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 alternative 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, trace elements, and pesticides. The review used information from appropriate comparative studies conducted in New Zealand and overseas. However, because of the shortage of data on nutrient dynamics under organic systems in New Zealand,, we also used a nutrient balance model (OVERSEER) and a nitrogen leaching 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 according to the Bio-Gro New Zealand production standards can be sustainable if sufficient amounts of nutrient are returned to match removal and losses. Biodynamic farming may be unsustainable because nutrients removed in farm produce 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 sustainability of organic systems if no attempt is made to address natural deficiencies common in New Zealand soils. The reduced use of pesticides may be beneficial for the wider environment. The main conclusion is that a concerted research effort is urgently required to address various soil and environmental quality issues associated with the large-scale adoption of organic farming practices in New Zealand.