A visual guide to estimating stubble value to livestock

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Key point

  • Green shoot and grain are the only feed in stubble that provide sufficient energy for weight gain.

Key message

While crop stubbles can be a valuable source of feed in mixed farming enterprises, not all stubbles are of equal value and stubble bulk does not necessarily translate into animal performance. A new assessment tool to estimate the grazing value of stubbles will help growers to make the most of this resource. It will be available on the Grain & Graze website in July/August.

Crop stubbles are a useful source of feed after harvest when green pasture is scarce, and grazing helps to reduce high stubble loads for better establishment of subsequent crops. Research has shown no negative impact on soil health or subsequent crop yields, so long as sufficient stubble is retained to prevent wind erosion and maintain water infiltration.

The GRDC-supported Grain & Graze 3 program has developed a guide to help growers estimate the grazing value of stubble. Stubble quality can vary between crops and seasons due to improved harvest efficiency and weed control, and can change quickly across a paddock, particularly once grazing begins or after summer rain.

Estimating feed value

The value of feed is determined by the amount of residual grain and green plant growth present, including summer weeds and shot grain. Once this is eaten, animals will lose weight.

Research for Grain & Graze 3* found that sheep lost weight once the available grain or green shoots fell below 40 kilograms per hectare of grain, or 40kg/ha of green shoots (shot grain and weeds).

Digestibility (metabolisable energy) is the main factor that determines feed intake. Sheep will eat the
most digestible feed first (grain and green) and leave the least digestible (straw and trash) until last.

A feed needs more than 7.4 megajoules of metabolisable energy per kilogram of dry matter (DM) for weight gain. Protein is also important for growth and lactation, with levels above 12 per cent required. These levels are only found in green shoots and grain (Table 1).

To estimate the quantity of useful feed from cereal stubbles, count the number of grains and green shoots in a 0.1 metre square (32 x 32 centimetres) quadrat (see Figure 1 and Table 2). For other grains, the number of grains counted per 0.1m2 that equate to 100kgha is: lupins – eight, field peas and chickpeas – five, and faba beans – two.

Ground cover

Maintaining adequate ground cover is critical in lower-rainfall environments. A minimum of 50 to 70 per cent ground cover (about 1.0 to 1.5 tonnes of DM/ha) must remain on paddocks to prevent wind erosion, with standing, anchored stubble 10cm high is twice as effective at reducing wind erosion as loose flat stubble.

Figure 1 A new visual guide will help growers to use the number of grain and green shoots in a 0.1mquadrat to
estimate the quantity of useful feedfrom cereal stubbles. Images for assessing stubble ground cover
are also available on the Grain & Graze website.
Photo showing 40kg/ha grains and green shoots in a 0.1mw quadrat40kg/ha Photo showing 60kg/ha grains and green shoots in a 0.1m-square quadrat60kg/ha Photo showing grains and green shoots in a 0.1m2 quadrat to estimate useful feed from cereal stubbles140kg/ha

SOURCE: Southern Farming Systems

Table 1 Average feed value of crop components in stubble.
Feed value Wheat and barley stubble Lentil stubble
Grain Green shoots Standing straw Loose trashGrainStraw
Digestibility  (as % digestible DM) 82–87 59–73 38–40 40–41 92 36
Metablisable energy (MJ/kg DM) 12.7–13.2 8.5–11.0 5.0–5.3 5.3 13.1 4.6
Crude protein (%) 9.5–13.5 15.9–18.7 1.2–2.8 2.0–4.0 27.5 6.7

SOURCE: Grain & Graze

Table 2 Conversion rates for cereal grain and green shoot counts into kilograms of dry matter per hectare.
Quadrat grain count conversion to kg grain/ha Quadrat green shoot count conversion to kg DM/ha
Grains counted (number/0.1m2) Approx. quantity of grain (kg/ha) Green shoots counted (number/0.1m2) Approx. quantity of DM (kg/ha)
6 20 7 20
13 40 14 40
20 60 21 60
26 80 28 80
33 100 35 100

SOURCE: Grain & Graze

GRDC Research Code SFS00028

More information:

Alison Frischke,
0429 922 787,
alison@bcg.org.au

'Estimating the grazing value of stubble' tool, Grain & Graze 3

* Conducted by Southern Farming Systems, Birchip Cropping Group, Eyre Peninsula Agricultural Research Foundation and Ag Excellence Alliance.