The nutritive value of grazing modern crop stubbles

Summary

New crop cultivars, alternate crop species, modern harvesters and a reduction in the density of volunteer pasture plants have affected the nutritional value of modern crop stubbles that are grazed by sheep. Ewes typically graze stubbles during mating and early pregnancy, when access to high quality feed is critical for good reproductive performance.

A recent scoping study found that modern crop stubbles are notoriously variable in quality, with the feeding value of wheat stubbles ranging between 60 and 190 DSE grazing days/ha for sheep. Non-cereal crops are usually found to be even more variable. Producers have relied on building up knowledge through observation or trial and error for supplementary feeding and mob rotations when grazing sheep on stubbles.

This project will provide producers with up-to-date information on the feeding value of modern stubbles. In addition, the project team are examining variability in the feed value of chaff heaps and the requirements for supplementary feeding of sheep grazing stubbles.

Objectives

The main objectives of this project are to:

• deliver up to date information, in digital and print formats, on the nutritional value of stubbles (and chaff piles) of modern crop cultivars harvested with modern equipment
• provide improved knowledge of the value and supplementary feeding strategies for grazing chaff heaps
• produce an online integration tool and hard copy communication materials to specify expected grazing days and supplementary feeding requirements for selected scenarios.

Key findings

1. The results of this project confirmed that stubbles and chaff (excluding grains) are primarily a low quality source of forage, with an energy density of ranging from 4-8 MJ ME/kg, and typically around 6 MJ ME/kg for the edible components of chaff. 
2. Edible components of barley and lupin chaffs were mostly higher quality than wheat and canola chaffs, however all were below the maintenance requirements of sheep of 7.5-8 MJ ME in feed. 
3. Farmers need to ensure that sheep have access to other high-quality feed such as spilled grains, supplements or green forage to maintain or grow sheep grazing stubbles and chaff. Even the higher quality chaff components are of relatively low feeding value, and when offered ad libitum will only provide about one third to one half of the daily maintenance requirements of sheep. 

Benefits to industry

Most broadacre crops are grown in mixed farming areas, where cropping and livestock enterprises are combined. In these areas, stubbles make up an important part of the seasonal feedbase, except where the business is cropping only or stock are kept off stubbles for soil management reasons. It is estimated the crop stubbles grown in Australia could provide about three billion ewe grazing days, or enough forage to feed Australia’s ~65 million sheep flock for six weeks.

Future research

1. Further field studies comparing grazing of stubbles with and without chaff aggregated in chaff piles. Measure livestock performance, and the selective grazing of spilled grain and chaff in these paddocks. In particular, barley, lupin and canola stubbles should be investigated, and existing data from grazing trials needs to be analysed and published. 
2. Extension around consistent use of terminology when discussing grazing stubbles. For example, sheep grazing days and MJ ME/ha to indicate feed value  
3. Development of tools to enable farmers to rapidly assess stubble quality, such as in-field NIRS feed quality assessment 
4. Further measurement of the quantity and intake of unharvested grains in stubbles and chaff, across a range of crop species  
5. A large-scale GxExM experiment to understand the factors driving nutritive value of chaff and stubbles in different seasons, soils and crop management conditions.     
6. Selective grazing behaviour of livestock offered chaff and stubbles for other crop species should be considered. 
7. Selective grazing behaviour to be assessed in situ, to compare diet selection and livestock performance as compared with the results of the animal house study.  
8. Validation of the Stubble Grazing Calculator, via Producer Demonstration Sites in collaboration with farmer groups to test how well the calculator can predict the feeding value of stubbles in terms of the number of mob grazing days to reach a liveweight change target. A range of livestock classes and crop types (i.e. additional to mature ewes on wheat stubbles) could be tested.