Influence of establishment date on summer cover crops on soil organic carbon contribution and weed controlling properties

During 2019, in a field experiment on Helgegården (Kristianstad), the establishment, biomass production (above and below ground) and the weed competition of four intermediate crops will be evaluated. The intermediate crops buckwheat, Phacelia, hemp and oilseed radish are established as sole crops and in combination with a nitrogen-fixing bottom crop. Buckwheat and Phacelia are intercropped with Persian clover while hemp and oilseed radish are intercropped with hairy vetch or common vetch.

Establishing intermediate crops in the middle of July limits which cultures (e.g. early potatoes and early carrots) they can be combined with. A later seeding of intermediate crops can increase the possibilities with other cultures as a part of a sustainable crop rotation with cereals, cabbage, onions and food potatoes. Both Phacelia and oilseed radish have shown strong weed competition when established well, even when seeding took place as late as the middle of August.

Intermediate crops contribute to soil organic carbon built-up both by the aboveground biomass when it is incorporated into the soil and by the root biomass. Earlier studies have shown that the contribution from root biomass to stable carbon is up to 3 times as high per weight unit compared to the aboveground biomass.