Speaker
Description
Sowing a legume crop every third year in a crop rotation of cereal and canola can be profitable while increasing the resilience and sustainability of modern farming systems. Some of the benefits include increased soil nitrogen (N) availability and improved rotational and environmental outcomes. In no-till farming systems, sowing large-seeded legumes into retained cereal residues facilitates stubble retention, reduce N tie-up and improves the conversion of carbon-rich cereal stubbles into stable soil organic matter. We explored whether additional benefits to the sustainability and resilience of the farming system was possible by increasing the intensity of legumes by either sowing a legume, or a legume-oilseed intercrop mix every second year followed by a cereal. These effects were explored at both small-plot and larger on-farm paddock scale and explore the reasons for low adoption of pulse crops on commercial farms in southeastern Australia, despite experimental evidence of economic and environmental benefits of these diverse systems.
Two fully phased replicated field experiments (2018-2023) confirmed that legume inclusion in Diverse 3-year cropping rotations can be as profitable as Baseline rotations (canola-wheat-barley) currently favoured by farmers. The average 6-year gross margin (GM) in the Diverse 3-year rotation was 4.3% lower and total chemical costs 5% higher than the Baseline(H) system, however, systems incorporating a legume were less risky (higher profit:cost ratio) with up to 66% reductions in synthetic nitrogen (N) fertiliser usage. The reduced synthetic N in the Diverse system represented only 9% of the total GM compared to 22% in the Baseline(H) system (Table 1). Increasing legume intensity in a Diverse 2-year rotation resulted in a 15-16% reduction in GM compared to the Baseline(H) or Intense Base(H) and 7% increase in chemical costs. However, there was a 63% reduction in fertiliser cost and 81% decrease in synthetic nitrogen costs compared to Baseline(H), which represented only 6% of GM costs for synthetic nitrogen.
Intercrops have focussed on pulse/oilseed mixtures comprising fababean/canola or chickpea/linseed due to specific synergistic benefits related to improved N fixation, reduced disease epidemics such as Ascochyta Blight, Chocolate spot caused by Botrytis fabae and Botrytis cinerea and to improve legume height and support for improved harvesting. The 6-year GM from intercrop-wheat rotations was significantly lower (34%) compared to the Baseline(H) with similar profit:cost ratio (1.19:1). However, the sustainability and resilience were improved including 75% less synthetic N and 27% less chemicals required (Table 1). The faba-canola mixture generally produced more legacy N compared to the chickpea/linseed. In 2023, an average rainfall year (550mm) with low Ascochyta Blight, the chickpea monoculture grain yield was 3.65 t/ha. T and there was a 58% reduction in chickpea grain yield when linseed was sown with chickpeas in alternate rows with 0.9 t/ha linseed grain yield. In mixed rows and chickpea sown at half rate, the chickpea yield reduction increased to 86% (yield of 0.5 t/ha) and linseed yield increased to 1.55 t/ha (Table 1).
At farm scale, when the business is managed at a high level of efficiency, changing management strategies to include legumes was effective and profitable for growers by reducing the: (i) amount of synthetic N required, (ii) herbicide resistant ryegrass weed seedbank, and (iii) economic fluctuations at the whole-farm level. In 2022 at our paddock scale long-term farming systems experiment, the faba bean/canola intercrop yielded 3.8 t/ha of faba bean and 0.5 t/ha of canola compared to 2.3 t/ha and 3.3 t/ha in faba bean and canola monocultures, respectively. The coefficient of variation was reduced by 30% in the intercrop with 86% less fungicides applied. The canola supported the faba bean crop reducing the disease pressure and yield loss.
Our work suggests outcomes of experimental research on the value of diverse crops into cereal-based systems should be combined with a clear understanding of farm- and industry level constraints in Australia. There are significant challenges moving from a cereal-canola rotation to include a pulse grain at farm scale including capital for machinery and equipment, new farmer skills, pulse grain price volatility, extra grain storage and reduced cash-flow with more grain stored. There’s considerably higher skill levels and extra costs for seed separation at harvest for intercropping farmers. These logistical issues at farm-scale remain a barrier to wider adoption despite promising results at experimental scales.
| Keywords | Legume nitrogen; intercrop; economics; sustainability; farm scale. |
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