So với hệ sinh thái tự nhiên nói chung, agroecosystems đã tương đối mở Bởi vì chu kỳ dinh dưỡng Họ đang thiết kế để sản xuất sản phẩm dinh dưỡng giàu Đó là thu hoạch và loại bỏ khỏi hệ thống. Agroecosystems Nhiều hơn bị rò rỉ hơn Cần được. Sự tiếp xúc của đất và làm đất canh tác mùa giữa chất dinh dưỡng có thể gây ra lớn Tổn thất qua lọc và xói mòn, ô nhiễm đất và nước bề mặt, và yêu cầu đầu vào phân bón lớn để duy trì năng suất (Cox và Atkins, 1979; Odum, 1969) | CHAPTER 8 Field-Scale Nutrient Cycling and Sustainability Comparing Natural and Agricultural Ecosystems Joji Muramoto Erie C. Ellis Zhengfang Li Rodrigo M. Machado and Stephen R. Gliessman CONTENTS Flow Analysis and the Soil-Plant Organic and Conventional Strawberry Systems in California and in Observational Uncertainty Nitrogen Flows and Indicators of Nutrient Total System Net Cycling Nutrient Cycling in Agroecosystems vs. Natural Future Studies. 131 Conclusions. 132 References. 132 INTRODUCTION Nutrient cycling the movement of nutrients from the biotic components of ecosystems to their abiotic components and back again is an essential function 121 2001 by CRC Press LLC 122 AGROECOSYSTEM SUSTAINABILITY DEVELOPING PRACTICAL STRATEGIES of all ecosystems Odum 1969 . Nutrient cycles are never completely closed all systems receive some external inputs . from precipitation and experience some losses to the outside environment . through denitrification . Compared to natural ecosystems in general agroecosystems have relatively open nutrient cycles because they are designed to produce nutrient rich products that are harvested and removed from the system. Many agroecosystems are more leaky than need be. The tillage and exposure of soils between cropping seasons can cause large nutrient losses through leaching and erosion contaminating ground and surface waters and requiring large fertilizer inputs to maintain yields Cox and Atkins 1979 Odum 1969 . The more closed an agroecosystem s nutrient cycle the more it will resemble natural ecosystems and will be ecologically sustainable over the long-term Ewel 1999 Jarrell 1990 Woodmansee 1984 . In designing sustainable agroecosystems it is useful to compare indicators of nutrient cycling between different management patterns of .
