WHEN it comes to irrigation water and nitrogen fertiliser, more is not necessarily better for maize silage.
FutureDairy research has shown that although higher levels of water and nitrogen application generally result in higher maize yields, the nutritional value drops because the increase in grain percentage is offset by an increase in fibre content.
"Don't just focus on the yield of your maize crop," FutureDairy researcher Associate Professor Yani Garcia said. "Manage your maize crop to optimise both yield and nutritive quality."
He said that nitrogen and water use efficiency were interrelated.
In trials led by FutureDairy's Dr Rafiq Islam, fully irrigated maize resulted in silage with a lower content of crude protein and metabolisable energy. Nitrogen fertilisation can counterbalance this to some extent.
"Nitrogen use efficiency improves with irrigation; and water use efficiency improves with nitrogen application," Assoc Prof Garcia said. "But there is a point where the marginal return decreases, and it's not profitable to increase inputs beyond that level. We refer to that level as the 'optimal level'."
Assoc Prof Garcia said the message for farmers was to aim to 'optimise' nitrogen and water applications.
"In practice, aim at about 80-90% of maximum water and nitrogen requirements to reduce the risk of the penalty in quality," he said.
"In the past we focused mostly on yield but we couldn't achieve the quality we wanted. Because of its high yields, maize is a big user of water and nutrients, so there are significant savings to be made through an approach to 'optimise' rather than maximise these inputs.
"So when planning fertiliser applications for a maize crop, take into account irrigation water availability. Never apply the full amount of nitrogen to your crop unless you are sure water will not be limiting. And you'll achieve better value for money by applying nitrogen at the 'optimal level'."
Optimising the value from nitrogen application to maize crops involves meeting nutritional requirements and the correct timing of application.
The nitrogen needs of a maize crop are greatest when the crop is growing rapidly, from about 45cm high to grain fill.
Fertigation (applying fertiliser with irrigation water) in three or four stages is the ideal way to apply nutrients to a maize crop. If this is not possible, split nitrogen application into about half pre-sowing and about half at the V6 stage (or when the sixth leaf has emerged).
Maize is one of the most efficient users of water per kilogram of dry matter produced, due to its high yields.
The timing of application is important to achieve optimal yields and silage quality.
Assoc Professor Garcia advises farmers to prioritise irrigation around crop establishment and the four-to-five week period around tasselling.
"Remember, maize uses most of its water requirements - 70% - in the three weeks either side of tasseling," Assoc Prof Garcia said. "Make sure that maize receives its irrigation needs at this time."
For more information refer to FutureDairy tech note 5, Growing maize for silage, available at website www.futuredairy.com.au.
FutureDairy's major sponsors are Dairy Australia, Department of Primary Industries NSW, DeLaval and the University of Sydney.