EVERY year growers make an important decision - will they cut some, or perhaps even all, of their crops to hay?
There are a variety of reasons why growers cut for hay, rather than taking the grain through to harvest, but one factor that should be top of mind is the cost of the nutrient loss to the soil once that hay is exported.
Norton Agronomic director Robert Norton, an independent crop nutrition specialist, said growers choose to cut for hay for four main reasons.
"Firstly if a crop has been specifically sown for hay, such as an oat crop, or secondly, it might be that there is a weed problem, with cutting a paddock for hay early to remove some of the weed seed burden is a good strategy," Dr Norton said.
"The other strategy that comes up is if a crop has been frosted or droughted, just to relieve some of the financial pressure to get something out of the crop by cutting it for hay and baling it.
"Lastly is that the price for hay is so compulsive to look at so growers take the money and cut the crop for hay before it runs up to grain."
The decision to cut for hay is usually an economic decision, rather than an agronomic one.
However depending on the timing of cutting, it may be possible to preserve a bit of soil moisture for the next season's crop by terminating the current crop before it goes into the heavy water use period during grain fill.
While some moisture may be left behind, there are many other nutrients that are taken from the soil when exporting for hay.
"A wheat crop that potentially has a three tonne per hectare grain yield, will export about 60 kilograms of nitrogen, 10kg of phosphorus, 12kg of potassium and a little bit of sulphur as well," Dr Norton said.
"If the same wheat crop has been cut earlier in the season for hay, a 3t grain crop would probably yield about a 6t/ha wheat cut for hay, so instead of 60kg you're exporting 100kg of nitrogen, about the same of phosphorus, but 10 times the amount of potassium and about 2.5 times the amount of sulphur.
"With so much more being exported in hay cutting, that needs to be factored into the nutrient budgets when you come back around to the following crop."
The reason so much extra potassium is lost is that most of that nutrient in the plant is stored in the straw or stubble.
There is very little potassium, only about 4kg/t, in grain about 20kg/t in hay, most of which is stored in the vegetative material and taken when cut for hay.
"With that 3t wheat crop, in addition to the grain removal nitrogen, potassium, phosphorus and sulphur, if you bale the stubble and take it away, you're still removing the nutrients that are in the straw," Dr Norton said.
"That would be about 35kg of nitrogen in a baled stubble from a 3t crop, about 70kg more potassium and a little bit more sulphur.
"You're increasing the amount of nutrient that is being removed and a lot of that nutrient would have been recycled in a stubble retention system, so your drain of nutrients in a stubble that's baled from a what crop is about the say as when it's cut for hay."
