The Tasmania Institute of Agriculture is a specialist institute at the University of Tasmania with a mandate to deliver research, industry development and education for the agri-food industry of Tasmania and Australia.
TIA is committed to delivering highly relevant research and spans agricultural systems, food safety and innovation, horticulture, and livestock production.
They recently held a field day showcasing the dairy research facility in Northern Tasmania and some of their projects.
The Elliott site is home to an irrigated working dairy farm milking close to 400 cows.
It is also home to a farmlet trial (using mini farms) looking into halving synthetic nitrogen use on a pasture-based system while maintaining pasture and cow production.
Research fellow Pieter Raedts said the trial was into its third and final year, and while they were awaiting final results there have been some interesting findings to date.
The trial consisted of four farmlet paddocks.
- Farmlet one was seeded with 80 per cent perennial rye grass and 20 per cent white clover, and receives 300kg of synthetic nitrogen annually.
- Farmlet two was seeded with 80 per cent perennial rye grass and 20 per cent white clover, and receives 150kg of synthetic nitrogen annually.
- Farmlet three was seeded with 40 per cent perennial rye grass, 30 per cent white clover and 30 per cent plantain, and receives 150kg of synthetic nitrogen annually.
- Farmlet four was seeded with a multi species mix of 40 per cent grasses (tall fescue, perennial rye grass, cocksfoot and brome), 30 per cent clovers (white, red and strawberry clovers) and 30 per cent plantain with a little bit of chicory. This farmlet receives no synthetic nitrogen application.
Pieter said the trial to date had indicated it was possible to replace some synthetic nitrogen fertiliser by including clover in the pasture.
Farmlets so far have been highly productive, with F1, 2 and 3 growing close to our target of 20 t/dm per ha per year, while the 0 synthetic nitrogen treatment farmlet grows about 15-20 per cent or so less.
“It is important to acknowledge that farmlet 1 with best practice 300kg of nitrogen annually to grow 20 t/dm per ha is not a high level to begin with — Tasmanian DFMP benchmarking data shows around 225kg of synthetic nitrogen being used to grow around 13t/dm per ha.”
Farmlet one is the control farmlet and all farmlets follow standard Tasmanian management practices.
“The grazing and cow management was determined by our steering committee using grazing principles common in Tasmania. The steering committee includes dairy farmers,” Pieter said.
“Microbes live in the nodules on clover roots and take nitrogen out of the air and provide this to the clover plant in exchange for some carbohydrates — it is a true symbiotic relationship.
“We also inoculated the clover seed just before seeding with rhizobia bacteria to ensure this symbiosis would happen.”
With the high amount of clover we achieved in our farmlets (20 to 30 per cent of the DM grown), sufficient nitrogen seems to have been fixed out of the air to replace the reduced synthetic nitrogen applications in farmlet two and three.
Pieter said they fully expected the clover in Farmlet one to disappear very quickly during the trial due to the normal use of synthetic N — they were surprised to see it mostly retained.
In Farmlets three and four, the plantain did not survive over time; we assume possibly due to high growth rates of other pasture species as the farmlets are very productive.
The trial herds were balanced before each lactation, with cows in lactation two to six and an average weight of 560kg.
So no heifers or old cows were used, to reduce the risk of animal variation during the lactation.
Farmlets one to three were stocked at 3.94 cows per ha, while farmlet four was stocked at 3.0 cows per ha due to the expected lower pasture growth rate.
The cows were all fed 6kg DM per day of concentrates in the dairy until after mating (up to a total of max 1500 kg during the lactation), and in peak lactation consumed 17kg DM via pasture. Any feed gaps were filled with silage.
Pieter noted 17kg DM grass intake is high while also eating 6kg DM concentrate, which probably was made possible by the high clover content of the pasture.
Per cow production across all farmlets was similar at around 630kg of milk solids per lactation. The kg milk solids sold per farmlet was above 2300 per ha for farmlet one, two and three, while farmlet four with a lower stocking rate achieved just above 1800kg
To address the risk of bloat, cows received automatically 20-25ml of a bloat drench on top of their concentrate in the dairy during milking.
Pieter said preliminary data from this farmlet trial was showing you could reduce nitrogen applications if you have at least 20 to 25 per cent clover in your pasture.