Nutrient potential of biosolids and urea derived organo-mineral fertilisers in a field scale experiment using ryegrass (Lolium perenne L.)

Biosolids derived organo-mineral fertilisers (OMF) are designed to reduce fertiliser inputs, but may lead to excessive accumulation of soil P. Two OMF formulations comprised of biosolids (BS), urea and potassium at NPK ratios of 10:4:4 (OMF10) and 15:4:4 (OMF15) were investigated. Effects of OMF on ryegrass (Lolium perenne L.) yields and crop P content, together with soil nutrients (total C and N, organic matter, pH) were explored and compared to BS and urea in a three year field trial. In addition the soil microbial community (biomass C, phospholipid fatty acid - PLFA and multiple substrate induced respiration - MSIR) were assessed at the end of the experiment. All fertilisers (rates 0-250 kg N ha−1) produced similar yields with the exception of urea, which had reduced yield at 250 kg N ha−1. Soil total carbon increased where BS and OMF10 were applied but not with OMF15 and urea. Crop P was not affected by fertiliser applications and no organic matter accumulation were observed with urea. Comparable yields produced by the application of OMF compared to urea suggest that OMF is a promising alternative to inorganic fertiliser. Soil microbial biomass was greater in BS plots compared to urea indicating an increased supply of substrates for microorganisms in the former. Soil microbiological analysis indicates change in the community PLFA profile in autumn, but an altered MSIR functional profile in spring. Changes in available P suggest OMF replenished supplies of utilised nutrient and maintains soil P levels.