When making decisions on when to apply nitrogen, base them on the potential response rate in conjunction with your feed budget and feed requirements.
Ensuring the extra pasture grown is consumed will maximise the return on the investment. Leaf stage grazing will assist to maximise growth and consumption of these pastures.
When using leaf stage grazing, aim to graze pastures between the two- to three-leaf stage, leaving a post-grazing residual of four to six centimetres between clumps.
Urea continues to be the cheapest source of nitrogen.
There is no difference in the response rates of different forms of nitrogen (for example, urea verses DAP) unless there is another nutritional deficiency.
The best response will come from those paddocks with few other limiting factors.
Paddocks with better species composition, high density, good fertility (P, K and S) and limited weeds with no waterlogging will respond best.
Nitrogen should be applied at a rate of 25 to 50kg per hectare (about 50 to 100kg urea/ha) two to three days either side of grazing to allow the plant to fully utilise the nitrogen for growth.
Applying earlier than three days before grazing increases the risk of nitrates and reduces the potential response from the nitrogen applied.
Applying less than 25kg N/ha often results in unpredictable responses, while applying above 50kg N/ha can result in a reduced response per kg N applied.
Cooler temperatures in winter result in a lower response to nitrogen than in spring or autumn though this does not mean it is not cost-effective.
With high supplement feed prices and quality feed being scarcer, this makes nitrogen a viable option. If soil temperatures drop below 4°C response rates will be very low.
The use of nitrogen does not increase the rate of leaf appearance but increases the size of the leaf, increasing the volume of feed available to be grazed.
This can lead to the occurrence of canopy closure before the three-leaf stage is reached, particularly in tetraploid varieties.
Canopy closure is the point when no light can reach the bottom of the canopy and can be identified when we are no longer able to see the ground through the canopy of the plant.
It is best to graze at the point of canopy closure than to allow plant death and decay to occur which will lead to wastage.
■More information on utilising nitrogen can be found at: fertsmart.dairyingfortomorrow.com.au/dairy-soils-and-fertiliser-manual
■A tool available to help calculate this point for your situation is the Dairy Nitrogen Fertiliser Advisor: vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/nitrogen-advisor
■For more information, phone Sarah Clack at Agriculture Victoria, Tatura, on 5824 5502 or email: sarah.clack@ecodev.vic.gov.au
—Sarah Clack, dairy extension officer, Agriculture Victoria , Tatura
8°C