The impact of land-use intensification on soil physical quality and plant yield response in the North Otago Rolling Downlands

Abstract

The New Zealand agricultural industry is currently undergoing a large drive for increased productivity. Fuelling this will primarily require greater 'on-farm' landuse intensification involving increasing farm inputs to gain a large increase in farm product outputs. The North Otago Rolling Downlands (NORD) region of New Zealand has traditionally been drought-prone and limited to extensive sheep farming. The establishment of a large district irrigation scheme in spring 2006 will result in large scale intensification of land-use across the NORD region. A field trial has been established in North Otago on a common NORD Pallic soil type (Timaru silt loam) to determine the effect of land use intensification on soil quality and plant yield response. The treatments compare newly sown pasture vs. winter grazed forage crop, irrigated vs. dryland and sheep vs. cattle grazing. The application of irrigation water in 2004/2005 resulted in 17.5 kg pasture DM/mm of irrigation water and 24 kg pasture DM/mm of irrigation water for the drier 2005/ 2006 growing season. Results from the pasture trial suggest that both cattle grazing and irrigation (particularly in combination) are decreasing soil quality with a macroporosity of 9% v/v from pasture plots following the 2004/2005 season compared to 18% v/v for the dryland sheep treatment. In the 2005/2006 season, cattle irrigated plots had a macroporosity of 11% v/v from pasture plots c.f 19% v/v for the dryland sheep treatment To date, this measured decrease has had no significant effect on pasture or crop yield suggesting that soil quality has not yet fallen below a critical level for production under irrigated farming systems. However, further monitoring is required to assess the long term effects as strong trends are emerging that indicate soil quality decline under the cattle grazed and cropping treatments. Keywords: land-use intensification, soil quality, irrigation, cattle grazing, sheep grazing, forage cropping, compaction, pasture yield