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Published: 21 May 2019

Australians love apples.

We each eat around nine kilograms every year, or roughly one apple per week.  And we expect an apple that is crunchy, sweet, with a vibrant colour and delicious flavour every day of the year.    

Tasmanian Institute of Agriculture (TIA) researcher Dr Nigel Swarts says many consumers now want more than just high-quality fruit, they want fruit that is responsibly produced in every sense of the word.

“More and more consumers are looking for fruit that not only tastes great all year round, they are concerned about how fruit is grown, how safe it is to eat and its environmental footprint.

“Nitrogen is hands down the most important nutrient when it comes to managing fruit quality, but managing nitrogen use is also proving to be a real environmental winner”.

Research by the team at TIA and Plant and Food Research New Zealand is uncovering how premium fruit quality and environmental stewardship can be achieved through efficient use of nitrogen in the orchard. The research is answering questions about where nitrogen is stored in the tree, why timing of application has such a big impact on fruit quality as well as how nitrogen moves through the soil after rain or fertigation.  

Dr Swarts says the results are a paradigm shift from the old ways of applying most of your annual fertilizer in spring just before the trees first wake up.

“We’ve learnt that apple trees are very efficient users and storers of nitrogen with almost half of the tree’s nitrogen requirement coming from stored nitrogen and the other half from root uptake”.

Apple trees use stored nitrogen up until a few weeks after bud burst and then switch to uptake from roots.

“Our research shows that delaying nitrogen application until mid-November then applying small regular amounts of nitrogen up to 3-5kg N/ha (total 20 -30 kg N/ha) through December, drip fed through fertigation systems will supply the apple tree with enough nitrogen to drive leaf and shoot growth as well as set up the crop for the season.”  

Nitrogen from decaying plant material also needs to be considered in the annual nitrogen budget and can contribute up to 30 kg/ha.

Dr Swarts says very little or no nitrogen needs to be applied from December until after harvest.

“This effectively keeps nitrogen levels in fruit tissue at almost deficiency levels, reducing tissue breakdown during storage so that apples stay crunchy right through the year”, he said.

After harvest nitrogen levels need to be quickly restored to build nitrogen storage levels in the tree.

Dr Swarts says this little and often strategy to pre and post-harvest nitrogen application has a twofold benefit.  

“Our research shows that by using this strategy, little or no nitrogen leaches below the root zone and secondly that emissions of nitrous oxide, a potent greenhouse gas, are kept to a bare minimum.”

“The beauty of this is that apple growing will be among the lowest greenhouse gas emitters based on tonnes of produce for any agricultural crop and deliver great credentials in environmental protection,” he said.

As growers seek to develop top quality fruit for consumers year-round, efficient nitrogen management will help them meet consumers’ expectations for good environmental stewardship.

The Improved Productivity and Profitability for the apple and pear industry project is part of the apple and pear levy-funded PIPS program, which focuses on providing research outcomes on productivity, irrigation, pests and soils for the apple and pear industry.