Nitrogen – its free!
Using fertiliser in the autumn, especially nitrogen and phosphate significantly increases your chances of good crop emergence and establishment.
A ready supply of phosphate aids root growth. With more roots there is potential for greater nitrogen uptake.
Phosphate has very poor soil mobility, moving less than 1mm, so placement at drilling (IDEALLY placed below and to the side of the seed) means that roots can find it easily.
As well as assisting tap root growth phosphate also aids secondary root formation and assists in root structure development
Fertiliser recommendations for canopy development state that for every 1 unit of green leaf area your crop need 50 kg of N/ha.
NVZ rules allow up to 30kg/ha of nitrogen to be applied in the autumn, the extra 20 kg will therefore have to come from the soil.
This in part comes from mineralisation (the process by which organic N is converted into inorganic forms available to plants.)
Several factors affect mineralisation rates. The Carbon:Nitrogen ratio of the organic matter in the soil. Temperature; greater when warm, less when cool. Soil moisture: Ideally at 80–100% field capacity
These factors (and others) regulate microbial activity and hence the release of nitrogen to the growing plant.