A comparison of soil and environmental quality under organic and conventional farming systems in New Zealand

Organic fanning in its various forms is seen by many as a sustainable alter native to conventional farming. This review considers and compares aspects of soil and environmental quality associated with organic and conventional farming systems under New Zealand conditions. The sustainability parameters considered include soil quality, nutrient dynamics, nutrient budgets, trac e elements, and pesticides. The review used information from appropriate co mparative studies conducted in New Zealand and overseas. However, because o f the shortage of data on nutrient dynamics under organic systems in New Ze aland,, we also used a nutrient balance model (OVERSEER) and a nitrogen lea ching estimation model to assess the comparative sustainability of typical model systems. Interpretation of the measured data coupled with the results of the modelling exercise suggests that organic farming carried out accord ing to the Bio-Gro New Zealand production standards can be sustainable if s ufficient amounts of nutrient are returned to match removal and losses. Bio dynamic farming may be unsustainable because nutrients removed in farm prod uce are not adequately replaced. Soil organic matter content and biological activity is generally higher under both types of organic system than under conventional systems. Trace element availability and use may limit the sus tainability of organic systems if no attempt is made to address natural def iciencies common in New Zealand soils. The reduced use of pesticides may be beneficial for the wider environment. The main conclusion is that a concer ted research effort is urgently required to address various soil and enviro nmental quality issues associated with the large-scale adoption of organic farming practices in New Zealand.