L P Smith, known to his friends and colleagues as 'LP', died on 10 October 2001 aged 86 in Ilkley, Yorkshire where he had spent his retirement near the Dales, which he always remembered with affection from his youth. He was for many years Head of the Agricultural Branch of the Meteorological Office. Plant pathologists will remember him best for the 'Smith Period', a forecasting scheme for potato late blight.
He was a pupil at Leeds Grammar School, where he won a scholarship to Queens College, Oxford. He read mathematics and physics and graduated with a BA in Mathematics in 1937. He joined the Meteorological Office and he remained on its staff until his retirement 40 years later. After appointments to Kew Observatory, Croydon and RAF stations at home and in the Middle East during the Second World War, he returned to the Met Office to establish a new branch responsible for all aspects of agricultural meteorology. This proved to be an inspired appointment, for he had a flair for establishing friendly and fruitful contacts both with farmers and with agricultural scientists. In due course the success of his work led to a special merit promotion and to the award of a Nuffield travelling fellowship, which enabled him to make extensive visits throughout the Commonwealth and Europe.
In 1961, the World Meteorological Organisation (WMO) asked LP to prepare a report on agricultural meteorology to be used as part of its contribution to the World Hunger Campaign and this was published as a contribution to FAO's basic study series. In the following year, his rapidly growing international reputation led to his appointment as a member of WMO's Commission for Agricultural Meteorology, of which he was President twice. His Methods in Agricultural Meteorology, published in 1975, distilling much of his own experience, provided a contemporary review of an expanding field of research. Each chapter is prefaced by quotations from leading writers but a quote of his from the preface maybe appropriate: 'The first duty of a scientist is not to worship knowledge, but to question it'. He also produced a series of 10 Technical Notes for WMO and his booklet on Weather and food was the first in FAO's Basic Studies Series. In 1965 he was awarded the Groves Memorial Prize for meteorology. In the 1960s and 1970s LP was increasingly involved with international aspects of his field and WMO awarded him a certificate honouring 20 years of dedicated service.
Much of his time was spent attending and chairing meetings and he continued to accept many requests to lecture at home and abroad as well as to write. None of this prevented a keen and enthusiastic response to any current problems brought to his attention and discussion of problems from the field were always rewarding. His analysis of a problem was incisive and penetrating and backed by a huge and wide experience.
Shortly after he joined the Meteorological Office, LP inaugurated a series of Agricultural Memoranda and he and his colleagues subsequently produced over 200 of these documents, primarily for the benefit of staff in the advisory services such as ADAS.
His 'Smith Period' was the result of reworking the 1950-1955 operations charts of A Beaumont (of the 'Beaumont Period', the classic UK potato late blight forecasting scheme published in 1947) to test the validity of using a shorter period of higher humidity. He found that 29 out of the 43 failures of Beaumont would have been valid using a 90% humidity criterion for 11 h in each of two days instead of the 75% for 48 h. Smith records that "The differences in effectiveness of the two systems, however, would appear to be small in practice and there would be little point in altering an established system unless the benefits are likely to be considerable". It was not until 1975 that the Smith period came into full operation and formed the basis of blight forecasting in the UK. It is still the most widely used forecasting scheme in the UK and has proved to be very robust. Topically, LP published a paper in Nature on an analysis of the foot and mouth disease outbreak of 1967, concluding that weather played a greater part in the spread of the disease than was previously recognised. One of his final contributions was a book written in collaboration with Harold Croxall, a former ADAS plant pathologist, on The Fight for Food, published in 1984. In it, the authors identify the wide range of factors influencing, and often limiting, agricultural production; a forerunner of our current concerns in defining global food security.
It should also be recorded that LP was a fine rugby football referee and was a senior member of the London Society of Rugby Referees for many years.
This obituary has been modified from one prepared by John Monteith for publication in the Quarterly Journal of the Royal Meteorological Society and with additional material from John Jenkins, to reflect more his contribution to plant pathology.
Nigel Hardwick, Central Science Laboratory
Croxall HE, Smith LP, 1984. The fight for food. London, George Allan and Unwin.
Smith LP, 1956. Potato blight forecasting by 90 per cent humidity criteria. Plant Pathology 5, 83-87.
Smith LP, 1975. Methods in agricultural meteorology. Oxford, Elsevier.
Smith LP, Hugh-Jones ME, 1969. The weather factor in foot and mouth disease epidemics. Nature 223, 712-715.
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