Near infrared reflectance spectroscopy (NIRS) has been developed for estimation of the nutrient content of livestock manures and biosolids via multiple, rapid, scanning of fresh samples. The initial focus of this research was on the development of robust calibration models, for estimation of dry matter, total N, NH4-N, SO3, P2O5, K2O, MgO and pH, covering a range of manure types and treated biosolids. This process requires very large numbers of samples in order to cover the range of likely analyses, sample and NIR spectral variability. In 2008-2009, a total of almost 2300 samples were collected, from throughout the UK and Ireland, with the active participation of industry partners. These manures were all scanned and, from the NIR spectral database, Principal Component Analysis (PCA) was used to select a proportion of samples for chemical analysis following a robust sample homogenisation procedure developed within earlier research. Some of these manure and biosolids samples were also selected for N mineralisation and N recovery studies using ryegrass sown in pots in order to develop a calibration model for the estimation of N release from the organic component of manure N.
Keywords: Organic manures; biosolids; analysis; nutrients; nitrogen mineralisation; recycling.
Current methods of laboratory analysis for organic materials are slow, relatively expensive and can give inconsistent results for solid and semi-solid materials. Consequently, they are rarely analysed. The resulting uncertainty means that farmers and growers are unaware of the nutrient content of organic materials and, therefore, generally fail to allow for the nutrients supplied following the application of manures to land. Growers therefore tend to apply unnecessarily high rates of inorganic fertilisers (Anon, 2008), as “insurance” for optimal yields, in addition to the often substantial nutrient supply from the organic materials. Interest in manures and biosolids as nutrient sources has increased as a result of increased fertiliser prices and farmers are more receptive to the use of practical aids for improved recycling of manures.
Near infrared reflectance spectroscopy (NIRS) has greatly improved precision and reliability in the analysis of forages and is now used routinely for the analysis of grain. In recent research, NIRS has shown considerable potential for estimating the nutrient content of manures and slurries from multiple, rapid, scanning of fresh samples (Reeves and Van Kessel, 2000; Smith et al, 2005). The aim of the current research is to promote the sustainable recycling of organic manures and residues through the development of NIRS as a robust and reliable technology for multi-nutrient analysis. The research involved the development of calibration models for estimation of the content of dry matter (DM), total N, NH4-N, SO3, P2O5, K2O, MgO and pH in a range of manure types, including cattle and pig slurries, farmyard manures and treated biosolids. In addition to the conventional analysis capability, the research aimed to develop a calibration model for the estimation of N release from the organic component of manure N, using data from small-scale studies on N recovery by ryegrass following mineralisation of the organic N content of selected manures and biosolids.