What was it all about?

Perennial tree cropping systems have two dependent components: the treeline and the inter-row. The treeline area contains the plants and the majority of crop roots, and it is where cropping inputs such as fertilizers and water tend to be directed. Processes are more dynamic in the highly-managed treeline and so it receives more attention by orchardists.

Both the treeline and the inter-row have significant potential benefits for apple and cherry productivity as well as potential to sequester carbon in soils and reduce nitrous oxide emissions, two important greenhouse gas emission mitigation options.

In this project, which ran from 2013 to 2016, two orchard floor practices were evaluated for greenhouse gas emissions as well as effects on soil and productivity.

The trials were carried out on a commercial apple orchard at Orange, NSW and a cherry orchard at Young, NSW. Trial conditions were:

• Control – standard industry practice with herbicides used to prevent weed growth and tree organic matter (pruning, leaf and fruit fall) input left
  
  
• Scrape treatment - herbicides were used to prevent weed growth but all organic matter input was removed, and wheat straw mulch, lucerne straw mulch (apple orchard site only), or compost (cherry orchard only) was applied evenly under the treeline.

The inter-row was managed either as the Control with a mown grass sward maintained or Scrape with no grass cover and all organic matter input removed from the inter-row. Greenhouse gas impacts were assessed by measuring soil nitrous oxide emissions together with any changes in soil carbon. Productivity was assessed through fruit yields and quality.

The key learnings from the project are:

• Nitrous oxide emissions in deciduous tree crops were among the lowest recorded for Australian agriculture, most likely due to low rates of nitrogen fertiliser, cool temperate growing conditions and highly efficient drip irrigation systems
  
  
• When compared with international studies, the emissions intensity is world leading, producing very low emissions during growth per tonne of fruit in both apple and cherry orchards 
  
  
• The trade-offs between nitrous oxide emissions and soil carbon sequestration are difficult to estimate
  
  
• In this project, the applications of some organic amendments increased nitrous oxide emissions but only the compost treatment increased soil carbon stocks
  
  
• In the short term the compost treatment was the only one with a positive greenhouse gas balance. The lucerne straw treatment, on the other hand, had a negative greenhouse gas balance with the increased nitrous oxide emissions not off-set by increased soil carbon. 
  
  
• Long term effects are difficult to assess without further monitoring to see how permanent soil carbon sequestration is.

The researchers recommended that growers manage irrigation and nitrogen fertiliser applications to match plant requirements in order to reduce nitrous oxide emissions while still producing high yields.

ACT NOW

Read the researchers’ fact sheet on reducing nitrous oxide emissions