Solubilization of rock phosphate by Penicillium bilaiae – soil phosphorus management in organic crop production

Abstract

Phosphorus deficiency is a major problem on most organic farms in Saskatchewan. Phosphorus levels have been decreasing in soil due to crop removal without the use of amendments to resupply P to the soil. Rock phosphates are naturally occurring phosphorus minerals, generally accepted as phosphorus amendments in organic crop production. Penicillium bilaiae (JumpStart®) is a fungal inoculant originally isolated from southern Alberta soils. P. bilaiae is thought to solubilize phosphorus minerals in soil and to enhance phosphorus availability to plants. There are several hypothesized mechanisms by which microorganisms enhance the dissolution of phosphorus minerals. For calcium phosphorus minerals such as rock phosphates, two mechanisms are considered most likely: 1) acidification by the exuded protons and organic acids and by the production of carbon dioxide, and 2) the complexation of cation partners of phosphorus by the exuded organic acids. This paper reviews properties of rock phosphates and P. bilaiae, and discusses potential phosphorus-solubilization mechanisms of P. bilaiae. Finally, this paper introduces experiments that investigate phosphorus-solubilization mechanisms of P. bilaiae.