Biological Contributions to Plant Phosphorus Uptake in Organic and Conventional Dairy Farm Soils

K.D. Schneider¹, R.P. Voroney¹, D. Lynch², M. Main², K. Dunfield¹, C. Hamel³ and I. O’Halloran¹

Abstract
Recent studies exploring soil fertility on organic dairy farms in Ontario have reported low soil test phosphorus (P) values. However, soil test P values were not found to significantly correlate with yield, with some farms showing acceptable yields, despite the soil tests indicating low P availability. It has been suggested that increased soil biological activity in organically-managed systems is involved in providing the crop with P not measured by the standard soil test.

The objective of this research was to explore the relationships between arbuscular mycorrhizal fungi (AMF) root colonization, AMF diversity, phosphatase activity, and productivity of organic farming systems. Three long-term (>20 years) organically managed dairy farms in south western Ontario were selected from an initial screening of 10 farms. These farms had forage fields showing low soil test P values, but relatively high yields. From each farm, one second or third year forage field was selected having a relatively flat topography and as close to uniform management as possible. Three conventional dairy farm fields with a long-term history of water-soluble P fertilizer application and located in close proximity to the organic sites were included in the study to enable a comparison. Just prior to the first cut of hay (June 2009), root, plant, and soil samples were collected from each field. Additional plant samples were collected at each subsequent cut of hay to obtain a measure of total forage yield and plant P uptake.

Initial results support that while yields were generally lower on the organic fields, AMF root colonization and alkaline phosphatase activity were greater in organic systems, both of which may contribute to crop P nutrition. It is anticipated that this research will assist in understanding P fertility and cycling in low-input agricultural systems.


Source
Proceedings of the Joint Conference of the Canadian Society of Soil Science and the Canadian Society of Agronomy, Beyond Organics session. Saskatoon, Saskatchewan. 20-24 June 2010.


Author Locations and Affiliations
(1) School of Environmental Sciences, University of Guelph
(2) Department of Plant and Animal Sciences, Nova Scotia
Agricultural College
(3) Agriculture and Agri-Food Canada, Swift Current, SK


Posted July 2010