Successive frosts and lack of rain has hindered crops in the Southern Mallee and Northern Wimmera this season. In more severe cases, if useful amounts of biomass had been grown with the June-July rainfall and the warmer temperatures, you may have already made the decision to cut the crop for hay. If the crop has been left to mature and the cost of harvesting is higher than the value of the grain (establishment and growing costs are already spent– you cannot retrieve them) you may want to graze the paddock to salvage some economic value and to manage the stubble for the following sowing operation.
As plants mature digestibility falls from about 80% part-way through stem elongation to about 60% between anthesis and grain ripening. Post-harvest, the digestibility of cereal stubble will be below 40%. The higher the digestibility the faster digestion can occur, allowing for higher intake, nutrient uptake and consequently animal production. Therefore a greener crop is of greater nutritional value.
Many cereal crops that experienced frost incurred stem damage on the main stem, and maybe the 1st and 2nd primary tillers. In cases, this affected the embryonic head inside the stem. With moisture, plants responded and initiated new secondary tillers from lower nodes on these stems in an attempt to still produce grain. Production of protein and carbohydrate would have continued in surviving and new stems and leaves. A droughted cereal crop would have continued protein and carbohydrate storage until it simply ran out of moisture. With less or no ability to translocate protein and energy stores into the grain, the nutritional value of these mature plants should be greater than harvested stubble.
A failed canola crop can be grazed but careful grazing management is needed to avoid health issues caused by nitrates. Canola crops grown on fertile legume paddocks or that have had high nitrogen inputs that then become stressed, pose more of a risk. Stock will adjust to high nitrates, but care is needed to minimise potential problems. Start with a small number of stock and monitor the animals closely, particularly for the first three days. If there are no problems you can introduce the rest of the mob. Remove immediately if there is any unusual behaviour. Ensure animals are not hungry, and have partial gut fill when turned into the paddock. Start with short grazing periods, and allow stock to have access to some alternative feed such as hay or grain or access to an adjacent paddock with different feed to dilute canola intake. Chemical withholding periods for herbicides need to be adhered to.
For all crops, to know with certainty what the nutritional value of your crop or stubble is, it must be tested. Contact FeedTest on p:1300 655474 or [email protected] for kits.
If feed is so scarce that you are considering putting the sheep into crops, think carefully about whether to hold on to those sheep. A failed crop won’t supply a lot of feed (unless it’s very weedy) and sheep sales income, even if stock are not in great condition, will contribute to a better cash flow position.
