Intensive organic production systems and issues of sustainability

Sustainability, variously described as a ‘journey rather than a destination’ to a ‘composite quality’ defies exact definition. Differentiation of sustainability into component indicators is somewhat easier to grapple with; sustained productivity, economic viability and guaranteed product quality are a few of the obvious parameters that may be easily quantified. Indeed, organic productions systems (OPS) are recognised as providing produce quantitatively free of agrochemicals, and with high nutritive value, but their impact (ideally positive) on landscapes, ecosystems and environmental quality, the substance of Environmental Management Systems, are less quantifiable. For better or worse, the expected environmental outcomes of OPS are wide-ranging, and possibly not achievable. A recent survey of organic customers (Meldrum 2006) shows that > 75% believe OPS are better for the environment; and it is up to the scientific community to substantiate these beliefs and to develop guidelines to ensure that OPS are better for the environment. With a focus on intensive horticulture in the tropics and subtropics, I consider the contributions to OPS and environmental sustainability of live mulching and organic amendments. Their primary roles as nutrient sources, as conditioners of soil physical quality, as determinants of cation exchange capacity, and as major contributors to the maintenance of soil organic matter are discussed, as too are interactions between these, and their relationships to the topical issues of sequestration of atmospheric carbon. I argue that well defined criteria with respect to expectations for each of these roles must be adhered to in order to ‘journey towards the composite quality of sustainability’.