Spray it or Spread it: nitrogen in apple orchards

The price of nitrogen fertilizers is going up. So, in trying to get the biggest bang for the nitrogen fertilizer dollar, the following two questions have been asked:

1. Can an apple orchard's nitrogen requirements be managed by only using foliar urea?
   
2. What would it cost relative to other inorganic nitrogen sources?

Researchers at Agriculture & Agri-Food Canada Pacific Agri-Food Research Centre in Summerland compared foliar and soil applied urea as way to reduce soil nitrate-nitrogen leaching¹. While their results showed that foliar applied urea reduced soil nitrate-nitrogen leaching, the results can also help answer these two questions.

Using an established apple orchard (6 year-old Gala/M9 orchard, 1250 trees/ha) each tree received a total of 50 g N/tree/yr (62.5 kg N/ha/yr). The total rate was divided between 7 applications between mid-May to mid-August. The soil was loamy sand.

Can an apple orchard's nitrogen requirements be managed only using foliar urea?

The soil and foliar applied urea had the following effects:

• Average current shoot growth was greater for trees receiving soil applied urea.
  
• Nitrogen concentration in 1-year old wood had no significant differences between urea applications, but was significantly higher than the zero nitrogen control.
  
• Leaf nitrogen and leaf colour were not significantly different between soil and foliar applied urea treatments, but were significantly greater than the zero nitrogen control
  
• Yields were not significantly different between trees receiving soil or foliar applied urea treatments, but were greater than the zero nitrogen control

For their BC growing conditions, they were able to manage nitrogen using foliar applied urea.

What would it cost, relative to other inorganic nitrogen sources?

Based on an application rate of 50 g N/tree/year (62.5 kg N/ha/yr) the chart below outlines product costs. Nitrogen applied as ammonium nitrate or fertigated was not included in the project but is listed here for comparison.

Both foliar and soil applied urea applications could be used to manage an apple tree's nitrogen nutrition. But the foliar applied urea would cost about twice as much as soil applied to achieve the same results.

¹ Dong, S., Neilsen, D., Neilsen, G., Fuchigami, L. 2005. Foliar N application reduces soil NO3-N leaching loss in apple orchards Plant & Soil 268:357-366