"Focusing on nitrogen (N) leaching alone to improve sustainability and performance can be problematic," says Ballance Agri-Nutrients Science Extension Josh Verhoek.
"Factors which you can't control - such as soil type and climate - influence N leaching, so there's only so far you can go with that approach. And concentrating on N leaching ignores N lost as ammonia and nitrous oxide gas via volatilisation," Josh explains.
"An easier, more environmentally and economically beneficial approach to reducing environmental losses and increasing N efficiency is to focus on N surplus."
Nitrogen surplus is calculated by subtracting N outputs (the total N in products removed from the farm) from N inputs (fertiliser, purchased feed and biological clover N fixation). The lower the N surplus, the more efficiently N is used.
Josh recommends decreasing N surplus by bringing less N onto the farm in the form of imported feed. In its place, he says to look at better matching pasture supply to demand.
My Pasture Planner - a decision support tool designed to optimise pasture response to applied N fertiliser - can help with this. It provides a visual comparison of feed supply and demand, and shows how N applications can be used to lift the supply curve during a particular month to fill a feed gap.
My Pasture Planner uses Total N soil test information to identify strategic N fertiliser applications, so N fertiliser placement and rates can be tailored.
"The Total N soil test will help identify the N supplying power of the soil over different blocks," Josh explains. "This allows you to tactically apply more N to low Total N areas that are going to be more responsive, and less or no N to high Total N areas. This could either mean spending the same amount on N but getting more grass (by applying tactically to low Total N areas), or saving money by reducing applications on some areas with high Total N."
In doing this, Josh says My Pasture Planner can help you decrease your N surplus, as N isn't wasted by either applying too much or at an inappropriate time of year.
"When you're applying N, using a fertiliser coated with a urease inhibitor, such as SustaiN, helps to minimise N lost as ammonia gas, and keep more in the ground for plant use and increased pasture production."
Compared to standard urea, SustaiN's AGROTAIN® coating cuts N volatilisation losses by around 50%1 and increases N efficiency, with research showing over a wide range of conditions the average increase in pasture yield is 5%2.
SustaiN is also more convenient than standard urea and can be applied at any time of year when a crop or pasture needs N, without the need for sufficient rainfall within eight hours to reduce volatilisation losses.
"SustaiN does cost about 10% more than standard urea, but on top of its environmental benefits and convenience, you get a greater response than from urea. For example, applying it at 80 kilograms per hectare (kg/ha) at a $7/kg of milk solids (MS) payout could generate an additional $8/ha over standard urea," Josh says.
More information on SustaiN is available at ballance.co.nz/SustaiN.My Pasture Planner is only available to Ballance customers. For more information, see ballance.co.nz/my-pasture-planner. The tool was developed in collaboration with AgResearch and partly funded by the Ministry for Primary Industries Primary Growth Partnership.
1 Foundation for Arable Research, (2016) Nitrogen Application on Ryegrass. From the Ground Up, Issue 86, Winter 2016. 10-11.
2 FAR Arable Update No 61, November 2008. "Comparing urea and Sustain for broadcasting over maize."