Are differences in soil quality between organic and conventional farming systems greater in more energy-intensive sectors?

摘要

The Agricultural Research Group on Sustainability (ARGOS) has undertaken a longitudinal study of primary agricultural production in New Zealand to improve economic, environmental, social and ecological performance of its farms and orchards. As part ofthese objectives we report on a six year investigation of soil quality between Conventional, Organic and alternative management systems for three production sectors; Sheep and Beef (SB), Dairy (DY) and Kiwifruit (KF). The relative intensity of each sector was ranked according to energy use per unit land area and was the basis of a hypothesis to test whether differences in soil quality increase between management systems with increasing sector intensity. For each sector, ARGOS established twelve clusters of farms with each cluster consisting of a farm or orchard from each management system matched as well as possible in terms of size, climate, topography and soil type. Properties of one management system constituted a panel. A range of soil measurements were made for each property covering fertility, soil organic matter, biology and physical condition. The quantitative data was analysed using a mixed model fitted with restricted maximum likelihood (REML) whilst qualitative data was analysed using a multinomial regression model run in R. Ten of the 24 soil properties measured (pH, exch-Ca, BS%, mineralisable-N, soil bulk density, moisture content, porosity, aggregation and earthworm numbers and weights) had statistically significant interactions thatsupported our premise that differences in soil quality between Conventional and Organic increased with land-use intensity. These differences reached their maximums in the KF panels, our most intensively managed sector in terms of energy use per unit area. A majority, however, of soil properties had significant management effects but not all were supportive of Organic, and were often minor compared to differences between panels. Integrated was the most sustainable and best performed system in the SB panel and had better soil quality, due to the modest amounts of fertiliser used to improve production, and lower total energy costs per weight of product. Some improvements in soil quality were found in the DY panel under Organic management but many panel members are still in a transitional stage and further effects may still follow. KF had the worst soil quality overall but a large part of this can be attributed to running a modern commercial orcharding system. Adopting Organic management practice in KF orchards, however, improved soil quality.