IntroductionOrganic farms within a system approach should be able to fix enough nitrogen by means of leguminous crops. Besides peas, beans and leguminous cover crops, fodder crops play an important role in nitrogen fixation.
In Dutch conditions, arable farms often have alfalfa or grass-clover in rotation with other crops. Alfalfa or grass-clover is sold to cattle farms of the fodder industry, thus exporting a lot of nitrogen, phosphorus, potassium an organic matter. At the same time, manure or compost is brought into the farm.An alternative strategy for using the alfalfa or grass-clover biomass could be the direct use of the green material as fertilizer. A rough calculation indicates that keeping alfalfa on the farm instead of selling it and buying animal manure is almost cost-neutral, and with increasing prices for organic manures there will be a financial advantage for the use of cut-and-carry fertilizers (“maaimeststoffen”).
The Louis Bolk Institute is momentary leading the research around the cut-and-carry fertilizers in Holland. A three-year project has finished 31 December 2010, and the research will be continued. At an arable farm in Ens, Northeast Polder, the Netherlands, several field experiments will be realized in 2011-2015, related to optimizing the use of farm-produced N-rich organic material. The research so far has shown that the fertilizing value ta crop level is comparable with or better that manure. Nevertheless many questions are still to be addressed, both at the practical (how to organise it at farm level) and scientific level.
As contribution to this research project, a thesis student can join parts of the work. Options are:
- Literature review on the theme
- Contribution to the field experiments and elaboration of the results
- Model calculations with the NDICEA model
- Nutrient budgets for N, P and K
- Organic matter fluxes, carbon fluxes, carbon balances