Issues related to the management of nutrients on organic dairy farms: Nitrate leaching and maintaining soil nutrient levels

Abstract

It is often claimed that nutrient management in organic dairying is more environmentally sustainable than its conventional counterpart. Organic dairy farmers often focus on pH, trace elements and nutrient ratios rather than the major nutrients such as phosphorus. As a consequence of less nutrient input, the environmental impacts of organic dairy systems may be smaller than for conventional farms. Some of these issues were explored by surveying eight organic farms in the North Island. The objectives of the nutrient management plans along with trends in soil test values were examined. OVERSEER® Nutrient Budgeting software was used to quantify maintenance fertiliser requirement for the organic dairy farms and likely trends in nutrient status. Nitrogen leaching from the organic farms was also assessed using OVERSEER®. This study suggest that while the current nutrient status of organically managed soils is not dissimilar to that found on conventional farms, sustainable nutrient management on organic dairy farms is an emerging challenge. Of particular note here is a decline in phosphorus status. While organic dairy farms leach much less nitrogen than conventional farms, some of these advantages are eroded when efficiency indicators are invoked. A field trial has been established to identify products that will help organic farmers increase soil nitrogen and phosphorus nutrition. Keywords: organic dairying, nutrient management, nitrogen leaching, nitrogen conversion efficiency, environmental efficiency