A Routine Laboratory Method to Determine Phosphorus Availability, Capacity, and Release Characteristics for Soils.

Phosphorus (P) is an essential nutrient for plant growth and is often applied to agricultural land to increase crop production. Many chemical solutions have been proposed to extract available forms of P in soils and use the information to assess soil P for crop production and as bases for making recommendation. An anion exchange resin (AER) was used in water as a P sink to determine available P in a wide range of soils. An AER has an advantage over chemical extractants because it uses water and can measure both soil P capacity and rate of P release in addition to available P in soil. In this study, 26 US benchmark soils were selected to represent a wide range of properties and climatic factors. We determined soil P by using perforated-nylon fabric bag that contains resin beads. The bag was immersed in soil suspension and shaken for a specific period to release soil P. Phosphorus retained by resin was removed by using a sodium chloride solution and measured by ICP-OES. To develop the method, several laboratory experiments were conducted to investigate effects of soil: solution ratio, efficiency of chloride solution, shaking period, and factors related to different soils, resins and nylon fabrics on P extraction. Based on data derived from these experiments, the double-point AER extraction method was developed to determine P availability, capacity, and release characteristics for soils. The soil P data obtained from the DP-AER method correlated significantly with P determined by the conventional soil P tests (Olsen, Bray1and Mehlich3).