Grassland Nitrogen. - book reviews

Ecology, Jan, 1997 by Daniel G. Milchunas

Basic ecological research in soil-plant-animal interactions and in land-atmosphere exchanges of nutrients has, until recently, lagged behind research conducted with agricultural production as the focus. In this regard, Grassland nitrogen may serve as a valuable source of information to ecologists that may not otherwise have a good grasp of literature published in journals such as Agronomy Journal, Journal of Agricultural Science, Fertilizer Research, Grass and Forage Science. This book is clearly oriented towards agricultural and environmental sciences, and these are its stated audiences. A second aspect of the scope of the book is the primary focus on anthropogenic grassland in climates that would otherwise be forest. The first figure shows North American grasslands occupying areas east of the Mississippi River, the Rocky Mountains, and the far west coast; semiarid to subhumid grasslands of the Great Plains and grasslands of southwestern U.S. are not included. Europe and New Zealand are considered areas of temperate grassland. Although the preface and introductory chapter clearly state the scope, the title of the book can easily be misleading to ecologists who may be more likely to think of anthropogenic grasslands as "seeded pasture." Much of the research cited in the book is from work conducted in rye grass/clover swards in the U.K., but the author has made an effort to extend this base to include research from other systems.

Given the above potential limitations of setting and scope, there is much in this book that would be of interest to ecologists, particularly those working in areas of plant-animal interactions, trace gas fluxes, and nutrient enrichment. Chapter 2 is a basic, but comprehensive, examination of uptake of nitrogen by plants, and effects on all aspects of growth. As with much of the book, comparisons are made across a range of fertilizer treatments, providing perspectives across availability gradients. Two chapters provide a good overview of the role of herbivores in nitrogen cycling. The emphasis is on cattle and sheep in sown pastures, with only cursory mention of the large amount of research conducted in native grasslands. For those working in native grasslands, there are many relevant, useful data and references that I have never seen cited in ecological literature. Coverage on excreta is broad and intensive, but is very weak on consumption and digestion. Effects on the animal is not an emphasis. Three chapters deal with transformations of nitrogen in the soil, and two chapters with volatilization. Emphasis is on fertilizer, grazing, and plowing effects. Several chapters have sections on environmental impacts. Five of the 16 chapters are on uses and effects of fertilizers and their interactions with abiotic and biotic factors and other nutrients. This book could be titled "almost everything you ever wanted to know about U.K. pastures," and must be an extension agent's dream in that country. The last chapter briefly presents nitrogen balances in cut, in heavily grazed and intensively managed pastures, and in "rough" or native grasslands, but there is little attempt at synthesis.

The text is sometimes very densely packed with facts and numbers, but good organization and flow throughout make this a book that can easily be read by students, managers, and researchers. Unlike many scientific books, no prior knowledge of a particular term or concept is necessary, yet there is sufficient depth and detail in the science that is presented. Figures and tables are simple and to the point, but there were many places where additional ones could have been useful.

This is not a book that most research ecologists interested in native-grassland nitrogen would want to purchase, but one that most would want to at least look through and have available in the library. It would be a must for ecologists and plant and animal agriculturalists, managers, and advisors working in intensively managed sown pastures, particularly in many parts of Europe. It is a fine example of a blending of basic and applied research placed in a format understandable to even producers - one that I would consider handing to many western U.S. ranchers who are highly skeptical about why one would ever want to measure something like ammonia volatilization.

DANIEL G. MILCHUNAS Colorado State University Department of Rangeland Ecosystem Science and Natural Resource Ecology Laboratory Ft. Collins, Colorado 80523