Changing Soil Biological Health in Agroecosystems

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 Agroecosystem Sustainability and Soil Health . . . . . . . . . . . . . . . . . . . . . . . 336 Organic Carbon and Its Distribution in Soils . . . . . . . . . . . . . . . . . . . . . . . . . 339 Organic Carbon as an Indicator of Biological Health in Agroecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 The Quality and Quantity of Crop Debris Returned to the Soil . . . 343 The Growth and Turnover of Plant Roots. . . . . . . . . . . . . . . . . . . . . . 343 Cultivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 Managing Soil Biological Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 INTRODUCTION In an agricultural context, the complexity surrounding the concept of sustainability and the difficulty of moving from consideration of theoretical definitions to practical action currently provide an important issue for researchers (Fresco and Krooneneberg 1992; Park and Seaton 1995; Moffatt et al., 1999). When examining criteria associated with sustainability, there is support for considering the ecological underpinning of production systems that interact with the natural environment (Lowerance, 1990). This is associated with the view that it is desirable for ecosystems to be able to sustain function and thus maintain a given level of productivity into the future.