The effect of amount and timing of nitrogen application to drilled crisp lettuce crops on head weight at maturity

Abstract

Much of the recent increase in crisp lettuce production in the U.K. has been marketed as heavily trimmed solid ‘Iceberg’ heads, wrapped in plastic film. Supermarkets want ‘Iceberg’ lettuce with a minimum trimmed weight of 450 g (Anon. 1983) and consistency of product, but the mean head weight of crisp lettuce at maturity can vary considerably from one sowing to another as a result of environmental conditions earlier in growth (Pew, Gardner & Bessey, 1984; Wurr & Fellows, 1984). In midsummer, some sowings of the most popular variety Saladin can produce larger and heavier heads thanc supermarkets require and the cause of this variation needs to be understood in order to increase the proportion of crops meeting supermarket needs.