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Literature Review on the Availability of Phosphorus from Compost in Relation to the Nitrate Regulations
Literature Review on the Availability of Nitrogen from Compost in Relation to the Nitrate Regulations Two research reports conducted by Cré for the EPA STRIVE Programme have been published. The research was kindly funded by the EPA. A special thanks is due to Dr. Munoo Prasad (Compost Research & Advisory) for writing them and to the following people for reviewing them: Tom McDonnell (Kilmainhamwood Compost), Dearbhail Ni Chualain and Dr. Bill Carile, (Bord na Mona Horticulture), Dr. Brian Donlon (Environmental Protection Agency) and Dr. John O’Neill (Department of Environment, Heritage and Local Government).
The Availability of Phosphorus and Nitrogen The nitrate regulations give recommendations of nutrient input for a range of horticultural and agricultural crops. The availability of phosphorus from pig, poultry, cattle and other livestock manure, spent mushroom compost are accepted as from inorganic fertiliser (superphosphate). The regulations have given the availability of phosphorus from compost the same availability of phosphorus from cattle manure (100% available).
The availability of nitrogen (N) from pig, poultry, cattle, and other livestock manure, spent mushroom compost and other types of composts is taken to be between 25 to 50%. The regulations have given the availability of nitrogen from compost the same as cattle manure (30%). However, there is a possibility of special derogation if data can be provided regarding release rate from compost. The reports reviewed literature and has determined the release rate of phosphorus and nitrogen from compost.
Nitrogen The availability of N from compost is effected greatly by the feedstock in which the compost was derived and stability (often only 0-20% or even negative in the first year and 0-8% in the following years). Until more detailed research is conducted it is recommended that the guidelines developed by Wallace (2006) of using the C:N ratio of the compost to determine the availability is used as outlined in the Table 1 below.
Table 1. C:N ratio in relation to potentially mineralisable N
Phosphorus There are limited publications available on the P availability from composts, as it has not been studied in great depth in comparison to the large number of publications available on the availability of N.
The availability of phosphorus from compost was determined after reviewing publications on pot trials, incubation trials, field trials and leaching trials. Based on the information from the publications the author made a judgement on the approximate availability of phosphorus from different types of compost in Table 2.
There is a need to emphasise the interdependency of P and N in compost in the regulations. It is not nitrate leaching from compost that could be a potential problem from compost application; rather it is P that could be potential problem. It is phosphorus which is the deciding factor in most cases on the application of compost and not the nitrogen content.
Table 2. Proposed phosphorus availability from various composts made from different feedstock relative to superphosphate
What do these research reports mean in practice? The Nitrate Regulations provide a special derogation if data can be provided regarding the release rate from compost. The reports reviewed literature and has determined the release rate of nitrogen and phosphorus from compost. Compost producers need to test their compost for its carbon to nitrogen ratio and based on this the corresponding nitrogen availability can be determined (See Table 1). The phosphorus content of different types of compost is shown in Table 2 and compost producers can use this when applying compost.
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