Non-uniformity of environmental conditions in greenhouse lettuce production increases the risk of N pollution and lower product quality

Although it is well known that environmental conditions in greenhouse crops are often not uniform, this is rarely taken into account in research into the factors determining product quality and pollution. Yet non-uniformity o f irrigation, radiation and effect of compaction doubtless plays a fundamen tal part in the problems of quality (uniform size) and N pollution faced in lettuce production under plastic. A monitoring study of four lettuce crops showed a high degree of environmental non-uniformity, structured by the cr opping methods used, and partly responsible for the variability in lettuce size. A model of the behaviour of the soil-plant system showed that this no n-uniformity leads to serious N pollution: meeting the needs of the most di sadvantaged plants leads to over-irrigation and over-fertilisation in nitro gen in some zones of the tunnel. If this non-uniformity is ignored, solutio ns may be proposed that do not match the objectives set in terms of product quality and environmental protection.