Nitrogen and Phosphorus Availability From Various Composted Wastes For Use In Irish Agriculture And Horticulture

Current environmental EU legislation promotes recycling and recovery from organic waste products. Compost has been identified as an alternative to inorganic fertilisers and animal slurries as a nutrient source for crop plants. This study aimed to investigate nitrogen (N) and phosphorus (P) availability from various composted waste through detailed characterisations, complemented by short term lab incubations and long term plant growth experiments. Twenty-five composts were selected and classified by their groups. The composts were characterised by multiple different analytical techniques. Two incubation studies were conducted. One investigating N and P mineralisation potential of the composts and the second on the effects or soil type on P mineralisation. Two large glasshouse based pot experiments were then conducted. A subsequent stability study of two separate methods on mechanical biological treated waste was also investigated for a potential relationship. Characterisation of the composts highlighted the difference between compost feedstocks with the manure waste being distinctly separate from the other groups. The biowaste groups identified as either food waste or brown bin waste. The incubation experiment highlighted that N mineralisation was more predictable than P. From the pot experiment only manure waste mineralised N above 10%. All of the other groups mineralised minute amounts. Prediction of N mineralisation was found to be more accurate from lignin and neutral detergent fibre content over the more traditional C/N ratio. Mineralisation of small amounts of organic N occurred in summer months. There was a distinct lack of a relationship between the P incubation and pot experiment. Plant uptake of P was higher than expected for all treatments. The manure waste composts were higher in cumulative P uptake than inorganic fertiliser. Stability in composts was found not to affect mineralisation or induce immobilisation. The effects of soil type on composts were most pronounced in composts lower in fulvic acid. The composts with higher humic acid were not found to significantly mineralise a higher amount of P. The stability study investigating oxygen uptake rate (OUR) and respiration index (AT4) on the mechanical biological treated waste showed a high correlation between the two methods where AT4 was below 40 mg O2.g DM-1. The findings point to a possible reassessment of compost quality guidelines for composts. The availability of P is far greater and therefore should be considered the primary nutrient available from compost. The stability parameter for manure waste compost may also need assessing as it is unachievable in reasonable composting time frame. The biowaste compost has proven to be high in P. There is also the potential to develop quite specifically produced composts based on their feedstock and composting length for particular agronomic or environmental needs. Compost application is a feasible source of nutrients and organic matter due to escalating fertiliser prices and more stringent regulations surrounding fertilisers and slurries