The Four R’s of Nitrogen Management: Right Rate

Good nitrogen management (and all nutrient management) involves applying:

• the Right Source of nutrient (e.g. manure, compost, granular fertilizer)
• at the Right Rate,
• in the Right Place, and
• at the Right Time.

The Four R’s help to guide decision-making when it comes to nutrient inputs. Over the next few weeks, we will be exploring the Four R’s and what they mean, starting this week with the Right Rate.

What happens when you do not have the right nitrogen (N) application rate?

If N rate is too high:

• There is environmental risk of excess N entering waterways and the air (e.g. greenhouse gas).
• Excessive vegetative growth can be caused, which can compromise development of other harvestable parts and/or lead to pest issues.
• Money is wasted in applying N that the crops do not need.

If N rate is too low:

• Crop yield suffers.

How do you determine the right rate of N?

The Right Rate must take into account:

• Crop demand – each crop has a different need for N, which is also affected by expected or desired yield.
• Soil nutrient supply – all existing sources of N, which may include:
  • N from soil organic matter
  • N from cover crops, especially legumes
  • N carry-over from previous years of manure/compost

As a result, the “right” rate may not look the same for all fields within a farm.

What tools can farmers use to help determine the right N rate?

Nutrient Balance Calculations:

• Forward-planning tool.
• The agronomic balance take the total amounts of existing N and subtracts the crop N requirement, to calculate the total remaining N input needed to make up the difference.
• Check out this calculator resource on the Government of BC’s website. You can plug in field and yield info specific to your farm.