EFFECTS OF AIR-POLLUTION ON RICE YIELD IN THE PAKISTAN PUNJAB

A study using open-top chambers ventilated with ambient or charcoal fi ltered air in the vicinity of Lahore, Pakistan demonstrated reductions of 42% and 37% in the grain yield of two cultivars of rice (Oryza sat iva L.). This yield reduction was primarily due to the reduction in me an panicle number per plant, although significant effects of filtratio n on 1000 grain weight and the number of filled grains per panicle wer e also detected. The 6-h daily mean O-3 concentrations were only 10-20 nl litre(-1) during the monsoon season, but increased to 30-55 nl lit re(-1) later in the growing season, while the mean NO2 concentration d uring the experiment was 12 nl litre(-1). On the basis of experience i n North America and Japan, the reductions in yield in the present stud y are substantially greater than might be predicted. The reasons for t his discrepancy are discussed, together with the implications for effe cts on rice yield in other regions of south and south-east Asia.