The term 'Green Revolution' was coined by Mr William Gaud of the United States in 1968 to refer to the productivity revolution that had then begun in wheat and rice. I coined the term 'Evergreen Revolution' 15 years ago to stress that to achieve improvements in crop productivity in perpetuity, technologies used must be environmentally and economically sustainable.

Fertiliser trials with wheat and rice in the 1950s revealed that the varieties then cultivated lodge (fall over) when 20 kg of nitrogen is applied per hectare. As well as making the crop difficult to harvest, lodging makes it difficult to provide irrigation during grain development, when the crop benefits most from water availability. With these varieties, it is difficult to get an enhanced response to additional nutrients and water.

India's search for crops that could respond to higher levels of nutrition started in 1952, when a programme was initiated for crossing fertiliser-responsive japonica rice with standard Indica strains. The goal was to select lines with the ability to use 100 kg of nitrogen, producing five tonnes of rice, per hectare. Several genetic problems including semi-sterility arose, rendering the search difficult. With the advent in the 1960s of semi-dwarf, non-lodging varieties, interest in Japonica crosses waned, and semi-dwarfed Indica rices provided the material for breeding high-yielding varieties.

When I joined the Indian Agricultural Research Institute (IARI) in late 1954, I started a research programme for developing non-lodging, fertiliser-responsive varieties of wheat, along the lines of the work already begun in rice. The research strategy had three components: crosses between cultivated bread wheat and the semi-dwarf, stiff-straw Compactum and Sphaerococcum sub-species; induction of stiff-straw mutants through the use of radiation and chemical mutagens; and increasing straw stiffness through chemical treatment. Unfortunately, in all three approaches, short and stiff straw was always associated with short panicles (flower clusters) and fewer grains, and yields stagnated at less than one tonne per hectare.

During the late 1950s, publications began to appear on the work of Dr Orville Vogel in the United States on the transfer of drawfing genes to North American winter wheats. Dr Vogel was kind enough to send seeds of Gaines, a semi-dwarf varieties of spring wheat, which would grow better under the short days of India's winter. In March 1962, a few dwarf sprint wheat strains were grown in IARI fields. Their phenotype was most impressive; they had reduced height but long panicles, unlike the earlier hybrids and mutants. In 1963, Dr Borlaug sent a wide range of semi-dwarf wheat, which provided the material for accelerated advances in productivity.

Wheat production in India rose from 10 million tonnes in 1964 to 17 million in 1968, and similar results were obtained with semi-dwarf varieties of rice.

At the dawn of the 21st century, we can look back with pride and satisfaction on the revolution in agriculture during the 20th century. But there is no room for complacency, as we face several new problems. An increasing population leads to increased demand for food but reduced per capita availability of arable land and irrigation water. At the same time, there is increasing damage to the ecological foundations of agriculture.

While dramatic new technological developments are taking place, particularly in the field of biotechnology, their environmental, safety and social implications are yet to be fully understood. Finally, gross capital formation in agriculture is declining in both public and private sectors.

Since land and water will be diminishing resources, there is no option in the future except to produce more food and other agricultural commodities from less arable land and irrigation water. The emerging scientific progress on the farms can be called an 'evergreen revolution', emphasising that the advance in productivity will be sustainable over time because it is rooted in the principles of ecology, economics, social and gender equity and employment generation.

M.S. Swaminathan's research foundation is based in Chennai and committed to harnessing science and technology for environmentally sustainable and socially equitable development.