Likely fit of summer and winter forage crop options in Central West farming systems

Author: Lindsay Bell, CSIRO | Date: 24 Jul 2015

Take home message

  • Several winter forages provide alternative break crop options for grain cropping systems.
  • Forage brassicas could provide similar crop rotation benefits to canola, can produce > 5 t DM/ha reliably in drier regions (typically 60-80% of forage cereal options) and are resistant to key soil-borne pathogens.
  • Several field pea varieties could provide flexible dual-purpose options which can produce forage yields of up to 80% of oats, to provide N inputs, weed management and crop rotational benefits.
  • Summer forage options such as millet, sorghum and legumes like lablab could be used to transition to summer crop phase to provide disease and weed management benefits.

Introduction

Across the northern grains regions, annual-cereal forages, particularly oats and forage sorghum, are the most common forage crops grown for livestock in mixed farming enterprises. Yet there are a range of other forage options such as forage legumes and forage brassicas that could provide rotational benefits in cropping systems. Forage brassicas could be used in a similar break crop role to canola in southern Australia, without the high risk associated with canola production in drier and hotter environments in the northern grains region. Summer and winter annual and short-lived perennial legumes are also available (e.g. lablab, burgundy bean, sulla, field pea, vetch) that can also provide break crop benefits along with fixing atmospheric nitrogen for subsequent crops.

In this paper we provide some data on the relative biomass production of a range of forage crop options that might be utilised in grain crop rotations in the central west region. A summary of these various characteristics amongst the forage options discussed are provided in Table 2.

Winter forage break crop options

Forage brassicas

Forage brassicas are often used in high rainfall livestock systems but could also provide an alternative break crop option in the place of canola in northern farming systems. Where the viability of canola is compromised by dry conditions and/or hot conditions during grain fill, a forage brassica could perform a similar role in the rotation to provide weed and disease management without the high risks associated with canola production. Forage rape are very high quality and remain leafy throughout the growing season because they possess a high vernalisation requirement, which prevents them from becoming reproductive.

We have compared the forage production of forage cereals with some readily available cultivars of forage rape (cv. Winfred, Interval and Leafmore), leafy turnip (cv. Hunter) and kale at several locations in southern Queensland and northern NSW (see Figures 1-3). This has shown the production from forage brassicas to be less than from forage cereals, typically around 60-80%, but nonetheless they have reliably produced > 5t/ha of forage in dry winter conditions. The leafy turnip and kale generally produced less biomass than the forage rape, and the leafy turnip were more affected by dry conditions. Most of these experiments involved forage brassicas sown in late autumn or early winter, yet their sowing window opens much earlier and is likely to provide more forage production in regions with more winter rainfall.

Like forage brassicas, several winter canola varieties, which also require vernalisation that delays (but doesn’t stop) reproductive development, are now available commercially (e.g. CB-Taurus, Hyola® 971). These can be sown early (March or April) to provide early winter grazing and then can either be locked up for grain yield in favourable seasons or continue to be grazed.

We have also conducted some preliminary testing of the effects of the forage brassicas on root lesion nematode populations (Pratylenchus thornei) to see if they are effective at reducing populations. The current research indicates that like canola, most varieties do not host RLN but they do not greatly reduce the population either (see Figure 5 and Table 1). There appears there could be some variation amongst cultivars in their resistance to RLN but this requires more investigation before it can be confirmed.

A range of questions remain about how best to utilise forage brassicas in a grain cropping system. For example, they may have potential as part of an integrated weed management program by sowing in spring to provide strong competition and diversified weed control options over summer. However, this remains to be tested experimentally. 

Figure 1. Comparison of biomass production (bars) and growth rate (label; kg/ha/day) of 4 forage brassicas (blue), 4 forage cereals (orange), 5 forage legumes (green) and 1 herb (light blue) grown at Pilton, southern Qld in 2011.

Figure 1. Comparison of biomass production (bars) and growth rate (label; kg/ha/day) of 4 forage brassicas (blue), 4 forage cereals (orange), 5 forage legumes (green) and 1 herb (light blue) grown at Pilton, southern Qld in 2011.

 

Figure 2. Biomass production from 3 winter forage cereals (orange), 5 forage brassicas (blue) and a forage pea on the Eastern Darling Downs in 2012.

Figure 2. Biomass production from 3 winter forage cereals (orange), 5 forage brassicas (blue) and a forage pea on the Eastern Darling Downs in 2012.

Figure 3. Comparison of biomass production from 5 field pea cultivars (green), 2 vetch cultivars (red), the perennial legume sulla (light green) and 4 forage brassicas at Tulloona, NSW in 2013.

Figure 3. Comparison of biomass production from 5 field pea cultivars (green), 2 vetch cultivars (red), the perennial legume sulla (light green) and 4 forage brassicas at Tulloona, NSW in 2013.

Field pea – a flexible dual-purpose option

Field peas also provide a highly flexible option that could be used for either grain or forage that provide alternatives to other winter pulses (e.g. chickpea, fababeans). In poorer seasons, when forage availability is limited they might contribute forage to livestock, while in better seasons, when forage is more plentiful, they are grown for grain. One disadvantage of field pea compared to other winter forage options is that they typically have poor regrowth after grazing and are probably better suited to crash grazing (i.e. high intensity grazing over a short period of time) or cutting for hay.

We have compared the forage production of several field pea types and varieties and found little difference amongst them (See Fig 3 and 4). In our experiments over several seasons and conditions in southern Queensland and northern NSW, field peas have yielded between 4 and 8 t DM/ha. Again this is typically less than can be achieved from a forage cereal sown under the same conditions. Forage production of field pea is also similar to common vetch but higher than the first year production of perennial legumes such as Lucerne or sulla.

Field peas also offer several rotational benefits in grain cropping systems. Firstly, some varieties of field pea provide one of few winter legumes that are known to be resistant to root lesion nematodes. Cultivars Morgan and PBA Percy have been shown to be resistant and don’t increase RLN numbers.

Using field peas for hay making could also be a useful tool for managing weed seed set in problem weeds. Secondly, being a legume they can provide significant amounts of nitrogen to subsequent crops. Nitrogen inputs are also higher if grazed by livestock (because N is retained in the field) rather than if cut for hay or harvested for grain, where much of the N in biomass is removed. Field peas are effective fixers of atmospheric N, with 50-80% of plant N fixed. This means that a field pea crop producing 5 t DM/ha of forage would have fixed 110-170 kg of N/ha (including root material). If the crop was grazed by livestock 75-100 kg of N/ha retained in the field, while if it was harvested for grain or hay only 60-80 or 35-60 kg N/ha would be retained, respectively.  

Figure 4. Comparison of biomass production from 2 forage cereals (orange), 5 field pea cultivars (green), and 3 vetch cultivars (blue) at 3 sites in 2010 in south-western Qld; Billa Billa sown on 10 June (medium colour), Billa Billa sown 18 July (light colours) and Inglestone (darkest colours).

Figure 4. Comparison of biomass production from 2 forage cereals (orange), 5 field pea cultivars (green), and 3 vetch cultivars (blue) at 3 sites in 2010 in south-western Qld; Billa Billa sown on 10 June (medium colour), Billa Billa sown 18 July (light colours) and Inglestone (darkest colours).

Figure 5. Populations of Pratalenchus thornei through the soil profile following 5 cultivars of forage brassica (blue), field pea cv. Morgan (green) and oats cv. Genie (orange) compared to wheat cv. Kennedy (dark red), wheat cv. Mackellar (light red) and starting nematode levels (black).

Figure 5. Populations of Pratalenchus thornei through the soil profile following 5 cultivars of forage brassica (blue), field pea cv. Morgan (green) and oats cv. Genie (orange) compared to wheat cv. Kennedy (dark red), wheat cv. Mackellar (light red) and starting nematode levels (black).

Table 1. Populations of Pratalenchus thornei (0-30 cm) following various forage break crop options at Tulloona, NSW in 2013. No statistically significant differences were evident.

Crop sown

Nematodes/g soil

Chickpea (PBA HatTrick)

5.5

Sulla

4.1

Kale

2.1

Forage rape cv. Leafmore

18.6

Forage rape cv. Interval

3.4

Forage rape cv. Winfred

3.9

Vetch cv. Blanch fleur

10.8

Vetch cv. Popany

4.1

Field pea cv. PBA Coogee

14.3

Field pea cv. PBA Hayman

8.4

Field pea cv. Morgan

2.8

Field pea cv. PBA Percy

2.7

Field pea cv. PBA Wharton

11.5

Other annual or short-lived perennial forage legumes

Like field peas (discussed above), several other annual and short-lived perennial forage legumes could play a useful role as rotation crops for cereals in farming systems. They provide high quality forage and can provide significant nitrogen inputs to the cropping system, though their other rotational benefits are less well understood or quantified.

Common and purple vetch are more tolerant of grazing than field pea and are capable of producing similar levels of biomass (Fig 1, 3 and 4).  Common vetch are soft-seeded and should not cause long-term issues of weed control in subsequent crops, however, wooly pod vetch (e.g. Namoi) should be avoided as it is hard seeded and seed can last for several years in the soil. Several experiments in southern Queensland showed Purple vetch cv. Popany to be less productive than snail medic and sulla (below), but at Tulloona in 2013 it produced similar biomass to the field pea and other vetch cultivars and more than sulla.

Annual medics that can regenerate from seed have historically had a role in cropping systems on alkaline clay soils; the most suitable is snail medic. Snail medic can produce equivalent of other legumes in its establishment year (see Fig. 1) and in subsequent years can establish quickly from seed following autumn rains so that it can often out-yield other sown annual forage crops including oats. However, control of recruiting seedlings in crops for several years after the medic is a major problem to their wider use in cropping systems, unless they are to be used regularly in the crop rotation (e.g. 1:1 with a cereal crop).

On sandy and/or acidic soils other annual pasture legumes such as Biserulla or Pink Serradella should be used in preference to medics. Though there is limited data on their performance in the northern grains region.

Sulla (Hedysarum coronarium) is a short-lived winter-growing perennial legume from the Mediterranean. Sulla is slower to establish and produce forage over winter than the annual legumes (e.g. vetch, medics and field pea) but is more productive than Lucerne over its first winter and spring (see Fig 1 and 3). Sulla can have very high growth rates of 60-80 kg DM/ha/day during early spring and on several occasions has produced equal forage yield to oats; in most cases production is 50-75% of oats. Sulla has the potential to survive 2-3 years, but root rot diseases, wet or exceptionally dry conditions over summer will greatly reduce plant numbers (30-50% of first year density).  Sulla can provide higher N inputs than the annual legumes (60-150 kg N/ha/yr) but little is known about its impacts on soil-borne diseases of crops. There is some evidence at one experimental site where numbers of Pratylenchus thornei were twice as high under sulla than adjacent oats and lucerne, but this remains to be validated elsewhere. Sulla does dry the soil profile more than annual forage crop options (25-50 mm), but less than Lucerne. Its other features are:

  • Best suited to alkaline clay soils
  • Non-bloating
  • High quality forage (3% N, 70% DMD)
  • Contains compounds that may help control worms
  • Dormant over summer, growth peaks in autumn and spring

Summer forage crop options

Several summer-growing forage crops could be used in cropping systems in the central west of NSW. They could provide options to utilise summer rainfall and manage ground cover over summer in crop rotations (e.g. following winter pulse crops), while also filling seasonal feed gaps in summer or autumn. Double cropping into a summer forage out of a winter legume or cereal could be an effective ways to break out of a winter crop rotation for 18 months – 2 years to allow control of winter crop weeds and diseases and use of alternative herbicide chemistry. The summer forage would allow some return to be achieved as opposed to a long fallow (12 months) leading into and out of summer crop (e.g. grain sorghum) in the sequence. 

Table 2. Summary of relative performance of winter and summer forage crop options for key attributes in grain cropping systems in central west NSW (*** - high, **-moderate, *-low).

Forage option

Forage production

Grazing tolerance

N inputs

RLN control

Crop weed management

Residual soil water

System role/fit

Winter forages

Oats

***

***

-

**

*

**

Alternative to winter grain cereals

Forage brassicas

**

***

-

***

***

**

Replace canola where unviable or risky

Field pea

**

*

**

**

**

***

Replace Chickpea or Fababean, dual-purpose

Vetch

**

***

**

?

**

***

Replace winter pulses

Snail medic

**

***

**

?

**

***

Rotation with cereals, hard seed problem

Sulla

 

***

***

?

**

*

2-3 year phase, alternative to lucerne

Summer forages

Forage sorghum

****

***

-

**

***

**

Transition to summer crop phase

Millet

***

**

-

***

***

***

Soil cover after winter pulses, dual-purpose

Lablab

***

**

***

***

**

**

Alternative to mungbeans

Cowpea

**

*

**

**

**

**

Alternative to mungbeans

Soybeans

***

*

***

*

**

**

Dual-purpose alternative to mungbeans

Forage sorghum

A large variety of forage sorghum hydrids are available that can provide very rapid summer production (growth rates > 100 kg/ha/d are typical). Biomass yields of >10 t DM/ha are reported at Trangie, 80 days after sowing. However, grazing should be initiated earlier (height 60-80cm) to maximise forage quality, which declines rapidly as the crop develops. Forage sorghum also require high levels of available N to optimise their production and quality. Forage sorghum is better suited to cattle grazing than sheep, as it quickly gets too high for sheep grazing,  

The advantage of a forage sorghum over a grain sorghum in the farming system is that it could be terminated earlier (e.g. 70 days c.f. > 100 days) after providing some grazing and allow the soil profile more time to refill.

Millet

Several millets can be utilised as forage crops but also be continued to harvest grain should the opportunity present itself. Millets are less productive (50-60%) than forage sorghum but have higher forage quality and maintain this for longer than forage sorghum. If grazing is managed carefully millet also provides excellent stubble cover over summer and hence could be an effective option in the system following a winter pulse (e.g. chickpea) to increase soil cover. Most millets have been found to be resistant to both Pratylenchus thornei and P. neglectus. Millets are probably more susceptible to establishment problems, owing to their small seed and need to be sown shallow (< 30 mm).

Annual legume forages

Three annual legumes have some potential for use as summer forage break crop options in grain cropping systems. They have the advantage of providing significant N inputs, and produce higher quality forage than grasses above. These could be used instead of Mungbeans in the system to provide a better disease break and greater N inputs owing to higher biomass production. 

Lablab is the most productive summer legume forage option and is able to produce 5-8 t DM/ha reliably in southern Qld and northern NSW; it performs best on alkaline clay soils. Lablab is the more tolerant of grazing than the other two annual legumes mentioned here, and can be used to build a high quality forage bank over summer to be utilised in autumn. Two main varieties are readily available, cv. Highworth is later flowering with higher biomass production potential and cv. Rongai is earlier flowering and typically less productive.

Lablab is large seeded allowing it to be drilled 5-10 cm into the soil. Lablab is resistant to both RLN species and can provide a dense canopy good for breaking down crop residues that harbour crown rot and other cereal diseases. Because of its high productivity lablab is capable of fixing large amounts of nitrogen and frequently contributes 50-150 kg of N to the soil. Some evidence of double cropping lablab and wheat has shown to be highly effective at capturing summer rainfall and providing N inputs, but in dry conditions there is likely to be an impact on yield of following wheat due to lower soil water.

Cowpea is typically less productive than lablab and less tolerant of grazing but is better suited to lighter textured or acidic soils. It too is resistant to P. neglectus and moderately resistant to P. thornei and would provide disease break benefits to cereal crop diseases. Because of its lower biomass production, cowpea will contribute less fixed N than lablab.  

Soybean can also be used as a high quality forage-hay crop, but recovers poorly after grazing or cutting, so generally only provides 1 cut or grazing opportunity. Some dual-purpose varieties are available now for this purpose. Soybean can produce similar biomass to lablab, but is less tolerant of moisture stress than lablab. In some areas in northern NSW, growers sow soybean to provide a flexible option to be grazed or cut for hay in poor seasons or is left to produce grain in better seasons. Soybean is less beneficial to managing nematodes, it is susceptible to P. thornei, but can also contribute large amounts of N to subsequent crops if biomass is not removed from the field.

Burgundy bean

Burgundy bean is a perennial summer growing legume that can persist for 3-4 years. It is suitable on a wide range of soil textures and is the most cold tolerant of the available tropical forage legumes, though it still goes dormant in winter (from late May to early Sept). Burgundy bean can produce in excess of 5–8 t/ha/yr of DM in pure swards in southern Queensland, but is generally less productive than annual lablab in the first year, but produces similar or higher yields in subsequent years. If allowed to set seed it will recruit to produce thicker and more productive stands in the second year. Experimental data on N fixation in burgundy bean suggests that N fixation is less efficient than lablab and soybean. The impacts of burgundy bean on soil-borne diseases are unclear, but the crop can handle non-selective herbicides once it is dormant in winter; this could be used strategically to control winter weeds and/or oversow other forages in winter. It’s other features are:

  • Non-bloating
  • Germinates and grows under cooler conditions than other tropical legumes
  • Easily established & regenerates well from seed each year
  • Extremely palatable and selectively grazed – often grazed out unless spelled regularly and to allow seed set
  • Might be grown in association with grasses, but may be difficult to maintain beyond 3-4 years because of its high palatability

Some further considerations for alternative forages

There are some additional aspects that should be considered in order to optimise the performance of forage crop options in cropping systems

  1. Residual herbicides – many legumes and other broadleaf options are highly susceptible to residual chemicals often used during cereal crop rotations (e.g. Ally® or Glean®).
  2. Livestock grazing – some of the forages mentioned here can have risks of adverse animal health impacts if not managed carefully. In particular, the risk of bloat on high quality winter legumes and the risk of high nitrate in forage brassicas need to be considered. In forage brassicas, the risk can be reduced by avoiding grazing shortly after fertiliser if applied or on fertile paddocks before the crop is sufficiently large to dilute nitrate in the forage.
  3. Legume innoculation and fertilisation – the forage legumes mentioned here all require inoculation with their appropriate inoculant group to maximise their performance. Forage legumes also benefit from application of P and S at sowing – they often have higher P requirements than cereal crops.
  4. Sowing depth – sowing depth of several forages is also important to optimise establishment, particularly in small-seeded species. Forage brassicas, sulla and burgundy bean all require seed depth of < 25 mm – depths greater than this will reduce emergence. Other larger seeded species (e.g. snail medic, vetches, pea, lablab) can be drilled much deeper.

Acknowledgements

The results of research reported here were undertaken as part of the Grain and Graze project was 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.

We would like to thank those growers who hosted the experiments reported here.

Contact details

Lindsay Bell
CSIRO
PO Box 102, Toowoomba 4350, Qld
Ph: 07 4688 1221 or 0409 881 988
Email: Lindsay.Bell@csiro.au