Does soil anion storage capacity affect plant response to Olsen P status?

In New Zealand horticulture there is a widely-held opinion that target soil test P (Olsen P) values increase with soil anion storage capacity (ASC) – an idea that arose in the 1986 Fertiliser Recommendations of Wood et al. with little supporting evidence. We report a direct test of whether ASC influences plant response to soil Olsen P. This was carried out with three soils of different ASC values (14%, 75% and 92%) under glasshouse conditions where supply of other nutrients was not limiting. For each soil we generated samples with 10 different Olsen P values. These were then used to grow spring onion (Allium fistolosum L.) in 0.25-L containers kept moist with P-free nutrient solution. The Olsen P values ranged from 3 to 51 μg g⁻¹. Plant growth varied strongly with soil Olsen P, but regression slopes for plant mass on Olsen P showed no differences associated with ASC. A further analysis filtered out possible effects of variations in pH and the mass of soil in each pot. Again this indicated no influence of ASC on plant responsiveness to Olsen P. Our results suggest caution in using the 1986 recommendations for determining application rates of P fertiliser for vegetables. [ABSTRACT FROM AUTHOR]