Effect of soil organic matter management on soil characteristics, potato yield and potato disease in an intensive potato growing system (MERMOLD)

The MERMOLD project (2019-2022) was a collaboration between industry and research partners. The project was owned by Sunndalspotet AS and managed by the Norwegian Centre for Organic Agriculture (NORSØK). The other partners were Standard Bio AS, Ecopro AS and Landbruk Nordvest. Production of potatoes is a specialised industry, and commonly occurs on farms without animal husbandry. Hence, cereals are often the only other crop being grown, and with a lack of animal manure and growing of perennial ley, in combination with intensive soil tillage for potatoes, soil organic matter (SOM) tends to decline. The main objective of this project was to assess if cover crop and organic amendment practices could increase SOM storage, and possibly affect potato yields and soil-borne diseases. To do so, we established a field experiment in July 2019 to: (i) assess under field conditions with and without cover crop the impact of a single application of various organic materials to soil (biochar+liquid digestate, solid digestate, or farmyard manure) on SOM storage; (ii) quantify the impact of cover crop and application of organic materials on potato yields and potato diseases; (iii) discuss a suitable cover crop and organic soil amendment practice for potato cropping systems in this part of Norway. Furthermore, we performed a laboratory incubation to (iv) measure under controlled conditions the effect of organic amendments on carbon dioxide (CO2) emissions from the experimental soil. Our results show that: a single addition of organic materials increased SOM storage, especially in the farmyard manure and biochar+ liquid digestate treatments, while the presence of cover crop did not significantly affect SOM storage. Yet, the cover crop significantly increased potato yield in 2021 and reduced the severity of potato diseases by 10% in the post-harvest potatoes in 2020 and 2021, while the number of marketable potatoes after storage in 2021 was increased by 37%. Organic amendments did not significantly affect potato yield or quality, but the proportion of marketable potatoes tended to be higher in the treatments where organic materials were applied 2 years after the application