Applying nitrogen fertiliser at the right time and in multiple sessions reduces losses that would occur when too much N is given when a crop has no need for it at that moment.
leaching problem arises when there is more ni- trate than the crop can take up during periods of heavy rain. It is a particular problem for bare stubbles in winter when rainfall is higher and there is no crop taking up any nitrogen. That is why cover crops are valuable, as they can cap- ture this nitrogen. Nitrification inhibitors are also useful, as they delay the conversion of am- monium to nitrate by about 6-10 weeks. Fron- tier has even looked at tackling losses from soil by taking soil out of the equation with a foliar approach. Last year, Mr Downing looked at supplying the first 70kg/ha as solid fertiliser and the remaining 110kg/ha in two foliar splits. “We didn’t end up killing the crop and it yielded similar to the control,” he says. “The re- sults look promising and we will be repeating the trials this year.”
4. Apply the right rate In season, farmers should be prepared to
revise fertiliser rates up or down and not sim- ply stick to the original plan. Crop imagery and biomass measurements from drones and satellites, along with N sensors and tissue test- ing, are useful tools for seeing how crops are taking up N and getting a better estimate of their requirements.
5. Apply at the right time Applying smaller amounts across more splits generally improves fertiliser use efficiency. “One limitation is with nitrogen+sulphur prod- ucts, as this ties you into specific rates and tim- ings,” he says. However, there are other ways to apply sulphur, such as liquid fertiliser, low-sul- phur products and specific sulphur products such as Polysulphate, giving farmers more flex- ibility over N fertiliser timings. “Go by condi- tions, not calendar date,” Mr Downing says, pointing out that the first and last applications are the ones at greatest risk of losses. The first
dressing is key to get the crop off and running in the spring and preserve tillers, but it is also the most at risk of leaching. “So you need to ensure there is sufficient crop growth to en- sure uptake, and monitoring soil temperature will help with this.” Conversely, with the last dose, dry soils with high temperatures can be a problem, increasing ammonia volatilisation and reducing nitrogen uptake. “Be prepared to pull the timing earlier if it is looking to be warm and dry like last year,” he says.
6. Apply accurately Finally, get your fertiliser spreader tray tested and ensure it is as accurate as possible. Poor accuracy can be a real problem with wider bouts. Technology is helping, with auto shut- off helping avoid overlaps with irregular field shapes and Mr Downing says there is even an Amazone spreader that adjusts spread pattern according to wind direction and speed.
▶ FUTURE FARMING | 24 May 2019 37
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