Agricultural History Review, Volume 53 Part 2 (2005), p. 268

In the 1960s Professor Leigh, then at the beginning of his career, was appointed to the new ARC Unit of Nitrogen Fixation at the University of Sussex. The unit was finally closed in the 1990s, and this book is in effect a discursive account of the historical background to its work.

After an opening chapter that sketches the main themes of the book, there follows a chapter on the development of farming across the world, including native American, Mayan, and Chinese agriculture, and a discussion of what Roman agricultural writers said about manure. Leigh concludes from this that the supply of fixed nitrogen has determined the supply of food and thus the size of the human population throughout history. He then goes on to examine the history of English agriculture, and especially the role of guano and Chilean nitrate in the nineteenth century. The following chapter describes the rise of agricultural chemistry, and in particular the contributions of Davy, Boussingault, Liebig, and Lawes and Gilbert to explaining how inorganic fertilizers worked, and of Hellriegel and Wilfarth in demonstrating that the presence of nitrifying bacteria on their roots enabled legumes to fix their own nitrogen. At the end of the nineteenth century, Leigh argues, it was clear that the increasing agricultural production needed to feed the expanding world population would eventually be threatened by diminishing stocks of existing nitrogenous fertilizers. This led to a search for some means of fixing nitrogen from the air so that it could be used by non-leguminous plants. The result was the Birkeland–Eyde process, which relied on enormous quantities of cheap hydro-electricity and so was only ever adopted in Norway, the cyanamide process, which was also energy-intensive, and the one that eventually came to dominate the nitrogen fertilizer industry, the Haber-Bosch process.

The remainder of the story of inorganic fertilizers is about their increased adoption by farmers and the growth of the business on an international scale, but Leigh has little to say about this. His attention turns instead to the problem of biological nitrogen fixation, with which most of his career was concerned. If the nitrifying bacteria that fix nitrogen for legumes could be transferred on to non-leguminous plants, the need for fertilizer, and thus the cost of food production, would becorrespondingly reduced. There might also be an additional environmental benefit, in that the nitrogen would be produced as the plant needed it, and so would be less likely to escape into groundwater and produce eutrophication problems. From the 1960s the chemistry and biochemistry of the process received much scientific attention, summarized clearly in Chapter Six. Over thirty years much was learned, but not enough: ‘the ultimate secret of biological nitrogen fixation’, Leigh tells us, ‘still eludes all attempts to uncover it’ (p.186). We are left with fertilizers as our principal source of nitrogen. For those who see this as a problem, Leigh devotes his final chapter to an evaluation of the role of fertilizer nitrogen in eutrophication, human health, and global warming. He is more optimistic than other writers have been. ‘The overall balance of the effects of nitrogen and its compounds on humankind is not absolutely clear’, he concludes, ‘but currently it seems overwhelmingly positive’ (p.219). There are risks of eutrophication, ‘but these should be manageable’ (p.217). Leigh see this as ‘an epic tale of human endeavour... the problem of feeding the human race is really solved’ (p.219). There are villains – the motives of politicians and commercial companies are ‘not to be trusted’ (p.217) – but there are also heroes, in the formof science and the scientists ‘whose inquisitiveness, imagination, and application have placed the ultimate solution to the age-old problem of feeding the population of the world in our hands’ (p.220).

This claims to be a book written for that mythical beast, the general reader. It is not for the scientific specialist, for Leigh has already edited a summary of the research (Nitrogen fixation at the millennium (Elsevier, 2002). Neither is it for historians of science and technology, for they will find its approach out of sympathy with their current methodologies. Nor is it for specialist agricultural historians, for it contains much that is already available elsewhere, notably in V.Smil, Enriching the earth (MIT Press, 2001), and only one chapter of new material – on the activities of the Nitrogen Fixation Unit – that they will find fresh and interesting. Given the author’s admitted regret at no longer having ‘the immense privilege of studying a challenging problem with a minimum of bureaucratic interference’ (p.viii), it may perhaps be aimed most directly at those who with-drew the funding from the Unit, to show them where the basic research that it did fits into the wider picture.