INVERSE METHOD TO ESTIMATE MINERALIZATION RATE CONSTANTS FOR NITROGENSIMULATION-MODELS - INTERACTION BETWEEN SAMPLING STRATEGY AND QUALITYOF PARAMETER ESTIMATES

Sustainable agricultural practices and land application of wastes requ ire that the accession of nitrate to groundwater be within acceptable limits. Simulation modelling is a valuable aid to the development and testing of management practices that achieve this goal, but requires u nbiased and precise parameter estimates. Here we consider the role of simple lysimeter-based techniques, which may yield only a single integ ral observation in the form of total solute leached or total drainage, in supplementing infrequent concentration data for the purposes of pa rameter optimisation. The utility of such techniques was evaluated usi ng a simulation model to create a 'no-error data set' of nitrate conce ntration values and summary observations of the total mass of nitrate leached and total drainage over a 182-day period. From that no-error d ata set a more realistic data set incorporating random error was creat ed. By using those concentrations, the value of the mass of nitrate le ached or total drainage was evaluated by their effect on the unbias an d precision of optimised mineralisation or evaporation parameters. The effects of observation weight, error in the observations, and 2 other experimental strategies involving a higher intensity of solute sampli ng were also tested. It was found that the summary observations, such as those obtainable from simple lysimeter-based techniques, had the po tential to reduce bias and improve the precision of the optimised para meters. The consequence of this effectiveness was that error in the su mmary observations led to considerable error in the optimised paramete rs.