Organic residual streams

25 January 2021

Under controlled circumstances, in the laboratory or the greenhouse, organic residual streams can contribute to soil resilience. In the open field, such contribution appears to be more difficult to determine within the measured period. Residual streams, however, do contribute to soil fertility because they contain nutrients and organic matter.

This has emerged from a four-year study by Wageningen University & Research. Eurofins Agro analyzed the soil and the composition of the residual streams for this study. The final report, “Driving soil resilience by applying organic matter,” was completed in December 2020.

The study compared ten different residual products for their ability to increase a soil’s resistance to pathogens. The products came from residual and side streams from the consumer sector (compost), the food industry (keratin from chicken feathers and pig bristles), livestock farming (pig manure pellets), agricultural industry (degreased seeds), nature areas (grass and ditch cuttings), and mushroom cultivation (grown, composted manure). The products varied in organic matter content and nutrient composition, C/N ratio (3 to 27) and decomposition rate (3 to 50 mmol O2/kg organic matter per hour).

Research

The effect of these products was first tested in two different sandy soils in pot tests under controlled conditions, then for a year in the open field in a clay soil and two years in a sandy soil. To test whether disease resistance had developed, a few weeks after application, we tested how much damage occurred in a susceptible crop after the addition of a pathogen.

Results

The pot tests demonstrated that several products could promote sandy soil disease resistance to the Rhizoctonia solani fungus in sugar beets and the Meloidogyne hapla nematode in lettuce. No disease resistance was demonstrated for the Pythium intermedium fungus in hyacinths.

In the field, the organic products were tested under practical conditions in the cultivation of sugar beets in a clay soil. In clay soil, none of the treatments showed disease resistance to R. solani in sugar beets. A new biotest with Pythium ultimum in cress did show differences in disease resistance.

In potatoes and sugar beets in sandy soil, the products were applied according to current fertilization rules, in which follow up feeding of nitrogen (N), phosphate (P) and potassium (K) by means of artificial fertilizers was done in accordance with fertilization recommendations. It was demonstrated that the crop yields were generally comparable to the artificial fertilizer control.

In order to determine whether the disease resistance of the soil had improved by adding the residual products, three plant pathogens were added, and the effect was measured in a test crop in the greenhouse. This showed that the added products had only a slight impact on the disease resistance properties of the soil in the field.

Conclusion

The organic residual streams tested can be applied effectively as fertilizer, thus reducing the amount of artificial fertilizer required. The crop growth and yields were generally comparable to the artificial fertilizer control. In a few cases there were even positive effects, such as a higher yield and less potato scab infestation. Under controlled circumstances in greenhouse tests, various organic residual streams stimulated disease resistance of the soil. This effect was more limited in the field tests.

In the cress biotest there were a few products that stimulated disease resistance in the field to Pythium. This biotest says something about the general disease resistance since Pythium is sensitive to competition for space and nutrients.