Addressing biological limitations on nutrient cycling in organic cropping systems

  • Term: Four years, beginning in 2016

  • Funding Amount: $124,936

  • Lead Researcher(s): Bobbi Helgason (AAFC)

  • Funding Partners: None

Project Description

Nitrogen and phosphorus limitations are a particular concern in organic production systems as there are limited external inputs which can be used to augment their availability. The limited opportunity for external macronutrient additions means that long-term organic crop production is particularly reliant on the provision of inorganic nutrients by biologically-mediated processes. For example, perennial and annual legumes are often used in rotation as a means of supplying nitrogen through biological fixation. The long-term ACS field trial has shown that even with diverse cropping rotations that include legumes, crop yields were consistently lower under organic compared to conventional management systems.

This work will explore the specific nature of the nutrient limitations on long-term organically managed systems, by adding nitrogen and phosphorus fertilizers as well as extra crop residues to identify the most limiting factors to crop growth and microbial activity. It is hypothesized that: 1) phosphorus limitation is the key factor limiting crop growth; 2) alleviation of phosphorus limitation will create a nitrogen limited system; and 3) an overarching carbon limitation is severely limiting the ability of the microbial community to compensate for the lack of fertilizer additions. This project will evaluate nitrogen, phosphorus and carbon additions alone and in combination to test these hypotheses and to identify strategies for combating long-term productivity reduction in organic systems. The use of inorganic fertilizers can provide an immediate response that will inform the development of a longer-term strategy for restoring productivity by means that would be appropriate to organic production.