Soil compaction and recovery cycle on a Southland dairy farm: implications for soil monitoring

This paper quantifies soil compaction and natural recovery of soil physical properties during a 3-year trial on a dairy farm in Southland, New Zealand. The study investigated the magnitude of soil compaction over spring, and natural recovery of soil physical properties over summer and autumn. Changes in soil physical condition were measured while pastures were intermittently grazed by lactating dairy cows, and also over winter when cows were removed from pasture. Soil bulk density at 0-5 cm increased (P<0.001) during spring by up to 0.20 Mg/m(3). During spring 2000, macroporosity (volumetric % of pores >30 mum) at 0-5 cm decreased (P<0.001) from 13.5 to 7.5%, with similar trends in spring 2002. Many of the soil physical properties showed significant recovery over summer and autumn. Bulk density decreased (P<0.001) by 0.09 Mg/m(3), from December 2001 to May 2002. Soil macroporosity also recovered markedly during summer and autumn. Macroporosity increased (P<0.001) from 12.5% in December 2001 to 18% in May 2002. Significant changes in soil compaction and recovery were also measured at 5-10 cm depth. For many soil physical properties, recovery over winter was much less than over summer and autumn. Implications of the compaction and recovery cycle are discussed in terms of measurement protocols appropriate to routine monitoring of soil physical condition.