Modelling water pollution by leached soluble phosphorus, part 2: Simulation of effects of manure management

Predictive simulations have been carried out with the ANIMO model describing soluble phosphorus (P) leaching, for a number of scenarios concerning spreading of organic manures. Scenarios include ‘good’ and ‘bad’ management of manures on dairy farms, as well as a case study on an arable farm which receives large quantities of litter from a poultry unit. Alternative scenarios with a poorly performing field drainage system, either due to poor design or due to drains being partially blocked, were also simulated by adjusting the parameters of the multi-layer hydrological model linked to ANIMO. Results show very high levels of soluble organic P leaching, particularly where excessive quantities of manure have been spread over a small land area. Regarding inorganic P leaching, since ANIMO can only simulate the soluble component of this, parallel simulations were carried out using another model (MACRO) which can also simulate leaching of colloidally-transported inorganic P. Results show leaching of total inorganic P (including the colloidal component) at high levels following spreading of excessive quantities of manure, but not at such high levels as for organic P leaching. The soluble component tends to be a very small proportion of total inorganic P, although this component is somewhat higher with the poor drainage system (but still lower than the colloidal inorganic P loss).