OSC Subproject A: Fertility

Biologically based fertility management

Organic agriculture prohibits the use of synthetically produced fertilizers, but encourages the use of suitable crop rotations, manures and composts, and approved amendments to sustain soil fertility and promote a biologically active soil.

While nitrogen can be readily managed through the use of legumes in rotations, phosphorus is not so easy to manage. Rock phosphorus sources that are acceptable in organic production typically have very low availability for crops, and can be very expensive to apply. In many cases, an adequate supply of phosphorus exists in the soil but it is very difficult for plant roots to extract because it is relatively immobile and is bound to soil particles or organic matter.

Some plants have developed associations with arbuscular mycorrhizal fungi (AMF), where the AMF is much smaller in diameter and can explore a larger soil volume than roots. This association can provide significant volumes of phosphorus as well as various micronutrients for crops.

The relationship between AMF, crops, and crop management is poorly understood, despite the availability of a few sources of AMF inoculants. Management practices (e.g. tillage, fertilization, pesticide use, crop types and cultivar) all can influence AMF activity. As a result, some farmers have observed little response to fertilizer phosphorus, or, a lack of deficiency symptoms in the crop despite low phosphorus levels detected in soil tests.

This research strives to model the relationship between AMF, crop and management practices. It will allow farmers (organic and conventional) to better manage their crops to take advantage of AMF associations, and will allow soil testing laboratories to make more accurate recommendations. As a result, this project will increase the profitability and competitiveness of Canadian farmers.

The research activities that make up this subproject are:

• Activity A.1: Characterizing soil phosphorus dynamics and availability under organic crop production
• Activity A.2: Predictive tools for characterizing mycorrhizal contributions to phosphorus uptake by organic crops