Moorhead says the most common issue he sees in cultivated brassica crops is the failure to spray out existing pasture before working the paddock. Twitch and browntop won’t just die through being turned over or worked; spray is needed, too, to ensure these weed grasses are not still present when renewing pasture after brassica crops.
Moorhead says that with direct-drilled paddocks the single biggest cause of crop failure after insects and slugs is not using enough nitrogen fertiliser. Soil organic matter ties up soil nitrogen and this will eventually become plant available in a direct-drilling situation. This soil nitrogen will not become plant available until around the end of the growing phase in autumn, so nitrogen needs to be applied to prevent a shortage in the early stages of growth.
Undersupplying nitrogen early means running the risk of a crop failure and increases the crop’s vulnerability to pests.
“All economics with brassicas sit with yield. When it comes to black-and-white economics, for every tonne of feed you grow, you’ve got cheaper feed.”
For this reason growers needed to have a clear expectation of what yield could be achieved on a property given any physical limitations, then focus on moisture and nutrients in order to achieve that expectation.
Nutrient levels are key to achieving targeted yields. Moorhead emphasises the importance of knowing available nitrogen levels as part of a soil test before planting.
“The best saving you can get from doing a soil test is asking for it to include a soil available nitrogen test, so at least you can then make an informed decision on nitrogen use.”
He says phosphate should generally be supplied at upwards of 40kg/P/ha and nitrogen in multiple dressings of 35-48kg/N/ha for brassica crops depending on yield expectation. Trace elements are key, too, with boron (B) being traditionally recognised as being important for brassica development and molybdenum (Mo) deficiency becoming more common. While it has not been a big problem until recently, more cases of Mo deficiency are being seen every year. It often shows up in plants as a whiptail symptom similar to hormone chemical damage.
Kale: Kale is reliable in a range of climates and soil types, making it an attractive option for many farms throughout the country.
Moorhead points to the fact that kale is a high-quality crop on average, but the variability within the plant is something people need to be aware of when feeding it. It is crucial to get allocation right when feeding and avoid the “Speights box” situation where stock are getting about as much nutritional benefit from eating the lower end of a lower stalk with less than 6% crude protein as they would from consuming a cardboard beer box.
A 2008 survey of kale management practices for feeding dairy cows in Canterbury, done by Glen Judson (Agricom) and Grant Edwards (Lincoln University) was designed to consider the former industry perception that it was impossible to put condition on cows using kale. This research has shown the crucial importance of correct feed allocation.
The survey showed dramatic variation between the amounts of kale that a farmer thought they were feeding and the quantity of feed actually allocated. In almost all cases the two differed and the allocation contained less kg/DM/cow/day than the farmer believed he or she was offering. The biggest cause of this was imprecise break sizes. Shifting breaks by fencepost or other landmark can result in dramatic feed availability differences.
Moorhead says there have been substantial improvements in feed allocation since the survey which, along with other Lincoln University research, has proven there is potential for cows to eat a lot of kale in a day and, if well fed, put on condition.
“The primary change in winter feeding is that people are now measuring paddock widths and can finally allocate based on actual area rather than estimated or fixed break sizes.”
He says kale variety descriptions are often quite crude and exactly how individual plants will look in a paddock is heavily influenced by sowing rate. Every individual cultivar has different potential for stem size, leaf holding and height,with taller types such as Gruner and Caledonia always providing extra yield in the stem only.
Kale is a reliable second crop winter brassica and has a limited risk of club root. This is still a risk to be wary of: “It’s a very evil thing,” Moorhead says.
He warns that club root is transported in mud and water, for example on muddy tractor tyres or cows moving between paddocks, meaning once it is on a property it will later show up in paddocks that were historically clean. It can also be on a farm for years before it is activated, something that is generally caused by wet summer conditions.
Swedes: Swede crops offer the benefits of high-quality feed throughout the plant and the ability to achieve high utilisation, over and above 85%.
Moorhead warns swedes are more variable in their performance and are strictly a first crop brassica in a rotation.
“Trying a second year of swedes will see them absolutely monstered by diseases.”
Swedes can be susceptible to club root, dry rot and can get viruses. Rape and turnips are similarly sensitive and for these reasons all three crops should be considered as limited beyond the first year of a brassica rotation.
Swedes grow well on clay downs with good levels of soil organic matter but tend to be limited in dry environments. The swede is a “phosphate feeder” – phosphate drives bulb development.
“You can get beautiful swede crops on relatively low nitrogen inputs if your phosphate inputs are high enough.”
More on forage crops with Dr Warwick Scott in the Country-Wide September issue
Weed controls vital
Though not actually a brassica, fodderbeet is growing in use.
Allister Moorhead, of Agricom, says there are some key considerations for people looking to profit from what is fundamentally a high-cost crop to establish, at around $2000/ha.
Though high yield potential makes it an attractive feed option for many people, fodderbeet failures prove an expensive exercise.
“Look at it not as a brassica but as a maize type plant. If you think about fodderbeet like maize then you’re on to the thought process to manage it.”
A key consideration with fodderbeet is the fact that it will not outcompete weeds, making timing of weed controls vital to a successful crop.
Moorhead says that once this is accepted the weed control programmes are actually quite straightforward and it is then just a matter of getting timing right. Fodderbeet also needs greater accuracy in feed transitioning times so as to achieve higher intakes needed to build the cow up over a couple of weeks. Increasing intake too quickly elevates the risk of acidosis. It also may be necessary to feed extra supplements in conjunction with fodderbeet to maintain protein levels.
“Because it is low fibre and low in protein you may need silage or other supplements as well so fodderbeet can become an expensive option in terms of per day costs for a wintering crop.”
Fodderbeet offers uniform quality throughout the plant and can follow other brassicas in a rotation providing there are no residual spray issues and soils are not too heavily compacted.
More on fodderbeet agronomy, costs & returns in Country-Wide September issue
