the intercrop treatments had a ~50% reduction in profitability in year 1, however showed a ~12% increase in the following winter cash crop (canola)
• Cost associated with separating the wheat and chickpea within an intercrop mix will be a potential barrier for adoption (up to $95 per tonne).

Introduction

Intercropping is where two or more species are sown and harvested together with the objective of harvesting grain of both species, whilst companion cropping is where two or more species are sown together with the objective of harvesting grain from a single species, while the other species is terminated using herbicides. Claimed benefits include N-fixation, reduced disease, improved nutrient uptake, weed suppression, soil structure benefits and mycorrhiza hosting (Fletcher, et al 2020). Neither of these techniques (intercropping/companion cropping) are common practice in large-scale rainfed cropping systems across Australia, however they have been used for centuries throughout the world on a smaller scale. Over recent years there has been increased global interest in these approaches as sustainable farming systems and greater productivity from a unit of farmland are sought.

The land equivalent ratio (LER) is a concept in agriculture that describes the relative land area required under sole cropping (monoculture) to produce the same yield as under intercropping. An LER greater than 1.0 (or 100%) indicates that production is higher in the intercropping system compared to monoculture. For example, a LER of 1.25 (or 125%) indicates that two monocrops planted in equal proportion would require 25% more land to produce the equivalent yield achieved by intercropping the two crops. Studies from overseas and limited work in Australia have shown that LER of greater than 1 (or 100%) are achievable for intercropping systems involving both monocot and dicot species.

There has been little research on the role and benefits of intercropping and companion cropping in large scale cropping systems, and the necessity for further research has been highlighted by recent studies (Fletcher, et al 2016, 2020). The review by Fletcher et al (2016) highlighted the lack of information available to Australian grain growers and identified areas for future research – genotypic adaptation for intercrop/companion species, rotational benefits, yield variability between companion species and regional adaptation and management complexity versus productivity.

This project evaluated the role of companion and intercropping using chickpea and wheat in central NSW. The project looked at land equivalent ratio and gross margin return to growers, but also investigated the role of companion/intercrops to increase residual stubble cover to increase summer fallow efficiency when compared to fallows managed after chickpea crops.

The project was set up to answer the following research questions in central NSW farming systems:

1. Can grain yield, grain quality and profitability be improved by growing a pulse (chickpea) and cereal (wheat) crop together? Should either species be terminated or is there net benefit in harvesting both?
2. What is the impact of soil water use efficiency in-crop and soil water storage (residual soil water at harvest and subsequent fallow efficiency) for the following crop after companion/intercrops of wheat and chickpea?
3. Is there an optimum plant density for each species, and should the proportion change if the aim is to maximise grain yield and/or improve fallow efficiency/groundcover post-harvest?
4. Should crop species be separated and sown in alternate drill rows, or mixed within the one drill row?
5. What is the legacy effect on the soil nitrogen balance and grain yield in subsequent crops following an intercrop/companion cropping system using wheat and chickpea?

Table 1. Site details for Canowindra & Condobolin experiments.

a = +/- from the long-term average.

Table 2. Treatments applied at Canowindra & Condobolin experiments.

a = Species mixed (% of targeted plant population/m² for each crop type) within row.
b = Seeding rate % calculated for best practice at each location.
c = Hybrid forage sorghum sown (Condobolin 7/12/21 & Canowindra 23/12/21) at 10 kg/ha & terminated 45 days after sowing.

Legacy benefits (yield and profit) to the following winter cash crop (2022) were measured via sowing canola (45Y93CL) at 3 kg/ha with a single disc plot seeder over the previous 2021 companion treatments. Canowindra was sown on 25 April, and Condobolin on 6 May with 50 kg/ha of MAP fertiliser applied with the seed and no additional nitrogen fertiliser.

Results & discussion

Seasonal conditions and plant establishment

The 2021 season could be described as a relatively soft season with above average rainfall at both sites. Canowindra received 193 mm above the long-term average of 599 mm, whilst Condobolin received 371 mm above the long-term average of 431 mm. The 2021/2022 summer period (Nov–May) was extremely wet at both sites, with 176 mm above the long-term average of 346 mm at Canowindra, and 276 mm above the long-term average of 260 mm at Condobolin. The wet summer negated any soil water legacy benefits across the various stubble type configurations.

Plant density achieved for the wheat monoculture was 139 plants m² at Canowindra (target 140 plants m²) and 108 plants m² for Condobolin (target 120 plants m²). Chickpea monoculture was 44 plants m² and 33 plants m² at Canowindra (target 45 plants m²) and Condobolin (target 35 plants m²), respectively. Refer to Appendix Table 1 and Table 2 for plant density results across the various ratio treatments within the companion mixes.

Productivity (grain yield)

The Canowindra site achieved an average wheat yield of 6.84 t/ha (ranged from 1.61–9.29 t/ha) and 1.11 t/ha (ranged from 0.01–1.90 t/ha) for chickpeas. Condobolin wheat yields were less, with an average of 5.02 t/ha (ranged from 0.09–7.26 t/ha) and 0.97 t/ha (ranged from 0.07–2.58 t/ha) for chickpeas. Refer to Appendix table 1 and 2 for grain yield and quality results.

Table 3 illustrates grain yield at Canowindra and Condobolin as a percentage of the monoculture controls. Grain yield for each species was higher when sown as a monoculture compared to the intercrop/companion mixes, with a 5–9% yield benefit with additional N to the wheat monoculture treatment.

The land equivalent ratio (LER) identified that intercrop mixes (Treatments 3, 4 and 5) required on average 14% less land to grow the same amount of grain as a monoculture. LER (%) ranged from 78% to 142% and tended to be higher (~30%) at the Canowindra site (HRZ) compared to Condobolin (LRZ). Wheat out-competed chickpea for light and resources, and the plant density/proportion needed to contain at least 50% chickpea for any productivity benefit to be realised. For example, when wheat dominated the mix (W75%_C25%) the chickpea component yielded 8–19% of the chickpea monoculture compared to 42–78% in the W25%_C75% mix. Sowing species in alternate rows helped reduce the competitive advantage of wheat (by providing space) and further increased chickpea yield by ~12%, but this increase in chickpea yield came at the expense of wheat yield (~18% reduction). Therefore, there was no LER benefit by sowing in alternating rows verses mixed within row.

Termination of wheat or chickpea within the companion mix reduced productivity and highlighted again the competitive advantage of wheat over chickpeas. For example, terminating wheat at GS55 produced a 63% grain yield reduction in chickpea, and terminating chickpea at GS60 produced a ~10% grain yield reduction in wheat (compared to monoculture treatments).

Table 3. Productivity of intercrop and companion treatments at Condobolin and Canowindra expressed as yield (t/ha), percentage of monoculture control and LER (%) in 2021.

a = Spray-out treatment not 100% effective, with seasonal conditions that favoured crop regrowth.
b = Refer to Appendix Table 1 for plant establishment, biomass, harvest index, grain yield and grain quality results.
c = Refer to Appendix Table 2 for plant establishment, biomass, harvest index, grain yield and grain quality results.

Legacy effects (water, nitrogen and following canola crop) post intercrop/companion

Stubble type configurations had no effect on soil water accumulation over the summer fallow period due to above average summer rainfall at both trial site locations (Site details in Table 1).

Averaged across both sites, there was a nitrogen legacy benefit of ~73 kgN/ha derived from the chickpea monoculture compared to wheat monoculture. Soil nitrogen increased by up to 40 kgN/ha when the chickpea proportion/density increased from 25% to 75%. Growing a summer cover crop post chickpeas reduced mineral N by ~82 kgN/ha.

On average, canola grain yield increased by 12% following the chickpea monoculture compared to wheat monoculture. As the proportion of chickpea raised from 25%, 50% to 75% the grain yield of canola was 98%, 108% to 113%, respectively of the yield after wheat monoculture. Interestingly, the chickpea and wheat spray-out treatment (companion treatments) increased yield by 5% and 8%, respectively.

Table 4. Legacy effects derived post intercrop and companion treatments for mineral nitrogen (kgN/ha), plant available water (PAW mm) (measured May 2022) and subsequent canola grain yield (t/ha) and oil (%) in 2022.

a= Mineral N and PAW (mm) measured in May 2022 via 5 soil cores bulked together per plot.
b= Mineral N depths include 0–10 cm, 10–30 cm, 30–60 cm and 60–90 cm.
c= PAW depths include 0–10 cm, 10–30 cm, 30–60 cm, 60–90 cm and 90–120 cm.

Profitability

Year one (intercrop and companion treatments)

Averaged across both sites, treatment gross margins ranged from $-237/ha to $1737/ha. The wheat monoculture was $1622/ha and chickpea monoculture much lower at $425/ha. The addition of nitrogen to the wheat monoculture treatment was the most profitable (6% higher than wheat monoculture) at $1737/ha, and the least profitable was the wheat spray-out companion treatment ($-237/ha). Whilst the intercropped treatments performed well from a productivity perspective, there was a ~50% reduction in profitability compared to the wheat monoculture due to price received for each crop, and additional expenses associated with seed separation.

A commercial quote to separate the wheat from chickpea was $95/t, as two passes would be required. First pass would separate wheat from chickpeas but likely leave white heads and trash from the wheat in the chickpeas ($35/t), and the second pass would involve cleaning the chickpeas with high wind speed and the use of a gravity table ($60/t). Therefore, a 5 t/ha yielding crop mix would cost $475/ha to separate the two species.

Table 5. Gross margin ($/ha) of the intercrop and companion treatments over 2021 and 2022.
Percentages are % gross margins relative to the ‘Wheat_100 treatment’

*Refer to appendix Table 3 and 4 regarding input costs and prices.

Year two (legacy crop – canola)

Averaged across both sites, gross margins ranged from $1702 to $2033/ha. The chickpea monoculture and intercropped treatments with greater than 50% chickpeas had between a 9–15% increase in gross margin over the wheat monoculture. The W50_C50_plusN had the highest gross margin at $2033/ha.

The wheat monoculture and wheat plus N were the highest gross margin treatments over this two-year study. Interestingly, intercropped treatments with a proportion ≥50 % chickpea had a higher gross margin than chickpea monoculture, however it’s likely that the chickpea monoculture might provide longer legacy benefits.

Comments and observations about managing intercrop/companion

Intercropping is highly reliant on pre-emergent herbicide chemistry for successful weed control.  Based on current pesticide registrations, in-crop herbicide options are often limited (or non-existent) and growers need to be familiar with label requirements and withholding periods prior to selecting the species crop mix. Crop safety with pre-emergent herbicides is often higher in a knife point press wheel system compared to disc seeders, and some labels do not include registration that allows use in disc seeding systems.

Harvest management and desiccation timing can be difficult for a wheat/chickpea intercrop mix, particularly with late season rainfall as chickpea are indeterminate and wheat more determinate in their flowering pattern. Desiccation timing may need to be compromised, and preference towards the species of greater economic value should be considered (seasonally specific).

Chickpeas grown as a companion or intercrop (with wheat) tend to grow taller, branch less, have fewer pods per plant and an increased height to ‘lowest’ pod, compared to chickpea grown in a monoculture. Therefore, harvest height will be slightly higher.

Despite prophylactic fungicide application, Ascochyta blight was visually present within the chickpea monoculture at Canowindra but absent within a companion/intercrop mix. It is assumed that the wheat stubble reduced rain splash spread of inoculum into the upper canopy.

Chickpea spray-out treatment was scheduled to occur at peak biomass (GS65), however in reality the chickpeas needed to be terminated at GS60 due to label restrictions and crop safety for the wheat cash crop. For example, the last chance to terminate chickpeas is either awn peep or wait until after the dough stage of wheat.

A Group 1 grass selective herbicide was applied to the wheat spray-out treatment at GS49, however it took 3–4 weeks for visual signs of a ‘kill’ on the wheat. Water and nutrients would have translocated during the 3–4 week lag phase.

Unless grading/separation occurs at harvest (which adds complexity) there would also need to be adequate storage facilities on-farm for the mixed grain.

Summary

These results suggest that intercropping systems for growing high value cash crops (wheat and chickpeas) in central NSW may have productivity benefits, but profitability was severely reduced due to the costs associated with seed grading/separation and price received for each grain type. Cost of seed separation will be a major barrier to adoption if not addressed.

Intercropping is a much more complex farming system with high reliance on pre-emergent herbicides for successful weed control (little to no in-crop herbicide options), and harvest management/desiccation timing can be problematic due to managing a combination of indeterminate (chickpea) and determinate (wheat) maturity plant types.

Intercropping did improve overall productivity, with an average 12% (and up to 40%) less land required than monoculture crops to grow the same amount of grain. Sowing the correct plant density ratio for each species was important to ensure that one species did not dominate and ‘choke out’ the remaining species. In these two experiments, wheat was more competitive than chickpea and the proportion of chickpea needed to be at least 50% of the intercrop mix for benefits to be realised. Another option to reduce the competitive advantage of wheat was to sow each species in alternating rows, however whilst this improved the chickpea yield (at the expense of wheat yield) it reduced overall productivity (LER%).

Compared to the wheat monoculture, the companion cropping concept of terminating either the wheat or chickpea resulted in less production and profitability over this two-year study. Terminating the wheat caused major yield penalties to the chickpeas, whilst terminating the chickpeas had much less effect on wheat yield. Neither companion treatments were as profitable as the wheat monoculture.

These results highlight the residual benefits (largely N & disease) of having pulse crops within the farming system, and intercropping could be a tool to make the ‘pulse crop’ more profitable for that season whilst also providing elevated levels of ground cover to help drive fallow efficiency. However further research is required to evaluate if a pulse monoculture has longer lasting benefits compared to an intercrop. Grain prices for pulse crops are renowned for being highly variable, and intercropping might take away some of the price risk volatility as the wheat component will be the main income driver of the intercrop.

References

Fletcher A, Kirkegaard J, Peoples M, Robertson M, Whish J and Swan T (2016) Prospects to utilise intercrops and crop variety mixtures in mechanised, rain-fed, temperate cropping systems. Crop & Pasture Science. 2016; 67(12):1252-1267.

Fletcher A, Kirkegaard J, Condon G, Swan T, Greer K, Bremer E and Holding J (2020) The potential role of companion and intercropping systems in Australian grain farming – should we be considering them. Dubbo GRDC update proceedings.

Acknowledgements

This experiment was part of the project ‘Investigating the value of companion cropping systems for growing high value cash crops (wheat and chickpea) in Central NSW’, BLG126, 2021–2022, a joint investment by GRDC and NSW DPI under the Grains Agronomy and Pathology Partnership (GAPP).

We sincerely thank Viridis Ag ‘Gindurra aggregation’ Canowindra, and staff from Condobolin Agriculture and Research and Advisory Station for hosting the field experiments.

Contact details

Colin McMaster
NSW Department of Primary Industries
Orange Agriculture Institute, Forrest Road
Ph: 0427 940 847
Email: colin.mcmaster@dpi.nsw.gov.au

Date published

February 2023

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.

Appendix Table 1. Plant establishment, biomass, grain yield, harvest index (HI) and grain quality (protein and test weight minimum (TWT)) from intercrop/companion treatment at Canowindra -2021.

*Chickpea yield was lower at Canowindra compared to Condobolin, presumably due to incidence of Ascochyta blight and cooler temperatures (i.e., pod set requires daily mean temperatures >15°C).

Appendix Table 2. Plant establishment, biomass, grain yield, harvest index (HI) and grain quality (protein and test weight minimum (TWT) from intercrop/companion treatment at Condobolin -2021.

Appendix Table 3. Input costs, grain prices and assumptions used for Canowindra gross margins.

*Grain prices adjusted according to receival grade and price derived from AWB Parkes.
*Variable costs adjusted to suit various treatments but derived from 2022 GRDC Farm gross margin and enterprise planning guide.
*$95/T seed grading/separation costs included in various intercrop treatments.

Appendix Table 4. Input costs, grain prices and assumptions used for Condobolin gross margin.

*Grain prices adjusted according to receival grade and price derived from AWB Parkes.
*Variable costs adjusted to suit various treatments but derived from 2022 GRDC Farm gross margin and enterprise planning guide.
*$95/T seed grading/separation costs included in various companion treatments.

GRDC Project Code: DPI2108-009BLX,