Protein levels in southern wheat crops last season appeared to tip the conventional wisdom of "soft finish, low protein" on its head. Researchers are less surprised.
"Producers who understand the role of the nitrogen cycle in the crop should have expected the results," they say. CSIRO Plant Industry scientists John Angus, Mark Peoples and Anthony van Herwaaden say that attention to the nitrogen cycle translates into premium payments.
Understand climate related to nitrogen cycle.
Graingrowers targeting high protein segregations such as Durum or Prime Hard need to be continually assessing the impact of soil temperature and moisture levels on the level of available nitrogen. They need to make decisions about their fertiliser strategy at three critical periods of the crop's development and they need to learn from the experience of previous seasons.
Dr van Herwaaden says that there were many similarities between the seasons of 1995 and 1999, and that if you understand the impact of the season on the availability of nitrogen you'll have a better chance of getting your fertiliser strategy right.
"Work starts with a deep soil nitrogen test before sowing," he says. "In CSIRO trials last season we saw the level of available nitrogen jump from 110 kg/ha to 180 kg/ha in just 35 days during April and May. We can explain that by what's known as the 'Birch Effect'.
"Rain after a long dry spell results in a burst of mineralisation and we get a pulse of available nitrogen. Most crops in southern NSW and Victoria were sown in that burst of nitrogen last year and available nitrogen at sowing has an impact on yield."
Explaining that cold weather and waterlogging results in de-nitrification and the loss of N from the soil, Dr van Herwaaden says that last season's relatively dry, mild winter meant that mineralisation just kept bubbling along.
"It also meant that the crops weren't stressed and as a consequence produced fewer tillers, limiting yield potential but signalling high protein levels."
Not everyone had a good harvest last year. A number of crops sown early in the southern area were caught by a dry September and hayed-off, but the good October-November rains that followed sparked another 'Birch Effect' and another pointer to a high-protein harvest.
"The level of available nitrogen up until the end of tillering will have a bearing on yield and to some extent on protein harvested. Anything applied between booting and flowering will make a difference to the level of protein harvested."
The message for season 2000? Any part of the wheatbelt that received those big rains around Christmas and the follow-up falls in January should have experienced another 'Birch Effect'. "I'd be surprised if those people had anything less than 100 kg/ha of available nitrogen out there now," says Dr van Herwaaden.
Contact: Dr Anthony van Herwaaden 02 6246 5097