The effects of road dust on agricultural and horticultural production systems in New Zealand

Abstract

Road dust emissions cause considerable productive losses to farming systems adjoining unsealed rural roads. Yet these costs are currently excluded from economic appraisals, required by the National Roads Board with each roading improvement project proposal.

This study evaluates the magnitude and types of road dust effects on farming systems, based on an extensive literature review and numerous personal interviews. Findings indicate that the main causes of road dust cost are; photosynthetic yield loss, increased levels of pest, disease and weed incidence, dirty produce and reduced pollination. The magnitude of these costs, however, are highly dependent on environmental, roading, biological and economic factors.

A computer simulation model of road dust emission, distribution and effects on farming systems is developed. This model, which is exploratory in nature, predicts approximately according to a priori expectations. The model is built on a modular basis, so that components of the model can easily be refined as new data becomes available. Also, the model is user friendly, thus allowing simple testing of sensitive variables.

Application of the model shows that high value, intensively grown horticultural crops suffer the greatest costs from road dust, but traditional pastoral type farms, in comparison, incur only relatively minor costs. In addition, the magnitude of costs calculated using the road dust model suggests that road dust costs to farming systems should be included in the economic appraisal of roading improvement projects.

However, further applied research to refine and validate the model would be desirable.