Organomineral Fertilisers: Nitrogen Dynamics and Evaluation of Agronomic Characteristics

The production of sewage-sludge in the UK is set to increase due to population growth and stringent requirements for the treatment of effluents. Recycling to agricultural land is regarded as the best practicable environmental option and currently represents the main disposal route. A novel method recently developed by United Utilities-plc, allows organomineral fertilisers to be produced by blending mineral fertilisers with biosolids thereby improving the N:P:K biosolids' ratios. Using this method, two OMFs with different N concentrations have been formulated: OMF10 (10%N) and OMF15 (15%N). The purpose of this study was to identify the effects of the use of OMFs on agricultural crops and grassland. To achieve this aim, a number of interconnected experiments using two soil types (sandy loam and clay loam), two OMFs, urea, and digested cake (3%N) as a base for comparison, have been set up. The experiments included the use of small plots (field) with winter wheat (Triticum aestivum L.), pots (greenhouse) with rye-grass (Lolium perenne L.), and an incubation experiment (laboratory). Results from the plot trial indicated that the use of OMFs produced similar (p=0.690) crop yields as urea (10516 and 10325kg ha-1 respectively) and that the most economic rates of N (MERN) were 287, 222, and 207kg [N] ha-1 for OMF10, OMF15, and urea respectively. The pot trial showed significant differences (p<0.001) in yield between the control and the treatments with respect to the fertiliser type. After three cuts, grass yield was found to increase with the N content in the fertiliser and specifically with the concentration of readily available N. Similarly, increased application rate of N and concentration of readily available N in the fertiliser were found to have a significant effect (p<0.001) upon the N content of harvested plant material measured on average after three cuts.