This study compares a traditional agricultural approach to minimise N pollution of groundwater (incorporation of crop 3-Methyladenine residues) with applications of small amounts of biodiesel co-product (BCP) to arable soils. incorporated into experimental ground mesocosms of depth equal to plough layer (23?cm) and placed in an exposed netted tunnel to simulate field conditions. Leachate was collected after rainfall RGS11 between the autumn of 2009 and spring of 2010. Treatment with BCP resulted in less total-N transferred from ground to water over the entire period with 32.1 18.9 13.2 and 4.2?mg?N?kg?1 ground leached cumulatively from your control grass straw and BCP treatments respectively. More than 99?% of nitrate leaching was prevented using BCP. Accordingly soils provided with crop residues or BCP showed statistically significant increases in ground N and C compared to the control (no incorporation). Microbial biomass indicated by ground ATP concentration was also highest for soils given BCP (sp. (Nakashimada et al. 2009) 1 3 by sp. (Papanikolaou et al. 2008) and Omega-3 fatty acids by sp. (Ethier et al. 2011). Many of these existing uses require a high purity of glycerol (>97?%) whereas the co-product from biodiesel production (BCP) usually consists of around 60?% glycerol (Zhou et al. 2008) being a mixture of methanol water potassium and/or sodium salts soaps residual biodiesel fatty acids and traces of unreacted mono- di- and triglycerides (Thompson and He 2006; Kongjao et al. 2010). Purification of BCP to extract glycerol of sufficient purity is often prohibitively expensive (Zhou and Boocock 2006) whereas the initial step of recovering the excess methanol by distillation is usually economically favourable with this methanol often being re-used to make more biodiesel (Raghareutai et al. 2010). We hypothesised that BCP could be applied to the ground to cause increased immobilisation of NO3-N by the ground microbial biomass. If more effective than traditional methods the proposed management could provide multiple beneficial impacts for the environment and agriculture and therefore the efficiency of biodiesel production. The effects of BCP incorporation 3-Methyladenine on N leaching and total microbial biomass were therefore compared with those of milled grass and cereal straw incorporation. Materials and Methods Overview Application of de-methylated (normally unrefined) BCP to ground was hypothesised (1) to increase immobilisation of NO3-N by the ground microbial biomass and furthermore (2) that the effect would be greater and more rapid than traditional methods using plant-residue incorporation. This was investigated in a series of three experiments. Experiment 1 was a preliminary study to determine if incorporation of BCP affected extractable NO3-N and total microbial biomass and to establish an approximate response to application rate. Experiment 2 traced the NO3-N NH4-N organic-N and microbial biomass-N dynamics over time following application of BCP. Experiment 3 compared N leaching between BCP and crop residues in an arable ground over a winter period common of Northern Europe. This was conducted in ‘semi-natural’ conditions i.e. mesocosm-lysimeters in the 3-Methyladenine open air environment. Ground 3-Methyladenine Sampling and Preparation Three soils were sampled from three long-term experiments at Rothamsted Research Hertfordshire UK (50°50′ N 0 W). The soils’ main characteristics are reported in Table?1. All soils were Chromic Luvisols. Table 1 Ground properties Ground 1 was obtained from the long-term Hoosfield experiment which received a single dressing of chalk (150-250 t ha-1) in the nineteenth century. Since then it has not received any other amendment including chemical or organic fertiliser. Hoosfield is usually a flinty silty clay loam classified as Batcombe Series (Avery 1980) and was sampled in February 2008 Ground 2 was a fine silty loam over clayey drift taken from the cereal rotation of the Highfield Ley-Arable Experiment (Johnston et al. 2009) again classified as Batcombe Series (Avery 1980) and sampled in June 2009 Ground 3 was obtained from the ‘Long Hoos’ site which has been under long-term arable rotations since the 1950s or earlier. The ground is usually a flinty clay loam over clay with sand inclusion (Batcombe-Carstens series; Avery 1980) sampled in November 2009 All soils were collected using a 2.5-cm auger to a depth of 0-23?cm in a ‘W’ pattern across the sites. The bulked cores were stored.