THE VALUE of organic materials goes way beyond its nominal nutrient value, according to a new AHDB government and industry funded report.

The latest research findings also suggest the role of organic materials in stimulating biological activity could be more critical than the amount (weight/number) of organisms in the soil.

Based on the analysis of numerous field and plot trials across England, Northern Ireland and Scotland, the report offers a wealth of information on the influence of organic matter on the yield and quality of cereals and oilseed rape.

While organic materials are seen as a valuable source of plant nutrients and can be used to make large savings in the use of manufactured fertilisers, they have other plus points in their favour.

Until this study, those other benefits were poorly understood. Dr Amanda Bennett, who manages natural resources research at AHDB, said: “To reveal the non-nutrient benefits of applying organic matter, you require trials that account for the nutrient effect and part of this work set out to do just that.”

Field trials were set up to produce full nitrogen response curves in the presence and absence of four organic matter amendments – anaerobic digestate, compost, farmyard manure and crop residues.

Each autumn for four consecutive years, amendments were applied at several rates (0, 1, 1.75, 2.5 and 3.5 tonnes of carbon per ha) in field experiments at Rothamsted Research.

Yields increased quickly in response to amendments.

At the 2.5 tonne rate, for example, it took as little as two years for yield increases to become statistically significant, compared to the control.

Analysis of data, from multiple trials, also showed benefits continued (although at a reduced level) for at least two years after applications ceased.

Crops responded well to amendments and yielded more than expected in relation to the nitrogen applied, around 10% more.

Despite considerable effort, no clear cause of the non-nutrient yield response was found. Results, however, suggested the mass or number of soil organisms may not be as critical as the activity of the organisms present and this warranted further investigation.

Use of organic amendments was associated with a greater degree of yield consistency in trials, confirming they can be used as part of efforts to promote resilience in growing systems.

The research was funded by AHDB, Defra and the Waitrose Agronomy Group and was led by Rothamsted Research.