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Department of Crop and Soil Sciences Pennsylvania State University University Park, PA 16802
(wcurran{at}psu.edu)
Robert L. Zimdahl, Blackwell Publishing, 2121 State Avenue, Ames, IA 50014. 2004. 220 p. $79.99. ISBN 0-8138-0279-2.
The second edition of Weed-Crop Competition—A Review, is a welcome addition. When I was an M.S. candidate conducting competition research in lentils in the mid-1980s, the first edition was invaluable in designing research and writing my thesis. This book's focus is interference in the narrow sense of crop–weed competition and examines research published in the journals Weed Science, Weed Technology, and Weed Research from 1980 to mid-2002. Earlier work is also referenced. There is no attempt to include any of the literature on allelopathy. This book should prove very useful to both students and faculty for teaching or designing weed interference research. It provides enough information to assemble a series of lectures or points to literature citations that can be explored more fully.
The book starts with a historical perspective that describes how weed competition research has evolved over the last 30 years. Zimdahl discusses how weed biology research is moving from the predictive phase to the quantification of processes. The second chapter discusses the definition of plant competition in a broad sense. Although a number of definitions are provided and discussed, a simple one, "competition is a struggle between a crop and a weed for a resource that is in short supply," sometimes makes the most sense.
Chapters 3 and 4 cover the role of competition in the community and the influence of competition on individual plants. Levels of competition and the processes that control them, the effect of density in the community, community composition, and some theories of competition are presented and discussed. Zimdahl stresses the need for more mechanistic, ecologically focused research.
Chapters 5 and 6 are the meat of the book. Chapter 5 reviews the effect of weed density on crop yield loss. More than 25 crops are included and arranged alphabetically. Literature citations are placed at the end of each crop section. Some crop entries, such as those for soybean and wheat, include a section that summarizes more recent weed competition research results by weed species. The sixth chapter addresses duration of weed interference including the critical period concept. The chapter includes some nice summary data for different crops that identify the length of early weed competition tolerated without yield loss, the weed-free period required, and crops identified with a critical period.
Chapter 7 addresses the elements of competition including nutrients, light, and water. Zimdahl reveals that, while the elements of competition are mentioned frequently in the literature, there has been little attempt to explain their mechanisms. The eighth chapter is about integrated weed management. It also asks the question whether past competition research has had an impact. Chapter 9 explores the methods used to study weed–crop competition. Additive designs, substitutive experiments including replacement series, and response models are discussed. The tenth chapter explores modeling as it relates to weed competition. The chapter includes sections on conceptual, simulation or analytical, empirical, mechanistic or ecophysiological models, decision-aid models, and thresholds. This chapter was not in the first edition and provides a nice review.
The final chapter is a conclusion. More than 650 publications are cited in the book and the review led Zimdahl to three major conclusions. First, weeds do compete with crops and reduce yield and quality. Second, weed science will benefit from closer integration with plant ecology, especially with regard to the study and understanding of plant coexistence. Third, modeling has become an important aspect of modern weed management and will likely become more important to future systems. Zimdahl continues to stress the importance of basic ecological theory and principles and their incorporation into weed science and weed management systems.
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