Grains Research and Development

Date: 18.01.2013

Study shows ways to cut pasture renovation costs

Author: Brad Nutt

Pasture Seed

On-farm seed production is a low-cost way to bulk up high-quality annual pastures, which can benefit subsequent crops and whole-farm returns

Key points

  • Increasing the legume content of pastures may improve returns from livestock enterprises and reduce crop inputs
  • Producing pasture legume seed from a nursery paddock can reduce the cost of seed for a large-scale pasture improvement program
  • Lowering seed cost can allow higher sowing rates that are more competitive with weeds and provide material for twin or summer sowing and green manuring

Pasture renovation in mixed-farming systems need not be a costly exercise. There are several species that can be grown for seed on-farm, allowing increased areas to be planted at high sowing rates.

A pasture phase renovated with annual legumes will provide several benefits to subsequent grain crops.

The biological nitrogen fixation provided by the legumes and their associated root nodule bacteria builds soil fertility and reduces the reliance on applied artificial nitrogen fertiliser. Generally, pasture legume dry matter in spring contains 2.5 to four per cent nitrogen and most of this is sourced from the atmosphere. This nitrogen is released gradually over time as the legume biomass breaks down in the soil, creating an effective slow-release fertiliser.

A pasture phase may also help with weed management. A densely regenerated legume component can compete well against weeds. If there is soil moisture and space within crops, something will grow and it may as well be a legume that is at the same time improving soil fertility. Spray-topping pastures in spring may help control grass weed seed set.

In addition, legume-based pastures provide high-quality forage for livestock.

Pasture seed production

To highlight the benefits of on-farm pasture seed production for renovating pastures, the cost was calculated for two scenarios – a conservative average yield, and a high yield that could be expected in favourable seasons (Tables 1, 2, 3, 4, 5, 6).

Under these scenarios the cost of seed produced before cleaning ranges from $0.20 a kilogram with French serradella (pod) at high yields, to $1/kg with bladder clover at conservative yields (Table 3).

With the exception of the soft-seeded forms of French serradella, the harvested seed or pod will have high levels of hard seed dormancy and low germination – although this is a benefit when used for twin-sowing.

Seed in this form is not suitable for traditional sowing without seed scarification (scratching or cracking the hard outer coat of a seed to help it germinate) and in the case of hard-seeded serradella, dehulling and seed scarification. This processing increases the cost of production by $0.30/kg.

In the case of hard-seeded serradella, the seed content and extraction rates need to be considered along with the processing cost.

One of the benefits of French serradella is that it has more seeds and therefore higher rates of extraction, resulting in a lower cost structure compared to yellow serradella (Table 4).

Cleaned scarified seed can be sown dry before the seasonal break in situations with a low expected weed burden, or after the seasonal break and after a knockdown weed control.

Using seed produced on-farm, even at double the sowing rates suggested for a seed crop, can dramatically reduce the seed cost (Table 5).

A small nursery paddock can provide enough seed to expand the area sown. For example, up to 50 hectares can be sown using seed produced from a 1ha seed nursery (when yields are high).

Twin or summer sowing

An alternative use of seed or pod produced on-farm is in twin or summer sowing.

Both use unprocessed seed or pod that has a high level of hard-seed dormancy. This avoids the extra cost associated with stimulating the germination.

Twin sowing refers to sowing pasture seed with a cereal or canola crop, where little of the legume will emerge in the crop because of the pasture’s hard-seed dormancy, but will gradually become non-dormant over the following summer and autumn.

A similar principle applies with summer sowing but the seed is sown after the cereal or oilseed crop is harvested.

Twin and summer sowing have the advantage of making full use of rainfall and can provide two to three times the dry matter production of pasture compared with that produced from normal pasture seeding. This is because the pastures emerge early when soil temperatures are still warm.

Twin sowing has the additional benefit of being a one-pass operation for simultaneously seeding both grain and pasture crops.

High sowing rates are required with these methods, but the production of seed on-farm can keep the seed cost to less than $50/ha (Table 6).

When selecting a pasture species to sow for on-farm seed production, consider the soil type and purpose for which the seed is being produced.

In general, serradella is suited to acidic-to-neutral course-textured soils, while bladder clover is suited to mildly acid-to-neutral loams and clays.

Soft-seeded French serradella

The soft-seeded French serradellas CadizPBR logo and ElizaPBR logo are suited to short phases of pasture or green fallow between extended crop sequences. They are easily harvested and do not need to be dehulled or scarified.

Rhizobial inoculation is encouraged for seed crops, although the benefit of inoculation for general sowing is debatable, particularly in a paddock with a recent history of lupins.

CadizPBR logo flowers in about 115 days when sown in May, while ElizaPBR logo flowers two to three weeks earlier.

It is best to direct-harvest French serradella. Crop lifters or extension fingers can assist if the crop has packed down under late rain.

French serradella is not suited to swathing or suction harvesting. It is important to monitor serradella seed crops for budworm in spring and control them if they are present.

As a guide to storage volume, French serradella pod is about 50 to 60 per cent of the weight of wheat for the same volume.

Hard-seeded French serradella

The methods used to produce hard-seeded French serradella pod are similar to those used for soft-seeded cultivars. The main difference is the high hard-seed content at harvest.

The two cultivars available are MarguritaPBR logo(semi-erect) and EricaPBR logo (prostrate), and each has a maturity similar to CadizPBR logo. These cultivars will persist through one year of crop once a hard-seed reserve has developed in the soil. About 50 per cent of the hard-seed reserve of MarguritaPBR logo or EricaPBR logo will break down each summer and autumn.

Although not as hardy or persistent as yellow serradella, these cultivars are easier to harvest and are highly suitable for sowing as pod when twin or summer sowing.

Hard-seeded French serradella is not suited to autumn cleaning. Hard-seeded French serradella can be dehulled and scarified using a simple stone-type seed scarifier.

Yellow serradella

Although yellow serradella is difficult to harvest, it persists well and the production of seed for on-farm use can reduce the cost of pasture improvement using this species.

The three most common cultivars are YelbiniPBR logo (very-early-season maturity), CharanoPBR logo (early-season maturity) and SantoriniPBR logo (mid-season maturity).

When harvesting yellow serradella, it is important to aggressively thresh the pod to break it into small segments for ease of movement through the header. Before harvesting the entire area, partially fill the header box to ensure the pod will flow.

If the yellow serradella crop has badly lodged or the pod has shed, rake the stubble into windrows using a hay or pinwheel rake. The crop then can be lifted into the harvester using a pick-up front. An alternative is to use a vacuum harvester.

About 30 per cent of the hard-seed reserve will break down each summer and autumn and the pasture stand will persist through one or two crops.

All three cultivars have a staggered germination that provides an opportunity to autumn clean the pasture.

Although pods can be established with twin or summer sowing they are not as suited to these techniques as hard-seeded French serradella.

Bladder clover

Bladder clover is easily harvested with a conventional header if sufficient height is achieved, although crop-lifting fingers are needed to assist entry into the front.

The seed heads thresh well to produce a clean, pure seed sample. If the crop is too low it can be raked into windrows with a hay or pinwheel rake and lifted into the harvester with a pick-up front.

Bladder clover seed has a thick seed coat that requires a diamond disk scarifier to achieve high rates of seed germination. An alternative is to use unscarified seed for twin or summer sowing.

About 60 to 70 per cent of the bladder clover hard-seed reserve will break down each summer and autumn.

Legal obligations

Growers thinking about producing their own pasture seed need to check the commercial status of the cultivar – for example, obligations under point-of-sale contracts – to confirm what they can do with the seed.

Table 1: Seed prices, sowing rates, harvesting efficiency and processing costs used to calculate cost of on-farm pasture seed production

Pasture species Estimated retail seed price $/kg Sowing rate of high germination seed kg/ha Estimated harvest efficiency % Cleaning costs $/kg Dehulling and cleaning costs $/kg
Source: Brad Nutt, Department of Agriculture and Food, WA.
French serradella pod (soft seeded)
3.50 10 75 0.30 Not applicable
French serradella pod (hard seeded) 8.5 5 75 0.30 0.80
Yellow serradella seed 15 5 40 0.50 1
Bladder clover seed 6.5 10 60 0.30 Not applicable

Back to Pasture seed production

Table 2: Input costs required to produce pasture seed on-farm.

Operation $/ha
Total (not including species-specific costs shown in Table 1) 200
Note: The allowance for herbicides used in this example could be considerably lower in situations with low weed burdens. The cost of inoculation has not been accounted fro because it can range from $2/ha to more than $20/ha, depending on which method is used.
Source:Brad Nutt, Department of Agriculture and Food, WA.
Sowing 15
Fertiliser (120kg/ha 3:1 super:potash) 80
Herbicides (glyphosate knockdown, trifluralin, broadleaf and grass control, blanket wiping, desiccants) 75
Insecticides (Talstar®, alpha-cypermethrin) 15
Harvesting 15

Back to Pasture seed production

Table 3: Total and harvested yields that could be expected from nursery seed crops of annual pasture legumes and the associated cost of production at two yield scenarios (average and high yield) before and after seed cleaning.*

Species Expected total yield1(kg/ha) Harvested yield1 (kg/ha) Seed or pod produced - pre-cleaning ($/ha) Seed or prod produced - including cleaning ($/ha)
Average High Average High Average High Average High
*Based on inputs and harvest efficiency shown in Tables 1 and 2.
1 The pasture seed yields and harvesting efficiency quoted for the various pasture legume species are derived from a combination of grower feedback and experimental results.
2 Bladder clover is harvested as bare seed and commercial seed cleaning would include scarification to enhance germination to more than 75 per cent.
Source: Brad Nutt, Department of Agriculture and Food, WA
French serradella pod (soft seeded) 500 1500 375 1125 0.63 0.21 0.93 0.51
French serradella pod (hard seeded) 500 1500 375 1125 0.64 0.21 0.95 0.52
Yellow serradella pod 800 2000 320 800 0.78 0.31 1.28 0.81
Bladder clover seed 400 1000 240 600 1 0.4 1.3 0.7

Back to Pasture seed production

Table 4: Seed content, extraction rates and the production costs associated with dehulling hard-seeded French serradella and yellow serradella in two yield scenarios1

Species
 
Seed content of whole pod %
 
Dehulling efficiency %
 
Dehulled seed yield kg/ha produced Dehulled seed $/ha produced
Average yield High yield Average yield High yield
1The dehulling costs refer to yellow serradella and hard-seeded French serradella cultivars that are harvested in pod form. Freshly harvested pod of these serradellas have high levels of hard seed and low germination and further processing is required to remove the seed from the pod to allow scarification to enhance seed germination. Soft-seeded French serradella normally has no hard-seed dormancy and therefore has high levels of germination in the pod.
Source: Brad Nutt, Department of Agriculture and Food, WA
French serradella pod (hard seeded)
60 70 158 473 2.17 1.26
Yellow serradella
35 50 56 140 5.46 2.79

Back to Pasture seed production

Table 5: Seed cost and potential area that could be sown at high sowing rates when seed is produced on-farm

Species
 
Sowing rate (kg/ha)
 
Seed cost ($/ha) when sowing seed produced from a nursery with: Potential area that could be sown from the 1ha of seed from a nursery with:
Average yield High yield Average yield High yield
Note: All species were sown as scarified high-germination seed with the exception of soft-seeded French serradella, which is sown as pod.
Source: Brad Nutt, Department of Agriculture and Food, WA
French serradella pod (soft seeded) 20 18.53 10.18 19 56
French serradella pod (hard seeded) 15 32.48 18.83 11 32
Yellow serradella seed 10 48.10 22.70 7 20
Bladder clover seed 15 18.00 9.00 16 40

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TABLE 6: The seed cost per hectare and potential area that could be sown using unprocessed, dormant hard-seeded annual pasture legumes when the seed is produced on-farm using twin or summer sowing.

Species
 
Sowing rate (kg/ha)
 
Seed cost ($/ha) when sowing seed produced from a nursery with: Potential area that could be sown from the 1ha of seed from a nursery with:
Average yield High yield Average yield High yield
Source: Brad Nutt, Department of Agriculture and Food, WA
French serradella seed (hard seeded) 40 25.60 8.53 9 28
Yellow serradella pod 60 46.88 18.75 5 13
Bladder clover unscarified seed 30 30.00 12.00 8 20

Back to Twin or summer sowing

More information:

Brad Nutt,
08 9368 3870,
bradley.nutt@agric.wa.gov.au

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