Crop diversification and weeds Acronym: PRODIVA

Summary

Diversification of crop sequences (WP 1): Perennial weed species can be managed when cover crops / green manure crops are included in the crop sequence but interventions must be species dependent, e.g. Elytrigia repens can be promoted by green manures because they prevent post-harvest cultivations. Cirsium arvense and Sonchus arvensis are two perennials that can be controlled by full-season grass-clover subjected to regular mowing for green manuring purposes and this measure has immediate application.
Cover crops for diversification (WP 1):
 Fast growing cover crops producing copious biomasses are generally useful for the suppression of weeds but need to be abandoned when severe infestations of Elytrigia repens require post-harvest cultivations for effective control. Growers should pay attention to the growth characteristics of cover crops when deciding on species.
 Clover species like alsike clover, red clover and white clover are suitable cover crops for weed suppression including other attributes beneficial to crop production under Northern conditions. Not only cover crop species but also their varieties are of interest. This knowledge has immediate application and legumes will have fertility building benefits as well. Vigorous cover crop growth after harvest enhances both the competition against weeds and nitrogen accumulation in the soil.
 Some cover crop species (e.g. Melilotus alba) can remain troublesome volunteer weeds, particularly if reduced tillage is applied. An important constrain for consideration when planning the inclusion of cover crop in the cropping system.
Crop species mixtures (WP 2): Sole pea is a weak competitor in comparison with spring barley. Intercropping the two species has not demonstrated a consistent and greater suppressive ability against weeds than sole spring barley. Thus, clear recommendations cannot be made on the basis of the work in PRODIVA.
Mixtures of spring barley or oat varieties (WP 3): Variety mixtures did not deviate much in their competitive abilities in comparison with the varieties grown solely. The most promising blends were often those containing a competitive variety that was also highly competitive when grown solely. Use of variety mixtures in practise should be reasoned in considerations regarding yield preservation and the alleviation of leaf diseases.
Weed survey and information retrieval (WP 4): Crop diversity management on 71 farms involved region specific practices. Surveys of weed species and abundances of 207 fields with organic spring cereals indicated region specific weed communities. Only few effects of the crop diversification measures applied on the farms could be related to weed species and densities.
Stakeholder involvement (WP 5): PRODIVA provides an applied overview of the most problematic weed species in the participating regions. This information to farmers and the public is made in all PRODIVA national languages. Success stories of farmers using crop diversification measures revealed crop compositions in rotations as the most important tool for weed management.