GroundCover™ Supplement Issue: 129 | 15 Jun 2017 | Author: Alison Frischke
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.
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.
GRDC Research Code SFS00028
0429 922 787,
'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.