tailieunhanh - Tropical Agroecosystems - Chapter 2

Vào cuối thiên niên kỷ mới nhất, hệ thống nông nghiệp nhiệt đới mở rộng hơn một bề mặt của khoảng 20 triệu km vuông, chiếm gần một tỷ người từ 50 khác nhau châu Phi, châu Á và Mỹ Latinh nước kém phát triển (Anders, 1990). Hệ thống nông nghiệp nhiệt đới (TASS) được tìm thấy trong một khổng lồ nhiều điều kiện môi trường tương phản (MacArthur, 1976a; quốc gia Hội đồng nghiên cứu, 1993): phạm vi địa hình từ vùng đất thấp bằng phẳng đến vùng cao nguyên rất dốc; đất dao động từ mức độ vừa phải màu mỡ rất unfertile; phạm. | Chapter 2 Plant-Plant Interactions in Tropical Agriculture Luis Garcia-Barrios CONTENTS Introduction Interference Intraspecific Interference in Monocrops Evaluating Intraspecific and Interspecific Interference Effects in Two-Species Stands Interference Coexistence and Overyielding in a Two-Species Stand The Competitive Production Principle Revisited A Word on Interference in Weed-Crop Systems Studying Competitive Interactions in Many Species Stands Allelopathy Facilitation Direct Facilitation Indirect Facilitation The Interplay of Plant Interactions in Environmental Gradients Some Consequences for Tropical Agriculture Interference in Productivity Gradients Plant Interactions and System Design and Management Frequency of Land-Use Rotation Intercropping Intensity Relay Crops Crops Associated with Service Plants Full Intercrops The Percentage of Tree Canopy Cover in the Field 2003 by CRC Press LLC Conclusions References INTRODUCTION At the end of the last millennium tropical agricultural systems extended over a surface of about 20 million square kilometers occupied by nearly a billion people from 50 different African Asian and Latin American underdeveloped countries Anders 1990 . Tropical agricultural systems TASs are found in an enormous variety of contrasting environmental conditions MacArthur 1976a National Research Council 1993 topography ranges from flat lowlands to very steep highlands soils range from moderately fertile to very unfertile temperature ranges from cool to hot humidity ranges from extremely wet to very dry primary vegetation ranges from tropical rainforests to semiarid shrub lands. The variety of TASs is even greater ranging from shifting agriculture to highly technified agroindustrial plantations due to the distinct social cultural and economic conditions and to the different intensities under which these environments and their resources are being used Ruthenberg 1976 Hougthon 1994 . Nevertheless most of tropical agriculture shares the following .