Residual effects of various systems for the use of green manure crops

Project manager: Birgitta Båth, Department of Crop Production Ecology, SLU.

Planned but not implemented trial: Green manure crops with nitrogen-fixing leguminous plants adds locally produced nitrogen to the cropping system. This is an important element in crop rotations on farms with organic production of vegetables.

Different ways to handle the nitrogen fixated by green manure crops and how this influences the delivery of plant nutrient, population dynamics of pests and their predators and also the product quality were investigated in a project financed by FORMAS "The ecology of cultivation systems. Green manure crops as a multifunctional tool in vegetable growing".

In one of the field-trials, situated south of Ultuna at Krusenberg, four green manure strategies were studied during the growth-season 2004:

• direct incorporation, 
• mulching, 
• digestion and 
• composting, 

in an experiment with leek for sale. Three different amounts of green manure were added by mulching, digested residue and compost. The amounts were based on the treatment with direct incorporation:

1. the same amount of nitrogen
2. the same amount of carbon
3. the estimated amount of available nitrogen.

In the mulch treatment, an amount based on a practical point of view was also included.

In order to get an overall picture of the different strategies to use green manure crops, the residual effects will be studied during the cropping season 2005. Fresh- and dry weights of biomass and uptake of nitrogen will be measured at two times in a cereal crop or in ryegrass.