Break crop options in cropping rotations

Take home messages

• Pastures can be a productive and profitable break crop option for mixed farming systems in the Upper South East of South Australia.
• Up to a 26% increase in wheat yields has been achieved following a pasture phase compared to a wheat on wheat rotation.
• A pasture phase can be used in a rotation to decrease annual ryegrass populations.
• Initial gross margins are responsive to a legume in the rotation.

Background

As part of the GRDC-SARDI Strategic Research Agreement (Program 5, Regional Agronomy Capacity) the project ‘Integrated Farming Systems in the Medium Rainfall Zone’ commenced in the Upper South East (USE) of South Australia (SA) in 2017.

The expected outcome of the project is that by 2021, growers in the Medium Rainfall Zone (MRZ) of the South East (SE) and their advisers will have access to new relevant information on diverse crop rotations and integrated farming systems, particularly the incorporation of a pasture phase. This will allow for better crop sequencing decision making, with the aim of increasing farm sustainability, diversity and ultimately profitability, through the adoption of improved rotations and break crop management options.

Two rotation trials were established as part of this project at Bordertown and Sherwood in 2017.

The rotation trials are evaluating the following:

1. What is the magnitude of impact of an annual pasture legume in the integrated farming system rotation in the MRZ of the USE on subsequent crops?
2. Is the break effect (environmental, agronomic, economic and risk) of an annual pasture legume phase comparable to that of pulse and canola break crops?
3. Do double breaks increase subsequent wheat yields compared to single breaks?
4. Does the break effect impact on the second wheat crop and beyond?

This paper addresses three key questions relating to the rotation trials:

1. What is the best rotation of crops/pastures for growers in this area?
2. What are the agronomic benefits of using a pasture as a break crop option?
3. How do the economics of an annual pasture break crop compare to that of other break crop options?

The Bordertown and Sherwood trials have been statistically designed for a four-year rotation. The first year of sequences were sown in 2017 and the final sequences were sown in May 2020. The sequences are phased throughout the four years, to minimise the bias of seasonal conditions and commodity fluctuations. Therefore, data presented prior to the completion of the rotations is only a snapshot, providing an insight into the full results.

Key Question 1 - What is the best rotation of crops/pastures for growers in this area?

The inclusion of an annual pasture legume into the cropping rotation can provide integrated farming systems with a diverse and flexible break crop option. Understanding the value of pastures as a break crop is complex and incorporates agronomic, environment and economic components.

The rotation trials are evaluating nine crop types (cereals (wheat, barley and oats), canola, faba bean, lentil at Bordertown and lupin at Sherwood, and three different annual pasture legumes, subterranean clover, balansa clover and burr medic) across 16 different rotations. The rotations include continuous wheat, continuous pastures, and single and double break crop options.

Data generated from the rotation trials at Bordertown and Sherwood suggest that the inclusion of a pasture legume break crop phase can be a profitable and productive option, not only in the break crop year, but in the subsequent years.

A simple way of looking at the data generated from the rotation trials is to review wheat yields following different break crop options over several years. Discussed in the following sections are preliminary results of single and double break crops and subsequent wheat yields.

An annual pasture legume as a single break crop option

In 2018 at Sherwood wheat grain yields were responsive to a legume break crop (Figure 1). Wheat yields averaged 3.69t/ha and as shown in Figure 1 were greater following balansa clover and subterranean clover, compared to a canola and cereal break crop. There was up to a 26% increase in wheat yields following balansa clover compared to a wheat on wheat rotation.

Figure 1. Sherwood 2018 wheat grain yields (t/ha), following different crop types sown in 2017. Error bars indicate standard error (P value (<0.001), LSD 0.454).

In 2019 at Sherwood wheat yields averaged 4.61t/ha (Table 1). In 2019 there was a 12% increase in wheat yields following a subterranean clover (4.88t/ha), compared to a wheat on wheat rotation (4.36t/ha) (Table 1). The break crop faba bean also increased wheat yields significantly compared to a wheat on wheat rotation.

Table 1. Sherwood 2019 wheat grain yields (t/ha) following different crop types sown in 2018.

Means with the same letter are not significantly different (P =0.05)

Wheat yields averaged 5.35t/ha at Bordertown in 2018 (Table 2). As shown in Table 2, wheat yields were not significantly greater following a legume break crop compared to a cereal break crop.

Table 2. Bordertown 2018 wheat grain yields (t/ha), following different crop types sown in 2017.

In 2019 Bordertown wheat averaged 4.82t/ha. In contrast to 2018 a significant difference was measured between the single break crop options (Figure 2). A break crop of subterranean clover increased yields by 24% compared to a wheat on wheat rotation. The use of lentil and burr medic as break crops also significantly increased wheat grain yields compared to a wheat on wheat rotation.

Figure 2. Bordertown 2019 wheat grain yields (t/ha), following different crop types sown in 2018. Error bars indicate standard error (P value (<0.001), LSD 0.81).

The benefits of a single pasture legume break crop on subsequent wheat yields has been realised in years with lower wheat production. At Sherwood a response was measured in 2018 when wheat yields averaged 3.69t/ha, compared to no significant response in 2019 when wheat yields averaged 4.61t/ha. At Bordertown no significant response was measured when wheat yields averaged 5.35t/ha, but in 2019 when wheat yields had a lower yield average of 4.82t/ha a response was measured.

Pastures as a double break crop option

The rotation trials have evaluated the use of a double break crop and the impact on subsequent wheat yields. To-date there is only one-year of data to review. At Bordertown the value of a double break of pasture or a canola X pasture double break increased subsequent wheat yields by over 15% compared to a grower rotation of oat X faba bean X wheat rotation (Table 3). Double breaks that include a pasture increased subsequent wheat yields by up to 1.45t/ha, compared to a continuous wheat rotation.  After initial analysis at Sherwood the value of a double break crop option has not been realised (data not presented).

Table 3. Bordertown 2019 wheat grain yields (t/ha), following different rotations, 2017 crop type X 2018 crop type.

Means with the same letter are not significantly different (P =0.05)

Key Question 2 - What are the agronomic benefits of using a pasture as a break crop option?

The agronomic benefits of pastures as a break crop option include reductions in weeds, pests and diseases; improved soil water supply, extraction, retention and water use efficiency; and increased soil mineral nitrogen, organic carbon and soil fertility.

Of particular interest in the rotation trials is the benefit experienced from the reduction in annual ryegrass (ARG) populations with the inclusion of a pasture in the rotation. Sequencing can impact on ARG populations, but often it is in conjunction with other factors. Factors contributing to ARG population reductions can include, but is not limited to, seeding conditions and success of pre-emergent herbicides, subsequent herbicide options and timing of applications, time of sowing and seeding rates, crop establishment, crop competition and management of crop for either grazing, hay or grain.

In 2017 ARG populations were lower at Bordertown (site average three plants/m²), compared to Sherwood (site average 56 plants/m²), with populations generally greater in cereal plots compared to the other crop types.

In 2018 at both sites, crops following cereals had higher ARG plant numbers, 34 ARG plants/m² at Bordertown and 225 ARG plants/m² at Sherwood, compared to plots following a pasture break crop, 23 ARG plants/m² at Bordertown and 47 ARG plants/m² at Sherwood.

Table 4. Annual ryegrass (ARG) plants/m² in wheat in 2019 and 2020, following different rotations, average of a single break of either canola/faba bean/lentil or lupin, a single break or double break of subterranean clover and continuous wheat.

This result was replicated in 2019 at both sites. As shown in Table 4, a continuous wheat rotation had 72 plants/m² at Bordertown and 209 plants/m² at Sherwood. A double break of subterranean clover had three plants/m² ARG numbers at Bordertown and 14 plants/m² at Sherwood, compared to the average of a single break of canola, faba bean or lentil/lupin which averaged 63 plants/m² at Bordertown and 128 plants/m² at Sherwood. At Sherwood the double break of subterranean clover had lower ARG plants/m² compared to a single break, this was not replicated at Bordertown, where ARG numbers were low in both single and double break options of subterranean clover.

In 2020 a continuous wheat rotation had 35 ARG plants/m² at Bordertown and 69 ARG plants/m² at Sherwood (Table 4). A double break of subterranean clover had 0 ARG plants/m² at Bordertown and 24 plants/m² at Sherwood. As shown in Table 4 and similar to 2019 there was little difference in ARG plant numbers following a double break or a single break of subterranean clover at Bordertown, and at Sherwood the double break of subterranean clover had lower ARG plant numbers compared to the single break. The subterranean break crop rotations had fewer ARG plants compared to the average of a single break of canola, faba bean or lentil/lupin.

Key Question 3 - How do the economics of an annual pasture break crop compare to that of other break crop options?

An initial gross margin (GM) ($/ha) has been completed for the three years; 2017, 2018 and 2019 of the rotation. When all rotations have been phased (2020 harvest), a full economic and sensitivity analysis will be completed. This will accommodate commodity price fluctuations and seasonal differences.

Figure 3 presents a snapshot of five different rotations at Sherwood and their calculated GM. The rotations presented are continuous wheat, continuous subterranean clover, grower rotation (faba bean, wheat and canola), a single break of subterranean clover and a double break of subterranean clover. The GM ($/ha) has been calculated based on cropping inputs ($/ha) (seed, herbicide, insecticide, fungicide and fertiliser. It does not include labour, machinery costs, levies, insurances, or EPR (full inputs are available on request)), subtracted from the income ($/ha) (commodity price ($/t) X production (grain/hay harvested t/ha)).

At Sherwood wheat is being managed to achieve a 4.5t/ha crop and canola a 2.0t/ha crop. Importantly, the pasture GM has been calculated as if it was a hay crop. It is recognised that this undervalues the pasture as a commodity and in the final analysis the value of pasture as a grazing option will be calculated.

In 2017 wheat at Sherwood averaged 2.9t/ha, it was FED 1 quality, with a commodity price of $215.00/t and a GM of $114/ha was achieved. Faba bean achieved a GM of $842/ha, based on a 3.8t/ha yield and a commodity price of $315.00/ha. Subterranean clover, as a hay option produced 3.0t/ha, with the lowest input cost of $200.00/ha (compared to $510/ha for wheat and $355/ha for faba bean). A commodity price of $190/ha resulted in a GM of $370/ha.

In 2018 wheat following a subterranean clover yielded 4.1t/ha compared to a continuous wheat rotation yield of 3.3t/ha, representing in a 26% wheat yield increase. The input costs were lower following a subterranean clover and faba bean compared to following a wheat. This is because less N was required to achieve a 4.5t/ha crop, due to higher residual soil N following a legume compared to a continuous wheat rotation. Wheat on wheat plots achieved FED 1 quality ($320/ha commodity price), whereas wheat following the legumes achieved APW1 quality ($370/ha commodity price). The continuous pasture hay produced 5.6t/ha and had a commodity price of $190/ha.

In the third year of the rotation; 2019, a double break of subterranean clover had a subsequent wheat yield of 4.9t/ha, compared to the continuous wheat rotation of 4.2t/ha. Both rotations achieved H2 for quality with a commodity price of $315/ha. Wheat input costs were higher in the continuous wheat treatment, a result of lower soil N compared to the rotations which included a legume phase. Canola produced 2.0t/ha, with an input cost of $480/ha and a commodity price of $570/ha. The continuous pasture phase again had the lowest input costs, yielded 4.3t/ha and had a higher commodity price compared to the two previous years of $250/ha.

Figure 3. Sherwood rotation trial gross margin (GM) ($/ha) for 2017, 2018 and 2019. The GM ($/ha) has been calculated based on cropping inputs ($/ha) (seed, herbicide, insecticide, fungicide and fertiliser. It does not include labour, machinery costs, levies, insurances, or EPR (full inputs are available on request)), subtracted from the income ($/ha) (commodity price ($/t) X production (grain/hay harvested t/ha)).

Over the three years the combined GM is responsive to a legume phase. In this simplistic review of five rotations at Sherwood, over the three years (2017, 2018 and 2019) the continuous wheat rotation had the lowest combined GM of $1513/ha, compared to the grower rotation (FB-W-C) of $2480/ha, the single break of subterranean clover $2390/ha and the double break of subterranean clover $2328/ha. The continuous pasture had a three-year GM of $2124/ha.

Conclusion

The inclusion of a pasture legume break crop phase in the rotation can be a profitable and productive option, not only in the break crop year, but in the subsequent years.

Wheat yield increases of up to 26% have been achieved following a pasture break crop compared to a wheat on wheat rotation. The benefits of single pasture break crop on subsequent wheat yields has been realised in years with lower wheat yields. The use of a pasture phase can reduce annual ryegrass populations. The snapshot GM presented in this paper has shown that an annual pasture legume can be a profitable break crop option and that the GM has been responsive to the inclusion of a legume in the rotation.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. This research has been funded through the GRDC-SARDI Strategic Research Agreement (Program 5, Regional Agronomy Capacity). The ongoing cooperation of the Johnson family at Bordertown and the Menz Family at Sherwood is greatly appreciated.

Useful resources

Angus JF, Kirkegaard JA, Hunt JR, Ryan MH, Ohlander L, Peoples MB (2015) Break crops and rotations for wheat. Crop & Pasture Science 66, 523-552.

Ewing MA, Flugge F (2004) The benefits and challenges of crop-livestock integration in Australian agriculture. In ‘Proceedings 4th International Crop Science Congress’, Brisbane, Australia.

Kirkegaard JA, Christen O, Krupinsky J, Layzell D (2008) Break crop benefits in temperate wheat production. Field Crop Research107, 185-195.

Pearce AL, Turner F (2015) Final Report Crop Sequencing Project (CSP00146) – South East of South Australia – Lochaber.

Contact details

Amanda Pearce
74 Struan House Road, Naracoorte SA 5271
PO Box 618, Naracoorte SA 5271
0407 400 939
Amanda.pearce@sa.gov.au