FEEDING THE TEN BILLION
PLANTS AND POPULATION GROWTH
L.T. EVANS
CAMBRIDGE UNIVERSITY PRESS 1998
PART VI
Chapter 6: The Second Billion (1825-1927)
6.1 Introduction: The entry of science
The population of the world doubled, from one to two billion, in the century following 1825, with most of the increase still being in Asia. The period was characterized by a rise in food supply per head from less than 2000 to more than 3000 Calories per day in the countries of western Europe and, from the middle of the 19th century, by a sharp rise in the proportion of animal protein in the diet. These changes were associated with the beginnings of agricultural research, stimulated by Humphry Davy’s lectures on agricultural chemistry, resoundingly launched by Justus von Liebig from Giessen in 1840, and epitomized by the motto of the Royal Agricultural Society of England at its establishment in 1838: ‘Practice with Science’.
- For the period under consideration, significant improvement in crop yields was largely confined to western Europe and Japan.
- Crop yields on some of the cleared lands of the New World began to decline after the initially high soil fertility was exhausted.
Until the middle of the 19th century, crop yields were thought to be limited by the supply of farmyard manure: the more livestock the farmer could carry, the higher his yields. The discovery of nitrogen fixation in legumes by Hellriegel and Wilfarth in 1886 explained their long-recognized beneficial effects in crop rotations. Even before that, however, one-fifth of the arable land in northern Europe was under leguminous crops, which are thought to have provided more nitrogen to cereals than did the farmyard manure.
In the second half of the 19th century, however, the limitations on crop yields by the supplies of farmyard manure and green manures were lessened as mineral fertilizers began to be used, especially after the introduction of superphosphate and the demonstrations at Rothamsted of the returns in yield from the application of N, P and K fertilizers. Sir John Russell referred to these fertilizers as ‘the first and for long the only application of science to agriculture.’
That other ancient but periodic and unpredictable limitation on yields, by the diseases and pests of crops, also seemed on the threshold of control as a result of scientific research following the work of Millardet and others in France on the use of verdigris, Paris green and other disease and pest-controlling chemicals. Then, as our two billion approached, came the beginnings of biological control.
- The introduction of new crops, e.g. of soybeans into the USA, continued throughout the 1825-1927 period, with botanical gardens playing a major role, particularly in the redistribution of crops adapted to the tropics.
- Aiding such redistribution was the recognition that plant responses to daylength, as well as to temperature, played an important role in the adaptation of crops to new environments.
- The selection of superior lines of crops was practiced by many farmers and, increasingly, by seed companies such as that of Vilmorin in France, founded in 1727.
- This period also saw the development of plant hybridization, leading to the publication of Mendel’s laws governing genetic segregation in 1866, their rediscovery in 1900 and their rapid application to plant breeding.
- As science increasingly permeated agriculture, the questions of how to support research, extend its findings and educate agriculturists in their adoption became a matter of urgency.
- In England J.B. Lawes continued the tradition of the landed gentry in supporting agricultural experimentation, but on a scale unmatched by his predecessors when he established Rothamsted as the first agricultural experiment station.
- At the same time in Germany Justus von Liebig, with his challenging views on plant nutrition, was attracting many students from overseas to his laboratory at Giessen.
- The impact of his writings and those of Albrecht Thaer was such that several German states established agricultural experiment stations.
- The institutionalization of government funding for agricultural research in the USA began in 1862 with the establishment of the US Department of agriculture and the provision of land to the various states to establish colleges of ‘agriculture and the mechanic arts’.
- The wave of public support for agricultural research and education then rolled on to Japan in the Meiji Period (1868-1911).
- By the time the population of the world reached two billion in about 1927, the need for publicly-funded research and education in agriculture was widely accepted even though its benefits in such areas as the nutrition, pathology, introduction and improvement of plants had only just begun to flow.
6.2 Justus von Liebig and plant nutrition
6.3 Mineral fertilizers and microbial inoculants
6.4 Vines and Verdigris: the chemical control of plant disease
6.5 Crop plant improvement, before and after Mendel
6.6 Daylength and soybeans
6.7 The trace nutrient gold rush
6.8 biological control of pests and weeds
- The term ‘biological control’ was introduced in 1919 for the control or regulation of pest populations by natural enemies i.e. predators, parasites or pathogens.
We are concerned with the consequences of the introduction of crops to new regions. In quite a few instances they left their pests behind, at least initially, but in many cases the pest accompanied or caught up with the crop but left their own natural enemies behind. In such circumstances the pests may cause great damage to the crop, threatening its usefulness in its new environment and inspiring a search for its natural enemies.
- The first spectacularly successful example of this kind of biological control was in California in 1889, the pest being the cottony-cushion scale which was devastating the citrus industry of the state.
- The successes in pest control have been mainly with perennial plants such as tree crops, stone fruits, olives and particularly citrus, as well as introduced forest trees.
- The life cycles and management of the major food grains tend to limit the effectiveness of biological control.
Introduced enemies now control more than 70 species of weedy plants, mainly in rangelands and perennial crops. Their effectiveness on weeds of the staple food crops is subject to the same limitations as apply to the crops themselves. Nevertheless, biological control was an exciting and valuable agricultural innovation, one which deploys our understanding of the subtleties of the web of life. There are still many opportunities for its application, and for its full flowering as the key to integrated pest management (p.160).
6.9 Botanic gardens and plant introductions
Chapter 7: The Third Billion (1927-1960)