Organic materials have an important role in stimulating biological activity and as a result yields increase quickly. This indicates that the value goes beyond its nutrient value, according to a new report.
Organic materials are a valuable source of plant nutrients and can be used to make large savings in the use of manufactured fertilisers. The nutrient benefits of organic materials are well described in the AHDB Nutrient Management Guide (RB209) but 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.”
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 hectare) 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 about 10 per cent more than expected in relation to the nitrogen applied.
Despite considerable effort, no clear cause of the non-nutrient yield response was found. It could be that the mass or number of soil organisms may not be as critical as the activity of the organisms present and this warrants 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 system resilience.
The full report, which includes information on the influence of tillage approaches, the effect of pretreating crop residues before incorporation and guidance on costs and quality of amendments, can be accessed via cereals.ahdb.org.uk/organicmatter
The research was funded by AHDB, Defra and the Waitrose Agronomy Group and was led by Rothamsted Research.