Nitrogen, Threat or Benefaction? The Spectre at the Feast

The world today is a very different place from what it was in about 1900. It is a very different place from what it was even in the 1960s. This is not to say that the worries and preoccupations of 1900 and the 1960s have just disappeared. Rather, they still remain, but as a consequence of the activities of the Club of Rome and the many similar organisations that have arisen since then, people are much more conscious of them. The famous energy crisis of 1973, provoked by the rapid quadrupling of the price of oil, hardly a natural process, served to push such considerations to the fore. The simple questions that were once posed (such as “How shall we feed a growing population?”) have been joined to many others. Is there a limit to population growth beyond which the potential food supply will really be exceeded? Is there a limit beyond which the perturbation of the environment by human actions will produce changes that will irretrievably damage both people and the environment? Are there really limits to growth? What can we reasonably do that will not produce disaster? This is a far cry from the Victorian and even old-fashioned capitalistic and Soviet attitudes that seemed then and still seem to assume that humans, being at the pinnacle of evolution (or, alternatively, being placed at the pinnacle of animal life by God), were free to exploit Earth and its resources as much as seemed necessary. Even to attempt to answer such questions, it is necessary to understand what the current state of Earth and the environment really are, and this is not simply a matter of looking out of the window and making a snap judgement, or even looking out of several windows over a certain period. It is necessary to do serious research and then attempt to make sound judgements. This is no trivial matter because often there is little objective guidance as to what constitutes a sound judgement. The idea that human activities are upsetting the current equilibrium between people and the environment is based upon a misconception.

The Triumph of Industrial Chemistry: The Industrial Response to Sir William Crookes

In 1905, Sir William Crookes published a book entitled The Wheat Problem in which he reiterated what he had said in his British Association address of 1898. The content and tone are familiar: “The fixation of nitrogen is vital to the progress of civilized humanity, and unless we can class it among the certainties to come, the great Caucasian race will cease to be foremost in the world, and will be squeezed out of existence by races to whom wheaten bread is not the staff of life.” A whole gamut of processes for fixing nitrogen was described in a book published in 1914, and in 1919 an eminent U.S. electrochemist, H. J. M. Creighton, published a series of three papers entitled “How the Nitrogen Fixation Problem Has Been Solved.” However, the broader story was only just beginning to unfold. In about 1925, J. W. Mellor, in a justly celebrated sixteen-volume compendium, simply took Creighton at his word and stated quite baldly: “The problem has since [Crookes’ lecture] been solved.” Mellor describes not one but six processes that he believed were of industrial significance. These were: (1) the direct oxidation of dinitrogen by dioxygen to yield, initially, nitrogen oxides, as was undertaken in the Norwegian arc process; (2) the absorption of dinitrogen by metal carbides, subsequently developed as the cyanamide process; (3) the reaction of dinitrogen and dihydrogen by what has become known as the Haber process, or, more justifiably, the Haber–Bosch process; (4) the reaction of dinitrogen with metals, followed by treatment of the resultant nitrides with water; (5) the reaction of dinitrogen with carbon to form cyanides; and (6) the oxidation of dinitrogen during the combustion of coal or natural gas. Of these, only the first three really reached the stage of industrial exploitation, and only the Haber–Bosch process has been applied to any degree of significance since about 1950. The history of these three major developments is traced below. One of the first industrially significant reactions to be developed at the beginning of the twentieth century had already been known for more than 100 years.

The Development of English Agriculture and the Recognition of the Fertiliser Deficit

So far, it has been shown that nitrogen is an important constituent of living things and that its availability may be limited if soil is not carefully husbanded. Older civilisations have discovered ways of supplying the required nitrogen through the use of fallows or fertilisers of different kinds, such as green fertilisers or manures. Such knowledge must have developed only slowly. The Romans occupied a vast swathe of Europe and parts of Asia and applied their agricultural techniques, as described in the previous chapter, wherever they found them useful. They had realised that a two-crop rotation was not very productive in that half the cultivable fields were lying fallow at any one time. They developed three-field rotations and applied fertilisers and green manures. However, they never succeeded in avoiding the presence of fallow altogether. This chapter concentrates primarily on the British Isles, for which a vast amount of information is available. Historians of agriculture tend to believe that even Bronze Age farmers were aware of the value of dung and that they probably practised primitive two-field rotations. They did not have a plough other than the ard, which was essentially a hard-pointed shaft that was dragged through the soil by oxen or even pushed through the soil by human brute force. More sophisticated ploughs did not reach Britain until later. Traces of the ancient fields or terraces are still evident in parts of Scotland and on the chalk hills of southern England. These are in open areas that must have been the most appropriate for agriculture since much of the rest of lowland Britain was covered by dense forest, as in the Weald of Sussex and Kent. The Weald (the name derives from the same root as the modern German word Wald, meaning wood or forest) is the area of the two counties between the chalk hills of the North and South Downs. These hills are seemingly contrarily called Downs because the name is derived from a Germanic word for dunes. They have been settled for many thousands of years, and the remains of hill forts are evident in many places.

The Continuing Mystery of Biological Nitrogen Fixation

Fritz Haber was not blinded by his own achievements. Even in 1921, just when his own work was becoming widely recognised, he could state: “It may be that this solution is not the final one. Nitrogen bacteria teach us that Nature, with her sophisticated forms of the chemistry of living matter, still understands and utilises methods which we do not as yet know how to imitate.” The realisation that this was the case prompted a lot of speculation, but scientific advances in biological fixation still awaited a strategic breakthrough. In addition, chemistry, and especially inorganic chemistry, went into decline. The academic world seemed to believe that the chemistry of simple species such as dinitrogen was completed. There was no single clarion call, comparable to that of Crookes in 1898, for the regeneration of research into nitrogen fixation, but the pressure for it built up in a variety of unexpected ways. Perhaps the seminal influence on the field arose in the 1960s. The stimulus can be seen in the changes that occurred after World War II. In 1945, when much of the world was on its knees, having sustained grave losses of material and people, the impetus was to restart and rebuild. By about 1960, there was the appreciation in some areas that technology could not be applied to the environment indefinitely, nor could standards of living continue to rise without some unpleasant consequences. Western governments were not keen to hear such ideas. The British government, for example, produced a policy document called “Food from our own Resources,” the aim of which was to guide the United Kingdom towards self-sufficiency in food, avoiding the possibility of the country being starved as a result of a siege of the sea lanes by a potential enemy. The difficulties of maintaining food supplies from the Empire in the face of a sea blockade were a principal reason why food had been severely rationed in Britain during World War II. A consequence of this policy was that farmers were encouraged to produce as much food as they could, by whatever methods seemed most appropriate, and the era of intensive agriculture really got into its stride.

The Discovery of Nitrogen and the Disappearance of Alchemical Nitre: The Rise of Agricultural Chemistry in the Eighteenth and Nineteenth Centuries

So far, we have seen how sophisticated systems of agriculture had grown up in many different places and at various times in order to overcome problems associated with the decline of soil fertility arising from continuous exploitation. In Europe and elsewhere, it was clearly understood that manures and various materials such as potassium (or sodium) nitrate could rejuvenate the soil, and empirically probably little more could have been achieved in this direction. Nevertheless, the supply of the products capable of doing this was clearly limited. Only when the scientific basis of the action of fertilisers and manures had been fully understood could further advances be made, and this only happened with the scientific revolution, which began to flower in the sixteenth century and continues in bloom to this day. The empirical experience of centuries seems to have led to the supposition in Europe that the air was somehow involved in restoring the fertility of soils and in the facilitation of plant growth. However, the reason for this influence could not have been presented in modern terms. A lot of the discussion was centred about the mysterious substance nitre, which was then not simply the salt we recognise today. There are many instances of statements to the effect that nitre was absorbed from the air and even references in the older literature to aerial nitre. Solid nitre was, of course, very well-known in the form of saltpetre and was widely employed as a constituent of gunpowder. This kind of nitre could also be used as a fertiliser, though there was not enough of it around to “waste” by spreading it on the soil. Then, as is often true today, warfare was regarded as a more important use for such a resource. Nitre could be extracted from manures and from ashes, and, because it was a crystalline solid, it certainly was not the mysterious something that was present in the air. There was no understanding of the modern notions of elements and compounds. It would take a long time—two centuries—for a truly scientific approach to agricultural chemistry to be developed, but it is still worthwhile to enquire what exactly writers of treatises in the mid-seventeenth century really meant.

The Development of Agriculture: Maintaining Soil Fertility

The reason why nitrogen is necessary for all living things was established in chapter 1. We also saw the kind of intellectual and theoretical basis upon which the scientific understanding of that necessity had to be established. We now consider the other side of the nitrogen coin: the kinds of agriculture that were actually practised in various selected parts of the world at different times. It is generally accepted that from the earliest times when human beings first lived in groups, they gathered their food wherever they happened to find it, or else they hunted it. The development of agriculture presumably implied that people became rather less peripatetic because they had to return to their crops, at the least to harvest them. At about the same time, they began to domesticate animals, and this must also have considerably restricted their mobility. Whether they noticed that land became less productive as they repeated cultivation on the same plots year after year can only be surmised. All this occurred about 8000 years ago. There is perhaps one caveat. If people lived in an area where food was plentiful and easy to gather, they would not have needed to wander so far to find their nourishment, but the idea of widespread, static settlements of sedentary hunter-gatherers is not a popular one among the experts. Once people started to live in cities, there must have been significant changes in agricultural practice, for at least two reasons. First, it is not simple to dismantle a city of permanent buildings every few years and to move it to a more convenient spot for growing crops, so people no longer did that. They tended to stay put. Second, the mere fact that there were people in the cities such as artisans, artists, and priests, who were not productive agriculturally but who needed to be fed, meant that those who continued to raise crops had to produce more food than subsistence farmers who fed only their immediate dependants. The new farmers had to supply food not only to themselves and to their families but also to all the non-agriculturalists living in the cities.

Nitrogen Fixation, Agriculture, and the Environment

This book tells the story of how humans have used their ingenuity throughout history to maintain soil fertility and to avoid famine through productive agriculture. The struggle to provide sufficient food has been a preoccupation of humanity since the earliest times. As circumstances have changed and as lifestyles have changed, the way in which the food supply has been ensured has also changed. The story of how different peoples have developed solutions to what is essentially the same problem tells us much about human beings of all kinds and in all ages. It shows us how humans have optimised the opportunities available to them by using the resources, both physical and intellectual, that have been available to them. It shows us the similarity amongst human beings of every era. It also demonstrates how one generation builds upon the knowledge of its predecessors to provide a solution that is appropriate to the new conditions, and it also illustrates the way in which science is gradually and painfully built by generations of researchers in a cooperative undertaking that slowly refines the models of reality used to analyse nature. Traditionally, agriculturalists have tended to be conservative, and this is very understandable. It is stupid to experiment with questionable new methods if you know that the old techniques work and that not using them will risk a year of famine. The Egyptian and the Britons depicted ploughing with very similar implements in figure 1.1 would probably have shared many ideas on how best to raise crops. A survey of how some ancient civilisations attempted to solve the problems of maintaining soil fertility is given in chapter 2. Many of their techniques are still applied somewhere in the world to this day. The main focus of this book will be on the story of the essential nutrient nitrogen because nitrogen is often the element whose supply limits the agricultural productivity of many food systems. Nitrogen is an element that many people know a little about. Nitrogen gas comprises about 80% of Earth’s atmosphere, though this was not known 250 years ago, nor would such a statement have made much sense then.