Nitrogen efficiency on dairy farms

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FutureDairy's research has found that a complementary forage system

(CFS) achieved the most efficient use of nitrogen at the ‘whole farm level,' compared with other dairying systems used around the world.

A CFS involves allocating a portion of the farm to intensive forage production to increase productivity from home-grown feed. It usually involves growing forage crops, sometimes double or triple cropping. Crops are selected to complement each other. For example they may include a legume for nitrogen fixation, a bulk crop such as a cereal or maize for silage, and a brassica (forage rape) to break pest and disease cycles.

FutureDairy project leader, Associate Professor Yani Garcia, said the research - conducted by postgraduate student, Santiago Farina - measured the nitrogen efficiency for FutureDairy's CFS farmlet study and compared the results with other dairy systems studied throughout Australia and internationally.

The CFS in FutureDairy's trial at Camden near Sydney involved allocating 35% of the farm for double or triple cropping, with the rest of the farm used for intensively managed pasture.

Under this CFS, 45% of all nitrogen entering the farm was converted into milk. This compares with an average of about 26% for Australian dairy farms* and about 16% overseas.**

"At 45% nitrogen efficiency, FutureDairy's complementary forage system converted more than one and a half times the amount of nitrogen into milk than the average for Australian dairy farms," said Assoc Professor Garcia.

The key to the nitrogen efficiency of the CFS the higher amount of milk produced from home-grown feed. This came from the combination of the bulk crop (eg maize) and a legume crop and the fact that the pasture area in the CFS had high yields (20 t DM/ha) given the leven of nitrogen fertiliser applied (250kg/ha).

Overall the CFS utilised 24.8 t DM/ha/year which meant that the nitrogen entering the farm as bought-in feed was minimised with cows receiving about 1t DM concentrates/cow/lactation.

Compared with other intensification systems such as relying heavily on purchased feed, the CFS has a lower potential environmental impact, in terms of producing more milk per unit of nitrogen entering the farm.

"The CFS gives dairy farmers another option for increasing their farm productivity in a sustainable way," Assoc Professor Garcia said.

Nitrogen hot spots

Trials conducted by the FutureDairy team at Camden, NSW monitored nutrient movement around the dairy farm, revealing ‘hot spots' of nitrogen surplus within the system - in specific locations and during certain times of the season.

FutureDairy project leader, Associate Professor Yani Garcia, said the trials - conducted by postgraduate student, Santiago Farina - found that nitrogen hot spots occur in places that cows congregate that don't have growing pastures or forages to use the nitrogen; for example laneways and feedpads..

"Cows excrete excess nitrogen in dung and urine. The amount of nitrogen excreted in a particular area is directly proportional to the amount of time the cows spend in each spot," said Associate Professor Garcia.

Left unmanaged, these hot spots represent a waste of money and potential risk to the environment.

For example the study measured 2 tonnes of N/year lost as excreta in the laneways on a 22ha farmlet.

"The good news is that relatively simple management practices can cut the level of nitrogen at these hot spots," he said.

A good place to start is with strategies to encourage cows to move away from laneways and into the paddocks where nitrogen in excreta can be recycled back into the soil.

"Examples include providing more water troughs and shade inside the grazing paddock. These will be good for animal welfare as well as the environment," Associate Prof Garcia said.

The Cool Cows website (www.coolcows.com.au) has practical information and design guidelines for installing water troughs and shade on dairy farms.